ABB RELION 611 Series Technical Manual page 103

1MRS757454 D
611 series
Technical Manual
protection of transformer LV terminals and short lines. The functionality and
performance of the proposed overcurrent protections can be summarized as seen in the
table.
Table 69: Proposed functionality of numerical transformer and busbar overcurrent protection.
DT = definite time, IDMT = inverse definite minimum time
O/C-stage Operating char.
HV/3I> DT/IDMT
HV/3I>> DT
HV/3I>>> DT
LV/3I> DT/IDMT
LV/3I>> DT
LV/3I>>> 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.
A070980 V2 EN
Figure 41: Numerical overcurrent protection functionality for a typical sub-
transmission/distribution substation (feeder protection not
shown).Blocking output = digital output signal from the start of a
protection stage, Blocking in = digital input signal to block the
operation of a protection stage
Protection functions
Selectivity mode Operation speed
time selective low
blockable/time high/low
selective
current selective very high
time selective low
time selective low
blockable high
Section 4
Sensitivity
very high
high
low
very high
high
high
97