operate signal from Zone extension logic is obtained from the OPR_Z_EXTN output,
which is used to trip the circuit breaker and initiate the autoreclosing (the AR shot).
The activation of the BLOCK input blocks the OPR_Z_EXTN output.
Loss of load logic
Loss of load logic is enabled with
Operation mode
= "Loss of load".
When the loss of load operation mode is enabled, a time-delayed overreaching zone
is allowed to trip instantaneously if the loss of load current condition is detected.
The loss of load function does not operate in case of a three-phase fault
as all the phases are faulty. Therefore, none of the current values drops
below the
Minimum current
setting, meaning that the loss of load current
condition cannot be detected.
Loss of load logic can be described using a module diagram.
CB_CL_CMD
LOSSLOAD_ACC
BLOCK
OPR_LOSSLOAD
Initialization
Trip logic
I_A
I_B
I_C
I3P
Loss of load
current
detection
Figure 701: Functional module diagram of Loss of load logic
Initialization
The Initialization module gives an enabling signal to the Trip logic module when
the values of all three phase currents are above the set value of
Load current value
for more than the time set with
Load release on time
. The enabling signal has a
drop-off delay defined with the
Load release off Tm
setting.
Loss of load current detection
The Loss of load current detection module gives an enabling signal to the Trip logic
module if any of the phase current values drops below the
Minimum current
setting
due to a remote end breaker opening and, simultaneously, the value of at least one
phase current exceeds the value of the
Load current value
setting due to a fault.
Such a condition has to be valid for longer than the
Minimum current time
setting.
Trip logic
The operate signal is obtained from the OPR_LOSSLOAD output if the enable signal
is received from both Initialization and Loss of load current detection modules
and, simultaneously, a fault is seen by the overreaching zone connected to the
LOSSLOAD_ACC input.
1MRS759142 F
Protection related functions
REX640
Technical Manual
1233
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