During daily operation, it's crucial to regularly inspect the surface of the porcelain sleeve on the surge arrester. If the surface becomes heavily contaminated, it can lead to uneven voltage distribution. In a surge arrester with parallel shunt resistors, an increase in voltage on one component can cause a significant rise in current through the resistor, potentially leading to its failure and operational issues. This may also affect the arc-quenching performance of the valve-type arrester. Therefore, if the porcelain sleeve is severely soiled, immediate cleaning is necessary to prevent potential problems.
It's important to check the arrester’s lead wires and grounding conductor for signs of burning or broken strands, as well as any damage to the discharge recorder. These checks are essential for identifying hidden defects. Additionally, ensure that the seal at the top of the arrester is intact, as a poor seal can allow water ingress, which might result in serious accidents. Inspect the cement joint between the porcelain sleeve and flange to confirm it is tight. Install a waterproof cover on the 10 kV valve arrester’s lead to prevent rainwater from entering. Also, verify that the electrical distance between the arrester and the protected equipment meets the required standards, keeping the arrester as close as possible to the equipment. After thunderstorms, check the recorder’s operation and measure the leakage current. If the power frequency discharge voltage deviates from the standard, the arrester should be repaired or tested. If the discharge recorder moves too often, it should be inspected and repaired. Cracks in the porcelain sleeve or cement joint, as well as loose flanges or rubber mats, require immediate attention.
Regularly check the insulation resistance of the arrester using a 2500-volt megohmmeter. Compare the measured value with previous readings. If there's no significant change, the arrester can continue operating. A significant drop in insulation resistance usually indicates poor sealing, moisture, or a short circuit in the spark gap. If the resistance falls below the acceptable level, further testing of the arrester's characteristics is necessary. A sharp increase in resistance may point to internal issues such as poor contact, component breakage, or spring slack. These conditions should be addressed promptly to avoid failures.
To detect hidden internal faults in valve-type arresters, a preventive test should be conducted before the annual thunderstorm season. This helps ensure the arrester is functioning properly when it's most needed.
Installation of Valve-Type Arresters
1. The installation location of the valve-type arrester should be as close as possible to the equipment being protected. For a 10 kV transformer, the maximum electrical distance should be less than 15 meters for single-line incoming lines frequently operated during thunderstorms, less than 23 meters for two-way incoming lines, and less than 27 meters for three-way incoming lines. If the distance exceeds these values, the arrester should be installed on the busbar.
2. The arrester must be installed vertically, not tilted. Ensure the leads are securely connected, and avoid applying stress to the arrester’s terminals.
3. To prevent interference with the power system during normal operation or after lightning strikes, the arrester should be placed within the protection range of the fuse.
4. The lead wire size for the valve-type arrester should not be smaller than 16 mm² for copper or 25 mm² for aluminum. The grounding conductor and the metal casing of the protected equipment must be reliably connected to the grounding grid, with a grounding resistance of no more than 5Ω.
Handling Faults in Valve-Type Arresters
Valve-type arresters may experience various abnormal conditions during operation. It's essential to identify and address these issues promptly.
1. If cracks are found in the porcelain sleeve under normal weather conditions, the arrester should be taken out of service immediately and replaced with a qualified unit. During thunderstorms, if cracks are detected, the arrester should remain in operation until after the storm, then be treated accordingly. If the crack causes a flashover but the system is not grounded, the faulty phase arrester should be deactivated if possible.
2. If there is an internal fault or the casing is broken, it could lead to a ground fault. Personnel should avoid approaching the arrester. The faulty arrester can be disconnected via a circuit breaker or manually by grounding.
3. If the arrester suddenly explodes during operation, and the system has not been permanently grounded, the faulty phase isolation switch should be opened after the storm to disable the arrester and replace it with a qualified unit. If the system is already grounded, do not use the isolator to disconnect the faulty arrester.
4. If the action indicator is burned black, the grounding lead is blown, the valve resistance is invalid, or the spark gap arc quenching performance has deteriorated, the arrester should be tested electrically or disassembled for inspection.
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