Power Transformer Short Circuit Type Test

[sambapati]

One of the major requirement of our utility company is to require prospective power transformer suppliers to submit a type test report performed by an independent testing company like KEMA or CESI. The particular test that we are interested is the full short circuit test done either at KEMA or CESI test facilities or witnessed by KEMA or CESI representatives in case the test was done at the suppliers factory.

Recently, we have one supplier who submitted a short circuit type test report for a 1-phase transformer instead of the required 3-phase test. Is it acceptable to accept this 1-phase test in lieu of the required 3-phase test?

Appreciate any comments on this inquiry.

 

[prc]

Generally test on single phase transformer is not accepted for 3 phase unit. Short circuit test is checking not only winding but also the lead take out, interaction of current in one phase with other etc. But remember test report of single phase test on 3 phase unit is acceptable. In case of very large units, when test lab capacity become a limitation, it is acceptable to go for 1.5 phase or single phase testing instead of 3 phase short circuit test.

 

[sambapati]

Thank you very much prc. What i have read on iec 60076-5 or ansi c57.12.90 is that 1-phase test can be done on a 3-phase unit in case the test facilities is limited. I also conform to your caution that a 1-phase test can also be accepted if the pxf unit is very large and cannot be constructed as a 3-phase unit.

MY inquiry is about the bidder submitting a short circuit type test report done on a 500mva, 345kv 1-phase transformer unit which they have claimed to be acceptable to our required 3-phase short circuit test for a 230kv, 300mva, auto-transformer unit. We know that it is not possible to construct a 3-phase unit on a 1500 MVA bank rating but we only require 3-phase short circuit test on a smaller 300mva, 230kv-115kv auto-pxf which we have many units installed in our substations.

The question is; can we accept the 1-phase short circuit test result from a big transformer unit instead of our required 3-phase test for a smaller transformer unit.

Again to prc, thanks for the response. Can you provide a reference technical document on this specific issue?

 

[waross]

How much money will be saved by accepting the transformer over competing transformers?
How much money will be saved by doing a single phase test rather than a three phase test?


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[prc]

Sambapati- Unfortunately your question is still not clear to me. The standard for comparing whether the earlier tested unit can be considered for the offered transformer is Annexure B of IEC 60076-5.You can see the requirements there. 500 MVA 345 KV 1 phase is an auto or two winding? Normally customers will not accept a test done on a single phase unit for an offered 3 phase unit.
waross- Short circuit test in high power labs (with special generators) is done like this. If the rating is say up 100 MVA 10 % impedance 3 phase ( for 1000 MVA short circuit power, the lab generator capacity should be 6000 MVA or more to take care of the drop etc) 3 Phase test can be done up to 500-1000 MVA . But if the SC rating is more, lab will go for 1.5 phase test ie single phase voltage will be used and full power in one phase and half power in other two phases. But if the Sc power exceeds even that single phase test will be done on one phase and repeat in other phases. Cost of testing -well I will say not much difference. It is more based on size of transformer and number of shifts involved.

 

[sambapati]

Thanks prc and waross. Our requirement is to buy a 3-phase unit rated 300mva, 230-115kv-13.8kv auto-transformer. To be a qualified supplier, new bidders should provide a short circuit withstand test for a 3-phase transformer unit on ratings similar to or greater than the specs of our requirement. One of the bidder submitted a test report done on a 1-phase unit rated 500mva, 345kv and told us they are technically acceptable to our requirement based on iec 60076-5. Is this acceptable?

To answer prc inquiry, the 1-phase unit rated 500mva, 345kv is an auto transformer type.
To waross, I cannot provide a cost comparison because our office is not privy to the bid cost.

Many thanks again to both of you.

 

[waross]

Hi prc.
The cost of testing I was considering was the cost to the supplier of an in-house test versus the cost of sending the transformer out to a lab with greater capacity testing gear to provide test results that meet the bid specs.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[prc]

Waross, the short circuit test is a special test. No transformer manufacturer has in-house facility for conducting that test. The cost of testing such a large transformer in a high power lab will be anything between 50-70% of price of transformer !

 

[Sazirul]

I have two Transformer in my factory. First one is 33/11KV and second one is 11/0.415KV. I received two transformer in a single day. I checked the documents and asked them about the test and they told me every test they performed with our transformer. This company is only one transformer manufacturer in my country who have all the necessary equipment to run any kind of power transformer testing.

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