85DTTR relay

[bejoyeleengineer]

Hello,

What is the purpose of the 85 direct transfer relay? is it used for the Breaker failure scheme. i.e, if the breaker fails in another substation, then the relay will send a command through the 85DTTR relay to the remote substation to trip the breaker at the other end.
my question is - is the 85DTTR used in case of a breaker failure or is it used when other faults like phase to phase faults etc occurs and there after sends a command for tripping the breaker at the remote substation.

 

[richxtlc]

You are correct it that is sends a direct trip to the remote location to open the circuit breaker in the event of a breaker failure at your end. The breaker failure could be failure to open or an internal failure in which the breaker opens but faults internally.

 

[kingpb]

by definition an 85 relay according to IEEE C37.2 is:

Device number 85?pilot communications, carrier or pilot-wire relay: A device that is operated, restrained, or has its function modified by communications transmitted or
received via any media used for relaying.

The fact that they are using it for breaker failure is an option, it can be used for any function whereby you are wanting to send information to another location, typically of some distance away.

 

[richxtlc]

Yes, you are correct about the designation 85, but the DTTR designation states its function as a Direct Transferred Tripping relay

 

[kingpb]

My reference was in the fact that it may be used for breaker failure, But it is not limited to breaker failure as the OP is suggesting, it can be used for any trip signal intended to go over some distance to another device.

 

[richxtlc]

When a relay is used as a DTTR there is no inherent delay in tripping, it is the equivalent of a remote trip switch. Most relays as you have stated are used to communicate a fault has occured on the feeder (trip) or that a fault has occured outside the zone of protection (no trip or block tripping). A direct transfer trip is a special relay usually dedicated to transfer tripping.