sepam 20 user manual - Schneider Electric

Protection functions Rate of change of frequency
ANSI code 81R
PCRED301005EN - 06/2008
MT10877
Operation
This function picks up when the rate of change of frequency (ROCOF) of the positive
sequence voltage overshoots the set point.
If only one VT is connected (U21), the function is inhibited.
It includes a definite time delay T.
Block diagram
Vd
f
> 0.5 Vn
< Fmax
> Fmin
Characteristics
& dF/dt
> + dFs/dt
< - dFs/dt
dFs/dt set point
Setting 0.1 to 10 Hz/s
Resolution 0.1 Hz/s
Accuracy tripping ±5 % or ±0.1 Hz/s
Time delay T
no tripping ±3 % or ±0.05 Hz/s
Setting 100 ms to 300 s
Accuracy ±2 % or ±25 ms
Resolution 10 ms or 1 digit
Characteristic times (1)
Operation time pick-up < 170 ms (130 ms typical)
Overshoot time < 100 ms
Reset time
(1) In reference conditions (IEC 60255-6).
< 100 ms
1
T
0
time delayed
output
signal “pick-up”
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