Study On Transient Overvoltage Caused By Switching Operations

Power system consists of a number of generators, transformers, switch apparatus, reactors, capacitors, transformers and other power system equipment. In all of above, switch apparatus play a pivotal role for power system safe and stable operation. In this paper, the electrical transient characteristics of switch apparatus are done as follows:1. Transient recovery voltage is an important index of circuit breaker capacity. The initial rise of TRV is high, so it is difficult to extinguish arc. Mayr arc is only ap-plicable for the description of high resistors after current zero, while Cassie arc is good at descrbing low resistance conditions before current zero. By connecting Cassie and Mayr arc model in series, the TRV of a245kV,50kA breaker is simulated under L75and L90short line fault by ATP-EMTP simulation package. Initial part of the tran-sient recovery voltage have a significant impact on the interrupter after current zero. It is not ideal for small cooling power circuit breakers, such as air circuit breakers, to break short line fault.2. Residual charge of disconnector is an important influencing factor of VFTO It is often simulated used the following methods:one is capacitance with initial volt-age; the other is charging negative polarity power ahead of schedule. Distribution pa-rameter transmission line with initial voltage model is proposed. VFTO of a stand-alone single-outlet550kV GIS is calculated, and compared this method with above two’s. It is indicated that residual discharge is modeled precisely by the distri-bution parameter transmission line with initial voltage model, which has a certain ref-erence value.To research the open switch apparatus, tower grounding resistance for the lightning protection performance of a750kV GIS has been calculated through EMTP. Result shows as follows:1)Due to minimum current of soil ionization up to hundreds kilo ampere, impulse resistance of tower has a little effect compared without considering soil ionization;2) With tower grounding resistance reducing, not only can reduce the energy passed metal oxide arrester, also magnitude of lightning intrusion voltage is lower.3) For lightning protection work, substation operators should focus on the open switch apparatus combined with the transmission lines, the availability of measures to prevent lightning invasion, and insulation of electrical equipment on a regular basis with the checksum.