Transient Analysis and Simulation of a Single-Phase Grounding Fault in 20kV Small Resistance Grounding System

摘要

In recent years, the distribution network adopting 20kV instead of 10kV has gained wide recognition in reducing the power supply radius and improving the power supply quality. In the southern power grid of China, cities such as Shenzhen, Zhuhai and Guangzhou have carried out pilot projects for the construction of 20kV power grids.20kV systems are often used in urban power distribution system, the concentration of the load and the limitation of outgoing-lines lead to a large cable scale, the system capacitor current often exceeds 100 amps or reach to hundreds of amps. Once a fault occurs, it will have an impact on power supply stability and personal safety. At present, relevant researches on 20kV small resistance grounding systems focus on their economic, steady-state characteristics and protection strategies. However, as the scale of the system continues to increase, the various transient processes that may be triggered and their influences to the electrical equipment still lack operational experience and theoretical evaluation. In this paper, combined with a ground fault of 20kV system and its potential transformer(PT) fault, the electromagnetic transient simulation is used to reproduce the transient over-voltage and over-current of the fault process, so that the cause of the fault is confirmed. The variation law of the over-voltage amplitude with the network scale is discussed, and the cause of failure of PT fault is put forward. The conclusions drawn by the paper can provide reference for the network scale planning, protection formulation, defect Monitoring and analysis of the 20kV neutral point via small resistance grounding system in the future.