Siemens SIPROTEC 4 7VK61 Manual page 137

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
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
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"
voltage failure monitoring
>FAIL:Feeder VT (No. 361).
SIPROTEC 4, 7VK61, Manual
C53000-G1176-C159-5, Edition 05.2018
Logic diagram of the additional measuring-voltage failure detection
VT FuseFail (No. 170), VT FuseFail>10s (No. 169), the additional measuring
Fail U absent (No. 168) and binary input VT miniature circuit breaker
Fail U absent (No. 168) will be issued. The effect of
Functions
2.7 Monitoring Functions
Fail U absent
137