Trip Circuit Supervision - Alarm or Trip 1

[NickParker]

When there is a trip circuit supervision alarm, do you trip the breaker using the other trip coil (there are 2 trip coils) or only alarm so that it gives the operator time to investigate. Note that trip circuit supervision is backed by 50BF.

 

[cranky108]

Most of the time, manual, and SCADA trip is only on trip circuit one. If there is an alarm, the operator should dispatch a technician to investigate.

About the only time you would trip on an alarm is if it was something small, like a generator of less than one MW, where it may not justify an elaborate protection scheme. These small units we use for breaking the water pressure in a water pipe, and are not our main source of energy. We would trip the unit on a relay alarm, or maybe a trip coil alarm.

 

[System Protection]

Alarm.

Both trip coils should get energized by your protective relays so there should be no reason to trip immediately as it should still clear normally via the other trip circuit if you did have a fault.

 

[RRaghunath]

Trip circuit supervision is wired for alarm in all cases where there are two trip coils, generally speaking.
All protection trips are wired to both the trip coils and thus protection trip is ensured even with only one healthy trip coil.

R Raghunath

 

[NickParker]

Had a discussion with my colleague; he says it is okay to provide only alarm; however asking the tripping operations to be transferred to Under voltage release (yes, we also have under voltage release in addition to the 2 opening coils)
he also says that there is a difference between opening coil and tripping coil.
Opening coil --> Intended for normal on/off operations
Tripping coil --> Intended only for Tripping operations.
I think both are same; may be he was referring to under voltage release as Tripping coil

 

[System Protection]

Perhaps "procedurally" the two coils are different.

I don't recall ever seeing a physical difference.

I have seen one trip coil used for control handle/SCADA and the other coil used for protection BUT the Breaker Failure Relay upon initiation would energize the "operational" trip coil. It was referred to as a "retrip".

Either way I would highly recommend that your protective relays have the ability to energize both trip coils in some way or another.

 

[crshears]

I agree with RRaghunath; alarm only. This is a loss of redundancy notification that requires prompt action, but not normally a situation that requires tripping the equipment out of service.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[wcaseyharman]

I’ve only ever seen it as an alarm within large power stations, that includes older stations with single trip coils.

 

[FreddyNurk]

So trip coil supervision is normally used when there's a risk that the coil itself has been disconnected or is otherwise non-functional. It is done as a positive operation check (i.e. confirm that the trip circuit is intact and operational) as opposed to just hoping that the circuit integrity has been maintained whilst de-energised and waiting for a trip signal.

Why not just use an under-voltage release instead?
It's not always available or practical depending on the size and operational voltage of the breaker it's being used on. As size goes up so does the hold in current and associated heating effects, and the coil itself thus needs to be rated for continuous duty. An under-voltage release is effectively a trip coil, it's just that it's operation is opposite.

It's possible to burn out a short duty rated trip coil by leaving the coil energised after a trip operation.

The decision on whether to trip or just alarm is generally left to a risk assessment and the balance between protecting the equipment versus maintaining supply, as well as the overall protection scheme. If you're running a dual redundant (X and Y etc) protection scheme an alarm on a trip supervision would be appropriate. If protection of plant is more important than maintaining supply either trip via Breaker Fail (if configured) or attempting to trip the faulted coil on an alarm might be more appropriate.

EDMS Australia