VAMP 257 - Rate of Change of Frequency (ROCOF) Protection (81 R)

VAMP 257 Feeder and motor manager
Technical description
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VAMP 24h support phone : +358 (0)20 753 3264
VM257.EN002
Setting parameters of underfrequency stages:
f<, f<< (81L)
Parameter Value Unit Default Description
f<, f<< 40.0 … 64.0 Hz 48.0 Frequency setting
t<, t<< 0.10 … 300.0 s 3.00 (t<)
0.10 (t<<)
Definite operation time
Ublock 2…100 %Un 40
Undervoltage blocking
limit
S_On
Enabled;
Disabled
- Enabled Start on event
S_Off
Enabled;
Disabled
- Enabled Start off event
T_On
Enabled;
Disabled
- Enabled Trip on event
T_Off
Enabled;
Disabled
- Enabled Trip off event
Measured and recorded values of underfrequency stages:
f<, f<< (81L)
Parameter Value Unit Description
Measured
value
f Hz Frequency
SCntr - Start counter (Start) reading
TCntr - Trip counter (Trip) reading
Flt Hz Min. fault value
Recorded
values
EDly %
Elapsed time as compared to
the set operating time; 100%
= tripping
2.3.22. Rate of change of frequency (ROCOF)
protection df/dt (81R)
Rate of change of frequency (ROCOF or df/dt) function is used
for fast load shedding, to speed up operation time in over- and
under-frequency situations and to detect loss of grid. For
example a centralized dedicated load shedding relay can be
omitted and replaced with distributed load shedding, if all
outgoing feeders are equipped with VAMP relays.
A special application for ROCOF is to detect loss of grid (loss of
mains, islanding). The more the remaining load of the local
generator differs from the load before the loss of grid, the better
the ROCOF function detects the situation.
Frequency behaviour during load switching
Load switching and fault situations may generate change in
frequency. A load drop will increase the frequency and
increasing load will decrease the frequency, at least for a while.
The frequency may oscillate after the initial change. After a
while the control system of the generator(s) will drive the