TRIP COIL 2

[tszpun]

Hello experts,
In my project, i have a requirement like this : "remote trip signal shall be wired directly to circuit breaker trip coil".

Could somebody confirm my understanding:
If i am not mistaken there are two types of wiring a trip signal:
1) Trip signal wired to IED or Relay
2) Trip signal wired to directly trip coil.
So in this case, as per project requirement, we should not wire the trip comamnd to IED, but i need to wire it directly to trip coil. Is this correct?

 

[che12345]

Dear Mr. bazraabat (Industrial)(OP)28 May 22 05:25
"...In my project... requirement : "remote trip signal shall be wired directly to circuit breaker trip coil".... So as per requirement, #1. we should not wire the trip comamnd to IED, but #2. i need to wire it directly to trip coil. Is this correct? "

#1. Yes, should not wire the trip command to IED.
#2. Yes, wire it directly to the trip coil.
BTW: What is the reason that you raise the question " ..... to wire the trip command to IED ... "
Che Kuan Yau (Singapore)

 

[tszpun]

Thank you for the reply.
I asked just to confirm my understanding, because i was not sure if i understood it correctly. Your reply ensures me tht ive understood correctly. Thank you.

By the way, what is the reason to wire directly to trip coil? Is there any reason behind that? Is this just to avoid malfunction/outage of IED?

 

[RRaghunath]

tszpun,
"what is the reason to wire directly to trip coil? Is there any reason behind that? Is this just to avoid malfunction/outage of IED?" - You are right. It is to prevent failure to trip due to problem in interface relay or IED.
When you are wiring the remote trip signal directly to trip coil, make sure the voltage drop as the trip col picks up is within acceptable range. Otherwise, you may have a situation that the trip coil fails to pickup leading to failure to trip and probably burning of the trip coil as well.

 

[tszpun]

Thank you for the suggestion.
Regarding the voltage drop, to avoid this issue, i was thinking to use DC coil, instead of AC coil. I hope it will erase all the problems with voltage drop, right?

 

[che12345]

Dear Mr. tszpun (Industrial)(OP)28 May 22 08:10
"....Regarding the voltage drop, to avoid this issue, #1. i was thinking to use DC coil, instead of AC coil. #2. I hope it will erase all the problems with voltage drop, right? "
#1. Both AC or DC are widely used. In general, use 110 V AC or DC would not face voltage drop problem within say 50m. Attention: If AC trip power supply is taken from the AC power source, the (shunt release) [ would NOT operate!] when the AC power source failed. Very often, the trip coil power is taken from the battery bank, therefore it would be DC coil. Note: the DC from the battery is understood to be secured even when the AC power source fails/tripped.
#2. NO. Either ( AC or DC ) coil, both must take the [voltage-drop] into consideration for long distance wiring, or voltage say lower than 24V AC/DC.
FYI: For the ( same conductor size ), the AC/DC [ copper resistance is the same]. For AC , the total value is the (impedance) , where the [inductance is generally NOT very significant at 50/60Hz].
Che Kuan Yau (Singapore)

 

[Sn00ze]

@tszpun

I think you got your question answered but I wanted to weigh in on "trip signal wired to IED". I can only think of very specific instances where you would do this instead of directly to the TC (DTT/BF).

Which leads me to wonder, why this is even a question? it is generally considered a "bad design" if your protection has already indicated that your equipment needs to be tripped (CB). why would you ever re-route it via another device other than it being a DTT to remote site or that is the only way to trip the device (possible a GIS). you are only adding more time to the fault and increasing your fault current, also adding another point of failure, etc.

 

[stevenal]

Wiring directly to the coil is a bad idea. The trip circuit is designed so the 52a contact will interrupt the highly inductive coil current. Perhaps the requirement is "remote trip signal shall be wired directly to circuit breaker trip circuit".

 

[bacon4life]

Wiring directly to the trip coil avoids several kinds of failure. These failures include things like:
1 loss of power to the IED
2 failure of IED input sensor
3 failure of IED output contact
4 failure of additional wire terminations
5 programming mistake where the input is not correctly mapped to the output contact
6 Inadvertent operation during IED startup/shutdown. The designer must be very careful about selection of NO vs NC contacts. Using a NC closed output contact could result in an inadvertent trip whenever the IED reboots.

I have lots of cases where I prefer not to wire directly to the trip coil including:
-Test switches. The statement from the OP could be interpreted as prohibiting test switches. Test switches add a possible failure mode, but vastly simplify testing and troubleshooting. Although some US utilities used to avoid test switches, this is changing; NERC testing requirements are very hard to fulfill without test switches.
-Mechanical lockout relays. Often trips signals hit a lockout relay instead of directly going to the trip coil.
-Increased contact rating. As RRaghunath mentioned, many contacts not rated for trip coil current.
-Isolation of DC circuits. Sometimes there is more than 1 DC circuit involved in control of a breaker.
-Contact multiplication. A single device may need to trip 2 or more breakers. High voltage circuit breakers typically have two trip coils and independent pole breaker could have up to 9 trip coils.
-Trip seal-in. Momentary trip signals such as transformer sudden pressure relays typically require an additional relay to seal-in the momentary trip signal.
-Supervision for trip signals. Devices like temperature monitors, low oil level sensors, and pressure relief devices sometimes require at least 2 separate sensors to operate before tripping the transformer.
-Flagging/monitoring-Trip signals coming from devices without flags to indicate they tripped can be a nightmare to troubleshoot. If the activating device does not have flagging, the trip can all be send through an IED that will monitor the trip signals and provide event details to the operator. Note that this configuration slightly reduces dependability while vastly increasing maintainability.