Oil-immersed transformers, also known as oil-immersed transformer test. Oil-immersed transformers 1000kVA and above, shall be installed outdoor thermometer type signal, and then the distant signal. 800kVA and above should be installed oil-immersed transformer gas relay and pressure protection device, 800kVA transformer oil in accordance with the following requirements, in consultation with the manufacturer, but also can be equipped with gas relay. Dry-type transformers shall be specified by the manufacturer, the installation of a temperature measuring device, and more generally for the 630kVA transformer installations. Phase distinction can be divided into three-phase transformers and single-phase transformer. In the three-phase power system, the general application of the three-phase transformer, when the oversized transport conditions and subject to the three-phase power system can also be applied consisting of three single-phase transformer transformer group. Winding distinction can be divided into two-winding transformer and three-winding transformers. Transformers are usually two-winding transformer, namely on the core has two windings, one for the primary winding, one for the secondary winding. Three-winding transformer larger capacity transformer (5600 kVA or more) to connect the three different voltage power lines. In exceptional circumstances, also applied more windings. Structural classification can be divided into core transformers and transformer steel. As compared with the winding package in the core periphery core type transformer; core package as compared with steel transformer winding periphery. But both are slightly different in structure, there is no essential difference in principle. Power transformers are all core type. Main transformer iron core, winding, fuel tank, oil pillow, bushings, tap-and gas relays and other components. 1.1 core core is a magnetic circuit portion of the transformer. To generate hysteresis loss and eddy current loss and fever runtime. To reduce heat loss and reduce the size and weight, the core using less than 0.35mm high magnetic permeability of cold-rolled grain-oriented silicon steel composition. In accordance with the winding in the core of the arrangement, there are core type and steel type of points. In the large-capacity transformer, the core loss of the heat emitted from the insulating oil can be taken away when the cycle is sufficient to achieve good cooling effect, often a cooling oil passage in the core. 1.2 coil winding and core are the core elements of the transformer. Since the winding itself or joints resistance contact resistance by I2Rt known to produce heat. It is not long winding higher than nominal current to pass. In addition, a large electromagnetic force generated in the winding through the short-circuit current damage the transformer. The basic winding concentric and overlapping of two. The main fault is a short circuit transformer winding and housing shorted turns. Interturn insulation aging is mainly due to short circuit or overload due to short-circuit the transformer and through the insulation against mechanical damage generated. The oil in the transformer decreased, resulting in oil when exposed winding, interturn short circuit can occur; another crossing the short circuit, overcurrent effect the winding deformation, mechanical damage to the insulation will generate a short circuit between turns. When the inter-turn short circuit, internal short circuit winding current may exceed the rating, but the entire winding current may not exceed the rating. In this case, gas protection action, the situation is serious, the differential protection device will be action. The causes of the housing is also due to short circuit or insulation aging oil moisture, oil drops, or due to lightning and over-voltage generated by the operation. In addition, in the event of a short circuit when crossing, leaving winding deformation due to over-current, short circuit will also have to shell phenomenon. When the case of a short circuit, usually gas protective devices and ground protection action. 1.3 tank body of oil-immersed transformers (winding and core) are housed in a tank filled with transformer oil, steel plate welded into the tank. The small transformer tank by tank shells and cover composition, the body of the transformer housing on the box, the lid can be lifted out of the body of open repair