Do you know Glass Insulators?

Glass insulators, particularly toughened glass insulators, are widely used in power transmission lines to secure conductors to poles and maintain electrical insulation between them.

As one of the critical components in high-voltage transmission lines, the performance of these insulators directly impacts the operational safety of the entire line.

Due to their self-destruction upon reaching zero value and ease of maintenance, glass insulators have become a popular choice in various applications. Their ability to maintain electrical integrity while withstanding environmental stresses makes them indispensable in modern power transmission systems.

We can customize electrical glass insulators according to your needs and welcome you to visit our factory for guidance and inspection.

• Overhead Line Insulators ' How to Choose the Number of Pieces?

• The application of power pole insulators in 10kv transmission lines

Introduction

Overhead Line Insulators ' How to Choose the Number of Pieces? What are the specific basis and logic behind it? 

You will get efficient and thoughtful service from Yipeng.

When it comes to choosing the number of insulator pieces for overhead lines, understanding the underlying principles and voltage considerations is crucial. This comprehensive guide will help you make informed decisions to ensure reliable and safe operation of your transmission lines'

Introduction to Power Pole Insulators

Power pole insulators play a crucial role in the reliability and safety of 10kV transmission lines. These insulators, commonly known as porcelain bottles, are vital for supporting and insulating conductive electrical components on power poles. Understanding their composition, mechanical characteristics, and specific applications ensures optimal performance in various environments. This article delves into the types of power pole insulators, their key functions, and their application in 10kV transmission lines.

Types of Glass Insulators

Comprehensive Guide to the Best Glass Insulators

What are the common classifications and models of glass insulators?

Toughened glass insulators, composed of glass and metal fittings, are crucial components used in high-voltage and ultra-high-voltage AC and DC transmission lines for insulation and suspending conductors. They are highly reliable and perform well in a variety of environmental conditions, making them essential for the safe and efficient operation of power transmission systems.

1. Standard Type

The standard type of toughened glass insulators is widely used across various transmission lines. It provides reliable insulation and mechanical support, making it suitable for general-purpose applications.

2. Anti-Pollution Type

Anti-pollution glass insulators are designed for use in areas with heavy pollution. These insulators feature a special design that reduces the accumulation of contaminants, thereby maintaining their insulating properties and extending their service life.

3. Aerodynamic Type

Aerodynamic glass insulators are designed to minimize the impact of wind and other aerodynamic forces. Their shape reduces drag, making them suitable for use in high-wind areas or on tall transmission towers.

4. Spherical Type

Spherical glass insulators have a distinct shape that provides enhanced mechanical strength and better performance under various loading conditions. They are often used in challenging environments where additional durability is required.

5. Ground Wire Type

Ground wire glass insulators are used to insulate the ground wire in transmission lines. They are essential for preventing unwanted electrical currents from flowing through the ground wire, thereby protecting the overall system.

6.Electrified Railway Contact Network Type

These insulators are specifically designed for use in the electrified railway contact networks. They provide reliable insulation and mechanical support, ensuring the safe and efficient operation of electrified railways.

7. DC Type

Direct current (DC) glass insulators are specifically engineered to handle the unique requirements of DC transmission lines, ensuring stable performance and longevity in these specialized applications.

Models of Toughened Glass Insulators

Suspended Toughened Glass Insulators Standard Models: FC70/146, FC70/127, FC100/146, FC100/127, FC120/146, FC120/127, FC160/170, FC160/155, FC160/146, FC210/170, FC240/170, FC300/195

Anti-Pollution Models: FC7P/146, FC70P/146, FC70PL/146, FC70SPE/146, FC10P/146, FC100P/146, FC100PL/146, FC100SPE/146, FC12P/146, FC120P/146, FC120PL/146, FC120SPE/146, FC16P/155, FC160P/146, FC160P/170, FC21P/170, FC210P/170

Reinforced Models: LXY-70, LXY1-70, LXY-100, LXY-120, LXY3-160, LXY3-210, LXY-240, LXY3-300 Anti-

Pollution Reinforced Models: LXHY4-70, LXHY-70, LXHY5-70, LXHY4-100, LXHY4-120, LXHY3-160, LXHY4-160, LXHY5-160, LXHY6-160, LXHY3-210, LXHY-300, LXHY3-300, LXAY-210, LXAY-160, LXAY-120, LXAY1-120 Railway Models: LXY-70T, LXHY-100T, LXDY-100CN, LXDY-70CN

These insulator models are engineered to meet a variety of operational requirements, providing reliable performance in different environmental and electrical conditions.'

