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The metal oxide surge arrester (MOA) is connected in parallel with the distribution transformer during normal operation, with the upper terminal connected to the ground and the lower terminal grounded. When an overvoltage occurs in the line, the distribution at this time will withstand the three-part voltage drop generated by the overvoltage through the arrester, lead and grounding device, called residual voltage. In these three parts of the overvoltage, the residual voltage on the arrester is related to its own performance, and the residual voltage value is constant. The residual voltage on the grounding device can be eliminated by connecting the grounding down conductor to the transformer housing and then connecting it to the grounding device. How to reduce the residual voltage on the lead becomes the key to the protection of the distribution. The impedance of the lead is related to the frequency of the current passed. The higher the frequency, the stronger the inductance of the wire and the greater the impedance. From U=IR, it is known that to reduce the residual voltage on the lead, it is necessary to reduce the lead impedance. A feasible way to reduce the lead impedance is to shorten the distance of the MOA from the distribution, to reduce the lead impedance and reduce the lead voltage drop. The arrester should be installed at a point closer to the distribution transformer.
2. The low voltage side of the transformer should also be installed.
If the MOA is not installed on the low-voltage side of the transformer, when the high-voltage side arrester discharges the lightning current to the earth, a voltage drop is generated on the grounding device, and the voltage drop acts on the neutral point of the low-voltage side winding through the distribution transformer. Therefore, the lightning current flowing in the low-voltage side winding will cause the high-voltage side winding to induce a very high potential (up to 1000 kV) according to the ratio, which will be superimposed with the lightning voltage of the high-voltage side winding, resulting in the neutral point potential of the high-voltage side winding. Raise, break through the insulation near the neutral point. Article source: http://Read.aspx?NewsId=23 If MOA is installed on the low-voltage side, when the high-voltage side MOA discharges the potential of the grounding device to a certain value, the low-voltage side MOA starts to discharge, so that the low-voltage side winding outlet end The potential difference from the neutral point and the outer casing is reduced, which eliminates or reduces the effect of the "inverse transformation" potential.
3. The MOA ground wire should be connected to the transformer housing.
The grounding wire of the MOA should be connected directly to the distribution transformer housing, and then the housing is connected to the ground. It is a mistake to connect the grounding wire of the arrester directly to the ground and then introduce another grounding wire from the grounding peg to the transformer casing. In addition, the grounding wire of the arrester should be shortened as much as possible to reduce the residual voltage.
4. Regularly inspect the test in strict accordance with the requirements of the regulations
The MOA is tested for insulation resistance and leakage current on a regular basis. Once the MOA insulation resistance is found to be significantly reduced or broken down, it should be replaced immediately to ensure safe and healthy operation of the transformer.
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