Line Transfer Trip Criteria

[cmott07]

Fellow Power Folks,

I've been tasked with evaluating the need for Line Transfer Trip schemes (primary is DCB) on a handful of 115, 230, and 500kV Transmission Lines.

Our criteria currently states that it should be applied only on transmission lines where "infeed or impedance limit fault current contributions to values below relay setpoints under network conditions" or where sequential tripping is not acceptable.

This criteria seemed to work well in the age of EM relaying but doesn't hold up well with newer, more flexible digital relaying (as they can be set much more sensitively).

Does anyone have any thoughts/tips on developing an easier to apply/less subjective criteria?

I've read several papers/threads/etc discussing the "strength" of the source but mostly in reference to Generation transfer tripping.

Any help is greatly appreciated.

 

[davidbeach]

Personally, I'd prefer transfer trip (DUTT/POTT in my case) any place I can get it. At 230kV and above it is essentially mandatory for high speed tripping for a faults. At lower voltage it depends on configuration and sensitivity to zone 2 clearing.

 

[odlanor]

This criteria seemed to work well in the age of EM relaying because you had to PAY for transfer-trip configuration.
Nowadays with digital relaying TT is part of relay.
So you do not need to make this discrimination: the price already include TT.

 

[mgtrp]

"So you do not need to make this discrimination: the price already include TT."

Of course, there is still the minor cost of installing the communication system to transmit the transfer trip between substations...

 

[odlanor]

I guess that SEL MIRRORED BITS™ Communications is part of line protection relay of SEL relays.

 

[JG2828]

Why not go with Line Current Differential? As long as you have a digital channel or direct fiber communications.

http://www.selinc.com/sel-311l/

 

[westex]

Regardless of Kv we use DTT on any line that has beaker-and-half. The DTT is initiated by one of the two breaker failure LORs in a Breaker-and-half. Think of DTT as an extension of BF. The way we transmit DTT is using a wave trap with a duel line tuner (because we also have DCB) or fiber. If we go with the wave trap we use a Pulsar 10F-10B. If we use the fiber than I just run a couple of wires over the to telcomm panel and the telcomm bunch do the rest, so not sure there.

 

[ASimmons23]

I am using 311L's for primary line differential protection (POTT) for 230kV, 69kV and 13.8kV transmission as well as a 351S for backup diff. scheme (DCB).

For high speed transfer tripping, the 311L's with F.O. communications is the way to go.