sepam 20 user manual - Schneider Electric

3
Protection functions Underfrequency
ANSI code 81L
3/34
MT10543
Operation
The function picks up when the positive sequence voltage frequency is below the set
point and if the positive sequence voltage is more than 20 % of Vnp (Unp/3).
If a single VT is connected (U21), the function picks up when the frequency is below
the set point and the U21 voltage is more than 20 % of Unp.
It includes a definite time delay T.
Block diagram
U32
U21
Vd
Vd > 0.2 Vnp (1)
(1) Or U21 > 0.2 Unp if only one VT.
If there is only one sensor (U21), the voltage signal is connected to terminals 1
and 2 of the connector CCT640, whatever the phase.
Characteristics
&
F < Fs
Fs set point
Setting 45 to 50 Hz or 55 to 60 Hz
Resolution 0.1 Hz
Accuracy (1) ±0.1 Hz
Pick-up / drop-out difference
Time delay T
0.2 Hz ±0.1 Hz
Setting 100 ms to 300 s
Accuracy (1) ±2 % or ±25 ms
Resolution
Characteristic times
10 ms or 1 digit
(1)
Operation time pick-up < 100 ms (typically 80 ms)
Overshoot time < 100 ms
Reset time < 100 ms
(1) In reference conditions (IEC 60255-6) and df/dt < 3 Hz/s.
T
0
time-delayed output
“pick-up” sortie
PCRED301005EN - 06/2008