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

5.2.2 Scaling Relationships in Transformer Manufacturing . . . . . . . . . . . . . . . . . . . . . . 5-9

5.3 TECHNICAL DESIGN INPUTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12

5.3.1 Design Line 1 Representative Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-18

5.3.2 Design Line 2 Representative Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-19

5.3.3 Design Line 3 Representative Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-20

5.3.4 Design Line 4 Representative Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-20

5.3.5 Design Line 5 Representative Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-21

5.3.6 Design Line 9 Representative Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-22

5.3.7 Design Line 10 Representative Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-23

5.3.8 Design Line 11 Representative Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-24

5.3.9 Design Line 12 Representative Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25

5.3.10 Design Line 13 Representative Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-26

5.4 MATERIAL AND LABOR INPUTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-27

5.4.1 Material Prices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29

5.4.2 Material Inputs to the Design Software—Liquid-Immersed . . . . . . . . . . . . . . . . 5-30

5.4.3 Material Inputs to the Design Software—Dry-type . . . . . . . . . . . . . . . . . . . . . . . 5-33

5.4.4 Labor Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-37

5.5 RESULTS OF THE ANALYSIS ON EACH DESIGN LINE . . . . . . . . . . . . . . . . . . . . . 5-44

5.6 FOUR EXAMPLE TRANSFORMER DESIGNS AND COST BREAKDOWNS . . . . . 5-55

5.6.1 Design Details Report for Non-Evaluated Transformer from Design Line 1 . . . 5-55

5.6.2 Design Details Report for Evaluated Transformer from Design Line 1 . . . . . . . 5-59

5.6.3 Design Details Report for Non-Evaluated Transformer from Design Line 12 . . 5-63

5.6.4 Design Details Report for Evaluated Transformer from Design Line 12 . . . . . . 5-67

5.7 TEAR-DOWN ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-71

LIST OF TABLES

Table 5.2.1 Product 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 . . . . . . . . . . . . . . . . . . 5-7

Table 5.2.4 Dry-Type, Medium-Voltage, Single-Phase Design Lines . . . . . . . . . . . . . . . . . . . 5-8

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

Table 5.2.6 Common Scaling Relationships in Transformers . . . . . . . . . . . . . . . . . . . . . . . . 5-10

Table 5.3.1 A and B Grid Combinations used by Software to Generate Design Database . . 5-13

Table 5.3.2 A and B Fan Combinations used by Software to Generate Design Database . . . 5-14

Table 5.3.3 Core Steel Grades, Thicknesses and Associated Losses . . . . . . . . . . . . . . . . . . . 5-15

Table 5.3.4 Core Configurations Used in Each Design Line . . . . . . . . . . . . . . . . . . . . . . . . . 5-16

Table 5.3.5 Design Option Combinations for the Representative Unit from Design Line 1 . 5-18

Table 5.3.6 Design Option Combinations for the Representative Unit from Design Line 2 . 5-19
5-ii

Table 5.3.7 Design Option Combinations for the Representative Unit from Design Line 3 . 5-20

Table 5.3.8 Design Option Combinations for the Representative Unit from Design Line 4 . 5-21

Table 5.3.9 Design Option Combinations for the Representative Unit from Design Line 5 . 5-22

Table 5.3.10 Design Option Combinations for the Representative Unit from Design Line 9 . 5-23

Table 5.3.11 Design Option Combinations for the Representative Unit from Design Line 10 5-24

Table 5.3.12 Design Option Combinations for the Representative Unit from Design Line 11 5-25

Table 5.3.13 Design Option Combinations for the Representative Unit from Design Line 12 5-26

Table 5.3.14 Design Option Combinations for the Representative Unit from Design Line 13 5-27

Table 5.4.1 Manufacturer’s Material Prices for Liquid-Immersed Design Lines . . . . . . . . . . 5-30

Table 5.4.2 Marked-up Material Prices for Liquid-Immersed Units, Five-Year Average 

Price Scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-31

Table 5.4.3 Summary Table of Fixed Material Costs for Liquid-Immersed Units . . . . . . . . . 5-33

Table 5.4.4 Manufacturer’s Material Prices for Dry-Type Design Lines . . . . . . . . . . . . . . . . 5-34

Table 5.4.5 Marked-up Material Prices for Dry-Type Units, Five-Year Average Price 

Scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-35

Table 5.4.6 Summary Table of Fixed Material Costs for Dry-Type Units . . . . . . . . . . . . . . . 5-37

Table 5.4.7 Labor Markups for Liquid-Immersed and Dry-Type Manufacturers . . . . . . . . . . 5-38

Table 5.4.8 Summary of Labor Times for Liquid-Immersed Units . . . . . . . . . . . . . . . . . . . . 5-41

Table 5.4.9 Summary of Labor Times for Dry-Type Units . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-43

Table 5.6.1 Bill of Materials for Non-Evaluated Transformer from Design Line 1 . . . . . . . . 5-58

Table 5.6.2 Bill of Materials for Evaluated Transformer from Design Line 1 . . . . . . . . . . . . 5-62

Table 5.6.3 Bill of Materials for Non-Evaluated Transformer from Design Line 12 . . . . . . . 5-66

Table 5.6.4 Bill of Materials for Evaluated Transformer from Design Line 12 . . . . . . . . . . . 5-70

LIST OF FIGURES

Figure 5.3.1 A and B Combination Software Inputs used in the Engineering Analysis . . . . . 5-14

Figure 5.3.2 Graphic of Single-Phase Core Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-16

Figure 5.3.3 Graphic of Three-phase Core Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-17

Figure 5.3.4 Cruciform Core Cross-Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-17

Figure 5.4.1 Standard Method of Cost Accounting for Standards Rulemaking . . . . . . . . . . . . 5-27

Figure 5.5.1 Scatter Plot of Manufacturer Selling Price and Efficiency for Design Line 1 . . . 5-45

Figure 5.5.2 Scatter Plot of Manufacturer Selling Price and Efficiency for Design Line 2 . . . 5-46

Figure 5.5.3 Scatter Plot of Manufacturer Selling Price and Efficiency for Design Line 3 . . . 5-47

Figure 5.5.4 Scatter Plot of Manufacturer Selling Price and Efficiency for Design Line 4 . . . 5-48

Figure 5.5.5 Scatter Plot of Manufacturer Selling Price and Efficiency for Design Line 5 . . . 5-49

Figure 5.5.6 Scatter Plot of Manufacturer Selling Price and Efficiency for Design Line 9 . . . 5-50

Figure 5.5.7 Scatter Plot of Manufacturer Selling Price and Efficiency for Design Line 10 . . 5-51

Figure 5.5.8 Scatter Plot of Manufacturer Selling Price and Efficiency for Design Line 11 . . 5-52

Figure 5.5.9 Scatter Plot of Manufacturer Selling Price and Efficiency for Design Line 12 . . 5-53

Figure 5.5.10 Scatter Plot of Manufacturer Selling Price and Efficiency for Design Line 13 . . 5-54

Figure 5.6.1 Manufacturer Selling Price Breakdown, Non-Evaluated Transformer from 

Design Line 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-59

Figure 5.6.2 Manufacturer Selling Price Breakdown, Evaluated Transformer from 

Design Line 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-63

Figure 5.6.3 Manufacturer Selling Price Breakdown, Non-Evaluated Transformer from 
5-iii

Design Line 12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-67

Figure 5.6.4 Manufacturer Selling Price Breakdown, Evaluated Transformer from 

Design Line 12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-71

Figure 5.7.1 Tear-down Plot Comparison, Design Line 7, 75kVA Three-phase Dry-type . . . 5-73
a

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

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

convention, the Department developed eight product classes, shown in Table 5.2.1. These product

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 product classes, <60

kilovolt (kV) BIL and >60 kV BIL. Based on input from manufacturers, the Department elected to

increase the differentiation of medium-voltage, dry-type transformers, and create three product

classes of BIL ratings: 20–45 kV BIL, 46–95 kV BIL, and >96kV BIL (see section 3.3). 

Within each of these product classes, distribution transformers are further classified by their

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

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

properties, efficiency levels vary by both product class and kVA rating. For NEMA’s TP 1-2002,a

there are 99 kVA ratings across all the product classes (see section 3.7.1). For the Department’s

rulemaking, because of the greater degree of differentiation around the BIL rating in mediumvoltage, dry-type transformers, there are 95 kVA ratings across all the product classes, as shown in

Table 5.2.1.
5-2

Table 5.2.1 Product Classes and Number of kVA Ratings

Distribution Transformer Product 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

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 95

The Department recognized that it would be impractical to conduct a detailed engineering

analysis of the manufacturer’s selling price-efficiency relationship on all 95 kVA ratings, so it

sought to develop an approach that simplified the analysis while retaining reasonable levels of

accuracy. The Department 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,

the Department simplified the analysis by creating 10 engineering design lines, which group

together kVA ratings based on similar principles of design and construction. The 10 design lines

subdivide the product classes, to improve the accuracy of the engineering analysis. These 10

engineering design lines differentiate the transformers by insulation type (liquid-immersed or drytype), number of phases (single or three), and primary insulation levels for medium-voltage, drytype (three different BIL levels). 

The Department 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 95 to 10. It then extrapolated the results of its analysis from the unit

studied to the other kVA ratings within that same engineering design line. The Department

performed this extrapolation in the national impacts analysis (see Chapter 10). The technique 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 the Department’s 10 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

PC* 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, 408Y/277V secondary

6

9

Dry-type, medium-voltage, threephase, 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, threephase, 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, threephase, 46-95kV BIL 15–500 300 kVA, 150/C, three-phase, 60Hz, 12470V primary,

480Y/277V secondary, 95kV BIL

12 Dry-type, medium-voltage, threephase, 46-95kV BIL 750–2500 1500 kVA, 150/C, three-phase, 60Hz, 12470V

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

10 13 Dry-type, medium-voltage, threephase, 96-150kV BIL 225–2500 2000 kVA, 150/C, three-phase, 60Hz, 12470V

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

* PC means product class (see Chapter 3 of the TSD). The Department calculated the analytical results for PC5, PC7,

and PC9 based on the results for their three-phase counterparts. The Department did not select any representative units

from the single-phase, medium-voltage product classes (PC5, PC7 and PC9) because of their low sales volume.

Liquid-immersed transformers are divided into five engineering design lines, based on their

tank shape, number of phases, and kVA ratings. The Department believes that this breakdown

enables the analysis to identify and capture a more accurate representation of the manufacturer’s

selling price and efficiency relationship. Dry-type distribution transformers are broken into five

engineering design lines, primarily according to their BIL levels. The Department 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 9, 11, or 13, depending on whether the BIL rating is 20-45

kV, 46-95 kV, or 96-150 kV.

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

design lines may not be the standard BIL levels associated with a given primary voltage. The

Department selected a slightly higher BIL level for the representative units from these design lines

to ensure that any minimum efficiency standard would not excessively penalize customers

purchasing transformers at higher BIL ratings within the range. For example, a 300 kVA with a

4160V primary is called a “5kV class” transformer and would normally be built with a 30kV BIL

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

If the candidate minimum efficiency standard were set based on a 30kV BIL, it may not be possible

to achieve that same efficiency rating for customers ordering 60kV BIL. Thus, the Department

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.
5-4

The remainder of this section discusses each of the ten 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, liquidimmersed distribution transformers, ranging from 10 kVA to 167 kVA. Transformers in this design

line typically have BIL levels 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 higherrated 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. The

Department decided to analyze these two types of distribution transformers separately for the

engineering and LCC analyses. Transformers in this design line typically have BIL levels ranging

from 30 kV and 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, liquid-immersed

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 BIL levels 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 3 is a 500 kVA round-tank, as this is a

common rating and 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 with 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
5-5

typically have BIL levels 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 BIL levels 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 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, the

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

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 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 dry-type

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 dry-type

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, the Department 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 voltage is typically less

than or equal to 15 kV and the secondary voltage is less than or equal to 600 V. 
5-6

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, the Department selected the

300 kVA rating as the representative unit for analysis.

Design Line 12. Design line 12 represents three-phase, medium-voltage, ventilated dry-type

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 Line 13. As a further extension on the dry-type, three-phase, medium-voltage BIL

ranges, the Department analyzed 96 kV to 150 kV BIL, in a 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

smaller range of kVA ratings, 225 kVA to 2500 kVA. As most of the sales activity in this design

line occurs in the higher kVA ratings, the representative unit selected for design line 13 is a 2000

kVA transformer. This unit is a common rating in this size range, and occurs toward the high end of

the range covered by this design line (225 kVA, 300 kVA, 500 kVA, 750 kVA, 1000 kVA, 1500

kVA, 2000 kVA, and 2500 kVA).

In addition to the three product 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 product 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, and thus it does not warrant the level of effort involved in conducting analysis on these specific

units. The Department decided instead to scale the analysis findings from three-phase units to the

single-phase units by dividing by three. In this way, the Department was able to concentrate

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

transformer product classes.

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 product 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. For example, DL 1 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
5-7

Product Class 1 

Liquid-Immersed, 

Single-Phase 

 Product Class 2 

Liquid-Immersed, 

Three-Phase 

kVA Rectang. 

Tank 

Round 

Tank kVA Design 

Lines 

10 15 

15 30 

25 45 

37.5 75 

50 112.5 

75 150 

100 225 

167 300 

250 500 

333 750 

500 1000 

667 1500 

833 2000 

 2500 DL 1 DL 2 DL 3 

Rep Unit

Rep Unit

DL 4 

Rep Unit

DL 5 

Rep Unit

Rep Unit

kVA is the representative unit for DL 1. Similarly, the representative unit for DL 2 is the 25 kVA

unit. 

