发电机自励磁发生根源及其对特高压输电线运行的影响

Cause of Generator Self-excitation and Its Influences on Operation of UHV Transmission Lines

发电机带长线路运行时,由于线路分布电容电流的助磁作用,常引起发电机的自励磁。特高压输电线分布电容大,引起自励磁的可能性更大。对发电机自励磁的研究,一般从参数谐振和参数周期性变化的角度进行分析,未涉及自励磁产生的根源。文中认为发电机自励磁的根源是电容性电流的助磁作用产生的正反馈使系统发生自激振荡。对励磁回路断开且xd=xq的理想隐机发电机,在无参数的周期性变化且只考虑相同的直轴和交轴阻尼绕组的情况下,用劳斯稳定判据证明了线路电容达到一定值时产生自激振荡自励磁的必然性,并用实例仿真进行了证明。文中对发电机—特高压输电线系统末端甩负荷引起的自励磁过电压进行了研究,并研究了在甩负荷瞬间投入金属氧化物避雷器(MOA)以抑制过电压的可行性。

Self-excitation of generators may occur due to the large capacitive currents of the long distance ultra-high voltage（UHV） transmission lines connected to a generator.It may cause severe overvoltage and consequently damage electric power equipments and insulators of the transmission lines.As such,its original cause,mechanism of development and methods of suppression must be carefully studied.In literature,generator self-excitation is generally considered as parametric resonance due to the cyclical variations of the parameters of the generator.This paper denotes that the original cause of the generator self-excitation is the positive feedback action due to the additive magnetizing effect of the capacitive current on the dynamic system consisting of generators,transformers and transmission lines.This standpoint is proved by using Routh stability criterion and digital simulation of an ideal non-salient pole generator,whose xd=xq,with excitation circuit opened and the same damper windings on the direct and quadrature axis.The self-excitation also occurs in such conditions although there are no cyclical variations of the parameters of the generator.Besides,the theoretical study and digital simulation of self-excitation overvoltage due to load rejection at the end of the actual generator-UHV transmission-line system are also given.The feasibility of overvoltage suppression by inserting metal oxide arrester（MOA） at the moment of load rejection is proven as well.