ABB RELION REX640 Technical Manual page 380

Protection functions
4.1.4.5 Operation principle
The function can be enabled and disabled with the
corresponding parameter values are "on" and "off".
The operation of GAEPVOC can be described by using a module diagram. All the
modules in the diagram are explained in the next sections.
Figure 225: Functional module diagram
Arming check
The fundamental frequency component of the three measured phase-to-phase
generator side voltages are compared with setting
voltages are below the set
ARMED signal is set to TRUE and simultaneously Level detector is enabled.
The value of
condition that can occur when the system is under extreme stress conditions. When
the generator returns to service and the voltage exceeds the
setting, the scheme is automatically removed from service (Level detector disabled)
after a time delay (
GAEPVOC must only be activated when the generator is out-of-service and disabled
when the generator is online.
Activation of BLOCK input resets the ARMED output to FALSE state.
Level detector
The measured peak-to-peak values of three phase currents are compared with the
set
Timer.
Timer
Once activated, Timer activates the START output. The time characteristic is
according to DT. When the operation timer has reached the value set by
delay time , the OPERATE output is activated. If a drop-off situation occurs, the Timer
reset state is activated. If the reset timer reaches the value set by
Timer resets.
380
I3P
U3P
BLOCK
Arm set voltage must be set lower than any emergency low voltage
Disarm delay time setting ) and the ARMED output is set to FALSE.
The setting value of
Disarm set voltage .
of
Start value . If the measured values exceed Start value , an enable signal is sent to
I_A
Level
I_B
detector
I_C
U_AB
Arming
U_BC
check
U_CA
Arm set voltage for longer than Arm delay time , the
Arm set voltage should be less than the setting value
1MRS759142 F
Operation setting . The
Timer OPERATE
t
START
ARMED
Arm set voltage . If all measured
Disarm set voltage
Operate
Reset delay time ,
Technical Manual
REX640