1 | Building Technologies Program eere.energy.gov

NOPR Rulemaking Stage

Framework

Document

Preliminary

Analysis NOPR Final

Rule Date

Screening

Analysis

Engineering

Analysis

Energy Use and 

End-Use Load 

Characterization

Shipments

Analysis

National

Impact

Analysis

Markups for 

Equipment Price 

Determination

Life-Cycle

Cost and

Payback 

Period Analysis

Market & 

Technology 

Assessment

Manufacturer 

Impact Analysis

Compliance 

Date
2 | Building Technologies Program eere.energy.gov

Goals of the Engineering Analysis

Downstream Analyses

• Life-Cycle Cost and 

Payback Period Analysis

• National Impact Analysis

Manufacturer Selling Price –

Efficiency Relationship

Manufacturer 

Selling Price

Efficiency Level

• To evaluate design options that improve efficiency.

• To characterize manufacturer selling price (MSP) versus 

efficiency for higher-efficiency distribution transformers.
3 | Building Technologies Program eere.energy.gov

Engineering Analysis:

Methodology

 Subdivide 10 equipment class groupings into 14 design lines 

based on similar principles of design. Identify rep units. 

 Identify design option combinations to characterize the 

spectrum of possible efficiencies.

 Identify materials prices, markups, labor requirements, and 

other cost components for each design option combination.

 Use Optimized Program Service (OPS) software to model 

optimized designs based on several hundred A and B values.

 Develop efficiency levels (ELs) that span the range of 

efficiency from the baseline to the maximum technologically 

feasible.

 Scale results to other equipment classes not analyzed.

Choose Rep. 

Design Lines and 

Units

Select Higher 

Efficiency 

Design Options

Develop Cost 

Inputs

Model Optimized 

Designs Based 

on A’s and B’s

Develop ELs

Scale to 

Equipment 

Classes Not 

Analyzed
4 | Building Technologies Program eere.energy.gov

Engineering Design Lines and 

Representative Units

• Subdivide equipment classes into 14 engineering 

design lines based on similar principles of design 

and construction.

– Five liquid-immersed,

– Three LVDT, and

– Six MVDT.

• Span a range of kVA ratings for which the 0.75 

scaling rule would provide accurate results.

• Select one representative unit from each engineering 

design line.

Choose Rep. 

Design Lines and 

Units

Select Higher 

Efficiency 

Design Options

Develop Cost 

Inputs

Develop ELs

Model Optimized 

Designs Based 

on A’s and B’s

Scale to 

Equipment 

Classes Not 

Analyzed
5 | Building Technologies Program eere.energy.gov

Low Voltage, Dry Type Equipment 

Class to Design Line Mapping

Choose Rep. 

Design Lines and 

Units

Select Higher 

Efficiency 

Design Options

Develop Cost 

Inputs

Develop ELs

Model Optimized 

Designs Based 

on A’s and B’s

Scale to 

Equipment 

Classes Not 

Analyzed
6 | Building Technologies Program eere.energy.gov Equipment Class Design Line

Type of Distribution 

Transformer

kVA 

Range Representative Unit

3 6 Dry-type, low-voltage, 

single-phase 15–333

25 kVA, 150°C, single-phase, 60Hz, 

480V primary, 120/240V secondary, 

10kV BIL

4

7 Dry-type, low-voltage, 

three-phase 15–150

75 kVA, 150°C, three-phase, 60Hz, 

480V primary, 208Y/120V secondary, 

10kV BIL

8 Dry-type, low-voltage, 

three-phase 225–1000

300 kVA, 150°C, three-phase, 60Hz, 

480V Delta primary, 208Y/120V 

secondary, 10kV BIL

Low-Voltage, Dry-Type Design Lines 

and Representative Units
7 | Building Technologies Program eere.energy.gov

Identify Transformer Design Option 

Combinations

• Select design option combinations.

– Vary core configurations, core steels, and winding materials.

– Capture most common designs and maximum efficiency.

Choose Rep. 

Design Lines and 

Units

Select Higher 

Efficiency 

Design Options

Develop Cost 

Inputs

Develop ELs

Model Optimized 

Designs Based 

on A’s and B’s

Design Option Designs Considered

Core Configuration 

(Type)

Wound core distributed gap;

Stacked butt-lap;

Stacked full miter;

Step-lap miter;

Stacked cruciform miter.

Core Configuration 

(Construction)

1-Phase: Shell and Core type.

