Functions
2.14 Monitoring Functions
SIPROTEC, 7SD80, Manual
E50417-G1140-C474-A1, Release date 09.2011
173
Figure 2-71 Logic diagram of the additional measuring-voltage failure detection „Fail V absent“
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 transformer
secondary circuit, individual or all measuring loops may mistakenly see a voltage of zero. Simultaneously ex-
isting 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 over-
current protection as emergency function is possible during voltage failure, provided that the time overcurrent
protection is parameterized accordingly (refer to Section 2.4). In the event of a measuring voltage failure due
to a short circuit or a broken conductor in the voltage transformer secondary circuit, individual or all measuring
loops may mistakenly see a voltage of zero. Simultaneously existing load currents may then cause spurious
pickup. When such a measuring voltage failure is detected, those protection functions are blocked whose mea-
suring 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 2.4).
Figure 2-72 shows the effect on protection functions of measuring voltage failure detected by the „fuse failure
monitor“ „VT FuseFail“ (no. 170), „VT FuseFail>10s“ (no. 169), additional measuring voltage failure
monitoring „Fail V absent“ (no. 168) and binary input of voltage transformer miniature circuit breaker
„>FAIL:Feeder VT“ (no. 361).
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