Line tripping on transformer inrush

[HamburgerHelper]

Is there anyway to get around a line with 9 or so transformers from tripping out on inrush? I know that you have to hit it just right for it happen so it is kind of a rare bird. Do some people use harmonic restraint, time overcurrent curves, or just a delay to give the inrush a chance to decay some before making a decision as to whether to trip out or not? The inrush is tripping out phase distance protection.

 

[JG2828]

I don't think phase distance protection usually has a harmonic restraint setting. It can however have a time delay setting. Do you have a oneline or a sketch of this system? You have 1 line with 9 transformers fed from it. Is the distance relay protecting the line or the transformers? Which direction is it facing?

 

[HamburgerHelper]

No, our distance relaying doesn't have harmonic restraint but I was thinking that something like that could be used because you see it in transformer protection relays. The line tripped on reclosing on a long forward looking zone that was long enough to see the inrush.

 

[JG2828]

Possibly shorten the zone 1 distance zone so it falls short of the transformers and add a zhone 2 distance zone with a time delay longer than the inrush?

 

[alexfox]

No, our distance relaying doesn't have harmonic restraint but I was thinking that something like that could be used

Call and sell that to the SEL/Basler/GE development teams.


Do you have a magnitude/time estimate for the transient during reclose? What does the TCC for the relay look like and how adjustable is it?

 

[ZapSib]

Some distance protection are available with inrush restraint ( e.g.

http://www.schneider-electric.com/download/ww/en/results/0/0/19071615-MiCOM-P44x-current/0/).

That being said, is it the inrush itself causing the maloperation ? Did you check if the CT goes onto saturation ( due to long DC decay) ?
Can this be the root cause ?