Page 232 - Practical Power System and Protective Relays Commissioning

232 Practical Power System and Protective Relays Commissioning

Dead time of autoreclosing relay:
The time between the autoreclosing scheme being energized and the
operation of the contacts which energize the circuit-breaking closing circuit.
On all but instantaneous or very high-speed reclosing schemes, this time is
virtually the same as the CB dead time.
Dead time of CB:
The time between the fault arc being extinguished and the CB contacts
remaking.
High-speed reclosing scheme:
A scheme whereby a CB is automatically reclosed within 1 second after a
fault trip operation.
Lock-out of autoreclosing relay:
A feature of the autoreclosing scheme which, after tripping of the CB,
prevents further automatic reclosing.
Delay autoreclosing (DAR) scheme:
A scheme whereby the automatic reclosing of the CB following a fault
trip operation is delayed for a time in excess of 1 second.
Multishot reclosing:
An operation sequence providing more than one reclosing operation on a
given fault before lock-out of the CB occurs.
Opening time of a CB:
The time from the energizing of the trip coil until the fault arc is
extinguished.
Operation time of protection:
The time from the inception of the fault to the closing of the tripping
contacts of the relay. Where a separate tripping relay is employed, its open-
ing time is included.
Reclaim time:
The time following a successful closing operation, measured from the instant
the autoreclose relay makes contact, which must elapse before the autoreclose
relay will initiate a reclosing sequence in the event of a further fault incident.
Single shot autoreclosing:
An operation sequence providing only one reclosing operation, lock-out
of the CB occurring on a subsequent tripping.
Refer to Figs. 18.6.30 and 18.6.31 for an autoreclosing cycle for transient
and permanent faults.

18.6.11.2 Autoreclosing for Transmission Lines
For 500-kV lines, only lines to ground faults are candidates to allow high-
speed autoreclose.
High-speed auto reclosing (unsupervised) should be applied where it sup-
ports system stability or if load continuity is a concern.