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Functions
2.6 Voltage Protection 27, 59
[7sj80-ueberspgs-schutz-20061219, 1, en_US]
Figure 2-44
Undervoltage Protection 27
2.6.3
Function
Undervoltage protection consists of two definite time elements (27-1 PICKUP and 27-2 PICKUP). There-
fore, tripping can be time-coordinated depending on how severe voltage collapses are. Voltage thresholds and
time delays can be set individually for both elements.
The dropout ratio for the two undervoltage elements (= V
Like the other protection functions, the undervoltage protection operates in an extended frequency range.
This ensures that the protection function is ensured even for the protection of decelerating motors, for
instance. However, the r.m.s. value of the positive voltage component is considered too small when the
frequency deviates considerably so that the device will tend to overfunction.
Figure 2-45
shows a typical voltage profile during a fault for source side connection of the voltage trans-
formers. Because full voltage is present after the circuit breaker has been opened, current supervision CS
described above is not necessary in this case. After the voltage has dropped below the pickup setting, tripping
is initiated after time delay 27-1 DELAY. As long as the voltage remains below the dropout setting, reclosing
is blocked. Only after the fault has been cleared, i.e. when the voltage increases above the dropout level, the
element drops out and allows reclosing of the circuit breaker.
124
Logic diagram of the overvoltage protection
/V
) can be set.
dropout value
pickup value
E50417-G1140-C343-A8, Edition 12.2017
SIPROTEC 4, 7SJ80, Manual
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