3-Phase: 3-legged, 5-legged and Symmetric Core.

Core Steels

Silicon steel: M12, M6, M5, M4, M3, M2.

Domain refined silicon steel: H-0 DR (dry-type), 

ZDMH (liquid-immersed).

Amorphous steel: SA1 (Dry-type and Liquid)

Winding materials Copper;

Aluminum.

Scale to 

Equipment 

Classes Not 

Analyzed
8 | Building Technologies Program eere.energy.gov

Identify Transformer Design Option 

Combinations (Continued)

Design 

Option

Core 

Material

Conductor 

Primary

Conductor 

Secondary

Core/Coil Design 

Type

1 M12 Al Al 3-leg stacked butt-lap

2 M12 Cu Al 3-leg stacked butt-lap

3 M6 Al Al 3-leg stacked butt-lap

4 M6 Al Al 3-leg stacked full miter

5 M4 Cu Al 3-leg stacked full miter

6 M3 Al Al 3-leg stacked full miter

7 M3 Al Al 3-leg step-lap miter

8 M3 Al Al 3-leg distributed gap core

9 H-0 DR Al Al 3-leg stacked full miter

10 H-0 DR Al Al 3-leg step-lap miter

11 ZDMH Al Al 3-leg distributed gap core

12 H-0 DR Cu Cu 3-leg stacked full miter

13 SA1 Al Al 5-leg distributed gap core

14 SA1 Cu Cu 5-leg distributed gap core

Choose Rep. 

Design Lines and 

Units

Select Higher 

Efficiency 

Design Options

Develop Cost 

Inputs

Develop ELs

Model Optimized 

Designs Based 

on A’s and B’s

Example of Design Option Combinations Analyzed

DL7: 75 kVA low-voltage dry-type, three-phase.

Scale to 

Equipment 

Classes Not 

Analyzed
9 | Building Technologies Program eere.energy.gov

Engineering Analysis:

Markups and Labor Rate

• DOE determined materials prices and labor requirements 

through conversations with manufacturers and experts.

• DOE determined markups and labor rates from census 

data, SEC filings, and manufacturer interviews.

Choose Rep. 

Design Lines and 

Units

Select Higher 

Efficiency 

Design Options

Develop Cost 

Inputs

Develop ELs

Model Optimized 

Designs Based 

on A’s and B’s

Markup / Cost Input Markup Notes

Scrap and handling

2.5 % Standard scrap and handling; applied to 

materials

1.5 % Prefabricated amorphous cores

4.0 % Additional scrap on fully mitered cores

Factory overhead 12.5 % Applied to materials

Shipping $ 0.28 /

pound

Added prior to profit markup; Approximately 

4–8% of MSP

Fully-burdened hourly 

labor rate $ 51.52 Applied to total labor hours

Non-production 25 % Applied to total cost for SG&A, R&D, 

warranty/risk provisions, and profit factor

Scale to 

Equipment 

Classes Not 

Analyzed
10 | Building Technologies Program eere.energy.gov

Engineering Analysis:

Modeling Optimized Designs

• Optimized Program Service (OPS) software conducts 

design runs.

• As an input to the OPS software, economic parameters 

(A and B values) are varied to simulate a range of 

customer orders, creating a database of transformer 

designs.

• Approximately 2,500 unique designs for each of the 

fourteen representative units within each of the fourteen 

design lines.

Choose Rep. 

Design Lines and 

Units

Select Higher 

Efficiency 

Design Options

Develop Cost 

Inputs

Develop ELs

Model Optimized 

Designs Based 

on A’s and B’s

Scale to 

Equipment 

Classes Not 

Analyzed
11 | Building Technologies Program eere.energy.gov

Engineering Analysis:

Modeling Optimized Designs

• OPS design software output includes:

– Construction and winding instructions for the core and coil 

(e.g., core dimensions, high- and low-voltage windings, tap 

locations, insulation, cooling ducts, and labor).

– Bill of materials and electrical analysis report.

• Material, labor costs and markups are combined to 

determine the manufacturer’s selling price (MSP).

• Temperature-corrected efficiency determined from OPS 

software electrical analysis report.

Choose Rep. 

Design Lines and 

Units

Select Higher 

Efficiency 

Design Options

Develop Cost 

Inputs

Develop ELs

Model Optimized 

Designs Based 

on A’s and B’s

Scale to 

Equipment 

Classes Not 

Analyzed
12 | Building Technologies Program eere.energy.gov

• DOE was unable to identify a company that could model 

symmetric core designs.

