To: D

Distrib

Energ

Subje

Dear 

This a

Stake

accur

docum

be us

websi

1

2

3

4

5

A

DOE Stakeho

bution Transfo

gy Efficiency D

 

 

 

 

ect: DOE Dist

Stakeholder: 

analysis of Dis

eholders who 

rate analysis a

ments. It is my

eful. I will po

ite for all inter

. Introductio

. Reference

. Analysis 

. Conclusion

. Recomme

A. Introduc

In 2007, I w

to address

Departmen

A very larg

Meetings. 

manufactu

analyzed a

IEEE Tran

Transform

Proposals.

I am not a 

findings in 

energy effi

Regardles

any of the 

the team. 

I have exa

recognize 

application

reasonable

Standards

lders for 

ormer 

Determination

tribution Tran

stribution Tra

have request

and recomme

y suspect tha

ost a word ver

rested parties

on 

es 

ns 

ndations 

ction 

was elected t

s Stakeholder

nt Of Energy 

ge task force 

 This task for

urers, users a

and reported a

sformers Com

ers Subcomm

.

stakeholder b

this report ar

iciencies for M

s of the efficie

stakeholders

amined distrib

the difficulty o

ns. However,

e selection fo

. 

n 

sformer Load

ansformer Loa

ted that I prov

endations bas

at a multiplicity

rsion on my IE

s to access. T

o be Chairma

rs’ concerns a

(DOE) regula

now meets re

rce now has a

nd other inter

at each meet

mmittee’s site

mittee, Task F

but will gladly

re understood

Medium Volta

ency levels th

s, this attempt

ution transfor

of finding a on

 several type

r use in settin

ding Study 

ading was pro

vide insight. M

sed on my pe

y of stakehold

EEE Transfor

The following 

an of an IEEE

and issues wit

ations for Dist

egularly at eac

about 100 me

rested parties

ing with minu

e at www.tran

Force for Rev

y participate w

d by those wh

age and Low V

hat are selecte

t to display fac

rmer loading f

ne shoe fits a

s of informati

ng Distribution

3704

Char

Octob

Ph

Fx

Cell

phop

www

ompted by the

My objective 

rsonal experi

ders may find

rmers Commi

topics will be

E Transformer

th current and

tribution Trans

ch of the IEE

embers and is

s. Data is reg

utes and prese

sformerscom

iew of DOE E

where needed

ho will be sele

Voltage Distri

ed and of any

ctual informa

from 1992 thr

all approach fo

on have been

n Transforme

 High Ridge R

lotte, NC 282

ber 9, 2011 

704-846-3

704-845-2

704-236-3

pkinson@hvol

.hvolt.com

e interest of a

is to provide 

ence and oth

d this analysis

ttee DOE Ene

e addressed: 

rs Committee

d proposed ch

sformer Ener

E Transforme

s composed o

gularly accum

entations pos

mmittee.org , D

Energy Efficie

d to be sure th

ecting the nex

ibution Transf

y predisposed

tion should p

rough presen

or all transfor

n available to

er Energy Effic

Rd 

270 

3290 

2520 

3320 

t.com

a number of 

unfiltered 

her backgroun

s and report to

ergy Efficienc

e Task Force 

hanges to the

rgy Efficiency

ers Committe

of 

ulated, 

sted on the 

Distribution 

ency 

hat the 

xt round of 

formers. 

d positions of

rove useful to

t and 

rmer 

 make a 

ciency 

1

nd 

o

cy 

e

. 

e 

f

o
2

B. References: 

1. FERC Form 1 Data 

2. Electric Utility Total Owning Cost history 

3. NEMA TP-1 from 2002 and from 1996 

4. Distribution Transformer Size Optimization by Forecasting Customer Load by Jerrod 

Luze, Black Hills Power, Rapid City, South Dakota. 

