5-i

CHAPTER 5. ENGINEERING ANALYSIS

TABLE OF CONTENTS

5.1 INTRODUCTION ............................................................................................... 5-1

5.2 STRUCTURING THE ENGINEERING ANALYSIS........................................ 5-1

5.2.1 Summary of Design Line Coverage..................................................................... 5-8

5.2.2 Scaling Relationships in Transformer Manufacturing....................................... 5-10

5.3 TECHNICAL DESIGN INPUTS ...................................................................... 5-13

5.3.1 A and B Loss Valuation Inputs.......................................................................... 5-14

5.3.2 Core Material Options........................................................................................ 5-16

5.3.3 Core Configurations........................................................................................... 5-17

5.3.3.1 Standard Core Configurations................................................................ 5-18

5.3.3.2 Symmetric Core Configurations............................................................ 5-20

5.3.3.3 Core Deactivation Technology .............................................................. 5-23

5.3.4 Less-Flammable Liquid-Immersed Transformers ............................................. 5-25

5.3.5 Design Line 1 Representative Unit.................................................................... 5-26

5.3.6 Design Line 2 Representative Unit.................................................................... 5-27

5.3.7 Design Line 3 Representative Unit.................................................................... 5-27

5.3.8 Design Line 4 Representative Unit.................................................................... 5-28

5.3.9 Design Line 5 Representative Unit.................................................................... 5-29

5.3.10 Design Line 6 Representative Unit.................................................................... 5-30

5.3.11 Design Line 7 Representative Unit.................................................................... 5-31

5.3.12 Design Line 8 Representative Unit.................................................................... 5-32

5.3.13 Design Line 9 Representative Unit.................................................................... 5-33

5.3.14 Design Line 10 Representative Unit.................................................................. 5-34

5.3.15 Design Line 11 Representative Unit.................................................................. 5-35

5.3.16 Design Line 12 Representative Unit.................................................................. 5-36

5.3.17 Design Line 13A Representative Unit ............................................................... 5-37

5.3.18 Design Line 13B Representative Unit ............................................................... 5-38

5.3.19 Newly Optimized Designs and Previously Optimized Designs ........................ 5-38

5.4 MATERIAL AND LABOR INPUTS................................................................ 5-39

5.4.1 Material Prices................................................................................................... 5-41

5.4.2 Material Inputs to the Design Software – Liquid-Immersed ............................. 5-43

5.4.3 Material Inputs to the Design Software – Dry-Type ......................................... 5-48

5.4.4 Labor Costs........................................................................................................ 5-53

5.5 EFFICIENCY LEVELS..................................................................................... 5-59

5.5.1 Criteria for Selecting Efficiency Levels ............................................................ 5-60

5.5.2 Efficiency Levels Selected................................................................................. 5-60

5.6 RESULTS OF THE ANALYSIS ON EACH DESIGN LINE.......................... 5-63

5.6.1 Traditional Core Designs for the Reference Case.............................................. 5-63

5.6.2 Symmetric Core Designs for the Reference Case.............................................. 5-77

5.7 3 EXAMPLE TRANSFORMER DESIGNS & COST BREAKDOWNS......... 5-86

5.7.1 Design Details Report for Transformer from Design Line 1............................. 5-87

5.7.2 Design Details Report for Transformer from Design Line 7............................. 5-91
5-ii

5.7.3 Design Details Report for Transformer from Design Line 12........................... 5-95

LIST OF TABLES

Table 5.2.1 Equipment Classes and Number of kVA Ratings........................................ 5-2

Table 5.2.2 Engineering Design Lines (DLs) and Representative Units for Analysis... 5-3

Table 5.2.3 Liquid-Immersed Design Lines and Representative Units.......................... 5-8

Table 5.2.4 Dry-Type, Low-Voltage Design Lines and Representative Units............... 5-9

Table 5.2.5 Dry-Type, Medium-Voltage, Single-Phase Design Lines........................... 5-9

Table 5.2.6 Dry-Type, Medium-Voltage, Three-Phase Design Lines.......................... 5-10

Table 5.2.7 Common Scaling Relationships in Transformers...................................... 5-11

Table 5.3.1 A and B Grid Combinations Used by Software to Generate Design Database

........................................................................................................................................ 5-15

Table 5.3.2 A and B Fan Combinations Used by Software to Generate Design Database

........................................................................................................................................ 5-15

Table 5.3.3 Core Steel Grades, Thicknesses and Associated Losses............................ 5-17

Table 5.3.4 Core Configurations Used in Each Design Line........................................ 5-18

Table 5.3.5 Design Adjustments for Simulated Symmetric Core Designs................... 5-23

Table 5.3.6 Core Deactivation Technology Components, Cost and Weight................ 5-25

Table 5.3.7 Design Option Combinations for the Representative Unit from Design Line 1

........................................................................................................................................ 5-26

Table 5.3.8 Design Option Combinations for the Representative Unit from Design Line 2

........................................................................................................................................ 5-27

Table 5.3.9 Design Option Combinations for the Representative Unit from Design Line 3

........................................................................................................................................ 5-28

Table 5.3.10 Design Option Combinations for the Representative Unit from Design Line 

4...................................................................................................................................... 5-29

Table 5.3.11 Design Option Combinations for the Representative Unit from Design Line 

5...................................................................................................................................... 5-30

Table 5.3.12 Design Option Combinations for the Representative Unit from Design Line 

6...................................................................................................................................... 5-31

Table 5.3.13 Design Option Combinations for the Representative Unit from Design Line 

7...................................................................................................................................... 5-32

Table 5.3.14 Design Option Combinations for the Representative Unit from Design Line 

8...................................................................................................................................... 5-33

Table 5.3.15 Design Option Combinations for the Representative Unit from Design Line 

9...................................................................................................................................... 5-34

Table 5.3.16 Design Option Combinations for the Representative Unit from Design Line 

10.................................................................................................................................... 5-35

Table 5.3.17 Design Option Combinations for the Representative Unit from Design Line 

11.................................................................................................................................... 5-35

Table 5.3.18 Design Option Combinations for the Representative Unit from Design Line 

12.................................................................................................................................... 5-36
5-iii

Table 5.3.19 Design Option Combinations for the Representative Unit from Design Line 

13A................................................................................................................................. 5-37

Table 5.4.1 Typical Manufacturer‘s Material Prices for Liquid-Immersed Design Lines5-

44

Table 5.4.2 Marked-up Material Prices for Liquid-Immersed Units, Current Year (2010) 

Price Scenario ................................................................................................................ 5-46

Table 5.4.3 Summary Table of Fixed Material Costs for Liquid-Immersed Units....... 5-48

Table 5.4.4 Manufacturer‘s Material Prices for Dry-Type Design Lines..................... 5-49

Table 5.4.5 Marked-up Material Prices for Dry-Type Units, Current Year (2010) Price 

Scenario.......................................................................................................................... 5-50

Table 5.4.6 Summary Table of Fixed Material Costs for Dry-Type Units................... 5-53

Table 5.4.7 Labor Markups for Liquid-Immersed and Dry-Type Manufacturers........ 5-54

Table 5.4.8 Summary of Labor Times for Liquid-Immersed Units.............................. 5-57

Table 5.4.9 Summary of Labor Times for Dry-Type Units.......................................... 5-59

Table 5.5.1 Summary of Baselines and Efficiency Levels for Distribution Transformer 

Representative Units...................................................................................................... 5-61

Table 5.5.2 Summary of Incremental Manufacturer Selling Prices Over the Baseline for 

Distribution Transformer Representative Units............................................................. 5-62

Table 5.7.1 Bill of Materials for Transformer from Design Line 1.............................. 5-90

Table 5.7.2 Bill of Materials for Transformer from Design Line 7.............................. 5-94

Table 5.7.3 Bill of Materials for Transformer from Design Line 12............................ 5-99

LIST OF FIGURES

Figure 5.3.1 A and B Combination Software Inputs Used in the Engineering Analysis.. 5-

16

Figure 5.3.2 Graphic of Single-Phase Core Configurations......................................... 5-19

Figure 5.3.3 Graphic of Three-phase Core Configurations .......................................... 5-19

Figure 5.3.4 Cruciform Core Cross-Section ................................................................. 5-20

Figure 5.3.5 Graphic of Symmetric Core Configuration .............................................. 5-21

Figure 5.4.1 Method of Cost Accounting for Distribution Transformers Rulemaking 5-40

Figure 5.6.1 Engineering Analysis Results, Design Line 1 .......................................... 5-64

Figure 5.6.2 Engineering Analysis Results, Design Line 2 .......................................... 5-65

Figure 5.6.3 Engineering Analysis Results, Design Line 3 .......................................... 5-66

Figure 5.6.4 Engineering Analysis Results, Design Line 4 .......................................... 5-67

Figure 5.6.5 Engineering Analysis Results, Design Line 5 .......................................... 5-68

Figure 5.6.6 Engineering Analysis Results, Design Line 6 .......................................... 5-69

Figure 5.6.7 Engineering Analysis Results, Design Line 7 .......................................... 5-70

Figure 5.6.8 Engineering Analysis Results, Design Line 8 .......................................... 5-71

Figure 5.6.9 Engineering Analysis Results, Design Line 9 .......................................... 5-72

Figure 5.6.10 Engineering Analysis Results, Design Line 10 ...................................... 5-73

Figure 5.6.11 Engineering Analysis Results, Design Line 11 ...................................... 5-74

Figure 5.6.12 Engineering Analysis Results, Design Line 12 ...................................... 5-75

Figure 5.6.13 Engineering Analysis Results, Design Line 13A ................................... 5-76

Figure 5.6.14 Engineering Analysis Results, Design Line 13B ................................... 5-77
5-iv

Figure 5.6.15 Symmetric Core Engineering Analysis Results, Design Line 4............. 5-78

Figure 5.6.16 Symmetric Core Engineering Analysis Results, Design Line 5............. 5-79

Figure 5.6.17 Symmetric Core Engineering Analysis Results, Design Line 7............. 5-80

Figure 5.6.18 Symmetric Core Engineering Analysis Results, Design Line 8............. 5-81

Figure 5.6.19 Symmetric Core Engineering Analysis Results, Design Line 9............. 5-82

Figure 5.6.20 Symmetric Core Engineering Analysis Results, Design Line 10........... 5-83

Figure 5.6.21 Symmetric Core Engineering Analysis Results, Design Line 11........... 5-84

Figure 5.6.22 Symmetric Core Engineering Analysis Results, Design Line 12........... 5-85

Figure 5.6.23 Symmetric Core Engineering Analysis Results, Design Line 13B........ 5-86

Figure 5.7.1 Manufacturer Selling Price Breakdown, Transformer from Design Line 1. 5-

91

Figure 5.7.2 Manufacturer Selling Price Breakdown, Transformer from Design Line 7. 5-

95

Figure 5.7.3 Manufacturer Selling Price Breakdown, Transformer from Design Line 125-

100
5-1

CHAPTER 5. ENGINEERING ANALYSIS

5.1 INTRODUCTION

This chapter provides the technical support documentation on the engineering analysis, 

evaluating both liquid-immersed and dry-type distribution transformers. The purpose of the 

engineering analysis is to estimate the relationship between the manufacturer‘s selling price of a 

transformer and its corresponding efficiency rating. This relationship serves as the basis for the 

subsequent cost-benefit calculations for individual customers, manufacturers, and the nation (see 

Chapter 8, Life-Cycle Cost and Payback Period Analyses).

5.2 STRUCTURING THE ENGINEERING ANALYSIS

As discussed in the market and technology assessment (Chapter 3), distribution 

transformers are classified by their insulation type (liquid-immersed or dry-type), the number of 

phases (single or three), the primary voltage (low-voltage or medium-voltage for dry-types) and 

the basic impulse insulation level (BIL) rating (for dry-types). Following this convention, the 

U.S. Department of Energy (DOE) developed ten equipment classes, shown in Table 5.2.1. 

These equipment classes were adapted from the National Electrical Manufacturers Association 

(NEMA)‘s TP 1 classification system, although they do not follow the classification system 

precisely. NEMA‘s TP 1 classifies medium-voltage, dry-type distribution transformers into two 

equipment classes, ≤ 60 kilovolt (kV) BIL and > 60 kV BIL. Based on input from manufacturers, 

DOE elected to increase the differentiation of medium-voltage, dry-type transformers, and create 

three equipment classes of BIL ratings: 20–45 kV BIL, 46–95 kV BIL, and ≥ 96kV BIL (see 

Chapter 3, section 3.3).

Within each of these equipment classes, DOE further classified distribution transformers 

by their kilovolt-ampere (kVA) rating. These kVA ratings are size categories, indicating the 

power handling capacity of the transformers. Due to differences in construction methods and 

material properties, efficiency levels vary by both equipment class and kVA rating. For NEMA‘s 

TP 1-2002,1there are 99 kVA ratings across all the equipment classes (see Chapter 3, section 

3.7.1). For DOE‘s rulemaking, because of the greater degree of differentiation around the BIL 

rating in medium-voltage, dry-type transformers, there are 115 kVA ratings across all the 

equipment classes, as shown in Table 5.2.1.

 

1 NEMA‘s TP 1-2002 can be found online at: http://www.nema.org/stds/tp1.cfm#download.
5-2

Table 5.2.1 Equipment Classes and Number of kVA Ratings

Distribution Transformer Equipment Class kVA Range Number of kVA 

Ratings

1. Liquid-immersed, medium-voltage, single-phase 10–833 13

2. Liquid-immersed, medium-voltage, three-phase 15–2500 14

3. Dry-type, low-voltage, single-phase 15–333 9

4. Dry-type, low-voltage, three-phase 15–1000 11

5. Dry-type, medium-voltage, single-phase, 20-45 kV BIL 15–833 12

6. Dry-type, medium-voltage, three-phase, 20-45 kV BIL 15–2500 14

7. Dry-type, medium-voltage, single-phase, 46-95 kV BIL 15–833 12

8. Dry-type, medium-voltage, three-phase, 46-95 kV BIL 15–2500 14

9. Dry-type, medium-voltage, single-phase, > 96 kV BIL 75–833 8

10. Dry-type, medium-voltage, three-phase, > 96 kV BIL 225–2500 8

Total 115

DOE recognized that it would be impractical to conduct a detailed engineering analysis 

of the manufacturer‘s selling price-efficiency relationship on all 115 kVA ratings, so it sought to 

develop an approach that simplified the analysis while retaining reasonable levels of accuracy. 

DOE consulted with industry representatives and transformer design engineers and developed an 

understanding of the construction principles for distribution transformers. It found that many of 

the units share similar designs and construction methods. Thus, DOE simplified the analysis by 

creating 14 engineering design lines, which group together kVA ratings based on similar 

principles of design and construction. The 14 design lines subdivide the equipment classes, to 

improve the accuracy of the engineering analysis. These 14 engineering design lines differentiate 

the transformers by insulation type (liquid-immersed or dry-type), number of phases (single or 

three), and primary insulation levels for medium-voltage, dry-type (three different BIL levels). 

DOE then selected one unit from each of the engineering design lines for study in the 

engineering analysis and the life-cycle cost (LCC) analysis (see Chapter 8), reducing the number 

of units for analysis from 115 to 14. It then extrapolated the results of its analysis from the unit 

studied to the other kVA ratings within that same engineering design line. DOE performed this 

extrapolation in the national impacts analysis (see Chapter 10). The technique it used to 

extrapolate the findings on the representative unit to the other kVA ratings within a design line is 

referred to as ―the 0.75 scaling rule.‖ This rule states that, for similarly designed transformers, 

costs of construction and losses scale to the ratio of kVA ratings raised to the 0.75 power. The 

relationship is valid where the optimum efficiency loading points of the two transformers being 

scaled are the same. An example of how DOE applied this scaling appears in section 5.2.1 of this 

chapter. A technical discussion on the derivation of the 0.75 scaling rule appears in Appendix 

5B.

Table 5.2.2 presents DOE‘s 14 design lines and the representative units selected from 

each engineering design line for analysis. Descriptions of each of the design lines and the 

rationale behind the selection of the representative units follow Table 5.2.2.
5-3

Table 5.2.2 Engineering Design Lines (DLs) and Representative Units for Analysis

EC* DL Type of Distribution 

Transformer

kVA 

Range

Representative Unit for this

Engineering Design Line

1

1

Liquid-immersed, single-phase, 

rectangular tank 10–167 50 kVA, 65 C, single-phase, 60Hz, 14400V primary, 

240/120V secondary, rectangular tank

2

Liquid-immersed, single-phase, 

round tank 10–167 25 kVA, 65 C, single-phase, 60Hz, 14400V primary, 

120/240V secondary, round tank

3 Liquid-immersed, single-phase 250–833 500 kVA, 65 C, single-phase, 60Hz, 14400V primary, 

277V secondary

2

4 Liquid-immersed, three-phase 15–500 150 kVA, 65 C, three-phase, 60Hz, 12470Y/7200V 

primary, 208Y/120V secondary

5 Liquid-immersed, three-phase 750–2500 1500 kVA, 65 C, three-phase, 60Hz, 

24940GrdY/14400V primary, 480Y/277V secondary

3 6

Dry-type, low-voltage, singlephase 15–333 25 kVA, 150 C, single-phase, 60Hz, 480V primary, 

120/240V secondary, 10kV BIL

4

7

Dry-type, low-voltage, threephase 15–150 75 kVA, 150 C, three-phase, 60Hz, 480V primary, 

208Y/120V secondary, 10kV BIL

8

Dry-type, low-voltage, threephase 225–1000 300 kVA, 150 C, three-phase, 60Hz, 480V Delta 

primary, 208Y/120V secondary, 10kV BIL

6

9

Dry-type, medium-voltage, 

three-phase, 20-45kV BIL 15–500 300 kVA, 150 C, three-phase, 60Hz, 4160V Delta 

primary, 480Y/277V secondary, 45kV BIL

10 Dry-type, medium-voltage, 

three-phase, 20-45kV BIL 750–2500 1500 kVA, 150 C, three-phase, 60Hz, 4160V primary, 

480Y/277V secondary, 45kV BIL

8

11 Dry-type, medium-voltage, 

three-phase, 46-95kV BIL 15–500 300 kVA, 150 C, three-phase, 60Hz, 12470V primary, 

480Y/277V secondary, 95kV BIL

12 Dry-type, medium-voltage, 

three-phase, 46-95kV BIL 750–2500 1500 kVA, 150 C, three-phase, 60Hz, 12470V 

primary, 480Y/277V secondary, 95kV BIL

10

13

(A & 

B)

Dry-type, medium-voltage, 

three-phase, 96-150kV BIL 225–2500

300 kVA, 150 C, three-phase, 60Hz, 24940V primary, 

480Y/277V secondary, 125kV BIL

2000 kVA, 150 C, three-phase, 60Hz, 24940V 

primary, 480Y/277V secondary, 125kV BIL

* EC means equipment class (see Chapter 3 of the TSD). DOE did not select any representative units from the 

single-phase, medium-voltage equipment classes (EC5, EC7 and EC9), but calculated the analytical results for EC5, 

EC7, and EC9 based on the results for their three-phase counterparts.

DOE divided liquid-immersed transformers into five engineering design lines, based on 

their tank shape, number of phases, and kVA ratings. DOE believes that this breakdown enables 

the analysis to identify and capture a more accurate representation of the manufacturer‘s selling 

price and efficiency relationship. DOE broke dry-type distribution transformers into eight 

engineering design lines, primarily according to their BIL levels. DOE believes this level of 

disaggregation is necessary to capture important differences in the price-efficiency relationship, 

particularly as the BIL level varies. For example, a 300 kVA, three-phase, dry-type unit could be 

classified in design lines 8, 9, or 11, or 13A, depending on whether the BIL rating is 10 kV (lowvoltage), 20-45 kV, 46-95 kV, or 96-150 kV.

For design lines 9 through 13B, the representative units selected for some of the dry-type 

design lines may not be the standard BILs associated with a given primary voltage. DOE selected 

a slightly higher BIL for the representative units from these design lines to ensure that any 

minimum efficiency standard would not excessively penalize customers purchasing transformers 
5-4

at higher BIL ratings within the range. For example, a 300 kVA transformer with a 4160V 

primary is called a ―5kV class‖ transformer and would normally be built with a 30kV BIL. 

However, customers may also choose to order this transformer with 45kV BIL or 60kV BIL. If 

the minimum efficiency level were set based on a 30kV BIL, it may not be possible to achieve 

that same efficiency rating for customers ordering 60kV BIL. Thus, DOE evaluated the middle 

BIL level (in this example, 45kV BIL), making it slightly easier to comply for a lower BIL, and 

not too difficult (or impossible) for the higher BIL.

The remainder of this section discusses each of the 14 engineering design lines, providing 

a description and explanation of the transformers covered.

Design Line 1. This is the basic, high-volume line for rectangular-tank, single-phase, 

liquid-immersed distribution transformers, ranging from 10 kVA to 167 kVA. Transformers in 

this design line typically have BILs ranging from 30 kV to 150 kV and a tap configuration of 

four 21⁄2 percent taps—two above and two below the nominal voltage. Tap configurations enable 

transformer users to maintain full (rated) output voltage by slightly increasing or decreasing the 

number of turns in the primary in anticipation of an input voltage slightly above or below the 

rated nominal. This design line has a primary voltage less than 35 kV, and a secondary voltage 

less than or equal to 600 Volts (V).

The representative unit selected for design line 1 is a 50 kVA pad-mounted unit, as this is 

a high shipment volume rating, and is approximately the middle of the kVA range for this design 

line (10 kVA, 15 kVA, 25 kVA, 37.5 kVA, 50 kVA, 75 kVA, 100 kVA, and 167 kVA). 

Engineering design considerations and manufacturing differences led to the placement of 250 

kVA and higher-rated units in design line 3.

Design Line 2. This is the basic, high-volume line for round-tank (pole-mounted), singlephase, liquid-immersed distribution transformers, ranging from 10 kVA to 167 kVA. Although 

some manufacturers tend to employ the same basic core/coil design for design line 1 and design 

line 2, others may have design differences between pad-mounted and pole-mounted 

transformers. DOE decided to analyze these two types of distribution transformers separately for 

the engineering and LCC analyses. Transformers in design line 2 typically have BILs ranging 

from 30 kV to 150 kV, a tap configuration of four 21⁄2 percent taps—two above and two below 

the nominal, a primary voltage less than 35 kV, and a secondary voltage less than or equal to 600 

V. 

The representative unit selected for design line 2 is a 25 kVA pole-mounted unit, as this 

is a high-volume rating for pole-mounted transformers, and is on the lower end of the kVA range 

for this design line (10 kVA, 15 kVA, 25 kVA, 37.5 kVA, 50 kVA, 75 kVA, 100 kVA, and 167 

kVA). Engineering design considerations and manufacturing differences led to the placement of 

250 kVA and higher-rated units in design line 3.

Design Line 3. This design line groups together single-phase, round-tank, liquidimmersed distribution transformers, ranging from 250 kVA to 833 kVA. Together, design lines 1 

through 3 cover all the single-phase, liquid-immersed units (there are no standard kVA ratings 

between 167 and 250 kVA). Transformers in this design line typically have BILs ranging from 
5-5

30 kV to 150 kV, a tap configuration of four 21⁄2 percent taps—two above and two below the 

nominal, a primary voltage less than 35 kV, and a secondary voltage less than or equal to 600 V.

The representative unit selected for design line 3 is a 500 kVA round-tank, as this rating 

occurs in the middle of the kVA range for this design line (250 kVA, 333 kVA, 500 kVA, 667 

kVA, and 833 kVA). Although high currents result from having a 277 V secondary at the larger 

kVA ratings, high current bushings are available, and a market does exist for these transformers.

Design Line 4. Design line 4 represents rectangular tank, three-phase, liquid-immersed 

distribution transformers, ranging from 15 kVA to 500 kVA. Transformers in this design line 

typically have BILs ranging from 30 kV to 150 kV, a tap configuration of four 21⁄2 percent taps—

two above and two below the nominal, a primary voltage less than 35 kV, and a secondary 

voltage less than or equal to 600 V.

The representative unit selected for design line 4 is a 150 kVA transformer, as this is a 

common rating in this design line and occurs approximately in the middle of the kVA range (15 

kVA, 30 kVA, 45 kVA, 75 kVA, 112.5 kVA, 150 kVA, 225 kVA, 300 kVA, and 500 kVA). 

Design Line 5. Design line 5 represents rectangular tank, three-phase, liquid-immersed 

distribution transformers, ranging from 750 kVA to 2500 kVA. Together, design lines 4 and 5 

cover all the three-phase, liquid-immersed units (there are no standard kVA ratings between 500 

and 750 kVA). Transformers in this design line typically have BILs ranging from 95 kV to 150 

kV, a tap configuration of four 21⁄2 percent taps—two above and two below the nominal, a 

primary voltage less than 35 kV, and a secondary voltage less than or equal to 600 V. 

The representative unit selected for this design line is a 1500 kVA transformer, as this is 

a common rating in this size range, and occurs in the middle of the kVA range for this design 

line (750 kVA, 1000 kVA, 1500 kVA, 2000 kVA, and 2500 kVA).

Design Line 6. Design line 6 represents single-phase, low-voltage, ventilated dry-type 

distribution transformers, ranging from 15 kVA to 333 kVA. Transformers in this design line 

typically have BIL ratings of 10 kV and a ―universal‖ tap arrangement, meaning six 21⁄2 percent 

taps, two above and four below the nominal. DOE selected this tap arrangement based on 

recommendations from manufacturers who produce transformers at these ratings. The primary 

and secondary voltages are both 600 V or below.

The representative unit selected for design line 6 is a 25 kVA transformer, as this is a 

common rating in this size range, and occurs toward the low end of the kVA ratings for this 

design line (15 kVA, 25 kVA, 37.5 kVA, 50 kVA, 75 kVA, 100 kVA, 167 kVA, 250 kVA, and 

333 kVA).

Design Line 7. Design line 7 represents three-phase, low-voltage, ventilated dry-type 

distribution transformers, ranging from 15 kVA to 150 kVA. Because the kVA range of threephase ratings is broad and construction techniques differ, DOE split the range of three-phase, 

low-voltage, dry-type transformers into design line 7 and design line 8, so the engineering 

differences in core-coil design and manufacturing would be more readily apparent. Transformers 
5-6

in this design line typically have BIL ratings of 10 kV and a ―universal‖ tap arrangement, 

meaning six 21⁄2 percent taps, two above and four below the nominal. The primary and secondary 

voltages are both 600 V or below.