• DOE gathered information on symmetric cores through 

manufacturer interviews, published literature, and limited 

designs provided by manufacturers.

– Using these data sources, DOE roughly estimated the costefficiency relationship of symmetric core designs.

• DOE did receive limited design data from manufacturers of 

symmetric core transformers, and may issue some analysis 

to the extent that it is able.

Engineering Analysis:

Symmetric Core Designs

Choose Rep. 

Design Lines and 

Units

Select Higher 

Efficiency 

Design Options

Develop Cost 

Inputs

Develop ELs

Model Optimized 

Designs Based 

on A’s and B’s

Scale to 

Equipment 

Classes Not 

Analyzed
13 | Building Technologies Program eere.energy.gov

Engineering Analysis:

Develop efficiency Levels

• DOE identified efficiency levels (ELs) that span the range of 

distribution transformer efficiencies from the baseline to the 

maximum technologically feasible efficiency.

• Factors DOE considered in setting ELs:

Choose Rep. 

Design Lines and 

Units

Select Higher 

Efficiency 

Design Options

Develop Cost 

Inputs

Develop ELs

Model Optimized 

Designs Based 

on A’s and B’s

Benchmark efficiency levels (e.g., NEMA Premium)

Equally spaced efficiency increments

Harmonization across single-phase and the per-phase 

kVA equivalent three-phase design lines.

Scale to 

Equipment 

Classes Not 

Analyzed
14 | Building Technologies Program eere.energy.gov

Engineering Analysis:

Modeled Designs from DL1

Rep Unit from DL1: 50 kVA liquid-immersed, single-phase, pad-mounted

$1,500 

$2,000 

$2,500 

$3,000 

$3,500 

$4,000 

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

Manufacturer Selling Price ($)

Efficiency at 50% Load, Temperature Corrected

M5_CuAl_dgw_sh

M3_AlAl_dgw_sh

M3_CuAl_dgw_sh

M2_AlAl_dgw_sh

M2_CuAl_dgw_sh

ZDMH_AlAl_dgw_sh

ZDMH_CuCu_dgw_sh

SA1_AlAl_dgw_sh

SA1_CuCu_dgw_sh

CSLs

CSL 0 CSL 1 CSL 2 CSL 3 CSL 4 CSL 5 CSL 6
15 | Building Technologies Program eere.energy.gov

Developing Trial Standard Levels for 

the NOPR

• If DOE issues a NOPR, it will select trial standard levels 

(TSLs) based on groupings of ELs, such as:

– Per-phase harmonization, minimum LCC, and maximum NPV.

• These TSLs may consider any interaction between 

equipment classes.

• DOE will select its proposed standard level in the NOPR 

from the list of TSLs developed.

Choose Rep. 

Design Lines and 

Units

Select Higher 

Efficiency 

Design Options

Develop Cost 

Inputs

Develop ELs

Model Optimized 

Designs Based 

on A’s and B’s

Scale to 

Equipment 

Classes Not 

Analyzed
16 | Building Technologies Program eere.energy.gov

Engineering Analysis:

Scaling Results

• DOE scaled the total losses (TL) from a representative unit 

to other unanalyzed kVA ratings (S) within a design line 

using the 0.75 Scaling Rule:

TL1 = TL0 x (S1 / S0)0.75

• Costs of construction and losses can be scaled when 

design parameters are held constant, including:

– frequency, magnetic flux density, current density and 

insulation level.

Choose Rep. 

Design Lines and 

Units

Select Higher 

Efficiency 

Design Options

Develop Cost 

Inputs

Develop ELs

Model Optimized 

Designs Based 

on A’s and B’s

Design Line 7 (LVDT, 3-phase, 15 – 150 kVA): 

75 kVA Representative Unit

15

kVA

30

kVA

45

kVA

75

kVA

112.5

kVA

150

kVA

 Scale Results

Scale to 

Equipment 

Classes Not 

Analyzed
17 | Building Technologies Program eere.energy.gov
18 | Building Technologies Program eere.energy.gov

Backup Slides

Backup Slides
19 | Building Technologies Program eere.energy.gov

Liquid-Immersed Equipment Class to 

Design Line Mapping

Rectangular Round

Tank Tank

10

15

25

37.5

50

75

100

167

250

333

500

667

833

Equipment Class 1

Liquid-Immersed,

Single-Phase

kVA

DL 1DL 2 DL 3

Rep Unit

Rep Unit

Rep Unit

Design

Lines

15

30

45

75

112.5

150

225

300

500

750

1000

1500

2000

2500

Equipment Class 2

Liquid-Immersed,

Three-Phase

kVA

DL 4 DL 5

Rep Unit

Rep Unit

Choose Rep. 

