Distribution transformer is one of the important equipment in the power supply and distribution system of industrial and mining enterprises and civil buildings. It reduces the 10(6)kV or 35kV network voltage to the 230/400V busbar voltage used by users. This type of product is suitable for AC 50 (60) Hz, three-phase maximum rated capacity of 2500kVA (single-phase maximum rated capacity of 833kVA, single-phase transformer is generally not recommended), can be used indoors (outdoor), and the capacity is 315kVA and below It can be installed on the pole, the ambient temperature is not higher than 40℃, not lower than -25℃, the maximum daily average temperature is 30℃, the maximum annual average temperature is 20℃, the relative humidity does not exceed 90% (ambient temperature 25℃), the altitude not more than 1000m. If it does not conform to the above conditions of use, appropriate quota adjustments should be made in accordance with the relevant provisions of GB6450-86.
Both the winding and the iron core are the core components of the transformer. Since the winding itself has resistance or there is contact resistance at the joint, it can be known from Joule’s law that heat is generated. Therefore, the winding cannot pass a current higher than the rated current for a long time. In addition, a large electromagnetic force will be generated on the windings to damage the transformer when the short-circuit current is passed. The basic windings are concentric and overlapping.
The main faults of transformer windings are short-circuit between turns and short-circuit to the casing. Turn-to-turn short circuit is mainly due to insulation aging, or due to the overload of the transformer and the mechanical damage to the insulation during a traversing short circuit. When the oil level in the transformer drops, so that when the winding is exposed to the oil level, an inter-turn short circuit can also occur; in addition, when there is a cross-circuit, the winding is deformed due to the overcurrent effect, and the insulation is mechanically damaged, and an inter-turn short circuit will also occur. When shorted between turns, the current in the shorted winding may exceed the rated value, but the overall winding current may not exceed the rated value. In this case, the gas protection operates, and the differential protection device will also operate when the situation is serious. The cause of short-circuit to the casing is also due to aging insulation or moisture in the oil, a drop in the oil level, or due to lightning and operating overvoltage. In addition, when a cross-circuit occurs, the winding is deformed due to overcurrent, and a short-circuit to the casing will also occur. When short-circuiting the casing, it is generally the action of the gas protection device and the action of the grounding protection.