There are five liquid-immersed design lines, three single-phase and two three-phase, as

shown in Table 5.2.3. To capture any design differences between a single-phase pole and a padmounted transformer, the Department analyzed units in both DL 1 and DL 2, 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 product classes (abbreviated “PC”) for medium-voltage, single-phase,

dry-type units. As discussed in section 3.4, National Shipment Estimate, these units have an

extremely low shipment volume. All three product classes shown in Table 5.2.4 together represent

less than one-third of one percent of dry-type shipments on both a per-unit and an MVA-capacity

basis. Thus, the Department did not consider it appropriate to conduct analysis of any units from

these three product classes.

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

Department 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 the table) for these three product classes. The Department used the

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

shown in their respective rows, following the application of the quotient. For example, in the single
5-8

Dry-Type, Medium-Voltage, Single-Phase

kVA

PC 5* 

Low BIL 

20-45kV 

PC 7 

Med BIL 

46-95kV 

PC 9 

High BIL 

>96kV 

15 - 

25 - 

37.5 - 

50 - 

75 

100 

167 

250 

333 

500 

667 

833 

DL9 / 3

Virtual RU

DL11 / 3

Virtual RU

DL13 / 3

Virtual RU

Virtual RU

DL10 / 3

Virtual RU

DL12 / 3

phase (20–45kV BIL) column, the representative unit from DL 9 is a three-phase 300 kVA unit, so

it scales to a single-phase, 100 kVA unit in Table 5.2.4. 

Table 5.2.4 Dry-Type, Medium-Voltage, Single-Phase Design Lines

Table 5.2.5 presents the product classes for the medium-voltage, three-phase, dry-type

distribution transformers and each of the design lines and respective representative units. For the

higher volume and larger range of kVA ratings, the Department used two separate design lines for

each, to maintain accuracy. However, for the very high BIL levels ($96kV BIL), one design line

(DL 13) covers all the ratings from 225kVA to 2500kVA. Within DL 13, the Department did not

extrapolate the results of this unit to ratings lower than 150kVA because there were no shipments at

these ratings in the shipments analysis and it is very unlikely that they would be built.
5-9

Dry-Type, Medium-Voltage, Three-Phase

kVA PC 6 

Low BIL 

20-45kV 

PC 8 

Med BIL 

46-95kV 

PC 10 

High BIL 

>96kV 

15 - 

30 - 

45 - 

75 - 

112.5 - 

150 - 

225 

300 

500 

750 

1000 

1500 

2000 

2500 

DL 9 

DL 11 

DL 13 

Rep Unit Rep Unit DL 10 

DL 12 

Rep Unit Rep Unit

Rep Unit

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

5.2.2 Scaling Relationships in Transformer Manufacturing

The Department 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 the Department 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.

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 cross-sectional 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
5-10

shape as the transformer being scaled. Table 5.2.6 depicts the most common scaling relationships in

transformers.

Table 5.2.6 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 5.2.6 can be used 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. The Department’s

application of the 0.75 scaling rule in this analysis is always less than an order of magnitude.

To illustrate how the scaling laws are used, 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:

NL1

 = NL0 × (S1 / S0)

0.75 

 Eq. 5.1

where:

NL1

 = no-load losses of transformer “1,”
5-11

NL0 = no-load losses of transformer “0,”

S1 = kVA rating of transformer “1,” and

S0 = kVA rating of transformer “0.”

and

TL1

 = TL0 × (S1 / S0)

0.75

 Eq. 5.2

where:

TL1

 = total losses of transformer “1,” and

TL0

 = total losses of transformer “0.”

Equations 5.1 and 5.2 can be manipulated algebraically to show that the load loss also varies

to the 0.75 power. Starting with the concept that total losses equals no-load losses plus load losses,

we can derive the relationship for load loss (LL), and show that it also scales to the 0.75 power. 

Specifically:

LL1

 = TL1 - NL1 Eq. 5.3

where:

LL1

 = load losses of transformer “1”

Inserting the TL1

 and NL1 terms into this equation, we find:

LL1

 = (TL0 × (S1 / S0)

0.75) - (NL0

 × (S1 / S0)

0.75) Eq. 5.4

LL1

 = (TL0- NL0 )× (S1 / S0)

0.75 Eq. 5.5

LL1

 = (LL0 ) × (S1 / S0)

0.75 Eq. 5.6

Where:

LL0

 = load losses of transformer “0.”
5-12

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. A detailed

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

The Department used the 0.75 scaling rule to scale the analysis findings on each of the

representative units within the 10 design lines to the 85 kVA ratings that were not analyzed. The

Department applied the scaling rule within the design lines in the national impact analysis (Chapter

10), where it calculated efficiency ratings for the 85 kVA ratings not analyzed.

5.3 TECHNICAL DESIGN INPUTS

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

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

Department 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. The software’s output is used to generate an

estimated cost of manufacturing materials and labor, which is then converted 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 manufacturer. In some cases, however,

the Department captured tooling costs associated with manufacturing mitered cores by applying

adders to the steel price. 

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 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. 
5-13

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.

The Department 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.

The Department 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, as in the advance notice of proposed rulemaking (ANOPR), 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.

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 was new for the notice of proposed rulemaking (NOPR). The Department understands that

the ratio of A to B represents an implicit loading for the transformer. Therefore, the Department

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 the Department’s loading analysis (i.e., 35 percent and 50 percent). Calling

this approach the “fan,” 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 NOPR.
5-14

Figure 5.3.1 A and B Combination Software Inputs used in the Engineering 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.

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

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

LCC analysis, the Department removed any duplicate designs from the engineering database.

The Department 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). 

Within each of the design lines discussed in the sections starting at 5.3.1, the Department 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
5-15

using different core configurations, core steels, and winding materials. To capture this variation in

designs, DOE analyzed the 10 representative units using 5–11 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. 

M43 core steel is non-oriented grain silicon steel and is rolled in much 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, including nominal thickness and core losses per pound of

steel. Note that the core losses per pound of steel are given as a function of the magnetic flux

density, measured in Tesla.

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

M43 0.0185 2.10 Watts/lb at 1.5 T Non-oriented grain silicon steel

M36 0.0185 2.00 Watts/lb at 1.5 T Non-oriented grain silicon steel

M19 0.0185 1.65 Watts/lb at 1.5 T Non-oriented grain silicon steel

M6 0.014 0.66 Watts/lb at 1.5 T

0.94 Watts/lb at 1.7 T Grain-oriented silicon steel

M5 0.012 0.53 Watts/lb at 1.5 T

0.83 Watts/lb at 1.7 T Grain-oriented silicon steel

M4 0.011 0.51 Watts/lb at 1.5 T

0.74 Watts/lb at 1.7 T Grain-oriented silicon steel

M3 0.009 0.45 Watts/lb at 1.5 T

0.70 Watts/lb at 1.7 T Grain-oriented silicon steel

M2 0.007 0.41 Watts/lb at 1.5 T Grain-oriented silicon steel

H-0 DR 0.009 0.60 Watts/lb at 1.7 T “Domain-refined, high permeability” grade

silicon steel

SA1 0.001 0.08 Watts/lb at 1.3 T Amorphous core steel (silicon and boron); flux

density limitation - testing at 1.3 T

ZDMH 0.009 0.34 Watts/lb at 1.5 T

0.46 Watts/lb at 1.7 T

Imported silicon steel, magnetic domainrefined by mechanical process 

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

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 10 design lines. The Department selected these configurations,

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

construction methods for these kVA ratings in the US market. Note that, for design lines 2, 3, and

9, the Department analyzed two different core construction configurations.
5-16

Table 5.3.4 Core Configurations Used in Each Design Line

Design Line # Phases Core Configurations Used in the Engineering Analysis

DL 1 1 Wound core - distributed gap, shell-type

DL 2 1 Wound core - distributed gap, shell-type or core-type

DL 3 1 Wound core - distributed gap, shell-type or core-type

DL 4 3 Wound core - distributed gap, 5-leg

DL 5 3 Wound core - distributed gap, 5-leg

DL 9 3 Stacked, butt-lap or mitered joint, 3-leg

DL 10 3 Stacked, cruciform, mitered joint, 3-leg

DL 11 3 Stacked, mitered joint, 3-leg

DL 12 3 Stacked, cruciform, mitered joint, 3-leg

DL 13 3 Stacked, cruciform, mitered joint, 3-leg

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 laminations on either side. 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 transformer’s

operating sound level. Figure 5.3.2 illustrates the two types of single-phase core configurations.

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

In the engineering analysis, the Department considered the three-legged construction techniques for

the three-phase dry-types and five-legged construction for the three-phase liquid-immersed

transformers. Figure 5.3.3 below illustrates the difference between the three-legged and the fivelegged 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. The Department recognizes that there are a variety of approaches

to mitered core construction: “scrapless T-mitering,” “full-mitering,” and “step-mitering.” The

Department modeled full-mitered cores. 

 

Figure 5.3.2 Graphic of Single-Phase Core Configurations
5-17

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 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.

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.

Figure 5.3.3 Graphic of Three-phase Core Configurations

Figure 5.3.4 C r u c i f o r m C o r e

Cross-Section
5-18

5.3.1 Design Line 1 Representative Unit 

Design line 1 (DL 1) 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: 1.0–3.5 percent

For DL 1, DOE selected eight 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 eight

design option combinations to represent the most common construction practices for this

representative unit. 

Table 5.3.5 Design Option Combinations for the Representative Unit from Design Line 1

Core Material High-Voltage

Conductor

Low-Voltage

Conductor

Core Design Type

M6 Al (wire) Al (strip) Shell - DG* Wound Core

M6 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 Cu (wire) Al (strip) Shell - DG Wound Core

M2 Cu (wire) Cu (strip) Shell - DG Wound Core

ZDMH Cu (wire) Cu (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.

The Department analyzed each of the eight design option combinations using the matrix of

A and B values described in Tables 5.3.1 and 5.3.2, creating 4,144 designs.
5-19

5.3.2 Design Line 2 Representative Unit 

Design line 2 (DL 2) 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: 1.0–3.5 percent

For DL 2, DOE selected 10 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 5.3.6 Design Option Combinations for the Representative Unit from Design Line 2

Core Material High-Voltage

Conductor

Low-Voltage

Conductor

Core Design Type

M6 Al (wire) Al (strip) Shell - DG Wound Core

M6 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 Cu (wire) Al (strip) Shell - DG Wound Core

M3 Cu (wire) Cu (strip) Shell - DG Wound Core

M2 Cu (wire) Al (strip) Shell - DG Wound Core

M2 Cu (wire) Cu (strip) Shell - DG Wound Core

ZDMH Cu (wire) Cu (strip) Shell - DG Wound Core

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

The Department analyzed each of the 10 design option combinations using the matrix of A

and B values described in Tables 5.3.1 and 5.3.2, creating 5,180 designs.
5-20

5.3.3 Design Line 3 Representative Unit 

Design line 3 (DL 3) 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:

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-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: 2.5–5.75 percent

For DL 3, the Department 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 chose design option combinations to

represent the most common construction practice for this representative unit. 

Table 5.3.7 Design Option Combinations for the Representative Unit from Design Line 3

Core Material High-Voltage

Conductor

Low-Voltage

Conductor

Core Design Type

M6 Al (wire) Al (strip) Shell - DG Wound Core

M4 Cu (wire) Al (strip) Shell - DG Wound Core

M3 Cu (wire) Al (strip) Shell - DG Wound Core

M2 Cu (wire) Al (strip) Shell - DG Wound Core

M2 Cu (wire) Cu (strip) Shell - DG Wound Core

ZDMH Cu (wire) Cu (strip) Shell - DG Wound Core

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

The Department analyzed each of the seven design option combinations using the matrix of

A and B values described in Tables 5.3.1 and 5.3.2, creating 3,626 designs.

5.3.4 Design Line 4 Representative Unit 

Design line 4 (DL 4) 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)
5-21

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

Winding Configuration: Lo-Hi (Core-Type)

Core: Wound core - distributed gap, 5-leg

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

Impedance Range: 1.5–3.0 percent

For DL 4, DOE selected seven design option combinations of core steel and winding types

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 5.3.8 Design Option Combinations for the Representative Unit from Design Line 4

Core Material High-Voltage

Conductor

Low-Voltage

Conductor

Core Design Type

M6 Al (wire) Al (strip) 5-Leg DG Core

M4 Al (wire) Al (strip) 5-Leg DG Core

M3 Cu (wire) Al (strip) 5-Leg DG Core

M2 Cu (wire) Al (strip) 5-Leg DG Core

M2 Cu (wire) Cu (strip) 5-Leg DG Core

ZDMH-price 1 Cu (wire) Cu (strip) 5-Leg DG Core

SA1 (Amorphous) Cu (wire) Cu (strip) 5-Leg DG Core

The Department analyzed each of the seven design option combinations using the matrix of

A and B values described in Tables 5.3.1 and 5.3.2, creating 3,626 designs.

5.3.5 Design Line 5 Representative Unit 

Design line 5 (DL 5) 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-Type)

Core: Wound core - distributed gap, 5-leg
5-22

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

Impedance Range: 4.5-7.0 percent

For DL 5, the Department 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 practices for the representative unit.

Table 5.3.9 Design Option Combinations for the Representative Unit from Design Line 5

Core Material High-Voltage

Conductor

Low-Voltage

Conductor

Core Design Type

M4 Al (wire) Al (strip) 5-Leg DG Core

M4 Cu (wire) Al (strip) 5-Leg DG Core

M3 Cu (wire) Al (strip) 5-Leg DG Core

M2 Cu (wire) Al (strip) 5-Leg DG Core

M2 Cu (wire) Cu (strip) 5-Leg DG Core

ZDMH Cu (wire) Cu (strip) 5-Leg DG Core

SA1 (Amorphous) Cu (wire) Cu (strip) 5-Leg DG Core

The Department analyzed each of the seven design option combinations using the matrix of

A and B values described in Tables 5.3.1 and 5.3.2, creating 3,626 designs.