Design Lines and 

Units

Select Higher 

Efficiency 

Design Options

Develop Cost 

Inputs

Develop ELs

Scale to 

Equipment 

Classes Not 

Analyzed

Model Optimized 

Designs Based 

on A’s and B’s
20 | Building Technologies Program eere.energy.gov

Low-Voltage Dry-Type Equipment 

Class to Design Line Mapping

kVA Design Line

15

25

37.5

50

75

100

167

250

333

Equipment Class 3

Dry-Type, Low Voltage,

Single-Phase

 

 

DL 6

Rep Unit

kVA Design Line

15

30

45

75

112.5

150

225

300

500

750

1000

 

 

Equipment Class 4

Dry-Type, Low Voltage,

Three-Phase

Rep Unit

DL 7 DL 8

Rep Unit

Choose Rep. 

Design Lines and 

Units

Select Higher 

Efficiency 

Design Options

Develop Cost 

Inputs

Develop ELs

Scale to 

Equipment 

Classes Not 

Analyzed

Model Optimized 

Designs Based 

on A’s and B’s
21 | Building Technologies Program eere.energy.gov

Medium-Voltage Dry-Type Equipment 

Class to Design Line Mapping

Choose Rep. 

Design Lines and 

Units

Select Higher 

Efficiency 

Design Options

Develop Cost 

Inputs

Develop ELs

Scale to 

Equipment 

Classes Not 

Analyzed

Model Optimized 

Designs Based 

on A’s and B’s

EC 6 EC 8 EC 10

20-45kV 46-95kV >96kV

15 -

30 -

45 -

75 -

112.5 -

150 -

225

300

500

750

1000

1500

2000

2500

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

DL 13 (A & B)

Rep Unit

Rep Unit

Rep Unit

Rep Unit

Rep Unit

Rep Unit
22 | Building Technologies Program eere.energy.gov Equipment Class Design LineType of Distribution 

Transformer

kVA

Range Representative Unit

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

Liquid-Immersed Design Lines and 

Representative Units
23 | Building Technologies Program eere.energy.gov

Liquid-Immersed Design Lines and 

Representative Units Equipment Class Design LineType of Distribution 

Transformer

kVA

Range Representative Unit

2

4 Liquid-immersed, 

three-phase 15–500

150 kVA, 65°C, three-phase, 60Hz, 

12470Y/7200V primary, 208Y/120V 

secondary

5 Liquid-immersed, 

three-phase 750–2500

1500 kVA, 65°C, three-phase, 60Hz, 

24940GrdY/14400V primary, 

480Y/277V secondary
24 | Building Technologies Program eere.energy.gov

Low-Voltage Dry-Type Design Lines 

and Representative Units Equipment Class Design LineType of Distribution 

Transformer

kVA

Range Representative Unit

3 6 Dry-type, low-voltage, 

single-phase 15–333

25 kVA, 150°C, single-phase, 60Hz, 

480V primary, 120/240V secondary, 

10kV BIL

4

7 Dry-type, low-voltage, 

three-phase 15–150

75 kVA, 150°C, three-phase, 60Hz, 

480V primary, 208Y/120V secondary, 

10kV BIL

8 Dry-type, low-voltage, 

three-phase 225–1000

300 kVA, 150°C, three-phase, 60Hz, 

480V Delta primary, 208Y/120V 

secondary, 10kV BIL
25 | Building Technologies Program eere.energy.gov

Medium-Voltage Dry-Type Design 

Lines and Representative Units Equipment Class Design LineType of Distribution 

Transformer

kVA

Range Representative Unit

6

9

Dry-type, mediumvoltage, three-phase, 20-

45kV BIL

15–500 300 kVA, 150°C, three-phase, 60Hz, 4160V 

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

10

Dry-type, mediumvoltage, three-phase, 20-

45kV BIL

750–2500 1500 kVA, 150°C, three-phase, 60Hz, 4160V 

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

8

11

Dry-type, mediumvoltage, three-phase, 46-

95kV BIL

15–500 300 kVA, 150°C, three-phase, 60Hz, 12470V 

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

12

Dry-type, mediumvoltage, three-phase, 46-

95kV BIL

750–2500 1500 kVA, 150°C, three-phase, 60Hz, 12470V 

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

10 13 (A 

& B)

