Power transformer protection with distance relays

[amps21]

Distance relays have been proposed as backup relays for transformer protection, primary protection being Differential relays. Any thoughts on
1. what zones / logic should be used.
2. Some have recommended using POTT schemes. Anybody using this?
3. Ways to mitigate inrush

Thx

 

[opmgr1]

There are some interesting discussions on inrush mitigation in thread238-235674.
Why use distance relay as back up for transformer protection? Why not 50/51 and distance relays for your transmission lines?

 

[amps21]

Basically for the following, probably only one of which may not be possible with a 50/51
a. High speed protection with POTT
b. Breaker Failure
c. Bus backup with either reverse zone or far looking forward

opmgr1,
By mitigating inrush, i meant logic/ways etc. in a relay to inhibit it from tripping on an inrush, but still keeping the protection on for any failures on energization etc.

Thanks

 

[slavag]

Hi.
Usually 21 function used as back-up protection for the generator-trafo units.
We hade here some thread on the topic.
But with "zero" time it protect only 75% of trafo, second zone not so fast, you need selectivity with other protection.
for the transmission or distribution trafos, 21 is unusuall protection, but maybe you have block: trafo-line?
Best Regards.
Slava

 

[amps21]

Thanks for your replies. I am researching more on this. I shall let know when i find out more.

 

[DiscoP]

There is some information in the D30 Manual (GE Multilin) on this application.