Shunt Trip with Ground fault sensor
Shunt Trip with Ground fault sensor
(OP)
Can anyone tell me how fast a shunt trip device opens a 480V breaker, typically anyway? I assume it varies with design. Do any designs reliably trip in < 5 cycles? Can anyone send a link to a shunt trip spec sheet showing trip times?
I have a collection of 480V MCCs fed by 480V power switchgear. The power switchgear feeders have ground fault trips. I am trying to determine if a ground fault sensor + a shunt trip scheme in the MCC buckets can operate fast enough to trip ahead of the ground fault trips in the power switchgear. The pwr swgr feeder grounds trip in the 0.15-0.25sec range, but could be slowed down if we wanted to accept loosing coordination with the bus ties.
I have a collection of 480V MCCs fed by 480V power switchgear. The power switchgear feeders have ground fault trips. I am trying to determine if a ground fault sensor + a shunt trip scheme in the MCC buckets can operate fast enough to trip ahead of the ground fault trips in the power switchgear. The pwr swgr feeder grounds trip in the 0.15-0.25sec range, but could be slowed down if we wanted to accept loosing coordination with the bus ties.






RE: Shunt Trip with Ground fault sensor
It will also depend on the ground fault relays you select for this application.
RE: Shunt Trip with Ground fault sensor
So adding two cycles to the max instantaneous clearing time should be conservative. I'm sure the breaker manufacturer can provide actual timing data.
For ground fault sensors, some breakers can be fitted with low energy shunt trip coils that may operate a little faster.
RE: Shunt Trip with Ground fault sensor
Here is a link to a bulletin describing the Square D 'Ground Censor' ground fault system that is of similar type to what you will find available to install on your MCC. It shows time delays (trip times) of 0.1 seconds (6 cycles) and up.
Theoretically, individual MCC breakers will serve a much smaller load than a feeder breaker so the ground fault pickup current will also come into the picture when considering coordination.
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RE: Shunt Trip with Ground fault sensor
I cannot give make/model; too many. The facility has ~7-800 loads being fed out of ~50 MCCs. There is no ground fault sensing in the feeders coming out of the MCCs, but there is ground fault sensing in the upstream power switchgear. A few times they have had ground faults in loads take out the whole MCC.
The comments and link told me a lot. Thanks. It gives me some feeling how fast a good shunt trip can be. It appears they can be faster than the upstream switchgear.
However, one more question: Some molded case breakers (the facility has lots of these) have external trip mechanisms that bolt onto the front of the breaker. A solenoid operated arm flips the switch on the front of the breaker. It is not clear to me how fast such devices are. Any hints?
RE: Shunt Trip with Ground fault sensor
The devices normally used to open the breaker in a fault (other than the trip unit) are the shunt trip or the undervoltage trip. This are internal to the breaker and operate by tripping the mechanism open, this giving a very quick operating time.
RE: Shunt Trip with Ground fault sensor
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RE: Shunt Trip with Ground fault sensor
RE: Shunt Trip with Ground fault sensor