Effects Of Shunt Capacitor Of Qianyuan Substation On Power Grid Harmonics And Countermeasures

The installation of shunt capacitors on low-voltage busbars is widely utilized in power systems to balance the reactive load, regulate the voltage and improve the power factor within a substation. With the pervasive utilization of electronic and electric devices, harmonic pollution in the power grid gets worse. This situation makes the shunt capacitor in the substation amplify harmonic waves or even seriously amplify the harmonic current by producing resonance with the inductor, affecting the stability of operation of shunt capacitors in some electrical substations. Through studying reasons for the frequent failure of a 35kV shunt capacitor in the 220kV Qianyuan substation of Yuhang Power Supply Company and the countermeasures, this dissertation carries out an analysis of the effects of shunt capacitors on power system harmonics and gives countermeasures to solve analogous problems in practice.This dissertation conducts a theoretical analysis and study about the harmonic model in a substation and discovers that in different switching methods, the shunt capacitor bank may amplify the high harmonics in the power grid, leading to failure of capacitors due to excessively large harmonic current in the capacitor circuit. Studies show that the suppression of power system harmonics can be realized through measures such as expanding the capacity of the shunt capacitor bank and adjusting the reactance ratio of the electrical reactor in the shunt capacitor bank. This dissertation evaluates each of the measures and particularly discusses the performance and feasibility of suppressing harmonics by adjusting selective reactance ratios. It emphatically analyzes the harmonics in the 220kV Qianyuan substation:extracting systematic parameters, selecting simplified models that base on the typical busbars short-circuit impedance to analyze the capacitor’s impact on harmonics, carrying out quantitative analysis and calculation of the impact of the current reactance ratio on the amplification of harmonics in the current power system. At last, this dissertation finds out the most appropriate reactance ratio on the basis of real-life power grid harmonics and works out the final scheme for revamping; it also produces a targeted and detailed program for examining all harmonics components and specifically records and analyzes the changes of harmonics in different switching methods of a capacitor. Experimental data and the operation status of the revamped capacitor prove that the above said scheme is able to suppress power system harmonics to a great deal and to solve the practical problem of frequent capacitor failure.