5.3.6 Design Line 9 Representative Unit 

Design line 9 (DL 9) 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, butt-lap; Stacked, mitered

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

Impedance Range: 3.0–6.0 percent

For DL 9, the Department selected five design option combinations of core steel and

winding material, based on input from manufacturers and other technical experts. With the
5-23

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 5.3.10 Design Option Combinations for the Representative Unit from Design Line 9

Core Material High-Voltage

Conductor

Low-Voltage

Conductor

Core Design Type

M6, 29 gauge Al (wire) Al (wire) 3-Leg Stacked Buttlap

M6, 29 gauge Cu (wire) Cu (wire) 3-Leg Stacked Full Miter**

M5 Al (wire) Al (wire) 3-Leg Stacked Full Miter

M3 Cu (wire) Al (strip) 3-Leg Stacked Full Miter

H-O DR* Cu (wire) Cu (strip) 3-Leg Stacked Full Miter

* H-O DR is a domain-refined, high permeability core steel, and represents the max tech for dry-type units.

** Full Miters are not step-miters, but are mitered joints for all three legs. These cores are stacked three by three. 

The Department analyzed each of the five design option combinations using the matrix of A

and B values described in Tables 5.3.1 and 5.3.2, creating 2,590 designs.

5.3.7 Design Line 10 Representative Unit 

Design line 10 (DL 10) 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

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

Impedance Range: 4.0-6.0 percent

For DL 10, the Department selected five 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. 
5-24

Table 5.3.11 Design Option Combinations for the Representative Unit from Design Line 10

Core Material High-Voltage

Conductor

Low-Voltage

Conductor

Core Design Type

M6 Al (wire) Al (strip) 3-Leg Mitered Cruciform

M6 Cu (wire) Cu (strip) 3-Leg Mitered Cruciform

M4 Cu (wire) Al (strip) 3-Leg Mitered Cruciform

M3 Cu (wire) Cu (strip) 3-Leg Mitered Cruciform

H-O DR* Cu (wire) Cu (strip) 3-Leg Mitered Cruciform

* H-O DR is a domain-refined, high permeability core steel, and represents the max tech for dry-type units.

The Department analyzed each of the five design option combinations using the matrix of A

and B values described in Tables 5.3.1 and 5.3.2, creating 2,590 designs.

5.3.8 Design Line 11 Representative Unit 

Design line 11 (DL 11) 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

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

Impedance Range: 3.0-7.0 percent

For DL 11, the Department selected five 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. 
5-25

Table 5.3.12 Design Option Combinations for the Representative Unit from Design Line 11

Core Material High-Voltage

Conductor

Low-Voltage

Conductor

Core Design Type

M6 Al (wire) Al (strip) 3-Leg Stacked Full Miter**

M6 Cu (wire) Cu (strip) 3-Leg Stacked Full Miter

M4 Cu (wire) Al (strip) 3-Leg Stacked Full Miter

M3 Cu (wire) Cu (strip) 3-Leg Stacked Full Miter

H-O DR* Cu (wire) Cu (strip) 3-Leg Stacked Full Miter

* H-O DR is a domain-refined, high permeability core steel, and represents the max tech for dry-type units.

** Full Miters are not step-miters, but are mitered joints for all three legs. These cores are stacked three by three. 

The Department analyzed each of the five design option combinations using the matrix of A

and B values described in Tables 5.3.1 and 5.3.2, creating 2,590 designs.

5.3.9 Design Line 12 Representative Unit 

Design line 12 (DL 12) 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

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

Impedance Range: 4.0–7.0 percent

For DL 12, the Department selected five 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. 
5-26

Table 5.3.13 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

M6 Cu (wire) Cu (strip) 3-Leg Mitered Cruciform

M4 Cu (wire) Al (strip) 3-Leg Mitered Cruciform

M3 Cu (wire) Cu (strip) 3-Leg Mitered Cruciform

H-O DR* Cu (wire) Cu (strip) 3-Leg Mitered Cruciform

* H-O DR is a domain-refined, high permeability core steel, and represents the max tech for dry-type units.

The Department analyzed each of the five design option combinations using the matrix of A

and B values described in Tables 5.3.1 and 5.3.2, creating 2,590 designs.

5.3.10 Design Line 13 Representative Unit 

Design line 13 (DL 13) 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: 12470 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

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

Impedance Range: 4.0–7.0 percent

For DL 13, the Department selected five 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. 
5-27

Direct

Labor

Direct

Labor Direct

Material

Direct

Material Overhead Overhead Selling Selling General &

Admin. Admin. R & D R & D Interest Interest

Indirect Labor

Full Production Cost 1 Non-Production Cost

Indirect Material

Maintenance

Depreciation

Taxes

Insurance related

to assets

Mkt. research

Advertising

POS promotion

Sales person

salary + travel

+ commission

Logistics

- Warehousing

- Delivery

- Record

 keeping

- Order entry/

 processing

Costs of

service &

staff units

General

corporate

costs

- comp. etc.

Costs

associated

with efforts

to find new

or improved

products or

production

processes

Costs

of

borrowing

funds

1

 Tax Reform Act of 1986, essentially, requires companies to measure cost of goods sold as the full production cost of the goods sold.

Full Cost of Product Full Cost of Product

Code

compliance

Modernization

Cust. service

Figure 5.4.1 Standard Method of Cost Accounting for Standards Rulemaking

Table 5.3.14 Design Option Combinations for the Representative Unit from Design Line 13

Core Material High-Voltage

Conductor

Low-Voltage

Conductor

Core Design Type

M6 Al (wire) Al (strip) 3-Leg Mitered Cruciform

M6 Cu (wire) Cu (strip) 3-Leg Mitered Cruciform

M4 Cu (wire) Al (strip) 3-Leg Mitered Cruciform

M3 Cu (wire) Cu (strip) 3-Leg Mitered Cruciform

H-O DR* Cu (wire) Cu (strip) 3-Leg Mitered Cruciform

* H-O DR is a domain-refined, high permeability core steel, and represents the max tech for dry-type units.

The Department analyzed each of the five design option combinations using the matrix of A

and B values described in Tables 5.3.1 and 5.3.2, creating 2,590 designs.

5.4 MATERIAL AND LABOR INPUTS

The Department uses a standard method of cost accounting 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 a product.

The full production cost and the non-production cost equal the manufacturer’s selling price

of the product. Full production cost is a combination of direct labor, direct materials, and overhead. 
5-28

The overhead contributing to full production cost includes indirect labor, indirect material,

maintenance, depreciation, taxes, and insurance related to company assets. Non-production cost

includes the cost of selling (market research, advertising, sales representatives, logistics), general

and administrative costs, research and development (R&D), interest payments, and profit factor (not

shown). 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.

The Department developed estimates of the costs listed in Figure 5.4.1 from the U.S.

Industry Census Data Reports for 1992 and 1997, manufacturer interviews, and Securities and

Exchange Commission (SEC) 10-K reports for ACME Electric Corporation, Powell Industries, Inc.,

Magnetek, Inc., and Hammond Manufacturing Company Limited. It then refined these estimates

through meetings and dialogue with transformer manufacturers in early 2002. 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).

• 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. The Department only applied factory overhead to the direct material

production costs.

• Non-production: 25 percent markup. This markup reflects costs including selling, general

and administrative, R&D, interest payments, and profit factor. The Department applied the

non-production markup to the sum of direct material, direct labor, and factory overhead. 

The following example shows how the Department applied the markups to the materials, and

how it determined the manufacturer selling price. Consider a 300kVA 45kV BIL three-phase, drytype transformer designed for a $1.50 A and a $0.30 B. This design has $2,785 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 $1,167. The factory overhead on this design is $348, as it is only applied to the

material cost (i.e., 12.5 percent of $2,785). The non-production cost is $1,075, since the 25 percent

is applied to the material, labor, and factory overhead costs (i.e., 25 percent of $2,785 + $1,167 +

$348). Thus, in total, DOE estimates this 300kVA three-phase transformer to have a manufacturer

selling price of $5,375. 

5.4.1 Material Prices

The Department received considerable input from manufacturers concerning recent increases

in the cost of materials, particularly core steel. The Department used prices of core steel, conductor,

mineral oil, insulation, and other materials as an input to the transformer design software used for
5-29

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 materials (e.g., pounds of core steel, pounds of conductor),

making the impact of more expensive materials even more significant at higher efficiencies.

The Department 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 U.S. 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. The Department conducted the engineering

analysis using two material price scenarios: 1) a five-year average of the material prices (in constant

2004$) from 2000, 2001, 2002, 2003, and 2004, and 2) a more recent material price sensitivity,

using material prices from the first quarter (Q1) of 2005. OPS gathered both the five-year average

and the Q1 2005 material prices in the same manner, providing consistency to the two pricing

scenarios used in the engineering analysis. The consideration of a second set of material prices in

the engineering analysis was directly in response to comments received, during the review of the

ANOPR analysis, indicating that material prices are increasing rapidly and the historical lows of

recent past were unlikely to be experienced again. The results of the Q1 2005 engineering analysis

are presented in Appendix 5C.

The Department noted that the most critical material input to a distribution transformer,

electrical core steel, had increased by more than 100 percent for some M-grades between the fiveyear average price and Q1 2005 (see Table 5.4.1). For this reason, the Department researched the

grain-oriented electrical steel market to gain a better understanding of the main players and some of

the factors influencing this significant price increase (see Appendix 3A). 

In Chapter 8 on the LCC analysis, the Department presents results on its sensitivity analyses

conducted on various LCC inputs, which included material prices. In Chapter 8, the Q1 2005

material price is referred to as the “high” price scenario and the 2000–2004 average price scenario is

called the “medium” price scenario. The Department then developed a hypothetical "low" price

scenario to establish a lower bound for the LCC sensitivity analysis. It based the low price scenario

on material prices in 2002 (the calender year with the lowest $/pound for M6 core steel) and reduced

all the material prices in that year by 15 percent. These material prices can be found in the material

price tables presented in this section. The resulting low-price scenario 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 liquid-immersed transformer

manufacturer in Q1 2005, the hypothetical low material prices (for the LCC material price
5-30

sensitivity, presented in Chapter 8), and the 2000–2004 five-year average prices (all in constant

2004$). The highlighted columns are the prices that DOE used in the engineering analysis.

Table 5.4.1 Manufacturer’s Material Prices for Liquid-Immersed Design Lines

Material 

Q1

2005

$/lb.

2002 

-15%

2004$/

lb.

5-yr

Avg.

2004$/

lb.

2004

2004$/

lb.

2003

2004$/

lb.

2002

2004$/

lb.

2001

2004$/

lb.

2000

2004$/

lb.

M2 core steel 1.71 0.76 0.95 0.95 0.88 0.89 1.00 1.04

M3 core steel 1.63 0.65 0.80 0.80 0.78 0.76 0.82 0.86

M4 core steel 1.56 0.64 0.76 0.75 0.72 0.75 0.79 0.81

M6 core steel 1.42 0.57 0.70 0.69 0.69 0.67 0.72 0.74

ZDMH (mechanically-scribed core steel) 2.75 1.23 1.47 1.50 1.42 1.45 1.47 1.51

SA1 (amorphous) - finished core, volume

production 2.50 1.68 2.00 2.09 1.98 1.98 1.99 1.98

Copper wire, formvar, round #10-20 2.25 1.11 1.55 2.10 1.48 1.31 1.37 1.47

Copper wire, enameled, round #7-10

flattened 2.21 1.09 1.51 2.05 1.45 1.28 1.34 1.42

Copper wire, enameled, rectangular sizes 2.65 1.18 1.76 2.51 2.02 1.39 1.46 1.42

Aluminum wire, formvar, round #9-17 1.56 1.15 1.43 1.53 1.41 1.35 1.43 1.45

Aluminum wire, formvar, round #7-10 1.58 1.16 1.46 1.54 1.43 1.36 1.45 1.50

Copper strip, thickness range 0.020-0.045 2.92 1.86 2.32 2.50 2.24 2.19 2.31 2.35

Copper strip, thickness range 0.030-0.060 2.84 1.79 2.24 2.44 2.15 2.11 2.23 2.27

Aluminum strip, thickness range 0.020-

0.045 1.66 1.30 1.54 1.60 1.58 1.53 1.47 1.53

Aluminum strip, thickness range 0.045-

0.080 1.69 1.24 1.45 1.51 1.49 1.46 1.39 1.42

Kraft insulating paper with diamond

adhesive 1.56 1.32 1.59 1.56 1.54 1.55 1.62 1.66

Tank steel 0.50 0.29 0.35 0.35 0.33 0.34 0.37 0.38

Mineral oil 2.40 1.45 1.71 1.80 1.73 1.71 1.60 1.72

The Department then marked up the raw material prices presented in Table 5.4.1 using the

manufacturer’s internal markups discussed in section 5.4. 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). The Department then

used the marked-up material prices as inputs to the transformer design software. During the

manufacturer site visits in early 2002, the Department found this approach to be consistent with that

of several manufacturers who operate their own, proprietary transformer design software. Table

5.4.2 shows the markup steps being applied to the five-year average material price scenario

(2000–2004).

