Ground faults tripping main circuit breaker
Ground faults tripping main circuit breaker
(OP)
I've seen several issues with our selective coordination of breakers in the plant. Today we had a 480V coil go to ground and it tripped the MCCB feeding it and also the GE magne-blast main circuit breaker in the main substation. There were several circuit breakers in between these two. The magne-blast is located in the main 4160 switchgear and feeds the substation transformer. Then there is a GE AK-2-50 with an AC Pro trip unit in and feeding the MCC is a GE AK-2-25 also with an AC Pro. The ground fault pick up is 320A with a 10ms delay time. These units never pick up a ground fault, the main circuit breaker always trips along with the MCCB. Luckily we don't see a ground fault too often. Where can I find information on setting the units properly. Before I started working in this plant, a short circuit analysis was performed, and reccomendations were made for setting up the AC PRO units. I'm guessing that mistakes must have been made somewhere, and I'd like to look into this deeper.






RE: Ground faults tripping main circuit breaker
What type of transformer is the 4160-480? Wye-wye? If delta-wye, it should not have seen the ground fault. Your main should not have instantaneous ground fault protection in any case to allow for downstream devices to pick up and clear.
RE: Ground faults tripping main circuit breaker
Where are you loacted? I probally know someone in your area.
RE: Ground faults tripping main circuit breaker
A NETA member company should be able to help you with reviewing the coordination, making recommendations if necessary, and testing the breakers and protective devices.
RE: Ground faults tripping main circuit breaker
RE: Ground faults tripping main circuit breaker
For laughs here is the current configuration of the AC PRO
CT Rating 600
LT Pick Up 600
LT Pick Up delay 10s
ST Pick Up 2400
ST Pick Up delay .30s
ST I^2T Off
Instantaneous P/U 6000
Ground Fault P/U 320
Ground Fault Delay .10s
Ground Fault I^2T On
Unbalance P/U off
This is installed on a GE AK-2-25 600A breaker feeding an MCC. Normaly this MCC draws around 100A
RE: Ground faults tripping main circuit breaker
I know a very good engineer in Phoenix
http://www.cbssw.com/
Ask for Dan
jimgineer, you are allowed to post a web address and contact name, no email addresses or phone numbers as I understand the rules.
RE: Ground faults tripping main circuit breaker
Where can I find good information on this branch of the field? Protective relays and circuit breakers is something that definately interests me. Any reccomendations on books?
RE: Ground faults tripping main circuit breaker
www.PowerEngineersLLC.com
RE: Ground faults tripping main circuit breaker