The distribution office is responsible for turning the electricity of the high-voltage grid into low-voltage electricity, and then transmitting it out, and also has the functions of monitoring, regulating, and distributing the input voltage of the grid. In addition, the capacity of the substation is relatively large.

The power distribution station does not have to change voltage or the input voltage is relatively low, and mainly focuses on the distribution, control and protection of the power supply to the user. The capacity of the distribution station is relatively small.

Simply put, power transformation is to change the voltage introduced from the outside into the voltage suitable for your use, and power distribution is to distribute electricity to the various points of electricity inside your unit. Of course, the power distribution office can achieve both functions. In the power system, the power plant converts the natural primary energy into electricity and sends electricity to distant power users. In order to reduce the power loss and line impedance voltage drop on the transmission line, the voltage needs to be increased. In order to meet the safety needs of power users, the voltage must be reduced and distributed to each user, which requires a substation that can raise and lower the voltage and distribute electrical energy. Therefore, the substation is an electrical device in the power system through its transformation voltage, acceptance and distribution of electrical energy, it is the intermediate link between the power plant and the power user, and at the same time, the voltage level of the power grid is linked through the substation, the role of the substation is to transform the voltage, transmission and distribution of electrical energy. The substation consists of power transformer, distribution device, secondary system and necessary auxiliary equipment.

The transformer is the central equipment of the substation, which uses the principle of electromagnetic induction. The power distribution device is a device in which all the switching appliances and the current carrying conductor auxiliary equipment in the substation are connected together. Its role is to receive and distribute electrical energy. The distribution device is mainly composed of bus bar, high voltage circuit breaker switch, reactor coil, transformer, power capacitor, lightning arrester, high voltage fuse, secondary equipment and other necessary auxiliary equipment. Secondary equipment refers to the equipment that measures, controls, monitors and protects the primary system status. The circuit composed of these devices is called the secondary circuit, which is generally referred to as the secondary system. The equipment of the secondary system includes measuring device, control device, relay protection device, automatic control device, DC system and necessary auxiliary equipment.