The main measures for preventing direct lightning strikes on low-voltage overhead transmission lines

I. Core Measure: Installation of Overhead Ground Wires (Shield Wires)

This is the most effective and fundamental direct lightning protection measure, particularly suitable for lightning-prone areas or critical lines.

Principle: One or two well-grounded metal wires (typically galvanized steel strands) are installed atop utility poles above the power lines. During lightning discharge, the ground wire acts as the preferred point of strike, channeling the massive lightning current into the ground through the grounding device, thereby protecting the conductors below from direct lightning hits.

Applicable Scenarios: 

Regions with frequent lightning activity (high average annual thunderstorm days). 

Lines supplying critical loads requiring high reliability. 

Lines passing through hilly or elevated terrain with high soil resistivity.

II. Supplementary Measure: Installation of Surge Protectors (SPDs)

SPDs are primarily used to limit lightning-induced overvoltages. They serve as a crucial supplement to ground wires and are the main protection method for lines without ground wires.

Principle: SPDs are connected in parallel between the line (phase conductor) and the ground. Under normal operation, they exhibit high impedance and do not affect the system. When a dangerous lightning overvoltage occurs on the line, their impedance rapidly decreases to a low value, instantly diverting the lightning current and limiting the residual voltage to a level tolerable by equipment. This protects line insulators and electrical devices. Afterward, they quickly return to a high-impedance state.

Installation Locations: 

Line endpoints: at the substation outlet and the end of the line (before entering user premises). 

Critical poles such as branch poles, terminal poles, and angle poles. 

Intermediate sections of long lines, installed at regular intervals (e.g., every 200–500 meters). 

Entrances to particularly critical users or equipment.

III. Fundamental and Critical Measure: Improving Grounding Systems

The effectiveness of all lightning protection measures relies on proper grounding. Without adequate grounding, neither ground wires nor surge arresters can function effectively.

Requirements: 

The grounding resistance of poles should be as low as possible (typically ≤30Ω, which may be relaxed to ≤50Ω in areas with high soil resistivity). 

Grounding down conductors for ground wires and surge arresters must have reliable connections and sufficientcross-sectional area.

Grounding electrodes should be buried in moist soil. If necessary, soil replacement, use of resistance-reducing agents, or increasing the number of grounding electrodes can be employed to lower grounding resistance.

IV. Utilizing Existing Structures as Natural Air Terminals

This is an economical and practical method but has certain limitations.

Principle: If structures such as buildings or trees taller than the line exist nearby and their protective zone covers the line, these natural objects can provide a degree of protection.

Note: This method is unreliable, as trees may be cut down, and their high resistance may cause side flashes during lightning strikes, endangering the line. It should not be relied upon as a primary measure.

V. Other Technical and Administrative Measures

1. Installation of Arcing Gaps: In some cases, small arcing gaps can be installed in parallel with insulators. During overvoltage events, the gap breaks down first, protecting the insulator from flashover. However, this may cause line tripping and requires coordination with auto-reclosing devices. 

2. Use of Porcelain Cross-Arms or Enhanced Insulation: While not preventing direct lightning strikes, this improves the line’s withstand capability, reduces the probability of power arc formation, and lowers the risk of tripping. 

3. Operation and Maintenance: Regular inspections to ensure ground wires, surge arresters, and grounding down conductors are well-connected, free from corrosion, and undamaged; periodic measurement of grounding resistance to ensure compliance with requirements.

Summary and Recommendations

For direct lightning protection of low-voltage overhead lines, a combined approach is typically adopted: 

For critical lines in lightning-intensive areas: Prioritize the "ground wire + robust grounding" method, supplemented with surge arresters at key points. 

For general lines: The most economical and practical solution is "multi-point installation of surge arresters + ensuring proper grounding for every pole."

In all cases: Adequate grounding is the cornerstone of all lightning protection measures and must be given high priority.