1. It should be installed on the side close to the distribution transformer
The metal oxide arrester (MOA) is connected in parallel with the distribution transformer during normal operation, the upper end is connected to the line, and the lower end is grounded. When there is an overvoltage on the line, the distribution transformer at this time will withstand the three-part voltage drop generated when the overvoltage passes through the arrester, the lead and the grounding device, which is called residual voltage. Among these three parts of overvoltage, the residual voltage on the arrester is related to its own performance, and its residual voltage value is certain. The residual voltage on the grounding device can be eliminated by connecting the grounding down-conductor to the distribution transformer casing and then connecting it to the grounding device. How to reduce the residual voltage on the lead becomes the key to protect the distribution transformer. The impedance of the lead is related to the frequency of the current passing through it. The higher the frequency, the stronger the inductance of the wire and the greater the impedance. From U=IR, it can be seen that to reduce the residual voltage on the lead, the lead impedance must be reduced, and the feasible way to reduce the lead impedance is to shorten the distance between the MOA and the distribution transformer, so as to reduce the lead impedance and reduce the lead voltage drop, so The arrester should be installed close to the distribution transformer.
2. The low-voltage side of the distribution transformer should also be installed
If there is no MOA installed on the low-voltage side of the distribution transformer, when the high-voltage side arrester discharges the lightning current to the ground, a voltage drop will be generated on the grounding device, and the voltage drop will simultaneously act on the neutral point of the low-voltage side winding through the distribution transformer casing. Therefore, the lightning current flowing in the low-voltage side winding will induce a high potential (up to 1000 kV) in the high-voltage side winding according to the transformation ratio. This potential 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. rise, breaking down the insulation near the neutral point. If the MOA is installed on the low-voltage side, when the high-voltage side MOA discharges and raises the potential of the grounding device to a certain value, the low-voltage side MOA begins to discharge, so that the potential difference between the low-voltage side winding outlet end and its neutral point and the shell is reduced. Can eliminate or reduce the effect of "inverse transformation" potential.
3. The MOA ground wire should be connected to the distribution transformer shell
The ground wire of the MOA should be connected directly to the distribution transformer case, and then the case is connected to the earth. It is wrong to connect the ground wire of the arrester to the ground directly, and then lead another ground wire from the ground stake to the transformer casing. In addition, the ground wire of the arrester should be as short as possible to reduce the residual voltage.
4. Regular maintenance test in strict accordance with the requirements of the regulations
Regularly measure the insulation resistance and leakage current of the MOA. Once the insulation resistance of the MOA is found to be significantly reduced or broken down, it should be replaced immediately to ensure the safe and healthy operation of the distribution transformer.
