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.
5.9.6
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.
If the fault is located on the adjacent feeder or bus within the reach
of the overreaching zone, the tripping and the AR initiation take place
during an external fault.
Setting guidelines
The
Load current value setting must be set below the minimum three-phase load
current during the healthy state. A security factor of 0.5 is used:
Load current value = 0.5 · I
minload
I
minload
minimum load current during normal operation conditions
The loss of load function is released after
Load release on time is elapsed and
the load current in all three phases is above the
Load current value setting. If the
current values drop below the
Load current value setting, the release condition
stays activated until the drop-out delay time has expired (the
Load release off Tm
setting). The value of
Load release off Tm is by default set to "0.3 s". The Load
release on time setting is used to increase the security of the loss of load function,
for example, in the case of transient inrush currents during the energizing of a
power transformer. When there is no need for delaying the release, the
Load release
on time is set to zero in applications.
The
Minimum current setting is used to detect the loss of load condition in healthy
phases during the fault. The
Minimum current setting is set to a value higher
than the maximum current flowing in the healthy phases during the fault when
Protection related functions
1MRS759142 F
1234
REX640
Technical Manual