Zone 2 time delays
Zone 2 time delays
(OP)
For an obsolete sub-transmission system chunk without active breaker failure schemes, would anyone see an issue reducing Zone 2 delays down to 8-10 cycles instead of the typical 20-25 cycle delay? In so far the reduced delay appears to be advantageous but I am sure I am missing something.






RE: Zone 2 time delays
RE: Zone 2 time delays
RE: Zone 2 time delays
RE: Zone 2 time delays
RE: Zone 2 time delays
RE: Zone 2 time delays
RE: Zone 2 time delays
Zone 2 always coordinates with a non delayed Zone 1 which is set to about 85% for any given line being protected. 20-25 Cycles is typical for zone 2 as its usually coordinating with breaker failure. BF is set to 10 cycles allowing any given breaker to clear in 3 cycle plus a safety margin which then derives the zone 2 timing. I say usually- because in this case due to the age of the 69kv system and parts of the 115kv system there is currently no active BF protection, however over the years the bulk oil breakers have been replaced with 3 cycle SF6 breakers speeding up the overall clearing time.
The 69kv system is fed from the 115kv system, and the 115 from 345kv which contains the bulk generation. However, for various reasons generation is being added to the lower levels necessitating faster clearing times.
RE: Zone 2 time delays
Do you know how long all these breakers actually take to clear faults, particularly the first fault in many months? Not every breaker trips in the advertised time on the first try. Do you now have a system with your 20-25 that works well but will be rife with over tripping at 8 or 9 cycles? All those spec values look nice on paper, but sometimes reality likes to throw a curve ball. Pushing Murphy causes him to have tendency to push back.
RE: Zone 2 time delays
I'm glad you brought up tripping speed. New SPS2 SF6 breakers are advertised to trip in 3 cycles, but the fault studies are simulated with a 5 cycle breaker tripping time (6 total). 3.5 cycles on 2 cycle 362kv breakers.
The idea is that since BF is rare, and already covered by zone 2/3/4, and a 10 cycle BF timer has proven well on the 345kv system (breakers that work are opening before that) reducing the zone 2 time just above the maximum worst case zone 1 clearing (8-10 cycles) would provide fast enough tripping speeds to prevent generation instability. Of course the other option is keeping a 25 cycle zone 2 at the risk of tripping local generation.