Odd Potential Transformer Readings
Odd Potential Transformer Readings
(OP)
I am using a 4200:120V three-phase P.T. and connecting it Line-to-Line on the Primary in an open delta configuration. The secondary side is an open delta as well. When I put a voltmeter on it, I am reading 120V across each phase (Vab, Vbc, Vca). But when I am reading line to ground, I get 306V, 215V and 303V (Vag, Vbg, Vcg). Why am i getting these readings phase to ground? Its causing the meter to read 9000V-Vab,Vbc, but Vca is 4160V. Any suggestions on what the problem is?






RE: Odd Potential Transformer Readings
To where are you actually measuring to, physically.
RE: Odd Potential Transformer Readings
RE: Odd Potential Transformer Readings
RE: Odd Potential Transformer Readings
It’s likely the floating {ungrounded} secondaries are being excited by primary voltage, particularly if a 10MO meter is used for measurements. It is a serious misapplication to omit secondary grounding called for in ANSI/IEEE Std C57.13.3 ...Grounding of Instrument Transformer Secondary Circuits and Cases
This information is usually also included in instrument-transformer manufacturer’s literature. Fortunately transmission voltages were not involved.
RE: Odd Potential Transformer Readings
Try shunting the meter leads with a 180K?, 2-watt resistor.
RE: Odd Potential Transformer Readings
What u r measuring is stray voltages off the core and harmonics and junk but I don't think you are measuring anything useful. Your meter is probably ok. Have you tried your meter lately in a known live cct?
I'm not quite up on line voltage monitoring but it seems to me that it would be difficult to monitor anything with an open delta style t/f. 120, 120, and 0 only tells me 2/3 of the information - or am I missing something here?
RE: Odd Potential Transformer Readings
RE: Odd Potential Transformer Readings