The representative unit selected for design line 7 is a 75 kVA transformer, as this is a 

common rating in this size range, and occurs in the middle of the kVA ratings for this design line 

(15 kVA, 30 kVA, 45 kVA, 75 kVA, 112.5 kVA, and 150 kVA).

Design Line 8. Design line 8 represents three-phase, low-voltage, ventilated dry-type 

distribution transformers, ranging from 225 kVA to 1000 kVA. Transformers in this design line 

typically have BIL ratings of 10 kV and a tap arrangement of four 21⁄2 percent taps, two above 

and two below the nominal. The primary and secondary voltages are both 600 V or below.

The representative unit selected for design line 8 is a 300 kVA transformer, as this is a 

common rating in this size range, and occurs toward the lower end of the range of kVA ratings 

included in this design line (225 kVA, 300 kVA, 500 kVA, 750 kVA, and 1000 kVA).

Design Line 9. Design line 9 represents three-phase, medium-voltage, ventilated dry-type 

distribution transformers, ranging from 15 kVA to 500 kVA. To accommodate the broad kVA

range and to allow for engineering differences in construction principles and associated costs, 

DOE split the three-phase, medium-voltage, dry-type units into design lines 9 and 10. 

Transformers in design line 9 typically have primary voltages less than or equal to 5 kV with a 

BIL rating between 20 kV and 45 kV. The secondary voltage is less than or equal to 600 V and 

the tap arrangement is typically four 21⁄2 percent taps, two above and two below the nominal. 

The representative unit selected for design line 9 is 300 kVA, as this is a common rating 

in this size range, and occurs near the high end of the kVA ratings for this design line (15 kVA, 

30 kVA, 45 kVA, 75 kVA, 112.5 kVA, 150 kVA, 225 kVA, 300 kVA, and 500 kVA).

Design Line 10. Design line 10 represents three-phase, medium-voltage, ventilated drytype distribution transformers, ranging from 750 kVA to 2500 kVA. Transformers in this design 

line typically have primary voltages less than or equal to 5 kV with a BIL rating between 20 kV 

and 45 kV. The secondary voltage is less than or equal to 600 V and the tap arrangement is 

typically four 21⁄2 percent taps, two above and two below the nominal.

The representative unit selected for this design line is a 1500 kVA transformer, as this is 

a common rating, and occurs in the middle of the kVA range for this design line (750 kVA, 1000 

kVA, 1500 kVA, 2000 kVA, and 2500 kVA). 

Design Line 11. Design line 11 represents three-phase, medium-voltage, ventilated drytype distribution transformers, ranging from 15 kVA to 500 kVA. This design line parallels 

design line 9, with a higher primary insulation level, 46 kV to 95 kV BIL. Because dry-type 

transformer designs and, more importantly, the efficiency of those designs, are strongly 

influenced by changes in BIL, DOE considered these higher BIL ratings separately. The typical 

tap arrangement is four 21⁄2 percent taps, two above and two below the nominal. The primary 
5-7

voltage is typically less than or equal to 15 kV and the secondary voltage is less than or equal to 

600 V. 

The kVA ratings in design line 11 are 15 kVA, 30 kVA, 45 kVA, 75 kVA, 112.5 kVA, 

150 kVA, 225 kVA, 300 kVA, and 500 kVA. The shipments for this design line are primarily in 

the kVA range inclusive of and between 225 kVA and 500 kVA; therefore, DOE selected the 

300 kVA rating as the representative unit for analysis.

Design Line 12. Design line 12 represents three-phase, medium-voltage, ventilated drytype distribution transformers, ranging from 750 kVA to 2500 kVA. This design line parallels 

design line 10, with a higher primary insulation level, 46 kV to 95 kV BIL. The typical tap 

arrangement is four 21⁄2 percent taps, two above and two below the nominal. The primary voltage 

is typically less than or equal to 15 kV and the secondary voltage is less than or equal to 600 V. 

The representative unit selected for this design line is a 1500 kVA transformer, as it is a 

common rating in this size range and BIL rating, and it occurs in the middle of the kVA range 

covered by this design line (750 kVA, 1000 kVA, 1500 kVA, 2000 kVA, and 2500 kVA). 

Design Lines 13A and 13B. As a further extension on the dry-type, three-phase, mediumvoltage BIL ranges, DOE originally analyzed 96 kV to 150 kV BIL in a single design line 

ranging from 225 kVA to 2500 kVA. The 225 kVA rating is considered to be the lowest kVA 

rating where one would expect to see a unit with a BIL greater than 110 kV. The typical tap 

arrangement is four 21⁄2 percent taps, two above and two below the nominal. The primary voltage 

is typically less than or equal to 35 kV and the secondary voltage is less than or equal to 600 V.

This third set of dry-type, three-phase, medium-voltage distribution transformers spans a 

wide range of kVA ratings. (225 kVA, 300 kVA, 500 kVA, 750 kVA, 1000 kVA, 1500 kVA, 

2000 kVA, and 2500 kVA). Based on comments received after the preliminary analysis, DOE 

decided to split the former design line 13 into two design lines, 13A and 13B, in order to 

improve scaling accuracy within EC10. The representative unit selected for design line 13A is a 

300 kVA transformer. This unit is a common rating in this size range, and occurs toward the low 

end of the range covered by this design line. The representative unit selected for design line 13 B 

is a 2000 kVA transformer, which occurs toward the high end of the range covered by this design 

line.

In addition to the three equipment classes for dry-type, medium-voltage, three-phase 

distribution transformers (for which there are five engineering design lines) presented in Table 

5.2.1, there are three equipment classes for single-phase, dry-type, medium-voltage units. As 

discussed in Chapter 3, the shipment volume for single-phase, dry-type, medium-voltage 

transformers is very low as a percentage of the total dry-type shipments. Additionally, the total 

megavolt-ampere (MVA) capacity of single-phase, dry-type, medium voltage transformers is 

relatively low as a percentage of the total MVA capacity for dry-type, medium voltage 

transformers. Therefore, it does not warrant the level of effort involved in conducting analysis on 

these specific units. DOE decided instead to scale the analysis findings from three-phase units to 

the single-phase units by establishing the same energy conservation standard requirement on a 
5-8

 ̳per phase‘ basis. In other words, DOE would scale the energy conservation standard 

requirements for a three-phase 1500 kVA medium-voltage dry-type to be the same for a singlephase 500 kVA medium-voltage dry-type unit. In this way, DOE was able to concentrate 

resources and improve the accuracy in other, higher volume and more important distribution

transformer equipment classes. DOE used the same approach in the previous rulemaking for 

distribution transformers.

5.2.1 Summary of Design Line Coverage

The following four tables summarize the coverage of each of the design lines in relation to 

the various equipment classes and kVA ratings. The abbreviation DL stands for design line, and 

the row in the table where the phrase ―Rep Unit‖ appears indicates the kVA rating of the 

representative unit from that design line. The representative unit is the kVA rating that DOE 

analyzed in the engineering and LCC analyses. For example, DL1 stands for design line 1, 

spanning from 10 to 167 kVA liquid-type, single-phase. The label ―Rep Unit‖ appears in row 50 

kVA, indicating that the 50 kVA is the representative unit for DL1. Similarly, the representative 

unit for DL2 is the 25 kVA unit. 

There are five liquid-immersed transformer design lines, three single-phase and two threephase, as shown in Table 5.2.3. To capture any design differences between a single-phase pole 

and a pad-mounted transformer, DOE analyzed units in both DL1 and DL2, spanning the same 

kVA ratings (10 kVA to 167 kVA). On the three-phase liquid-immersed side, there is no overlap 

between those two design lines.

Table 5.2.3 Liquid-Immersed Design Lines and Representative Units

 

Table 5.2.4 presents the low-voltage, dry-type design lines. For single-phase units, one 

design line spans all nine kVA ratings. For the three-phase units, two design lines cover the 11 

Rectangular Round

Tank Tank

10

15

25

37.5

50

75

100

167

250

333

500

667

833

Equipment Class 1

Liquid-Immersed,

Single-Phase

kVA

DL 1DL 2 DL 3

Rep Unit

Rep Unit

Rep Unit

Design

Lines

15

30

45

75

112.5

150

225

300

500

750

1000

1500

2000

2500

Equipment Class 2

Liquid-Immersed,

Three-Phase

kVA

DL 4 DL 5

Rep Unit

Rep Unit
5-9

kVA ratings in that equipment class. There is no overlap in the design lines for low-voltage drytype transformers.

Table 5.2.4 Dry-Type, Low-Voltage Design Lines and Representative Units

Table 5.2.5 presents equipment classes (abbreviated ―EC‖ in this table) for mediumvoltage, single-phase, dry-type units. As discussed in Chapter 3, section 3.4 (National Shipment 

Estimate), these units have a low shipment volume and low total MVA capacity. All three 

equipment classes shown in Table 5.2.5 together represent less than one-quarter of one percent of 

dry-type shipments on an MVA capacity basis, and less than one percent of medium-voltage drytype shipments on an MVA capacity basis. Thus, DOE did not consider it appropriate to conduct 

analyses of any units from these three equipment classes.

As an alternative to investing time and resources analyzing these low-volume units, DOE 

used the results from the medium-voltage, three-phase, dry-type units (presented in Table 5.2.6) 

and divided those findings by three, creating virtual (calculated) representative units (labeled as 

―Virtual RU‖ in Table 5.2.5) for these three equipment classes. DOE used the representative 

units from design lines 9, 10, 11, 12, 13A, and 13B. These virtual representative units are shown 

in their respective rows, following the application of the quotient. For example, in the single 

phase (20-45kV BIL) column, the representative unit from DL9 is a three-phase 300 kVA unit 

(see Table 5.2.6), so it scales to a single-phase, 100 kVA unit in Table 5.2.5.

Table 5.2.5 Dry-Type, Medium-Voltage, Single-Phase Design Lines

kVA Design Line kVA Design Line

15 15

25 30

37.5 45

50 75

75 112.5

100 150

167 225

250 300

333 500

750

1000

Equipment Class 3

Dry-Type, Low Voltage,

Single-Phase

Equipment Class 4

Dry-Type, Low Voltage,

Three-Phase

DL 6

Rep Unit

Rep Unit

DL 7 DL 8

Rep Unit
5-10

Table 5.2.6 presents the equipment classes (abbreviated ―EC‖ in this table) for the 

medium-voltage, three-phase, dry-type distribution transformers and each of the design lines and 

respective representative units. Because those equipment classes have high volumes and large 

ranges of kVA ratings, DOE used two separate design lines for each, to maintain accuracy. 

Within DL13A, DOE did not extrapolate the results of this unit to ratings of 150kVA and below 

because there were no shipments at these ratings in the shipments analysis and it is very unlikely 

that they would be built.

Table 5.2.6 Dry-Type, Medium-Voltage, Three-Phase Design Lines

5.2.2 Scaling Relationships in Transformer Manufacturing

DOE simplified the engineering analysis by creating design lines, selecting representative 

units from these design lines, and scaling the results of the analysis on these representative units 

within their respective design lines. This section briefly introduces the scaling relationship DOE 

used to extrapolate the findings on the representative units to the other kVA ratings. A more 

detailed discussion of the derivation of the 0.75 scaling rule is provided in Appendix 5B.

kVA

EC 5

Low BIL

EC 7

Med BIL

EC 9

20-45kV 46-95kV High BIL >96kV

15 -

25 -

37.5 -

50 -

75

100

167

250

333

500

667

833

Dry-Type, Medium Voltage, Single-Phase DL9 / 3

Virtual RU

DL11 / 3

Virtual RU

Virtual RU

DL13 / 3 (A&B)

DL10 / 3

Virtual RU

DL12 / 3

Virtual RU

Virtual RU

kVA

EC 6

Low BIL

EC 8

Med BIL

EC 10

20-45kV 46-95kV High BIL >96kV

15 -

30 -

45 -

75 -

112.5 -

150 -

225

300

500

750

1000

1500

2000

2500

Dry-Type, Medium Voltage, Three-Phase DL 9 DL 11 DL 10 DL 12

DL 13 (A & B)

Rep Unit

Rep Unit

Rep Unit

Rep Unit

Rep Unit

Rep Unit
5-11

The scaling formulae are mathematical relationships that exist between the kVA ratings 

and the physical size, cost, and performance of transformers. The size-versus-performance 

relationships arise from fundamental equations describing a transformer's voltage and kVA 

rating. For example, when the kVA rating, voltage, and frequency are fixed, the product of the 

conductor current density, core flux density, core cross-sectional area, and total conductor crosssectional area is constant. 

To illustrate this point, consider a transformer with four fixed variables: frequency, 

magnetic flux density, current density, and BIL rating. If one enlarges (or decreases) the kVA 

rating, then the only parameters free to vary are the core cross-section and the core window area 

through which the windings pass. Thus, to increase (or decrease) the kVA rating, the dimensions 

for height, width, and depth of the core/coil assembly scale equally in all directions. Analysis of 

this scaling relationship reveals that each of the linear dimensions varies as the ratio of kVA 

ratings to the 1⁄4 power. Similarly, areas vary as the ratios of kVA ratings to the 1⁄2 power and 

volumes vary as the ratio of the kVA ratings to the 3⁄4 or 0.75 power, hence the term "0.75 scaling 

rule." Application of the 0.75 scaling rule assumes that the efficiency profile of a given 

transformer will have the same shape as the transformer being scaled. Table 5.2.7 depicts the 

most common scaling relationships in transformers.

Table 5.2.7 Common Scaling Relationships in Transformers

Parameter Being Scaled Relationship to kVA Rating

(varies with ratio of kVAx)

Weight (kVA1/kVA0)

3/4

Cost (kVA1/kVA0)

3/4

Length (kVA1/kVA0)

1/4

Width (kVA1/kVA0)

1/4

Height (kVA1/kVA0)

1/4

Total Losses (kVA1/kVA0)

3/4

No-load Losses (kVA1/kVA0)

3/4

The following three relationships are true as the kVA rating increases or decreases, if the 

type of transformer (liquid-immersed or dry-type, single-phase or three-phase), the primary 

voltage, the core configuration, the core material, the core flux density, and the current density 

(amperes per square inch of conductor cross-section) in both the primary and secondary 

windings are all held constant:

1. The physical proportions are constant (same relative shape),

2. The eddy loss proportion is essentially constant, and

3. The insulation space factor (voltage or BIL) is constant.

In practical applications, it is rare to find that all of the above are constant over even 

limited ranges; however, over a range of one order of magnitude in both directions (e.g., from 50 

kVA to 5 kVA or from 50 kVA to 500 kVA), the scaling rules shown in Table 5.2.7 can be used 
5-12

to establish reasonable estimates of performance, dimensions, costs, and losses. In practice, these 

rules can be applied over even wider ranges to estimate general performance levels.

To illustrate how DOE used the scaling laws, consider two transformers with kVA ratings 

of S0 and S1. The no-load losses (NL) and total losses (TL) of these two transformers would be 

depicted as NL0 and TL0, and NL1 and TL1. Then the relationships between the NL and TL of the 

two transformers could be shown as follows:

Equation 5.2.1

NL1 = NL0 (S1 / S0)

0.75

where:

NL1 = no-load losses of transformer ―1,‖

NL0 = no-load losses of transformer ―0,‖

S1 = kVA rating of transformer ―1,‖ and

S0 = kVA rating of transformer ―0.‖

and

Equation 5.2.2

TL1 = TL0 (S1 / S0)

0.75

where:

TL1 = total losses of transformer ―1,‖ and

TL0 = total losses of transformer ―0.‖

Equation 5.2.1 and Equation 5.2.2 can be manipulated algebraically to show that the load 

loss also varies to the 0.75 power. Starting with the concept that total losses equal no-load losses 

plus load losses, DOE can derive the relationship for load loss (LL), and show that it also scales 

to the 0.75 power. Specifically:

Equation 5.2.3

LL1 = TL1 - NL1

where:

LL1 = load losses of transformer ―1‖

Inserting the TL1 and NL1 terms into this equation, DOE finds:
5-13

Equation 5.2.4

LL1 = (TL0 (S1 / S0)

0.75) - (NL0 (S1 / S0)0.75)

Equation 5.2.5

LL1 = (TL0 - NL0) (S1 / S0)

0.75

Equation 5.2.6

LL1 = (LL0) (S1 / S0)

0.75

where:

LL0 = load losses of transformer ―0.‖

Thus, the 0.75 scaling rule can be applied to estimate the losses of a transformer, given 

the losses and kVA rating of a reference (analyzed) unit. However, in order for this rule to be 

applicable, the transformer type must be the same, and key parameters—such as the type of core 

material, core flux density, and conductor current density in the high and low voltage windings—

must be fixed. Additionally, use of the 0.75 scaling rule assumes that the efficiency profile of a 

given transformer will have the same shape as the transformer being scaled. See Appendix 5B 

for detailed discussion on the derivation of the 0.75 scaling rule. 

DOE used the 0.75 scaling rule to scale the analysis findings on each of the representative 

units within the 14 design lines to the 102 kVA ratings that it did not analyze. DOE applied the 

scaling rule within the design lines in the national impact analysis (Chapter 10), where it 

calculated efficiency ratings for the 102 kVA ratings not analyzed.

5.3 TECHNICAL DESIGN INPUTS

For all 14 representative units, the engineering analysis explored the relationship between 

the manufacturer selling prices and corresponding transformer efficiencies. For this analysis, 

DOE contracted Optimized Program Service, Inc. (OPS) in Ohio, a software company 

specializing in transformer design since 1969. Using a range of input parameters and material 

prices, the OPS software produces a design. This design has specific information about the core 

and coil, including physical characteristics, dimensions, material requirements, and mechanical 

clearances, as well as a complete electrical analysis of the final design. This optimized, practical 

transformer design, the bill of materials, and an electrical analysis report contain sufficient 

information for a manufacturer to build the unit. DOE uses the software‘s output to generate an 

estimated cost of manufacturing materials and labor, which it then converts to a manufacturer 

selling price by applying markups.

The electrical analysis report estimates the performance of the transformer design 

(including efficiency) at 25 percent, 35 percent, 50 percent, 65 percent, 75 percent, 100 percent, 

125 percent, and 150 percent of nameplate load. The software output provides a clear 

understanding of the relationship between cost and efficiency because it provides detailed data 

on design variances, as well as a bill of materials, labor costs, and efficiency. The software does 

not capture retooling costs associated with changing production designs for a specific 
5-14

manufacturer. In some cases, however, DOE captured tooling costs associated with 

manufacturing mitered cores by applying adders to the steel price. 

5.3.1 A and B Loss Valuation Inputs

One of the inputs to the design software consisted of a range of what are known in the 

industry as A and B evaluation combinations (see Chapter 3, section 3.6, Total Ownership Cost 

Evaluation). The combination of A and B input to the design software mimics a distribution 

transformer purchase order. The A parameter represents a customer's present value of future 

losses in the transformer core (no-load losses). The B value represents a customer's present value 

of future losses in the windings (load losses). The B parameter is never larger than A, as this 

would imply a specification for a transformer whose average load would be more than 100 

percent of the nameplate load. The A and B values take into account a range of factors that 

usually vary from customer to customer. 

The A and B values are expressed in terms of dollars per watt of loss. The greater the 

values of A and B, the greater the importance a customer attaches to the value of future 

transformer losses. As A and B values increase, the customer places greater importance on 

reducing the watts of core and winding losses, respectively, and so the customer chooses a more 

energy-efficient transformer.

DOE used broad ranging combinations of A and B evaluation formulae (presented in 

Table 5.3.1 and Table 5.3.2) to create a complete set of efficiency levels for each design option 

combination analyzed. The efficiency levels spanned from a low-first-cost unit to a maximum 

technologically feasible (―max-tech‖) design. For the low-first-cost design, the A and B 

evaluation values were both $0/watt, indicating that the customer does not attach any financial 

value to future losses in the core or coil of the transformer. For the maximum technologically 

feasible design, the A and B evaluation values were very high, pushing the software to design at 

the highest efficiencies achievable.

DOE created its combinations of A and B evaluation formulae combining two techniques 

to ensure there were sufficient designs in the database for the analysis. The first technique was to 

create a  ̳grid‘ of A and B combinations. The  ̳grid‘ technique involved increasing the value of A 

by a step value, and then increasing the B value from zero to that value of A, using a different 

step value. Thus, if A had incremental steps of $0.25 and B had steps of $0.20, the combinations 

would work as follows: ($0.00, $0.00), ($0.25, $0.00), ($0.25, $0.20), ($0.50, $0.00), ($0.50, 

$0.20), ($0.50, $0.40), ($0.75, $0.00), and so on. Table 5.3.1 presents the ranges and incremental 

steps for the A and B combinations used in the three grids.
5-15

Table 5.3.1 A and B Grid Combinations Used by Software to Generate Design Database

Grid 

Number

A values

and increments

B values

and increments

Resultant # of

(A, B) combinations

1 $0 to $2 by 0.25 steps $0 to $2 by 0.20 steps 47

2 $2.50 to $8 by 0.50 steps $0 to $8 by 0.40 steps 157

3 $9 to $16 by 1.00 steps $3 to $8 by 0.50 steps 85

The second technique for generating A and B evaluation formulae in the engineering 

analysis is called the ―fan.‖ DOE understands that the ratio of A to B represents an implicit 

loading for the transformer. Therefore, DOE created a set of (A, B) values in which the B is 

calculated from the A. The B term is calculated as the A times the percent load squared. In other 

words, if A equals $1 and DOE is interested in calculating the appropriate B for a 50 percent 

root-mean-square (RMS) load, then it would be $1 times (0.50)^2, or $0.25. Thus, the 

combination of ($1.00, $0.25) represents approximately a 50 percent RMS load. As with the 

―grid,‖ the A values increased with a step function, and B values were calculated as fractions of 

A so that the ratio of A to B encompassed the RMS loading points that were identified in DOE‘s 

loading analysis (i.e., 35 percent and 50 percent). DOE calculated the B values for each A at the 

following RMS loading points: 5 percent, 10 percent, 15 percent, 20 percent, 25 percent, 30 

percent, 35 percent, 40 percent, 45 percent, 50 percent, 55 percent, and 60 percent. Table 5.3.2

presents the range of the two fan combinations used in the analysis.

Table 5.3.2 A and B Fan Combinations Used by Software to Generate Design Database

Fan 

Number

A values

and increments

B values

and increments

Resultant # of

(A,B) 

combinations

1 $0 to $2 by 0.50 steps 5% to 60% implicit loading by 5% steps 47

2 $3 to $16 by 1.00 steps 5% to 60% implicit loading by 5% steps 182

When used together, these two techniques created a broad spectrum of A and B 

combinations as inputs to the OPS software. Figure 5.3.1 illustrates the coverage of designs for 

the 518 A and B combinations. DOE used each of these A and B pairs with each combination of 

core steel and winding material analyzed for each representative transformer design line studied.
5-16

Figure 5.3.1 A and B Combination Software Inputs Used in the Engineering Analysis

Occasionally, the design software generated the same transformer design for two 

different A and B combinations, creating duplicate designs in the engineering analysis database. 

DOE removed these duplicate designs before the engineering database was imported into the 

LCC analysis. Similarly, DOE removed any designs that yielded an efficiency value below the 

current standard level efficiency.

5.3.2 Core Material Options

DOE understands that there are many ways to build a transformer, even with constant 

kVA and voltage ratings. For instance, manufacturers can vary the core steels (e.g., M2, M3, 

M6), the winding materials (aluminum or copper), and core configurations (shell or core-type). 

For each of the design lines, DOE provides tables listing the design option combinations that it 

used to analyze each of the representative units. Depending on customer needs, the cost of 

materials, the capital equipment in their facility, and the skills of their labor force, manufacturers 

make decisions on how to manufacture a given transformer using different core configurations, 

core steels, and winding materials. To capture this variation in designs, DOE analyzed the 14

representative units using 5 – 8 different design option combinations of core type, core steel, and 

winding material. As discussed in the technology assessment (see Chapter 3), core steel is 

produced in a range of qualities (from an efficiency perspective). M2 core steel is oriented grain 

silicon steel and has thin laminations, and consequently has very low losses. M12 core steel is 
5-17

non-oriented grain silicon steel and is rolled in thicker laminations, thus contributing to higher 

core losses. Table 5.3.3 lists all the steel types used in the analysis, and properties associated 

with these steels. Each steel grade provides the nominal thickness and core losses per pound of 

steel, under a specified typical magnetic flux density, measured in Tesla (T).

Table 5.3.3 Core Steel Grades, Thicknesses and Associated Losses

Steel 

Grade

Nominal 

Thickness 

inches

Core Loss at 60 Hz

Watts per Pound at 

magnetic flux density*

Notes / Remarks

M12 0.014 1.36 Watts/lb at 1.5 T Non-oriented grain silicon steel

M6 0.014 0.60 Watts/lb at 1.5 T

0.84 Watts/lb at 1.7 T

Grain-oriented silicon steel

M5 0.012

0.51 Watts/lb at 1.5 T

0.74 Watts/lb at 1.7 T

Grain-oriented silicon steel

M4 0.011

0.46 Watts/lb at 1.5 T

0.66 Watts/lb at 1.7 T

Grain-oriented silicon steel

M3 0.009

0.39 Watts/lb at 1.5 T

0.60 Watts/lb at 1.7 T

Grain-oriented silicon steel

M3 Lite 

Carlite 0.009

0.39 Watts/lb at 1.5 T

0.59 Watts/lb at 1.7 T

Grain-oriented silicon steel with insulative coating

M2 0.007

0.38 Watts/lb at 1.5 T

0.58 Watts/lb at 1.7 T

Grain-oriented silicon steel

M2 Lite 

Carlite 0.007

0.37 Watts/lb at 1.5 T

0.57 Watts/lb at 1.7 T

Grain-oriented silicon steel with insulative coating

H-0 DR 0.009

0.34 Watts/lb at 1.5 T

0.47 Watts/lb at 1.7 T

Domain-refined, high permeability grade silicon 

steel

ZDMH 0.009

0.38 Watts/lb at 1.5 T

0.57 Watts/lb at 1.7 T

Imported silicon steel, magnetic domain- refined 

by mechanical process 

SA1 0.001

0.108 Watts/lb at 1.35 T

0.098 Watts/lb at 1.3 T

Amorphous core steel (silicon and boron); flux 

density limitation - testing at ~ 1.3 T

* Watts of loss per pound of core steel are only comparable at the same magnetic flux density (measured in Tesla).

