Table of Contents

1. Introduction

2. The Initial Stage: Porcelain-Housed Metal Oxide Arresters

3. The Transitional Stage: Silicone Rubber MOA

4. The Advanced Stage: Composite Polymer Coated MOA

5. Key Technologies for Insulation Upgrade

6. Performance Comparison of Different Insulation Types

7. Conclusion

8. Frequently Asked Questions (FAQs)

1. Introduction

Metal oxide arresters (MOA) are critical components in power transmission and distribution systems, protecting equipment from overvoltage damage caused by lightning strikes and switching operations.

Insulation performance is the core of MOA reliability. As power systems develop towards high voltage, high capacity, and intelligence, the demand for insulation quality keeps rising.

The technical evolution of composite housing metal oxide arresters has been driven by the need for better insulation, lighter weight, and stronger adaptability to harsh environments. It has gone through three key stages, from traditional porcelain housings to silicone rubber, and then to advanced composite polymers.

2. The Initial Stage: Porcelain-Housed Metal Oxide Arresters

2.1 Structure and Working Principle

Porcelain-housed metal oxide arresters were the earliest mainstream type of MOA. They consist of a porcelain housing, zinc oxide (ZnO) varistor core, and end fittings.

The porcelain housing acts as the main insulation layer, isolating the internal varistor from the external environment. It relies on the high mechanical strength and insulation performance of porcelain to ensure stable operation.

In normal operation, the ZnO varistor has high resistance, allowing only a tiny leakage current to pass through. When overvoltage occurs, its resistance drops sharply, diverting the overcurrent to the ground.

2.2 Advantages and Limitations

Porcelain housings have excellent mechanical strength and high temperature resistance, able to withstand harsh weather conditions such as strong winds and heavy rains.

They also have good chemical stability, not easy to react with corrosive substances in the environment.

However, porcelain-housed arresters have obvious drawbacks. They are heavy, making transportation and installation difficult. The porcelain material is brittle, easy to crack when subjected to impact or thermal shock.

Their anti-pollution performance is poor too. In areas with heavy industrial pollution or high humidity, dirt easily accumulates on the surface, leading to insulation breakdown.

By the early 2000s, porcelain-housed MOA accounted for over 80% of the global market, but this share has declined rapidly with the emergence of new insulation materials.

3. The Transitional Stage: Silicone Rubber MOA

3.1 Technical Improvements

To solve the limitations of porcelain-housed arresters, silicone rubber MOA emerged in the 1990s. This type of arrester uses high-temperature vulcanized (HTV) silicone rubber as the outer insulation layer.

Silicone rubber material has excellent hydrophobicity and hydrophobic migration. Even if the surface is contaminated, the hydrophobicity can quickly recover, greatly improving anti-pollution performance.

The silicone rubber housing is lightweight, about 30-50% lighter than porcelain housings of the same specification, which simplifies transportation and installation.

3.2 Core Advantages and Application Scenarios

Silicone rubber MOA has good flexibility, able to withstand certain mechanical deformation without cracking. It also has excellent aging resistance, with a service life of 20-25 years under normal operating conditions.

It is particularly suitable for areas with heavy pollution, high humidity, and frequent lightning strikes, such as coastal areas, industrial zones, and mountainous regions.

By 2024, silicone rubber MOA accounted for 53% of the global MOA market, becoming the mainstream product in medium and low voltage power systems.

However, silicone rubber also has shortcomings. Its mechanical strength is lower than porcelain, and it is prone to wear and tear in harsh environments with strong ultraviolet radiation.

4. The Advanced Stage: Composite Polymer Coated MOA

4.1 Material Innovation

In recent years, with the continuous progress of insulation material technology, composite polymer coated MOA has become the new direction of technical evolution.

This type of arrester uses a composite polymer material (mainly epoxy resin composite or ethylene propylene diene monomer (EPDM) composite) as the outer insulation layer, combining the advantages of silicone rubber and porcelain.

The composite polymer material has higher mechanical strength than silicone rubber, and better anti-aging and anti-ultraviolet performance.

4.2 Performance Leap

Composite polymer coated MOA has excellent insulation performance, with a dielectric strength of up to 45 kV/mm, which is 1.5 times that of silicone rubber and 2.25 times that of porcelain.

