High Impedence Protection - Shunt Reactor

[inpran]

This is my 3rd project where in i'm commissioning a Shunt reactor protected with High Impedence Differential Protection ( rating 125 MVAr). I couldn't get a convincing answer as to Why are Shunt Reactors protected with High Impedence Differential Protection? Why not Low Impedence differential Protection?

Have any one of you come across a low impedence differential protection for reactor?

 

[odlanor]

I think the high-impedance differential has no restrictions coils and in consequence are more sensitive to low fault currents.

 

[Marmite]

High impedance protection has better stability for through faults. Low impedance protection requires an operate current and a restraint current which would normally utilise measurement of the neutral current to perform the calculation within the relay.
Regards
Marmite

 

[inpran]

Odlanor, Marmite,
Thanks for the replies.

 

[slavag]

I think its more historical standard.
HI is more simple and more sensitive ( newer LI is sensitive too), but request a high qulity of CT.

 

[inpran]

Salvag,
You are right, I'm trying to look at the details of the sensitivity issue of High Impedence v/s Low Impedence and found that for same CT characteristics, Low Impedence is more sensitive. And High Impedence has better sensitivity only with a better CT.