What are the product structures and performances of glass insulators?

Product Structure

toughened glass insulators are composed of an iron cap, a toughened glass component, and a steel foot, all bonded together using high-strength cement adhesive. The product utilizes the most advanced international cylindrical head structure, characterized by its small head size, light weight, high strength, and large creepage distance. This design significantly saves on metal materials and reduces the overall cost of transmission lines. Additionally, to accommodate live-line working requirements, the edge of the cap adopts the traditional domestic structural shape.

Performance Characteristics

Electrical Performance

The primary electrical performance of insulators is measured by their flashover characteristics, which refer to the disruptive discharge that occurs along the insulator's surface. Flashover characteristics are critical as they determine the insulator's ability to withstand various voltage stresses. Insulators are required to meet different voltage endurance levels depending on their voltage class. These metrics include power frequency dry and wet withstand voltage, lightning impulse withstand voltage, lightning impulse chopped wave withstand voltage, and operating impulse withstand voltage.

To prevent breakdown during operation, the breakdown voltage of an insulator is always higher than its flashover voltage. During factory tests, spark tests are conducted on breakable porcelain insulators by applying high voltage to induce frequent surface sparking for a specified duration to ensure they do not break down. Some insulators also undergo corona tests, radio interference tests, partial discharge tests, and dielectric loss tests.

For insulators used in high-altitude regions, the reduction in air density results in lower electrical strength, so their withstand voltage should be adjusted accordingly when converted to standard atmospheric conditions. Insulators in polluted environments have significantly lower flashover voltages when wet compared to their dry and wet flashover voltages. Therefore, in polluted areas, insulators should be reinforced or anti-pollution insulators should be used, which have a higher creepage ratio (the ratio of creepage distance to rated voltage) compared to standard types. DC insulators, compared to AC insulators, have poorer electric field distribution, attract more contamination, and have electrolytic effects, resulting in lower flashover voltage. Therefore, they generally require special structural designs and larger creepage distances.

Mechanical Performance

Insulators in operation are subjected to various mechanical forces, including the weight and tension of the conductors, wind force, ice load, the insulator's own weight, conductor vibration, mechanical forces during equipment operation, short-circuit electrodynamic forces, earthquakes, and other mechanical stresses. Relevant standards impose strict requirements on the mechanical performance of insulators.

Thermal Performance

Outdoor insulators must be capable of withstanding rapid temperature changes. For example, porcelain insulators must endure several cycles of heating and cooling without cracking. Insulation bushings, which carry current, must comply with relevant standards regarding temperature rise and permissible short-time current values for their components and insulation elements.

What are the advantages and disadvantages of glass insulators?

Introduction

Toughened glass insulators, primarily composed of SiO', B'O', Al'O', Na'O, K'O, and other natural raw materials, play a critical role in the transmission of high-voltage and ultra-high-voltage power lines. These insulators have become a popular choice in the power industry due to their superior mechanical and electrical properties. However, like any material, they come with their own set of advantages and disadvantages, which must be carefully considered in their application.

Advantages of Toughened Glass Insulators

1. High Dielectric Strength

Toughened glass insulators exhibit extremely high dielectric strength, significantly surpassing that of porcelain insulators. This characteristic makes them particularly effective in high-voltage applications, where insulation integrity is paramount.

2. Excellent Electrical Properties

Glass insulators have a high resistivity and a low thermal expansion coefficient. These properties ensure that they can withstand extreme voltage stresses and maintain their integrity over time without significant degradation. The dielectric constant of glass, ranging between 7 to 8, contributes to a greater main capacitance, resulting in more uniform voltage distribution across the insulator string, which helps reduce radio interference and corona loss.

