Figure 2-54 showa the logic diagram of the measured voltage failure monitoring. A failure of the measured
voltage is detected if the following conditions are met at the same time:
•
All 3 phase-to-earth voltages are less than FFM U<max (3ph)
•
At least 1 phase current is larger than PoleOpenCurrent or at least 1 breaker pole is closed (can be
set),
•
No protection function has picked up,
•
This condition persists for a settable time T V-Supervision (default setting: 3 s)
The time T V-Supervision is required to prevent that a voltage failure is detected before the protection
picks up.
If this monitoring function picks up, the indication
Fail U absent
(No. 168) will be issued. The effect of
this monitoring indication will be described in the following section “Effect of the Measuring Voltage Failure”.
[logikdia-zusaetzl-messspgausfall-wlk-010802, 1, en_GB]
Figure 2-54
Logic diagram of the additional measuring-voltage failure detection
Fail U absent
Effect of the measuring voltage failure
In the event of a measuring voltage failure due to a short-circuit or broken conductor in the voltage trans-
former secondary circuit, some or all measuring loops may mistakenly see a voltage of zero.
Figure 2-55 shows the effect on the protection functions in case that a measuring voltage is detected by the
“fuse failure monitor”
VT FuseFail
(No. 170),
VT FuseFail>10s
(No. 169), the additional measuring
voltage failure monitoring
Fail U absent
(No. 168) and binary input VT miniature circuit breaker
>FAIL:Feeder VT
(No. 361).
Functions
2.7 Monitoring Functions
SIPROTEC 4, 7VK61, Manual 137
C53000-G1176-C159-5, Edition 05.2018
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