4.1.4.5
Operation principle
The function can be enabled and disabled with the
Operation setting. 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.
Level
detector
ARMED
I3P
I_A
I_B
I_C
U3P
U_AB
U_BC
U_CA
BLOCK
Arming
check
OPERATE
START
Timer
t
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
Arm set voltage. If all measured
voltages are below the set
Arm set voltage for longer than Arm delay time, the
ARMED
signal is set to TRUE and simultaneously Level detector is enabled.
The value of
Arm set voltage must be set lower than any emergency low voltage
condition that can occur when the system is under extreme stress conditions. When
the generator returns to service and the voltage exceeds the
Disarm set voltage
setting, the scheme is automatically removed from service (Level detector disabled)
after a time delay (
Disarm delay time setting) and the
ARMED
output is set to FALSE.
GAEPVOC must only be activated when the generator is out-of-service and disabled
when the generator is online.
The setting value of
Arm set voltage should be less than the setting value
of
Disarm set voltage.
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
Start value. If the measured values exceed Start value, an enable signal is sent to
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
Operate
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
Reset delay time,
Timer resets.
Protection functions
1MRS759142 F
380
REX640
Technical Manual