Transformer Shorted Turns - instant failure or detectable by TTR?
Transformer Shorted Turns - instant failure or detectable by TTR?
(OP)
I was under the impression that when a shorted turn occurs on a 2-winding transformer, the fault will progress to failure (ground-fault or phase-to-phase fault resulting in transforme trip) very quickly. If that is true, then it seems there is not much usefulness for doing TTR test as a routine predictive test, is there? (if the transformer was operating normally without trips at the time we took it out of service, then it is very unlikely we will find a shorted turn during testing, right?).
The theory I have heard mentioned: a shorted turn (on either primary or secondary) acts like it's own teriary winding with a shorted output. There is present an induced voltage of volts-per-turn times number of shorted turns. The impedance in the shorted-turn loop is just the resistance of the wire and resistance of the short-circuit contact. (virtually no leakage inductance since this is mutually-linked flux). So unless the short-circuit is a high-resistance type, there will be very high current and rapid failure.
Any opinion? Any comments on the theory? Any experience in finding shorted turns on otherwise healthy transformer during predictive test?
Thanks in advance.
The theory I have heard mentioned: a shorted turn (on either primary or secondary) acts like it's own teriary winding with a shorted output. There is present an induced voltage of volts-per-turn times number of shorted turns. The impedance in the shorted-turn loop is just the resistance of the wire and resistance of the short-circuit contact. (virtually no leakage inductance since this is mutually-linked flux). So unless the short-circuit is a high-resistance type, there will be very high current and rapid failure.
Any opinion? Any comments on the theory? Any experience in finding shorted turns on otherwise healthy transformer during predictive test?
Thanks in advance.
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RE: Transformer Shorted Turns - instant failure or detectable by TTR?
Almost an instant failure i.e. a few cycles at most.
The only time that I will require a TTR test is when a transformer has been moved or jared in any way. I'll require a TTR prior to its move and after it has been set into place.
RE: Transformer Shorted Turns - instant failure or detectable by TTR?
The TTR test is very appropriate (on all taps) during acceptance testing. Unless you have moved the transformer or done something else that might cause a problem, there is little to be gained in repeating the test again.
In my 20 plus years in the testing business, I've not only not found it useful during maintenance testing, I have been repeatedly surprised at how obviously failed units can often "pass" the test.
RE: Transformer Shorted Turns - instant failure or detectable by TTR?
RE: Transformer Shorted Turns - instant failure or detectable by TTR?
RE: Transformer Shorted Turns - instant failure or detectable by TTR?