Trip Contact Not Rated to Trip Coil
Trip Contact Not Rated to Trip Coil
(OP)
Hi all,
I received a complaint from our client which indicates that the external trip relay used to energize the trip coil is having under-rated output contacts.
This relay is Phoenix Contact Part #PSR-SCP-24DC/ESP4/2X1/1X2, coil rating 24Vdc, output contacts rated at 110Vdc, 6A continuous/inrush rating, 42W (T=40ms)interrupting rating at inductive load, suitable for SIL 3 application.
The circuit breaker is Powell Vac-AR, 5kV, 3000A with trip and closing coils drawn current is 3.2A.
The circuit is generally wired so that this trip relay output NO contact is in series with the trip coil (in parallel with the protective/lockout relay contacts) and the trip relay NC contacts is wired in series with the circuit breaker closing coil as a closing interlock. This trip relay is operated on a non-fail safe and contacts only operate if the relay coil is energized. The comment is based on 42W at 110Vdc comparison with 3.2A trip/closing coil rating.
I disagree with the comment technically because the relay output contact wired to "close-In" or "make" to energize the trip coil which is rated at 3.2A. Since the output contact is rated at 6A, it should be ok. Furthermore,the trip or closing coil is de-energized by 51a and 52b simultaneously after the breaker operates.
Consequently, this also applies to the NC closing interlock contact on the closing coil circuit.
Do you agree with me? any thought otherwise?
I received a complaint from our client which indicates that the external trip relay used to energize the trip coil is having under-rated output contacts.
This relay is Phoenix Contact Part #PSR-SCP-24DC/ESP4/2X1/1X2, coil rating 24Vdc, output contacts rated at 110Vdc, 6A continuous/inrush rating, 42W (T=40ms)interrupting rating at inductive load, suitable for SIL 3 application.
The circuit breaker is Powell Vac-AR, 5kV, 3000A with trip and closing coils drawn current is 3.2A.
The circuit is generally wired so that this trip relay output NO contact is in series with the trip coil (in parallel with the protective/lockout relay contacts) and the trip relay NC contacts is wired in series with the circuit breaker closing coil as a closing interlock. This trip relay is operated on a non-fail safe and contacts only operate if the relay coil is energized. The comment is based on 42W at 110Vdc comparison with 3.2A trip/closing coil rating.
I disagree with the comment technically because the relay output contact wired to "close-In" or "make" to energize the trip coil which is rated at 3.2A. Since the output contact is rated at 6A, it should be ok. Furthermore,the trip or closing coil is de-energized by 51a and 52b simultaneously after the breaker operates.
Consequently, this also applies to the NC closing interlock contact on the closing coil circuit.
Do you agree with me? any thought otherwise?






RE: Trip Contact Not Rated to Trip Coil
1) use certain SEL relay that has hybrid outage contact designed for coil/close coil application
2) or, implement and drop-off delay so that 51a pellet or 51b pellet open fast than the relay contact to make the heat of the inrush.
RE: Trip Contact Not Rated to Trip Coil
RE: Trip Contact Not Rated to Trip Coil
RE: Trip Contact Not Rated to Trip Coil
David, dpc, do I really need to be concerned about this interposing relay interrupting the circuit breaker trip coil current if the breaker trip coil is wired in series to 52a contacts? The 52a contacts will interrupt the trip coil current flow after the breaker opening is completed. The input signal to this relay (Process Shutdown) is latched or maintained type..hence the contact remains closed even when the breaker opens.
The only concern I can think of are the following:
a. If the breaker fails to open and the trip current will be continuous, and then the relay resets.
b. The relay resets or drops out (due to low DC voltage or loss of DC), before the breaker opening is completed.
For 'a', we may be able to make some changes to the DCS logic such that a 52a contact will be added such that DCS will not be able to reset after a process shutdown signal is delivered if the 52a contact is closed. In addition, arc suppressors like the one suggested by david will be installed on the relay trip output.
For 'b', this is an inevitable scenario...probably, wiring this relay to the circuit breaker lockout should work. However, it might be a nuisance to operations to come over and do local reset for a breaker trip caused by the process SIS.
How about using the numerical relay input/output contacts and configure the output contact to directly trip the circuit breaker and activate the "seal-in" feature of the relay output contact (similar to GE F60)? Any thoughts?
RE: Trip Contact Not Rated to Trip Coil
Perhaps you ought to listen to your client. As was said above, it is more likely that the trip coil of the CB draws more like 10A on a 125V system. Do not play games with tripping circuits. Use a man-sized interposing relay after the Phoenix (such as the old ABB type RXMH or RXMVB latching relay). A melt down of the phoenix inside the electronic rack will destroy a lot of surrounding expensive goodies and may cause a fire. Saw it happen at least once.
Just some advice from the field.
rasevskii
RE: Trip Contact Not Rated to Trip Coil
You also need CBF protection if the breaker fails to open.
RE: Trip Contact Not Rated to Trip Coil
RE: Trip Contact Not Rated to Trip Coil
There is a concern if the breaker mechinacally hangs up that the contacts that closed to trip the breaker will be damaged attempting to open the trip coil current. I don't believe there is a solution except to do better breaker maintenance, bigger contacts, or an electronic interrupter with the existing contacts. It's a bad condition to have to remove protectine devices because the contacts were damaged by a stuck breaker.
It is a simular case with a slow breaker, and no one will admit it is slow. It will test good, after it is loosened. And will open and look like it work as expected. Only good relay event files will show the truth. But once the fault current is cleared by other devices, the relay contacts will release and then may be damaged.
RE: Trip Contact Not Rated to Trip Coil
Even relays built to these standards are not expected to interrupt trip coil current. A breaker auxiliary switch that has worked loose is another situation that will fry them. Crew:"The relay burnt up, we replaced it." Me:"Please return and inspect the auxiliary switch."
RE: Trip Contact Not Rated to Trip Coil
I really try to avoid any unnecessary interposing relays in trip circuits, but sometimes they are unavoidable. I also never use a plug-in relay in a trip circuit.
As long as the breaker auxiliary contact is working properly, the breaking current rating of the relay contact should not be a factor. But when I've talked about relay failures with manufacturers of new digital relays, the most common failure involves the trip circuit output contacts. And these are products are intended to be used to trip breakers.
RE: Trip Contact Not Rated to Trip Coil
I would bet that nearly all of those trip output "failures" was really a 52a failure that took out the output contact.
I agree the use of interposing relays should evaluated carefully. Added complexity, failure points, tripping delay, ...
RE: Trip Contact Not Rated to Trip Coil
RE: Trip Contact Not Rated to Trip Coil
RE: Trip Contact Not Rated to Trip Coil
To me contacts from same relay being used both in trip and close circuit is also a concern.
Also in your question I do no see if you had mentioned about OPEN/CLOSE switch, Local/Remote selector Switch? Other important thing is that from where you are energizing this interposing relay, are you using it for remote trip from SCADA or a push button installed on switchgear door?
RE: Trip Contact Not Rated to Trip Coil
RE: Trip Contact Not Rated to Trip Coil