a10jp
Electrical
- May 18, 2005
- 150
I have a general question on efficiency on distribution transformers. In our specification, we specifiy 20000/25000kVA transformers to be factory tested to the standard of NEMA TP 1. In this case, according to the standard, which specifies the minimum efficiency levels for NEMA Class I liquid filled distribution transformers, it says for for transformers 2500kVA and beyond, the minimum efficiency shall be 99.4%. This is from Table 4-1 in Section 4, which listed reference condition for Load Loss at 55% and at 50% nameplate loading.
The manufacturer factory test reports came out to, as an example, 99.37%/99.36%/99.35% forone transformer and 99.35%/99.34%/99.32% for another, etc. The results are close to 99.4%, but not quite.
When I asked the manufacturer to justify these test results, and to clarify what standard was used in conducting these tests, the reply was they categorize this as a power transformer vs a distribution transformers, the standard does not apply. The efficiency tested just happens to come out close to NEMA TP-1, even though the standard does not apply.
FUrther, the manufacture says that ANSI, NEMA nor IEEE do not specify efficiency for power transformers above 25000kVA for the reason that hihger efficiencyies require superior core steel and that may not be readily available. Current standards on power transformers govern only safety and construction but not on efficiency. The Mfr tried to optimize the design of power trans taking into account material cost that result in the least costs of ownership to the end-user under normal conditions....
This sounds like a standard industry response. My questions are:
1. Is it true, that efficiency does not exist for large transformers similiar to what we used?
2. Is 2500kVA the maximum limit on transformer capacity where one can truly comment on efficiency, and anything else larger than that is merely luck?
3. Even if it is true no standards exist for such large transformers, there must be a minimum efficiency you can use to determine the level of construction we are getting from the mfr?
4. One last thing, am I being too picky? Is perhaps 99.32% considered acceptable? Afterall, the standard only goes up to 2500kVA. It must be for a reason.
I like to understand more of the economic as well as technical justifications based on what was discussed above. If anyone has any comments, I will be glad to hear them. Thanks.
The manufacturer factory test reports came out to, as an example, 99.37%/99.36%/99.35% forone transformer and 99.35%/99.34%/99.32% for another, etc. The results are close to 99.4%, but not quite.
When I asked the manufacturer to justify these test results, and to clarify what standard was used in conducting these tests, the reply was they categorize this as a power transformer vs a distribution transformers, the standard does not apply. The efficiency tested just happens to come out close to NEMA TP-1, even though the standard does not apply.
FUrther, the manufacture says that ANSI, NEMA nor IEEE do not specify efficiency for power transformers above 25000kVA for the reason that hihger efficiencyies require superior core steel and that may not be readily available. Current standards on power transformers govern only safety and construction but not on efficiency. The Mfr tried to optimize the design of power trans taking into account material cost that result in the least costs of ownership to the end-user under normal conditions....
This sounds like a standard industry response. My questions are:
1. Is it true, that efficiency does not exist for large transformers similiar to what we used?
2. Is 2500kVA the maximum limit on transformer capacity where one can truly comment on efficiency, and anything else larger than that is merely luck?
3. Even if it is true no standards exist for such large transformers, there must be a minimum efficiency you can use to determine the level of construction we are getting from the mfr?
4. One last thing, am I being too picky? Is perhaps 99.32% considered acceptable? Afterall, the standard only goes up to 2500kVA. It must be for a reason.
I like to understand more of the economic as well as technical justifications based on what was discussed above. If anyone has any comments, I will be glad to hear them. Thanks.