Incorrect Ground Current Measurement
Incorrect Ground Current Measurement
(OP)
Hello,
I've had a ground fault in my system for which an event recorder (SR750) is giving me ground currents that are not possible. This is a 6900V delta system with a 400A (10ohm) neutral grounding resistor. The phase and ground currents shown from the recorder are as follows:
A = 2810A
B = 3216A
C = 6854A
G = 1265A
I know that mathematically, the zero sequence current is 1285.69A. However, the maximum current possibly flowing through ground is 400A, as set by the NGR.
Has anyone run into this scenario before? I am assuming it is just a measurement anomaly, but unsure as to what is causing it, whether it be the CTs, the AC signal filters, the firmware, etc.
Any insight would be greatly appreciated.
Thank you.
I've had a ground fault in my system for which an event recorder (SR750) is giving me ground currents that are not possible. This is a 6900V delta system with a 400A (10ohm) neutral grounding resistor. The phase and ground currents shown from the recorder are as follows:
A = 2810A
B = 3216A
C = 6854A
G = 1265A
I know that mathematically, the zero sequence current is 1285.69A. However, the maximum current possibly flowing through ground is 400A, as set by the NGR.
Has anyone run into this scenario before? I am assuming it is just a measurement anomaly, but unsure as to what is causing it, whether it be the CTs, the AC signal filters, the firmware, etc.
Any insight would be greatly appreciated.
Thank you.






RE: Incorrect Ground Current Measurement
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Incorrect Ground Current Measurement
I haven't fiddled with an SR750 or its event reports for quite a while. If you have waveform capture, that might be more revealing. Otherwise, you may need to resort to looking at the relay manual or talking with Multilin. I would not assume there is a relay error until you know how the "G" value is determined and eliminate the other possibilities. Relay error is probably the least likely problem.
RE: Incorrect Ground Current Measurement
RE: Incorrect Ground Current Measurement
RE: Incorrect Ground Current Measurement
RE: Incorrect Ground Current Measurement
I am just curious if anyone has ran across this issue before.
RE: Incorrect Ground Current Measurement
RE: Incorrect Ground Current Measurement
If the secondary of the Dyn transformer is connected with a 400A rated NGR, then there is no way that during a ground fault the max allowable ground fault current is greater than
400A. The ground fault current = 3 x zero seq current. Therefore, it looks like there is multiplication factor issue.
RE: Incorrect Ground Current Measurement
RE: Incorrect Ground Current Measurement
RE: Incorrect Ground Current Measurement