Failure analysis of No.2 main transformer in Fushun SiShui substation

the transformer is one of the most important equipment in power system, the maximum short current rated current is 2530 times or more when an outlet short circuit occurs,short current will produce great mechanical force which is hundreds of times larger than the normal operation, Under the action of the huge short circuit electromagnetic force, many components such as the winding of the transformer may be damaged. This paper describes the whole process of of 2# main transformer in Fushun SiShui substation accident analysis, and the turn-to-turn short circuit accident of the winding is caused by interphase short circuit of the cable, this also provides a scientific basis for the transformer’s fault detection. Introduction The transformer is one of the most important equipment in power system, Whether it is power plants, substations, transmission and distribution network, or the vast number of users and the various sectors of the national economy, are using a variety of transformers, because of the high cost and the status of the transformer, once the transformer accident will bring huge losses to the national economy. Transformer faults are generally divided into two categories In nature: thermal fault and discharge fault. Thermal failure is usually shown as the local overheating of the transformer and the temperature increases. According to its severity, thermal failure is often divided into four types: Mild overheating (generally less than 150 °C). Low temperature overheating (from 150 to 300°C), medium temperature overheating (from 300 to 700 °C) and high temperature overheating (above 700°C). The discharge fault is usually the degradation or deterioration of the transformer’s insulation performance under the high electric field strength. According to the different energy density of the discharge, it can be divided into three types: partial discharge, spark discharge and high energy arc discharge; According to the discharge of different parts, it is divided into Air gap discharge of the folding screen, Spark discharges between different potential insulation, Spark discharge caused by suspended potential, arborization discharge of the folding screen, Arc discharge caused by the dislocation tap switch, multipoint earthing discharge of the iron core, Power frequency continuation discharge, the turn-to-turn short circuit discharge of the winding ,winding to ground discharge and so on. The harm of transformer exit short circuit Current carrying cond in a magnetic field must bear the function of mechanical force, Therefore, due to the role of the current and the leakage magnetic field, the winding will produce electromagnetic force when the current flows the transformer winding, its magnitude is determined by the product of the leakage magnetic flux density and the wire current, The calculation formula of the wire force per unit length is f=Bli, The direction of the force is determined by the left hand rule. When the transformer operates under normal load, the force acting on the wire is very small, However, due to the outlet short circuit, the maximum short current will be 2530 times or even greater than the rated current, and the electromagnetic force generated in the short circuit is proportional to the square of the short current(because the electromagnetic force per unit length f=B 5th International Conference on Machinery, Materials and Computing Technology (ICMMCT 2017) Copyright © 2017, the Authors. Published by Atlantis Press. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/). Advances in Engineering, volume 126