2.2 Differential Protection
129
7UT613/63x Manual
C53000-G1176-C160-2
current of the 7UT613/63x) amounts to I
N
= 0.1 A at nominal conditions, with correct
matching.
Figure 2-48 Winding arrangement of summation and matching transformers 4AM5120
Differential Current
Monitoring
Whereas a high sensitivity of the differential protection is normally required for trans-
formers, reactors, and rotating machines in order to detect even small fault currents,
high fault currents are expected in case of faults on a busbar so that a higher pickup
threshold (above rated current) is conceded here. This allows for a continuous moni-
toring of the differential currents on a low level. A small differential current in the range
of operational currents indicates a fault in the secondary circuit of the current trans-
formers.
When, during normal load conditions, a differential current is detected in the order of
the load current of a feeder, this indicates a missing secondary current, i.e. a fault in
the secondary current leads (short-circuit or open-circuit). This condition is annunciat-
ed with time delay. The differential protection is blocked at the same time.
Feeder Current
Guard
With busbars a release of the trip command can be set if a threshold is exceeded by
one of the incoming currents. The currents of each feeder are monitored for over-
shooting of a set value. Trip command is allowed only when at least one of these cur-
rents exceeds a certain (settable) threshold.
2.2.7 Setting Notes
General Differential protection is only effective and available if this function was set during con-
figuration of the Functional Scope DIFF. PROT. = Enabled (address 112) . If the
function is not required Disabled is to be set.
Additionally, the type of protected object must be decided during configuration (ad-
dress 105 PROT. OBJECT). Only those parameters are offered which are reasonable
for the selected type of protected object; all remaining are suppressed.
The differential protection can be switched 1201 or DIFF. PROT. in address ON OFF.
The option Block relay allows to operate the protection but the trip output relay is
blocked.
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