2.15 Monitoring Functions
203
7SD610 Manual
C53000-G1176-C145-4
Figure 2-83 Broken-wire monitoring
Voltage Phase
Sequence
The phase rotation of the measured voltages is checked by monitoring of the voltage
phase sequence.
U
L1
before U
L2
before U
L3
This check takes place if each measured voltage has a minimum magnitude of
|U
L1
|, |U
L2
|, |U
L3
| > 40 V/√3
In case of negative phase rotation, the indication „Fail Ph. Seq.“ (No. 171) is
issued.
Asymmetrical Mea-
suring Voltage
Failure "Fuse
Failure Monitor".
In the event of a measured voltage failure due to a short circuit fault or a broken con-
ductor in the voltage transformer secondary circuit certain measuring loops may mis-
takenly see a voltage of zero. Simultaneously existing load currents may then cause
a spurious pickup.
If fuses are used instead of a secondary miniature circuit breaker (VT mcb) with con-
nected auxiliary contacts, then the („Fuse Failure Monitor“) can detect problems in the
voltage transformer secondary circuit. Of course, the miniature circuit breaker and the
„Fuse Failure Monitor“ can be used at the same time.
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