Study On Electrified Railway Harmonic And Recommendation Limits

With the development of power system, the power quality is requested to be better and better. Harmonic is the most general phenomenon in power system. And harmonic is the main index of power quality. The main harmonic problem in our country is consistency between utility and electrified railway. The length of electrified railway in our country is more than 18000km, and the condition of supply system is very complex. A great lot of harmonic produced by electrified locomotive (mainly including order 3, 5 and 7) is directly injected into utility. The effect of harmonic to utility must not be ignored. So restriction on harmonic injected into utility is imperative. But characteristics of traction load include single phase, unbalance and random, so harmonic of traction load is also different from harmonic of other load. At present the knowledge of traction load harmonic is limited, so full-scale and in-depth study on traction load harmonic is needed.Distribution characteristic of traction load harmonic is studied base on lots recorded harmonic data. The existing modeling method of harmonic is analyzed and the minimal square approach is proposed to fit the distribution of traction load harmonic. The checkout shows that the fitting effect is satisfying.This paper checkout the summation exponents adopted in IEC61000-3-6 through statistic of harmonic voltages that are injected into HOkV utility from traction substation. The result makes it out that summation exponents adopted in IEC61000-3-6 is not able to reflect the summation rules of harmonic voltage injected in HOkV utility from traction substation. This paper explores the summation rules of harmonic voltages of traction load based on lots of measurement data and new summation exponents suitable for traction load are proposed. It is proved that calculation results of adopting summation exponents are better than adopting summation exponent in IEC report by simulation.The impact of coincidence factors for distorting loads on distribution of harmonic emission limits is analyzed in detail. The coincidence factor of traction loads in a mountainous area is 0.3-0.5. The difference of harmonic emission limits when consideration and non-consideration are very obviously.Off-line analysis of traction load harmonic using measuring methodsbrought forward by IEC61000-4-7 and compare of all measuring methods are carried out in this paper. Hanning window is recommended to measure harmonic of traction load on condition that hardware of measuring instrument satisfies requirement of calculation speed.Based on compare of IEC61000-3-6 and GB/T14549, some problems that should be paid attention to when establishing or revising rational standard are proposed. The problems include harmonic emission limit, distributing method of harmonic emission limit (conformation of Si and St, summation exponents, coincidence factors), evaluation method.