Lightning Protection for Dry Type Transformers

1. Lightning Arrester Selection & Installation

(1) Core Requirements for Arresters

• Product Qualification: Purchase seamless metal oxide arresters through formal channels. Only use products that pass strict pre-operation tests (e.g., insulation resistance, leakage current) and meet operating requirements.
• Protection Purpose: Prevent lightning overvoltage from intruding into high-voltage/low-voltage lines and damaging the transformer’s internal insulation.

(2) Installation Location & Specifications

• Optimal Position: Install high-voltage arresters on the power line near the transformer’s high-voltage bushing. This blocks lightning waves before they penetrate the bushing, ensuring timely protection.
• Compliance with Standards: Follow electrical equipment installation specifications—avoid random placement (which renders protection ineffective). Ensure the arrester is correctly wired to the line and grounding system.

2. Preventive Testing for Arresters

• Test Cycle: Conduct regular preventive tests on in-service arresters. Focus on monitoring leakage current—immediately replace arresters whose leakage current exceeds the reference value (unqualified products).
• Test Focus: Verify the arrester’s ability to clamp overvoltage and discharge current, ensuring it functions normally when lightning strikes.

3. Grounding Resistance Standards & Maintenance

(1) Resistance Thresholds by Transformer Capacity

(2) Testing Requirements

• Test Frequency: Measure grounding resistance twice a year (April and July) to account for environmental changes (e.g., humidity) and potential welding point detachment.
• Rectification for Exceeding Thresholds:
  • If the test value exceeds the standard, extend the grounding wire and add grounding electrodes (e.g., copper-clad steel rods).
  • Adopt physical or chemical measures (e.g., backfilling with low-resistance soil, adding electrolytic grounding agents) to reduce resistance to the specified range.

4. Critical Risks of Substandard Grounding Resistance

• Lightning current cannot be effectively diverted to the ground during a strike.
• Lightning voltage may be transmitted to the transformer’s low-voltage side via the grounding wire, generating reverse overvoltage that damages insulation.

5. Key Implementation Principles

• Ensure the arrester and grounding system form a complete protection loop: Lightning current is clamped by the arrester and quickly discharged to the ground through the low-resistance grounding network.
• Regularly inspect the connection between the arrester, transformer shell, and grounding system—avoid loose or corroded joints that increase resistance.