Why do I need a high voltage cabinet

Power from the power station, usually through the transmission line to the various electricity places. According to the distance between the transmission power distance, the use of different high voltage. From China's current power situation, the transmission distance of 200 to 300 km when the use of 220 kV voltage transmission; in 100 km or so when using 110 kV; 50 km or so with 35 kV; in 15 km to 20 km When using 10 kV, and some with 6600 volts. Transmission voltage of 110 kV or more lines, known as ultra-high voltage transmission lines. In the long-distance transmission, China has 500 kV ultra-high voltage transmission lines.

Why use high-voltage transmission? This is from the transmission line on the loss of electricity power, when the current through the wire, there will be part of the energy into heat and lost. China's current widely used three-phase three-wire AC transmission line on the loss of electrical power: P consumption = 3I2R. R in the formula is the resistance of each transmission line, and I is the current in the transmission line. Assuming that the transmission distance is L, the resistivity of the transmission line used is ρ and the cross-sectional area is S, then R = ρ (L / S) = U / I.

It can be seen from the above equation that the transmission line cross-sectional area S is constant, the higher the transmission voltage U, the smaller the power consumption of the loss of power consumption; if the allowable loss of power consumption P consumption (usually not more than 10% of the transmission power) The higher the voltage, the smaller the cross-sectional area of the transmission conductor, which greatly saves the material used for the transmission wire.

From the two aspects of reducing the power consumption on the transmission line and saving the material used in the transmission wire, the long-distance transmission of electricity to use high voltage or ultra-high voltage.

But can not blindly improve the transmission voltage, with the transmission voltage is higher, the construction of transmission overhead lines, the use of various materials required more stringent, the higher the cost of the line. Therefore, from the actual situation, do the transmission line can reduce power consumption, but also save construction investment. High-voltage transmission can reduce the loss of electrical power, but from the power point of view, the generator can not produce 220 kV as high voltage, because the generator to produce such a high voltage, from its timber, structure and safe operation of production and so on There are almost impossible to overcome the difficulties. From the electricity side, the vast majority of electrical equipment can not run at high voltage. This determines the power generation, transmission to electricity to use a series of power transformers to increase or decrease the voltage. The transmission process of a large hydroelectric power station is shown in Figure 7-8. The AC power from the power station is first boosted by the transformer in the substation 1 to 220 kV and then transported to a distant central substation 2 Where the transmission transformer to the voltage drop to 10 kV, sent to the subordinate substation, in the substation 3 by the transmission transformer and then the voltage down to 35 kV. And then transported to the next level substation 4, the substation 4 and the transmission transformer voltage to 10 kV, and then sent to the user's substation 5, and finally the voltage into 380 volts / 220 volts, the supply Electrical equipment. Power from large hydroelectric power stations, through the transmission line to the user, the middle to go through five transform voltage (one liter, four down). For medium and small power plants, the number of intermediate conversion voltage is less, which should be based on the power of the TV issued by the transmission line and other specific circumstances to determine.

High-voltage cabinet is to accept the power plant transmission over the high voltage, in the high voltage cabinet with high-voltage switch to the distribution of the nearest user, and then transformer transformer, and then transported to the low voltage cabinet (conventional 380V) and then through the low-voltage switch (Load switch, disconnector, etc.) to the terminal electrical equipment.