Voltage check for 3 phase gen to ground and neutral
Voltage check for 3 phase gen to ground and neutral
(OP)
While checking the output of a gen to ground, voltage was 120, 120,then 104. Checking the same connector to neutral resulted in 120,120,120. What could cause the difference in the reading? BTW this has happened multiple times.





RE: Voltage check for 3 phase gen to ground and neutral
DaveWB
RE: Voltage check for 3 phase gen to ground and neutral
A combination of a distorted wave form and a D'arsonval meter movement can give strange results. I have twice seen unloaded Wye secondary transformer banks where the line to line voltages were obviously not the right ratio to the line to neutral voltages. I one instance we were able to put an oscilloscope on the circuit and the distorted waveform that was causing the erroneous readings with the D'arsonval meter were obvious. In both cases when a load was applied, the voltages corrected themselves.
In your case, it would have to be something that didn't effect the phases equally.
yours
RE: Voltage check for 3 phase gen to ground and neutral
See if you can get an oscilloscope and take a look at what you have, scopes are typically underutilized in the power industry, distorted waveforms can make meters and relays do strange things, not to mention actually changing the rms values. With the scope, check the peak to peak voltage readings and waveshape maybe it will show something different in c phase.
RE: Voltage check for 3 phase gen to ground and neutral
If you don't have a scope to validate the harmonic idea, then try taking the measurements at different times, ie, when certain equipment is running or not running and different times of the day. Is this a home generator or are you in a commericial or other building?