(1) struck by lightning. The high and low voltage lines of distribution transformers are mostly introduced by overhead lines, because they are located in mountainous areas and are subject to lightning strikes, so the proportion of distribution transformers damaged by lightning strikes is more than 30% of the overhaul during the thunderstorm season. ,
(2) Ferromagnetic resonance occurs in the system. Rural 10kV distribution lines have formed over-voltage conditions, in the system resonant overvoltage, the transformer a surge of current, at this time in addition to the transformer one side fuse, will damage the transformer windings. In some cases, the casing of the transformer will also cause flashover or explosion. ª¤
2 Insulation damage
(1) Low-voltage circuit fault and the rapid increase in load, so that the current of the transformer exceeds the rated current of dozens of times times, then the winding is affected by very large electromagnetic torque and shift, deformation. Due to the surge of current, the temperature is rising rapidly, resulting in accelerated insulation aging. ,
(2) winding insulation damp. This is due to poor insulation or low oil level. First, transformer insulation oil in storage, transportation or operation and maintenance, inadvertently make water, impurities or other oil mixed with oils, so that the strength of the insulation greatly reduced. Second, the production of the winding layer of paint is not thoroughly, dry, winding lead joint welding bad, the insulation is not complete, resulting in a short circuit between the turn. Third, the oil surface to reduce the insulating oil and air contact surface increased, the acceleration of water in the air into the oil will also reduce its insulation strength, when the insulation to a certain value will occur short-circuit.