Transformer Interlayer Isolation
Transformer Interlayer Isolation
(OP)
Anyone has an idea on how to test layer insulation within a winding on foil wound delta-wye transformer (115VAC, 400Hz) . The test will serve as an isolation and verification for shorts (latent that can not be discovered during functional testing) across layers test were interlayer winding is isolated. I am thinking of applying a high voltage (maybe high frequency pulsed) across the winding and monitor the current. Any ideas?





RE: Transformer Interlayer Isolation
Limit the current otherwise the test may be destructive.
Google: Hi-Pot Testing (and variations).
RE: Transformer Interlayer Isolation
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RE: Transformer Interlayer Isolation
Jacking up the test frequency will also raise eddy current losses in the core significantly, so the drop in Q at a higher test frequency due to one (partially) shorted leaky turn may not then be quite so obvious.
Possibly the best you can do is to shock excite the winding with a fast pulse, and watch the damped resonant decay. Count the number of cycles to half amplitude on a storage oscilloscope. If you have a number of identical transformers to test, any significant change in one transformer may be trying to tell you something.
RE: Transformer Interlayer Isolation
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Your body may be a temple. Mine is an amusement park...
RE: Transformer Interlayer Isolation
If you want to detect a hard short, then you could simply measure the end-to-end resistance using milli-ohm 4-wire techniques to see if the reading is lower than it should be (due to several turns being shorted out).
To detect defective insulation where it isn't quite shorted, then perhaps the transformer could be exercised for very brief periods (low duty cycle) at extreme voltages and 'listen' (*) for arcing (* noise burst at frequencies other than 400Hz). If it doesn't arc at voltages far above the operating spec, then it is probably good enough.
RE: Transformer Interlayer Isolation
A shorted turn is going to run fairly hot, perhaps it could even be seen with infrared sensitive equipment, or probed with a thermocouple down the edge of the winding.
Could the volts per turn be probed ? A shorted or leaky single turn would have conspicuously less voltage across it than all the other turns.
RE: Transformer Interlayer Isolation
See Baker Instruments http:
Gunnar Englund
www.gke.org
RE: Transformer Interlayer Isolation