Table 5.4.2 Marked-up Material Prices for Liquid-Immersed Units, Five-Year Average Price

Scenario
5-31

Item and Description

Material

Price*

Scrap &

Handling

Factory

Overhead

NonProduction Software

Input

M2 core steel $0.95 1.025 1.125 1.25 $1.37

M3 core steel $0.80 1.025 1.125 1.25 $1.17

M4 core steel $0.76 1.025 1.125 1.25 $1.10

M6 core steel $0.70 1.025 1.125 1.25 $1.01

ZDMH (mechanically-scribed core steel,

finished core) $1.47 + 0.30 1.015 1.125 1.25 $2.53

SA1 (amorphous material) - finished core,

volume production $2.00 1.015 1.125 1.25 $2.85

Copper wire, formvar, round #10-20 (DL

1,2,4) $1.55 1.025 1.125 1.25 $2.23

Copper wire, enameled, round #7-10

flattened (DL 3,5) $1.51 1.025 1.125 1.25 $2.18

Copper wire, enameled, rectangular sizes

(DL 3) $1.76 1.025 1.125 1.25 $2.54

Aluminum wire, formvar, round #9-17 (DL

1,2,4) $1.43 1.025 1.125 1.25 $2.08

Aluminum wire, formvar, round #7-10 (DL

3,5) $1.46 1.025 1.125 1.25 $2.10

Copper strip, thickness range 0.02-0.045

(DL 1,2,4) $2.32 1.025 1.125 1.25 $3.34

Copper strip, thickness range 0.030-0.060

(DL 3,5) $2.24 1.025 1.125 1.25 $3.23

Aluminum strip, thickness range 0.02-

0.045 (DL 1,2,4) $1.54 1.025 1.125 1.25 $2.22

Aluminum strip, thickness range 0.045-

0.080 (DL 3,5) $1.45 1.025 1.125 1.25 $2.09

Kraft insulating paper with diamond

adhesive $1.59 1.025 1.125 1.25 $2.29

Tank Steel $0.35 1.025 1.125 1.25 $0.50

Mineral oil (per gallon) $1.71 - 1.125 1.25 $2.40

* Five year average (2000– 2004) for materials expressed in 2004$ per lb. ZDMH includes $0.30/lb adder for finished

core.

Several manufacturers commented that the U.S. has a 31 percent anti-dumping import duty

on core steel produced in Japan. One of the core steels considered by the Department as a highefficiency grade steel for the liquid-immersed, wound-core units was ZDMH. ZDMH is a

mechanically scribed, grain-oriented electrical steel. The process for manufacturing this steel is

patented, and it is only produced in Japan. For the ANOPR analysis, the Department considered

two price points for ZDMH, one reflecting what a U.S. manufacturer would pay with the import

duty and the other reflecting what a manufacturer in Mexico or Canada would pay (no duty). The

duty only applies to ZDMH raw material; it does not apply to the material if ‘substantial rework’

were done prior to importation (e.g., building a transformer or a core outside the U.S. and then

importing it). The Department is concerned that if ZDMH offered a more cost-effective set of
5-32

liquid-immersed designs for standards compliance, it may give manufacturers outside the U.S. a

competitive advantage over domestic manufacturers.

For the NOPR analysis, the Department modified its use of ZDMH pricing in the

engineering analysis due to input received from several manufacturers. These companies indicated

to the Department that, if ZDMH offered the most cost-effective liquid-immersed designs, they

would out-source core fabrication to a Mexican or Canadian company and import finished cores. 

Finished ZDMH cores are not subject to the importation duty; thus, the ZDMH price did not include

the 31 percent import duty, but did include an adder for core processing. The manufacturer impact

analysis (MIA, see Chapter 12) discusses the effect of this scenario on U.S. transformer

manufacturer employment.

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. The Department 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 design line 1, a 50kVA single-phase pad-mounted unit, the high-voltage bushings are

two universal bushing wells, 15 kV, 95 BIL, 14400V, costing $7 each. The low-voltage bushings

are three threaded copper studs, 240/120V, 50 kVA, costing $20 for the set. Internal hardware costs

include a core clamp, nameplate, and other miscellaneous hardware costing $25.65. The finished

tank size (and associated cost) varies by design, but the average is approximately $130.

For design line 2, a 25kVA single-phase pole-mounted unit, the high-voltage terminal is a

single, wet-process porcelain bushing assembly, 15 kV, 125 BIL, costing $6.00. The low-voltage

terminals are three molded polymer bushings, 120/240V, 25 kVA, costing $8.00 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 is approximately $70.

For design line 3, a 500kVA single-phase unit, the high-voltage connector is a single, wetprocess porcelain bushing, 25 kV, 125 BIL, costing $6.00. The low-voltage bushings are two fourhole “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 $500 (including radiators).

For design line 4, 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 $360.
5-33

For design line 5, 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 $800.

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

Item DL 1 DL 2 DL 3 DL 4 DL 5

High voltage bushings $14 $6 $6 $21 $60

Low voltage bushings $20 $8 $60 $24 $160

Core clamp, nameplate, and misc. hardware $25.65 $19.15 $50.65 $75.65 $105.65

Transformer tank average cost* $130 $70 $500 $360 $800

* 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 in

Q1 2005, the hypothetical low material prices (for the LCC material price sensitivity, presented in

Chapter 8), and the 2000–2004 five-year average prices (all in constant 2004$). The highlighted

columns are the prices used in the engineering analysis.
5-34

Table 5.4.4 Manufacturer’s Material Prices for Dry-Type Design Lines

Material

Q1

2005

$/lb.

2002 

-15%

2004$/l

b.

5-yr

Avg.

2004$/l

b.

2004

2004$/l

b.

2003

2004$/l

b.

2002

2004$/l

b.

2001

2004$/l

b.

2000

2004$/l

b.

H-O DR core steel (domain-refined) 1.85 0.82 0.99 1.00 0.92 0.97 1.01 1.04

M3 core steel 1.63 0.65 0.80 0.80 0.78 0.76 0.82 0.86

M4 core steel 1.56 0.64 0.76 0.75 0.72 0.75 0.79 0.81

M5 core steel 1.47 0.60 0.72 0.73 0.63 0.70 0.77 0.77

M6 core steel 1.42 0.57 0.70 0.69 0.69 0.67 0.72 0.74

M19 core steel (26 gauge) 0.82 0.43 0.56 0.55 0.52 0.51 0.59 0.62

M36 core steel (29 gauge) 0.69 0.42 0.50 0.53 0.49 0.49 0.48 0.51

M36 core steel (26 gauge) 0.65 0.36 0.45 0.51 0.44 0.42 0.44 0.46

M43 core steel (26 gauge) 0.58 0.36 0.43 0.48 0.43 0.42 0.41 0.43

Copper wire, rectangular 0.1 x 0.2,

Nomex wrap 2.69 1.39 2.00 2.72 2.24 1.63 1.68 1.74

Aluminum wire, rectangular 0.1 x

0.2, Nomex wrap 2.05 1.71 2.06 2.04 2.01 2.01 2.10 2.13

Copper strip, thickness range 0.020-

0.045 2.92 1.86 2.32 2.50 2.24 2.19 2.31 2.35

Aluminum strip, thickness range

0.020-0.045 1.66 1.30 1.54 1.60 1.58 1.53 1.47 1.53

Nomex insulation (per pound) 18.00 15.38 18.11 18.00 17.76 18.09 18.39 18.29

Cequin insulation (per pound) 12.00 10.54 11.99 12.00 12.18 12.40 11.56 11.83

Impregnation (per gallon) 19.00 14.93 17.80 18.00 17.26 17.57 17.86 18.29

Enclosure Steel (per pound) 0.50 0.29 0.35 0.35 0.33 0.34 0.37 0.38

Winding combs (per pound) 10.00 8.79 10.24 10.00 10.15 10.34 10.51 10.22

On the following pages, all the material prices entered into the design software for dry-type

distribution transformers are given. As shown in these tables, the Department marked up the

material prices before being entering them into the design software.
5-35

Table 5.4.5 Marked-up Material Prices for Dry-Type Units, Five-Year Average Price Scenario

Item and Description Material

Price*

Scrap &

Handling

Factory

Overhead

NonProductionSoftware

Input

H-O DR core steel (domain-refined) $0.99 1.025 1.125 1.25 $1.43

M3 core steel $0.80 1.025 1.125 1.25 $1.17

M4 core steel $0.76 1.025 1.125 1.25 $1.10

M5 core steel $0.72 1.025 1.125 1.25 $1.04

M6 core steel $0.70 1.025 1.125 1.25 $1.01

M19 core steel (26 gauge) $0.56 1.025 1.125 1.25 $0.81

M36 core steel (29 gauge) $0.50 1.025 1.125 1.25 $0.72

M36 core steel (26 gauge) $0.45 1.025 1.125 1.25 $0.65

M43 core steel (26 gauge) $0.43 1.025 1.125 1.25 $0.62

Copper wire, rectangular 0.1 x 0.2,

Nomex wrapped

$2.00 1.025 1.125 1.25 $2.88

Aluminum wire, rectangular 0.1 x

0.2, Nomex wrapped

$2.06 1.025 1.125 1.25 $2.97

Copper strip, thickness range .02-

.045

$2.32 1.025 1.125 1.25 $3.34

Aluminum strip, thickness range .02-

.045

$1.54 1.025 1.125 1.25 $2.22

Nomex insulation (per pound) $18.11 1.025 1.125 1.25 $26.10

Cequin insulation (per pound) $11.99 1.025 1.125 1.25 $17.30

Impregnation (per gallon) $17.80 - 1.125 1.25 $25.03

Enclosure steel (per pound) $0.35 1.025 1.125 1.25 $0.50

Winding Combs (per pound) $10.24 1.025 1.125 1.25 $14.76

* Five-year average (2000–2004) for materials expressed in 2004$ per lb. Average compiled by Paul Goethe,

Optimized Program Service, January 2005.

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 line that had both buttlap and mitered designs, the Department used an adder in design

line 9. The adder specified an extra 10 cents per pound of core steel for full-mitered designs. More

detailed costing of the retooling costs for mitering equipment is captured in the 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 design line 9, a 300 kVA three-phase, medium-voltage dry-type transformer at 45 kV

BIL, the low-voltage and high-voltage terminal set costs $75. The secondary (low-voltage) bus-bar

is estimated 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 dog-bone ductspacers used for this design line cost $0.42 per foot. The Department estimated the miscellaneous

hardware costs at $25. The ventilated enclosure - a 14-gauge steel enclosure, base, and mounting
5-36

feet - varies with the size of the core-coil assembly for the 300 kVA unit, and costs approximately

$175.

For design line 10, a 1500 kVA three-phase, medium-voltage dry-type transformer at 45 kV

BIL, the low-voltage and high-voltage terminal set costs $120. The low-voltage bus-bar is

estimated to be fourteen feet at $10 per foot, or $140. The mounting frame that attaches the

core/coil assembly to the transformer enclosure costs approximately $120. The fiberglass dog-bone

duct-spacers used for this design line cost $0.52 per foot. The Department estimated the

miscellaneous hardware costs at $42. The ventilated enclosure - a 12-gauge steel enclosure, base,

and mounting feet - varies with the size of the core-coil assembly for the 1500 kVA unit, and costs

approximately $600.

For design line 11, 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. The

low-voltage bus-bar is estimated to be ten 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. The Department 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 $300. 

For design line 12, a 1500 kVA three-phase, medium-voltage dry-type at 95 kV BIL, the

low-voltage and high-voltage terminal set costs $135. The high-voltage terminal boards cost $27.

The low-voltage bus-bar is estimated to be sixteen feet at $12 per foot, or $192. The mounting

frame that attaches the core/coil assembly to the transformer enclosure costs $125. The fiberglass

dog-bone duct-spacers used for this design line cost $0.56 per foot. The Department estimated the

miscellaneous hardware costs at $54. The ventilated enclosure - a 12-gauge steel enclosure, base,

and mounting feet - varies with the size of the core-coil assembly for the 1500 kVA unit, and costs

approximately $770.

For design line 13, a 2000 kVA three-phase, medium-voltage dry-type at 125 kV BIL, the

low-voltage and high-voltage terminal set costs $150. The high-voltage terminal boards cost $27. 

The low-voltage bus-bar is estimated to be eighteen feet at $15 per foot, or $270. The mounting

frame that attaches the core/coil assembly to the transformer enclosure costs $175. The fiberglass

dog-bone duct-spacers used for this design line cost $0.60 per foot. The Department estimated the

miscellaneous hardware costs at $60. The ventilated enclosure - a 12-gauge steel enclosure, base,

and mounting feet - varies with the size of the core-coil assembly for the 2000 kVA unit, and costs

approximately $835. 
5-37

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

Item DL 9 DL 10 DL 11 DL 12 DL 13

LV and HV terminals (set) $75 $120 $100 $135 $150

HV terminal board(s) $27 $27 $27 $27 $27

LV bus-bar $80 $140 $80 $192 $270

Core/coil mounting frame $36 $120 $42 $125 $175

Nameplate $0.65 $0.65 $0.65 $0.65 $0.65

Dog-bone duct-spacer (ft.) $0.42 $0.52 $0.42 $0.56 $0.60

Winding combs (lb.) n/a n/a $10.24 $10.24 $10.24

Misc. hardware $25 $42 $32 $54 $60

Enclosure (12, 14 gauge) ~$250 ~$600 ~$300 ~$770 ~$835

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. The

Department 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, with the exception of the non-production markup. 

The Department developed the markups shown in Table 5.4.7 after reviewing publicly available

information and consulting with industry experts familiar with transformer manufacturing in the

U.S.
5-38

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

Item description Markup percentage Rate per hour

Labor cost per hour*

$ 14.31

Indirect Production** 33% $ 19.03

Overhead*** 30% $ 24.74

Fringe†

21% $ 29.93

Assembly Labor Up-time†† 43% $ 42.77

Non-Production Mark-up††† 25% $ 53.46

Cost of Labor Input to Software $ 53.46

* Cost per hour is from U.S. Census Bureau, 1997 Economic Census of Industry, published September 1999, Table 5,

page 9. 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, 1997 Economic Census of Industry, published September 1999, Table 3, page 8. Data for NAICS code 335311

"Power, Distribution and Specialty Transformer Manufacturing," 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 product and/or

reworking unsatisfactory units. The markup of 42 percent represents a 70 percent utilization (multiplying by 100/70).

