posted August 07, 2003 09:31 PM
--------------------------------------------------------------------------------
I work in the paper industry and recently we have experienced unusual voltages on one of our 480 V systems. The system is feed from a delta/Y HRG XFMR. We are currently reading the following line to ground voltages: A=550V, B=770V, C=950V. These voltages have been checked with a digital and analog meter. We have found the HRG on the XFMR to be burnt up and we assume that it is open, thus giving us an ungrounded system. I can see where you could get 480V to ground on this system now because of this issue, but don't have much of an explanation for these voltages. One thing to note on this issue is that this XFMR is paralled with another delta to Y XFMR. This XFMR however is ungrounded and has a hard ground on one phase of this system (A phase to Ground = 5 Volts). Someone stated that with these 2 systems being ungrounded now, that somehow we are measuring through multiple sets of windings on these systems. I can't see this be/ both XFMR's are delta to Y and I thought that this would eliminate circulating currents?? Another theory on what is going on is there is an arcing ground on this now ungrounded system and that this ground is causing capacitive charging on this system, thus causing the higher voltages. I am not familiar with capacitive charging. Can anyone help??
--------------------------------------------------------------------------------
I work in the paper industry and recently we have experienced unusual voltages on one of our 480 V systems. The system is feed from a delta/Y HRG XFMR. We are currently reading the following line to ground voltages: A=550V, B=770V, C=950V. These voltages have been checked with a digital and analog meter. We have found the HRG on the XFMR to be burnt up and we assume that it is open, thus giving us an ungrounded system. I can see where you could get 480V to ground on this system now because of this issue, but don't have much of an explanation for these voltages. One thing to note on this issue is that this XFMR is paralled with another delta to Y XFMR. This XFMR however is ungrounded and has a hard ground on one phase of this system (A phase to Ground = 5 Volts). Someone stated that with these 2 systems being ungrounded now, that somehow we are measuring through multiple sets of windings on these systems. I can't see this be/ both XFMR's are delta to Y and I thought that this would eliminate circulating currents?? Another theory on what is going on is there is an arcing ground on this now ungrounded system and that this ground is causing capacitive charging on this system, thus causing the higher voltages. I am not familiar with capacitive charging. Can anyone help??
