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Voltage Phase Sequence
Verification of the faulted phases, phase preference, direction measurement and polarisation with quadrature
voltages usually require clockwise rotation of the measured values. The phase rotation of the measured volt-
ages is checked by monitoring the voltage phase sequence
U
before U
L1
This check takes place if each measured voltage has a minimum magnitude of
|U
|, |U
|, |U
L1
L2
In case of negative phase rotation, the indication „Fail Ph. Seq." (No. 171) is issued.
Fast Asymmetrical Measuring Voltage Failure "Fuse Failure Monitor".
In the event of a measured voltage failure due to a short circuit fault or a broken conductor in the voltage trans-
former secondary circuit certain measuring loops may mistakenly see a voltage of zero. Simultaneously existing
load currents may then cause a spurious pickup.
If fuses are used instead of a voltage transformer miniature circuit breaker (VT mcb) with connected auxiliary
contacts, then the „Fuse Failure Monitor" can detect problems in the voltage transformer secondary circuit. Of
course, the VT miniature circuit breaker and the „Fuse Failure Monitor" can be used at the same time.
Figures 2-207 and 2-208 depict the logic diagram of the „Fuse Failure Monitor".
Figure 2-207
Fuse failure monitoring Part 1: Detection of asymmetrical measuring voltage failure
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
before U
L2
L3
| > 40 V/√3
L3
Functions
2.24 Monitoring Functions
425
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