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Section 10
Frequency protection
10.1.7.4
10.1.7.5
302
Blocking
It is possible to block underfrequency protection SAPTUF (81) partially or completely, by
binary input signals or by parameter settings, where:
BLOCK:
blocks all outputs
BLKTRIP:
blocks the TRIP output
BLKREST:
blocks the RESTORE output
If the measured voltage level decreases below the setting of MinValFreqMeas in the
preprocessing function both the PICKUP and the TRIP outputs are blocked.
Design
The frequency measuring element continuously measures the frequency of the positive
sequence voltage and compares it to the setting PUFrequency. The frequency signal is
filtered to avoid transients due to switchings and faults. The time integrator can trip either
due to a definite delay time or to the special voltage dependent delay time. When the
frequency has returned back to the setting of RestoreFreq, the RESTORE output is issued
after the time delay tRestore. The design of underfrequency protection SAPTUF (81) is
schematically described in figure 103.
1MRK 511 365-UUS A
Phasor measurement unit RES670 2.1 ANSI
Technical manual
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