5.3.3 Core Configurations

In addition to selecting a core steel, the manufacturer‘s selection of a core design may 

also contribute to the overall efficiency of a transformer. A transformer facility may be 

optimized to work around one or two core configurations. Table 5.3.4 provides a list of all the 

core configurations used for each of the 14 design lines. DOE selected these configurations, in 

combination with the range of core steels and winding materials, to represent the most common 

construction methods for these kVA ratings in the U.S. market.
5-18

Table 5.3.4 Core Configurations Used in Each Design Line

Design 

Line # Phases Core Configurations Used in the Engineering Analysis

DL1 1

Wound core - distributed gap;

Shell-type

DL2 1

Wound core - distributed gap;

Shell-type or core-type

DL3 1

Wound core - distributed gap;

Shell-type or core-type

DL4 3

Wound core - distributed gap or symmetric core;

5-leg

DL5 3

Wound core - distributed gap or symmetric core; 

5-leg

DL6 1

Wound core – distributed gap; or stacked, butt-lap or step-lap mitered;

Shell-type or core-type

DL7 3

Wound core - distributed gap or symmetric core; or stacked butt-lap, step-lap or full 

mitered; 

3-leg or 5-leg

DL8 3

Wound core - distributed gap or symmetric core; or stacked butt-lap, step-lap or full 

mitered; 

3-leg or 5-leg

DL9 3

Wound core - distributed gap or symmetric core; or stacked full mitered; 

3-leg or 5-leg

DL10 3

Wound core – distributed gap or symmetric core; or stacked, cruciform, mitered joint;

3-leg

DL11 3

Wound core – distributed gap or symmetric core; or stacked, step-lap or full mitered; 

3-leg or 5-leg

DL12 3

Wound core – distributed gap or symmetric core; or stacked, cruciform or step-lap

mitered joint;

3-leg or 5-leg

DL13

(A & 

B)

3

Wound core – distributed gap or symmetric core; or stacked, cruciform or step-lap

mitered joint;

3-leg or 5-leg

5.3.3.1 Standard Core Configurations

For the single-phase representative units, the configurations used are either core-type or 

shell-type. This applies whether the core consists of stacked or wound laminations of core steel. 

For wound cores, manufacturers generally employ a technique known as  ̳distributed gap.‘ This 

means that each lamination of core steel wound around the form will have a start and finish point 

(the  ̳gap‘), staggered with respect to the previous and the next lamination. Distributed gap core 

construction techniques are used to minimize the performance impact of the lamination joint 

gaps (reducing the exciting current) and, by locating inside the coil window, reduce the 
5-19

transformer‘s operating sound level. Figure 5.3.2 illustrates the two types of single-phase core 

construction.

Figure 5.3.2 Graphic of Single-Phase Core Configurations

Three-phase transformers can have three-legged, four-legged, five-legged, Evans, or 

symmetric cores. In the engineering analysis, DOE considered the three-legged construction 

techniques for the three-phase dry-types and five-legged construction for the three-phase liquidimmersed transformers. Some of the dry-type designs using an amorphous core also use a fivelegged construction technique. Figure 5.3.3 below illustrates the difference between the threelegged and the five-legged core construction techniques. A three-legged core is assembled from 

stacked laminations, the joints of which can be butt-lapped or mitered. Where there is an 

economic need to reduce core losses, particularly in keeping with the use of more efficient 

grades of core steel (M2 or M3), the mitered core tends to be selected. DOE recognizes that there 

are a variety of approaches to mitered core construction: ―scrapless T-mitering,‖ ―full-mitering,‖ 

and ―step-mitering.‖ DOE modeled full-mitered and step-mitered cores. 

Figure 5.3.3 Graphic of Three-phase Core Configurations

For larger kVA ratings, design economics may cause the selection of a cruciform core 

section, where multiple lamination widths are stacked in increasing and then decreasing widths 

to create a circular core form (or ―log‖) around which the windings are placed. Figure 5.3.4

SHELL TYPE CORE TYPE
5-20

illustrates the cruciform core by showing a cross-section. This figure shows four different widths 

of steel being used, but there can be fewer or more widths, depending on the design. By using a 

core configuration that better follows the contours of the windings, losses are again reduced, 

resulting in a more efficient transformer. The use of the three-legged core usually depends on the 

primary winding being delta-connected. If the primary winding is wye-connected, as is 

frequently the case for pad-mounted transformers used in underground distribution, the core 

configuration needs to be four-legged or five-legged.

Figure 5.3.4 Cruciform Core Cross-Section

The five-legged core is assembled from four wound-core loops, and is the common 

configuration for liquid-filled, three-phase distribution transformers having a wye-wye voltage 

connection. Again, this occurs for pad-mounted transformers used in underground distribution. 

The individual core loops have distributed gaps, as explained for single-phase, wound-core 

transformers.

5.3.3.2 Symmetric Core Configurations

In a symmetric core configuration, each leg of a three-phase transformer is identically 

connected to the other two. It uses a continuously wound core with 120 ̊ radial symmetry, 

resulting in a triangularly shaped core when viewed from above. In a traditional core, the center 

leg is magnetically distinguishable from the other two because it has a shorter average flux path 

to each. In a symmetric core, however, no leg is magnetically distinguishable from the other two. 

Figure 5.3.5 shows the configuration of the symmetric core design.2

 

2 Lundmark, Sonja. Computer Model of Electromagnetic Phenomena in Hexaformer. 2007. Available at: 

http://www.hexaformer.com/ExternaDokument/chalmers_report1.pdf.
5-21

 

Figure 5.3.5 Graphic of Symmetric Core Configuration

The symmetric core construction offers several advantages over traditional transformer 

cores. These include lowered weight, volume, no-load losses, noise, vibration, stray magnetic 

fields, inrush current, and power in the third harmonic. Transformers using this core construction 

can oftentimes use fewer pounds of core steel than a standard core would use to achieve a given 

efficiency. As a result, total material cost for symmetric core designs is typically lower than that 

of a standard transformer design. However, the advanced manufacturing processes necessary to 

produce the core increases the cost of labor and overhead for this core configuration. Similarly, 

the appropriate equipment requires large capital expenditures to manufacture this core type.

Because of zero-sequence fluxes associated with wye-wye connected transformers, 

symmetric core designs are best suited to delta-delta or delta-wye connections. While traditional 

cores can circumvent the problem of zero-sequence fluxes by introducing a fourth or fifth 

unwound leg, core symmetry makes extra legs inherently impractical. Yet another way to 

mitigate zero-sequence fluxes comes in the form of a tertiary winding, which is delta-connected 

and has no external connections. This winding is dormant when the transformer‘s load is 

balanced across its phases. Although symmetric core designs may, in theory, be made tolerant of 

zero-sequence fluxes by employing this method, it comes at extra cost and complexity. 

Using this tertiary winding, DOE believes that symmetric core designs can service nearly 

all distribution transformer applications in the United States. Most dry-type transformers have a 

delta connection and would not require a tertiary winding. Similarly, most liquid-immersed 

transformers serving the industrial sector have a delta connection. These market segments could 

use the symmetric core design without any modification for a tertiary winding. However, in the 
5-22

United States, most utility-operated distribution transformers are wye-wye connected. These 

transformers would require the tertiary winding in a symmetric core design.

DOE was unable to identify a company with commercial modeling software that could 

model symmetric core designs, but DOE did speak with many transformer manufacturers and 

industry experts about symmetric core designs. Through these conversations, DOE received 

information on a few symmetric core designs. These designs were insufficient to conduct a fullscale engineering analysis comparable to the other design types. In the preliminary analysis, 

DOE was able to approximate the cost-efficiency relationship for symmetric core designs based 

on trends in the data received from manufacturers, published literature, and through 

conversations with industry experts.

For each three-phase design line, DOE adjusted its traditional core designs to simulate a 

symmetric core design. To simulate the symmetric core design, DOE adjusted core losses, core 

weight, and labor costs. While these adjustments are rough approximations, they represent 

potential symmetric core designs for each design line.

To adjust core losses, DOE considered several symmetric core designs, conversations 

with manufacturers, and published literature. When examining the symmetric core data provided 

by manufacturers, DOE found that core losses for symmetric core designs range from 0 – 23 

percent less than the core losses of comparable traditional transformers. This aligns with 

literature published by Chalmers University, which claims that core losses can be reduced by up 

to 25 percent using symmetric cores.3 Using this data, DOE reduced core losses by 15.5 percent 

for its simulated symmetric core designs, which is the mean reduction from the examined data. 

DOE did not adjust the coil losses for the symmetric core designs compared to the traditional 

core designs.

In addition to reducing core losses, DOE reduced the core weight in the simulated 

symmetric core designs. Chalmers University literature estimates that symmetric cores reduce 

the total transformer weight by 12 percent.3 Manufacturer designs show a reduction in core 

weight of 15 – 25 percent compared to traditional transformer designs. Relying on these data 

sources, DOE reduced core weight by 17.5 percent for the simulated symmetric core designs, 

which is the mean reduction from the examined data.

DOE‘s research indicates that labor costs would increase for symmetric core designs 

compared to the labor requirements for comparable traditional transformer designs. From

speaking with manufacturers and examining symmetric core designs, DOE noted that labor costs 

may increase by 10 – 100 percent compared to the labor costs of traditional transformer designs. 

DOE increased the labor costs of its simulated symmetric core designs by 55 percent, which is 

the midpoint between the 10 percent and 100 percent estimates.

 

3

―Comparison Between Hexa- and Conventional E-type Core Three-Phase Transformers.‖ Available at: 

http://publications.lib.chalmers.se/cpl/record/index.xsql?pubid=74554.
5-23

 Table 5.3.5 identifies the adjustments DOE used to simulate the symmetric core designs. 

DOE applied these adjustments to each of the traditional three-phase transformer designs to 

develop a cost-efficiency relationship for symmetric core technology. DOE did not model a 

tertiary winding for the wye-wye connected liquid-immersed design lines. Based on its research, 

DOE believes that the losses associated with the tertiary winding may offset the benefits of the 

symmetric core design while also adding costs to the design. Instead, DOE modeled symmetric 

core designs for the three-phase, liquid-immersed design lines without a tertiary winding to 

examine the impact of symmetric core technology on the subgroup of applications that do not 

require the tertiary winding.

Table 5.3.5 Design Adjustments for Simulated Symmetric Core Designs

Range Core Losses [W]

(% Reduction)

Core Weight [lbs]

(% Reduction)

Labor Hours

(% Increase)

Minimum -0.0 -12.0 +10

Mean of Observations -15.5 -17.5 +55

Maximum -25.0 -25.0 +100

Section 5.6 presents cost-efficiency results for the simulated symmetric core designs. For 

each three-phase design line, DOE considered an additional efficiency level to characterize the 

maximum efficiency available using symmetric core technology.

Following the preliminary analysis, DOE received more detailed design data from Hex 

Tec, LLC, and used in data in attempting to draw the most direct possible comparison to its 

conventional designs of similar design lines. Based on this initial treatment of the data, DOE 

observed a competitive, but not superior, cost/efficiency proposition for symmetric core designs. 

Results are presented in Appendix 5A.

5.3.3.3 Core Deactivation Technology

Core deactivation technology employs a system of smaller transformers to replace a 

single, larger transformer. For example, three transformers sized at 25 kVA and operated in 

parallel could replace a single 75 kVA transformer. The smaller transformers that compose the 

system can then be activated and deactivated using core deactivation technology based on the 

loading demand. Currently, DOE is not considering core deactivation systems in the context of 

setting standards, but may explore doing so in the future.

Winding losses are proportionally smaller at lower load factors, but for any given current, 

a smaller transformer will experience greater winding losses than a larger transformer. As a 

result, those losses may be more than offset by the smaller transformer‘s reduced core losses. As 

loading increases, winding losses become proportionally larger and eventually outweigh the 

power saved by using the smaller core. At that point, the control unit (which consumes little 

power itself) switches on an additional transformer, reducing winding losses at the cost of 

additional core losses. The control unit knows how efficient each combination of transformers is 

for any given loading, and is constantly monitoring the unit‘s power output so that it will use the 

optimal number of cores. In theory, there is no limit to the number of transformers that may be 

paralleled in this sort of system, but cost considerations would imply an optimal number.
5-24

While core deactivation could save energy over a real world loading cycle, those savings 

might not be represented in the current DOE test procedure. Presently, the test procedure 

specifies a single loading point of 50 percent for liquid-immersed and medium-voltage dry-type 

transformers, and 35 percent for low-voltage dry-type. The real gain in efficiency for this 

technology is at loading points below the root mean square (RMS) loading specified in the test 

procedure, where some transformers in the system could be deactivated. At loadings where all 

transformers are activated, which may be the case at the test procedure loading, the combined 

core and coil losses of the system of transformers could exceed those of a single, larger 

transformer. This would result in a lower efficiency for the system of transformers compared to 

the single, larger transformer.

Therefore, DOE believes core deactivation technology may be at a disadvantage in the 

market based on the current test procedure, which specifies a single loading based on the RMS 

loading in the United States. DOE believes that the core deactivation system would engage all 

transformers at this loading, resulting in a lower efficiency reading than a standard, single 

transformer of equivalent size. However, the core deactivation system may save more energy 

than the standard transformer when all loading points that are experienced in service are 

considered. This is especially true for applications that have an average loading below the test 

procedure loading point.

DOE has not currently analyzed this technology in the engineering analysis or 

downstream analyses, but believes it could do so using its existing transformer designs. To 

analyze this technology, DOE would consider core deactivation systems composed of three 

identical transformers, each with one-third the kVA size of the analyzed design lines. This 

creates a core deactivation system of the same total kVA size as the analyzed design lines. Each 

of these core deactivation systems could be evaluated under various loading scenarios to identify 

the energy savings potential at loadings below and above the RMS load factor. While it is 

possible to manufacture core deactivation systems using different designs for each component 

transformer, it requires additional design complexities. For example, using different component 

transformer designs necessitates a similar winding design to maintain the impedance across each 

transformer at each load factor. These complexities would not need to be considered in the 

analysis when analyzing three identical component transformer designs.

To examine each component transformer design, DOE could scale the engineering 

analysis of its existing design lines to simulate a transformer of one-third the kVA size. DOE 

would scale the losses, manufacturer selling price (MSP), weight, and dimensions using the 0.75 

scaling rule explained in section 5.2.2. The resulting designs could be analyzed as component 

transformers for the core deactivation system. DOE could then simulate a core deactivation 

system by combining three identical component transformers and considering the losses at each 

loading point for the following three scenarios: (1) all three component transformers are 

activated, (2) two component transformers are activated, and (3) only one component 

transformer is activated. Given this information, DOE could simulate the performance of a core 

deactivation system by evaluating the scenario with the least losses for a given load factor.

Additionally, DOE would account for the added cost and weight of the core deactivation 

technology. The additional components include items such as contactors, current sensors, a 
5-25

programmable logic controller, circuit boards, additional wiring, and other miscellaneous items. 

DOE estimated the cost of these components for a medium to large transformer manufacturer, 

and also estimated the incremental weight added by the components. Table 5.3.6 outlines the 

estimated cost and weight of the core deactivation components.

Table 5.3.6 Core Deactivation Technology Components, Cost and Weight

Design Line 6 Design Line 7 Design Line 8

Core Deactivation Controller Cost 140 179 307

Other Components Cost [$] 237 312 882

Total Weight [lbs.] 22 50 141

DOE understands that core deactivation technology is most easily implemented in lowvoltage dry-type distribution transformer designs. Implementing core deactivation technology in 

medium-voltage distribution transformers is possible, but poses difficulties for switching the 

primary and secondary connections. DOE has not fully quantified these differences, but may do 

so in the future if it determines that core deactivation technology systems are within the 

rulemaking scope of coverage.

5.3.4 Less-Flammable Liquid-Immersed Transformers

For liquid-immersed distribution transformers, DOE studied the differences between 

mineral oil cooled units and less-flammable cooled units. DOE understands that the IEEE 

standard C57.12.80 divides less-flammable liquid-immersed (LFLI) transformers into two 

groups: KNAN (which have an insulating liquid with a fire point greater than 300 degrees 

Celsius) and LNAN (which have an insulating liquid with no measurable fire point). The fire 

point for mineral oil is approximately 175 degrees Celsius, and therefore this type of transformer 

is not used inside buildings or in areas designated as hazardous. While industry has a 

specification for KNAN for a certain degree of fire protection or LNAN for users who prefer an 

extra measure of safety, DOE will continue to refer to both KNAN and LNAN using the phrase 

 ̳less-flammable,‘ or LFLI.

DOE understands that the viscosity of the insulating liquid can have a slight impact on 

the efficiency of a transformer. When the viscosity is higher than mineral oil, transformer 

designers must make slightly larger cooling ducts to permit an easier flow of the fluid. Larger 

ducts result in larger physical size of the winding assembly and a greater mean number of turns

of the conductor, therefore contributing to a slightly higher load loss. However, as efficiency 

increases, the transformer will run cooler, which negates part of the need for larger cooling ducts. 

As such, LFLI transformers are still able to achieve the same efficiency levels as transformers 

using mineral oil. DOE verified this fact through conversations with manufacturers and industry 

experts. In fact, DOE was informed that LFLI transformers might be capable of higher 

efficiencies than mineral oil units since their higher temperature tolerance may allow the unit to 

be downsized and run hotter than mineral oil units.

For the KNAN transformers (i.e., those with a fire point of 300 degrees or greater), DOE 

is not aware of any viscosity differences with mineral oil that might impede designs or make 

efficiency levels significantly more difficult to reach. For LNAN transformers (i.e., those with no 
5-26

fire point), DOE understands that the viscosity under usual operating conditions is slightly 

greater than that of mineral oil, which may require design engineers to increase the duct size, 

leading to a marginal impact on efficiency. However, as explained above, DOE believes this 

increased viscosity is offset by the cooler operating temperature, which could allow the 

transformer to be downsized and run hotter. This would negate any impact on efficiency. Chapter 

2 provides additional discussion of less-flammable liquid-immersed transformers.

5.3.5 Design Line 1 Representative Unit

Design line 1 (DL1) represents rectangular-tank, liquid-immersed, single-phase 

distribution transformers, ranging from 10 kVA to 167 kVA. The representative unit selected for 

this design line is a 50kVA pad-mounted unit. The following are the technical specifications that 

constitute input parameters to the OPS design software:

KVA: 50 (liquid-immersed, rectangular-tank)

Primary: 14400 Volts at 60 Hz

Secondary: 240/120V

T Rise: 65 ̊C

Ambient: 20 ̊C

Winding Configuration: Lo-Hi-Lo (Shell-Type)

Core: Wound core - distributed gap

Taps: Four 21⁄2 percent, two above and two below the nominal

Impedance Range: 1.5–4.5 percent

For DL1, DOE selected nine construction combinations (called ―design option 

combinations‖), based on input from manufacturers and other technical experts. The core 

selected was shell-type, because the application is for a pad-mounted unit, and this shape is well 

suited to a rectangular tank. With the exception of the max-tech/high efficiency designs, DOE 

selected nine design option combinations to represent the most common construction practices 

for this representative unit. 

Table 5.3.7 Design Option Combinations for the Representative Unit from Design Line 1

Core Material High-Voltage 

Conductor

Low-Voltage 

Conductor Core Design Type

M5 Cu – wire Al – strip Shell – DG* Wound Core

M3 Al – wire Al – strip Shell – DG Wound Core

M3 Cu – wire Al – strip Shell – DG Wound Core

M2 Al – wire Al – strip Shell – DG Wound Core

M2 Cu – wire Al – strip Shell – DG Wound Core

ZDMH Al – wire Al – strip Shell – DG Wound Core

ZDMH Cu – wire Cu – strip Shell – DG Wound Core

SA1 (Amorphous) Al – wire Al – strip Shell – DG Wound Core

SA1 (Amorphous) Cu – wire Cu – strip Shell – DG Wound Core

* DG – Distributed gap wound core construction, where the core laminations are wound in such a way that the gap 

between the start and finish of a lamination is staggered in the cross-section of the core.

DOE analyzed each of the nine design option combinations using the matrix of A and B 

values described in Table 5.3.1 and Table 5.3.2, creating 1,924 designs.
5-27

5.3.6 Design Line 2 Representative Unit

Design line 2 (DL2) represents round-tank, liquid-immersed, single-phase distribution 

transformers, ranging from 10 kVA to 167 kVA. The representative unit selected for this design 

line is a 25kVA pole-mounted unit. The following are the technical specifications that constitute 

input parameters to the OPS design software:

KVA: 25 (liquid-immersed, round-tank)

Primary: 14400 Volts at 60 Hz (125 kV BIL)

Secondary: 120/240V

T Rise: 65 ̊C

Ambient: 20 ̊C

Winding Configuration: Lo-Hi-Lo (Shell-Type), Lo-Hi (Core-Type, for amorphous core)

Core: Wound core - distributed gap

Taps: Four 21⁄2 percent, two above and two below the nominal

Impedance Range: 1.0–4.5 percent

For DL2, DOE selected eleven design option combinations, based on input from 

manufacturers and other technical experts. With the exception of the max-tech/high-efficiency 

designs, DOE selected these design option combinations to represent the most common 

construction practices for the representative unit.

Table 5.3.8 Design Option Combinations for the Representative Unit from Design Line 2

Core Material High-Voltage 

Conductor

Low-Voltage 

Conductor Core Design Type

M5 Cu – wire Al – strip Shell – DG Wound Core

M4 Al – wire Al – strip Shell – DG Wound Core

M4 Cu – wire Al – strip Shell – DG Wound Core

M3 Al – wire Al – strip Shell – DG Wound Core

M3 Cu – wire Al – strip Shell – DG Wound Core

M2 Al – wire Al – strip Shell – DG Wound Core

M2 Cu – wire Al – strip Shell – DG Wound Core

ZDMH Al – wire Al – strip Shell – DG Wound Core

ZDMH Cu – wire Cu – strip Shell – DG Wound Core

SA1 (Amorphous) Al – wire Al – strip Core – DG Wound Core

SA1 (Amorphous) Cu – wire Cu – strip Core – DG Wound Core

DOE analyzed each of the eleven design option combinations using the matrix of A and 

B values described in Table 5.3.1 and Table 5.3.2, creating 2,301designs.

5.3.7 Design Line 3 Representative Unit

Design line 3 (DL3) represents round-tank, liquid-immersed, single-phase distribution 

transformers, ranging from 250 kVA to 833 kVA. The representative unit selected for this design 

line is a 500kVA round-tank transformer. The following are the technical specifications which 

constitute input parameters to the OPS design software:
5-28

KVA: 500 (liquid-immersed, round-tank)

Primary: 14400 Volts at 60 HZ (150kV BIL)

Secondary: 277 Volts

T Rise: 65 ̊C

Ambient: 20 ̊C

Winding Configuration: Lo-Hi (Shell-Type and Core-Type)

Core: Wound core - distributed gap

Taps: Four 21⁄2 percent, two above and two below the nominal

Impedance Range: 1.5–7.0 percent

For DL3, DOE selected twelve design option combinations of core steel and winding 

material, based on input from manufacturers and other technical experts. With the exception of 

the max-tech/high-efficiency designs, DOE chose design option combinations to represent the 

most common construction practice for this representative unit.

Table 5.3.9 Design Option Combinations for the Representative Unit from Design Line 3

Core Material High-Voltage 

Conductor

Low-Voltage 

Conductor Core Design Type

M5 Cu – wire Al – strip Shell – DG Wound Core

M4 Al – wire Al – strip Shell – DG Wound Core

M4 Cu – wire Al – strip Shell – DG Wound Core

M3 Al – wire Al – strip Shell – DG Wound Core

M3 Cu – wire Al – strip Shell – DG Wound Core

M2 Al – wire Al – strip Shell – DG Wound Core

M2 Cu – wire Al – strip Shell – DG Wound Core

ZDMH Al – wire Al – strip Shell – DG Wound Core

ZDMH Cu – wire Cu – strip Shell – DG Wound Core

SA1 (Amorphous) Al – wire Al – strip Core – DG Wound Core

SA1 (Amorphous) Cu – wire Cu – strip Shell – DG Wound Core

SA1 (Amorphous) Cu – wire Cu – strip Core – DG Wound Core

DOE analyzed each of the twelve design option combinations using the matrix of A and B values 

described in Table 5.3.1 and Table 5.3.2, creating 2,740 designs.

5.3.8 Design Line 4 Representative Unit

Design line 4 (DL4) represents rectangular tank, liquid-immersed, three-phase distribution 

transformers, ranging from 15 kVA to 500 kVA. The representative unit selected for this design 

line is a 150kVA transformer. The following are the technical specifications that constitute input 

parameters to the OPS design software:

KVA: 150 (liquid-immersed, pad mount)

Primary: 12470Y/7200 Volts at 60 Hz (95kV BIL)

Secondary: 208Y/120 Volts

T Rise: 65 ̊C

Ambient: 20 ̊C

Terminal Configuration: ANSI/IEEE C57.12.26, Loop Feed
5-29

Winding Configuration: Lo-Hi

Core: Wound core - distributed gap, 5-leg

Taps: Four 21⁄2 percent, two above and two below the nominal

Impedance Range: 1.2-6.0 percent

For DL4, DOE selected nine design option combinations of core steel and winding types 

based on input from manufacturers and other technical experts. With the exception of the maxtech/high-efficiency designs, DOE selected these design option combinations to represent the 

most common construction practice for the representative unit.

Table 5.3.10 Design Option Combinations for the Representative Unit from Design Line 4

Core Material High-Voltage 

Conductor

Low-Voltage 

Conductor Core Design Type

M5 Cu – wire Al – strip 5-Leg DG Core

M3 Al – wire Al – strip 5-Leg DG Core

M3 Cu – wire Al – strip 5-Leg DG Core

M2 Al – wire Al – strip 5-Leg DG Core

M2 Cu – wire Al – strip 5-Leg DG Core

ZDMH Al – wire Al – strip 5-Leg DG Core

ZDMH Cu – wire Cu – strip 5-Leg DG Core

SA1 (Amorphous) Al – wire Al – strip 5-Leg DG Core

SA1 (Amorphous) Cu – wire Cu – strip 5-Leg DG Core

DOE analyzed each of the nine design option combinations using the matrix of A and B 

values described in Table 5.3.1 and Table 5.3.2, creating 1,977 designs.

