Hi Gary,I have done this, but not checked it. So, I did just now. The 15/30 measured 175X at 124.2Vin. So this presents a possible large error depending on where the input is in the stream.
I believe we should be looking at both sides equivalently. If you feed 120V to sec and measure 0.784V at the primary, you should then feed 0.784V (or as near as you can get) to the primary and measure the secondary. Take the both ratio's and average. So I checked this.
Measurements of my 15/30: Feed sec = 124.2V, pri = 0.708V = ratio of 175.4 Feed pri = 0.76V, sec = 55.0V = ratio of 72.4 Average (72.4 + 175.4) / 2 = 124 turns ratio (125 expected)Decent considering meter error (and using a single meter). I'll try to go through this at various voltages to see how it plays out.
Gary, can you confirm on your NST's? If this works out decent on your NST's, then it's an easy procedure to ensure turns ratio accuracy as well as inductance ratio on transformers with no data (or confusing data).
Thanks for looking at that. Bart Lau, Gary wrote:
Hi Bart,As often as I have dispensed the same advice to measure and feed the mains voltage into the NST secondary and measure the primary to determine the sec/pri ratio, I don't recall ever having actually done that to mine. So, I just pulled out a 15/30 and a 15/60 NST.The 15/30 measured a ratio of 153X, so assuming a 120V primary, predicts a 18.3kV secondary. The 15/60 measured a ratio of 145X, so assuming a 120V primary, predicts a 17.4kV secondary. The meter that I used is a simple Fluke DMM, not RMS. But given that the NST is going backwards, I wouldn't think that it's getting near saturation and the associated waveform weirdness. Unfortunately I don't own a HV probe that I would trust to measure it in the normal operating sense. Have you done this and gotten closer to the faceplate voltage rating? Regards, Gary Lau MA, USA
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