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The effect of the signals
tion is described in the following section "Impact of the Measuring Voltage Failure".
Additional Measuring Voltage Failure Monitoring
If no measuring voltage is available after power-on of the device (e.g. because the voltage transformers are
not connected), the absence of the voltage can be detected and reported by an additional monitoring func-
tion. If the circuit-breaker auxiliary contacts are used, they should be used for monitoring as well.
shows the logic diagram of the measuring voltage failure monitoring. A failure of the measuring voltage is
detected if the following conditions are met at the same time:
•
All 3 phase-to-ground voltages are smaller than FFM V<max (3ph)
•
At least 1 phase current is larger than PoleOpenCurrent or at least 1 circuit-breaker pole is closed
(settable)
•
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
monitoring indication is described in the following section "Impact of the Measuring Voltage Failure".
[lo-zusaetzl-messspgausfall-110428, 1, en_US]
Figure 2-71
Impact of the Measuring Voltage Failure
In the event of a measuring voltage failure due to a short circuit or a broken conductor in the voltage trans-
former secondary circuit, individual or all measuring loops may mistakenly see a voltage of zero. Simultane-
ously existing load currents may then cause spurious pickup. When such a measuring voltage failure is
detected, those protection functions are blocked whose measuring principle is based on undervoltage. The
definite time overcurrent protection as emergency function is possible during voltage failure, provided that
the time overcurrent protection is parameterized accordingly (refer to Section
event of a measuring voltage failure due to a short circuit or a broken conductor in the voltage transformer
SIPROTEC 4, 7SD80, Manual
E50417-G1100-C474-A2, Edition 02.2018
VT FuseFail (no. 170) and VT FuseFail>10s (no. 169) on the protection func-
Failure: Voltage absent
Logic diagram of the additional measuring-voltage failure detection
Fail V absent (no. 168) is generated. The effect of this
Functions
2.14 Monitoring Functions
Figure 2-71
Fail V absent
2.4 Backup
overcurrent). In the
157
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