5.3.9 Design Line 5 Representative Unit

Design line 5 (DL5) represents rectangular tank, liquid-immersed, three-phase distribution 

transformers, ranging from 750 kVA to 2500 kVA. The representative unit selected for this 

design line is a 1500kVA transformer. The following are the technical specifications that 

constitute input parameters to the OPS design software:

KVA: 1500 (liquid-immersed, pad mount)

Primary: 24940GrdY/14400 Volts (125kV BIL)

Secondary: 480Y/277 Volts

T Rise: 65 ̊C

Ambient: 20 ̊C

Terminal Configuration: ANSI/IEEE C57.12.26, Loop Feed

Winding Configuration: Lo-Hi

Core: Wound core - distributed gap, 5-leg

Taps: Four 21⁄2 percent, two above and two below the nominal

Impedance Range: 5-7.5 percent

For DL5, DOE selected nine design option combinations of core steel and winding 

material, based on input from manufacturers and other technical experts. With the exception of 
5-30

the max-tech/high-efficiency designs, DOE selected these design option combinations to 

represent the most common construction practices for the representative unit.

Table 5.3.11 Design Option Combinations for the Representative Unit from Design Line 5

Core Material High-Voltage 

Conductor

Low-Voltage 

Conductor Core Design Type

M4 Cu – wire Al – strip 5-Leg DG Core

M3 Al – wire Al – strip 5-Leg DG Core

M3 Cu – wire Al – strip 5-Leg DG Core

M2 Al – wire Al – strip 5-Leg DG Core

M2 Cu – wire Al – strip 5-Leg DG Core

ZDMH Al – wire Al – strip 5-Leg DG Core

ZDMH Cu – wire Cu – strip 5-Leg DG Core

SA1 (Amorphous) Al – wire Al – strip 5-Leg DG Core

SA1 (Amorphous) Cu – wire Cu – strip 5-Leg DG Core

DOE analyzed each of the nine design option combinations using the matrix of A and B 

values described in Table 5.3.1 and Table 5.3.2, creating 1,294 designs.

5.3.10 Design Line 6 Representative Unit

Design line 6 (DL6) represents ventilated dry-type, single-phase, low-voltage distribution 

transformers, ranging from 15 kVA to 333 kVA. The representative unit selected for this design 

line is a 25 kVA transformer. The following are the technical specifications that constitute input 

parameters to the OPS design software:

KVA: 25 (dry-type)

Phases: Single

Primary: 480 Volts at 60 Hz (10 kV BIL)

Secondary: 120/240 Volts

T Rise: 150 ̊C

Ambient: 20 ̊C

Winding Configuration: Lo-Hi (for Core-Type and Shell-Type)

Core: Stacked, butt-lap; Wound core - distributed gap

Taps: Six 21⁄2 percent, two above and four below the nominal

Impedance Range: 1.5-6.0 percent

For DL6, DOE selected fourteen design option combinations of core steel and winding 

material, based on input from manufacturers and other technical experts. With the exception of 

the max-tech/high-efficiency designs, DOE selected these design option combinations to 

represent the most common construction practice for the representative unit.
5-31

Table 5.3.12 Design Option Combinations for the Representative Unit from Design Line 6

Core Material High-Voltage 

Conductor

Low-Voltage 

Conductor Core Design Type

M6 Al – wire Al – wire Stacked Core Butt-lap

M5 Al – wire Al – strip Stacked Core Butt-lap

M4 Al – wire Al – wire Stacked Core Butt-lap

M3 Al – wire Al – strip Stacked Core Butt-lap

M3 Al – wire Al – strip Core – Step-Lap Miter

M3 Al – wire Al – strip Core – DG Wound Core

M3 Cu – wire Al – wire Stacked Core Butt-lap

M3 Cu – wire Al – wire Stacked Shell Butt-lap

H-0 DR* Al – wire Al – strip Stacked Core Butt-lap

H-0 DR Al – wire Al – strip Core – Step-Lap Miter

H-0 DR Cu – wire Cu – wire Stacked Core Butt-lap

ZDMH Al – wire Al – strip Core – DG Wound Core

SA1 (Amorphous) Al – wire Al – strip Core – DG Wound Core

SA1 (Amorphous) Cu – wire Cu – wire Core – DG Wound Core

* H-0 DR is a domain-refined, high permeability core steel.

DOE analyzed each of the fourteen design option combinations using the matrix of A and 

B values described in Table 5.3.1 and Table 5.3.2, creating 4,298 designs.

5.3.11 Design Line 7 Representative Unit

Design line 7 (DL7) represents ventilated dry-type, three-phase, low-voltage distribution 

transformers, ranging from 15 kVA to 150 kVA. The representative unit selected for this design 

line is a 75 kVA transformer. The following are the technical specifications that constitute input 

parameters to the OPS design software:

KVA: 75 (dry-type)

Phases: Three

Primary: 480 Volts at 60 Hz (10 kV BIL)

Secondary: 208Y/120 Volts

T Rise: 150 ̊C

Ambient: 20 ̊C

Winding Configuration: Lo-Hi

Core: Stacked, butt-lap; Stacked, mitered; Wound core - distributed gap

Taps: Six 21⁄2 percent, two above and four below the nominal

Impedance Range: 1.5–6.0 percent

For DL7, DOE selected fourteen design option combinations of core steel and winding 

material, based on input from manufacturers and other technical experts. With the exception of 

the max-tech/high-efficiency designs, DOE selected these design option combinations to 

represent the most common construction practice for the representative unit.
5-32

Table 5.3.13 Design Option Combinations for the Representative Unit from Design Line 7

Core Material High-Voltage 

Conductor

Low-Voltage 

Conductor Core Design Type

M12 Al – wire Al – wire 3-Leg Stacked Butt-lap

M12 Cu – wire Al – wire 3-Leg Stacked Butt-lap

M6 Al – wire Al – wire 3-Leg Stacked Butt-lap

M6 Al – wire Al – wire 3-Leg Stacked Full Miter**

M4 Cu – wire Al – wire 3-Leg Stacked Full Miter

M3 Al – wire Al – wire 3-Leg Stacked Full Miter

M3 Al – wire Al – wire 3-Leg Step-Lap Miter

M3 Al – wire Al – wire 3-Leg DG Core

H-0 DR* Al – wire Al – strip 3-Leg Stacked Full Miter

H-0 DR Al – wire Al – strip 3-Leg Step-Lap Miter

ZDMH Al – wire Al – strip 3-Leg DG Core

H-0 DR Cu – wire Cu – wire 3-Leg Stacked Full Miter

SA1 (Amorphous) Al – wire Al – strip 5-Leg DG Core

SA1 (Amorphous) Cu – wire Cu – wire 5-Leg DG Core

* H-0 DR is a domain-refined, high permeability core steel.

** Full miters are not step-miters, but are mitered joints for all three legs. These cores are stacked three by three.

DOE analyzed each of the fourteen design option combinations using the matrix of A and 

B values described in Table 5.3.1 and Table 5.3.2, creating 4,165 designs.

5.3.12 Design Line 8 Representative Unit

Design line 8 (DL8) represents ventilated dry-type, three-phase, low-voltage distribution 

transformers, ranging from 225 kVA to 1000 kVA. The representative unit selected for this 

design line is a 300 kVA transformer. The following are the technical specifications that 

constitute input parameters to the OPS design software:

KVA: 300 (dry-type)

Phases: Three

Primary: 480V at 60 Hz (10 kV BIL) Delta Connected

Secondary: 208Y/120 Volts

T Rise: 150 ̊C

Ambient: 20 ̊C

Winding Configuration: Lo-Hi

Core: Stacked, butt-lap; Stacked, mitered; Wound core - distributed gap

Taps: Four 21⁄2 percent, two above and two below the nominal

Impedance Range: 3.0–7.0 percent

For DL8, DOE selected fifteen design option combinations of core steel and winding 

material, based on input from manufacturers and other technical experts. With the exception of 

the max-tech/high-efficiency designs, DOE selected these design option combinations to 

represent the most common construction practice for the representative unit.
5-33

Table 5.3.14 Design Option Combinations for the Representative Unit from Design Line 8

Core Material High-Voltage 

Conductor

Low-Voltage 

Conductor Core Design Type

M6 Al – wire Al – strip 3-Leg Stacked Butt-lap

M6 Cu – wire Cu – strip 3-Leg Stacked Full Miter**

M5 Al – wire Al – strip 3-Leg Stacked Butt-lap

M5 Al – wire Al – strip 3-Leg Stacked Full Miter

M4 Cu – wire Al – strip 3-Leg Stacked Full Miter

M3 Al – wire Al – strip 3-Leg Stacked Full Miter

M3 Al – wire Al – strip 3-Leg Step-Lap Miter

M3 Al – wire Al – strip 3-Leg DG Core

M3 Cu – wire Al – strip 3-Leg Stacked Full Miter

H-0 DR* Al – wire Al – strip 3-Leg Stacked Full Miter

H-0 DR Al – wire Al – strip 5-Leg Step-Lap Miter

ZDMH Al – wire Al – strip 5-Leg DG Core

H-0 DR Cu – wire Cu – strip 3-Leg Stacked Full Miter

SA1 (Amorphous) Al – wire Al – strip 5-Leg DG Core

SA1 (Amorphous) Cu – wire Cu – strip 5-Leg DG Core

* H-0 DR is a domain-refined, high permeability core steel.

** Full miters are not step-miters, but are mitered joints for all three legs. These cores are stacked three by three.

DOE analyzed each of the fifteen design option combinations using the matrix of A and B 

values described in Table 5.3.1 and Table 5.3.2, creating 4,557 designs.

5.3.13 Design Line 9 Representative Unit

Design line 9 (DL9) represents ventilated dry-type, three-phase, medium-voltage 

distribution transformers with a 20-45kV BIL, ranging from 15 kVA to 500 kVA. The 

representative unit selected for this design line is a 300 kVA transformer. The following are the 

technical specifications that constitute input parameters to the OPS design software:

KVA: 300 (dry-type)

Phases: Three

Primary: 4160V at 60 Hz (45 kV BIL) Delta Connected

Secondary: 480Y/277 Volts

T Rise: 150 ̊C

Ambient: 20 ̊C

Winding Configuration: Lo-Hi

Core: Stacked, mitered; Wound core - distributed gap

Taps: Four 21⁄2 percent, two above and two below the nominal

Impedance Range: 3.0–7.0 percent

For DL9, DOE selected thirteen design option combinations of core steel and winding 

material, based on input from manufacturers and other technical experts. With the exception of 

the max-tech/high-efficiency designs, DOE selected these design option combinations to 

represent the most common construction practice for the representative unit. 
5-34

Table 5.3.15 Design Option Combinations for the Representative Unit from Design Line 9

Core Material High-Voltage 

Conductor

Low-Voltage 

Conductor Core Design Type

M6 Cu – wire Cu – wire 3-Leg Stacked Full Miter**

M5 Al – wire Al – wire 3-Leg Stacked Full Miter

M3 Al – wire Al – strip 3-Leg Stacked Full Miter

M3 Al – wire Al – strip 3-Leg Step-Lap Miter

M3 Al – wire Al – strip 5-Leg DG Core

M3 Cu – wire Al – strip 3-Leg Stacked Full Miter

H-0 DR* Al – wire Al – strip 3-Leg Stacked Full Miter

H-0 DR Al – wire Al – strip 3-Leg Step-Lap Miter

ZDMH Al – wire Al – strip 5-Leg DG Core

H-0 DR Cu – wire Cu – strip 3-Leg Stacked Full Miter

SA1 (Amorphous) Al – wire Al – strip 5-Leg DG Core

SA1 (Amorphous) Cu – wire Cu – strip 3-Leg DG Core

SA1 (Amorphous) Cu – wire Cu – strip 5-Leg DG Core

* H-0 DR is a domain-refined, high permeability core steel.

** Full miters are not step-miters, but are mitered joints for all three legs. These cores are stacked three by three.

DOE analyzed each of the thirteen design option combinations using the matrix of A and 

B values described in Table 5.3.1 and Table 5.3.2, creating 5,948 designs.

5.3.14 Design Line 10 Representative Unit

Design line 10 (DL10) represents dry-type, three-phase, medium-voltage distribution 

transformers with a 20-45kV BIL, ranging from 750 kVA to 2500 kVA. The representative unit 

selected for this design line is a 1500 kVA transformer. The following are the technical 

specifications that constitute input parameters to the OPS design software:

KVA: 1500 (dry-type)

Phases: Three

Primary: 4160V at 60 Hz (45 kV BIL)

Secondary: 480Y/277 Volts

T Rise: 150 ̊C

Ambient: 20 ̊C

Winding Configuration: Lo-Hi

Core: Stacked, cruciform, mitered joint, 3-leg; Wound core - distributed gap

Taps: Four 21⁄2 percent, two above and two below the nominal

Impedance Range: 5.0-8.0 percent

For DL10, DOE selected ten design option combinations of core steel and winding 

material, based on input from manufacturers and other technical experts. With the exception of 

the max-tech/high-efficiency designs, DOE selected these design option combinations to 

represent the most common construction practice for the representative unit.
5-35

Table 5.3.16 Design Option Combinations for the Representative Unit from Design Line 10

Core Material High-Voltage 

Conductor

Low-Voltage 

Conductor Core Design Type

M5 Cu – wire Al – strip 3-Leg Mitered Cruciform

M4 Cu – wire Al – strip 3-Leg Mitered Cruciform

M3 Al – wire Al – strip 3-Leg Mitered Cruciform

M3 Al – wire Al – strip 3-Leg Step-Lap Miter

M3 Cu – wire Cu – strip 3-Leg Mitered Cruciform

H-0 DR* Al – wire Al – strip 3-Leg Mitered Cruciform

H-0 DR Al – wire Al – strip 3-Leg Step-Lap Miter

H-0 DR Cu – wire Cu – strip 3-Leg Mitered Cruciform

SA1 (Amorphous) Al – wire Al – strip 5-Leg DG Core

SA1 (Amorphous) Cu – wire Cu – strip 3-Leg DG Core

* H-0 DR is a domain-refined, high permeability core steel.

DOE analyzed each of the ten design option combinations using the matrix of A and B 

values described in Table 5.3.1 and Table 5.3.2, creating 2,369 designs.

5.3.15 Design Line 11 Representative Unit

Design line 11 (DL11) represents dry-type, three-phase, medium-voltage distribution 

transformers with a 46-95kV BIL, ranging from 15 kVA to 500 kVA. The representative unit 

selected for this design line is a 300 kVA transformer. The following are the technical 

specifications that constitute input parameters to the OPS design software:

KVA: 300 (dry-type)

Phases: Three

Primary: 12470 Volts at 60 Hz (95 kV BIL)

Secondary: 480Y/277 Volts

T Rise: 150 ̊C

Ambient: 20 ̊C

Winding Configuration: Lo-Hi

Core: Stacked, mitered joint, 3-leg; Wound core - distributed gap, 5-leg

Taps: Four 21⁄2 percent, two above and two below the nominal

Impedance Range: 3.0-7.0 percent

For DL11, DOE selected eleven design option combinations of core steel and winding 

material, based on input from manufacturers and other technical experts. With the exception of 

the max-tech/high-efficiency designs, DOE selected these design option combinations to 

represent the most common construction practice for the representative unit. 

Table 5.3.17 Design Option Combinations for the Representative Unit from Design Line 11

Core Material High-Voltage 

Conductor

Low-Voltage 

Conductor Core Design Type

M6 Cu – wire Cu – strip 3-Leg Stacked Full Miter**

M4 Cu – wire Al – strip 3-Leg Stacked Full Miter

M3 Al – wire Al – strip 3-Leg Stacked Full Miter

M3 Al – wire Al – strip 3-Leg Step-Lap Miter
5-36

M3 Cu – wire Cu – strip 3-Leg Stacked Full Miter

H-0 DR* Al – wire Al – strip 3-Leg Stacked Full Miter

H-0 DR Al – wire Al – strip 3-Leg Step-Lap Miter

ZDMH Al – wire Al – strip 3-Leg DG Core

H-0 DR Cu – wire Cu – strip 3-Leg Stacked Full Miter

SA1 (Amorphous) Al – wire Al – strip 3-Leg DG Core

SA1 (Amorphous) Cu – wire Cu – strip 5-Leg DG Core

* H-0 DR is a domain-refined, high permeability core steel.

** Full miters are not step-miters, but are mitered joints for all three legs. These cores are stacked three by three.

DOE analyzed each of the eleven design option combinations using the matrix of A and 

B values described in Table 5.3.1 and Table 5.3.2, creating 2,035 designs.

5.3.16 Design Line 12 Representative Unit

Design line 12 (DL12) represents dry-type, three-phase, medium-voltage distribution 

transformers with a 46-95kV BIL, ranging from 750 kVA to 2500 kVA. The representative unit 

selected for this design line is a 1500 kVA transformer. The following are the technical 

specifications that constitute input parameters to the OPS design software:

KVA: 1500 (dry-type)

Phases: Three

Primary: 12470 Volts at 60 Hz (95 kV BIL)

Secondary: 480Y/277 Volts

T Rise: 150 ̊C

Ambient: 20 ̊C

Winding Configuration: Lo-Hi

Core: Stacked, cruciform, mitered joint, 3-leg; Wound core - distributed gap, 5-leg

Taps: Four 21⁄2 percent, two above and two below the nominal

Impedance Range: 5.0–8.0 percent

For DL12, DOE selected eleven design option combinations of core steel and winding 

material, based on input from manufacturers and other technical experts. With the exception of

the max-tech/high-efficiency designs, DOE selected these design option combinations to 

represent the most common construction practice for the representative unit. 

Table 5.3.18 Design Option Combinations for the Representative Unit from Design Line 12

Core Material High-Voltage 

Conductor

Low-Voltage 

Conductor Core Design Type

M6 Al – wire Al – strip 3-Leg Mitered Cruciform

M5 Al – wire Al – strip 3-Leg Mitered Cruciform

M4 Cu – wire Al – strip 3-Leg Mitered Cruciform

M3 Al – wire Al – strip 3-Leg Mitered Cruciform

M3 Al – wire Al – strip 3-Leg Step-Lap Miter

M3 Cu – wire Cu – strip 3-Leg Mitered Cruciform

H-0 DR* Al – wire Al – strip 3-Leg Mitered Cruciform

H-0 DR Al – wire Al – strip 3-Leg Step-Lap Miter

H-0 DR Cu – wire Cu – strip 3-Leg Mitered Cruciform

SA1 (Amorphous) Al – wire Al – strip 5-Leg DG Core
5-37

SA1 (Amorphous) Cu – wire Cu – strip 5-Leg DG Core

* H-0 DR is a domain-refined, high permeability core steel.

DOE analyzed each of the eleven design option combinations using the matrix of A and 

B values described in Table 5.3.1 and Table 5.3.2, creating 3,243 designs.

5.3.17 Design Line 13A Representative Unit

Design line 13A (DL13A) represents dry-type, three-phase, medium-voltage distribution 

transformers with a ≥96kV BIL, ranging from 225 kVA to 2500 kVA. The representative unit 

selected for this design line is a 300 kVA transformer. The following are the technical 

specifications that constitute input parameters to the OPS design software:

KVA: 300 (dry-type)

Phases: Three

Primary: 24940 Volts at 60 Hz (125 kV BIL)

Secondary: 480Y/277 Volts

T Rise: 150 ̊C

Ambient: 20 ̊C

Winding Configuration: Lo-Hi

Core: Stacked, cruciform, mitered joint, 3-leg; Wound core - distributed gap, 5-leg

Taps: Four 21⁄2 percent, two above and two below the nominal

Impedance Range: 3.0–7.0 percent

For DL13A, DOE selected seven design option combinations of core steel and winding 

material, based on input from manufacturers and other technical experts. With the exception of 

the max-tech/high-efficiency designs, DOE selected these design option combinations to 

represent the most common construction practice for the representative unit. 

Table 5.3.19 Design Option Combinations for the Representative Unit from Design Line 

13A

Core Material High-Voltage 

Conductor

Low-Voltage 

Conductor Core Design Type

M5 Al – wire Al – strip 3-Leg Mitered Cruciform

M4 Al – wire Al – strip 3-Leg Mitered Cruciform

M3 Al – wire Al – strip 3-Leg Mitered Cruciform

M3 Al – wire Al – strip 3-Leg Step-Lap Miter

H-0 DR* Al – wire Al – strip 3-Leg Mitered Cruciform

ZDMH Al – wire Al – strip 3-Leg DG Core

SA1 (Amorphous) Al – wire Al – strip 5-Leg DG Core

* H-0 DR is a domain-refined, high permeability core steel.

DOE analyzed each of the seven design option combinations using the matrix of A and B 

values described in Table 5.3.1 and Table 5.3.2, creating 919 designs.
5-38

5.3.18 Design Line 13B Representative Unit

Design line 13B (DL13B) also represents dry-type, three-phase, medium-voltage 

distribution transformers with a ≥96kV BIL, ranging from 225 kVA to 2500 kVA. The 

representative unit selected for this design line is a 2000 kVA transformer. The following are the 

technical specifications that constitute input parameters to the OPS design software:

KVA: 2000 (dry-type)

Phases: Three

Primary: 24940 Volts at 60 Hz (125 kV BIL)

Secondary: 480Y/277 Volts

T Rise: 150 ̊C

Ambient: 20 ̊C

Winding Configuration: Lo-Hi

Core: Stacked, cruciform, mitered joint, 3-leg; Wound core - distributed gap, 5-leg

Taps: Four 21⁄2 percent, two above and two below the nominal

Impedance Range: 5.0–8.0 percent

For DL13B, DOE selected seven design option combinations of core steel and winding

material, based on input from manufacturers and other technical experts. With the exception of 

the max-tech/high-efficiency designs, DOE selected these design option combinations to 

represent the most common construction practice for the representative unit. 

Table 5.3.20 Design Option Combinations for the Representative Unit from Design Line 

13B

Core Material High-Voltage 

Conductor

Low-Voltage 

Conductor Core Design Type

M5 Al – wire Al – strip 3-Leg Mitered Cruciform

M4 Al – wire Al – strip 3-Leg Mitered Cruciform

M3 Al – wire Al – strip 3-Leg Mitered Cruciform

M3 Al – wire Al – strip 3-Leg Step-Lap Miter

H-0 DR* Al – wire Al – strip 3-Leg Mitered Cruciform

H-0 DR Al – wire Al – strip 3-Leg Step-Lap Miter

SA1 (Amorphous) Al – wire Al – strip 5-Leg DG Core

* H-0 DR is a domain-refined, high permeability core steel.

DOE analyzed each of the seven design option combinations using the matrix of A and B 

values described in Table 5.3.1 and Table 5.3.2, creating 1,848 designs.

5.3.19 Newly Optimized Designs and Previously Optimized Designs

DOE utilized a combination of newly optimized design runs and designs that were 

optimized during the preliminary analysis for distribution transformers. For each design option 

combination chosen, DOE generates designs based on 518 A and B factor combinations. These 

A and B factor combinations cover the spectrum of typical load loss and no-load loss valuations, 

generating a unique design across a range of efficiencies.
5-39

DOE understands that typically a design would be optimized based on the current material 

prices. Optimizing a design based on historical material prices may result in a differently 

optimized design, such as a design that utilizes relatively more conductor than core. However, 

DOE believes that it adequately covered the spectrum of possible designs for each design option 

combination used in the preliminary analysis based on the large sample of A and B factor 

combinations considered for each design option combination. As such, DOE believes that these 

designs are still valid when updated material prices are applied to them.

DOE updated the cost of these previous design runs by applying updated prices to the 

design‘s bill of materials. Effectively, DOE calculated the present cost of developing the same 

design that was used in the previous rulemaking. DOE also updated labor prices and applied the 

markups consistently with any newly optimized designs generated for the analysis.

While DOE believes that its approach of reusing previously optimized designs with 

updated material prices is reasonable, it plans to create newly optimized designs for the analysis 

as well. Currently, DOE has added in several new design option combinations, which are 

modeled with a newly optimized design. Additionally, DOE may choose to re-optimize the 

designs from the preliminary analysis rather than simply updating their material prices as the 

analysis progresses.

5.4 MATERIAL AND LABOR INPUTS

DOE uses a standard method of cost accounting with minor changes to determine the 

costs associated with manufacturing. This methodology is illustrated in Figure 5.4.1, where 

production costs and non-production costs are combined to determine the manufacturer‘s selling 

price of the equipment.
5-40

Figure 5.4.1 Method of Cost Accounting for Distribution Transformers Rulemaking

The full production cost and the non-production cost equal the manufacturer‘s selling 

price of the equipment. Full production cost is a combination of direct labor, direct materials, and 

overhead. The overhead contributing to full production cost includes indirect labor, indirect 

material, maintenance, depreciation, taxes, and insurance related to company assets. Nonproduction cost includes the cost of selling, general and administrative items (market research, 

advertising, sales representatives, logistics), research and development (R&D), interest 

payments, warranty and risk provisions, shipping, and profit factor. Because profit factor is 

included in the non-production cost, the sum of production and non-production costs is an 

estimate of the manufacturer‘s selling price.

DOE used several estimates of the costs listed in Figure 5.4.1 from DOE‘s previous 

rulemaking on distribution transformers, published in October 2007. The estimates from this 

rulemaking relied on U.S. Industry Census Data Reports, manufacturer interviews, and Securities 

and Exchange Commission (SEC) 10-K reports for several manufacturers. It then refined these 

estimates through meetings and dialogue with transformer manufacturers in 2010. The following 

markups resulted:

Scrap and handling factor: 2.5 percent markup. This markup applies to variable materials 

(e.g., core steel, windings, insulation). It accounts for the handling of material (loading 

into assembly or winding equipment) and the scrap material that cannot be used in the 

production of a finished transformer (e.g., lengths of wire too short to wind, trimmed core 

steel).

Amorphous scrap factor: 1.5 percent markup. This markup accounts for breakage of 

prefabricated amorphous cores and any scrap associated with assembling the windings on 

the core. Since amorphous cores are considered to be prefabricated, the regular scrap and 

handling factor is reduced.

Full Cost of Product

Full Production Cost

Direct 

Labor

Direct 

Material Overhead

Indirect Labor

Indirect 

Material

Maintenance

Depreciation

Taxes

Insurance 

related to 

assets

Non-Production Cost

Selling, 

General 

& Admin.

