Research On 10kV Power Network Neutral Grounding Through Nonlinear Resistance

The neutral grounding mode of the power system is a comprehensive technical problem which is associated with not only power system reliability, insulation coordination, electromagnetic interference, but also personal safety, etc. In recent years, cable lines are widely used with the development of civic 10kV power network. The vast usage of cables result in several problems such as the increase of system capacitive current, the occasional occurrence of faults caused by arc grounding or resonant grounding overvoltage. These problems reflect that the neutral grounding modes of civic power system are far from well working, especially in overvoltage restrain, single phase grounding capacitive current compensation and relay protection. As a result, it is an essential work to study new neutral grounding mode for 10kV power network, which can insure the reliability of power supply, personal and equipment safety, and should be economic, simple and convenient in assemble and operation. The 10kV electric network neutral grounding by nonlinear resistance as a new neutral grounding mode for power system is brought forward in this paper. Calculation models for systems with this new grounding mode of arc grounding overvoltage, PT resonant grounding overvoltage and break line overvoltage are built in this paper. As an instance, the overvoltages, energy absorbed by the ZnO nonlinear resistance under all kinds of overvoltages and the passing current ability of the ZnO nonlinear resistance are calculate for a 10kV electric network in Guizhou. The relay protection and interference over communication are also discussed. Results of calculations and discussions illustrate that the new neutral grounding mode can restrain overvoltage and over current effectively. The operation mode with ZnO nonlinear resistance grounding integrate the merits of both the resistance neutral grounding mode and the none grounding mode. It can lower the overvoltage level effectively, make sure continuous power supply while single grounding faults, enhance the reliability of power supply and eliminate the short circuit impact on equipments while faults. Besides, this grounding mode does not demand extremely high thermal capacitance over the nonlinear resistance. The emulational calculation results show the 10kV electric network neutral grounding by nonlinear resistance could be considered as a new kind of neutral grounding mode, could be used in the construction or reconstruction of 10kV electric network neutral grounding to eliminate the insulation fault to the lowest level.