Precautions for Installation and Use of Lightning Arrester

1. Install the arrester near the power distribution transformer

Metal oxide arrester (MOA) is connected in parallel with the transformer in normal operation. The upper end is connected to the line and the lower end is grounded. When there is overvoltage in the line, the transformer will be subjected to the overvoltage through the arrester, the lead and the ground device when the three parts of the voltage drop, known as residual voltage. In the three parts of overvoltage, the residual voltage on the arrester is related to its own performance, and its residual voltage value is certain. Residual pressure on the grounding device can be eliminated by connecting the grounding lead to the transformer housing and then to the grounding device. And how reduce the residual pressure on the lead becomes the key to protecting the transformer. The impedance of the lead is related to the frequency of the current passing through. The higher the frequency, the stronger the inductance of the wire and the greater the impedance. It can be seen from U=IR 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-pressure side of the transformer should also be installed

If there is no MOA installed on the low voltage side of the transformer distribution, when the lightning current is discharged from the arrester on the high voltage side to the earth, the 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 transformer distribution housing. Therefore, the lightning current flowing through the low-voltage side winding will induce a high potential (up to 1000 kV) in the high-voltage side winding according to the variable ratio. The potential will be superimposed with the lightning voltage of the high-voltage side winding, resulting in the rise of the potential at the neutral point of the high-voltage side winding and the breakdown of the insulation near the neutral point. If MOA is installed on the low-voltage side when the discharge of MOA on the high-voltage side increases the potential of the grounding device to a certain value, the MOA on the low-voltage side will start to discharge, and the potential difference between the outgoing end of the low-voltage side winding and its neutral point and the housing will be reduced. In this way, the influence of the "inverse conversion" potential can be eliminated or reduced.

3. The MOA ground cable should be connected to the transformer housing

The ground wire of the MOA should be connected directly to the distribution transformer housing, and then the housing should be connected to the ground. It is wrong to connect the grounding wire of the arrester directly to the earth and then lead another grounding wire from the grounding pile to the transformer housing. In addition, the grounding wire of the arrester should be shortened as much as possible to reduce residual pressure.

4. Regular maintenance tests in strict accordance with 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 transformer. 

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