Its weight is similar to silicone rubber MOA, but its service life can reach 25-30 years, 20-25% longer than silicone rubber MOA.

It also has strong resistance to chemical corrosion, able to adapt to harsh industrial environments with acid and alkali pollution.

In 2024, the global market share of composite polymer coated MOA reached 28.3%, and it is expected to grow at an annual rate of 6.8% in the next five years.

5. Key Technologies for Insulation Upgrade

5.1 Material Modification Technology

The core of insulation upgrade lies in material modification. For silicone rubber, nano-filler modification technology is adopted to improve its mechanical strength and anti-aging performance.

By adding nano-alumina or nano-silica fillers, the tensile strength of silicone rubber can be increased by 30-40%, and the anti-ultraviolet aging life can be extended by 5-8 years.

5.2 Molding Process Optimization

Advanced molding processes such as vacuum casting and pressure gel molding are used to ensure the compactness of the insulation layer.

This avoids the formation of air gaps inside the insulation layer, which can cause partial discharge and damage the insulation performance.

The qualified rate of insulation layers produced by these processes can reach 99.8%, which is 2.3 percentage points higher than the traditional molding process.

5.3 Quality Control System

A full-process quality control system is established for insulation materials and finished products. The insulation performance of materials is tested before production, including dielectric strength, hydrophobicity, and aging resistance.

Finished MOA products undergo strict lightning impulse test and switching impulse test to ensure they meet the requirements of IEC 60099-4 standard.

6. Performance Comparison of Different Insulation Types

The following table compares the key performance indicators of porcelain-housed, silicone rubber, and composite polymer coated MOA, providing a clear reference for product selection:

It can be seen from the table that composite polymer coated MOA has obvious advantages in comprehensive performance, while silicone rubber MOA balances performance and cost, and porcelain-housed MOA is gradually being phased out in most application scenarios.

7. Conclusion

The technical evolution of composite housing metal oxide arresters is a process of continuous optimization and innovation, driven by the development needs of power systems and the progress of insulation material technology.

From the traditional porcelain-housed MOA to the transitional silicone rubber MOA, and then to the advanced composite polymer coated MOA, each step of evolution has significantly improved the insulation performance, reliability, and adaptability of the product.

Insulation upgrade is the core of this evolution, and material innovation and process optimization are the key driving forces.

In the future, with the development of smart power grids and ultra-high voltage power transmission technology, composite polymer coated MOA will become the mainstream, and its insulation performance and intelligent level will be further improved.

8. Frequently Asked Questions (FAQs)

Q1: What is the main function of a metal oxide arrester (MOA)?

A1: MOA is mainly used to protect power equipment from overvoltage damage caused by lightning strikes, switching operations, and other transient overvoltage events. It limits the overvoltage to a safe range by virtue of the nonlinear resistance characteristics of the ZnO varistor.

Q2: What are the main differences between silicone rubber MOA and porcelain-housed MOA?

A2: Silicone rubber MOA is lighter, has better anti-pollution performance and flexibility, but lower mechanical strength than porcelain-housed MOA. Porcelain-housed MOA has higher mechanical strength but is heavy, brittle, and poor in anti-pollution performance.

Q3: Why is composite polymer coated MOA the future development direction?

A3: Composite polymer coated MOA combines the advantages of silicone rubber and porcelain, with high dielectric strength, long service life, good anti-pollution performance, and appropriate mechanical strength. It can adapt to the harsh operating environment of modern power systems and meet the demand for high reliability.

Q4: How to judge the insulation performance of MOA in actual operation?

A4: The insulation performance of MOA can be judged by testing the leakage current, dielectric loss, and other indicators. If the leakage current increases significantly or the dielectric loss exceeds the standard, it indicates that the insulation performance may be degraded and needs to be inspected and replaced in time.

Q5: What is the impact of insulation upgrade on the service life of MOA?

A5: Insulation upgrade can significantly extend the service life of MOA. For example, the service life of composite polymer coated MOA is 25-30 years, which is 1-2 times that of traditional porcelain-housed MOA. Good insulation performance can reduce the damage caused by partial discharge and environmental corrosion.