Table of Contents

1. Introduction: The Impact of Overvoltage on Transmission Lines

2. Core Principles of Transmission Line Overvoltage Protection

3. Transmission Line Arrester Selection: Key Factors and Criteria

4. Arrester Installation Location: Optimizing Protection Coverage

5. Grounding System: The Foundation of Effective Overvoltage Protection

6. Comprehensive Protection Strategy: Integrating Selection, Installation and Grounding

7. Performance Comparison Table: Different Protection Configurations

8. Industry Data and Practical Insights

9. Frequently Asked Questions (FAQs)

1. Introduction: The Impact of Overvoltage on Transmission Lines

Overvoltage is one of the most common threats to transmission line safety and stability. It can cause insulation breakdown, equipment damage, and even long-term power outages.

Lightning strikes and operational overvoltage are the two main causes. Statistics show that lightning accounts for 64.4% of all main grid line tripping faults, with 70% of 110kV line trips caused by lightning strikes.

Transmission line overvoltage protection is not a single component task. It requires a comprehensive strategy that combines arrester selection, scientific installation location, and reliable grounding system.

A poorly designed protection scheme can lead to ineffective protection, wasting resources while failing to prevent accidents. Even high-quality arresters will not perform well if installed incorrectly or matched with a substandard grounding system.

2. Core Principles of Transmission Line Overvoltage Protection

The core goal of overvoltage protection is to limit the overvoltage amplitude to a safe range, divert the overcurrent to the ground, and protect the transmission line and associated equipment.

2.1 Fault Current Diversion

When overvoltage occurs, the protection device (mainly the arrester) should act quickly to conduct the overcurrent to the ground, preventing it from damaging the line insulation.

This requires the arrester to have excellent response speed and current-carrying capacity.

2.2 Coordination Between Components

Transmission line arrester, installation location, and grounding system must work in coordination. No single component can achieve effective protection alone.

For example, a high-performance arrester will lose its effect if the grounding system has high resistance, as the overcurrent cannot be quickly diverted.

3. Transmission Line Arrester Selection: Key Factors and Criteria

Arrester selection is the first step in overvoltage protection. The right type and specification directly determine the protection effect.

There are three main types of transmission line arresters: zinc oxide arresters, silicon carbide arresters, and tube-type arresters. Each has its own advantages and applicable scenarios.

3.1 Voltage Level Matching

The arrester’s rated voltage must match the transmission line’s voltage level. Choosing a lower voltage level will cause the arrester to act frequently, reducing its service life.

Choosing a higher voltage level will delay the arrester’s action, failing to protect the line in time. For 110kV lines, 126kV arresters are usually selected; for 220kV lines, 252kV arresters are suitable.

3.2 Current-Carrying Capacity and Residual Voltage

Nominal discharge current reflects the arrester’s ability to divert overcurrent. Common levels are 5kV, 10kV, and 20kV, with 20kV suitable for UHV transmission lines.

Residual voltage is another key parameter. The lower the residual voltage, the better the protection for the line. Zinc oxide arresters have lower residual voltage than silicon carbide ones, making them more widely used.

3.3 Environmental Adaptability

Arresters must adapt to the local environment. For high-altitude areas (up to 4000m), special high-altitude arresters are required to resist low air pressure.

In cold regions, arresters with a low-temperature tolerance of -50℃ are needed to avoid performance degradation in extreme weather.

4. Arrester Installation Location: Optimizing Protection Coverage

The installation location of the transmission line arrester directly affects the protection range and effect. The core principle is to be close to the surge intrusion point and shorten the grounding path.

4.1 Key Installation Positions

For overhead transmission lines, arresters are mainly installed on tower tops, both ends of insulator strings, and line incoming sides. These positions can directly intercept lightning strikes or induced surges.

For UHV lines, arresters should also be installed at the junction of overhead lines and underground cables to prevent surges from spreading to the cable section.

4.2 Installation Spacing Requirements

The spacing between arresters depends on the line voltage level. For 110kV lines, the spacing should not exceed 10km; for 220kV lines, it should be controlled within 15km.

In areas with frequent lightning strikes, the spacing should be reduced by 30% to ensure full coverage.

4.3 Installation Notes

Arresters should be installed vertically to prevent water accumulation in the inner cavity. The angle with the horizontal line should not be less than 15°, especially in polluted areas.

