Zinc Oxide Arrester The zinc oxide surge arrester in the distribution system can effectively prevent lightning strikes on the distribution system.
In the three-phase four-wire distribution system, when the lightning strikes the high-voltage side, the voltage drop generated when the lightning current passes through the grounding resistance and the residual voltage of the zinc oxide arrester superimpose on the transformer winding, and it is easy to break down the insulation. When the grounding wire of the zinc oxide arrester and the transformer shell are connected together and grounded, the voltage applied to the high voltage winding is only the residual voltage of the zinc oxide arrester sheath, but at this time, the potential of the transformer shell increases, which may occur. Reverse flashover of the housing to the transformer low voltage winding. In order to prevent such reverse flashover, the neutral point on the low voltage side of the transformer is also connected to the housing, so that the potential on the low voltage side is also correspondingly increased. This method of connecting the zinc oxide arrester sheath ground lead, the transformer neutral point, and the housing to the ground is a so-called trinity; the lightning protection grounding method can effectively prevent equipment damage caused by lightning.
The Role of Zinc Oxide Arrester in Distribution System
However, when lightning strikes on the high-voltage side of the transformer, the zinc oxide surge arrester operates, and the voltage drop of the lightning current flowing through the grounding resistor acts on the neutral point of the low voltage side. The low-voltage side outlet line at this time corresponds to the grounding of the wire wave resistance. Therefore, most of the voltage drop is applied to the low-voltage windings. Inductance also causes the high-voltage windings to exhibit high voltages at variable ratios. Since the high-voltage winding terminal voltage is limited by the zinc oxide arresters, the high voltage will be distributed along the high-voltage windings. The maximum value occurs at the high voltage winding neutral point, which may breakdown the nearby insulation. At the same time, the high voltage along the high voltage winding is also very high in the longitudinal direction, and it is likely to break through the high voltage winding layers or the interturn insulation. Therefore, the grounding resistance value should be reduced as much as possible during construction, and the insulation level of the high-voltage winding neutral point should be increased when the transformer is inspected. In addition, when the low-voltage side lightning, because the low voltage insulation margin is higher than the high pressure, according to the transformation ratio to the high pressure side, it is possible to make the high-voltage side insulation breakdown, but also make the low-voltage electrical equipment insulation breakdown, causing people, Livestock casualties. Therefore, according to this situation, low-voltage surge arresters should also be installed on the low-voltage side of distribution transformers.
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