Study On The Influence Of Power Quality Of Traction Power Supply System To Power Metering

The energy metering of traction power supply system is the basis of the settlement of electricity between power sector and the railway sector. The accuracy of the measurement and rationality is a common concern for both sides. The energy metering device consisting of metering current transformer (CT), potential transformer (PT) and watt-hour meter is generally designed and manufactured under frequency sinusoidal and symmetrical conditions. the asymmetry and nonlinear traction load will create negative sequence and harmonic-based power quality problems, which will affect the rationality and accuracy of measurement. The study about influence created by these power quality problems and the analysis of the accuracy and rationality of the energy metering can provide a billing reference for both power supply and utilization, which has real economic significance.This study is mainly divided into two parts:one is to analyze the negative sequence and harmonic of traction power supply system. Another is to study the accuracy and rationality of measurement under the condition of negative sequence and harmonic. Main work includes:through the general analysis method of negative sequence, several common kinds of traction transformer of traction power supply system have carried on the theoretical calculation of negative sequence. SS4 type AC/DC electric locomotive and the CRH3 type AC/DC/AC electric locomotive are simulated in the MATLAB/Simulink and the net side harmonic current of two locomotives are also analyzed. The theoretical basis of three-phase circuit active power measurement, the working principle of induction and electronic watt-hour meter are introduced. A comprehensive analysis of the influence on the whole metering device given by negative sequence and harmonic are made. The error-frequency characteristic of current transformers and capacitor voltage transformers are simulated though EMTDC/PSCAD software, which is used to analyzed the impact of harmonics on metering transformers. Time division multiplier commonly used in electronic watt-hour meter are simulated in MATLAB/Simulink, and the error-frequency characteristic of the TDM was got. The causes and trend direction of negative sequence power and harmonic power is proved theoretically. The influence of trend direction to the rationality of measurement are researched. At last, reasonable power metering way of electrified railway are discussed in the current the power quality environment According to the previous analysis results.