In recent years, with the transformation of the power grid—especially the reconstruction of urban networks and the development of substation automation systems—many people may not have sufficient knowledge about the lightning protection and grounding of these equipment. This lack of understanding has led to numerous lightning-related accidents, causing system failures and serious damage to grid equipment. Therefore, it is crucial to discuss the issues of lightning protection and grounding in power supply and distribution systems, offering practical guidance for engineers and construction teams.
**1. Lightning Protection and Grounding of Transmission Lines**
The approach to lightning protection for transmission lines should be based on several factors, including the line's voltage level, load type, system operating mode, local lightning activity intensity, terrain, soil characteristics, and soil resistivity.
- For 35kV lines, it is generally not advisable to install lightning protection lines. However, a 1–2 km section near the substation’s incoming line should be equipped with a lightning protection line, especially in areas with high lightning activity or where metal oxide arresters are installed.
- 110kV lines should have lightning protection lines along the entire route. In mountainous areas, double lightning protection lines are recommended. In regions with fewer than 15 annual thunderstorm days or where lightning activity is minimal, lightning protection lines may not be necessary.
- For 220kV lines, lightning protection lines should be installed across the entire line, with double lines in critical areas. The protection angle of the lightning protection line on the tower should be between 20° and 30°, and the tower grounding must be properly implemented. The power frequency ground resistance should not exceed the values listed in Table 1, depending on soil resistivity.
For metal oxide arresters installed on 35kV lines, the following technical specifications are typically required:
- Continuous operating voltage (RMS) ≥ 40.8 kV
- Rated voltage (RMS) ≥ 51 kV
- DC 1 mA reference voltage ≥ 73 kV (range: 73–74 kV)
- Residual voltage at 5 kA discharge current:
- Lightning impulse ≤ 134 kV
- Operational impulse ≤ 114 kV
- Steep wave impulse ≤ 154 kV
- 2000 μs square wave current (peak) = 200 A
- Insulation configuration based on pollution level requirements
**2. Lightning Protection and Grounding of Distribution Lines**
Similar to transmission lines, distribution lines can also use lightning protection lines or arresters. The specific measures vary depending on the voltage level and line type.
- **10kV bare wire lines**: Lightning protection lines are generally used, but due to high cost and complexity, they are rarely installed now. Instead, lightning arresters are placed on lines with frequent lightning strikes, and proper grounding is ensured.
- **10kV insulated wire lines**: With the replacement of bare wires by cross-linked polyethylene overhead insulated wires in many cities, traditional lightning protection methods remain unchanged, leading to multiple incidents of insulation failure due to lightning. Current solutions include:
- Installing lightning protection lines (most effective but costly)
- Upgrading insulators to lightning-resistant types
- Installing arresters at intervals
- Extending the flash path to improve arc extinction
- Partially stripping the insulation to allow sliding arcs
- **Low-voltage distribution lines**: Low-voltage lines should be equipped with low-voltage arresters or breakdown fuses at the transformer outlet, with proper grounding. Grounding resistance should be ≤ 4Ω. Neutral lines in directly grounded systems should be grounded at the source. Repeated grounding is required at the ends of main and branch lines, with resistance ≤ 10Ω. For longer lines, grounding should be done at least three times. To prevent lightning waves from entering homes, the iron angle insulator on connecting lines should be grounded, with resistance < 30Ω. Special attention should be given to "one household, one meter" installations.
**3. Lightning Protection and Grounding of Power Cable Lines**
Power cables require different lightning protection strategies based on their voltage levels and structural features. For cables below 35kV, a surge arrester should be installed near the terminal, with proper grounding of the metal shielding and armor. For high-voltage cables (110kV and above), overvoltage may occur at ungrounded ends or sheath junctions during lightning surges, risking insulation breakdown. Protective options include:
- One end of the metal sheath connected to ground, the other to a protector
- Interconnected metal sheaths with Y-connection protectors
- Interconnected sheaths with Y or Δ wiring
- One end of the sheath connected to ground via an equalizing line
- One end of the sheath connected to a ground return line
Proper lightning protection and grounding should be considered from the design stage. Tailoring plans to local conditions and using high-quality, reliable equipment is essential. Following equipotential principles, establishing a common grounding grid and integrating all grounding and lightning protection measures will help ensure the safety and reliability of power lines and equipment against lightning threats.
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