I installed an COTS 3kVA 240VAC single phase isolation transformer on a project:
http://www.solahevidutysales.com/pdf/transformers/AutomationXfrmrs.pdfI wired the Taps to suit (240VAC primary, 240VAC secondary, ie 1:1 setup)
The unit powered up, but sometimes trips the (12A rated) circuit breaker on it's primary feed when you first turn it on. Without any secondary load, the unit gets extremely hot after around 10 min of operation (i'd guess an external case temperature of around 80 degC). I measured the primary voltage and current, shown below:
Yellow - Channel A = primary current via current probe at 100mV/amp
Blue - Channel B = primary voltage
it seems the current is extremely non-sinusoidal with 20A "Pulses" lasting 5ms lagging the voltage waveform, almost like something is saturating and the current is suddenly ramping up.
The unit does provide a 240VAC output voltage, as measured on a multimeter - sorry, didn't get time to scope the secondary yet.
So i guess questions to any transformer experts:
1) how hot should this sort of transformer run under no load? - rating is "80 degC rise at peak load
2) It's a 60Hz rated unit, we are at 50Hz, so i guess i'd expect a higher current ripple, but that should still be more sinusoidal surely?
3) Measuring the primary and secondary taps with an LCR meter shows inductances as expected (around 70mH Prim and Sec when wired 1:1). If taps were miss-labelled and hence mis-wired, i'd expect to see odd inductances across the taps?
4) Could a shorted turn cause this sort of behavoir?