NCI estimate.

††† Non-production markup reflects non-production costs, including selling, general, and administrative, R&D, interest

payments, and profit factor markups. Source: US Industry Census Data for 1992 and 1997; SEC 10-K reports for Acme,

Powell, Magnetek and Hammond; Manufacturer interviews, 2002. 

There are several labor steps involved in manufacturing a liquid-immersed transformer. The

Department 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. The labor involved in these activities is calculated 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, M4 is 0.10, M3 is

0.125, and M2 is 0.16. For DL3 and DL5, on M6 designs the constant is 0.05, M4 is 0.07,

M3 is 0.09, and M2 is 0.11. For the prefabricated cores—ZDMH and SA1 (Amorphous

material)—the labor for cutting, forming, and annealing is set 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
5-39

because some of the larger, liquid-immersed manufacturers wind multiple coils

simultaneously on the same winding machine. This manufacturing approach improves

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 (step-down)

transformer, the number of secondary turns is always less than the primary. For the liquidimmersed 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 an insulating tubing is slipped over the cable. This

is a fixed amount of labor, and does not vary with efficiency or design. The estimated times

are 0.5 hours for DL1 and DL4, 0.07 hours for DL2, 0.35 hours for DL3, and 1.0 hour for

DL5.

• 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

are 0.10 hours for DL1, 0.07 hours for DL2, 0.15 hours for DL3, 0.17 hours for DL4, and

0.25 hours for DL5.

• 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 time for core assembly is approximately 0.5 hours for DL1, 0.3 hours for DL2, 1.5 hours

for DL3, 1 hour for DL4, and 3.5 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 liquid-immersed design
5-40

lines are: 0.5 hours for DL1, 0.11 hours for DL2, 0.3 hours for DL3, 0.62 hours for DL4,

and 1.4 hours for DL5. 

• 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. The estimates of labor time

are 0.10 hours for DL1 and DL3, 0.05 hours for DL2, 0.15 hours for DL4, and 0.20 hours for

DL5.

• 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 are 0.10

hours for DL1, DL3, and DL4; 0.03 hours for DL2; and 0.15 hours for DL5.

• 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. The estimates of

labor time are 0.15 hours for DL1 and DL3, 0.07 hours for DL2, 0.20 hours for DL4, and

0.25 hours for DL5.

• 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. The estimates of labor time are

0.28 hours for DL1, 0.07 hours for DL2, 0.35 hours for DL3, 0.31 hours for DL4, and 0.75

hours for DL5.

• 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. The

estimates of labor time are 0.27 hours for DL1, 0.06 hours for DL2, 0.5 hours for DL3 and

DL4, and 3 hours for DL5.

Table 5.4.8 summarizes the estimates of labor time that DOE used for the five liquidimmersed units.
5-41

Table 5.4.8 Summary of Labor Times for Liquid-Immersed Units

Labor Activity DL 1

hrs.

DL 2

hrs.

DL 3

hrs.

DL 4

hrs.

DL 5 

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 0.07 0.35 0.50 1.00

Baking Coils 0.10 0.07 0.15 0.17 0.25

Core Assembly ~0.50 ~0.30 ~1.50 ~1.00 ~3.50

Tanking and Impregnating 0.50 0.11 0.30 0.62 1.40

Inspection 0.10 0.05 0.10 0.15 0.20

Preliminary Test 0.10 0.03 0.10 0.10 0.15

Final Test 0.15 0.07 0.15 0.20 0.25

Pallet Loading 0.27 0.06 0.50 0.50 3.00

Marking and Misc. 0.28 0.07 0.35 0.31 0.75

Likewise, there are several labor steps involved in manufacturing a dry-type transformer. 

The Department 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 short as 0.45 hours/inch for a 300 kVA, 45kV BIL three-phase,

medium-voltage unit to 0.9 hours/ inch for a 2000 kVA, 125kV BIL three-phase, mediumvoltage unit.

• 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. The 300kVA units, DL9 and DL11, both have

0.01 hours/turn. The 1500kVA units, DL10, DL12, and the 2000kVA DL13 all have the

same winding time—0.0125 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 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. The hours per turn vary from 0.035 to 0.125, depending on

the kVA rating (design line).
5-42

• 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 an 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 0.60 to 1.0 hours per unit.

• Assembly - This task involves installing the wound cores 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. The Department assumed the

assembly time varies by kVA rating, but does not vary by design within a kVA rating. For

example, the assembly time for a 1500kVA three-phase unit is estimated at six hours, while

the assembly time for a 300kVA three-phase unit is estimated at three 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 0.10

hours (6 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

0.10 hours (6 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 0.15 hours (9 minutes) for the smaller

kVA ratings 0.75 hours (45 minutes) for the larger units.

• 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 0.70 hours at the low end to 2.2 hours at the higher kVA ratings.

• 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 does not vary

with design or efficiency, but it does vary by kVA rating. The time estimate ranges from 1.0

hours at the low end to 2.0 hours at the higher kVA ratings.

• 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 five hours for the

300kVA up to eight hours for the 1500 and 2000kVA cabinets.
5-43

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 DL 9

hrs.

DL 10

hrs.

DL 11

hrs.

DL 12

hrs.

DL 13

hrs.

Core Stacking (hrs/inch) 0.45-0.55 0.70 0.70 0.80 0.90

Primary Winding (hrs/turn) 0.01 0.0125 0.01 0.0125 0.0125

Secondary Winding (hrs/turn) 0.035 0.125 0.035 0.125 0.125

Lead Dressing 0.60 1.00 0.60 1.00 1.00

Assembly 3.00 6.00 4.00 6.00 6.00

Inspection 0.10 0.25 0.10 0.25 0.25

Preliminary Test 0.10 0.50 0.15 0.50 0.50

Final Test 0.15 0.75 0.25 0.75 0.75

Enclosure Manufacturing 5.00 8.00 5.00 8.00 8.00

Packing 1.00 2.00 1.00 2.00 2.00

Marking and Miscellaneous 0.70 2.20 0.80 2.20 2.20
5-44

5.5 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 10 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. In addition to the results provided in this section, the Department prepared

scatter plots depicting the engineering analysis results for the 10 representative units, including

watts of core and coil loss and the weight by efficiency (see Appendix 5A). 

As discussed earlier in this chapter, the Department received several comments on the

ANOPR analysis that material prices, and particularly core steel, were experiencing a rapid increase. 

Therefore, in addition to its analysis on a five-year average material price (2000–2004) presented

here, the Department also conducted a current price scenario of Q1 2005. The engineering analysis

results of the Q1 2005 material price scenario are presented in Appendix 5C, along with a

comparison between these material prices and the five-year average. The Department also

calculated a hypothetical low-materials-price scenario, which represents a 15 percent reduction over

the materials prices in 2002 (the year in which M6 had the lowest $/pound between 2000 and 2004). 

The results of the low-price scenario are included in the LCC spreadsheets, where they were used

for an LCC sensitivity analysis.
5-45

Figure 5.5.1 presents a plot of the manufacturer selling prices and efficiency levels for the

full database of designs for the representative unit from design line 1, 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:

• NEMA’s TP 1-2002 efficiency level of 98.9 percent is met by most M3 and M2 core

designs. However, many of the M6 core designs exhibit efficiencies below this level.

• The amorphous metal (SA1) core extends the available efficiency for the transformers

beyond 99.6 percent, but at a significant cost.

500

1,000

1,500

2,000

2,500

3,000

98.40% 98.60% 98.80% 99.00% 99.20% 99.40% 99.60% 99.80%

Efficiency at 50% load, Temperature Corrected

Manufacturer Selling Price ($)

M6AlAl_sh

M6CuAl_sh

M3AlAl_sh

M3CuAl_sh

M2CuAl_sh

M2CuCu_sh

ZDMHCuCu_sh

SA1CuCu_sh

Figure 5.5.1 Scatter Plot of Manufacturer Selling Price and Efficiency for Design Line 1
5-46

Figure 5.5.2 presents a plot of the manufacturer sales prices and efficiency levels for the full

database of designs for the representative unit from design line 2, 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 NEMA TP 1-2002 standard of 98.7 percent can be achieved with several design option

combinations, including M3CuAl and M3CuCu.

• In most cases, the maximum efficiency available with conventional silicon core steels is

approximately 99.2 percent. However, the amorphous metal (SA1) provides efficiencies up

to about 99.5 percent.

400

600

800

1,000

1,200

1,400

1,600

1,800

98.00% 98.20% 98.40% 98.60% 98.80% 99.00% 99.20% 99.40% 99.60% 99.80%

Efficiency at 50% load, Temperature Corrected

Manufacturer Selling Price ($)

M6AlAl_sh

M6CuAl_sh

M4AlAl_sh

M4CuAl_sh

M3CuAl_sh

M3CuCu_sh

M2CuAl_sh 

M2CuCu_sh

ZDMHCuCu_sh

SA1CuCu_co

Figure 5.5.2 Scatter Plot of Manufacturer Selling Price and Efficiency for Design Line 2
5-47

Figure 5.5.3 presents a plot of the manufacturer sales prices and efficiency levels for the full

database of designs for the representative unit from design line 3, 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:

• All design option combinations have designs that meet or exceed the NEMA TP 1-2002

efficiency of 99.3 percent.

• In most cases, the maximum efficiency available is limited to approximately 99.6 percent. 

However, the amorphous metal design option combination provides efficiencies up to about

99.75 percent, with an available range from about 99.35 percent to nearly 99.75 percent.

1,000

3,000

5,000

7,000

9,000

11,000

13,000

15,000

98.90% 99.00% 99.10% 99.20% 99.30% 99.40% 99.50% 99.60% 99.70% 99.80%

Efficiency at 50% load, Temperature Corrected

Manufacturer Selling Price ($)

M6AlAl_sh

M4CuAl_sh

M3CuAl_sh

M2CuAl_sh

M2CuCu_sh

ZDMHCuCu_sh

SA1CuCu_co

Figure 5.5.3 Scatter Plot of Manufacturer Selling Price and Efficiency for Design Line 3
5-48

Figure 5.5.4 presents a plot of the manufacturer sales prices and efficiency levels for the full

database of designs for the representative unit from design line 4, 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:

• At the lower efficiencies, the M6 and M4 steel cores offer a low-cost option for increasing

efficiency, but do not meet the NEMA TP 1-2002 efficiency standard of 98.9 percent.

• The amorphous metal design option combination extends the available efficiency for the

transformers up to 99.6 percent, but at a significant cost.

1,500

2,500

3,500

4,500

5,500

6,500

7,500

98.20% 98.40% 98.60% 98.80% 99.00% 99.20% 99.40% 99.60% 99.80%

Efficiency at 50% load, Temperature Corrected

Manufacturer Selling Price ($)

M6AlAl_co

M4AlAl_co

M3CuAl_co

M2CuAl_co

M2CuCu_co

ZDMHCuCu_co

SA1CuCu_co

Figure 5.5.4 Scatter Plot of Manufacturer Selling Price and Efficiency for Design Line 4
5-49

Figure 5.5.5 presents a plot of the manufacturer sales prices and efficiency levels for the full

database of designs for the representative unit from design line 5, 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:

• Every design option combination has designs that meet the NEMA TP 1-2002 efficiency of

99.3 percent; however, many of the M6 and M4 core designs exhibit efficiencies lower than

99.3 percent.

• Beyond 99.5 percent, the SA1 core provides additional efficiency with increased cost. 

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

98.90% 99.00% 99.10% 99.20% 99.30% 99.40% 99.50% 99.60% 99.70% 99.80%

Efficiency at 50% load, Temperature Corrected

Manufacturer Selling Price ($)

M4AlAl_co

M4CuAl_co

M3CuAl_co

M2CuAl_co

M2CuCu_co

ZDMHCuCu_co

SA1CuCu_co

Figure 5.5.5 Scatter Plot of Manufacturer Selling Price and Efficiency for Design Line 5
5-50

Figure 5.5.6 presents a plot of the manufacturer sales prices and efficiency levels for the full

database of designs for the representative unit from design line 9, 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:

• NEMA’s TP 1-2002 efficiency level for this unit is 98.6 percent efficient. This level can be

achieved by using M6 or better core steels.

• Rapid increase in price is realized in the M3 and H-O DR core steels, as the efficiency level

increases. For example, moving a fraction of an efficiency level (e.g., from 99.0 percent to

99.5 percent) can almost double the price.

4,000

5,000

6,000

7,000

8,000

9,000

10,000

11,000

12,000

98.20% 98.40% 98.60% 98.80% 99.00% 99.20% 99.40% 99.60%

Efficiency at 50% load, Temperature Corrected

Manufacturer Selling Price ($)

M6AlAl_bl M6CuCu_mt

M5AlAl_mt M3CuAl_mt

HOCuCu_mt

Figure 5.5.6 Scatter Plot of Manufacturer Selling Price and Efficiency for Design Line 9
5-51

Figure 5.5.7 presents a plot of the manufacturer sales prices and efficiency levels for the full

database of designs for the representative unit from design line 10, a 1500kVA three-phase,

medium-voltage, 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:

• NEMA’s TP 1-2002 efficiency level of 99.1 percent is met by M4, M3, and HO core steel

designs.

• As the efficiency increases, the laser-scribed (H-O DR) and M3 steel cores have similar

costs.

