ABB RELION 620 Series Technical Manual page 901

1MRS757644 F
6.4.7
620 series
Technical Manual
In the example, the incoming feeder is carrying a load of 2.0 pu and both outgoing
feeders carry an equal load of 1.0 pu However, both HIxPDIF and HZCCxSPVC
consider the current as an increased differential or unbalance current because of the
broken CT wire in phase C. Both HIxPDIF and HZCCxSPVC receive the differential
current of approximately 1.0 pu The main differential protection HIxPDIF cannot
operate because of the higher current setting.
All CTs must have the same ratio.
The ALARM output of the CT supervision function can be used to energize an auxiliary
relay which can short-circuit the current CT wires, making the busbar differential
protection inoperative. This arrangement does not prevent unwanted operation of
HIxPDIF if the start setting is below the rated load. For example, if the start setting for
HIxPDIF in the example is set as 0.8 pu HIxPDIF operates before HZCCxSPVC.
Signals
Table 850: HZCCASPVC Input signals
Name Type
I_A SIGNAL
BLOCK BOOLEAN
Table 851: HZCCBSPVC Input signals
Name Type
I_B SIGNAL
BLOCK BOOLEAN
Table 852: HZCCCSPVC Input signals
Name Type
I_C SIGNAL
BLOCK BOOLEAN
Table 853: HZCCASPVC Output signals
Name Type
ALARM BOOLEAN
Table 854: HZCCBSPVC Output signals
Name Type
ALARM BOOLEAN
Supervision functions
Default Description
0 Phase A current
0=False Block signal for activating blocking mode
Default Description
0 Phase B current
0=False Block signal for activating blocking mode
Default Description
0 Phase C current
0=False Block signal for activating blocking mode
Description
Alarm output
Description
Alarm output
Section 6
895