The connecting line between the arrester and the grounding system should be as short as possible, with a length not exceeding 5m to reduce voltage drop.

5. Grounding System: The Foundation of Effective Overvoltage Protection

The grounding system is the key to diverting overcurrent to the ground. A poor grounding system will make the arrester’s protection ineffective, no matter how good it is.

5.1 Grounding Resistance Requirements

The standard grounding resistance for transmission line towers is ≤10Ω. In areas with high soil resistivity (such as rock and sandy soil), it can be relaxed to ≤30Ω with additional resistance reduction measures.

For lines in lightning-prone areas, the grounding resistance should be controlled below 5Ω to ensure rapid current diversion.

5.2 Grounding System Composition

The grounding system includes vertical grounding electrodes (hot-dip galvanized angle steel), horizontal grounding electrodes (hot-dip galvanized flat steel), and resistance reduction agents.

In high-resistivity soil, ion grounding electrodes or composite grounding electrodes are recommended to improve soil conductivity.

5.3 Maintenance of Grounding System

The grounding system should be inspected annually. Check for corrosion of grounding electrodes and loose connections.

In dry seasons, water the area around the grounding electrodes or add long-acting resistance reduction agents to prevent resistance increase.

6. Comprehensive Protection Strategy: Integrating Selection, Installation and Grounding

Comprehensive protection of transmission lines requires integrating arrester selection, scientific installation, and reliable grounding. It is not enough to focus on a single component.

First, select the appropriate arrester type and specification according to the line voltage level and environmental conditions.

Then, install the arrester at the optimal position to ensure full protection coverage. Finally, configure a high-quality grounding system to ensure rapid diversion of overcurrent.

In addition, it should be coordinated with other protection devices (such as insulators and reclosers) to form a multi-level protection system.

7. Performance Comparison Table: Different Protection Configurations

The following table compares the protection effect, failure rate, and cost of different overvoltage protection configurations. All data are based on industry tests and practical operation.

8. Industry Data and Practical Insights

Industry data shows the importance of a scientific overvoltage protection scheme for transmission lines.

Globally, overvoltage causes more than 30% of transmission line failures every year, resulting in economic losses of billions of dollars. In China, 64.4% of main grid line trips are caused by lightning overvoltage.

A study by the China Electric Power Research Institute found that using a comprehensive protection strategy (optimized arrester selection + scientific installation + reliable grounding) can reduce transmission line overvoltage failure rate by 85%.

For 110kV lines, after upgrading from silicon carbide arresters to zinc oxide arresters and optimizing the grounding system, the annual failure rate dropped from 8.2% to 2.1%.

In lightning-prone areas, installing arresters with reduced spacing and improving the grounding system can reduce lightning trip rate by 70%. For example, 4 lightning-attracting towers received 35 lightning strikes, but no tripping occurred in the covered transmission lines.

The IEEE has issued international standards for UHV transmission line overvoltage protection, which specify the selection criteria of arresters and the requirements of grounding systems, providing a basis for global transmission line protection design.

9. Frequently Asked Questions (FAQs)

Q1: What are the key factors for transmission line arrester selection?

A1: The key factors include voltage level matching, nominal discharge current, residual voltage, and environmental adaptability. The arrester’s rated voltage must match the line voltage, and the nominal discharge current should be selected according to the lightning activity in the area.

Q2: How to determine the installation location of transmission line arresters?

A2: The core principle is to be close to the surge intrusion point. Priority is given to tower tops, both ends of insulator strings, and line incoming sides. The spacing between arresters is determined by the line voltage level and lightning activity.

Q3: What is the standard grounding resistance for transmission line towers?

A3: The standard is ≤10Ω. In high-resistivity soil, it can be relaxed to ≤30Ω with resistance reduction measures. In lightning-prone areas, it is recommended to control it below 5Ω.

Q4: Can zinc oxide arresters replace silicon carbide arresters completely?

A4: Basically yes. Zinc oxide arresters have better protection performance, lower residual voltage, and no need for spark gaps. They are gradually replacing silicon carbide arresters, especially in 110kV and above power grids.

Q5: How often should the transmission line overvoltage protection system be inspected?

A5: The arrester should be inspected every 6 months, and the grounding system should be inspected annually. In areas with frequent lightning or extreme weather, the inspection frequency should be increased.