7,000

12,000

17,000

22,000

27,000

32,000

37,000

42,000

98.60% 98.70% 98.80% 98.90% 99.00% 99.10% 99.20% 99.30% 99.40% 99.50% 99.60%

Efficiency at 50% load, Temperature Corrected

Manufacture Selling Price ($)

M6AlAl_cf

M6CuCu_cf

M4CuAl_cf

M3CuCu_cf

HOCuCu_cf

Figure 5.5.7 Scatter Plot of Manufacturer Selling Price and Efficiency for Design Line 10
5-52

Figure 5.5.8 presents a plot of the manufacturer sales prices and efficiency levels for the full

database of designs for the representative unit from design line 11, 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 least-cost high-efficiency design path at 50 percent load varies between the M3, M4, and

H-O DR core steel design option combinations.

• The M6 cores offer the least-cost options only at the lowest efficiency levels. In general, the

transformers that use the M6 core steel are not the most cost-effective option available, and

many of the M6 designs do not meet the NEMA TP 1-2002 efficiency level of 98.5 percent.

4,000

6,000

8,000

10,000

12,000

14,000

16,000

97.60% 97.80% 98.00% 98.20% 98.40% 98.60% 98.80% 99.00% 99.20% 99.40%

Efficiency at 50% load, Temperature Corrected

Manufacturer Selling Price ($)

M6CuCu_mt

M4CuAl_mt

M3CuCu_mt

HOCuCu_mt

M6AlAl_mt

Figure 5.5.8 Scatter Plot of Manufacturer Selling Price and Efficiency for Design Line 11
5-53

Figure 5.5.9 presents a plot of the manufacturer sales prices and efficiency levels for the full

database of designs for the representative unit from design line 12, a 1500kVA three-phase,

medium-voltage, 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:

• NEMA’s TP 1-2002 efficiency level of 99.0 percent is met by M4, M3, and HO core steel

designs.

• Above 99.3 percent efficiency, the H-O DR steel design option combination has a slight cost

advantage over the M3 core. 

15,000

20,000

25,000

30,000

35,000

40,000

45,000

98.60% 98.80% 99.00% 99.20% 99.40% 99.60%

Efficiency at 50% load, Temperature Corrected

Manufacturer Selling Price ($)

M6AlAl_cf

M6CuCu_cf

M4CuAl_cf

M3CuCu_cf

HOCuCu_cf

Figure 5.5.9 Scatter Plot of Manufacturer Selling Price and Efficiency for Design Line 12
5-54

12,000

22,000

32,000

42,000

52,000

62,000

98.90% 99.00% 99.10% 99.20% 99.30% 99.40% 99.50% 99.60% 99.70%

Efficiency at 50% load, Temperature Corrected

Manfuacturer Selling Price ($)

M6AlAl_cf

M6CuCu_cf

M4CuAl_cf

M3CuCu_cf

HOCuCu_cf

Figure 5.5.10 Scatter Plot of Manufacturer Selling Price and Efficiency for Design Line 13

Figure 5.5.10 presents a plot of the manufacturer sales prices and efficiency levels for the

full database of designs for the representative unit from design line 13, 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:

• NEMA’s TP 1-2002 efficiency level of 99.0 percent is met by all core steel design option

considerations considered by the Department.

• At efficiency levels of 99.3 percent and above, the M3 steel core and H-O DR steel cores

have similar costs and efficiency gains.
5-55

5.6 FOUR EXAMPLE TRANSFORMER DESIGNS AND COST BREAKDOWNS

This section presents some of the OPS transformer designs from the Department’s

engineering analysis database. As discussed earlier, to prepare a cost-efficiency relationship on

selected representative units, the Department contracted OPS, a software company specializing in

transformer design since 1969. Using a range of input parameters and material prices, OPS created

more than 33,000 transformer designs for the Department’s analysis. For each design, the software

generated 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, two designs from each of the two

superclasses (i.e., liquid-immersed and medium-voltage, dry-type) are presented in this section. As

these practical designs illustrate, the software output was used to create a bill of materials, which

DOE 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 four distribution transformers presented are two each from two design lines—1 and 12. 

Across all the design lines, the complete database of designs contains 33,152 distribution

transformer specification and winding sheets, bills of materials, and performance reports. This

design database was used by the LCC analysis (see Chapter 8) as it simulated purchases of

distribution transformers in the marketplace.

Design Line 1: 50 kVA single-phase, liquid-immersed

• M6 core steel with an aluminum primary and secondary windings (M6AlAl) at a $0.00 A

and a $0.00 B evaluation formula.

• M3 core steel with a copper primary winding and an aluminum secondary winding

(M3CuAl) at a $1.50 A and a $0.38 B evaluation formula.

Design Line 12: 1500 kVA three-phase, medium-voltage, dry-type 

• M6 core steel with aluminum primary and secondary windings (M6AlAl) at a $0.00 A and a

$0.00 B evaluation formula.

• M3 core steel with copper primary and secondary windings (M3CuCu) at a $0.50 A and a

$0.08 B evaluation formula. 

For each of the four 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.

5.6.1 Design Details Report for Non-Evaluated Transformer from Design Line 1

A design specification report for a 50kVA single-phase, liquid-immersed transformer

appears below. This design incorporates M6 core steel, with an aluminum primary and an

aluminum secondary conductor. The evaluation factors for this design are $0.00 A and $0.00 B. 
5-56

The bill of materials and associated breakdown of costs for this design are also reported, after the

design and electrical analysis reports.

OPTIMIZED PROGRAM SERVICE

 CLEVELAND OHIO 101800

 2005- 3- 1 5:40: 6

DG-CORE SHELL TYPE TRANSFORMER NL1PM6ALAL 

FREQUENCY 60.0 KVA RATING 50.00 @ 100.00% DUTY CYCLE

CORE DG-M6 M 6 THICKNESS .0140

 D: 6.738 E: 2.073 F: 3.104 G: 7.476 EFF. AREA 26.952 WEIGHT 203.850

WINDING FORM: INS. DIM. 6.988 X 4.331 THICKNESS .072 LENGTH 6.976

 COIL SPECIFICATIONS

 -------------------

WNDG WIRE LENGTH MEAN TURNS MARGIN WT

----------------------------------------------------------------------

S1 .0267X 6.2262 AL 31.83 25.47 .375 6.204

P1 1 #14.5 ROUND AL 5643.34 35.83 .375 18.182

S2 .0267X 6.2262 AL 57.67 46.13 .375 11.238

NUMBER OF COILS 1 TOTAL BARE CONDUCTOR WEIGHT 35.558

WNDG TURNS LO TAP HI TAP LAYRS T/L LAYR INS SEC. INS BUILD

----------------------------------------------------------------------

S1 15.0 15 1.0 1(.00500) 1(.03000) .471

P1 1800.0 1710.0 1890.0 21 92.0 3(.00500) 1(.10000) 1.677

S2 15.0 15 1.0 1(.00500) 1(.05000) .471

 TOTAL BUILD(%) 92.51

WNDG TAPS: TURNS( VOLTS)

----------------------------------------------------------

P1 1755.0( 14040.00) 1845.0( 14760.00) 1890.0( 15120.00)

WNDG INTERNAL DUCTS(100.00) %EFF EXTERNAL DUCTS(100.00) %EFF

----------------------------------------------------------------

S1 3 .125 X .125 IN. END 

P1 6 .125 X .125 IN. END .125 X .125 IN. END 

S2 1 .125 X .125 IN. END .125 X .125 IN. END 

 ELECTRICAL ANALYSIS

 -------------------

 FULL-LOAD TAP VOLTS TEST LOAD RESIST. CURRNT

WNDG VOLTS LOW HIGH KV CURRENT @20 C. DENS. %REG

----------------------------------------------------------------------

P1 14400.00 13680.00 15120.00 34.5 3.541 27.52329 1293.

S1 118.32 10.0 208.330 .00256 1253. 1.4

S2 117.77 10.0 208.330 .00463 1253. 1.9
5-57

 F.L. N.L.

FLUX DENS. 17.120 17.262 LEAKAGE INDUCTANCE MHYS 217.723

CORE LOSS 174.699 179.762 POWER FACTOR 1.0000

COIL LOSS 828.787 .028 IMPEDANCE % 2.54

EXCIT. VA 367.167 417.373 EFFICIENCY % 98.03

EXCIT. CURR. .025 .029 TANK OIL GAL 41.86

AMBIENT TEMP. 20.00 NOMINAL LENGTH 14.50

TEMP.RISE 65.00 NOMINAL DEPTH 16.20

OPERATING TEMP. 85.00 NOMINAL HEIGHT 11.62

 2

 COND. I R LOSS = 806.3795

 COND. EDDY CURRENT LOSS = 2.2476

 OTHER STRAY LOSS = 20.1595

 K VALUE = 1.0000

%LOAD %REG %EFF %IR %IX %IZ COIL LOSS TEMP. RISE

------------------------------------------------------------------------

 25 .35 98.24 .341 .504 .608 45.690 28.6

 35 .50 98.49 .484 .703 .854 90.911 33.6

 50 .75 98.54 .717 1.004 1.234 192.395 44.2

 65 1.03 98.43 .980 1.307 1.633 341.577 58.6

 75 1.22 98.32 1.156 1.509 1.901 464.858 65.0

 100 1.64 98.03 1.545 2.018 2.542 828.772 65.0

 125 2.07 97.70 1.938 2.531 3.188 1299.377 65.0

Table 5.6.1 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 the

bottom of the table to arrive at the manufacturer’s selling price. This table provides the bill of

materials for a non-evaluated transformer from design line 1, a 50kVA single-phase, liquidimmersed, pad-mount M6 design, with an aluminum primary and an aluminum secondary. The

Department generated this design using a $0.00 A and a $0.00 B.
5-58

Bill of Materials and Labor for liquid-immersed, single-phase, pad-mount, 50kVA

A$ Input $0.00

B$ Input $0.00

Efficiency at 50% load 98.56%

Material item Type quantity $ each $ total

Core steel* (lb) M6-.014 204 0.70 $ 143.49 $ 

Primary winding* (lb) Aluminum wire, formvar, round #9-17 18 1.43 $ 26.00 $ 

Secondary windings* (lb) Aluminum strip, thickness range 0.02-0.045 17 1.54 $ 26.90 $ 

Winding form & insulation* (lb) Kraft insulating paper with diamond adhesive 4 1.59 $ 5.59 $ 

Oil (gal) - 42 1.71 $ 71.57 $ 

Tank - 1 132.95 $ 132.95 $ 

Core clamp - 1 15.00 $ 15.00 $ 

Nameplate - 1 0.65 $ 0.65 $ 

Bushings HV & LV 1 34.00 $ 34.00 $ 

Misc. hardware - 1 10.00 $ 10.00 $ 

Scrap factor 1.0% 2.02 $ 

Total Material Cost $ 468.17

Labor item hours rate $ total

Lead dressing 0.50 42.77 21.39 $ 

Inspection 0.10 42.77 4.28 $ 

Baking coils 0.10 42.77 4.28 $ 

Tanking and impregnating 0.50 42.77 21.39 $ 

Preliminary test 0.10 42.77 4.28 $ 

Final test 0.15 42.77 6.42 $ 

Pallet loading 0.27 42.77 11.55 $ 

Marking and miscellaneous 0.28 42.77 11.98 $ 

Winding the primary 0.19 42.77 8.08 $ 

Winding the secondary 0.45 42.77 19.25 $ 

Cutting, forming, and annealing 0.38 42.77 16.31 $ 

Core assembly 0.29 42.77 12.23 $ 

Handling and slitting factor (on material) 1.50% 3.03 $ 

Total Labor 3.306 42.77 144.44 $ 

Manufacturing Cost (Material + Labor) $ 612.61

Factory Overhead (Materials only) 12.5% 58.52 $ 

Non-production Cost Markup 25.0% 167.78 $ 

Manufacturer Selling Price $ 838.91

* indicates those items to which the scrap factor (1.0%) and the handling and slitting factor (1.5%) are applied.

This bill of materials is based on non-rounded core dimensions.

Table 5.6.1 Bill of Materials for Non-Evaluated Transformer from Design Line 1
5-59

Figure 5.6.1 provides a summary of the costs contributing to the total selling price of the

non-evaluated transformer from design line 1. For this design, approximately 56 percent of the final

manufacturer selling price is direct material and scrap. Labor accounts for 17 percent of the price

and, together, the factory overhead and selling price account for 27 percent.

5.6.2 Design Details Report for Evaluated Transformer from Design Line 1

A design specification report for a 50kVA single-phase, liquid-immersed transformer

appears below. This design incorporates M3 core steel, with a copper primary and an aluminum

secondary. The evaluation factors for this design are $1.50 A and $0.38 B. The bill of materials

and associated breakdown of costs for this design are also reported, after the design and electrical

analysis reports.

