ABB RELION REX640 Technical Manual page 1140

Section 5
Protection related functions
1134
When the zone extension operation mode is enabled, the autoreclosing function
DARREC enables a fast fault clearance that covers the entire length of the protected
feeder. This is achieved by allowing a time-delayed overreaching zone to trip
instantaneously when a fault occurs. For this purpose, one of the DSTPDIS zones can
be configured with an independently set reach.
After the overreaching zone instantaneously trips, the autoreclosing sequence starts.
If the fault is transient, the system may get restored in the first shot of AR. However,
in case of a persistent fault only the first trip of the AR sequence is accelerated by Zone
extension logic. During the rest of the sequence, Zone extension logic is blocked and
AR initiation is performed selectively by the time-graded distance zones.
If the fault is located on the adjacent feeder or bus within the reach of
the overreaching zone, tripping and AR initiation take place in an
external fault.
Zone extension logic can be described using a module diagram.
EX_ACC
AR_READY
AR control
NONDIR_ST
BLOCK
GUID-52F07A05-74F4-4CEB-A3AA-521CF2F537B4 V1 EN
Figure 613: Functional module diagram of Zone extension logic
AR control
The AR control module supervises the zone acceleration by monitoring the status of
the AR_READY and NONDIR_ST input signals. The READY output signal from the
autorecloser (AR) function, which indicates the status of the autoreclosing, is
connected to the AR_READY input. The start signal from the non-directional zone is
connected to the NONDIR_ST input. If the non-directional zone is not available for
this, then the start output from the overreaching zone with the biggest reach or GFC
can be used instead.
The permission for zone acceleration is given if AR_READY = TRUE, that is, the AR
function is ready to start a new AR sequence. If the set reclaim time of the AR function
expires before the fault is cleared, the NONDIR_ST input signal is used to block the
activation of the zone acceleration. This ensures that the accelerated trip followed by
the AR initiation is not repeated for the same fault regardless of the reclaim time
setting and the reach of the overreaching zone connected to the EX_ACC input.
Otherwise, this could lead to pumping of the circuit breaker, that is, the repetition of
the first shot without being able to complete the desired AR sequence.
Zone
OPR_Z_EXTN
acceleration
1MRS759142 C
REX640
Technical Manual