Over Current Protection (Oc); Earth Fault Protection (Ef) - GE P741 Technical Manual

Application Notes
MiCOM P741, P742, P743
i DZ
I>DZ
I>1
For each PU connected to a Feeder Circuit Breaker (not on bus couplers or bus sections)
For the phase:
•
I>DZ must be below 80% of the minimum Dead Zone fault level (and if possible bigger
than the maximum load).
•
I>DZ Time delay must be at least 50ms if the CB status positions are used (any value
otherwise).
For the Neutral (if used):
•
IN>DZ must be below 80% of the minimum Dead Zone earth fault.
•
IN>DZ Time delay must be at least 50ms if the CB status positions are used (any value
otherwise).
2.2.2

Over Current protection (OC)

Two stages overcurrent protection is available in each Peripheral Unit.
The first stage I>1 is either DT or IDMT, the second I>2 stage is DT only.
Both can be individually blocked using ddb signal in the PSL:
•
Block phase overcurrent stage 1 time delay (I>1 Timer Block)
•
Block phase overcurrent stage 2 time delay (I>2 Timer Block)
2.2.3

Earth Fault protection (EF)

Two stages neutral overcurrent i.e. Earth Fault protection is available in each Peripheral
Unit.
The first stage IN>1 is either DT or IDMT, the second stage IN>2 is DT only.
Both can be individually blocked using ddb signal in the PSL:
•
Block earth fault stage 1 time delay (IN>1 Timer Block)
•
Block earth fault stage 2 time delay (IN>2 Timer Block)
2.2.4 Stub protection
When a one and half breaker scheme is protected by a P74x, the stub protection can be
done using a simple time delayed overcurrent element in each PU.
The activation of this protection has to be set in the PSL and activated when all the
associated isolators are open.
Trip
DZ1
I I
bias2
bias1
Ibias1: DZ1 => busbar trip,
Ibias2: DZ2 => no trip
DZ2
Restrain
i bias
P74x/EN AP/Na7
(AP) 6-15
P3956ENa
AP