High Impedance Bus Differential Relay (KAB)
High Impedance Bus Differential Relay (KAB)
(OP)
I've come across an odd situation in a switchyard outside of a power plant. An electro-mechanical high impedance differential relay (KAB) is used as bus differential protection. As is practice, a lockout contact is used to short-circuit the varistor in order to prevent it from overheating.
I would understand completely, if the KAB tripped this lockout, but the unit differential (a separate device) actually trips the lockout that shorts across the varistor of the KAB. I just can't think of a reason this would be done.
I assume this was done in error long ago, but I would like some confirmation.
I would understand completely, if the KAB tripped this lockout, but the unit differential (a separate device) actually trips the lockout that shorts across the varistor of the KAB. I just can't think of a reason this would be done.
I assume this was done in error long ago, but I would like some confirmation.






RE: High Impedance Bus Differential Relay (KAB)
RE: High Impedance Bus Differential Relay (KAB)
It looks like it might have come about from a lack of contacts on the bus differential lockout, but there is no way the unit differential lockout is serving the intended purpose.