ABB Relion 670 Series Technical Reference Manual page 569

1MRK505222-UUS C
9.3.2.2
9.3.2.3
9.3.2.4
Technical reference manual
issued on the RESTORE output, when the frequency recovers to a value higher than
the setting RestoreFreq. A positive setting of PUFreqGrad, sets SAPFRC (81) to
PICKUP and TRIP for frequency increases.
To avoid oscillations of the output PICKUP signal, a hysteresis has been included.
Time delay
Rate-of-change frequency protection SAPFRC (81) has a settable definite time delay,
tTrip. .
Trip signal issuing requires that the rate-of-change of frequency condition continues
for at least the user set time delay, tTrip. If the PICKUP condition, with respect to the
measured frequency ceases during the delay time, and is not fulfilled again within a
user defined reset time, tReset, the PICKUP output is reset, after that the defined reset
time has elapsed. Here it should be noted that after leaving the hysteresis area, the
PICKUP condition must be fulfilled again and it is not sufficient for the signal to only
return back into the hysteresis area.
The RESTORE output of SAPFRC (81) is set, after a time delay equal to the setting of
tRestore, when the measured frequency has returned to the level corresponding to
RestoreFreq, after an issue of the TRIP output signal. If tRestore is set to 0.000 s the
restore functionality is disabled, 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 RestoreFreq and tRestore.
Blocking
Rate-of-change frequency protection (SAPFRC, 81) can be partially or totally blocked,
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 IntBlockLevel, both the
PICKUP and the TRIP outputs, are blocked.
Design
Rate-of-change frequency protection (SAPFRC, 81) measuring element continuously
measures the frequency of the selected voltage and compares it to the setting
Section 9
Frequency protection
563