Recloser Coordination with Station Breaker Low-Set Relays
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Solution Overview
Problem
The implementation of reclosers on short electric power distribution feeders with low-set instantaneous overcurrent (IOC) relays is limited due to complications in protection coordination, leading to increased momentary power interruptions and stress on distribution system assets, and there is a need to coordinate these reclosers with fuse-saving schemes to minimize the impact of faults.
Innovation Solution
A method involving time-current coordination (TCC) curves for low-set IOC relays is used to determine a feasible range of time delays for reclosers, allowing for effective coordination with station circuit breakers and fuses, enabling the localization of faults and reducing the frequency of power interruptions while minimizing the impact on fuse-saving schemes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reclosers are implemented on short distribution feeders with low-set IOC relays, then momentary power interruptions are reduced and fault localization is improved, but protection coordination becomes complicated and fuse-saving schemes are impacted
Solution Approach 1:
The patent modifies the time delay parameter of the low-set IOC relay to enable proper coordination with reclosers. By adjusting the time delay setting, the relay allows the recloser to operate first for temporary faults, avoiding unnecessary station breaker trips and maintaining fuse-saving scheme effectiveness while reducing momentary interruptions.
Solution Approach 2:
The recloser acts as an intermediary device between the low-set IOC relay and the station breaker. It provides an additional layer of protection coordination, handling temporary faults locally before the station breaker trips, thereby simplifying the overall coordination scheme and preserving fuse-saving operations.
2Productivity
If reclosers are used to reduce momentary power interruptions, then power quality is enhanced, but the coordination with fuse-saving schemes becomes more difficult
Solution Approach 1:
The patent adjusts the time delay parameter of the low-set IOC relay to coordinate with recloser operations. This parameter modification ensures that for temporary faults, the recloser has sufficient time to clear the fault before the station breaker trips, thereby maintaining fuse-saving scheme effectiveness while improving power quality by reducing momentary interruptions.
3Loss of time
If the station breaker trips quickly for faults, then fault clearance time is reduced, but fuse-saving operations are compromised
Solution Approach 1:
The recloser performs preliminary action by attempting to clear temporary faults before the station breaker trips. The low-set IOC relay with modified time delay allows this preliminary recloser operation to occur, preserving fuses for genuine permanent faults while still providing quick response for temporary conditions.
Solution Approach 2:
By modifying the time delay parameter of the low-set IOC relay, the system creates a time window that allows reclosers to operate first for temporary faults. This parameter adjustment ensures that fuses are only blown when necessary for permanent faults, maintaining fuse-saving operations while achieving rapid fault clearance.
Data Source
AI summary
A time-current coordination (TCC) curve for a programmable low-set instantaneous overcurrent (IOC) relay for at least one station breaker in an electrical distribution feeder with a fuse-saving scheme and a method of coordinating at least one recloser with the station breaker in the said feeder, for the reduction of frequency of power interruptions encountered by at least one load on the feeder and wherein the method includes the steps of:(a) feasible selection of a range for a time delay of a station breaker's programmable low-set IOC relay;(b) choosing a time delay based on a fuse-saving relation; and optionally(c) locating the recloser on the feeder.