Mkt. research

Advertising

Point of Sale 

promotion

Cust. service

Sales person 

salary + travel 

+ commission

Logistics

R & D

Costs 

associated with 

efforts to find 

new or 

improved 

products or 

production 

processes

Code 

Compliance

Modernization

Interest

Costs of 

borrowing 

funds

Warranty 

& Risk Shipping

Costs of 

freight for 

final delivery

Profit
5-41

Mitered scrap factor: 4.0 percent markup. An additional scrap markup applies to steel 

used in full-mitered cores. This markup represents material cut from the notch in the 

yoke.

Factory overhead: 12.5 percent markup. Factory overhead includes all the indirect costs 

associated with production, indirect materials and energy use (e.g., annealing furnace), 

taxes, and insurance. DOE only applied factory overhead to the direct material production 

costs.

Shipping: $0.28 per pound for each transformer. The shipping costs include the freight 

from a manufacturer‘s facility to the customer. This shipping cost does not include any 

freight charges for the customer to subsequently move the transformer to its end-use 

location. DOE applied the shipping charge prior to applying the profit markup based on 

feedback from manufacturer interviews in 2011.

Non-production: 25 percent markup. This markup reflects costs including selling, 

general and administrative, R&D, interest payments, warranty and risk provisions, and 

profit factor. DOE applied the non-production markup to the sum of direct material, 

direct labor, and factory overhead.

The following example shows how DOE applied the markups to the materials, and how it 

determined the manufacturer selling price. Consider a 300kVA 45kV BIL three-phase, dry-type 

transformer designed with a $1.50 A and a $0.30 B. This design has $4,795 of materials, 

including M6 core steel, copper primary and secondary windings, and all the transformer 

hardware. There are approximately 27 hours of labor involved in manufacturing this design, 

resulting in a labor cost of $1,367. The factory overhead on this design is $599, as it is only 

applied to the material cost (i.e., 12.5 percent of $4,795). The shipping cost is $504, based on a 

weight of 1,792 pounds. The non-production cost is $1,706, since the 25 percent is applied to the 

material, labor, factory overhead, and shipping costs (i.e., 25 percent of $4,795 + $1,391 + $599

+ $504). Thus, in total, DOE estimates this 300kVA three-phase transformer to have a

manufacturer selling price of $9,033.

5.4.1 Material Prices

DOE used prices of core steel, conductor, mineral oil, insulation, and other materials as an 

input to the transformer design software used for the engineering analysis. As the price of one 

material increases or decreases relative to the other materials, the software will modify its design 

and increase or decrease the amount of that material while balancing other design parameters, 

creating a cost-optimized transformer. Material pricing is also critical because the manufacturer‘s 

selling prices calculated in the engineering analysis are based on a bill of materials that includes 

specifications for pounds of steel, pounds of conductor, gallons of mineral oil, tank dimensions, 

and so on. Therefore, as material prices increase, so will the manufacturer‘s selling price. 

Furthermore, as discussed in Chapter 3, energy-efficient transformers tend to incorporate more 
5-42

materials (e.g., pounds of core steel, pounds of conductor), making the impact of more expensive 

materials even more significant at higher efficiencies.

DOE contracted OPS to develop material price estimates for the engineering analysis. 

OPS used data from their own records as well as data provided by transformer manufacturers and 

material suppliers and wholesalers. Although not all transformer manufacturers pay the same 

amount per pound for electrical-grade steels, due to varied contract negotiations, these prices are 

intended to be representative of a standard quantity order for a medium- to large-scale U.S. 

transformer manufacturer.

DOE supplemented that price data by aggregating information obtained during interviews 

with manufacturers of distribution transformers. After the preliminary analysis, DOE received 

feedback that volatility in the conductor commodities markets made it difficult to consider any 

price accurate for any length of time because the rate of price movement was high relative to 

typical purchase contract terms.

DOE received feedback that a more accurate way to develop conductor prices would be to 

establish a processing ―adder,‖ or cost required to form the finished good from underlying 

commodity. The adder would change much more slowly in time than the price of the processed 

commodity, and would allow derivation of conductor prices by summing the processing adder 

and the price of the underlying commodity in exchanges such as COMEX and London Metal 

Exchange. DOE intends to continue deriving conductor prices in this manner in future updates to 

the analysis.

DOE conducted the engineering analysis using material prices over a five-year time 

period from 2006-2010, all in constant 2010$. Using the material prices from this time period, 

DOE considered a current (2010) material price, a minimum price (based on 2006 prices), and a 

maximum price (based on 2008 prices) for its analysis. This was done to account for variation in 

pricing for the different materials, which could have a significant impact on the total cost of the 

distribution transformer. All transformer designs that were newly optimized used the current 

2010 material price, which DOE used as its reference case. The maximum and minimum prices 

were then applied to these same designs to generate a manufacturer selling price for each of 

those scenarios. The results of the current 2010 material prices are presented here in Chapter 5, 

while the results of the minimum and maximum material prices are presented in Appendix 5C.

DOE noted that the price of the most critical material input to a distribution transformer, 

electrical core steel, had varied significantly for some M-grades over the five-year time horizon 

(see Table 5.4.1). For this reason, DOE researched the grain-oriented electrical steel market to 

gain a better understanding of the main players and some of the factors influencing these price 

fluctuations (see Appendix 3A). 

In the LCC analysis (Chapter 8), DOE presents results on its sensitivity analyses 

conducted on various LCC inputs, which included material prices. In Chapter 8, the 2008 

material price scenario is referred to as the ―high‖ price scenario, the 2010 price scenario is 

called the ―medium‖ price scenario, and the 2006 material price scenario is referred to as the 

―low‖ price scenario. DOE chose to utilize the current 2010 material price in the reference case 
5-43

after receiving feedback from transformer manufacturers and suppliers of core steel indicating 

that current prices would be a better price indicator than a five-year average price. These material 

prices can be found in the material price tables presented in this section. The resulting 

manufacturer selling prices are provided in the LCC spreadsheets.

5.4.2 Material Inputs to the Design Software – Liquid-Immersed

Table 5.4.1 presents the material prices for a typical manufacturer of liquid-immersed

transformers over the five-year 2006-2010 time horizon, indicating the current, minimum, and 

maximum prices (all in constant 2010$). The highlighted columns are the prices that DOE used 

in the engineering analysis.
5-44

Table 5.4.1 Typical Manufacturer’s Material Prices for Liquid-Immersed Design Lines

Material Units 2010 

Price

2010$

Min. 

Price 

(2006 

–

25%)

2010$

Max. 

Price 

(2008 

+ 

25%)

2010$

2010

2010$

2009

2010$

2008

2010$

2007

2010$

2006

2010$

M6 core steel $/lb $ 

1.46 

$ 

0.94 

$ 

2.19 

$ 

1.46 

$ 

1.64 

$ 

1.75 

$ 

1.58 

$ 

1.26 

M5 core steel $/lb $ 

1.51 

$ 

0.99 

$ 

2.24 

$ 

1.51 

$ 

1.67 

$ 

1.79 

$ 

1.61 

$ 

1.32 

M4 core steel $/lb $ 

1.59 

$ 

1.03 

$ 

2.30 

$ 

1.59 

$ 

1.70 

$ 

1.84 

$ 

1.64 

$ 

1.38 

M3 core steel $/lb $ 

1.88 

$ 

1.06 

$ 

2.60 

$ 

1.88 

$ 

1.96 

$ 

2.08 

$ 

1.70 

$ 

1.41 

M3 core steel (Lite Carlite) $/lb $ 

1.95 

$ 

1.47 

$ 

2.44 

$ 

1.95 

$ 

- 

$ 

- 

$ 

- 

$ 

- 

M2 core steel $/lb $ 

2.00 

$ 

1.32 

$ 

2.79 

$ 

2.00 

$ 

2.01 

$ 

2.23 

$ 

2.18 

$ 

1.76 

M2 core steel (Lite Carlite) $/lb $ 

2.10 

$ 

1.58 

$ 

2.63 

$ 

2.10 

$ 

- 

$ 

- 

$ 

- 

$ 

- 

ZDMH (mechanicallyscribed core steel) $/lb $ 

2.05 

$ 

1.41 

$ 

3.22 

$ 

2.05 

$ 

2.02 

$ 

2.57 

$ 

2.29 

$ 

1.88 

SA1 (amorphous) finished 

core, volume production $/lb $ 2.38 

$ 

1.72 

$ 

3.64 

$ 

2.38 

$ 

2.29 

$ 

2.91 

$ 

- 

$ 

- 

Copper wire, formvar, round 

#10-20 $/lb $ 4.87 

$ 

3.33 

$ 

5.97 

$ 

4.87 

$ 

3.81 

$ 

4.77 

$ 

4.78 

$ 

4.44 

Copper wire, enameled, 

round #7-10 $/lb $ 4.84 

$ 

3.31 

$ 

5.93 

$ 

4.84 

$ 

3.78 

$ 

4.74 

$ 

4.75 

$ 

4.41 

Copper wire, enameled, 

rectangular sizes $/lb $ 4.97 

$ 

3.41 

$ 

6.09 

$ 

4.97 

$ 

3.91 

$ 

4.87 

$ 

4.88 

$ 

4.54 

Aluminum wire, formvar, 

round #9-17 $/lb $ 3.07 

$ 

2.30 

$ 

3.91 

$ 

3.07 

$ 

3.00 

$ 

3.13 

$ 

3.08 

$ 

3.07 

Aluminum wire, formvar, 

round #7-10 $/lb $ 2.57 

$ 

1.93 

$ 

3.28 

$ 

2.57 

$ 

2.50 

$ 

2.63 

$ 

2.58 

$ 

2.57 

Copper strip, thickness range 

0.02-0.045 $/lb $ 4.97 

$ 

3.41 

$ 

6.09 

$ 

4.97 

$ 

3.91 

$ 

4.87 

$ 

4.88 

$ 

4.54 

Copper strip, thickness range 

0.030-0.060 $/lb $ 4.97 

$ 

3.41 

$ 

6.09 

$ 

4.97 

$ 

3.91 

$ 

4.87 

$ 

4.88 

$ 

4.54 

Aluminum strip, thickness 

range 0.02-0.045 $/lb $ 2.08 

$ 

1.56 

$ 

2.67 

$ 

2.08 

$ 

2.01 

$ 

2.14 

$ 

2.09 

$ 

2.08 

Aluminum strip, thickness 

range 0.045-0.080 $/lb $ 2.08 

$ 

1.56 

$ 

2.67 

$ 

2.08 

$ 

2.01 

$ 

2.14 

$ 

2.09 

$ 

2.08 

Kraft insulating paper with 

diamond adhesive $/lb $ 1.52 

$ 

1.17 

$ 

1.93 

$ 

1.52 

$ 

1.54 

$ 

1.54 

$ 

1.56 

$ 

1.56 

Mineral oil $/gal $ 

3.35 

$ 

1.94 

$ 

3.84 

$ 

3.35 

$ 

2.89 

$ 

3.07 

$ 

2.51 

$ 

2.59 

Tank Steel $/lb $ 

0.38 

$ 

0.32 

$ 

0.60 

$ 

0.38 

$ 

0.39 

$ 

0.48 

$ 

0.43 

$ 

0.43 

DOE then marked up the raw material prices presented in Table 5.4.1 using the 

manufacturer‘s internal markups discussed in section 5.4.1. DOE used the marked-up material 

prices as inputs to the transformer design software for optimization, even though the material 

prices do not receive the markup during DOE‘s cost calculation. The cost calculation applies the 
5-45

markups to the total material cost. During its manufacturer site visits in 2010, DOE found this 

approach to be consistent with that of several manufacturers who operate their own, proprietary 

transformer design software. For example, a raw material price of $1.00/lb. would be marked up 

to $1.44/lb., reflecting the handling and scrap factor (2.5 percent), the factory overhead (12.5 

percent), and the non-production markup (25 percent). DOE did not include shipping costs as a 

markup of the raw material because these costs were based on the weight of the design, not a 

percentage markup. Table 5.4.2 shows the markup steps being applied to the current 2010

material price scenario.
5-46

Table 5.4.2 Marked-up Material Prices for Liquid-Immersed Units, Current Year (2010)

Price Scenario

Item and Description Units

Current 

2010 Price

2010$

Scrap & 

Handling

Factory

Overhead

NonProductionSoftware 

Input

M6 core steel $/lb $ 

1.46 

 

1.025 

 

1.125 

 

1.25 

$ 

2.10 

M5 core steel $/lb $ 

1.51 

 

1.025 

 

1.125 

 

1.25 

$ 

2.18 

M4 core steel $/lb $ 

1.59 

 

1.025 

 

1.125 

 

1.25 

$ 

2.28 

M3 core steel $/lb $ 

1.88 

 

1.025 

 

1.125 

 

1.25 

$ 

2.70 

M3 core steel (Lite Carlite) $/lb $ 

1.95 

 

1.025 

 

1.125 

 

1.25 

$ 

2.82 

M2 core steel $/lb $ 

2.00 

 

1.025 

 

1.125 

 

1.25 

$ 

2.88 

M2 core steel (Lite Carlite) $/lb $ 

2.10 

 

1.025 

 

1.125 

 

1.25 

$ 

3.03 

ZDMH (mechanically-scribed core 

steel) $/lb $ 

2.05 

 

1.025 

 

1.125 

 

1.25 

$ 

2.95 

SA1 (amorphous) finished core, 

volume production $/lb $ 

2.38 

 

1.015 

 

1.125 

 

1.25 

$ 

3.40 

Copper wire, formvar, round #10-

20 $/lb $ 

4.87 

 

1.025 

 

1.125 

 

1.25 

$ 

7.02 

Copper wire, enameled, round #7-

10 $/lb $ 

4.84 

 

1.025 

 

1.125 

 

1.25 

$ 

6.98 

Copper wire, enameled, 

rectangular sizes $/lb $ 

4.97 

 

1.025 

 

1.125 

 

1.25 

$ 

7.17 

Aluminum wire, formvar, round 

#9-17 $/lb $ 

3.07 

 

1.025 

 

1.125 

 

1.25 

$ 

4.43 

Aluminum wire, formvar, round 

#7-10 $/lb $ 

2.57 

 

1.025 

 

1.125 

 

1.25 

$ 

3.71 

Copper strip, thickness range 0.02-

0.045 $/lb $ 

4.97 

 

1.025 

 

1.125 

 

1.25 

$ 

7.17 

Copper strip, thickness range 

0.030-0.060 $/lb $ 

4.97 

 

1.025 

 

1.125 

 

1.25 

$ 

7.17 

Aluminum strip, thickness range 

0.02-0.045 $/lb $ 

2.08 

 

1.025 

 

1.125 

 

1.25 

$ 

3.00 

Aluminum strip, thickness range 

0.045-0.080 $/lb $ 

2.08 

 

1.025 

 

1.125 

 

1.25 

$ 

3.00 

Kraft insulating paper with 

diamond adhesive $/lb $ 

1.52 

 

1.025 

 

1.125 

 

1.25 

$ 

2.18 

Mineral oil $/gal $ 

3.35 

 

1.000 

 

1.125 

 

1.25 

$ 

4.71 

Tank Steel $/lb $ 

0.38 

 

1.025 

 

1.125 

 

1.25 

$ 

0.55 
5-47

The price used for a prefabricated amorphous core is based on prices of finished cores 

from North American manufacturers. In the previous rulemaking for distribution transformers, 

DOE analyzed the cost importing finished cores from overseas. Since that time, several North 

American core manufacturers have begun producing amorphous cores. For the preliminary 

analysis, DOE considered the price of a prefabricated amorphous core bought from a North 

American core manufacturer.

In addition to the aforementioned materials that vary during the design optimization 

process (e.g., core steel, windings, insulation), there are other direct materials inputs that are 

fixed costs and generally do not influence the design or vary with efficiency rating. These 

include direct materials, such as the high- and low-voltage bushings and the core clamps. DOE 

also prepared estimates of the tank fabrication cost, based on the optimized transformer design 

(the software considers this variable) and the labor necessary to build the tank. Table 5.4.3

summarizes all the estimated fixed material costs and estimates of the tank costs for each of the 

five liquid-immersed design lines.

For DL1, a 50kVA single-phase pad-mounted unit, the high-voltage bushings are two 

universal bushing wells, 15 kV, 95 BIL, 14400V, costing $14 each. The low-voltage bushings 

are three threaded copper studs, 240/120V, 50 kVA, costing $30 for the set. Internal hardware 

costs include a core clamp, nameplate, and other miscellaneous hardware costing $41.65. The 

finished tank size (and associated cost) varies by design, but the average cost is approximately 

$143.

For DL2, a 25kVA single-phase pole-mounted unit, the high-voltage terminal is a single, 

wet-process porcelain bushing assembly, 15 kV, 125 BIL, costing $6. The low-voltage terminals 

are three molded polymer bushings, 120/240V, 25 kVA, costing $8 for the set. Internal hardware 

costs include a core clamp, nameplate, and other miscellaneous hardware, costing $19.15. The 

finished tank sizes (height and diameter) vary by design, but the average cost is approximately 

$73.

For DL3, a 500kVA single-phase unit, the high-voltage connector is a single, wet-process 

porcelain bushing, 25 kV, 125 BIL, costing $6. The low-voltage bushings are two four-hole ―J‖ 

Spade 500kVA, 277V, costing $60 for the set. The internal hardware includes a core clamp 

($30), nameplate ($0.65), and miscellaneous hardware ($20), totaling $50.65. The design 

software optimized the tank cost with each design, including radiators (external cooling) for this 

kVA rating. The resultant finished round tank has a diameter of 33" to 52", with an average cost 

of approximately $629 (including radiators).

For DL4, a 150kVA three-phase, pad-mounted unit, the high-voltage bushings are three 

externally clamped, universal high-voltage bushing wells, 8.3/14.4 kV, 95 BIL, costing $7 each. 

The low-voltage bushings are three copper studs at $8 each. The internal hardware includes core 

clamps ($30), nameplate ($0.65), and miscellaneous hardware ($45), totaling $75.65. The 

optimized finished tank sizes measure 50 inches high and vary in width and depth. The finished 

rectangular, welded tank has an average cost of approximately $389.
5-48

For DL5, a 1500kVA three-phase, pad-mounted unit, the high-voltage bushings are three 

externally clamped, universal high-voltage bushing wells, 15.2/26.3 kV, 125kV BIL, costing $20 

each. The low-voltage bushings are four externally clamped bushings, each having six-hole 

spade, costing $160 for the set. The internal hardware includes core clamps ($60), nameplate 

($0.65), and miscellaneous hardware ($45), totaling $105.65. The optimized finished tank sizes 

measure 70 inches high and vary in width and depth. The finished rectangular, welded tank, 

including radiators as specified by the design software, has an average cost of approximately 

$1,016.

Table 5.4.3 Summary Table of Fixed Material Costs for Liquid-Immersed Units

Item DL1 DL2 DL3 DL4 DL5

High voltage bushings $28 $6 $6 $21 $60

Low voltage bushings $30 $8 $60 $24 $160

Core clamp, nameplate, and misc. hardware $41.65 $19.15 $50.65 $75.65 $105.65

Transformer tank average cost* ~$143 ~$73 ~$629 ~$389 ~$1,016

* Transformer tank steel is used in the design optimization software and varies with the efficiency (and size) of each 

design. DL3 and DL5 include calculated costs of radiators, which are scaled for each design based on the required 

cooling surface area.

5.4.3 Material Inputs to the Design Software – Dry-Type

Table 5.4.4 presents the material prices for a typical dry-type transformer manufacturer 

over the five-year 2006-2010 time horizon, indicating the current (2010), minimum (2006), and 

maximum (2008) prices (all in constant 2010$) The highlighted columns are the prices DOE 

used in the engineering analysis.
5-49

Table 5.4.4 Manufacturer’s Material Prices for Dry-Type Design Lines

Material Units 2010 

Price

2010$

Min. 

Price 

(2006 

–

25%)

2010$

Max. 

price 

(2008 

+ 

25%)

2010$

2010

2010$

2009

2010$

2008

2010$

2007

2010$

2006

2010$

M36 core steel (26 

gauge) $/lb $ 

0.66 

$ 

0.46 

$ 

0.84 

$ 

0.66 

$ 

0.67 

$ 

0.67 

$ 

0.84 

$ 

0.62 

M19 core steel (26 

gauge) $/lb $ 

0.91 

$ 

0.56 

$ 

1.19 

$ 

0.91 

$ 

0.82 

$ 

0.96 

$ 

0.95 

$ 

0.75 

M12 core steel $/lb $ 

1.03 

$ 

0.85 

$ 

1.60 

$ 

1.03 

$ 

1.09 

$ 

1.28 

$ 

1.24 

$ 

1.13 

M6 core steel $/lb $ 

1.46 

$ 

0.94 

$ 

2.19 

$ 

1.46 

$ 

1.64 

$ 

1.75 

$ 

1.58 

$ 

1.26 

M5 core steel $/lb $ 

1.51 

$ 

0.99 

$ 

2.24 

$ 

1.51 

$ 

1.67 

$ 

1.79 

$ 

1.61 

$ 

1.32 

M4 core steel $/lb $ 

1.59 

$ 

1.03 

$ 

2.30 

$ 

1.59 

$ 

1.70 

$ 

1.84 

$ 

1.64 

$ 

1.38 

M3 core steel $/lb $ 

1.88 

$ 

1.06 

$ 

2.60 

$ 

1.88 

$ 

1.96 

$ 

2.08 

$ 

1.70 

$ 

1.41 

M2 core steel $/lb $ 

2.00 

$ 

1.32 

$ 

2.79 

$ 

2.00 

$ 

2.01 

$ 

2.23 

$ 

2.18 

$ 

1.76 

H-0 DR core steel (laser 

scribed) $/lb $ 2.06 

$ 

1.41 

$ 

3.23 

$ 

2.06 

$ 

2.38 

$ 

2.58 

$ 

2.27 

$ 

1.89 

SA1 (amorphous) finished 

core, volume production $/lb $ 2.38 

$ 

1.72 

$ 

3.64 

$ 

2.38 

$ 

2.29 

$ 

2.91 

$ 

- 

$ 

- 

Copper wire, rectangular 

0.1 x 0.2, Nomex wrapped $/lb $ 4.52 

$ 

3.07 

$ 

5.53 

$ 

4.52 

$ 

3.46 

$ 

4.42 

$ 

4.43 

$ 

4.09 

Aluminum wire, 

rectangular 0.1 x 0.2, 

Nomex wrapped

$/lb $ 

2.97 

$ 

2.23 

$ 

3.78 

$ 

2.97 

$ 

2.90 

$ 

3.03 

$ 

2.98 

$ 

2.97 

Copper strip, thickness 

range 0.02-0.045 $/lb $ 4.97 

$ 

3.41 

$ 

6.09 

$ 

4.97 

$ 

3.91 

$ 

4.87 

$ 

4.88 

$ 

4.54 

Aluminum strip, thickness 

range 0.02-0.045 $/lb $ 2.08 

$ 

1.56 

$ 

2.67 

$ 

2.08 

$ 

2.01 

$ 

2.14 

$ 

2.09 

$ 

2.08 

Nomex insulation $/lb $ 

24.50 

$ 

13.72 

$ 

29.03 

$ 

24.50 

$ 

24.73 

$ 

23.23 

$ 

20.71 

$ 

18.29 

Cequin insulation $/lb $ 

5.53 

$ 

3.84 

$ 

6.09 

$ 

5.53 

$ 

5.12 

$ 

4.87 

$ 

5.13 

$ 

5.12 

Impregnation $/gal $ 

22.55 

$ 

17.16 

$ 

27.31 

$ 

22.55 

$ 

22.71 

$ 

21.85 

$ 

22.23 

$ 

22.88 

Winding combs $/lb $ 

12.34 

$ 

6.08 

$ 

15.41 

$ 

12.34 

$ 

12.70 

$ 

12.33 

$ 

11.99 

$ 

8.10 

Enclosure Steel $/lb $ 

0.38 

$ 

0.32 

$ 

0.60 

$ 

0.38 

$ 

0.39 

$ 

0.48 

$ 

0.43 

$ 

0.43 

On the following pages, all the material prices entered into the design software for drytype distribution transformers are given. As shown in these tables, DOE marked up the material 

prices before being entering them into the design software.
5-50

Table 5.4.5 Marked-up Material Prices for Dry-Type Units, Current Year (2010) Price 

Scenario

Item and Description Units

Current 

2010 Price

2010$

Scrap & 

Handling

Factory

Overhead

NonProductionSoftware 

Input

M36 core steel (26 gauge)

$/lb $ 

0.66 

 

1.025 

 

1.125 

 

1.25 

$ 

0.95 

M19 core steel (26 gauge)

$/lb $ 

0.91 

 

1.025 

 

1.125 

 

1.25 

$ 

1.31 

M12 core steel $/lb $ 

1.03 

 

1.025 

 

1.125 

 

1.25 

$ 

1.49 

M6 core steel $/lb $ 

1.46 

 

1.025 

 

1.125 

 

1.25 

$ 

2.10 

M5 core steel $/lb $ 

1.51 

 

1.025 

 

1.125 

 

1.25 

$ 

2.18 

M4 core steel $/lb $ 

1.59 

 

1.025 

 

1.125 

 

1.25 

$ 

2.28 

M3 core steel $/lb $ 

1.88 

 

1.025 

 

1.125 

 

1.25 

$ 

2.70 

M2 core steel $/lb $ 

2.00 

 

1.025 

 

1.125 

 

1.25 

$ 

2.88 

H-0 DR core steel (laser scribed) $/lb $ 

2.06 

 

1.025 

 

1.125 

 

1.25 

$ 

2.97 

SA1 (amorphous) finished core, 

volume production $/lb $ 

2.38 

 

1.015 

 

1.125 

 

1.25 

$ 

3.40 

Copper wire, rectangular 0.1 x 0.2, 

Nomex wrapped $/lb $ 

4.52 

 

1.025 

 

1.125 

 

1.25 

$ 

6.52 

Aluminum wire, rectangular 0.1 x 

0.2, Nomex wrapped $/lb $ 

2.97 

 

1.025 

 

1.125 

 

1.25 

$ 

4.29 

Copper strip, thickness range 0.02-

0.045 $/lb $ 

4.97 

 

1.025 

 

1.125 

 

1.25 

$ 

7.17 

Aluminum strip, thickness range 

0.02-0.045 $/lb $ 

2.08 

 

1.025 

 

1.125 

 

1.25 

$ 

3.00 

Nomex insulation $/lb $ 

24.50 

 

1.025 

 

1.125 

 

1.25 

$ 

35.31 

Cequin insulation $/lb $ 

5.53 

 

1.025 

 

1.125 

 

1.25 

$ 

7.97 

Impregnation $/gal $ 

22.55 

 

1.000 

 

1.125 

 

1.25 

$ 

31.71 

Winding combs $/lb $ 

12.34 

 

1.025 

 

1.125 

 

1.25 

$ 

17.79 

Enclosure Steel $/lb $ 

0.38 

 

1.025 

 

1.125 

 

1.25 

$ 

0.55 

As stated in section 5.3, the OPS software does not take into account retooling costs 

associated with changing production designs. Therefore, to partially capture these differential 

costs in the design lines that had both buttlap and mitered designs, DOE used adders in DL7 and 

DL8. The adders specified an extra 10 cents per pound of core steel for full-mitered designs. 
5-51

More detailed costing of the retooling costs for mitering equipment will be covered in the 

manufacturer impact analysis (MIA). (See Chapter 12.) 

