Arresters are devices that protect substations from lightning surges. When lightning surges passing through substations along the line exceed the arrester protection level, the arrester discharges first, and the lightning current is safely led to the earth through a good conductor. The grounding device is used to limit the lightning voltage amplitude below the level of the lightning impulse of the protected equipment, so that Electrical equipment is protected.
Use arrester should pay attention to what issues
1. Should be installed near the distribution transformer
The 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 overvoltage occurs on the line, the distribution transformer at this time will withstand the three-part pressure 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 the overvoltage, the residual voltage on the arrester is related to its own performance, and its residual pressure value is certain. The residual voltage on the grounding device can be eliminated by connecting the ground drop wire to the distribution shell and then connecting it to the grounding device. How and how to reduce the residual voltage on the lead become the key to protection and distribution. The impedance of the lead is related to the frequency of the passing current. The higher the frequency, the stronger the inductance of the wire and the greater the impedance. From U=IR, we can see that to reduce the residual voltage on the lead, we must reduce the lead impedance, and the possible method to reduce the lead impedance is to shorten the MOA distance from the distribution transformer, in order to reduce the lead impedance and reduce the lead voltage drop. Arrester should be installed near the distribution transformer more appropriate.
2. Distribution transformer should also be installed on the low pressure side
If the MOA is not installed on the low voltage side of the distribution transformer, when the high-voltage side arrester discharges the lightning current to the earth, a voltage drop will occur on the grounding device. The pressure drop will also act at the neutral point of the low-voltage side winding through the distribution transformer shell. 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 1000kV) according to the transformation ratio. This potential will be superimposed with the lightning voltage of the high-voltage side winding, resulting in the rise of the neutral point voltage of the high-voltage side winding. High, penetrate the insulation near the neutral point. If MOA is installed on the low-voltage side, when the high-side MOA discharge causes the potential of the grounding device to rise to a certain value, the low-voltage side MOA starts to discharge, so that the potential difference between the outlet side of the low-voltage side winding and its neutral point and the casing decreases. Can eliminate or reduce the influence of the "inverted" potential.
3. The MOA ground wire should be connected to the transformer shell
The grounding wire of the MOA should be directly connected to the distribution transformer enclosure, and then the enclosure should be connected to the earth. It is wrong to connect the grounding wire of the lightning arrester directly to the ground, and then another ground wire from the grounding stake to the transformer shell. In addition, the grounding wire of the arrester should be as short as possible to reduce the residual voltage.
4 in strict accordance with the regulations require regular maintenance test
The insulation resistance measurement and leakage current test are performed on the MOA regularly. 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 distribution transformer.
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