ABB 615 series Technical Manual page 226

Section 4
Protection functions
220
LV terminals and short lines. The functionality and performance of the proposed
overcurrent protections can be summarized as seen in the table.
Table 210: Proposed functionality of numerical transformer and busbar overcurrent protection. DT =
definite time, IDMT = inverse definite minimum time
O/C-stage Operating char.
HV/51P DT/IDMT
HV/50PHV/ DT
50P-1/2
HV/50P-3 DT
LV/51P DT/IDMT
LV/50P DT
LV/50P-3 DT
In case the bus-tie breaker is open, the operating time of the blockable overcurrent
protection is approximately 100 ms (relaying time). When the bus-tie breaker is closed,
that is, the fault current flows to the faulted section of the busbar from two directions, the
operation time becomes as follows: first the bus-tie relay unit trips the tie breaker in the
above 100 ms, which reduces the fault current to a half. After this the incoming feeder
relay unit of the faulted bus section trips the breaker in approximately 250 ms (relaying
time), which becomes the total fault clearing time in this case.
Selectivity mode Operation speed
time selective low
blockable/time high/low
selective
current selective very high
time selective low
time selective low
blockable high
1MAC059074-MB A
Sensitivity
very high
high
low
very high
high
high
615 series ANSI
Technical Manual