Setting Standards for Excellence

December 21, 1998

Ms. Brenda Edwards-Jones

Office of Codes and Standards, EE-43

Office of Energy Efficiency and Renewable Energy

United States Department of Energy

1000 Independence Avenue

Washington, DC 20585-0121

RE: Energy Conservation Program for Commercial Products: Test Procedures for Distribution

Transformers, Docket Number EE-TP-98-550

Dear Brenda:

The Transformer Section of the National Electrical Manufacturers Association ("NEMA") would

like to request to speak at the public hearing to be held at the Department on January 6, 1999.

The following are additional items NEMA will address during the public meeting These items are

separated into three categories ( 1) additional transformers that should be excluded from the

rulemaking; (2) temperature class corrections for Table 1 in the notice, and (3 ) the acceptability of

NEMA TP-2 Section 7.

Excluded Products

In the November 12, 1998 Federal Register (63 FR 63361), DOE discusses distribution

transformers that are to be exempted from this and future test procedures and standards ruleanakings.

The following is a list of transformers that are currently not excluded from DOS 's rulemaking. This

list is from NEMA TP-2, page 1, Section 1.1. NEMA believes that these transformers should be

excluded from the rulemaking . The rationale is given next to each type of transformer.

a. Dry-type transformers below 15 Wa - Transformers designed to operate below 15 Wa are _

typically not three phase and are very difficult to change the efficiency. In the majority of cases,

these transformers are not distribution transformers.

b. Transformers connected to converter circuits - these are considered rectifier transformers.

c. All rectifier transformers and transformers designed for high harmonics - These transformers are

r amcplated with both a Fundamental Frequency Power Rating as well as an RMS Power Rating

and hence clearly designed for a dedicated rectifier application . These design characteristics are

described in ANSI C57. 18.10 and are different from the losses and temperatures than those

National Electrical

Manufacturers Association

1300 North 17th Street, Suite 1847

Rosstyn , VA 22209

(703) 841-3Z00

FAX (703) 841-3300

 EE-RM/STD-00-550 COMMENT 45
described in C57,12.00 and 057.12.01 for distribution transformers. Rectifier transformers are

normally distinguishable by non-standard kVA ratings as well as non-standard voltage ratings,

but primarily, they are distinguished by the term "Rectifier Transformer" inscribed on the

nameplate, as required by ANSI C57.19.10. They may have 2 or more windings, and always

are designed to handle higher order harmonic currents that are associated with the commutation

of rectifier devices. Some are constructed with deliberate air gaps which are typically in butt cut

cores to accommodate d c current to prevent core saturation . Rectifier transformers are

normally.about 60% larger than general purpose transformers of equivalent fundamental

'frequency rating and have correspondingly large cores that proportionately raise core losses.

These transformers will not meet the same efficiency standard as general purpose transformers.

They some a niche market and provide a specific utility.

d. Autotransformers - These transformers are specially-made for specific applications and are

described in 057. 12.90; they differ from general purpose isolation transformers in that they have

one continuous winding with a tap for the output instead of two electrically isolated windings.

This construction feature guarantees a space utilization and electrical efficiency to exceed that of

the general purpose transformer. Furthermore, since parts size WA is defined as one half the

sum of the IcVA rating of all windings, and since autotransformers generally have a co-ratio

(common winding voltage divided by total winding voltage ) of more than SU%, then the

autotransformer efficiency will be considerably higher than the general purpose isolation

transformer efficiency.

e. Special impedance and harmonic transformers - Transformers outside the range of 4-9%, are

excluded. Transformers having a greater or lesser impedance than the 4-8% nominal band

(which fall within the range of the efficiency levels in TP-1), are designed to meet other

performance functions. These transformers arc characterized by exacerbated core sizes for low

impedance or by significant extra winding for high impedances . The- result of either excursion is

to distort the ability to meet the TP-I efficiency tables. Since the economics of building such

transformers is not attractive to the manufacturer, there would be no attempt to circumvent DOE

pilings by making all transformers this way because they would be more expensive to build.

Hence, the best policy is to exclude such transformers from mandatory testing requirements.

f. Sealed and non-ventilated transformers - sealed and non -ventilated transformers are for special

applications and have special designs. They have larger cores than non-sealed and ventilated

transformers to help keep them cool. Due to this larger core size, these type of transformers

have higher core losses.

9. Retrofit transformers - these types of transformers are designed for use in existing applications.

They have dimensional restrictions. The larger more efficient transformers, in many cases, are

unable to replace these units.

h. Transformers with tap ranges greater than 15 percent - These transformers are manufactured for

special applications, for example, as fiunacc transformers, and, therefore, represent a minimal

population. These transformers have a significant quantity of unused capacity and therefore,

operate at very low effective space factor . A consequence of this low space factor is that the

transformer core becomes significantly larger to surround the inactive winding . As a result, these

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 EE-RM/STD-00-550 COMMENT 45
transformers would have a difficult time meeting the same efficiency limits as general purpose

transformers,

i. Transformers with frequency other than 60 Hz - Transformers designed to 50 Hz operation will,

generally, have low induction for a test that might be conducted at 60 Hz, and will, consequently

test low on core loss at the 60 Hz frequency.. However, transformers that are designed to

operate at frequencies below 50 Hz, such as 25 Hz, or above 60 Hz, such as 400 Hz or higher,

could not reasonably be designed to meet the efficiency tables in TP-1. There are very few types

of these transformers in today's market and no standard for 400 Hz transformers.

Temperature Classes

DOE Report 6450-01 -P on page 18 in Table 1 shows reference temperatures. While table accuracy

is not directly relevant to the selection of reference temperatures for losses calculation , the only

recognized reference temperatures are as follows:

Reference Temperature

Full Load Average

Windin Rise Type of Product

75 55 Liquid and Class A Dry

.45 65 LiVid-lhcrmally upgraded Kraft

100 so Dry

135 115 Dry

170 150 D

Acceptability of NEMA TP-2 Section 7

Section 7 of NEMA TP-2 was written with particular care to allow for responsiveness of both large

and small manufacturers. There are three major assumptions that apply to the transformer industry

that are implicit in the NEMA TP-2, Section 7.

1. Standard deviation for losses average approximately 4% for distribution transformers

produced in present times.

2. Standard ANSI tolerances on losses are applied in NEMA TP-2 Section 7, which results in

a transformer being deemed acceptable if its measured losses at the 35% or 50% loads are

within s% of the required loss level. Hence, a transformer that exceeds the limit by more

than 9% must be discarded or reworked in order to bring it within the acceptable range.

3. A manufacturer will set his nominal losses to an economical point such that throw-aways

arc not excessive. This generally requires a three-sigma nominal mid-point to the throwaway point. Figure 1 shows percent of the population in 1 Sigma, 2 Sigma or 3 Sigma

limits. Since one standard deviation (sigma) is about 4%, this implies that the average

design must be act to meet the required, losses with margin. Furthermore, since the average

3

 EE-RM/STD-00-550 COMMENT 45
-&a11 transfomen prafud must meet the required &ciency, this furtha implies thnt 

evw kVA must be targded lo also mect the average efficienlcy with margin. 

The logic ofthese assum@a are !D le that it would be unreasonable far a 

mylufbctucr to dcliibuatcly O throw- try u, slip the efficiency d a whole kVA size because ck 8 * 

away LLna wnrld impore undo financial hardship on that mursdwo. 

If you have any questions, please hl fr& to call me at (703) 841-3245. 

 EE-RM/STD-00-550 COMMENT 45