ABB RELION REX640 Technical Manual page 545

1MRS759142 F
UB
3
UB
Beta
Ū
3H_N
The third harmonic bias voltage calculation shown in
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
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
open factor setting.
UB
3H
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" the module compares the neutral side third harmonic voltage U_3H_N to
the set
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
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
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.
REX640
Technical Manual
Beta U
= ×
3H_N
H
Magnitude of the third harmonic bias voltage
3H
Setting to achieve the required degree of security under healthy conditions
Neutral side third harmonic voltage phasor
Generator CB used setting set to "Yes" and the open position is sensed
CB open factor
= ×
Voltage N 3.H Lim .
Reset delay time , the operation timer resets and the START output is
Beta setting with the set constant CB
Beta × U
H N
3 _
Voltage selection is set to "No
Protection functions
(Equation 81)
Equation 81
is valid under all
(Equation 82)
Operate
545