OPTIMIZED PROGRAM SERVICE

 CLEVELAND OHIO 101800

 2005- 3- 1 8:52:41

DG-CORE SHELL TYPE TRANSFORMER NL1PM3CUAL 

FREQUENCY 60.0 KVA RATING 50.00 @ 100.00% DUTY CYCLE

CORE DG-M3 M 3 THICKNESS .0090

 D: 7.635 E: 1.786 F: 3.048 G: 7.372 EFF. AREA 25.909 WEIGHT 188.488

WINDING FORM: INS. DIM. 7.885 X 3.758 THICKNESS .072 LENGTH 6.872

Core/Coils 

23%

Other Material

33%

Labor

17%

Factory Overhead

7%

Selling Factor

20%

Figure 5.6.1 Manufacturer Selling Price Breakdown, Non-Evaluated

Transformer from Design Line 1
5-60

 COIL SPECIFICATIONS

 -------------------

WNDG WIRE LENGTH MEAN TURNS MARGIN WT

----------------------------------------------------------------------

S1 .0305X 6.1220 AL 35.24 26.43 .375 7.697

P1 1X 1 #16 ROUND H CU 6087.06 36.23 .375 45.437

S2 .0305X 6.1220 AL 61.30 45.97 .375 13.387

NUMBER OF COILS 1 TOTAL BARE CONDUCTOR WEIGHT 66.520

WNDG TURNS LO TAP HI TAP LAYRS T/L LAYR INS SEC. INS BUILD

----------------------------------------------------------------------

S1 16.0 16 1.0 1(.00500) 1(.03000) .563

P1 1920.0 1824.0 2016.0 19 107.0 4(.00500) 1(.10000) 1.423

S2 16.0 16 1.0 1(.00500) 1(.05000) .563

 TOTAL BUILD(%) 91.85

WNDG TAPS: TURNS( VOLTS)

----------------------------------------------------------

P1 1872.0( 14040.00) 1968.0( 14760.00) 2016.0( 15120.00)

WNDG INTERNAL DUCTS(100.00) %EFF EXTERNAL DUCTS(100.00) %EFF

----------------------------------------------------------------

S1 3 .125 X .125 IN. END 

P1 6 .125 X .125 IN. END .125 X .125 IN. END 

S2 1 .125 X .125 IN. END .125 X .125 IN. END 

 ELECTRICAL ANALYSIS

 -------------------

 FULL-LOAD TAP VOLTS TEST LOAD RESIST. CURRNT

WNDG VOLTS LOW HIGH KV CURRENT @20 C. DENS. %REG

----------------------------------------------------------------------

P1 14400.00 13680.00 15120.00 34.5 3.532 25.60013 1824.

S1 118.40 10.0 208.330 .00253 1118. 1.3

S2 117.91 10.0 208.330 .00439 1118. 1.8

 F.L. N.L.

FLUX DENS. 16.706 16.836 LEAKAGE INDUCTANCE MHYS 245.843

CORE LOSS 105.561 108.891 POWER FACTOR 1.0000

COIL LOSS 779.995 .008 IMPEDANCE % 2.70

EXCIT. VA 219.090 238.628 EFFICIENCY % 98.26

EXCIT. CURR. .015 .017 TANK OIL GAL 41.23

AMBIENT TEMP. 20.00 NOMINAL LENGTH 13.24

TEMP.RISE 65.00 NOMINAL DEPTH 16.98

OPERATING TEMP. 85.00 NOMINAL HEIGHT 10.94

 2

 COND. I R LOSS = 758.5084

 COND. EDDY CURRENT LOSS = 2.5240

 OTHER STRAY LOSS = 18.9627

 K VALUE = 1.0000
5-61

%LOAD %REG %EFF %IR %IX %IZ COIL LOSS TEMP. RISE

------------------------------------------------------------------------

 25 .33 98.81 .313 .565 .646 41.814 21.3

 35 .47 98.92 .446 .791 .908 83.412 26.5

 50 .69 98.88 .663 1.130 1.310 176.975 37.5

 65 .95 98.72 .907 1.471 1.728 314.794 52.2

 75 1.15 98.58 1.088 1.700 2.018 435.534 64.2

 100 1.55 98.26 1.461 2.273 2.702 779.984 65.0

 125 1.96 97.92 1.832 2.851 3.389 1222.869 65.0

Table 5.6.2 provides the bill of materials that 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 an evaluated transformer from design line 1, a 50kVA single-phase, liquid-immersed,

pad-mount M3 design, with a copper primary and an aluminum secondary. The Department

generated this design using a $1.50 A and a $0.38 B.
5-62

Bill of Materials and Labor for liquid-immersed, single-phase, pad-mount, 50kVA

A$ Input $1.50

B$ Input $0.38

Efficiency at 50% load 98.87%

Material item Type quantity $ each $ total

Core steel* (lb) M3-.009 188 0.80 $ 150.79 $ 

Primary winding* (lb) Copper wire, formvar, round #10-20 45 1.55 $ 70.29 $ 

Secondary windings* (lb) Aluminum strip, thickness range 0.02-0.045 21 1.54 $ 32.52 $ 

Winding form & insulation* (lb) Kraft insulating paper with diamond adhesive 4 1.59 $ 6.98 $ 

Oil (gal) - 41 1.71 $ 70.50 $ 

Tank - 1 131.88 $ 131.88 $ 

Core clamp - 1 15.00 $ 15.00 $ 

Nameplate - 1 0.65 $ 0.65 $ 

Bushings HV & LV 1 34.00 $ 34.00 $ 

Misc. hardware - 1 10.00 $ 10.00 $ 

Scrap factor 1.0% 2.61 $ 

Total Material Cost $ 525.22

Labor item hours rate $ total

Lead dressing 0.50 42.77 21.39 $ 

Inspection 0.10 42.77 4.28 $ 

Baking coils 0.10 42.77 4.28 $ 

Tanking and impregnating 0.50 42.77 21.39 $ 

Preliminary test 0.10 42.77 4.28 $ 

Final test 0.15 42.77 6.42 $ 

Pallet loading 0.27 42.77 11.55 $ 

Marking and miscellaneous 0.28 42.77 11.98 $ 

Winding the primary 0.20 42.77 8.62 $ 

Winding the secondary 0.48 42.77 20.53 $ 

Cutting, forming, and annealing 0.55 42.77 23.41 $ 

Core assembly 0.26 42.77 11.23 $ 

Handling and slitting factor (on material) 1.50% 3.91 $ 

Total Labor 3.491 42.77 153.24 $ 

Manufacturing Cost (Material + Labor) $ 678.46

Factory Overhead (Materials only) 12.5% 65.65 $ 

Non-production Cost Markup 25.0% 186.03 $ 

Manufacturer Selling Price $ 930.14

* indicates those items to which the scrap factor (1.0%) and the handling and slitting factor (1.5%) are applied.

This bill of materials is based on non-rounded core dimensions.

Table 5.6.2 Bill of Materials for Evaluated Transformer from Design Line 1
5-63

Figure 5.6.2 provides a summary of the costs contributing to the total selling price of the

evaluated 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 16 percent of the price

and, together, the factory overhead and selling price account for 27 percent.

5.6.3 Design Details Report for Non-Evaluated Transformer from Design Line 12

The following design report provides information on one of several designs DOE 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 2,590 designs in the

database) is for M6 core steel with aluminum primary and secondary windings, and a $0.00 A and a 

$0.00 B.

OPTIMIZED PROGRAM SERVICE

 CLEVELAND OHIO 101800

 2005- 3-12 12:58: 9

STRIP CRUC 3-PHASE TYPE TRANSFORMER L12M6ALAL 

FREQUENCY 60.0 MVA RATING 1.50 @ 100.00% DUTY CYCLE

CORE 9.929" CRUC STACK 9.929 GRADE M 6 THICKNESS .0140

WINDOW: 14.442 X 50.208 EFF. AREA 75.247 WEIGHT 5565.141 

WINDING FORM:INS. DIM. 10.457 X 10.457 THICKNESS .156 LENGTH 48.208

Core/Coils 

27%

Other Material

30%

Labor

16%

Factory Overhead

7%

Selling Factor

20%

Figure 5.6.2 Manufacturer Selling Price Breakdown, Evaluated

Transformer from Design Line 1
5-64

 COIL SPECIFICATIONS

 -------------------

WNDG WIRE LENGTH MEAN TURNS MARGIN WT

----------------------------------------------------------------------

S1 2X 1(.0167X38.2076) AL 46.38 42.82 5.000 69.450

P1 1X 2(.0668X .2318) AL 3407.39 66.57 5.750 116.001

NUMBER OF COILS 3 TOTAL BARE CONDUCTOR WEIGHT 556.355

WNDG TURNS LO TAP HI TAP LAYRS T/L LAYR INS SEC. INS BUILD

----------------------------------------------------------------------

S1 13.0 13 1.0 1(.01000) 1(.20000) 2.805

P1 585.0 555.8 614.3 15 1.0 1(.00001) 1(.00001) 1.182

 TOTAL BUILD(%) 84.56

WNDG TAPS: TURNS( VOLTS)

----------------------------------------------------------

P1 570.4( 12158.25) 599.6( 12781.75) 614.3( 13093.50)

 DISK INFORMATION

 -----------------

WNDG DISK WIDTH VOLTS/DISK BREAK TAPS SPACE

-------------------------------------------------------

P1 42 .493 311.750 .750 2(.50) 38( .375)

WNDG INTERNAL DUCTS( 90.00) %EFF EXTERNAL DUCTS( 90.00) %EFF

----------------------------------------------------------------

S1 3 .750 X .750 IN. FULL

P1 2 .750 X .750 IN. FULL

WNDG INT. DUCT AREA EXT. DUCT AREA TOTAL DUCT AREA

---------------------------------------------------------

S1 6800.8820 1617.2770 8418.1580

P1 .0000 2519.9360 5176.6380

 ELECTRICAL ANALYSIS

 -------------------

 FULL-LOAD TAP VOLTS TEST LOAD RESIST. CURRNT

WNDG VOLTS LOW HIGH KV CURRENT @20 C. DENS. %REG

----------------------------------------------------------------------

P1 12470.00 D 11846.50 13093.50 18.0 40.735 1.56703 1402.

S1 273.07 W 4.0 1804.300 .00049 1412. 1.4

 F.L. N.L.

FLUX DENS. 16.320 16.472 LEAKAGE INDUCTANCE MHYS 45.571

CORE LOSS 4645.135 4734.112 POWER FACTOR 1.0000

COIL LOSS 19994.840 .493 IMPEDANCE % 5.76

EXCIT. VA 8824.361 9869.501 EFFICIENCY % 98.38

EXCIT. CURR. .236 .264 OPEN ALT. DUCT 3 .00

AMBIENT TEMP. 20.00 NOMINAL LENGTH 73.11

TEMP.RISE 141.46 NOMINAL DEPTH 22.49

OPERATING TEMP. 161.46 NOMINAL HEIGHT 70.06
5-65

 CRUCIFORM PLATE WIDTHS

 W1 W2 W3 W4 W5

 9.929 8.843 7.394 5.579 3.281

 STACK HEIGHTS

 H1 H2 H3 H4 H5

 3.283 1.149 .907 .725 .542

 RESULTANT GROSS AREA: 77.977 CIRCLE AREA FILL: % 90.8

 MIN. WINDING FORM INSIDE DIAMETER: 10.457

 WINDING: S1 P1 

 TEMP RISE: 141. 116.

 2

 COND. I R LOSS = 19188.2900

 COND. EDDY CURRENT LOSS = 39.0233

 OTHER STRAY LOSS = 767.5314

 K VALUE = 1.0000

TEMP. AT LOW TAP 

----------------

S1 141.46

P1 121.72

 WIRE WRAP PER COIL

WNDG THICKNESS WEIGHT

-------------------------

P1 .00600 8.72106

 o

AT REFERENCE TEMP. 170.0

----------------------------

COIL LOSS = 20441.770

IMPEDANCE % = 5.763

%LOAD %REG %EFF %IR %IX %IZ COIL LOSS TEMP. RISE

------------------------------------------------------------------------

 25 .25 98.51 .241 1.402 1.423 944.956 47.0

 35 .36 98.76 .344 1.958 1.988 1890.136 54.1

 50 .55 98.85 .514 2.794 2.841 4033.891 68.2

 65 .78 98.79 .708 3.634 3.702 7212.068 86.3

 75 .94 98.71 .852 4.196 4.282 10014.870 100.3

 100 1.44 98.38 1.275 5.612 5.755 19994.840 141.5

 125 2.08 97.91 1.805 7.048 7.275 35411.180 190.8

Table 5.6.3 provides the bill of materials that 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 non-evaluated transformer from design line 12, a 1500kVA three-phase, medium-
5-66

voltage, dry-type design with M6 core steel and an aluminum primary and secondary. The

Department generated this design using a $0.00 A and a $0.00 B.

Bill of Materials and Labor for medium voltage, dry-type, 3-phase, 1500kVA

A$ Input $0.00

B$ Input $0.00

Efficiency at 50% load 98.81%

Material item Type quantity $ each $ total

Core steel* (lb) M6-.014 5565 0.70 $ 3,895.60 $ 

Primary winding* (lb) Aluminum wire, rectangular 0.1 x 0.2, Nomex wrapped 348 2.06 $ 715.95 $ 

Secondary winding* (lb) Aluminum strip, thickness range 0.02-0.045 208 1.54 $ 321.35 $ 

Winding form & insulation* (lb) Nomex insulation 110 1 $ 1,997.39 8.11 $ 

Enclosure 12-gauge steel 1 748.06 $ 748.06 $ 

Core clamp - 1 125.00 $ 125.00 $ 

Nameplate - 1 0.65 $ 0.65 $ 

LV buss bar (ft.) - 16 12.00 $ 192.00 $ 

HV tap board - 3 9.00 $ 27.00 $ 

HV terminals - 1 135.00 $ 135.00 $ 

Winding combs (lb.) - 70 10.24 $ 717.80 $ 

Duct spacers (ft.) 1318 0.56 $ 738.24 $ 

Impregnation (gal.) - 25 17.80 $ 443.74 $ 

Misc. hardware - 1 54.00 $ 54.00 $ 

Scrap factor 1.0% 69.30 $ 

Additional scrap on core** 4.0% 155.82 $ 

Total Material Cost $ 10,336.91

Labor item hours rate $ total

Lead dressing 1.00 42.77 42.77 $ 

Inspection 0.25 42.77 10.69 $ 

Preliminary test 0.50 42.77 21.39 $ 

Final test 0.75 42.77 32.08 $ 

Packing 2.00 42.77 85.54 $ 

Enclosure manufacturing 8.00 42.77 342.16 $ 

Marking and miscellaneous 2.20 42.77 94.09 $ 

Winding the primary 23.03 42.77 985.18 $ 

Winding the secondary 2.93 42.77 125.10 $ 

Core stacking 7.94 42.77 339.73 $ 

Core assembly 6.00 42.77 256.62 $ 

Handling and Slitting Factor (on material) 1.50% 103.95 $ 

Total Labor 54.603 42.77 2,439.31 $ 

Manufacturing Cost (Material + Labor) $ 12,776.21

Factory Overhead (Materials only) 12.5% 1,292.11 $ 

Non-production Cost Markup 25.0% 3,517.08 $ 

Manufacturer Selling Price $ 17,585.41

* 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.

