480V, 300KW, BESS System breaker ground fault trip 3

[power2engineer]

We have a 2.5 MVA 13.8KV (Y-G)/ 480V (Y-G) Utility power supplying power to Schneider Electric 4000A, 480V, 3 Ph, 4W QED6 Main Switchboard with MTZ breakers.
Building major loads Panels and other DG Sources are connected to this Main switchboard bus with their respective breakers.
One of the feeder is connecting 300KW, 480V, 3Ph BESS system (Manufacturer SOCOMEC) Feeder with 800A circuit breaker with Ground fault trip set at 160A Zero time delay.
This BESS system feeder breaker we experience frequent ground fault trip especially when there is heavy rains.
We did megger the BESS system feeder cables and found no insulation failure.
BESS system manual allows connection of BESS system to Phase, 4W system with Neutral and Ground bonded which is what our system.
Does anybody have any experience what may be the cause of this BESS Feeder breaker keeps tripping on Ground fault.
Please see system SLD file attachment.
Thanks for sharing your learned opinion.

 

[cuky2000]

Check for harmonics and higher-frequency noise, especially at the third harmonic. Those may be present in an electrical system and appear as fault current.
Electrical noise is a growing problem as more users utilize variable frequency drives, inverters, battery storage/UPS, and even LED lighting. To avoid nuisance trips, select a high-quality ground-fault relay that removes harmonic frequencies and other noise from its measurements.
SOURCE: Littelfuse

 

[power2engineer]

We already discussed this with BESS system manufacturer the quality of output from inverter supply is tightly monitors before the inverter is connected to Power system.

 

[jghrist]

With a grd Wye - grd Wye connection to the utility, the BESS system may be furnishing zero sequence current to utility system unbalanced load. There also may be unbalanced plant load causing neutral current. If the neutral is grounded both at the service entrance and at the BESS, there could be neutral current flowing through the grounding conductor, tripping the ground-fault relay. There should be only one ground connection to the neutral.

 

[che12345]

I have the following opinion for you consideration.
1. the XFMR (100T-TF2) is YNyn i.e. Pri. Y with N earthed and the Sec. Y with neutral earthed.
2. The BESS feeder cable is (AC-10) 3C/4C ? The breaker is 1.6 kA AF / 500 AT, as shown in the drawing.
Attention: a) Check whether set AT is 500 A or 800 A. If it is 500 A, it could be too low for the 300 kW load; which may? reach up to say around 450 A.
b) The XFMR (100T-TF2) Sec. Neutral is earthed. If the earthed Neutral is distributed to the BESS, the Neutral at the BESS SHALL NOT be earthed.
3. The drawing shows only one CT. It could be three/four CTs or one single ZCT.
Attention: a) For 3 line cable 3 CTs. For 4 line cables 4 CTs. For ZCT check that the earth wire does NOT go through the ZCT.
b) Drawing shows CT wired to remote on the relay panel. Check the insulation and connections.
4. Observation: For 300 kW load at say 450 A, EF setting at 160 A at zero time delay may need further study.
Suggestion: Add a short time delay at say <0.5 s. You may look into lowering the 160 A, if the short time delay is helpful.
Che Kuan Yau (Singapore)

 

[power2engineer]

1) jghrist - Neutral and ground are bonded only 1 place at transformer not at BESS
2) che12345 - Thanks for detail response!
2) a) The 1600A frame breaker has 800A Sensor plug and Ground fault pick up setting is 160A verfied. Upon trip breaker indicates reason for trip is Ground fault at 160A
b) The neutral is NOT bonded to Ground at BESS.
3) The CTs you see in the Single Line diagram are actually 3 CTs feeding into detect reverse power from battery to Grid Sweitzer 700G relay.
4) Will look into adding time delay for ground fault trip as suggested.

 

[alehman]

Zero time delay for GF seems very short. Is the a requirement of the BESS manufacturer?

Alan
The engineer's first problem in any design situation is to discover what the problem really is. Unk.

 

[waross]

The engineer's first problem in any design situation is to discover what the problem really is. Unk.

Very true.
lps for that.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!