Supervisory Functions
147
7SS52 V4 Manual
C53000-G1176-C182-3
Auxiliary voltage
supply failure
Usually, the isolator auxiliary voltage is sub-fused in each bay. If this auxiliary voltage
is missing, then all the isolators in this bay display the bit pattern 0/0 (neither OPEN
nor CLOSED). The indication "Bay DC fail G" (FNo. 10426/CU) and "Isol flt
alarm" (FNo. 10425/CU) are output. In order to prevent erroneous annunciations,
there is always a short delay of 500 ms for the response and the signalling of auxiliary
voltage failure. For the distinction of isolator faults, at least two isolators are to be
monitored. By cross-checking with the other isolator positions, this fault condition can
be detected. The bay with the faulted isolator is either assigned the old positions
according to the busbar protection (flip-flop relay characteristic) or all isolators of this
bay are considered to be CLOSED. The type of treatment can be set with the
parameter ISOL DC FAIL (6303/CU).
Wire break In the event of short-circuits in the feeders, the busbar protection remains stable even
with a wire break on the checkback signal lines for the isolator status. In that case the
isolator is considered to be CLOSED.
However, the so-called preferential treatment can lead to unselective tripping if all of
the following conditions apply:
• Wire break in the checkback signal line for the isolator status
• Isolator is in OPEN position
• Fault on one busbar
• Second isolator of the feeder is in CLOSED position
Non-selective tripping can be prevented by additional measures. Such measures
could be, for instance, interlocking of the TRIP command with the integrated overcur-
rent query or monitoring the pick-up of the feeder protection.
Wire breaks are annunciated in the central unit as isolator malfunction status individ-
ually for each feeder ("FltR $01 $02" (FNo. 176.1122/CU); e.g. $02 for
isolator 3).
The meaning of the isolator status indications is shown in the following table.
Table 5-1 Isolator status indications
Isolator status indication Meaning Reaction Alarm
CLOSED OPEN
1 0 Isolator CLOSED Isolator CLOSED Alarm "CLOSED" (
FNo. 176.1110/CU) *)
0 1 Isolator OPEN Isolator OPEN Alarm "OPEN"
(FNo 176.1110/CU) *)
1 1 Isolator status not
plausible
new isolator status accord-
ing to setting 6304/CU
"$01 $02"
(FNo. 176.1110/CU),
"FltP$01 $02"
(FNo. 176.1113/CU) and
"Isol fit pos M"
(FNo. 10428/CU),
“Isol flt alarm
”
(
FNo. 10425/BU)
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