Protection Engineering Basics and Schemes Protection Engineering | Page 127

We are taking example of one of the directional
overcurrent relay made by ABB for feeder protection, I
quote some detail from its manual-instruction.
I am quoting ABB overcurrent Directional Relay for
phase and ground fault detection in transmission line.
Type CR,CP,CRC and CRD type ABB relay are used to
isolate faulty area when current in given direction in it is
exceed from predetermined value (PMS), and CRQ type is
used for tracinf of ground faults. The directional unit
operates on negative sequence current and overcurrent
operate on residual current in ground.
pg. 127