Dry-type, mediumvoltage, three-phase, 96-

150kV BIL

225–2500

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

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

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

primary, 480Y/277V secondary, 125kV BIL
26 | Building Technologies Program eere.energy.gov

Engineering Analysis: Materials 

Prices for Core Steels

Material Units 2010 Price

[2010$]

2006 Price

[2010$]

2008 Price

[2010$]

M12 core steel $/lb 1.03 0.85 1.60

M6 core steel $/lb 1.46 0.94 2.19

M5 core steel $/lb 1.51 0.99 2.24

M4 core steel $/lb 1.59 1.03 2.30

M3 core steel $/lb 1.88 1.06 2.60

M3 core steel (Lite Carlite) $/lb 1.95 1.47 2.44

M2 core steel $/lb 2.00 1.32 2.79

M2 core steel (Lite Carlite) $/lb 2.10 1.58 2.63

ZDMH (mechanically-scribed core steel) $/lb 2.05 1.41 3.22

H-0 DR core steel (laser scribed) $/lb 2.06 1.41 3.23

SA1 (amorphous) finished core, volume 

production $/lb 2.38 1.72 3.64
27 | Building Technologies Program eere.energy.gov

Engineering Analysis: Materials Prices for 

Liquid-Immersed Design Lines

Material Units 2010 Price

[2010$]

2006 Price

[2010$]

2008 Price

[2010$]

Copper wire, formvar, round #10-20 $/lb 4.87 3.33 5.97

Copper wire, enameled, round #7-10 $/lb 4.84 3.31 5.93

Copper wire, enameled, rectangular sizes $/lb 4.97 3.41 6.09

Aluminum wire, formvar, round #9-17 $/lb 3.07 2.30 3.91

Aluminum wire, formvar, round #7-10 $/lb 2.57 1.93 3.28

Copper strip, thickness range 0.02-0.045 $/lb 4.97 3.41 6.09

Copper strip, thickness range 0.030-0.060 $/lb 4.97 3.41 6.09

Aluminum strip, thickness range 0.02-0.045 $/lb 2.08 1.56 2.67

Aluminum strip, thickness range 0.045-0.080 $/lb 2.08 1.56 2.67

Kraft insulating paper with diamond adhesive $/lb 1.52 1.17 1.93

Mineral oil $/gal 3.35 1.94 3.84

Tank Steel $/lb 0.38 0.32 0.60

Conductor and Miscellaneous Prices
28 | Building Technologies Program eere.energy.gov

Engineering Analysis: Materials 

Prices for Dry-Type Design Lines

Material Units 2010 Price

[2010$]

2006 Price

[2010$]

2008 Price

[2010$]

Copper wire, rectangular 0.1 x 0.2, Nomex

wrapped $/lb 4.52 3.07 5.53

Aluminum wire, rectangular 0.1 x 0.2, Nomex

wrapped $/lb 2.97 2.23 3.78

Copper strip, thickness range 0.02-0.045 $/lb 4.97 3.41 6.09

Aluminum strip, thickness range 0.02-0.045 $/lb 2.08 1.56 2.67

Nomex insulation $/lb 24.50 13.72 29.03

Cequin insulation $/lb 5.53 3.84 6.09

Impregnation $/gal 22.55 17.16 27.31

Winding combs $/lb 12.34 6.08 15.41

Enclosure Steel $/lb 0.38 0.32 0.60

Conductor and Miscellaneous Prices
29 | Building Technologies Program eere.energy.gov

Developing Trial Standard Levels for 

the NOPR

Choose Rep. 

Design Lines and 

Units

Select Higher 

Efficiency 

Design Options

Develop Cost 

Inputs

Develop ELs

Model Optimized 

Designs Based 

on A’s and B’s

Scale to 

Equipment 

Classes Not 

Analyzed

• Illustration of how TSLs are selected based on groupings of 

ELs:

– Combine liquid-immersed design lines using maximum EL 

available that does not use amorphous metal.

