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2 Functions
Current and Voltage
To detect swapped phase connections in the voltage and current input circuits, the
Phase Sequence
phase sequence of the phase-to-phase measured voltages and the phase currents
are checked by monitoring the sequence of same polarity zero transitions of the volt-
ages.
Direction measurement with cross-polarized voltages, path selection for impedance
protection, evaluation of positive sequence voltages for undervoltage protection and
unbalanced load detection all assume a clockwise phase sequence. Phase rotation of
measured voltages is checked by verifying the phase sequences of the voltages
U
and of the phase currents, in each case
I
Verification of the voltage phase rotation is done when each measured voltage is at
least
|U
verification of the current phase rotation is done when each measured current is at
least
|I
For counter-clockwise phase sequence (L1, L3, L2), the indications "Fail Ph.
Seq. U", (FNo. 176) or "Fail Ph. Seq. I", (FNo. 175) and in addition also the
OR-combination of these indications "Fail Ph. Seq.", (FNo. 171) are signaled.
For applications where a counter-clockwise measured values phase sequence ap-
pears, this must be notified to the device via the parameter 271 PHASE SEQ. or an
accordingly allocated binary input. If the phase sequence is thereby changed, in the
device phases L2 and L3 are reversed internally for calculation of the symmetrical
components, and the positive and negative sequence currents thereby exchanged
(see also Section 2.33). The phase- related indications, malfunction values, and mea-
sured values are not affected by this.
Fuse Failure Monitoring
In case of a measuring voltage failure caused by a short circuit or a phase failure in
the voltage transformer secondary system, a zero voltage can be simulated to individ-
ual measuring loops. The measuring results of the undervoltage protection, the imped-
ance protection and other voltage-dependent protective functions may be falsified in
this way, possibly causing an unwanted operation.
If for example fuses are used instead of a secondary miniature circuit breaker with cor-
respondingly connected auxiliary contacts, then the fuse failure monitoring can
become active. Of course the miniature circuit breaker and the fuse failure monitor can
be used at the same time.
170
leads U
leads U
L1
L2
L3
leads I
leads I
.
L1
L2
L3
|, |U
|, |U
| > 40 V/√3,
L1
L2
L3
|, |I
|, |I
| > 0,5 I
.
L1
L2
L3
N
7UM61 Manual
C53000-G1176-C127-3
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