Similar to the liquid-immersed designs, there are fixed (and some partially variable) 

hardware costs associated with dry-type distribution transformers. These are discussed 

individually and then summarized in Table 5.4.6.

For DL6, a 25 kVA single-phase, low-voltage, dry-type transformer, the low-voltage and 

high-voltage terminal set costs $4. The mounting frame that attaches the core/coil assembly to 

the transformer enclosure costs approximately $9.25. The fiberglass dog-bone duct-spacers used 

for this design line cost $0.24 per foot. DOE estimated the miscellaneous hardware costs at 

$4.50. The ventilated enclosure – a 16-gauge steel enclosure, base, and mounting feet – varies 

with the size of the core-coil assembly for the 25kVA unit, and costs approximately $50.

For DL7, a 75 kVA three-phase, low-voltage, dry-type transformer, the fixed hardware 

costs are $9 per phase for the high-voltage terminal board with connection points. DOE 

estimated the secondary (low-voltage) bus-bar to be seven feet at $1.50 per foot, or $10.50. The 

mounting frame that attaches the core/coil assembly to the transformer enclosure costs 

approximately $19. The fiberglass dog-bone duct-spacers used for this design line cost $0.32 per 

foot. DOE estimated the miscellaneous hardware costs at $7. The ventilated enclosure – a 14-

gauge steel enclosure, base, and mounting feet – varies with the size of the core-coil assembly 

for the 75kVA unit, and costs approximately $90.

For DL8, a 300 kVA three-phase, low-voltage, dry-type transformer, the high-voltage 

terminal board costs $27. DOE estimated the secondary (low-voltage) bus-bar to be nine feet at 

$2.50 per foot, or $22.50. The mounting frame that attaches the core/coil assembly to the 

transformer enclosure costs approximately $36. The fiberglass dog-bone duct-spacers used for 

this design line cost $0.42 per foot. DOE estimated the miscellaneous hardware costs at $12. The 

ventilated enclosure – a 14-gauge steel enclosure, base, and mounting feet – varies with the size 

of the core-coil assembly for the 300kVA unit, and costs approximately $100.

For DL9, a 300 kVA three-phase, medium-voltage, dry-type transformer at 45 kV BIL, 

the low-voltage and high-voltage terminal set costs $75. DOE estimated the secondary (lowvoltage) bus-bar to be eight feet at $10 per foot, or $80. The mounting frame that attaches the 

core/coil assembly to the transformer enclosure costs approximately $36. The fiberglass dogbone duct-spacers used for this design line cost $0.42 per foot. DOE estimated the miscellaneous 

hardware costs at $25. The ventilated enclosure – a 14-gauge steel enclosure, base, and mounting 

feet – varies with the size of the core-coil assembly for the 300 kVA unit, and costs 

approximately $135.

For DL10, a 1500 kVA three-phase, medium-voltage, dry-type transformer at 45 kV BIL, 

the low-voltage and high-voltage terminal set costs $120. DOE estimated the low-voltage busbar to be 14 feet at $10 per foot, or $140. The mounting frame that attaches the core/coil 

assembly to the transformer enclosure costs approximately $120. DOE accounted for the cost of 

additional bracing in the amorphous design since the amorphous design uses a wound core rather 

than a round, cruciform core like the other designs. This extra bracing is needed for the 
5-52

amorphous design due to the size of DL10 (1500 kVA). The weight of the added bracing was 

calculated as 7 percent of the core and coil weight, and was multiplied by the price for enclosure 

steel to derive a cost. The bracing weighs 600 pounds on average and costs approximately $230. 

The fiberglass dog-bone duct-spacers used for this design line cost $0.52 per foot. DOE 

estimated the miscellaneous hardware costs at $42. The ventilated enclosure – a 14-gauge steel 

enclosure, base, and mounting feet – varies with the size of the core-coil assembly for the 1500 

kVA unit, and costs approximately $400.

For DL11, a 300 kVA three-phase, medium-voltage, dry-type at 95 kV BIL, the lowvoltage and high-voltage terminal set costs $100. The high-voltage terminal boards cost $27. 

DOE estimated the low-voltage bus-bar is estimated to be 10 feet at $8 per foot, or $80. The 

mounting frame that attaches the core/coil assembly to the transformer enclosure costs $42. The 

fiberglass dog-bone duct-spacers used for this design line cost $0.42 per foot. DOE estimated the 

miscellaneous hardware costs at $32. The ventilated enclosure – a 14-gauge steel enclosure, 

base, and mounting feet – varies with the size of the core-coil assembly for the 300 kVA unit, 

and costs approximately $200. 

For DL12, a 1500 kVA three-phase, medium-voltage, dry-type at 95 kV BIL, the lowvoltage and high-voltage terminal set costs $135. The high-voltage terminal boards cost $27. 

DOE estimated the low-voltage bus-bar is estimated to be 16 feet at $12 per foot, or $192. The 

mounting frame that attaches the core/coil assembly to the transformer enclosure costs $125. 

DOE accounted for the cost of additional bracing in the amorphous design since the amorphous 

design uses a wound core rather than a round, cruciform core like the other designs. This extra 

bracing is needed for the amorphous design due to the size of DL12 (1500 kVA). The weight of 

the added bracing was calculated as 7 percent of the core and coil weight, and was multiplied by 

the price for enclosure steel to derive a cost. The added bracing weighs 700 pounds on average 

and costs approximately $270. The fiberglass dog-bone duct-spacers used for this design line 

cost $0.56 per foot. DOE estimated the miscellaneous hardware costs at $54. The ventilated 

enclosure – a 14-gauge steel enclosure, base, and mounting feet – varies with the size of the 

core-coil assembly for the 1500 kVA unit, and costs approximately $450.

For DL13A, a 300 kVA three-phase, medium-voltage, dry-type at 125 kV BIL, the lowvoltage and high-voltage terminal set costs $115. The high-voltage terminal boards cost $27. 

DOE estimated the low-voltage bus-bar is estimated to be 10 feet at $10 per foot, or $100. The 

mounting frame that attaches the core/coil assembly to the transformer enclosure costs $50. The 

fiberglass dog-bone duct-spacers used for this design line cost $0.42 per foot. DOE estimated the 

miscellaneous hardware costs at $36. The ventilated enclosure – a 14-gauge steel enclosure, 

base, and mounting feet – varies with the size of the core-coil assembly for the 300 kVA unit, 

and costs approximately $200.

For DL13B, a 2000 kVA three-phase, medium-voltage, dry-type at 125 kV BIL, the lowvoltage and high-voltage terminal set costs $150. The high-voltage terminal boards cost $27. 

DOE estimated the low-voltage bus-bar is estimated to be 18 feet at $15 per foot, or $270. The 

mounting frame that attaches the core/coil assembly to the transformer enclosure costs $175. 

DOE accounted for the cost of additional bracing in the amorphous design since the amorphous 

design uses a wound core rather than a round, cruciform core like the other designs. This extra 
5-53

bracing is needed for the amorphous design due to the size of DL13B (2000 kVA). The weight of 

the added bracing was calculated as 7 percent of the core and coil weight, and was multiplied by 

the price for enclosure steel to derive a cost. The added bracing weighs 850 pounds on average 

and costs approximately $330. The fiberglass dog-bone duct-spacers used for this design line 

cost $0.60 per foot. DOE estimated the miscellaneous hardware costs at $60. The ventilated 

enclosure – a 14-gauge steel enclosure, base, and mounting feet – varies with the size of the 

core-coil assembly for the 300 kVA unit, and costs approximately $450.

Table 5.4.6 Summary Table of Fixed Material Costs for Dry-Type Units

Item DL6 DL7 DL8 DL9 DL10 DL11 DL12 DL13A DL13B

LV and HV terminals (set) $4 n/a n/a $75 $120 $100 $135 $115 $150

HV terminal board(s) n/a $27 $27 $27 $27 $27 $27 $27 $27

LV bus-bar n/a $10.50 $22.50 $80 $140 $80 $192 $100 $270

Core/coil mounting frame $9.25 $19 $36 $36 $120 $42 $125 $50 $175

Additional Bracing n/a n/a n/a n/a ~$230 n/a ~$270 n/a ~$330

Nameplate $0.65 $0.65 $0.65 $0.65 $0.65 $0.65 $0.65 $0.65 $0.65

Dog-bone duct spacer (ft.) $0.24 $0.32 $0.42 $0.42 $0.52 $0.42 $0.56 $0.42 $0.60

Winding combs (lb.) n/a n/a n/a n/a n/a $10.00 $10.00 $10.00 $10.00

Misc. hardware $4.50 $7 $12 $25 $42 $32 $54 $36 $60

Enclosure (12, 14 gauge) ~$50 ~$90 ~$100 ~$135 ~$400 ~$200 ~$450 ~$200 ~$450

LV = low voltage

HV = high voltage

5.4.4 Labor Costs

Labor costs are a critical aspect of the cost of manufacturing a distribution transformer. 

DOE used the same hourly labor cost for both liquid and dry-type distribution transformers. It 

developed the hourly cost of labor using a similar approach to the development of the cost of 

materials; however, it used different markups. DOE developed the markups shown in Table 5.4.7

after reviewing publicly available information, speaking with transformer manufacturers during 

2011, and consulting with industry experts familiar with transformer manufacturing in the U.S.
5-54

Table 5.4.7 Labor Markups for Liquid-Immersed and Dry-Type Manufacturers

Item description Markup percentage Rate per hour

Labor cost per hour*

$ 16.80 

Indirect Production** 33% $ 22.35 

Overhead*** 30% $ 29.05 

Fringe†24% $ 36.03 

Assembly Labor Up-time†† 43% $ 51.52

Fully-Burdened Cost of Labor 25% $ 64.40

* Cost per hour is from U.S. Census Bureau, 2007 Economic Census - Detailed Statistics, published October 2009. 

Data for NAICS code 3353111 "Power and distribution transformers, except parts" Production workers hours and 

wages.

** Indirect production labor (e.g., production managers, quality control) as a percent of direct labor on a cost basis. 

Navigant Consulting, Inc. (NCI) estimate.

*** Overhead includes commissions, dismissal pay, bonuses, vacation, sick leave, and social security contributions. 

NCI estimate.

† Fringe includes pension contributions, group insurance premiums, workers compensation. Source: U.S. Census 

Bureau, 2007 Economic Census - Detailed Statistics, published October 2009. Data for NAICS code 3353111 

"Power and distribution transformers, except parts" Total fringe benefits as a percent of total compensation for all 

employees (not just production workers).

†† Assembly labor up-time is a factor applied to account for the time that workers are not assembling units and/or 

reworking unsatisfactory units. The markup of 43 percent represents a 70 percent utilization (multiplying by 

100/70). NCI estimate.

There are several labor steps involved in manufacturing a liquid-immersed transformer. 

DOE prepared estimates of the amount of labor involved, some varying with the transformer 

design and others fixed on a per-unit basis. These steps are described below, and the amount of 

time dedicated to each is given in Table 5.4.8.

Cutting, Forming, and Annealing – This task involves cutting the core steel to lengths on 

a distributed-gap core cutting machine, forming the resulting ―donut‖ of core steel into a 

rectangular shape in a hydraulic press, and then annealing the core in a high temperature 

annealing furnace. DOE calculated the labor involved in these activities based on the 

weight of core (pounds) multiplied by a constant, which varies with the lamination 

thickness of the core steel. For DL1, DL2, and DL4, on M6 designs the constant is 0.08, 

M5 is 0.09, M4 is 0.10, M3 (with or without Lite Carlite) and ZDMH are 0.125, and M2

(with or without Lite Carlite) is 0.16. For DL3 and DL5, on M6 designs the constant is 

0.05, M5 is 0.06, M4 is 0.07, M3 (with or without Lite Carlite) and ZDMH are 0.09, and 

M2 (with or without Lite Carlite) is 0.11. For the prefabricated core — SA1 (amorphous 

material)—DOE set the labor for cutting, forming, and annealing to zero.

Primary Winding – This task entails winding the primary conductor of the transformer. It 

includes set-up time as well as winding time. The labor hours vary with the number of 

turns (per phase) for the primary winding. For DL1, DL2, and DL4, the winding time is 

0.0001 hours per turn. For these smaller kVA ratings (and smaller cores), this rate is very 

low because some of the larger, liquid-immersed manufacturers wind multiple coils 

simultaneously on the same winding machine. This manufacturing approach improves 
5-55

throughput and productivity at the facility. The rate of 0.0001 hours per turn equates to 

approximately one-third of a second per turn. On DL3 and DL5, due to the larger coil 

size associated with these units, the winding time is 0.002 hours per turn (approximately 

7.2 seconds per turn).

Secondary Winding – This task involves winding the secondary conductor of the 

transformer. It includes set-up time as well as winding time. On a distribution (stepdown) transformer, the number of secondary turns is always less than the primary. For 

the liquid-immersed units, which are taking a relatively high primary voltage and 

dropping to below 600V, the turns ratio can be as large as 100:1. For this reason, the 

hours per turn of the secondary are considerably higher than the primary, because there 

are fewer turns over which to amortize the set-up time as well as a slower winding rate 

for the secondary, which has larger cross-sectional area than the primary. For DL1, DL2, 

and DL4, the hours per turn of the secondary are 0.015 (54 seconds per turn); for DL3 

and DL5, the hours per turn are 0.02 (72 seconds per turn).

Lead Dressing – Once a wound coil is taken off the winding machine, work must be 

performed on the leads to prepare them for the next manufacturing step. Enamel is 

removed to enable good electrical connection and insulating tubing is slipped over the 

cable. This is a fixed amount of labor, and does not vary with efficiency or design. Lead 

dressing time ranges from 0.1 to 1 hour.

Coil Varnishing and Baking – Once they are complete, the coils are vacuum-dipped in 

varnish and baked in an oven to cure the varnish and enhance the integrity of the coil. 

This task varies slightly with kVA rating, but does not vary with efficiency. The 

estimated times range from 0.07 to 0.25 hours.

Core Assembly (―Lacing‖) – This task involves assembling and banding the annealed 

wound core laminations around varnished windings. The annealed bundle of core steel is 

disassembled from the inside out by grabbing approximately 1/4 inch bundles, then 

reassembling the core steel around the coils. Once all the laminations are reassembled, 

the core material is clamped to maintain the structure. The activity involves feeding a 

banding strip around the core material and using a locking clamp to compress and contain 

the core material. The labor rate varies with stack height and lamination thickness for 

each design. The average time for core assembly ranges from approximately 0.2 hours 

(for DL2) to 4.9 hours (for DL5).

Tanking and Impregnating – This task involves inserting and fastening the core/coil 

assembly into the tank. Then, a vacuum is pulled and oil is introduced to the tank. On 

round tanks, the vacuum and oil step is done through a lid attached to the top of the unit. 

On the rectangular and pad-mounted tanks, the vacuum is pulled in a chamber, which 

takes a little longer per unit. Finally, tap changers and bushings are mounted, and bolted 

connections made. The time for this activity does not vary with design or efficiency, but 

it does vary by kVA rating and tank shape. The estimates of labor time for the five liquidimmersed design lines range from 0.1 to 1.8 hours.
5-56

Inspection – This activity involves verifying that the transformer is assembled properly

and is up to a manufacturer's quality specification. This task includes inspecting the lead 

dressing, lead tie-up, and other quality certification specifications. The time for this 

activity does not vary with design or efficiency, but it does vary by kVA rating, from 

0.05 hours for the smallest units to 0.20 hours for the largest units.

Preliminary Test – This step involves conducting a test to ensure that the core/coil meets 

the specified turns ratio, polarity, core loss, etc. The time for this activity does not vary 

with design or efficiency, but it does vary by kVA rating from 0.05 to 0.15 hours.

Final Test – This activity involves testing of the final, assembled unit, with the core/coil 

assembly immersed in oil. This test verifies that the unit meets the guaranteed values, 

including core and coil losses, impedance, and dielectric tests. The time for this activity 

does not vary with design or efficiency, but it does vary by kVA rating from 0.1 to 0.25 

hours.

Pallet Loading – This activity involves preparing the transformer for shipping to the 

customer. This includes loading the finished transformer onto a pallet, banding the 

transformer to the pallet, wrapping, and all other necessary steps for shipping. The time 

for this activity does not vary with design or efficiency, but it does vary by kVA rating

from 0.15 hours for the smallest units to 3 hours for the largest units.

Marking and Miscellaneous – This task involves preparing any extra markings around the 

bushings or on the surface of the transformer and other miscellaneous labor associated 

with preparing the finished transformer for the customer. The time for this activity does 

not vary with design or efficiency, but it does vary by kVA rating from 0.08 to 0.35 

hours.

Table 5.4.8 summarizes the estimates of labor time that DOE used for the five liquidimmersed units.
5-57

Table 5.4.8 Summary of Labor Times for Liquid-Immersed Units

Labor Activity DL1

hrs.

DL2

hrs.

DL3

hrs.

DL4

hrs.

DL5

hrs.

Cutting, Forming, & Annealing ~1.00 ~0.75 ~4.00 ~3.00 ~8.50

Primary Winding (hrs/turn) 0.0001 0.0001 0.002 0.0001 0.002

Secondary Winding (hrs/turn) 0.015 0.015 0.020 0.015 0.020

Lead Dressing 0.50 0.1 0.35 0.75 1.00

Baking Coils 0.10 0.07 0.15 0.17 0.25

Core Assembly ~0.40 ~0.20 ~1.20 ~1.00 ~4.90

Tanking and Impregnating 0.30 0.11 0.65 0.50 1.80

Inspection 0.10 0.05 0.10 0.15 0.20

Preliminary Test 0.10 0.05 0.10 0.10 0.15

Final Test 0.15 0.1 0.15 0.20 0.25

Pallet Loading 0.5 0.15 0.75 0.50 3.00

Marking and Misc. 0.35 0.08 0.35 0.35 0.75

Likewise, there are several labor steps involved in manufacturing a dry-type transformer. 

DOE prepared estimates of the amount of labor involved, some varying with the transformer 

design and others fixed on a per-unit basis. These steps are described below, and the amounts of 

time dedicated to each are summarized in Table 5.4.9.

Core Stacking – This task involves stacking (assembling) the cut steel laminations into a 

distribution transformer core. The amount of labor for this task varies by kVA rating, 

stack height, and whether the core is grain-oriented or non-oriented. Thus, the labor for 

core stacking varies with the efficiency of the transformer. Approximate labor hours for 

core stacking vary from as little as 0.25 hours/inch for a 25 kVA single-phase, lowvoltage unit to 0.9 hours/inch for a 2000 kVA, 125kV BIL three-phase, medium-voltage 

unit. For the prefabricated core – SA1 (Amorphous material) – the labor for core stacking 

(i.e., cutting, forming, and annealing) is set to zero.

Primary Winding – This task encompasses winding the primary conductor of the 

transformer. It includes set-up time as well as winding time. The labor hours vary with 

the number of turns (per phase) for the primary winding, ranging from 0.001 to 0.023 

hours/turn.

Secondary Winding – This task involves winding the secondary conductor of the 

transformer. It includes set-up time as well as winding time. The winding time of the 

secondary is considerably higher than that of the primary, because there are fewer turns 

over which to amortize the set-up time as well as a slower winding rate for the secondary, 

which has larger cross sectional area. The hours per turn vary from 0.01 to 0.125, 

depending on the kVA rating (design line).

Lead Dressing – Once a wound coil is taken off the winding machine, work must be 

performed on the leads to prepare them for the next manufacturing step. Enamel is 
5-58

removed to enable good electrical connection and insulating tubing is slipped over the 

cable. For a given kVA rating, this is a fixed amount of labor, and does not vary with 

efficiency or design. The range is from 0.15 to 1.0 hours per unit.

Assembly – This task involves installing the wound coils onto the partially assembled 

core, and then lacing the top (yoke) laminations to complete the core. It also includes 

setting all the core clamps and completing the core/coil assembly. DOE assumed the 

assembly time varies by kVA rating, but does not vary by design within a kVA rating. 

For example, DOE estimated the assembly time for a 1500kVA three-phase unit at six 

hours, while DOE estimated the assembly time for a 75kVA three-phase unit at one hour. 

The only exception is for amorphous designs in dry-type design lines that are 1500 kVA 

or greater. For DL 10, DL 12, and DL 13B, DOE used an estimate of sixteen hours for 

assembly time to account for the added complexity of using an amorphous core in these 

large designs. This time estimate is based on time estimates for unpacking (2 hours), 

unlacing joints (1.5 hours), mounting cores in place (2 hours), re-lacing core joints (4 

hours), setting cores in place (1.5 hours), and attaching the framing and bolting (5 hours).

Inspection – This activity involves verifying that the transformer is assembled properly 

and is up to a manufacturer's quality specification. It includes inspecting the lead 

dressing, lead tie up, and other quality certification specifications. The time for this 

activity does not vary with design or efficiency, but it does vary by kVA rating. The time 

estimates vary from 0.05 hours (three minutes) for the smaller kVA ratings to 0.25 hours 

(15 minutes) for the larger units.

Preliminary Test – This step involves conducting a test to ensure that the core/coil meets 

the specified turns ratio, polarity, core loss, etc. The time for this activity does not vary 

with design or efficiency, but it does vary by kVA rating. The estimates of labor time 

range from 0.05 hours (three minutes) for the smaller kVA ratings to 0.5 hours (30 

minutes) for the larger units.

Final Test – This activity involves testing the final, assembled unit, with the core/coil 

assembly immersed in oil. This test verifies that the unit meets the guaranteed values, 

including core and coil losses, impedance, and dielectric tests. The time for this activity 

does not vary with design or efficiency, but it does vary by kVA rating. Similar to the 

preliminary test, the labor time estimates range from 0.1 hours (six minutes) for the 

smaller kVA ratings to 0.75 hours (45 minutes) for the larger units.

Enclosure Manufacturing – The labor estimate for this task encompasses all activity 

associated with the cutting, forming, assembly, priming, painting, and preparation of the 

enclosure. This labor estimate varies with the kVA rating, spanning from 0.75 hours for 

the 25kVA single-phase unit up to eight hours for the 1500 and 2000kVA cabinets.

Packing – This activity involves preparing the transformer for shipping to the customer. 

This includes loading the finished transformer onto a pallet, banding the transformer to 

the pallet, wrapping, and all other necessary steps for shipping. The time for this activity 
5-59

does not vary with design or efficiency, but it does vary by kVA rating. The time estimate 

ranges from 0.20 hours at the low end to 2.0 hours at the higher kVA ratings.

Marking and Miscellaneous – This task involves preparing any extra markings on the 

terminal board or on the surface of the transformer, and other miscellaneous labor 

associated with preparing the finished transformer for the customer. The time for this 

activity does not vary with design or efficiency, but it does vary by kVA rating. The labor 

estimate ranges from 0.20 hours at the low end to 2.2 hours at the higher kVA ratings.

Table 5.4.9 presents the hours of labor needed to complete each step in the manufacturing 

process for all design lines containing dry-type transformers.

Table 5.4.9 Summary of Labor Times for Dry-Type Units

Labor Activity DL6

hrs.

DL7

hrs.

DL8

hrs.

DL9

hrs.

DL10

hrs.

DL11

hrs.

DL12

hrs.

DL13A

hrs.

DL13B

hrs.

Core Stacking (hrs/inch) 0.25 0.25 –

0.35

0.38 0.55 0.70 0.70 0.80 0.70 0.90

Primary Winding (hrs/turn) 0.001 0.0015 0.01 0.008 0.0225 0.005 0.0125 0.005 0.0125

Secondary Winding (hrs/turn) 0.01 0.011 0.040 0.035 0.125 0.035 0.075 0.035 0.100

Lead Dressing 0.15 0.25 0.50 0.60 1.00 0.60 1.00 0.60 1.00

Assembly, 

[Amorphous designs]

0.35 1.00 2.50 3.00 6.00,

[16.00]

4.00 6.00,

[16.00]

4.00 6.00,

[16.00]

Inspection 0.05 0.05 0.10 0.10 0.25 0.10 0.25 0.1 0.25

Preliminary Test 0.05 0.05 0.10 0.10 0.50 0.15 0.50 0.15 0.50

Final Test 0.10 0.10 0.15 0.15 0.75 0.25 0.75 0.25 0.75

Enclosure Manufacturing 0.75 1.50 3.00 5.00 8.00 5.00 8.00 5.00 8.00

Packing 0.20 0.20 1.00 1.00 2.00 1.00 2.00 1.00 2.00

Marking and Miscellaneous 0.20 0.20 0.60 0.70 2.20 0.85 2.20 0.85 2.20

5.5 EFFICIENCY LEVELS

DOE analyzed designs over a range of efficiency values for each representative unit. 

Within the efficiency range, DOE developed designs that approximate a continuous function of 

efficiency. However, DOE analyzes the incremental impacts of increased efficiency by 

comparing discrete efficiency benchmarks to a constant baseline efficiency. The baseline 

efficiency evaluated for each representative unit is the existing standard level efficiency for 

distribution transformers established in DOE‘s previous rulemaking. The incrementally higher 

efficiency levels are meant to characterize the cost-efficiency relationship above the baseline. 

