Research On The Influence Of Harmonic On Shunt Capacitors In Distribution System And Its Countermeasures

Shunt compensation capacitors can effectively improve the system voltage level andeconomy of system operation, so they are widely used in all kinds of voltage level in thedistribution network. However, due to the widely use of nonlinear loads in recent years, theharmonic distortion in distribution network is getting more and more severe. Theinteraction between harmonic and shunt capacitors and the adverse consequence thatresulted from it can’t be ignored any more. Under the effect of harmonic, shunt capacitorsmay easily overload and cause a harmonic current amplification. Indeed they can lead toharmonic resonance in certain conditions, and cause over current and over voltage so as tothreaten operation security of capacitors themselves and the power system. Therefore, it isof great significance to deeply analyze the influence of all kinds of harmonic on the shuntcapacitors and research the measures to inhibit harmonic harm, aiming to guide capacitoroptimization to avoid the damage of capacitors caused by harmonic.This paper firstly introduces the harm of harmonic to the utility grid and electricequipment and the limit standard, and reviews the present related research on theinteraction of harmonic and shunt capacitors home and abroad, then points out the necessityof the study. Secondly, this paper thoroughly analyzes harmonic current amplification ofshunt capacitors, harmonic resonance principle and parameter matching conditions, andthen combines the operation limit of shunt capacitors and related accident cases in powersystem to explain the harm of harmonic to shunt capacitors.Building the harmonic model of components in distribution system is the foundationof subsequent analysis and calculation. Comprehensively considering the generalcharacteristics of harmonic, this paper builds the harmonic models of power system’s maincomponents, such as generator, transformer, transmission line and linear load, et al,harmonic source and put forward the superior network equivalent method. On the basis of harmonic network, this paper presents a simulation of shunt capacitors in an actualsubstation, and studies the response of voltage and current with different frequencyharmonic injection under different voltage level in allusion to all sorts of ways that theshunt capacitors are put into operation. After that this paper concludes the general rules ofshunt capacitors’ sensitivity of harmonic source’s frequency and location.Finally this paper conducts a simulation of the filtering effect of the passive filtercombination on the basis of systematically presenting the principles of common usedharmonic suppression methods at present and their respective advantages and disadvantages.Then it brings forward a design scheme of multi-tuning series band stop filter aiming at theshortage of passive filter. The device changes the inductance value by the way of setting theworking point of core inductor, so as to realize the device’s dynamic adjustment of tuningfrequency. This device can overcome the shortage of passive filters that their tuningfrequency is immutable and easily cause harmonic overflow.