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Siemens AG ⋅ May 1998
4.7.8.3 Supervision of the external CT circuits/
differential current supervision
Interruptions or short-circuits in the secondary cirĆ
cuits of the current transformers as well as errors in
the CT connections and errors in the system configuĆ
ration of the busbar protection are automatically recoĆ
gnised by the system and annunciated. The differenĆ
tial currents formed in the measuring systems on the
protection processing modules ZPS-BSZ 1 to ZPS-
BSZ3 are used for this function.
The differential current monitoring can be activated or
deactivated by the parameter DIFF.SUP
(DA 6303/ZE).
Each measuring system is individually supervised.
Under no-fault conditions the differential current of
each measuring system is approximately 0. If no feeĆ
ders are assigned to a measuring system, then diffeĆ
rential current and stabilizing current are set to 0. The
differential current supervision picks up, if the mean
value of the differential current exceeds a threshold
independently settable for ZPS-BSZ1 >DIFsup.:CZ
(DA 6306/ZE) or ZPS-BSZ2/3 >DIFsup.:BZ
(DA 6305/ZE) within a selected time T-DIFF-SUP
(DA 6304/ZE).
If the differential current falls below the threshold beĆ
fore the set time, then the time delay is restarted if it
occurs again.
The reaction after pick-up of the differential current
supervision can individually be parameterized for
ZPS-BSZ1 and ZPS-BSZ2/3 independent of each
other.
BSZ1: DIFF.SUP.CZ (DA 6308/ZE)
BSZ2/3: DIFF.SUP.BZ (DA 6307/ZE)
D Only alarm:
When the differential current exceeds or falls beĆ
low the limit, then a general coming/going alarm
"disturbance without protection blocking" is geneĆ
rated (FNo 1/ZE) a collective alarm for ZPS-
BSZ2/BSZ3 (FNo 92/ZE) and a specific alarm
"-Diff.-super.:BZz Lx from BSZy" (FNo 96 - 107;
112 - 123; 128 - 139/ZE) for BSZ2 and (FNo 144
- 155; 160 - 171; 176 - 187/ZE) for BSZ3 or
"Diff.-current-sup.:Checkz.Lx" (FNo 93; 94;
95/ZE).
D Blocking with automatic release:
When the differential current supervision picks up,
then a general coming alarm "disturbance with
protection blocking" (FNo 0/ZE) is generated and
a selective alarm "-Diff.-superv.:BZz Lx from
BSZy" or "Diff.-current-sup.:Checkz.Lx" coming.
If the differential current exceeds the set thresĆ
hold, then bus-zone selective protection blocking
is initiated. If the fault is on ZPS-BSZ1 (check
zone), then the complete protection is blocked.
When the measured value falls below the thresĆ
hold, then the blocking is cancelled and the going-
event is issued.
D Blocking with storage:
When the differential current supervision picks
up, then general coming-alarm "disturbance with
protection blocking " is generated and a specific
alarm"-Diff.-super.:BZz Lx from BSZy" or "Diff.-
current-sup.:Checkz.Lx" coming.
If the set threshold is exceeded, then bus-zone
selective protection blocking is initiated. If the fault
is on ZPS-BSZ1 (check zone, then the complete
protection is blocked. The blocking is cancelled
when the differential current falls below the thresĆ
hold and the blocking is additionally cancelled by
operation (DA 8500/ZE) or by binary input "BloĆ
DifSuprel." (BE4/ZE).
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