These efficiency levels are ultimately used by DOE if it decides to amend the existing energy 

conservation standards.
5-60

5.5.1 Criteria for Selecting Efficiency Levels

After the preliminary analysis, DOE considered several criteria when setting efficiency 

levels. First, DOE harmonized the efficiency values across single-phase transformers and the 

per-phase kVA equivalent three-phase transformers. For example, a 50 kVA single-phase 

transformer would have the same efficiency as a 150 kVA three-phase transformer. This 

approach is consistent with DOE‘s methodology from the previous rulemaking. As such, DOE 

selected equivalent efficiency levels for several of the representative units that have equivalent 

per-phase kVA ratings.

Second, DOE selected equally spaced efficiency levels by dividing the entire efficiency 

range into 5–7 evenly spaced increments. The number of increments depended on the size of the 

efficiency range. This allowed DOE to examine impacts based on an appropriate resolution of 

efficiency for each representative unit.

Finally, DOE adjusted the position of some of the equally spaced efficiency levels and 

examined additional efficiency levels. These minor adjustments to the equally spaced efficiency 

levels allowed DOE to consider important efficiency values based on the results of the software 

designs. For example, DOE adjusted some efficiency levels slightly up or down in efficiency to 

consider the maximum efficiency potential of non-amorphous design options. Other efficiency 

levels were added to consider important benchmark efficiencies, such as the NEMA Premium 

efficiency for low-voltage dry-type distribution transformers. Lastly, DOE considered additional 

efficiency levels to characterize the maximum-technologically feasible design for representative 

units where the harmonized per-phase efficiency value would have been unachievable for one of 

the representative units. DOE characterized a maximum-technologically feasible efficiency level 

for both standard core technology and symmetric core technology.

5.5.2 Efficiency Levels Selected

Table 5.5.1 presents the efficiency identified for each efficiency level (EL) in the 

engineering analysis. Table 5.5.2 presents the incremental MSP for each of the least-costly 

design options at each efficiency level.
5-61

Table 5.5.1 Summary of Baselines and Efficiency Levels for Distribution Transformer 

Representative Units

Design 

Line

Representative Unit

Baseline EL1 EL2 EL3 EL4 EL5 EL6 EL7

Eff.

[%]

Eff.

[%]

Eff.

[%]

Eff.

[%]

Eff.

[%]

Eff.

[%]

Eff.

[%]

Eff.

[%]

1

50 kVA, 65 C, single-phase, 60Hz, 

14400V primary, 240/120V 

secondary, rectangular tank 99.08 99.16 99.22 99.25 99.31 99.42 99.50 99.50

2

25 kVA, 65 C, single-phase, 60Hz, 

14400V primary, 120/240V 

secondary, round tank 98.91 99.00 99.07 99.11 99.18 99.31 99.41 99.46

3

500 kVA, 65 C, single-phase, 

60Hz, 14400V primary, 277V 

secondary 99.42 99.48 99.51 99.54 99.57 99.61 99.69 99.73

4

150 kVA, 65 C, three-phase, 

60Hz, 12470Y/7200V primary, 

208Y/120V secondary 99.08 99.16 99.22 99.25 99.31 99.42 99.50 99.60

5

1500 kVA, 65 C, three-phase, 

60Hz, 24940GrdY/14400V 

primary, 480Y/277V secondary 99.42 99.48 99.51 99.54 99.57 99.61 99.69 99.69

6

25 kVA, 150 C, single-phase, 

60Hz, 480V primary, 120/240V 

secondary, 10kV BIL 98.00 98.23 98.47 98.60 98.80 98.93 99.17 99.44

7

75 kVA, 150 C, three-phase, 

60Hz, 480V primary, 208Y/120V 

secondary, 10kV BIL 98.00 98.23 98.47 98.60 98.80 98.93 99.17 99.44

8

300 kVA, 150 C, three-phase, 

60Hz, 480V Delta primary, 

208Y/120V secondary, 10kV BIL 98.60 98.80 99.02 99.14 99.25 99.32 99.44 99.58

9

300 kVA, 150 C, three-phase, 

60Hz, 4160V Delta primary, 

480Y/277V secondary, 45kV BIL 98.82 98.99 99.12 99.28 99.38 99.50 99.59 99.59

10

1500 kVA, 150 C, three-phase, 

60Hz, 4160V primary, 480Y/277V 

secondary, 45kV BIL 99.22 99.31 99.40 99.50 99.53 99.60 99.67 99.67

11

300 kVA, 150 C, three-phase, 

60Hz, 12470V primary, 

480Y/277V secondary, 95kV BIL 98.67 98.81 98.94 99.06 99.13 99.32 99.50 99.50

12

1500 kVA, 150 C, three-phase, 

60Hz, 12470V primary, 

480Y/277V secondary, 95kV BIL 99.12 99.21 99.30 99.39 99.46 99.53 99.59 99.65

13

A

300kVA, 150 ̊C, three-phase, 

60Hz, 24940V primary, 

480Y/277V secondary, 125kV BIL

98.63 98.76 98.85 98.92 99.10 99.29 99.48 99.48

13

B

2000kVA, 150 ̊C, three-phase, 

60Hz, 24940V primary, 

480Y/277V secondary, 125kV BIL

99.15 99.23 99.31 99.38 99.43 99.49 99.58 99.58
5-62

Table 5.5.2 Summary of Incremental Manufacturer Selling Prices Over the Baseline for 

Distribution Transformer Representative Units

Design 

Line

Representative Unit

Baseline EL1 EL2 EL3 EL4 EL5 EL6 EL7 EL 8

$ $ $ $ $ $ $ $ $

1

50 kVA, 65 C, single-phase, 

60Hz, 14400V primary, 

240/120V secondary, 

rectangular tank

-

199 666 811 339 823 1168 N/A N/A

2

25 kVA, 65 C, single-phase, 

60Hz, 14400V primary, 

120/240V secondary, round 

tank

-

216 397 215 247 487 708 1185 N/A

3

500 kVA, 65 C, single-phase, 

60Hz, 14400V primary, 277V 

secondary

-

849 935 2481 1606 2131 4139 7002 N/A

4

150 kVA, 65 C, three-phase, 

60Hz, 12470Y/7200V 

primary, 208Y/120V 

secondary

-

574 1328 2211 1413 1164 1893 4681 N/A

5

1500 kVA, 65 C, three-phase, 

60Hz, 24940GrdY/14400V 

primary, 480Y/277V 

secondary

-

3472 3881 5886 6585 9350 25704 25704 N/A

6

25 kVA, 150 C, single-phase, 

60Hz, 480V primary, 

120/240V secondary, 10kV 

BIL

-

21 -11 -8 147 182 321 812 N/A

7

75 kVA, 150 C, three-phase, 

60Hz, 480V primary, 

208Y/120V secondary, 10kV 

BIL

-

145 73 241 158 447 641 1704 1704

8

300 kVA, 150 C, three-phase, 

60Hz, 480V Delta primary, 

208Y/120V secondary, 10kV 

BIL

-

519 742 904 2113 3862 2325 6734 N/A

9

300 kVA, 150 C, three-phase, 

60Hz, 4160V Delta primary, 

480Y/277V secondary, 45kV 

BIL

-

445 656 2,201 2,897 4,238 7,457 N/A N/A

10

1500 kVA, 150 C, threephase, 60Hz, 4160V primary, 

480Y/277V secondary, 45kV 

BIL

-

124 2,840 8,167 10,053 13,554 22,900 N/A N/A

11

300 kVA, 150 C, three-phase, 

60Hz, 12470V primary, 

480Y/277V secondary, 95kV 

BIL

-

606 2,065 3,001 3,072 4,720 8,307 N/A N/A

12

1500 kVA, 150 C, threephase, 60Hz, 12470V primary, 

480Y/277V secondary, 95kV 

BIL

-

2,000 3,587 6,815 12,107 15,458 19,020 28,951 N/A
5-63

13A

300kVA, 150 ̊C, three-phase, 

60Hz, 24940V primary, 

480Y/277V secondary, 125kV 

BIL

-

825 1,329 2,157 4,602 5,898 11,907 N/A N/A

13B

2000kVA, 150 ̊C, three-phase, 

60Hz, 24940V primary, 

480Y/277V secondary, 125kV 

BIL

-

1,136 4,553 7,776 11,830 19,143 27,991 N/A N/A

Note: Does not include symmetric core designs. Based on reference case traditional core designs only.

5.6 RESULTS OF THE ANALYSIS ON EACH DESIGN LINE

This section provides a visual representation of the results of the engineering analysis. 

The scatter plots in this section show the relationship between the manufacturer‘s selling price 

and efficiency for each of the 14 design lines. Each dot on the plots represents one unique design 

created by the software at a given manufacturer‘s selling price and efficiency level. The 

placement of each dot (and the uniqueness of each design) is dictated by the design option 

combinations (core steel and windings), core shape, A/B combination, and the variable design 

parameters generated by the design software. 

5.6.1 Traditional Core Designs for the Reference Case

The designs in this section represent the traditional core designs that DOE analyzed in the 

life-cycle cost and national impact analyses. In addition to the results provided in this section, 

DOE prepared scatter plots depicting the engineering analysis results for the 14 representative 

units, including watts of core and coil loss and the weight by efficiency (see Appendix 5A). 

Figure 5.6.1 presents a plot of the manufacturer selling prices and efficiency levels for the 

full database of designs for the representative unit from DL1, a 50kVA single-phase, liquidimmersed, pad-mounted distribution transformer. The efficiency levels shown in this plot 

represent transformers at 50 percent of nameplate load and are corrected for temperature. The 

following observations can be made about this scatter plot:

The current standard efficiency level of 99.08 percent is met by designs using M3 core 

steel or better.

The amorphous metal (SA1) core is the most cost-effective design for any efficiency 

level above 99.25 percent, and can reach efficiencies of 99.50 percent.
5-64

Figure 5.6.1 Engineering Analysis Results, Design Line 1

Figure 5.6.2 presents a plot of the manufacturer sales prices and efficiency levels for the 

full database of designs for the representative unit from DL2, a 25kVA single-phase, liquidimmersed, pole-mounted distribution transformer. The efficiency levels shown in this plot 

represent transformers at 50 percent of nameplate load and are corrected for temperature. The 

following observations can be made about this scatter plot:

The current standard efficiency level of 98.91 percent is met by designs using M3 core 

steel or better, though it can be met with M4 or even M5 core steel designs.

The amorphous metal (SA1) core is the most cost-effective design for any efficiency 

level above 99.10 percent, and can reach efficiencies up to 99.5 percent.

$1,500 

$2,000 

$2,500 

$3,000 

$3,500 

$4,000 

99.00% 99.10% 99.20% 99.30% 99.40% 99.50% 99.60%

Manufacturer Selling Price ($)

Efficiency at 50% Load, Temperature Corrected

M5_CuAl_dgw_sh

M3_AlAl_dgw_sh

M3_CuAl_dgw_sh

M2_AlAl_dgw_sh

M2_CuAl_dgw_sh

ZDMH_AlAl_dgw_sh

ZDMH_CuCu_dgw_sh

SA1_AlAl_dgw_sh

SA1_CuCu_dgw_sh

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6
5-65

Figure 5.6.2 Engineering Analysis Results, Design Line 2

Figure 5.6.3 presents a plot of the manufacturer sales prices and efficiency levels for the 

full database of designs for the representative unit from DL3, a 500kVA single-phase, liquidimmersed distribution transformer with radiators. The efficiency levels shown in this plot 

represent transformers at 50 percent of nameplate load and are corrected for temperature. The 

following observations can be made about this scatter plot:

The current standard efficiency level of 99.42 percent is met by designs using M3 core 

steel or better, though it can be met with some M4 core steel designs.

The amorphous metal (SA1) core is the most cost-effective design for any efficiency 

level above 99.55 percent, and can reach efficiencies above 99.65 percent.

$500 

$1,000 

$1,500 

$2,000 

$2,500 

$3,000 

98.80% 98.90% 99.00% 99.10% 99.20% 99.30% 99.40% 99.50% 99.60%

Manufacturer Selling Price ($)

Efficiency at 50% Load, Temperature Corrected

M5_CuAl_dgw_sh

M4_AlAl_dgw_sh

M4_CuAl_dgw_sh

M3_AlAl_dgw_sh

M3_CuAl_dgw_sh

M2_AlAl_dgw_sh

M2_CuAl_dgw_sh

ZDMH_AlAl_dgw_sh

ZDMH_CuCu_dgw_sh

SA1_AlAl_dgw_co

SA1_CuCu_dgw_co

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6 CSL 7
5-66

Figure 5.6.3 Engineering Analysis Results, Design Line 3

Figure 5.6.4 presents a plot of the manufacturer sales prices and efficiency levels for the 

full database of designs for the representative unit from DL4, a 150kVA three-phase, liquidimmersed distribution transformer. The efficiency levels shown in this plot represent 

transformers at 50 percent of nameplate load and are corrected for temperature. The following 

observations can be made about this scatter plot:

The current standard efficiency level of 99.08 percent is met by designs using M3 core 

steel or better.

The amorphous metal (SA1) core is the most cost-effective design for any efficiency 

level above 99.25 percent, but amorphous designs have a minimum efficiency of 99.27 

percent.

The amorphous designs can reach efficiencies up to 99.60 percent.

$-

$5,000 

$10,000 

$15,000 

$20,000 

$25,000 

99.40% 99.45% 99.50% 99.55% 99.60% 99.65% 99.70% 99.75% 99.80%

Manufacturer Selling Price ($)

Efficiency at 50% Load, Temperature Corrected

M5_CuAl_dgw_sh

M4_AlAl_dgw_sh

M4_CuAl_dgw_sh

M3_AlAl_dgw_sh

M3_CuAl_dgw_sh

M2_AlAl_dgw_sh

M2_CuAl_dgw_sh

ZDMH_AlAl_dgw_sh

ZDMH_CuCu_dgw_sh

SA1_AlAl_dgw_co

SA1_CuCu_dgw_sh

SA1_CuCu_dgw_co

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6 CSL 7
5-67

Figure 5.6.4 Engineering Analysis Results, Design Line 4

Figure 5.6.5 presents a plot of the manufacturer sales prices and efficiency levels for the 

full database of designs for the representative unit from DL5, a 1500kVA three-phase, liquidimmersed distribution transformer. The efficiency levels shown in this plot represent 

transformers at 50 percent of nameplate load and are corrected for temperature. The following 

observations can be made about this scatter plot:

The current standard efficiency level of 99.42 percent is met by designs using M3 core 

steel or better, though it can be met with some M4 core steel designs.

The amorphous metal (SA1) core is the most cost-effective design for any efficiency 

level above 99.50 percent, and can reach efficiencies up to 99.7 percent.

$2,500 

$3,500 

$4,500 

$5,500 

$6,500 

$7,500 

$8,500 

$9,500 

$10,500 

$11,500 

99.00% 99.10% 99.20% 99.30% 99.40% 99.50% 99.60% 99.70%

Manufacturer Selling Price ($)

Efficiency at 50% Load, Temperature Corrected

M5_CuAl_dgw_5leg

M3_AlAl_dgw_5leg

M3_CuAl_dgw_5leg

M2_AlAl_dgw_5leg

M2_CuAl_dgw_5leg

ZDMH_AlAl_dgw_5leg

ZDMH_CuCu_dgw_5leg

SA1_AlAl_dgw_5leg

SA1_CuCu_dgw_5leg

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6 CSL 7
5-68

Figure 5.6.5 Engineering Analysis Results, Design Line 5

Figure 5.6.6 presents a plot of the manufacturer sales prices and efficiency levels for the 

full database of designs for the representative unit from DL6, a 25kVA single-phase, lowvoltage, dry-type distribution transformer. The efficiency levels shown in this plot represent 

transformers at 35 percent of nameplate load and are corrected for temperature. The following 

observations can be made about this scatter plot:

The current standard efficiency level of 98.00 percent is met by designs using M6 core 

steel or better.

The NEMA Premium efficiency level of 98.60 percent is met by designs using M4 core 

steel or better.

The amorphous metal (SA1) core is the most cost-effective design for any efficiency 

level above 98.80 percent, and can reach efficiencies up to 99.40 percent.

$15,000 

$20,000 

$25,000 

$30,000 

$35,000 

$40,000 

$45,000 

$50,000 

$55,000 

$60,000 

$65,000 

99.40% 99.45% 99.50% 99.55% 99.60% 99.65% 99.70% 99.75% 99.80%

Manufacturer Selling Price ($)

Efficiency at 50% Load, Temperature Corrected

M4_CuAl_dgw_5leg

M3_AlAl_dgw_5leg

M3_CuAl_dgw_5leg

M2_AlAl_dgw_5leg

M2_CuAl_dgw_5leg

ZDMH_AlAl_dgw_5leg

ZDMH_CuCu_dgw_5leg

SA1_AlAl_dgw_5leg

SA1_CuCu_dgw_5leg

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6
5-69

Figure 5.6.6 Engineering Analysis Results, Design Line 6

Figure 5.6.7 presents a plot of the manufacturer sales prices and efficiency levels for the 

full database of designs for the representative unit from DL7, a 75kVA three-phase, low-voltage,

dry-type distribution transformer. The efficiency levels shown in this plot represent transformers 

at 35 percent of nameplate load and are corrected for temperature. The following observations 

can be made about this scatter plot:

The current standard efficiency level of 98.00 percent is met by designs using M12 core 

steel or better.

The NEMA Premium efficiency level of 98.60 percent is met by designs using M6 core 

steel or better.

The amorphous metal (SA1) core is the most cost-effective design for any efficiency 

level above 98.93 percent, and can reach efficiencies up to 99.40 percent.

$500 

$1,000 

$1,500 

$2,000 

$2,500 

$3,000 

97.80% 98.30% 98.80% 99.30% 99.80%

Manufacturer Selling Price ($)

Efficiency at 35% Load, Temperature Corrected

M6_AlAl_bl_co

M5_AlAl_bl_co

M4_AlAl_bl_co

M3_AlAl_bl_co

M3_AlAl_slm_co

M3_AlAl_dgw_co

M3_CuAl_bl_co

M3_CuAl_bl_sh

H0_AlAl_bl_co

H0_AlAl_slm_co

ZDMH_AlAl_dgw_co

H0_CuCu_bl_co

SA1_AlAl_dgw_co

SA1_CuCu_dgw_co

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6 CSL 7
5-70

Figure 5.6.7 Engineering Analysis Results, Design Line 7

Figure 5.6.8 presents a plot of the manufacturer sales prices and efficiency levels for the 

full database of designs for the representative unit from DL8, a 300kVA three-phase, lowvoltage, dry-type distribution transformer. The efficiency levels shown in this plot represent 

transformers at 35 percent of nameplate load and are corrected for temperature. The following 

observations can be made about this scatter plot:

The current standard efficiency level of 98.60 percent is met by designs using M6 core 

steel or better.

The NEMA Premium efficiency level of 99.02 percent is met by designs using M3 core 

steel or better.

The amorphous metal (SA1) core is the only design that can achieve an efficiency of 

99.40 percent or greater, and can reach efficiencies up to 99.60 percent.

$500 

$1,500 

$2,500 

$3,500 

$4,500 

$5,500 

$6,500 

$7,500 

$8,500 

$9,500 

97.80% 98.00% 98.20% 98.40% 98.60% 98.80% 99.00% 99.20% 99.40% 99.60%

Manufacturer Selling Price ($)

Efficiency at 35% Load, Temperature Corrected

M12_AlAl_bl_3leg

M12_CuAl_bl_3leg

M6_AlAl_bl_3leg

M6_AlAl_fm_3leg

M4_CuAl_fm_3leg

M3_AlAl_fm_3leg

M3_AlAl_slm_3leg

M3_AlAl_dgw_3leg

H0_AlAl_fm_3leg

H0_AlAl_slm_3leg

ZDMH_AlAl_dgw_3leg

H0_CuCu_fm_3leg

SA1_AlAl_dgw_5leg

SA1_CuCu_dgw_5leg

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6 CSL 7
5-71

Figure 5.6.8 Engineering Analysis Results, Design Line 8

Figure 5.6.9 presents a plot of the manufacturer sales prices and efficiency levels for the 

full database of designs for the representative unit from DL9, a 300kVA three-phase, mediumvoltage, dry-type transformer with a 45kV BIL. The efficiency levels shown in this plot represent 

transformers at 50 percent of nameplate load and are corrected for temperature. The following 

observations can be made about this scatter plot:

The current standard efficiency level of 98.82 percent is met by designs using M6 core 

steel or better.

The five-legged amorphous metal (SA1) core is the most cost-effective design for any 

efficiency level above 99.20 percent, and can reach efficiencies up to 99.59 percent.

$2,000 

$4,000 

$6,000 

$8,000 

$10,000 

$12,000 

$14,000 

$16,000 

$18,000 

98.40% 98.60% 98.80% 99.00% 99.20% 99.40% 99.60% 99.80% 100.00%

Manufacturer Selling Price ($)

Efficiency at 35% Load, Temperature Corrected

M6_AlAl_bl_3leg

M6_CuCu_fm_3leg

M5_AlAl_bl_3leg

M5_AlAl_fm_3leg

M4_CuAl_fm_3leg

M3_AlAl_fm_3leg

M3_AlAl_slm_3leg

M3_AlAl_dgw_3leg

M3_CuAl_fm_3leg

H0_AlAl_fm_3leg

H0_AlAl_slm_5leg

ZDMH_AlAl_dgw_5leg

H0_CuCu_fm_3leg

SA1_AlAl_dgw_5leg

SA1_CuCu_dgw_5leg

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6 CSL 7
5-72

Figure 5.6.9 Engineering Analysis Results, Design Line 9

Figure 5.6.10 presents a plot of the manufacturer sales prices and efficiency levels for the 

full database of designs for the representative unit from DL10, a 1500kVA three-phase, mediumvoltage, dry-type transformer with a 45kV BIL. The efficiency levels shown in this plot represent 

transformers at 50 percent of nameplate load and are corrected for temperature. The following 

observations can be made about this scatter plot:

The current standard efficiency level of 99.22 percent is met by designs using M5 core 

steel or better.

The amorphous metal (SA1) core is the most cost-effective design for any efficiency 

level above 99.40 percent, and can reach efficiencies up to 99.67 percent.

$6,000 

$8,000 

$10,000 

$12,000 

$14,000 

$16,000 

$18,000 

$20,000 

$22,000 

$24,000 

$26,000 

98.70% 98.80% 98.90% 99.00% 99.10% 99.20% 99.30% 99.40% 99.50% 99.60% 99.70%

Manufacturer Selling Price ($)

Efficiency at 50% Load, Temperature Corrected

M6_CuCu_fm_3leg

M5_AlAl_fm_3leg

M3_AlAl_fm_3leg

M3_AlAl_slm_3leg

M3_AlAl_dgw_5leg

M3_CuAl_fm_3leg

H0_AlAl_fm_3leg

H0_AlAl_slm_3leg

ZDMH_AlAl_dgw_5leg

H0_CuCu_fm_3leg

SA1_AlAl_dgw_5leg

SA1_CuCu_dgw_3leg

SA1_CuCu_dgw_5leg

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6
5-73

Figure 5.6.10 Engineering Analysis Results, Design Line 10

Figure 5.6.11 presents a plot of the manufacturer sales prices and efficiency levels for the 

full database of designs for the representative unit from DL11, a 300kVA three-phase, mediumvoltage, dry-type transformer with a 95kV BIL. The efficiency levels shown in this plot represent 

transformers at 50 percent of nameplate load. The following observations can be made about this 

scatter plot:

The current standard efficiency level of 98.67 percent is met by designs using M4 core 

steel or better.

The amorphous metal (SA1) core is the most cost-effective design for any efficiency 

level above 99.00 percent, and can reach efficiencies up to 99.50 percent.

$20,000 

$30,000 

$40,000 

$50,000 

$60,000 

$70,000 

$80,000 

$90,000 

99.15% 99.20% 99.25% 99.30% 99.35% 99.40% 99.45% 99.50% 99.55% 99.60% 99.65% 99.70%

Manufacturer Selling Price ($)

Efficiency at 50% Load, Temperature Corrected

M5_CuAl_mc_3leg

M4_CuAl_mc_3leg

M3_AlAl_mc_3leg

M3_AlAl_slm_3leg

M3_CuCu_mc_3leg

H0_AlAl_mc_3leg

H0_AlAl_slm_3leg

H0_CuCu_mc_3leg

SA1_AlAl_dgw_5leg

SA1_CuCu_dgw_3leg

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6
5-74

Figure 5.6.11 Engineering Analysis Results, Design Line 11

Figure 5.6.12 presents a plot of the manufacturer sales prices and efficiency levels for the 

full database of designs for the representative unit from DL12, a 1500kVA three-phase, mediumvoltage, dry-type transformer with a 95kV BIL. The efficiency levels shown in this plot represent 

transformers at 50 percent of nameplate load. The following observations can be made about this 

scatter plot:

The current standard efficiency level of 99.12 percent is met by designs using M5 core 

steel or better.

The amorphous metal (SA1) core is the most cost-effective design for any efficiency 

level above 99.40 percent, and can reach efficiencies above 99.65 percent.

$10,000 

$12,000 

$14,000 

$16,000 

$18,000 

$20,000 

$22,000 

$24,000 

$26,000 

$28,000 

$30,000 

98.50% 98.70% 98.90% 99.10% 99.30% 99.50% 99.70%

Manufacturer Selling Price ($)

Efficiency at 50% Load, Temperature Corrected

M6_CuCu_fm_3leg

M4_CuAl_fm_3leg

M3_AlAl_fm_3leg

M3_AlAl_slm_3leg

M3_CuCu_fm_3leg

H0_AlAl_fm_3leg

H0_AlAl_slm_3leg

ZDMH_AlAl_dgw_3leg

H0_CuCu_fm_3leg

SA1_AlAl_dgw_3leg

SA1_CuCu_dgw_5leg

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6
5-75

Figure 5.6.12 Engineering Analysis Results, Design Line 12

Figure 5.6.13 presents a plot of the manufacturer sales prices and efficiency levels for the 

full database of designs for the representative unit from DL13A, a 300kVA three-phase, 

medium-voltage, dry-type transformer with a 125kV BIL. The efficiency levels shown in this 

plot represent transformers at 50 percent of nameplate load and are corrected for temperature. 

The following observations can be made about this scatter plot:

The current standard efficiency level of 98.63 percent is met by designs using M4 core 

steel or better.

The amorphous metal (SA1) core is the most cost-effective design for any efficiency 

level above 99.10 percent, and can reach efficiencies up to 99.48 percent.