Design Line EL

1 2

2 2

3 3

4 2

5 2

TSL 1
30 | Building Technologies Program eere.energy.gov

NOPR Rulemaking Stage

Framework

Document

Preliminary

Analysis NOPR Final

Rule Date

Screening

Analysis

Engineering

Analysis

Energy Use and 

End-Use Load 

Characterization

Shipments

Analysis

National

Impact

Analysis

Markups for 

Equipment Price 

Determination

Life-Cycle

Cost and

Payback 

Period Analysis

Market & 

Technology 

Assessment

Preliminary 

Manufacturer 

Impact Analysis

Compliance 

Date
31 | Building Technologies Program eere.energy.gov

Purpose

• Market and Technology Assessment

– Characterize the distribution transformer market and industry.

– Identify the technology options to improve distribution transformer 

efficiency.

– Establish equipment classes.

• Screening Analysis

– Screen out technology options that DOE will not consider in the 

engineering analysis for distribution transformers based on several criteria.
32 | Building Technologies Program eere.energy.gov

Relationship of Market and Technology 

Assessment to Other Analyses

Market and Technology 

Assessment Equipment Classes

Technology options to improve efficiency

Screening Analysis

Design options to improve efficiency

Engineering Analysis
33 | Building Technologies Program eere.energy.gov

Equipment Classes

• DOE divides covered equipment into classes by:

– The Type of energy used,

– The Capacity, or

– Any performance-related features that affect consumer utility or 

efficiency.

• DOE considered 10 equipment class groupings by dividing the 

population of distribution transformers based upon:

– Type of transformer insulation: liquid-immersed or dry-type,

– Number of phases: single or three,

– Voltage class: low or medium (for dry-type units only), and

– Basic impulse insulation level (BIL): (for MVDT units only).
34 | Building Technologies Program eere.energy.gov

Distribution Transformers 

Equipment Class Groupings

There are 115 discrete kVA ratings across the ten equipment class groupings (ECG)

ECG Insulation Phases Voltage BIL kVA Range

1 Liquid-Immersed Single Medium --- 10-833 kVA

2 Liquid-Immersed Three Medium --- 15-2500 kVA

3 Dry-Type Single Low --- 15-333 kVA

4 Dry-Type Three Low --- 15-1000 kVA

5 Dry-Type Single Medium 20-45 kV BIL 15-833 kVA

6 Dry-Type Three Medium 20-45 kV BIL 15-2500 kVA

7 Dry-Type Single Medium 46-95 kV BIL 15-833 kVA

8 Dry-Type Three Medium 46-95 kV BIL 15-2500 kVA

9 Dry-Type Single Medium >96 kV BIL 75-833 kVA

10 Dry-Type Three Medium >96 kV BIL 225-2500 kVA
35 | Building Technologies Program eere.energy.gov

Distribution Transformers

2009 Industry Shipments

Equipment Class Grouping Units 

Shipped

MVA 

Capacity 

Shipped

1. Liquid-immersed, medium-voltage, single-phase 683,726 21,994

2. Liquid-immersed, medium-voltage, three-phase 49,739 32,266

3. Dry-type, low-voltage, single-phase 17,740 647

4. Dry-type, low-voltage, three-phase 206,929 15,778

5. Dry-type, medium-voltage, single-phase, 20-45 kV BIL 709 23

6. Dry-type, medium-voltage, three-phase, 20-45 kV BIL 522 257

7. Dry-type, medium-voltage, single-phase, 46-95 kV BIL 546 23

8. Dry-type, medium-voltage, three-phase, 46-95 kV BIL 2,074 3,655

9. Dry-type, medium-voltage, single-phase, ≥ 96 kV BIL 202 9

10. Dry-type, medium-voltage, three-phase, ≥ 96 kV BIL 1,286 2,206

TOTAL 963,473 76,858
36 | Building Technologies Program eere.energy.gov

Technology Options

Technology Option Material / Concept

 Conductor Materials for Coils

 Aluminum (wire and sheet)

 Copper (wire and sheet)

 Core Materials

 Cold-Rolled High Silicon (CRHiSi) Steel

 CRHiSi Domain-Refined Steels

 Amorphous Materials in Wound Core

 Geometry Modifications Adjust the cross-sectional area of the 

 core/conductor, or adjust volts per turn

 Symmetric Core Designs Continuously wound cores with 120 degree

 radial symmetry for three-phase designs

 Core Deactivation Technology

 A transformer is replaced by three smaller 

 transformers that are (de)activated in 

 response to changes in load demand.
37 | Building Technologies Program eere.energy.gov

• “Symmetric Core” designs are three-phase 

designs that use a continuously wound 

core with 120° radial symmetry.

