Trip vs. Unlatch Trip 1

[coloradog1]

Can someone explain the difference between "Trip conditions" and "Unlatch Trip conditions" for relay logic?

 

[ScottyUK]

Without knowing the context, one sounds like a trip & lockout function which requires external reset, while the other is a non-latching trip which clears when the cause of the trip has passed.

Where did you find these terms - any chance of the full text?


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If we learn from our mistakes I'm getting a great education!

 

[coloradog1]

SEL relay logic has both "TR" and "ULTR" Trip logic functions. If you look up a SEL 551 Relay Instruction Manual they refer to these as follows:

TR = Trip Conditoins
ULTR - Unlatch Trip Conditions

I could not upload the file due to size, but it can be found from SEL website or google.

 

[davidbeach]

When TR becomes true, the relay declares TRIP. TRIP remains true until various conditions become fulfilled, one of which is that ULTR becomes true.

 

[bacon4life]

ULTR doesn't add anything to the functionality for most schemes. However it can be used to maintain the trip signal until the breaker status contacts change, or until confirmation that a remote piece of equipment has opened.

 

[cranky108]

ULTR may not add to functionality, but it can cause problems if it is not applied correctly.

 

[tinfoil]

Trip conditions should be straighforward. These are whatever is necessary to cause the relay to require a TRIP.

However, there may be circumstances where you need to 'latch' the output to 'sustain' a trip until other requirements are met.

Maybe you want to wait until a motor operator opens a switch, then a limit switch contact in the switch control reports back that the switch is open (although this might be handled better by 'seal in' logic in the motor circuit). Once the switch contact reports 'open', you can 'stop tripping'.

Maybe you have an old external reclosing relay that has to go through a timed logic cycle after the 1st relay sends a 'trip', etc.

A lot of SCADA systems only like to send a short term (~0.5s) control output, and you may need to 'seal in' the relay's trip function for a longer period. Establishing necessary conditions for the trip signal to drop out may be more trustworthy than relying on a simple timer and assuming whatever it is has finished.