Working principle of box-type substation

box-type substation (referred to as box transformer) is a kind of high-voltage switchgear distribution transformer, low-voltage switchgear, electric energy metering equipment and reactive power compensation device according to a certain wiring scheme combined in one or several boxes of compact complete sets of power distribution device. It is suitable for the rated voltage 10/0.4KV three-phase AC system, as a line and distribution of electrical energy.

Compared with the European box with the same capacity, the structure of the American box is more reasonable. Because the European-style box transformer is the transformer and ordinary high-voltage electrical equipment installed in the same metal shell box, the transformer room temperature is very high, causing heat dissipation difficulties, affecting the output; on the other hand, in the box using ordinary high-voltage load switch and fuse, low-voltage switch cabinet, so the European-style box transformer volume is larger. The structure of American box transformer is different from that of European box transformer. From the layout point of view, its low-voltage room, transformer room, high-voltage room is not eye-shaped layout, but product-shaped layout. From the structural point of view, this box-type transformer is divided into front and rear parts. The front part is divided into high and low voltage operation intervals. The operation intervals include high and low voltage connection terminals, load switch operation handle, no-load voltage regulating section switch, plug-in fuse, oil level gauge, etc. The rear part is an oil injection tank and a heat sink. The transformer winding, iron core, high voltage load switch and fuse are put into the transformer oil tank. Oil-immersed metal oxide arresters are also used for

arresters. The transformer cancels the oil conservator and adopts the principle of constant volume of oil and air gap to design a sealed oil tank. The oil tank and radiator are exposed to the air and there is no difficulty in heat dissipation. Molded case circuit breaker is used as main circuit breaker and outgoing circuit breaker for low voltage circuit breaker. Due to the simplified structure, the floor area and volume of this box-type substation are greatly reduced. Due to its small volume and only one side of the door is opened, the required floor area is only 1/4 of that of the European box-type substation, and the volume is only 1/5-1/3 of that of the European box-type substation with the same capacity. The high-voltage side of American box transformer is protected by fuse, and the low-voltage side is protected by molded case automatic air circuit breaker, which is the same as that of China's 10kV distribution transformer. The high-voltage fuse protects the internal fault of the transformer, and the automatic air circuit breaker protects the overcurrent, short circuit and undervoltage fault of the low-voltage side line. The shortcomings of American box change. Because the load switch is immersed in the oil, the oil is carbonized and decomposed by the arc, producing harmful gases such as acetylene, which reduces the performance and causes accidents. No obvious disconnection point can be seen, and maintenance is inconvenient. Because the low-voltage protection and measurement methods in the United States are different from those in China, the American box transformer itself does not have low-voltage protection and measurement. In order to meet the needs of domestic users, the domestic box transformer is equipped with low-voltage distribution cabinet on the low-voltage side. Because the box-type transformer is under the direct sun for a long time, it affects the heat dissipation of the molded case circuit breaker, so that the circuit breaker cannot normally break the load and short-circuit current, which is easy to cause high-voltage side fault.