This bill of materials is based on non-rounded core dimensions.

Table 5.6.3 Bill of Materials for Non-Evaluated Transformer from Design Line 12
5-67

Figure 5.6.3 provides a summary of the costs contributing to the total selling price of the

non-evaluated transformer from design line 12. For this design, approximately 59 percent of the

final manufacturer selling price is direct material and scrap. Labor accounts for 14 percent of the

price and, together, the factory overhead and selling price account for 27 percent.

5.6.4 Design Details Report for Evaluated Transformer from Design Line 12

A design specification report for a 1500kVA three-phase, medium-voltage, dry-type

transformer appears below. This design incorporates M3 core steel, with copper primary and

secondary windings. The evaluation factors for this design are $0.50 A and $0.08 B. The bill of

materials and associated breakdown of costs for this design are also reported, after the design and

electrical analysis reports.

OPTIMIZED PROGRAM SERVICE

 CLEVELAND OHIO 101800

 2005- 3-12 19:22:57

STRIP CRUC 3-PHASE TYPE TRANSFORMER L12M3CUCU 

FREQUENCY 60.0 MVA RATING 1.50 @ 100.00% DUTY CYCLE

CORE 9.936" CRUC STACK 9.936 GRADE M 3 THICKNESS .0090

WINDOW: 13.354 X 50.940 EFF. AREA 74.572 WEIGHT 5550.538 

WINDING FORM:INS. DIM. 10.464 X 10.464 THICKNESS .156 LENGTH 48.940

 COIL SPECIFICATIONS

 -------------------

WNDG WIRE LENGTH MEAN TURNS MARGIN WT

----------------------------------------------------------------------

S1 2X 1(.0096X38.9404) CU 45.72 42.20 5.000 129.011

P1 1X 2(.0512X .1778) CU 3301.91 64.51 5.750 226.486

Core/Coils 

28%

Other Material

31%

Labor

14%

Factory Overhead

7%

Selling Factor

20%

Figure 5.6.3 Manufacturer Selling Price Breakdown, Non-Evaluated

Transformer from Design Line 12
5-68

NUMBER OF COILS 3 TOTAL BARE CONDUCTOR WEIGHT 1075.046

WNDG TURNS LO TAP HI TAP LAYRS T/L LAYR INS SEC. INS BUILD

----------------------------------------------------------------------

S1 13.0 13 1.0 1(.01000) 1(.20000) 2.620

P1 585.0 555.8 614.3 15 1.0 1(.00001) 1(.00001) .948

 TOTAL BUILD(%) 85.20

WNDG TAPS: TURNS( VOLTS)

----------------------------------------------------------

P1 570.4( 12158.25) 599.6( 12781.75) 614.3( 13093.50)

 DISK INFORMATION

 -----------------

WNDG DISK WIDTH VOLTS/DISK BREAK TAPS SPACE

-------------------------------------------------------

P1 42 .510 311.750 .750 2(.50) 38( .375)

WNDG INTERNAL DUCTS( 90.00) %EFF EXTERNAL DUCTS( 90.00) %EFF

----------------------------------------------------------------

S1 3 .750 X .750 IN. FULL

P1 2 .750 X .750 IN. FULL

WNDG INT. DUCT AREA EXT. DUCT AREA TOTAL DUCT AREA

---------------------------------------------------------

S1 6962.6350 1621.1610 8583.7960

P1 .0000 2516.7880 4898.1040

 ELECTRICAL ANALYSIS

 -------------------

 FULL-LOAD TAP VOLTS TEST LOAD RESIST. CURRNT

WNDG VOLTS LOW HIGH KV CURRENT @20 C. DENS. %REG

----------------------------------------------------------------------

P1 12470.00 D 11846.50 13093.50 18.0 40.680 1.51120 2286.

S1 273.23 W 4.0 1804.300 .00050 2411. 1.4

 F.L. N.L.

FLUX DENS. 16.477 16.622 LEAKAGE INDUCTANCE MHYS 44.500

CORE LOSS 3261.498 3377.035 POWER FACTOR 1.0000

COIL LOSS 19285.360 .285 IMPEDANCE % 5.61

EXCIT. VA 7133.554 7726.391 EFFICIENCY % 98.52

EXCIT. CURR. .191 .207 OPEN ALT. DUCT 3 .00

AMBIENT TEMP. 20.00 NOMINAL LENGTH 69.87

TEMP.RISE 138.10 NOMINAL DEPTH 21.58

OPERATING TEMP. 158.10 NOMINAL HEIGHT 70.81

 CRUCIFORM PLATE WIDTHS

 W1 W2 W3 W4 W5

 9.936 8.849 7.399 5.583 3.284

 STACK HEIGHTS
5-69

 H1 H2 H3 H4 H5

 3.285 1.150 .907 .726 .542

 RESULTANT GROSS AREA: 78.085 CIRCLE AREA FILL: % 90.8

 MIN. WINDING FORM INSIDE DIAMETER: 10.465

 WINDING: S1 P1 

 TEMP RISE: 138. 117.

 2

 COND. I R LOSS = 18519.0200

 COND. EDDY CURRENT LOSS = 25.5813

 OTHER STRAY LOSS = 740.7608

 K VALUE = 1.0000

TEMP. AT LOW TAP 

----------------

S1 138.10

P1 122.59

 WIRE WRAP PER COIL

WNDG THICKNESS WEIGHT

-------------------------

P1 .00600 6.62868

 o

AT REFERENCE TEMP. 170.0

----------------------------

COIL LOSS = 19877.280

IMPEDANCE % = 5.620

%LOAD %REG %EFF %IR %IX %IZ COIL LOSS TEMP. RISE

------------------------------------------------------------------------

 25 .24 98.88 .232 1.364 1.384 907.508 41.9

 35 .35 99.03 .332 1.907 1.935 1818.703 49.2

 50 .53 99.05 .497 2.723 2.768 3887.590 63.8

 65 .75 98.96 .684 3.542 3.608 6955.772 82.2

 75 .91 98.86 .823 4.091 4.173 9660.987 96.4

 100 1.39 98.52 1.231 5.473 5.610 19285.400 138.1

 125 2.00 98.05 1.742 6.873 7.090 34129.490 187.9

Table 5.6.4 provides the bill of materials that 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 an evaluated transformer from design line 12, a 1500kVA three-phase, mediumvoltage, dry-type transformer built with M3 core steel and copper primary and secondary windings. 

The Department generated this design using a $0.50 A and a $0.08 B.
5-70

Bill of Materials and Labor for medium voltage, dry-type, 3-phase, 1500kVA

A$ Input $0.50

B$ Input $0.08

Efficiency at 50% load 99.02%

Material item Type quantity $ each $ total

Core steel* (lb) M3-.009 5551 0.80 $ 4,440.43 $ 

Primary winding* (lb) Copper wire, rectangular 0.1 x 0.2, Nomex wrapped679 2.00 $ 1,361.68 $ 

Secondary winding* (lb) Copper strip, thickness range 0.02-0.045 387 2.32 $ 897.92 $ 

Winding form & insulation* (lb) Nomex insulation 110 1 $ 1,997.49 8.11 $ 

Enclosure 12-gauge steel 1 733.94 $ 733.94 $ 

Core clamp - 1 125.00 $ 125.00 $ 

Nameplate - 1 0.65 $ 0.65 $ 

LV buss bar (ft.) - 16 12.00 $ 192.00 $ 

HV tap board - 3 9.00 $ 27.00 $ 

HV terminals - 1 135.00 $ 135.00 $ 

Winding combs (lb.) - 62 10.24 $ 631.23 $ 

Duct spacers (ft.) - 1306 0.56 $ 731.11 $ 

Impregnation (gal.) - 23 17.80 $ 411.17 $ 

Misc. hardware - 1 54.00 $ 54.00 $ 

Scrap factor 1.0% 86.98 $ 

Additional scrap on core** 4.0% 177.62 $ 

Total Material Cost $ 12,003.20

Labor item hours rate $ total

Lead dressing 1.00 42.77 42.77 $ 

Inspection 0.25 42.77 10.69 $ 

Preliminary test 0.50 42.77 21.39 $ 

Final test 0.75 42.77 32.08 $ 

Packing 2.00 42.77 85.54 $ 

Enclosure manufacturing 8.00 42.77 342.16 $ 

Marking and miscellaneous 2.20 42.77 94.09 $ 

Winding the primary 23.03 42.77 985.18 $ 

Winding the secondary 2.93 42.77 125.10 $ 

Core stacking 7.95 42.77 339.97 $ 

Core assembly 6.00 42.77 256.62 $ 

Handling and Slitting Factor (on material) 1.50% 130.46 $ 

Total Labor 54.608 42.77 2,466.05 $ 

Manufacturing Cost (Material + Labor) $ 14,469.25

Factory Overhead (Materials only) 12.5% 1,500.40 $ 

Non-production Cost Markup 25.0% 3,992.41 $ 

Manufacturer Selling Price $ 19,962.07

* 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.

This bill of materials is based on non-rounded core dimensions.

Table 5.6.4 Bill of Materials for Evaluated Transformer from Design Line 12
5-71

Figure 5.6.4 provides a summary of the costs contributing to the total selling price of the

evaluated transformer from design line 12. For this design, approximately 60 percent of the final

manufacturer selling price is direct material and scrap. Labor accounts for 12 percent of the price

and, together, the factory overhead and selling price account for 28 percent.

5.7 TEAR-DOWN ANALYSIS

The Department purchased, tested, disassembled, and analyzed six transformers from design

line 7 for the engineering analysis. Although this technical support document (TSD) does not

contain analysis results for design line 7 due to passage of the Energy Policy Act of 2005, this teardown analysis is important for two reasons: 1) to demonstrate the predictive accuracy of the OPS

software, and 2) to validate the NOPR designs. The Department selected design line 7 because this

design line has the largest energy savings potential and because the representative unit (75 kVA

three-phase, low-voltage, dry-type) is readily available from wholesale distributors. This section

discusses the tear-down analysis on the six transformers and the results.

The Department purchased six transformers in early 2004—two ‘matched pairs’ from three

manufacturers. The two transformers from each manufacturer represented a low-first-cost unit and

a NEMA TP-1/Energy Star unit. The transformers were shipped directly to the testing facility,

Transformer Engineering Corporation (TEC) in Cleveland, Ohio. TEC has been a manufacturer of

custom-designed transformers, inductors, and other electro-magnetic components since 1937. TEC

has a 50,000-square-foot facility in Cleveland, which includes a top-notch testing laboratory.

Core/Coils 

33%

Other Material

27%

Labor

12%

Factory Overhead

8%

Selling Factor

20%

Figure 5.6.4 Manufacturer Selling Price Breakdown, Evaluated

Transformer from Design Line 12
5-72

The Department reviewed several manufacturer catalogues and identified matched pairs of

low-first-cost and NEMA TP-1 units. It purchased these units from a local distributor, and shipped

them to TEC for testing. In Cleveland, the transformers were subjected to the following tests:

• Core loss test

• Conductor resistance test

• Conductor loss test

• Temperature test

The Department recorded data for each of these tests, documenting all the critical

performance metrics for each of the six designs. It then carefully disassembled the transformers,

paying attention to the construction techniques, including type of steel and conductor. The

Department weighed all the pieces, and recorded physical attributes, such as core dimensions and

number of turns. It then put all of these physical dimensions into the OPS software, to model the

transformer that had just been disassembled. The OPS software used its electrical analysis program

to predict the values that had been measured in the laboratory. This step validated the predictive

capability of the software for generating performance metrics associated with its modeled designs. 

The OPS software accurately predicted the efficiency (including the core and coil losses), the

impedance, the inductance, and all the transformer performance metrics.

Once the NOPR engineering analysis designs were completed, the Department used the

results of the tear-down analysis to create a manufacturer’s selling price. In other words, using

measured variables such as the pounds of core steel and pounds of conductor, the Department costed

out the torn-down units using the same 2000–2004 average material prices and mark-ups, just as it

had done for the engineering analysis. The Department then plotted these six dots on the NOPR

manufacturer’s selling price-efficiency curve generated for design line 7. Figure 5.7.1 presents the

plot of these torn-down units. The six transformer tear-downs align perfectly with the design line 7

cost-efficiency curve.
5-73

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

94.50% 95.00% 95.50% 96.00% 96.50% 97.00% 97.50% 98.00% 98.50% 99.00% 99.50%

Efficiency at 35% load

Manfacturer Selling Price ($)

M36AlAl_bl

M19AlAl_bl

M6AlAl_bl

M6AlAl_mtt

M6AlAl_mtf

M4CuAl_mtf

M3CuCu_mtf

HOCuCu_mtf

Teardowns

TP-1: 98.0%

Manufacturer A:

Low Eff M36_bl

Manufacturer B:

Low Eff M19_bl

Manufacturer C: 

Low Eff M36_bl

Manufacturer B:

High Eff M6_bl

Manufacturer C:

High Eff M5_mt

Manufacturer A:

 High Eff M6_mt

Figure 5.7.1 Tear-down Plot Comparison, Design Line 7, 75kVA Three-phase Dry-type