5. DOE Chapter 6 Energy Use and End Use Load Characterization. 

6. ABB Total Ownership Cost (TOC) Calculator 

7. Loading Study of a Manufacturing Plant by Philip J Hopkinson, PE (1995 and 2005) 

8. Boston NEMA TP-1 Background (1995) 

9. Optimizing Energy Efficiency Standards for Low Voltage Distribution Transformers a 

thesis by Ken Harden of Schneider Electric at Purdue University 

10. NEETRAC Distribution Transformer Thermal Test Procedure from May 29, 2002 

11. My experience as a distribution transformer design engineer from 1966-2011 

 

C. Scope 

1. Medium Voltage Liquid Filled Distribution Transformers 

2. Medium Voltage Dry Type Distribution Transformers 

3. Low Voltage Dry Type Transformers. 

D. Assumptions 

1. Transformers always remain energized and core loss (no load loss) is always 

occurring. 

2. Transformer winding losses along with strays and eddies vary with the square of load 

current. 

3. Historical no load and load loss relationships may be a significant indication for future 

decisions. 

4. For all load considerations, peak transformer efficiency always occurs at the point 

where no load losses equal load losses. 

5. Highest transformer losses occur at the highest permissible load. Hence differences 

in alternative transformer efficiencies at the highest load have greater impact on total 

watt losses. 

6. Electric Utility Total Owning Cost (A and B factors) is representative of both the value 

of a watt saved and of their loading models. 

7. Load cycles vary by regions of the country, by seasons of the year and by time of 

day. 

8. RMS equivalent load is most representative of the watt losses that are being 

dissipated in the transformer in service. 

9. Routine tests at a manufacturer’s production facility should be converted to expected 

RMS equivalent load to verify the efficiency that will be most representative of the inservice condition. 

10. The DOE measurement point for efficiency will normally occur at the most 

representative RMS equivalent load, which may or may not be equal to the point of 

peak efficiency where core loss equals load loss. However the transformer is usually 

most optimally designed for lowest cost when the measurement point occurs at the 

point of peak efficiency. 

E. A look at the 25 kVA single phase pole type transformer 

1. The 25 kVA pole type transformer has been the most representative kVA rating for 

pole type transformers for many decades of time. 
3

2. Many of the relationships for the 25 kVA transformer apply broadly to other medium 

voltage transformers, such as Total Owning Cost relationships and loss ratios. 

3. During the 1960’s the 25 kVA transformer normally had 100 watts of core loss and 

300 watts of load loss. 

4. During the 1970’s Total Owning Cost relationships were introduced with two factors, 

called A and B. The A factor was the present worth of a watt saved and was 

measured in $ / watt. The B factor was applied to adjust full load winding loss to the 

value of load loss that is most representative of the normal expected operating 

condition, or the RMS equivalent load in service. Mathematically, the following is a 

good way to visualize B: 

B= (PU Load)^2 * A (1) 

Where PU load is the per unit load of the transformer. 

Here, if PU Load is 0.5 then B becomes: 

B at 0.5 load = 0.5^2 * A = 0.25 * A (2) 

5. In practice, the B factor is usually slightly greater than the square of per unit load 

times A to recognize the value associated with peak demand. By increasing B 

slightly, the transformer will have sufficiently low load losses as to maintain a 

relatively flat efficiency over wide changes in load. This is important because loading 

can vary significantly and even exceed transformer rated kVA. If the transformer 

efficiency deteriorates excessively at high load then the peak demand may result in 

higher net cost to serve the load. 

6. Total Owning cost formulas initially focused on an A factor of $3/watt and a B factor 

of $1/watt and remained in that range from the 1970’s to the mid 1980’s. 

7. During the 1980’s and 1990’s wide variations of loss evaluations occurred with A 

factors varying from a low of under a dollar to as high as $10/watt. Interestingly the B 

factors remained mostly in a range of 0.2-0.3 * A. 

8. In 1996, NEMA introduced TP-1, but derived from the relationship of a B factor = 0.25 

A. Many manufacturers were solicited to supply design data that became the basis 

for the published efficiencies. 

9. In 2007, the DOE published new mandatory efficiency values that became effective 

in 2010 that assumed an RMS equivalent load of 50% of nameplate. Manufacturers 

report that the same efficiencies may be reached by using TOC methods with an A 

factor of $4/watt and a B factor of $1/watt. 

