Study on the Mechanisms and Prediction Methods of Arcing Contact Erosion of High-voltage SF6 Circuit Breaker

Abstract

High-voltage SF6 circuit breaker (SF6 HVCB) is a key equipment in the power transmission system for breaking the fault current and protecting the safe and stable operation of the power grid. In the process of current breaking, the arcing contacts will be eroded subjecting to the heat of the arc, which will seriously affect the capability of breaking current and the electrical lifetime of the HVCB, and further endanger the safe and stable operation of the power grid. The investigation of the erosion mechanisms and prediction methods of arcing contacts erosion of HVCB can advance the theory of contacts erosion, improve the accuracy of massloss prediction of the arcing contacts to provide reference for the condition maintenance of the equipment. This thesis takes the SF6 HVCB as the research object and strives to lay a theoretical foundation for the development of monitoring system of arcing contacts erosion. Based on a 245kV/40kA live tank SF6 HVCB, an arcing contact erosion experimental platform is built using a noval fiber-optic sensor system. The use of optical approaches effectively avoids electromagnetic interference in a practical scenario. Using the combination of high-speed camera and multiple reflective mirrors, the macroscopic behavior of the arc is observed, which provides important reference for the install location of sensors. By using a noval fiber-optic sensor system, combined with photodiode and high-speed spectrometer, the trajectory and time-varying spectra of the arc roots on the arc contact surface are monitored synchronously, offering abundant experimental data for further investigation of massloss prediction algorithm of arcing contacts erosion. Using the spatial domain chromatic method to predict the massloss of arcing contacts, the prediction accuracy is improved by 31.0% compared to the existing widely used arc energy accumulation method. The macroscopic behavior of the arc in the SF6 HVCB and its effects on arcing contact erosion are studied. Using high-speed photography technology, the shape of the arc column, the spatial distribution of metal vapor of the arc column, and the mobility of the arc root on the contact surface are observed. The effects of the shape of the arc column and the mobility of the arc root on the erosion process are interpreted. Using the spatial domain chromatic method, the trajectory of the arc root on the contact surface is measured. The mobility of the arc root at different current levels is studied and a method for the massloss prediction of the arcing contacts at relative low currents is proposed. A prediction method of massloss of arcing contacts based on chromatic analysis of arc spectra is proposed. Through the analysis of chromatic spectral data both in the wavelength domain and time domain, a series of chromatic parameters representing the erosion characteristics of the arcing contacts are obtained, and the contacts erosion modes at various current amplitudes are identified. Furthermore, the chromatic parameters which are closely related to the arc contact ablation are selected. In combination with the linear regression algorithm, the prediction method for massloss of the arcing contacts at relative high currents is explored, the accuracy of massloss prediction has been improved by 39.1% comparing with using the square of current. A 3D thermal model of arcing contact erosion considering the movement of the arc root and the structure of the copper-tungsten material is proposed. The temperature, mass loss rate, and change of contact surface geometry are simulated and compared with the experimental data and the simulation results of a fixed arc root model. The influence of the root movement on the erosion process is further verified and explained. The simulated results of massloss of arcing contacts are obtained.