Zone Sequence Coordination
Zone Sequence Coordination
(OP)
After doing some relay testing, I've been doing a study of zone sequence coordination. Seems we inadvertently tested right at the pickup point used to transition the shot counter. Instruction manual suggested settings involve a time overcurrent pickup element that essentially drops out at the same point where it picks up. We watched the shot counter jump to the last step as relay locked out after tripping only once when we expected multiple reclosures/trips. It occurs to me that this testing situation is not that far from real world. While a fault current that provides exactly 10.000 A secondary might be unusual, it is easy enough to imagine a fault that crosses the pickup point many times before clearing.
An instruction manual from B says nothing at all about zone sequence coordination. Recommended settings from C appear to work like those of A. Manufacturer D uses a time overcurrent pickup to transition, but current must drop by 10% of pickup prior to the next transition. So after implementing the 10% bandwidth of D using logic equations back in A, it looks like we have reclosing that will coordinate with downstream reclosers for any possible fault current that does not evolve enough to cross over our 10% bandwidth prior to clearing.
An instruction manual from B says nothing at all about zone sequence coordination. Recommended settings from C appear to work like those of A. Manufacturer D uses a time overcurrent pickup to transition, but current must drop by 10% of pickup prior to the next transition. So after implementing the 10% bandwidth of D using logic equations back in A, it looks like we have reclosing that will coordinate with downstream reclosers for any possible fault current that does not evolve enough to cross over our 10% bandwidth prior to clearing.






RE: Zone Sequence Coordination
RE: Zone Sequence Coordination
RE: Zone Sequence Coordination
As far as the testing: a permanent fault was simulated via both secondary and primary injection with similar results. Testing right near the zone sequence pickup point would cause relay to skip one or more open intervals sometimes going straight to lockout on the first operation.
RE: Zone Sequence Coordination
RE: Zone Sequence Coordination
RE: Zone Sequence Coordination
RE: Zone Sequence Coordination
This was just the testing phase, so no actual feeder was yet connected. But I also like my settings to be flexible enough to add a recloser at some point, or for operators to reconfigure the system so that any substation feeder breaker that does not normally have a downstream recloser may be switched so that it does. No downside to having it turned on if no incorrect sequencing occurs.
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