Factory Short Circuit Test 1

[WrightMA]

I am to attend a factory short circuit test on a single phase transformer rated 100kV/7.2kV. This specific transformer has an impedance of 10%. This test will be a short circuit test done at rated current. The voltage (kV) that will be applied to the HV terminals is 10kV. How is it determined that 10kV should be applied to the HV terminals for this test?

 

[davidbeach]

The basic definition of % impedance. 100kV * 10% = 10kV.

 

[magoo2]

Another way of saying it is:
You have 10% impedance. With the transformer shorted, you only need 10% voltage to get rated current, so 10% of 100 kV gives 10 kV.

 

[racobb]

Sounds more like a %z test than a short circuit test. Short circuit is a design test, not generally an acceptance test.

Ask the question, how can they do a short circuit test at rated current? The secondary is shorted for the %z test.

I would not want the unit if they actually did a short circuit test on it.

Alan

 

[alehman]

Short circuit tests are normally used to measure impedance. Does not have to be at rated current.

Probably not a withstand test like this:

http://www.youtube.com/watch?v=jRC1pwXZFIc

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[WrightMA]

It is clear now. Thanks to all.

 

[Zogzog]

You sort of have it backwards. For a %Z test the secondaries are shorted and the SCC is measured. Full load secondary current is calculated.

A variable voltage source is connected to the primary and voltage is slowly raised while monitoring the SC current. As primary voltage is increased the SC current increases, when that current reached the calculated full load secondary current the test is stopped. The % of rated promary voltage that caused the shorted secondary to reach rated full load current is your %Z.

So for your transformer, if 9750V was the stopping point, the %Z would be 9.75% and is stamped on the nameplate.

 

[cflatters]

And thats why its often referred to as voltage impedance

 

[ausphil]

Correct that this is not a short circuit test. It is a measurement that is done with one winding shorted.

Don't foget they should also measure the watts being consumed at this rated current to calculate the Load Loss value.

ausphil

 

[JamesLearningCorner]

Hi guys,

I am new to EE, but I've read about this in books and still not very clear. When you short the secondary, all the impedances that the short circuit voltage will see are the Zp and Zs in series. With that said, I still don't know how we got 10V? Please use some number in your answer. Thanks!

 

[jghrist]

I am new to EE, but I've read about this in books and still not very clear. When you short the secondary, all the impedances that the short circuit voltage will see are the Zp and Zs in series. With that said, I still don't know how we got 10V? Please use some number in your answer. Thanks!

It's 10 kV, not 10V. See davidbeach's first response.

 

[JamesLearningCorner]

Yes, 10KV. Sorry about the mistake. I know the answer is 10kV, but I am still unclear, as I explained my reasons earlier.

Also, I remember reading some literature before that to get rated current in a short circuit test, the V short circuit is less than 5% of the rated voltage. In this problem, the rated voltage is 100KV, so the Vsc is actually 10%, which is >5%. Kinda more confused.

 

[dpc]

The required voltage depends on the transformer impedance. This is the main point of doing the test.



David Castor

http://www.cvoes.com