BESS Feeder Breaker Tripping on Ground Fault

[kingpb]

Odd situation, the BESS feeder breaker is tripping on ground fault. There is no ground fault. The relay voltage angles and magnitude seem normal as far as 120deg between phases, but neutral is seeing them in phase. What could the relay be seeing/casue this to happen? The situation happens very consistently every two weeks anywhere between 5 to 5:30 am.

 

[jaggedben]

How are you sure it's not a ground fault? Intermittent moisture or temperature condition related to the time of day?

Is the BESS typically operating or not during the relevant time period?

Where are you seeing 120deg phase separation if the 'neutral is seeing them in phase'? What is the voltage and number of wires to the equipment? Please describe more clearly.

 

[ggunn]

The relay voltage angles and magnitude seem normal as far as 120deg between phases, but neutral is seeing them in phase.

As measured how? I am trying to understand what you are saying; are you looking at oscilloscope tracings? "Neutral is seeing them in phase" makes no sense to me.

 

[kingpb]

All good questions, just digging into this now, so still gathering details. The waveforms have been captured by looking at Schneider Easergy P relays. The voltage capture shows voltage 120deg apart, but the currents are all on top of each other (same phase angle) almost identical magnitude. The current magnitude is roughly that which would be expected from the inverter during a faulted condition. EXCPET, their is no fault present. This is a 3ph system, with the BESS at 600V stepped up to 13.2KV through a Dy transformer. The neutral current is measured by 50G function, i.e. summing from the three phases, not directly measured as in 50N. The CTs have been checked to confirm they are wired properly.

 

[ggunn]

All good questions, just digging into this now, so still gathering details. The waveforms have been captured by looking at Schneider Easergy P relays. The voltage capture shows voltage 120deg apart, but the currents are all on top of each other (same phase angle) almost identical magnitude. The current magnitude is roughly that which would be expected from the inverter during a faulted condition. EXCPET, their is no fault present. This is a 3ph system, with the BESS at 600V stepped up to 13.2KV through a Dy transformer. The neutral current is measured by 50G function, i.e. summing from the three phases, not directly measured as in 50N. The CTs have been checked to confirm they are wired properly.

This is MV stuff and I have very little experience with MV, so I will hang up and listen.

 

[Melak 22]

If you are looking at 50G, which is 3I0, yes they would all be in phase.

How do you know there’s no ground fault? What’s the 50G pickup? What magnitude are you measuring for 3I0? Is the Bess a delta or wye system?

 

[jim dungar]

Are you sure the CT wiring is correct per the relay inputs versus function? it seems switchgear and relay engineers often do it differently, even if they have the same corporate name. Check the actual wiring not just the drawings.

We often used to run the Wye point of the 3 phase CTs through the relay's neutral CT input rather than supply an actual 4th CT. If wired this way the summing is done in the CTs.