Research On Over-Voltage Of Altiplano Railway's Long Distance Power Supply System

QingHai-Tibet railway which is the highest in altitude and the longest altiplano railway in the earth has been on operation commercially since July,1,2006.This railway meet a series of environment such as high altitude, extra chilliness, less oxygen, low air pressure, poor power resource etc.35kV power supply system served for QingHai-Tibet railway meet the basically challenge of poor power resource, so, long distance transmission line had to be adopted in 35kV power supply system. As a result of power system configuration itself and geography environment, the over-voltage of power supply system presents the difference between QingHai-Tibet railway's power supply system and the traditional 35kV power supply system. So, over-voltage of altiplano's long distance power supply system become a new research project. What's more, insulation material's insulation ability will decline in altiplano, so, the research on over-voltage is beneficial to set down insulation grade, and play an important role to keep the QingHai-Tibet railway work normally.This paper is interested in steady power frequency over-voltage and the switching over-voltage that have the character of transient and randomicity. Precise transmission line model (frequency dependent phase model) and professional electromagnetic transient simulation software EMTDC(electromagnetic transient program including direct current) has been used to study the over-voltage. Monte-carlo has been also introduced to study the switching over-voltage, and a number of voltage data have been got from the simulation, so, the problem of lass of data from field measure is solved. Then, MATLAB's data tools have been used to analysis the data in detail, and find out some character and statistical rule about the over-voltage. At last, field measure data verify and develop the research result.According to a number of simulation data, some result and conclusion can have been listed as follows: power frequency over-voltage is mainly related to the length of transmission line, and also related to transposed line , untransposed line, transmission line conductor's direct current resistance and soil resistance; initial over-voltage caused by single phase to ground fault could up to 3p.u, and decided by fault location and fault time mainly; over-voltage amplitude caused by three poles of breaker closing simultaneous is less than that cause by three poles of breaker closing in different time; and each phase to ground over-voltage meet random normal probability, however, the maxim of phase to ground voltage is more close to weibull probability. When three reclose breaker close on transmission line where the single phase to ground fault occurred, voltage of non-fault phase can up to 5p.u, this kind of over-voltage is mainly affected by transmission line's trap charge.