ABB Relion 650 Series Technical Manual page 270

Section 8
Frequency protection
8.3.6.1 Measurement principle
The rate-of-change of the fundamental frequency of the selected voltage is measured
continuously, and compared with the set value,
SAPFRC (81) is also dependent on the voltage magnitude. If the voltage magnitude decreases
below the setting
global base voltage parameter, SAPFRC (81) is blocked, and the output BLKDMAGN is issued. The
sign of the setting
change in frequency. If SAPFRC (81) is used for decreasing frequency that is, the setting
PUFreqGrad has been given a negative value, and a trip signal has been issued, then a 100 ms
pulse is issued on the RESTORE output, when the frequency recovers to a value higher than the
RestoreFreq . A positive setting of PUFreqGrad , sets SAPFRC (81) to PICKUP and TRIP for
setting
frequency increases.
To avoid oscillations of the output PICKUP signal, a hysteresis has been included.
8.3.6.2 Time delay
SAPFRC (81) has a settable definite time delay,
Trip signal issuing requires that SAPFRC (81) condition continues for at least the user set time
tTrip . If the PICKUP condition, with respect to the measured frequency ceases during the
delay,
delay time, and is not fulfilled again within a defined reset time, the PICKUP output is reset after
the reset time has elapsed.
The RESTORE output of SAPFRC (81) is set, after a time delay equal to the setting of
when the measured frequency has returned to the level corresponding to
issue of the TRIP output signal. If
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
264
MinValFreqMeas in the preprocessing function, which is set as a percentage of a
PUFreqGrad , controls if SAPFRC (81) reacts on a positive or on a negative
tRestore is set to 0.000 s the restore functionality is disabled,
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PUFreqGrad . Rate-of-change frequency protection
tTrip .
RestoreFreq and tRestore .
1MRK 506 326-UUS B
M14970-6 v4
M14970-10 v4
tRestore ,
RestoreFreq , after an
Line distance protection REL650
Technical manual