Residual Overvoltage Protection - ABB REU 610 Technical Reference Manual

1MRS755769
5 . 1. 4 . 4 .
Voltage Relay
Technical Reference Manual
The benefit of this function is that the voltage value measured during or after
a network fault is a good measure of how critical the fault is for a smaller
power plant. W hen the positive phase- sequence voltage value falls below the
critical limit, the power plant has to be disconnected from the network.
R E U 610 measuring the positive phase- sequence voltage complements other
methods used to disconnect smaller power plants. The application of these
methods is based on frequency and voltage measurement. The undervoltage
protection based on calculated positive phase- sequence voltage requires that
the relay is in three- phase use.
W hen the calculated positive phase- sequence voltage value U
the set start value of the stage U
5 0 ms' start time. W hen the set operate time at definite- time characteristic or
the calculated operate time at ID M T characteristic elapses, the stage generates
a trip signal. The stage is reset in 7 0 ms after the calculated positive phase-
sequence voltage value has ex ceeded the set start value of the stage.
The positive phase- sequence voltage is calculated as follows:
+ × +
8 D 8
=
8
V
a = 1∠ 120°
2
a = 1∠ - 120°
On a symmetrical network, this formula scales the positive phase- sequence
value to the same amplitude as the measured voltage signal.
S tage U<< can be set to be blocked when the measured voltage values fall
below 0.15 × U . In addition, the tripping of stage U< can be set to be
n
blocked by stage U<< start. The selection is made in S GF 4 .
S tage U < has a fix ed drop- off/ pick- up ratio of 1.04 .
1
Res i d u al ov er v oltage p r otec ti on
The residual overvoltage protection detects residual voltages caused by earth
faults.
W hen the residual voltage ex ceeds the set start value of the low- set stage U
the stage generates a start signal after a ~ 7 0 ms' start time. W hen the set
operate time elapses, the stage generates a trip signal.
S tage U > has a settable resetting time t
0
ex isting electromechanical relays or for reducing fault clearance times of
recurring, transient faults. If stage U
falls below the set start value of the stage, the start of the stage remains active
<, the stage generates a start signal after a ~
1
×
D 8
> for reset coordination with
0r
> has started and the residual voltage
0
REU 610
falls below
1s
( 2)
>,
0
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