Research On Traveling Wave Ranging Of HVDC Based On Wavelet Transform

High voltage direct current(HVDC)transmission technology is applied more and more widely in our country.Developing HVDC technology is the only way for the sustainable development of energy and economy in China.Once the HVDC system fails,it will bring great impact to the AC system at both ends,and even cause a large area blackout.The main fault type of HVDC system is line fault.When the DC transmission line is broken,it is important to detect the fault distance quickly and accurately to ensure the safe,reliable and continuous power supply.This paper is based on both ends of the bipolar HVDC system,the susceptible to noise interference and influence of high resistance grounding phenomenon existing in the traditional measurement methods,combining a traveling wave based on wavelet transform polarity comparison criterion,modulus maxima and wavelet threshold denoising method in single-ended wave maxima location scheme.The main contents of this paper are as follows:(1)On both ends of the bipolar HVDC system based on fault analysis process and characteristics of DC transmission lines,and propagation of fault traveling wave research,and the basic principle of single terminal fault location analysis.(2)The wavelet transform method is applied to the HVDC transmission line traveling wave fault location,wavelet transform theory,extreme value theory,polarity comparison of travelling wave principle and wavelet threshold denoising method of wavelet transform modulus,provide a theoretical basis for the fault location scheme.(3)A simulation model of 12-pulse bipolar HVDC system based on CIGRE HVDC standard is established in MATLAB / Simulink,and its normal operation state and several common fault states are simulated.According to the simulation results,the analysis of fault transient component changes.(4)The polarity comparison of travelling wave and modulus maxima criterion,the wavelet threshold denoising method and the single ended traveling wave maxima ranging combined with point of transient traveling wave transmission line fault detection object,using the fault voltage and current polarity comparison and reverse voltage traveling wave module maximum value for fault diagnosis.When high resistance grounding occurs,the method can be used to make up the deficiency of the maximum norm by comparing the distance measurement results with the line length.By combining the soft and hard threshold method and the modulus maximum distance measurement,we can eliminate the noise interference and improve the ranging accuracy.