Power transformer is a kind of static electrical equipment, which is used to change the AC voltage (current) of a certain value into another voltage (current) with the same frequency or several different values< br /> Static equipment with two or more windings, in order to transmit electric energy, converts the AC voltage and current of one system into the voltage and current of another system through electromagnetic induction at the same frequency. Usually, the values of these currents and voltages are different< br /> Power transformer is one of the main equipment in power plant and substation. The function of transformer is multifaceted. It can not only raise the voltage and send the electric energy to the power consumption area, but also reduce the voltage to the use voltage at all levels to meet the needs of power consumption. In short, the step-up and step-down must be completed by the transformer. In the process of transmitting electric energy in the power system, there will be two parts of loss: voltage and power. When transmitting the same power, the voltage loss is inversely proportional to the voltage, and the power loss is inversely proportional to the square of the voltage. The transformer is used to increase the voltage and reduce the power transmission loss< br /> The transformer is composed of two or more coil windings wound on the same iron core. The windings are connected through alternating magnetic field and work according to the principle of electromagnetic induction. The installation position of transformer shall be convenient for operation, maintenance and transportation, and a safe and reliable place shall be selected. When using the transformer, the rated capacity of the transformer must be reasonably selected. When the transformer operates without load, it needs large reactive power. These reactive power shall be supplied by the power supply system. If the capacity of the transformer is too large, it will not only increase the initial investment, but also make the transformer operate under no-load or light load for a long time, increase the proportion of no-load loss, reduce the power factor and increase the network loss. Such operation is neither economical nor reasonable. The selection of transformer capacity is too small, which will overload the transformer for a long time and easily damage the equipment. Therefore, the rated capacity of the transformer should be selected according to the needs of the power load, and should not be too large or too small< br /> Key words: high voltage switchgear series_ Low voltage switchgear series_ Transformer series_ Circuit breaker series_ Protection switch series_ Voltage box series