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 fully understand the importance of lightning protection and grounding for these equipment. This lack of knowledge has led to numerous lightning-related accidents, causing system failures and serious damage to grid equipment. Therefore, it's essential to discuss the lightning protection and grounding issues in power distribution systems, offering practical guidance for engineers and construction teams.
**1. Lightning Protection and Grounding of Transmission Lines**
The lightning protection strategy for transmission lines should be tailored based on factors such as line voltage level, load type, system operation mode, local lightning activity intensity, terrain, soil resistivity, and more.
- For 35kV lines, it is generally not recommended to install lightning protection lines. However, a 1–2 km lightning protection line can be installed at the incoming section of the substation. In areas with high lightning activity, metal oxide surge arresters are often used.
- 110kV lines should have lightning protection lines along the entire length. In mountainous regions, double lightning protection lines are required. However, in areas with fewer than 15 thunderstorm days annually or where operational experience indicates low lightning activity, lightning protection lines may not be necessary.
- 220kV lines must have full-length lightning protection lines, with double lines in certain areas. The protection angle of the lightning line on the tower should typically be between 20° and 30°, and proper grounding of the tower is essential. According to soil resistivity, the power frequency grounding resistance of the tower should not exceed the values listed in Table 1.
For metal oxide surge arresters on 35kV lines, the following technical specifications are usually required:
- Continuous operating voltage (RMS) ≥ 40.8 kV
- Rated voltage (RMS) ≥ 51 kV
- DC 1 mA reference voltage ≥ 73 kV (within 73–74 kV range)
- Residual voltage under standard discharge current (5 kA):
- Lightning impulse: ≤ 134 kV
- Operational impact: ≤ 114 kV
- Steep wave impact: ≤ 154 kV
- 2000 μs square wave current (peak): 200 A
- Insulation configuration determined by pollution level requirements
**2. Lightning Protection and Grounding of Distribution Lines**
Lightning protection for distribution lines follows similar principles as for transmission lines, using either lightning protection lines or surge arresters. Measures vary depending on the voltage level and line type.
- **10kV bare conductor lines**: Lightning protection lines are rarely used due to cost and complexity. Instead, surge arresters are installed in areas with frequent lightning activity, and tower grounding is implemented.
- **10kV insulated wire lines**: With the increasing use of cross-linked polyethylene overhead insulated wires in urban areas, traditional lightning protection methods remain unchanged, leading to multiple incidents of insulation failure due to lightning strikes. Current solutions include:
- Installing lightning protection lines (most effective but costly)
- Upgrading insulators to lightning-resistant types
- Installing surge arresters periodically
- Extending the flash path to help arc extinguish
- Partially stripping the insulation to allow sliding arcs
- **Low-voltage distribution lines**: Surge arresters or breakdown fuses should be installed at the transformer outlet, with grounding at the same time. Grounding resistance should not exceed 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 a maximum resistance of 10Ω. For longer lines, at least three groundings are needed. To prevent lightning waves from entering homes, the iron angle insulators on connecting lines should be grounded, with resistance below 30Ω. Special attention should be given to the "one household, one meter" system.
**3. Lightning Protection and Grounding of Power Cable Lines**
Power cables require different lightning protection strategies based on their voltage level and connection requirements. For 35kV and below cables, surge arresters are typically installed near the terminal, and the metal shielding and armor must be properly grounded. For high-voltage cables (110kV and above), overvoltage can occur at ungrounded ends or at sheath intersections during lightning surges, potentially causing insulation breakdown. Protection options include:
- One end of the cable sheath connected to ground, the other to a protector
- Interconnected sheaths with Y0 wiring
- Interconnected sheaths with Y or Δ wiring
- One end of the sheath connected to ground and a balancing line
- One end of the sheath connected to a return ground line
Proper lightning protection and grounding must be considered from the design stage. A practical plan should be adopted based on local conditions, and high-quality electrical equipment and reliable lightning protection devices should be selected. Following the equipotential principle, a common grounding grid should be established, ensuring comprehensive lightning protection and grounding so that our lines and equipment can avoid the risks of lightning strikes.
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