10. In 2011, many Utilities purchase transformers that just meet the DOE published 

efficiencies however some Utilities purchase transformers to a TOC owning cost 

formula that reaches beyond the DOE requirements. The most common TOC 

formula for premium efficiencies is: 

a. A = $5.91/watt 

b. B = $1.81/watt 

11. For any TOC relationship the RMS equivalent load is simply: 

RMS equivalent load = (B/A)^0.5 (3) 

12. Recall that in the 1960’s the 25 kVA no load watts were 100 and the load watts were 

300. Hence the assumed per unit load was: 

PU load in the 1960’s = (100/300)^0.5 = 0.58 (4) 

13. From the 1970’s to the mid 1980’s the assumed per unit load remained unchanged 

14. During the 1980’s to 2000, some owning cost formulas had a B that was 0.25 A 

hence: PU load in the 2000-2011 period has ranged from 0.5-0.58 for all popular 

owning cost formulas. 
F. Other Lo

1. The FE

total ki

relatio

namep

as sea

load d

it is in 

losses

50% o

2. Phil Ho

power 

transfo

ground

harmo

3. Typica

N

M

H

w

th

e

h

4. A Loo

oading relatio

ERC 1 report 

ilowatt-hours 

nship the sim

plate. Howev

asonal periods

oes not meas

its normal se

s that are pres

of nameplate. 

opkinson mad

to a manufac

ormers were m

ded wye conn

onics and mak

al load cycles 

Note that load

Mississippi Po

However, for 5

where the spe

hat occurs, an

xpenditures b

ighest loading

. 

ok at Low Vol

onships

shows total i

of sales of el

mple average l

ver, this includ

s where loadi

sure the losse

rvice. RMS e

sent over long

de a study of 

cturing plant. 

measured as 

nected transfo

king a path fo

are as shown

ing can be qu

ower and Flor

50% RMS equ

cific individua

ny peaks in lo

by the Utility t

g periods. 

ltage Transfo

nstalled capa

ectricity throu

load would ap

des many time

ing may be ei

es that are be

equivalent loa

g periods. Th

the loads on 

 The RMS eq

50% of name

ormers do a w

r zero sequen

n below: 

uite variable a

ida Power ca

uivalent load,

al loads are n

oading may re

to account for

ormers 

acity of distrib

ughout the Un

ppear to be a

es of light loa

ither light or h

eing dissipated

ad is a true m

he RMS equiv

typical indust

quivalent load

eplate. There

wonderful job 

nce currents. 

as a function o

ses or flatter 

, each profile 

ormalized. In

esult in additio

r generation r

bution transfor

nited States. 

 little more th

ad such as at 

heavy. The s

d by the trans

easure of the

valent load is 

trial transform

d to the liquid 

e he also lear

of absorbing 

of time of day

as in the com

is replaced b

n spite of the 

onal peak dem

requirements 

rmers and 

From this 

an 20% of 

night as well 

imple averag

sformer when

e transformer 

closer to the 

mers supplyin

filled 

rned that delta

 third 

y as in the 

mposite curve

by a flat curve

smoothing 

mand 

during the 

4

e 

n

g 

a: 

. 
1. Me

RM

35

2. Me

30

RM

mo

3. Th

19

typ

18

no

Figure 1 sh

Note that t

impact on 

transforme

load would

easurements 

MS equivalen

5% of namepl

easurements 

00 low voltage

MS equivalen

ore than 35%

he Cadmus G

990’s that sug

pe transforme

8% of namepl

ot clear for the

a. When R

efficien

by no lo

b. When R

efficien

load los

efficien

result o

load pe

c. Figure 

efficien

35% to

optimiz

hows total eff

the efficiency 

watts loss in 

er achieved pe

d be strikingly

at the DOE F

nt loading for L

ate. 

during the su

e dry transform

nt. However r

% which in tota

Group and Nor

ggested loadin

ers in some N

ate. It may b

e following rea

RMS equivale

ncy peaks at 3

oad losses is 

RMS equivale

ncy peaks at 1

sses is 42. H

ncy falls off ve

of this is that s

eriods and lea

1 below, cour

ncy plots for 3

 40% of name

zed for 30% a

ficiency versu

of the three t

the transform

eak efficiency

y large. 

