Table 216:
Setting for a five-step df/dt< operation
Load-shedding steps
Pickup value df/dt setting
Trip Tm df/dt setting
1
-0.005 · Fn /s (-0.25 Hz/s)
8000 ms
2
-0.010 · Fn /s (-0.25 Hz/s)
2000 ms
3
-0.015 · Fn /s (-0.25 Hz/s)
1000 ms
4
-0.020 · Fn /s (-0.25 Hz/s)
500 ms
5
-0.025 · Fn /s (-0.25 Hz/s)
250 ms
Once the frequency has stabilized, the shed load can be restored. The restoring operation
should be done stepwise, taking care that it does not lead the system back to the emergency
condition.
Table 217:
Setting for a five-step restoring operation
Load-shedding steps
Restoring pickup Val setting
Restore delay time setting
1
0.990 · Fn (59.4 Hz)
200000 ms
2
0.990 · Fn (59.4 Hz)
160000 ms
3
0.990 · Fn (59.4 Hz)
100000 ms
4
0.990 · Fn (59.4 Hz)
50000 ms
5
0.990 · Fn (59.4 Hz)
10000 ms
4.3.2.6
Signals
Table 218:
81LSH Input signals
Name
Type
Default
Description
F
SIGNAL
0
Measured frequency
dF/dt
SIGNAL
0
Rate of change of frequency
BLOCK
BOOLEAN
0=False
Block signal for activating the blocking mode
BLK_REST
BOOLEAN
0=False
Block restore
MAN_RESTORE
BOOLEAN
0=False
Manual restore signal
Table 219:
81LSH Output signals
Name
Type
Description
TRIP
BOOLEAN
Trip of load shedding
OPR_FRQ
BOOLEAN
Trip signal for under frequency
OPR_FRG
BOOLEAN
Trip signal for high df/dt
PICKUP
BOOLEAN
Pickup
ST_FRQ
BOOLEAN
Pick-Up signal for under frequency detection
Table continues on next page
Section 4
1MRS240050-IB C
Protection functions
280
REF615R
Technical Manual
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