Brief Analysis on the Aging of Traction Transformer Insulation

Abstract

In the power supply system of electrified railway, traction transformer is an important part and its running state plays an important role on the safety of railway operation. In this paper, we will analyze the transformer load curve, simulates the change of the temperature rise and discuss the influence of temperature on the transformer solid insulation under load condition. Introduction China’s power supply system of electrified railway uses single-phase power frequency ac system and electric locomotive traction load is actually the load of traction transformer, since it is beyond the provisions of GB/T15164 94, the traction transformer is more likely to breakdown compared with the ordinary power transformer. Operating experience shows that: we must have a correct understanding and treatment of the transformer’s fault and damage in order to improve the operation reliability, otherwise failure and damage will happen frequently and the same fault will be repeated. Therefore, analyzing the aging of traction transformer insulation will be of great importance on the improving of electricity quality and railway transportation safety, particularly under the premise that railway is developing towards high-speed passenger transport and more loading cargo transport. The load characteristics of traction transformer The variance of traction load in different circumstances has led to significant difference in traction transformer load and ordinary transformer load which are shown under: the track transformer when loaded has single-phase load、varying load、 track circuit、higher harmonic, etc. Traction transformer will transfer electric power from the three-phased power system to the two separately loaded overhead contact system and provide electric power respectively to the ascending and descending trains. The single phased load shall be the same ideally but usually varies in most state. Statistics shows that the rate of traction empty load in one lined electrified railway is 40% ~ 50%, and the load changes more frequently, which will inevitably cause the imbalance in three-phased power system and voltage fluctuation. Traction transformer will change and transfer the electricity from 110 kV (or 220 kV) three-phase power system into the two 27.5 kV overhead contact system. Given into consideration the line loss 10%, the rated voltage of overhead contact system is 25 kv, but the actual locomotive working voltage is frequently between 22-27.5 KV, so when the train passes by, instantaneous short circuit will happen (normally 70 times per year) due to flashover of the conductive support insulator, during which the electric current is 6-10 times of the rated curren. Therefore, the traction transformer shall have enough anti-short-circuit strength and impact resistance ability. Winding temperature rise simulation and calculation under typical load. According to the characteristics of the traction power supply system, railway departments have proposed idea of typical load curve (as shown in figure 1) on the basis of extensive investigation and numerous tests. Typical load curve reflects the load characteristics of the traction transformer. But the characteristics of the traction power supply system determine that the transformer load characteristics are ever changing, and there are sometimes still differences with the actual load International Conference on Materials, Environmental and Biological Engineering (MEBE 2015) © 2015. The authors Published by Atlantis Press 825 curve. In this paper, we will simulate and calculate the temperature of traction transformers according to the typical load curve shown in figure 1, and hence to make tests and research.