Page 233 - Practical Power System and Protective Relays Commissioning

Protection Relays Chapter | 18 233

FIGURE 18.6.30 Autoreclosing relay cycle for transient faults.

Reclosing on a noncritical transmission line should be performed at one
end first by the live bus/dead line. The other end(s) should be reclosed
through synchronizing equipment.
Reclosing on transmission lines near generation must consider the impact
on the machine shaft torque as well as system stability. If possible, utilize
10 seconds or longer delayed reclosing at the remote terminal to limit the
interaction with shaft oscillations and only reclose through system synchroni-
zation at the generation terminal.
Where system stability is a concern, the line may be tripped single
phase and high-speed autoreclosed. (Unbalance effects on zero-sequence
protection may require some evaluation by the applicant.) All multiphase
faults should trip three phase and consideration should be given to block-
ing autoreclosing.
High-speed autoreclose should only be applied for high-speed trips in
communications-aided Zone 2 trips in distance protection for stability-
critical and load-sensitive lines. High-speed autoreclosing should be dis-
abled or blocked for loss of communication channels. Lines that do not
use communications schemes should be reclosed through synchronizing
or voltage supervision. (The speed of clearing has a significant effect on
the rotor angle of the generators.) The faster that the fault is cleared, the
more time that is available to provide more retarding torque to bring the
rotor angle back into synchronism when the line is reclosed.