Auto-Reclosure
It has been found that most of the line faults on overhead transmission system are transient in nature. About 90% of faults are caused by lightning, birds, vines, tree branches etc. these conditions result in such arcing faults that if the fault energy is interrupted for a short period, the arc extinguishes and the line can be re-energised. This fact is employed as a basis for auto reclosure schemes. In such schemes, after the relays at both ends of the line have picked up, the circuit breakers are tripped as far as possible at the same time and reclosed after time has been allowed for deionization. The fault disappears if it is transient, and line is fully restored to service after the reclosure. If the fault is not cleared after the first reclosure, a double or triple attempt of isolation and reclosure can be made. If the fault persists, the breaker may permanently open till it is reset manually.
An auto reclosure consists essentially of an oil switch or breaker actuated by relays which make it open when predetermined current values flow through it. Reclosures are usually connected to protect portions of primary circuits and may take the place of line fuses. Auto reclosing may be single phase or three phase type. Mostly single phase auto reclosing breakers are preferred as most of the transmission faults are single phase to ground faults. Auto reclosing of three phase improves stability as the power remains transmitted through the two healthy phases when one phase is interrupted.
Written by arjun on October 12th, 2008 with
1 comment.
Read more articles on circuit breakers and Power System and Switchgear&Protection.
#1. August 4th, 2009, at 8:23 PM.
Thanks a lot that was one good piece of information keep posting more. And can someone please tell me where i can find full details about All types of Auto-reclosures. Thank you.