$30,000 

$40,000 

$50,000 

$60,000 

$70,000 

$80,000 

$90,000 

99.00% 99.10% 99.20% 99.30% 99.40% 99.50% 99.60% 99.70%

Manufacturer Selling Price ($)

Efficiency at 50% Load, Temperature Corrected

M6_AlAl_mc_3leg

M5_AlAl_mc_3leg

M4_CuAl_mc _3leg

M3_AlAl_mc_3leg

M3_AlAl_slm_3leg

M3_CuCu_mc_3leg

H0_AlAl_mc_3leg

H0_AlAl_slm_3leg

H0_CuCu_mc_3leg

SA1_AlAl_dgw_5leg

SA1_CuCu_dgw_5leg

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6 CSL 7
5-76

Figure 5.6.13 Engineering Analysis Results, Design Line 13A

Figure 5.6.14 resents a plot of the manufacturer sales prices and efficiency levels for the 

full database of designs for the representative unit from DL13B, a 2000kVA three-phase, 

medium-voltage, dry-type transformer with a 125kV BIL. The efficiency levels shown in this 

plot represent transformers at 50 percent of nameplate load and are corrected for temperature. 

The following observations can be made about this scatter plot:

The current standard efficiency level of 99.15 percent is met by designs using M5 core 

steel or better.

The amorphous metal (SA1) core is the most cost-effective design for any efficiency 

level above 99.43 percent, and can reach efficiencies up to 99.58 percent.

$15,000 

$17,000 

$19,000 

$21,000 

$23,000 

$25,000 

$27,000 

$29,000 

$31,000 

$33,000 

98.50% 98.60% 98.70% 98.80% 98.90% 99.00% 99.10% 99.20% 99.30% 99.40% 99.50% 99.60%

Manufacturer Selling Price ($)

Efficiency at 50% Load, Temperature Corrected

M5_AlAl_mc_3leg

M4_AlAl_mc_3leg

M3_AlAl_mc_3leg

M3_AlAl_slm_3leg

H0_AlAl_mc_3leg

ZDMH_AlAl_dgw_3leg

SA1_AlAl_dgw_5leg

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6
5-77

Figure 5.6.14 Engineering Analysis Results, Design Line 13B

5.6.2 Symmetric Core Designs for the Reference Case

The designs in this section represent the symmetric core designs that DOE analyzed in the 

life-cycle cost and national impact analyses during the preliminary analysis. As mentioned in 

section 5.3.3.2, DOE simulated symmetric core designs by adjusting design parameters from 

each of its traditional core designs in the reference case. This section presents graphs showing 

the traditional core designs and the symmetric core designs. Since the symmetric core designs 

yielded greater efficiencies than the original, traditional core designs, DOE considered an 

additional efficiency level for the max-tech efficiency level.

Figure 5.6.15 presents a plot of the manufacturer sales prices and efficiency levels for the 

simulated symmetric core designs compared to the traditional core designs for the representative 

unit from DL4, a 150kVA three-phase, liquid-immersed transformer. The efficiency levels 

shown in this plot represent transformers at 50 percent of nameplate load and are corrected for 

temperature. These symmetric core designs do not account for a tertiary winding, but rather 

analyze the cost-efficiency relationship of symmetric cores for the subgroup of distribution 

$40,000 

$45,000 

$50,000 

$55,000 

$60,000 

$65,000 

$70,000 

$75,000 

$80,000 

$85,000 

99.10% 99.20% 99.30% 99.40% 99.50% 99.60%

Manufacturer Selling Price ($)

Efficiency at 50% Load, Temperature Corrected

M5_AlAl_mc_3leg

M4_AlAl_mc_3leg

M3_AlAl_mc_3leg

M3_AlAl_slm_3leg

H0_AlAl_mc_3leg

H0_AlAl_slm_3leg

SA1_AlAl_dgw_5leg

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6
5-78

transformers that would not require a tertiary winding. The maximum efficiency achievable 

using a symmetric core design is 99.65 percent, represented by efficiency level 7.

Figure 5.6.15 Symmetric Core Engineering Analysis Results, Design Line 4

Figure 5.6.16 presents a plot of the manufacturer sales prices and efficiency levels for the 

simulated symmetric core designs compared to the traditional core designs for the representative 

unit from DL5, a 1500kVA three-phase, liquid-immersed transformer. The efficiency levels 

shown in this plot represent transformers at 50 percent of nameplate load and are corrected for 

temperature. These symmetric core designs do not account for a tertiary winding, but rather 

analyze the cost-efficiency relationship of symmetric cores for the subgroup of distribution 

transformers that would not require a tertiary winding. The maximum efficiency achievable 

using a symmetric core design is 99.75 percent, represented by efficiency level 7.

$3,000 

$4,000 

$5,000 

$6,000 

$7,000 

$8,000 

$9,000 

$10,000 

$11,000 

$12,000 

$13,000 

99.00% 99.10% 99.20% 99.30% 99.40% 99.50% 99.60% 99.70%

Manufacturer Selling Price ($)

Efficiency at 50% Load, Temperature Corrected

Traditional Core Designs

Symmetric Core Designs

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6 CSL 7
5-79

Figure 5.6.16 Symmetric Core Engineering Analysis Results, Design Line 5

Figure 5.6.17 presents a plot of the manufacturer sales prices and efficiency levels for the 

simulated symmetric core designs compared to the traditional core designs for the representative 

unit from DL7, a 75kVA three-phase, low-voltage, dry-type distribution transformer. The 

efficiency levels shown in this plot represent transformers at 35 percent of nameplate load and 

are corrected for temperature. The maximum efficiency achievable using a symmetric core 

design is 99.48 percent, represented by efficiency level 8.

$15,000 

$25,000 

$35,000 

$45,000 

$55,000 

$65,000 

$75,000 

99.40% 99.45% 99.50% 99.55% 99.60% 99.65% 99.70% 99.75% 99.80%

Manufacturer Selling Price ($)

Efficiency at 50% Load, Temperature Corrected

Traditional Core Designs

Symmetric Core Designs

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6 CSL 7
5-80

Figure 5.6.17 Symmetric Core Engineering Analysis Results, Design Line 7

Figure 5.6.18 presents a plot of the manufacturer sales prices and efficiency levels for the 

simulated symmetric core designs compared to the traditional core designs for the representative 

unit from DL8, a 300kVA three-phase, low-voltage, dry-type distribution transformer. The 

efficiency levels shown in this plot represent transformers at 35 percent of nameplate load and 

are corrected for temperature. The maximum efficiency achievable using a symmetric core 

design is 99.63 percent, represented by efficiency level 6.

$500 

$1,500 

$2,500 

$3,500 

$4,500 

$5,500 

$6,500 

$7,500 

$8,500 

97.80% 98.00% 98.20% 98.40% 98.60% 98.80% 99.00% 99.20% 99.40% 99.60%

Manufacturer Selling Price ($)

Efficiency at 35% Load, Temperature Corrected

Traditional Core Designs

Symmetric Core Designs

CSLs

CSL 0 CSL 1

CSL 2

CSL 3 CSL 4 CSL 5 CSL 6

CSL 7

CSL 8
5-81

Figure 5.6.18 Symmetric Core Engineering Analysis Results, Design Line 8

Figure 5.6.19 presents a plot of the manufacturer sales prices and efficiency levels for the 

simulated symmetric core designs compared to the traditional core designs for the representative 

unit from DL9, a 300kVA three-phase, medium-voltage, dry-type distribution transformer with a 

45kV BIL. The efficiency levels shown in this plot represent transformers at 50 percent of 

nameplate load and are corrected for temperature. The maximum efficiency achievable using a 

symmetric core design is 99.62 percent, represented by efficiency level 6.

$2,000 

$4,000 

$6,000 

$8,000 

$10,000 

$12,000 

$14,000 

$16,000 

$18,000 

$20,000 

98.40% 98.60% 98.80% 99.00% 99.20% 99.40% 99.60% 99.80%

Manufacturer Selling Price ($)

Efficiency at 35% Load, Temperature Corrected

Traditional Core Designs

Symmetric Core Designs

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6
5-82

Figure 5.6.19 Symmetric Core Engineering Analysis Results, Design Line 9

Figure 5.6.20 presents a plot of the manufacturer sales prices and efficiency levels for the 

simulated symmetric core designs compared to the traditional core designs for the representative 

unit from DL10, a 1500kVA three-phase, medium-voltage, dry-type distribution transformer 

with a 45kV BIL. The efficiency levels shown in this plot represent transformers at 50 percent of 

nameplate load and are corrected for temperature. The maximum efficiency achievable using a 

symmetric core design is 99.71 percent, represented by efficiency level 6.

$6,000 

$8,000 

$10,000 

$12,000 

$14,000 

$16,000 

$18,000 

$20,000 

$22,000 

$24,000 

$26,000 

98.70% 98.80% 98.90% 99.00% 99.10% 99.20% 99.30% 99.40% 99.50% 99.60% 99.70%

Manufacturer Selling Price ($)

Efficiency at 50% Load, Temperature Corrected

Traditional Core Designs

Symmetric Core Designs

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6
5-83

Figure 5.6.20 Symmetric Core Engineering Analysis Results, Design Line 10

Figure 5.6.21 presents a plot of the manufacturer sales prices and efficiency levels for the 

simulated symmetric core designs compared to the traditional core designs for the representative 

unit from DL11, a 300kVA three-phase, medium-voltage, dry-type distribution transformer with 

a 95kV BIL. The efficiency levels shown in this plot represent transformers at 50 percent of 

nameplate load and are corrected for temperature. The maximum efficiency achievable using a 

symmetric core design is 99.55 percent, represented by efficiency level 6.

$20,000 

$30,000 

$40,000 

$50,000 

$60,000 

$70,000 

$80,000 

$90,000 

99.10% 99.20% 99.30% 99.40% 99.50% 99.60% 99.70% 99.80%

Manufacturer Selling Price ($)

Efficiency at 50% Load, Temperature Corrected

Traditional Core Designs

Symmetric Core Designs

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6
5-84

Figure 5.6.21 Symmetric Core Engineering Analysis Results, Design Line 11

Figure 5.6.22 presents a plot of the manufacturer sales prices and efficiency levels for the 

simulated symmetric core designs compared to the traditional core designs for the representative 

unit from DL12, a 1500kVA three-phase, medium-voltage, dry-type distribution transformer 

with a 95kV BIL. The efficiency levels shown in this plot represent transformers at 50 percent of 

nameplate load and are corrected for temperature. The maximum efficiency achievable using a 

symmetric core design is 99.69 percent, represented by efficiency level 7.

$10,000 

$15,000 

$20,000 

$25,000 

$30,000 

98.60% 98.70% 98.80% 98.90% 99.00% 99.10% 99.20% 99.30% 99.40% 99.50% 99.60%

Manufacturer Selling Price ($)

Efficiency at 50% Load, Temperature Corrected

Traditional Core Designs

Symmetric Core Designs

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6
5-85

Figure 5.6.22 Symmetric Core Engineering Analysis Results, Design Line 12

Figure 5.6.23 presents a plot of the manufacturer sales prices and efficiency levels for the 

simulated symmetric core designs compared to the traditional core designs for the representative 

unit from DL13B, a 2000kVA three-phase, medium-voltage, dry-type distribution transformer 

with a 125kV BIL. The efficiency levels shown in this plot represent transformers at 50 percent 

of nameplate load and are corrected for temperature. The maximum efficiency achievable using a 

symmetric core design is 99.69 percent, represented by efficiency level 6.

$25,000 

$35,000 

$45,000 

$55,000 

$65,000 

$75,000 

$85,000 

$95,000 

99.00% 99.10% 99.20% 99.30% 99.40% 99.50% 99.60% 99.70% 99.80%

Manufacturer Selling Price ($)

Efficiency at 50% Load, Temperature Corrected

Traditional Core Designs

Symmetric Core Designs

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6 CSL 7
5-86

Figure 5.6.23 Symmetric Core Engineering Analysis Results, Design Line 13B

5.7 THREE EXAMPLE TRANSFORMER DESIGNS AND COST BREAKDOWNS

This section presents some of the OPS transformer designs from DOE‘s Engineering 

Analysis database. As discussed earlier, to prepare a cost-efficiency relationship on selected 

representative units, DOE contracted Optimized Program Service (OPS), a software company 

specializing in transformer design since 1969. Using a range of input parameters and material 

prices, more than 39,000 transformer designs were created by OPS for DOE‘s analysis. For each 

design, the software generates specific information about the core and coil, including physical 

characteristics, dimensions, material requirements and mechanical clearances, as well as a 

complete electrical analysis of the final design. For information on OPS and their software, visit 

their website: http://www.opsprograms.com/home.html.

To illustrate the typical output from the OPS software, a design from each of the three 

superclasses (i.e., liquid-immersed, low-voltage dry-type and medium-voltage dry-type) are 

presented in this section. As these practical designs illustrate, the software output is used to 

create a bill of materials, which is marked-up to arrive at the manufacturer‘s selling price. The 

OPS software provides an electrical analysis including efficiency, which, when plotted with the 

manufacturer‘s selling price, constitutes the primary output of the engineering analysis.

The three distribution transformers presented are from three design lines: 1, 7, and 12. 

Across all the design lines, the complete database of designs contains 39,618 distribution 

transformer specification and winding sheets, bills of materials, and performance reports. Any 

$30,000 

$40,000 

$50,000 

$60,000 

$70,000 

$80,000 

$90,000 

$100,000 

$110,000 

$120,000 

99.10% 99.20% 99.30% 99.40% 99.50% 99.60% 99.70% 99.80%

Manufacturer Selling Price ($)

Efficiency at 50% Load, Temperature Corrected

Traditional Core Designs

Symmetric Core Designs

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6
5-87

infeasible designs or designs below the minimum efficiency standard are removed and then this 

design database is used by the LCC analysis (see Chapter 8) as it simulates purchases of 

distribution transformers in the marketplace.

Design Line 1: 50 kVA single-phase, liquid-immersed. M2 core steel with copper

primary and aluminum secondary windings (M2CuAl) at a $3.00 A and a $1.20 B 

evaluation formula.

Design Line 7: 75 kVA three-phase, low-voltage dry-type. M6 full-mitered core 

steel with aluminum primary and secondary windings (M6AlAl) at a $0.50 A and 

a $0.10 B evaluation formula.

Design Line 12: 1500 kVA three-phase, medium-voltage dry-type. M3 step-lap 

core steel with aluminum primary and secondary windings (M3AlAl) at a $1.50 A 

and a $0.30 B evaluation formula.

For the three designs presented, the design detail report is followed by a bill of materials

showing the cost calculation, and a pie chart providing a breakdown of the final selling price.

5.7.1 Design Details Report for Transformer from Design Line 1

A design specification report for a 50kVA single-phase liquid-immersed transformer 

appears below. This design incorporates M2 core steel, with a copper primary and an aluminum 

secondary. The evaluation factors for this design are $3.00 A and $1.20 B. The bill of materials 

and associated breakdown of costs for this design are also reported, after the design and electrical 

analysis reports.
5-88
5-89

Table 5.7.1 provides the bill of materials which was calculated from the OPS design 

details report. This bill of materials uses the raw material prices given in this chapter for fixed 

and variable materials used in building the transformer. These materials are then marked-up at 
5-90

the bottom of the table to arrive at the manufacturer‘s selling price. This table provides the bill of 

materials for a transformer from design line 1, a 50kVA single-phase, liquid-immersed, padmount M2 design, with a copper primary and an aluminum secondary. This design was generated 

using a $3.00A and $1.20B.

Table 5.7.1 Bill of Materials for Transformer from Design Line 1

$ Each $ Total

$2.00 $430.42 

$4.84 $261.14 

$2.08 $49.64 

$1.52 $6.94 

$3.35 $125.93 

$140.34 $140.34 

$25.00 $25.00 

$0.65 $0.65 

$58.00 $58.00 

$16.00 $16.00 

$7.48 

$1,122 

$ Total

$25.76 

$5.15 

$15.46 

$5.15 

$7.73 

$25.76 

$18.03 

$9.79 

$23.18 

$34.52 

$12.88 

$11.22 

$194.65 

$1,316 

$140 

$210 

$364 

$2,031 

B$ Input $1.20 

Efficiency at 

50% load

99.00%

Bill of Materials and Labor for liquid-immersed, single-phase, pad-mount, 50kVA

A$ Input $3.00 

Primary 

winding* (lb)

Copper wire, formvar, round 

#10-20

53.93

Secondary 

windings* (lb)

Aluminum strip, thickness 

range 0.02-0.045

23.83

Material Item Type Quantity

Core Steel* (lb) M2-.007 215.75

Tank - 1

Core clamp - 1

Winding form & 

insulation* (lb)

Kraft insulating paper with 

diamond adhesive

4.34

Oil (gal) - 37.6

Misc. hardware - 1

Scrap Factor 1.00%

Total Material Cost

Nameplate - 1

Bushings HV & LV 1

Labor item Hours Rate

Lead dressing 0.5 51.52

Total Material Weight (lb) 748

Tanking and impregnating 0.3 51.52

Preliminary test 0.1 51.52

Inspection 0.1 51.52

Marking and miscellaneous 0.35 51.52

Winding the primary 0.19 51.52

Final test 0.15 51.52

Pallet loading 0.5 51.52

Core assembly 0.25 51.52

Handling and slitting factor (on material) 1.50%

Total Labor 3.56 51.52

Winding the secondary 0.45 51.52

Cutting, forming, and annealing 0.67 51.52

Manufacturer Selling Price**

Shipping Cost (Based on Total Weight) $0.22/lb

Non-production Cost Markup 25.00%

Manufacturing Cost (Material + Labor)

Factory Overhead (Materials only) 12.50%
5-91

* Indicates those items to which the scrap factor (1.0%) and the handling and slitting factor (1.5% are applied.

** Price based on rounded estimations. The non-rounded price may vary slightly.

Figure 5.7.1 provides a summary of the costs contributing to the total selling price of the 

transformer from design line 1. For this design, approximately 57 percent of the final 

manufacturer selling price is direct material and scrap. Labor accounts for 9 percent of the price, 

factory overhead accounts for 7 percent, and together, shipping and non-production costs account 

for 27 percent.

Figure 5.7.1 Manufacturer Selling Price Breakdown, Transformer from Design Line 1

5.7.2 Design Details Report for Transformer from Design Line 7

The following design report provides information on one of the several designs prepared 

to study the representative unit from design line 7. This is a 75kVA, three-phase, low-voltage, 

dry-type unit. The design shown here (out of the 39,618 designs in the database) is for M6 fullmitered core steel with aluminum primary and secondary windings, and a $0.50A and $0.10B.

Core/Coils

44%

Non-Production

18%

Shipping

9%

Factory Overhead

7%

Labor

9%

Other Material

13%
5-92
5-93

Table 5.7.2 provides the bill of materials which was calculated from the OPS design 

details report. This bill of materials uses the raw material prices given in this chapter for fixed 

and variable materials used in building the transformer. These materials are then marked-up at 

the bottom of the table to arrive at the manufacturer‘s selling price. This table provides the bill of 

materials for a transformer from design line 7, a 75kVA three-phase, low-voltage, dry-type M6 

design, with an aluminum primary and an aluminum secondary. This design uses a butt-lap core 

configuration, and was generated using a $0.50A and $0.10B.
5-94

Table 5.7.2 Bill of Materials for Transformer from Design Line 7

$ Each $ Total

$1.46 $438.44 

$2.97 $162.33 

$2.97 $91.88 

$24.50 $36.83 

$131.82 $131.82 

$19.00 $19.00 

$0.32 $7.54 

$0.65 $0.65 

$1.50 $10.50 

$9.00 $27.00 

$22.55 $26.53 

$7.00 $7.00 

$7.29 

$967 

$ Total

$12.88 

$2.58 

$2.58 

$5.15 

$10.30 

$10.30 

$77.28 

$30.40 

$52.55 

$69.55 

$51.52 

$10.94 

$336 

$1,303 

$121 

$141 

$356 

$1,921 

Bill of Materials and Labor for low-voltage, dry-type, three-phase, 75kVA

A$ Input $0.50 

Material Item Type Quantity

Core Steel* (lb) M6-.014 301.33

B$ Input $0.10 

Efficiency at 

35% load

98.12%

Winding form & 

insulation* (lb)

Nomex insulation 0.21

Enclosure 14-gauge steel 1

Primary 

winding* (lb)

Aluminum wire, rectangular, 

0.1x0.2, Nomex

54.6

Secondary 

windings* (lb)

Aluminum wire, rectangular, 

0.1x0.2, Nomex

30.9

Nameplate - 1

LV Buss Bar (ft.) - 7

Core clamp - 1

Duct spacers (ft., 

drop 2/3)

- 23.56

Misc. hardware - 1

Scrap Factor 1.00%

Total Material Cost

HV Terminal 

Board

- 3

Impregnation 

(gal.)

- 1.18

Labor item Hours Rate

Lead dressing 0.25 51.52

Total Material Weight (lb) 502

Final test 0.1 51.52

Packing 0.2 51.52

Inspection 0.05 51.52

Preliminary test 0.05 51.52

Winding the primary 0.59 51.52

Winding the secondary 1.02 51.52

Marking and miscellaneous 0.2 51.52

Enclosure manufacturing 1.5 51.52

Handling and slitting factor (on material) 1.50%

Total Labor 6.31 51.52

Core stacking 1.35 51.52

Core assembly 1 51.52

Non-production Cost Markup 25.00%

Manufacturer Selling Price**

Manufacturing Cost (Material + Labor)

Factory Overhead (Materials only) 12.50%

Shipping Cost (Based on Total Weight) $0.22/lb
5-95

* Indicates those items to which the scrap factor (1.0%) and the handling and slitting factor (1.5% are applied.

** Price based on rounded estimations. The non-rounded price may vary slightly.

Figure 5.7.2 provides a summary of the costs contributing to the total selling price of the 

transformer from design line 7. For this design, approximately 50 percent of the final 

manufacturer selling price is direct material and scrap. Labor accounts for 18 percent of the 

price, factory overhead accounts for 6 percent, and together, shipping and non-production costs 

account for 26 percent.

Figure 5.7.2 Manufacturer Selling Price Breakdown, Transformer from Design Line 7

5.7.3 Design Details Report for Transformer from Design Line 12

The following design report provides information on one of several designs prepared to 

study the representative unit from design line 12. This is a 1500kVA, three-phase, mediumvoltage, dry-type unit at 95kV BIL. The design shown here (out of the 39,618 designs in the 

database) is for M3 step-lap mitered core steel with aluminum primary and secondary windings, 

and a $1.50A and $0.30B. This is a different design option combination than the original design 

selected for the preliminary analysis, which was for M4 core steel with copper primary and 

aluminum secondary windings, and a $1.50A and $0.30B.

Core/Coils

36%

Non-Production

19%

Shipping

7%

Factory 

Overhead

6%

Labor

18%

Other Material

14%
5-96
5-97
5-98

Table 5.7.3 provides the bill of materials which was calculated from the OPS design 

details report. This bill of materials uses the raw material prices given in this chapter for fixed 

and variable materials used in building the transformer. These materials are then marked-up at 

the bottom of the table to arrive at the manufacturer‘s selling price. This table provides the bill of 

materials for a transformer from design line 12, a 1500kVA three-phase, medium-voltage, drytype design with M3 step-lap mitered core steel and aluminum primary and secondary windings. 

This design was generated using a $1.50A and $0.30B.
5-99

Table 5.7.3 Bill of Materials for Transformer from Design Line 12

* Indicates those items to which the scrap factor (1.0%) and the handling and slitting factor (1.5% are applied.

** Additional scrap on core due to mitering process.

*** Price based on rounded estimations. The non-rounded price may vary slightly.

Figure 5.7.3 provides a summary of the costs contributing to the total selling price of the 

transformer from design line 12. For this design, approximately 59 percent of the final 

$ Each $ Total

$1.88 $10,760 

$2.97 $1,851 

$2.08 $755 

$24.50 $4,153 

$820.43 $820 

$125.00 $125 

$0.56 $890 

$0.65 $0.65 

$12.00 $192 

$9.00 $27 

$135.00 $135 

$12.34 $1,186 

$22.55 $742 

$54.00 $54 

$606 

$22,296 

$ Total

$52 

$13 

$26 

$39 

$103 

$113 

$412 

$1,461 

$185 

$311 

$309 

$263 

$3,286 

$25,582 

$2,787 

$2,265 

$7,092 

Manufacturer Selling Price*** $37,727 

Shipping Cost (Based on Total Weight) $0.22/lb

Non-production Cost Markup 25.00%

Manufacturing Cost (Material + Labor)

Factory Overhead (Materials only) 12.50%

Core assembly 6 51.52

Handling and slitting factor (on material) 1.50%

Total Labor 58.7 51.52

Winding the secondary 3.6 51.52

Core stacking 6.04 51.52

Enclosure manufacturing 8 51.52

Winding the primary 28.35 51.52

Packing 2 51.52

Marking and miscellaneous 2.2 51.52

Preliminary test 0.5 51.52

Final test 0.75 51.52

Lead dressing 1 51.52

Inspection 0.25 51.52

Labor item Hours Rate

Total Material Cost

Total Material Weight (lb) 8,055

Misc. hardware - 1

Scrap Factor 1.00%

Winding combs 

(lb.)

- 96.11

Impregnation 

(gal.)

- 32.89

HV tap board - 3

HV Terminals - 1

Nameplate - 1

LV Buss Bar (ft.) - 16

Core clamp - 1

Duct spacers 

(ft.)

- 1,589.03

Winding form & 

insulation* (lb)

Nomex insulation 134

Enclosure 12-gauge steel 1

Primary 

winding* (lb)

Copper wire, rectangular, 

0.1x0.2, Nomex

622.58

Secondary 

windings* (lb)

Aluminum strip, thickness 

range 0.02 - 0.045

362.33

Material Item Type Quantity

Core Steel* (lb) M4-.011 5,738.61

B$ Input $0.30 

Efficiency at 

35% load

99.14%

Bill of Materials and Labor for medium-voltage, dry-type, three-phase, 1500kVA

A$ Input $1.50 
5-100

manufacturer selling price is direct material and scrap. Labor accounts for 9 percent of the price, 

factory overhead accounts for 7 percent, and together, shipping and non-production costs account 

for 25 percent.

Figure 5.7.3 Manufacturer Selling Price Breakdown, Transformer from Design Line 12

Core/Coils

35%

Non-Production

19%

Shipping

6%

Factory Overhead

7%

Labor

9%

Other Material

24%