• Advantages include lowered: weight, 

volume, no-load losses, noise, vibration, 

stray magnetic fields, inrush current, and 

power in the third harmonic.

• Best suited for delta-delta or delta-wye 

connections, though zero-sequence fluxes 

associated with wye-wye connections can 

be mitigated by a delta-connected tertiary 

winding.

Technology Assessment:

Symmetric Core Designs

Source: Lundmark, Sonja. “Computer Model of 

Electromagnetic Phenomena in Hexaformer.” 2007. 

http://www.hexaformer.com/ExternaDokument/chalmers_re

port1.pdf.
38 | Building Technologies Program eere.energy.gov

• Reduces core losses by using a system of smaller transformers to 

replace a single, larger transformer.

– Example: Three 25 kVA transformers in parallel replace a 75 kVA 

transformer.

• Control unit can activate and deactivate component transformers 

depending on the loading demands.

– Optimizes combination of transformers at given load.

• DOE is only aware of this technology in LVDT distribution 

transformers.

– Medium-voltage core deactivation systems have not been produced 

commercially, and pose difficulties for switching within the primary and 

secondary connections.

• Best suited for applications with low loading demands.

Technology Assessment:

Core Deactivation Technology
39 | Building Technologies Program eere.energy.gov

Core Deactivation Technology

Load vs. Efficiency

This figure is for illustrative purposes only, and is not based on actual 

DOE research

93

94

95

96

97

98

99

5 15 25 35 45 55 65 75 85 95

Efficiency %

Percentage of Full Rated Load

Core Deactivation System

Traditional Transformer Design

Test Procedure Loading
40 | Building Technologies Program eere.energy.gov

• While core deactivation technology could save energy over a load 

cycle, these energy savings may not be captured by the current test 

procedure specifying a single load factor.

• A weighted-average loss calculation using various loadings could 

better capture this technology’s energy savings potential.

Example:

Technology Assessment:

Core Deactivation Technology

Loading 

(%)

Losses 

(W)

Single Loading Point,

Load Frequency (%)

Weighted Average,

Load Frequency (%)

0 200.0 0 31

15 222.5 0 22

35 322.5 100 20

50 450.0 0 18

75 762.5 0 9

Average Losses 322.5 322.5
41 | Building Technologies Program eere.energy.gov

• DOE is not considering core deactivation technology in the context of 

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

– Scale each design to 1/3 its kVA and group them in sets of three.

– Account for additional cost and weight of the core deactivation technology.

– Analyze each core deactivation system using various loading scenarios.

• Core deactivation systems using non-identical component transformers.

– Each component transformer requires a similar winding design to maintain 

impedance at each loading.

• Based on conversations with manufacturers, core deactivation with 

MVDT has additional challenges.

Technology Assessment:

Core Deactivation Technology
42 | Building Technologies Program eere.energy.gov

Screening Analysis

Impacts on health or safety

Adverse impacts on equipment utility or availability to 

consumers

Practicability to manufacture, install, and service

Technological feasibility

Purpose

• Screen out technology options that DOE will not consider in the 

engineering analysis for distribution transformers.

Approach

• DOE will evaluate each technology option based on the following criteria:
43 | Building Technologies Program eere.energy.gov

Technology Options Screened 

Out of the Analysis

Technology Option Excluded Screening Criteria

Silver as a Conductor Material Practicability to manufacture, install, and service

High-Temperature 

Superconductors

Technological feasibility; 

Practicability to manufacture, install, and service

Amorphous Core Material in 

Stacked Core Configuration

Technological feasibility; 

Practicability to manufacture, install, and service

Carbon Composite Materials 

for Heat Removal Technological feasibility

High-Temperature Insulating 

Material Technological feasibility

Solid-State (Power Electronics) 

Technology

Technological feasibility;

Practicability to manufacture, install, and 

service.

Nanotechnology Composites Technological feasibility
44 | Building Technologies Program eere.energy.gov

• DOE may make available detailed design information for 

certain design lines and efficiency levels to allow 

manufacturers to compare with designs of their own.

• DOE may invite manufacturers to submit similar design 

information for their own designs. Such information, if 

submitted to a Department contractor, would be kept in 

confidence.

Engineering Validation