The role of zinc oxide lightning arrester in distribution system

by:Mings     2020-04-21
In a three-phase four-wire distribution system, when lightning high side, when the lightning current in grounding resistance pressure drop and the residual pressure of zinc oxide lightning arrester added together on transformer winding, easily breakdown of insulation. When the grounding line and transformer shell of the zinc oxide lightning arrester together and grounding, the effect on the high voltage winding of voltage only zinc oxide lightning arrester sheath residual pressure, but at this point is to improve the potential transformer casing, may occur from the shell to the low voltage transformer of inverse flashover. In order to prevent the inverse flashover, the low voltage side of transformer neutral point and connect them together on the shell, the low voltage side potential also increased accordingly. That the zinc oxide lightning arrester sheath grounding wire, transformer neutral point, the shell together and grounding method, called the trinity; Grounding protection device can effectively prevent lightning damage. However, when the distribution transformer hv side ground lightning, zinc oxide lightning arrester, when lightning current flows through the ground resistance of pressure drop on the neutral point on the low voltage side, the low voltage side line at this time is equivalent to the wave resistance grounding wire. As a result, most of the pressure drop is added on the low voltage winding, and through the inductance, high voltage winding will be effected according to the variable than in high voltage, because the voltage of the high voltage winding is restricted by zinc oxide lightning arrester, the high pressure distribution along the high voltage winding, produced in the high voltage winding neutral point * * * * * * value, may be near breakdown of insulation. At the same time the high pressure along the longitudinal voltage high voltage winding is big, is likely to breakdown the turn-to-turn insulation layer or high voltage winding. To try to reduce the grounding resistance value, so the construction of the transformer overhaul should pay attention to improve the level of high voltage winding neutral insulation. In addition, when the ground lightning on the low voltage side, due to the low voltage insulation margin than high pressure, according to the change than to the high side, it is likely to make high side insulation breakdown, and at the same time also can make low voltage electrical equipment insulation breakdown, causing casualties people and animals. Thus, according to this kind of situation, in variable should be installed on the low voltage side of low voltage surge arrester.
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