ABB RELION 670 Series Technical Manual page 684

Section 10
Frequency protection
and no output will be given. The restore functionality is only active for lowering frequency
conditions and the restore sequence is disabled if a new negative frequency gradient is detected
during the restore period, defined by the settings
10.3.7.3 Blocking
Rate-of-change frequency protection (SAPFRC, 81) can be partially or totally blocked, by binary
input signals or by parameter settings, where:
BLOCK:
BLKTRIP:
BLKREST:
If the measured voltage level decreases below the setting of
function, both the PICKUP and the TRIP outputs are blocked.
10.3.7.4 Design
Rate-of-change frequency protection (SAPFRC, 81) measuring element continuously measures the
frequency of the selected voltage and compares it to the setting
signal is filtered to avoid transients due to power system switchings and faults. The time
integrator operates with a definite delay time. When the frequency has returned back to the
setting of
signal has earlier been issued. The sign of the setting
function is used for raising or lowering frequency conditions. The design of SAPFRC (81) is
schematically described in figure 367.
678
blocks all outputs
blocks the TRIP output
blocks the RESTORE output
RestoreFreq , the RESTORE output is issued after the time delay tRestore , if the TRIP
RestoreFreq and tRestore .
MinValFreqMeas in the preprocessing
PUFreqGrad . The frequency
PUFreqGrad is essential, and controls if the
1MRK 502 066-UUS B
M14970-23 v5
M14970-34 v6
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