ABB RELION REX640, Техническое руководство, Страница: 545 / 1960

UB Beta
H 3
3H_N
U
= ×
(Equation 81)
UB
3H
Magnitude of the third harmonic bias voltage
Beta
Setting to achieve the required degree of security under healthy conditions
Ū
3H_N
Neutral side third harmonic voltage phasor
The third harmonic bias voltage calculation shown in
Equation 81
is valid under all
operating conditions if there is no generator circuit breaker between generator and
transformer. But if the generator circuit breaker is used, it is needed to reduce the
sensitivity of the protection when it is open. The use of the generator circuit breaker
is defined by
Generator CB used setting set to "Yes" and the open position is sensed
when the binary input
GCB_CLOSED
available is FALSE.
With the generator breaker in the open position, function desensitizes the
protection by multiplying the value of the
Beta setting with the set constant CB
open factor setting.
UB CB open factor Beta
3H
= × ×
U
H N 3 _
(Equation 82)
Neutral side third harmonic voltage is measured via a voltage transformer between
the generator neutral point and the earth. The magnitude of the third harmonic
biased voltage
UB_3H
is available in the Monitored data view.
Level detector
In the third harmonic differential method, Level detector compares the third
harmonic differential voltage with the third harmonic bias voltage. If the differential
voltage exceeds the biased voltage, the module sends an enabling signal to start
the timer.
If the terminal voltage is not available, that is,
Voltage selection is set to "No
voltage" the module compares the neutral side third harmonic voltage
U_3H_N
to
the set Voltage N 3.H Lim.
Timer
Once activated, Timer activates the
START
output. The Timer characteristic is
according to DT. When the operation timer has reached the value set by
Operate
delay time, the
OPERATE
output is activated. If the fault disappears before the
module operates, the reset timer is activated. If the reset timer reaches the value
set by
Reset delay time, the operation timer resets and the
START
output is
deactivated.
Timer calculates the start duration START_DUR value, which indicates the
percentage ratio of the start situation and the set operation time. The value is
available in the Monitored data view.
The binary input
BLOCK
can be used to block the function. The activation of the
BLOCK
input deactivates all outputs and resets internal timers.
1MRS759142 F Protection functions
REX640
Technical Manual
545