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) 841-3300described 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 

### 2transformers 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 Tem

### perature Full Load Average Windin Rise T

### ype 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 

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