Forrestal build

Low Voltage 

ummer month

mers suggest

repeated mea

al was close to

rtheast Utilitie

ng of less tha

Northeast loca

e true in som

asons: 

ent load is les

35% of load, t

approximate

ent load is as 

18% load then

However the c

ery quickly for

such transform

ad to the need

rtesy of Ken H

 conditions of

eplate. Note 

re considerab

us percent loa

transformers 

mers is drama

y at only 18%

ding in the ea

Dry Type tran

hs at a manuf

ted that loadin

asurements in

o the 35% as

es conducted 

n 35% of nam

ations and fou

me locations b

ss than 35% o

the ratio of tra

ly 10. 

low as 18% o

n the ratio of 

consequence 

r any conditio

mers may be 

d for greater t

Harden of Sc

f peak efficien

that at high lo

bly less efficie

ad courtesy of

is quite differe

tically differen

% of nameplate

arly 1990’s co

nsformers wa

facturing plan

ng could be le

n the winter m

ssumption for 

loading studi

meplate for lo

und loading to

but the conseq

of nameplate 

ansformer loa

of nameplate 

load losses d

of such a rat

ns of high loa

less efficient

total delivered

hneider Elect

ncy, ranging f

oad the trans

ent: 

f Ken Harden

ent at high lo

nt at high load

e kVA the fall

ncluded that 

as close to 

t of loads on 

ess than 35%

months was 

the year. 

ies in the late

w voltage dry

o be as low as

quences are 

and the 

ad loss divided

 and if 

divided by no 

io is that 

ading. The 

t during high 

d load. 

tric shows the

from 30% to 

sformers 

n of Schneider

ads. The 

ds. If a 

loff at high 

5

%

e

y

s

d

e 

r. 
G

H

Philip

Presid

Figure 2 sh

Ken Harde

seasons. 

G. Conclusi

1. Histo

loads

earlie

2. Histo

loads

startin

3. Instan

needs

4. Peak 

for a t

dema

H. Recomm

1. The D

betwe

depar

of 50%

2. Low V

Schn

inform

close

 J Hopkinson

dent & CEO H

hows a clear 

en. Note the c

This is the na

ions: 

rical purchase

s of 50-58% o

er forward to t

rical purchase

s of more than

ng with the in

ntaneous load

s daily and se

Demand nee

transformer s

ands on the lo

mendations: 

DOE Negotiat

een no load a

rture from his

% RMS equiv

Voltage loadin

eider Electric

mation and an

ly for rational

, PE 

HVOLT Inc. 

view of load v

clear differen

ature of much

es of medium

f nameplate R

today. 

es of low volt

n 40% of nam

troduction of 

ds are not a g

easonal effect

eds to be con

such that the h

oad supply. 

ting team sho

and load losse

storical relatio

valent load ha

ng information

c has done a c

ny departure f

. 

variation at a 

ces in season

 of the loadin

m Voltage tran

RMS Equivale

age dry trans

meplate prior t

NEMA TP-1 

good indicatio

ts to provide 

sidered in the

highest perm

ould work clos

es for Medium

nships should

as been in pla

n is not gener

commendable

from the 35%

plant in Tenn

nal loads by m

ng on low volta

nsformers hav

ent load in se

sformers have

to the mid 199

in 1996. 

on of RMS eq

adequate info

e establishme

issible loads 

sely with EEI 

m Voltage Util

d be carefully

ace since at le

rally available

e job of exam

% load assump

nessee, again

more than 2:1

age dry type 

ve been base

ervice from the

e been based

90’s and 35%

uivalent load

ormation. 

ent of load los

do not produc

for the prope

lity transforme

y studied. The

east back to t

e but Ken Har

mining conside

ption should b

 

n courtesy of 

1 between 

transformers

ed on expecte

e 1960’s or 

 on expected

% of nameplate

ing which 

ss allowance 

ce excessive 

r loss ratio 

ers. Any 

e assumption

the 1960’s. 

rden of 

erable 

be examined 

 

6

. 

ed 

e

n