sepam 20 user manual - Schneider Electric

Protection functions Positive sequence undervoltage
and phase rotation direction check
ANSI code 27D/47
PCRED301005EN - 06/2008
Operation
Positive sequence undervoltage
The protection picks up when the positive sequence component Vd of a three-phase
voltage system drops below the Vsd set point with
Vd
1
-- U21 a
3
with and
2 = ( – U32)
V =
U
------ a
3
j
e
2π
=
------
3
b it includes a definite time delay T
b it allows drops in motor electrical torque to be detected.
Phase rotation direction
This protection also allows the phase rotation direction to be detected.
The protection considers that the phase rotation direction is inverse when the positive
sequence voltage is less than 10 % of Unp and when the phase-to-phase voltage is
greater than 80 % of Unp.
MT10872
1
Vd -- V1 V2 a
3
2 = ( + + V3)
Block diagram
Vd
U21
(or V1)
Characteristics
Vd < Vsd
Vd < 0.1Un
U > 0.8 Un
Vsd set point
Setting 15 % Unp to 60 % Unp
Accuracy (1) ±2 %
Pick-up/drop-out ratio 103 % ±2.5 %
Resolution 1 %
Time delay
Setting 50 ms to 300 s
Accuracy (1) ±2 %, or ±25 ms
Resolution 10 ms or 1 digit
Characteristics times
Operating time pick-up < 55 ms
Overshoot time < 35 ms
Reset time < 35 ms
(1) In reference conditions (IEC 60255-6).
(2) Displays "rotation" instead of positive sequence voltage measurement.
T
&
0
time-delayed output
“pick-up” signal
rotation display (2)
3/5
3