Experimental Study On Fault Line Selection In Network Grounded With Arc Extinguishing Coil

Networks ungrounded are widely used to power distribution system in China, and the single phase grounding fault happens most frequently in distribution system. How to detect the fault line quickly and accurately is an important subject to protection relay.With the urban power distribution system in Chongqing, some experimental studies on fault line selection in network grounded with arc extinguishing coil are got on. The method theoretically overcomes that the former methods can not choose fault line when a single-phase grounding fault occurs in an over-compensating network grounded with extinguishing coil, by solving the zero sequence power direction of transient fundamental frequency with the instantaneous initial phases of the zero sequence voltage and current at fault moment. The method is independent of zero-sequence current's value, inductance compensation situation and harmonics components, so it is effective and robust.In this paper, first, the development history and theory of fault line selection in MV network grounded with arc extinguishing coil are reviewed, and some defects in the former methods are indicated. Second, the theory and technological means of the fault line selection based on the zero sequence power direction of transient fundamental frequency are introduced, and some experimental studies with physical simulation model in a laboratory are done. In order to prove the validity of the method based on the zero sequence power direction of transient fundamental frequency, some experimental studies with the urban power distribution system in Chongqing are finished. The field experimental studies are included as follows. (1) Considering 5 feeder lines on 10kV II bus at Liziba substation, different artificial single-phase grounding fault are produced. (2) Considering 12 feeder lines on 10kV II bus at Chuqimen substation, the device based on the method is operated for a long time.Through the finished experimental studies, some results can be concluded as follows. (1) At the bus, power cable terminal and line terminal, producing single-phase grounding fault, the method based on the zero sequence power direction of transient fundamental frequency behaves correctly. (2) The zero-sequence current initial phase in the fault line is opposite to the one in the non- fault line at the grounding moment, which is represented by the zero sequence power direction of transient fundamental frequency. (3) No matter when a single-phase grounding fault occurs, the zero-sequence current initial phase in the fault line is always opposite to the one in the non- fault line at the grounding moment.