Application - ABB RELION REX640 Technical Manual

Section 5
Protection related functions
5.9.6
1136
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.
The activation of the BLOCK input blocks the OPR_LOSSLOAD output. Temporary
blocking is achieved using the circuit breaker's close command pulse connected to the
CB_CL_CMD input. It is used to prevent an unwanted operation due to initial
transients after the breaker is closed, for example, in case of inrush currents.

Application

DSTPLAL is used in those applications where the conventional communication
scheme logic cannot be applied (when no communication channel is available), but
the user still requires a fast clearance for the faults on the entire feeder.
DSTPLAL enables a fast fault clearing during certain conditions, but it is unable to
replace the communication scheme logic due to a possible lack of selectivity during
the first trip and AR initiation and also as the loss of load logic cannot operate for
three-phase faults. DSTPLAL is controlled either by the autoreclosing (Zone
extension logic) or by monitoring the loss of load current (Loss of load logic).
Zone extension logic
The zone extension operation mode can be applied when the autoreclosing function
DARREC is in operation. When the zone extension is enabled, DARREC is used to
enable the fast fault clearance independent of the fault location on the protected
feeder. This is achieved by allowing a time-delayed overreaching zone to trip instantly
when a fault occurs. Also, if there are tapped loads on the protected feeder, it is
required to set a dedicated zone to initiate one or two shots as fast as possible before
the protection devices of these taps clear. If the fault is still present after these shots,
further tripping is delayed in accordance with the other zones so that the operation
becomes slower than the protection of the load taps, enabling it to clear. The final
tripping that ends the sequence is always performed selectively according to the time
grading of the zones.
1MRS759142 C
REX640
Technical Manual