Studay Over-Voltage On Neutral Grounding Via Small Reactor Of High-Voltage Transformers

The problem about neutral grounding mode of the electric power system is an integrated technical problem associated with power system reliability, insulation coordination, electromagnetic interference, and personnel safety. At present, Although partial neutral grounding in 220kV power system has several advantages such as simply and reliable zero sequence protection, circuit-breaker capability without the restriction of single-phase short-current and the light communication interference, it will take disadvantage in the choice of neutral protection equipments. Therefore, the protection method of surge arrester with protective gap cannot supply reliable protection in this model. This problem has not been solved correctly present.It is need that study better mode of neutral grounding.In this paper, the zero-sequence-impedance changes of transformer and power system are discussed in the condition of grounding by reactor, and the effects of reactance on the short circuit, zero-sequence protection and the insulation level of the neutral point of transformer are also analyzed. By analyzing the simulation results of EMTP, such conclusions can be reached: grounding by appropriate reactance can reduce the magnitude of system short circuit current, degrade the insulation level of neutral point of transformer, and fit with the performance of the zero sequence protection. Based on the conclusions above, such views are brought forward in this paper: grounding by appropriate reactor can choose the insulation level of the neutral point of transformer in 63kV,and MOA can be used to protect the neutral point against the over-voltage. At last, the range of the reactance is recommended as about 30-40 percent of zero-sequence impedance of transformer.