Configuration And Setting Of Sub-Feeder Protection In Distribution Network

Rationality of configuration and setting of distribution network protection exerts a fundamental influence on failure outage time and severity of voltage sag. Protection of subfeeder is an important composition of protection of distribution network, function of which is to prevent the cause of override trip in substation line outlet protection during failure of sub- circuit, thus enhancing quality of power supply to decrease customer outage costs. But now configuration and setting of sub- feeder protection receives inadequate attention, beyond the reach of due purpose. Thus, it’s necessary to carry out study on the configuration and setting of sub-feeder protection.The main research works of this paper concentrate on:(1) analyzing the configuration and setting of sub- feeder protection at home and abroad and pointing out existing issues of lacking discipline, configuration scheme without consideration of customer outage costs and inapplicability of traditional setting plan.(2) dividing sub-feeder into three types according to the configuration of outlet protection and position of the sub- feeders. The first type is the subfeeder locating within the protection scope of outlet instantaneous quick-break(I section); The second type is the sub- feeder locating within the protection scope of outlet with a time delay(0.1s to 0.15s) of I section; The third kind is the sub- feeder locating out of the protection scope of outlet I section, or the sub- feeder of out- of- service circuit in outlet I section.(3) putting forward configuration scheme of sub- feeder protection for overhead distribution network: the first type of sub- feeder is not configured with protection, if outlet protection adopts single shot reclosing to configure automatic dividing- point switch when load capacity of sub- feeder having a small proportion of overall feeder; The second type of sub- feeder is to configure protection of fuse when with a small loan capacity, otherwise, configure dividing- point switch; The third type of sub- feeder is to configure fuse protection of two section control(I and II section). Rationality of protection of configuration scheme is demonstrated through comparing with customer outage costs during failure.(4) proposing optimization of configuring fuse protection under the situation of load capacity satisfying requirements for the third class of sub- feeder in the cable distribution network. As cable network doesn’t adopt reclosing, fuse protection cannot be set. And subfeeder of fuse protection is no more configured with automatic dividing- point switch.(5) putting forward fuse selection scheme of sub- feeder and selecting rated current of sub- feeder fuse based on the principle ampere-second property.(6) proposing the setting program of protection for circuit breaker, set value of protection current in current I section is set according to 0.9 time of current value in the circuit outlet II section, value of current III section is set by escaping the maximum load current of sub- feeder, which action time limit is added with one-time range compared with protection of distribution transformer, and lowered one-time range compared by protection of outlet III section.(7) classifying specific sub- feeders on overhead and cable feeders in G city of the South and carrying out protection configuration as well as setting calculation of protection of circuit breaker and fuse protection. With the comparison of consumer outage costs before and after using the proposed scheme, feasibility and validity of the scheme are verified.This paper presents the configuration and setting scheme of sub- feeder protection, which can decrease failure outage time caused by the failure of sub- feeder with effect. It will be of great significance to improve the configuration and setting of protection of the distribution network as well as quality of power supply.