Abstract
For the Taiwan Power Company (Taipower), the margins of coordination times between the lateral circuit breakers (LCB) of underground 4-way automatic line switches and the protection equipment of high voltage customers are often too small. This could lead to sympathy tripping by the feeder circuit breaker (FCB) of the distribution feeder and create difficulties in protection coordination between upstream and downstream protection equipment, identification of faults, and restoration operations. In order to solve the problem, it is necessary to reexamine the protection coordination between LCBs and high voltage customers’ protection equipment, and between LCBs and FCBs, in order to bring forth new proposals for settings and operations. This paper applies linear programming to optimize the protection coordination of protection devices, and proposes new time current curves (TCCs) for the overcurrent (CO) and low-energy overcurrent (LCO) relays used in normally open distribution systems by performing simulations in the Electrical Transient Analyzer Program (ETAP) environment. The simulation results show that the new TCCs solve the coordination problems among high voltage customer, lateral, feeder, bus-interconnection, and distribution transformer. The new proposals also satisfy the requirements of Taipower on protection coordination of the distribution feeder automation system (DFAS). Finally, the authors believe that the system configuration, operation experience, and relevant criteria mentioned in this paper may serve as valuable references for other companies or utilities when building DFAS of their own.
Highlights
Power companies must continually improve the reliability of power supply and customer satisfaction through the enhancement of service quality
The distribution feeder automation system (DFAS) integrates computers, communications, and control technology into distribution systems. It is composed of control center facilities, feeder remote terminal units (FRTUs), feeder terminal units (FTUs), overhead/underground automatic line switches, and communication systems
This study investigates the coordination time intervals (CTIs) among the protection devices of the duty point of high voltage customers, automatic line switches lateral protection relays, feeder overcurrent protection relays, bus-interconnection overcurrent protection relays, and distribution transformer overcurrent protection relays, so that the entire protection scheme of the distribution systems can be formulated, for the two-level protection scheme below the feeder circuit breaker (FCB)
Summary
Power companies must continually improve the reliability of power supply and customer satisfaction through the enhancement of service quality. If a fault takes place in the outgoing section of a feeder, the upstream protection relay of the secondary of the distribution transformer should provide backup protection for the primary relay of the bus-interconnection. If a high voltage customer’s load current is below 30 A and the NX-40 current limit fuse is used for primary protection, an underground 4-way automatic line switch is used for backup protection. If the load current is between 151 and 300 A and a 600 A underground 4-way automatic line switch is used for primary protection, a Taipower feeder protection relay may be used for backup protection. For the transformer 51Z neutral relay, the transformer LCO ground relay, and the feeder LCO ground relay, the suggestions of Taipower engineers are as follows: 1. 51Z: IEC Normal Inverse
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