Correct application of the hottest metal oxide arr

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Correct use of metal oxide arrester in rural distribution transformer

1 It should be installed near the distribution transformer side

metal oxide arrester (MOA) in parallel with the distribution transformer during normal operation, with the upper end connected to the line and the lower end grounded. When there is overvoltage in the line, the distribution transformer at this time will bear the three part voltage drop generated when the overvoltage passes through the lightning arrester, lead wire and grounding device, which is called residual voltage. In 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 lead to the distribution transformer housing, and then connected 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. The higher the frequency, the stronger the inductance of the wire. Annealing treatment can be adopted after forming. The impedance of glycerol bath annealing treatment is greater. It can be seen from u=ir that in order 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. Therefore, the arrester should be installed near the distribution transformer, which is more appropriate if it fails to meet the requirements

2. The low-voltage side of the distribution transformer should also be installed

if MOA is not installed on the low-voltage side of the distribution transformer, when the lightning arrester on the high-voltage side discharges lightning current to the earth, a voltage drop will be generated on the grounding device, and the voltage drop will act on the neutral point of the winding on the low-voltage side through the distribution transformer housing at the same time. Therefore, the lightning current flowing through the low-voltage side winding will induce a high potential (up to 1000 kV) according to the transformation ratio of the high-voltage side winding. This potential will be superimposed with the lightning voltage of the high-voltage side winding, causing the neutral point potential of the high-voltage side winding to rise and breakdown the insulation near the neutral point. If MOA is installed on the low-voltage side, when the MOA discharge on the high-voltage side increases the potential of the grounding device to a certain value, the MOA on the low-voltage side begins to discharge, reducing the potential difference between the outgoing end of the winding on the low-voltage side and the neutral point and the shell, so as to eliminate or reduce the influence of the "reverse transformation" potential

3. MOA grounding wire should be connected to the distribution transformer shell

moa grounding wire should be directly connected to the distribution transformer shell. A prospective study report on the mechanical tests and clinical results of 120 patients with this device was published, and then the shell was connected to the earth. 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 shell. In addition, the grounding wire of lightning arrester should be shortened as far as possible to reduce residual voltage

4. The insulation resistance and leakage current of MOA shall be measured regularly in strict accordance with the requirements of the procedures. Once the insulation resistance of MOA is significantly reduced or broken down, the products touched shall be replaced immediately from the earliest aluminum and copper products to ensure the safe and healthy operation of the distribution transformer

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