3. Superior Mechanical Strength

Compared to porcelain insulators, toughened glass insulators offer higher tensile strength. The mechanical stability of glass is enhanced by the toughening process, which induces compressive stress on the surface, making it more resistant to mechanical stresses and environmental impacts.

4. Transparency and Quality Control

The inherent transparency of glass allows for easy detection of impurities, air bubbles, or defects during manufacturing, ensuring a higher quality product. This feature also aids in maintenance, as defects can be spotted visually without the need for complex testing equipment.

5. Longevity and Resistance to Aging

One of the most notable advantages of glass insulators is their resistance to aging. Unlike other materials, the electrical and mechanical properties of glass remain stable over time, providing long-lasting performance without significant degradation.

6. Self-Cleaning and Pollution Resistance

Glass insulators are less prone to dirt accumulation and are easier to clean compared to their porcelain counterparts. Their smooth surface reduces the adhesion of contaminants, which is particularly beneficial in polluted environments. This self-cleaning ability is enhanced in rainy conditions, making them ideal for use in areas with high levels of environmental pollution.

7. Enhanced Arc Resistance

Research has shown that glass insulators have better arc resistance compared to other materials. Even after multiple lightning strikes, which can cause localized surface burns, the new surface remains smooth and retains its insulating properties, ensuring continued reliability in adverse weather conditions.

8. Cost-Effectiveness

In terms of initial cost, glass is often cheaper than porcelain. When considering the total cost of ownership, including maintenance and operational costs, glass insulators can be more economical due to their durability, self-cleaning properties, and resistance to environmental stressors.

9. Zero-Value Self-Rupture Feature

A unique feature of toughened glass insulators is their zero-value self-rupture characteristic. In the event of a failure, the insulator will shatter, making it easily identifiable during routine inspections, even from the ground or via aerial surveys. This reduces the need for frequent pole-top inspections and decreases maintenance labor, especially in difficult-to-access areas.

Disadvantages of Toughened Glass Insulators

1. Lightweight and Higher Self-Rupture Rate

While the lightweight nature of glass insulators can be seen as an advantage, it also contributes to a higher self-rupture rate. The internal adhesive structure of the insulator, combined with differences in the thermal expansion coefficients of glass, cement, and steel components, can lead to greater compressive and shear stress during temperature fluctuations. This can result in the insulator becoming a zero-value insulator over time, especially in harsh climates with frequent temperature changes.

2. Maintenance Challenges

Despite the ease of visual inspection, the higher self-rupture rate means that toughened glass insulators may require more frequent replacements than their porcelain counterparts. This could potentially lead to increased maintenance costs, especially in regions where extreme weather conditions prevail.

3. Economic Considerations

Although the initial cost of glass insulators is lower, the overall economic impact must consider the costs associated with detecting zero-value insulators, manual cleaning, and potential power outages due to maintenance. Over time, the cost of maintaining glass insulators may increase, depending on the voltage level and environmental conditions, making the initial cost advantage less significant.

What are the classifications of glass insulators according to glass materials?

Types of Glass Used in Electrical Insulators Glass has long been a fundamental material in the manufacturing of electrical insulators due to its excellent insulating properties and durability. The classification of glass used in electrical insulators depends largely on its chemical composition.

1. Quartz Glass

Composition and Properties: Quartz glass is primarily composed of silica (SiO') and is produced by heating silica sand or crystal powder at temperatures around °C. It contains virtually no alkali content, which contributes to its high electrical resistivity and low dielectric loss. Quartz glass is known for its superior insulation properties and minimal thermal expansion coefficient. Additionally, it offers excellent chemical stability.

Applications: Due to its outstanding electrical insulation and stability under high temperatures, quartz glass is ideal for use in high-frequency insulators and other advanced electrical applications where performance and reliability are critical.

2. Soda-Lime Glass

Composition and Properties: Soda-lime glass, the most common type of glass used worldwide, consists mainly of silica, soda (Na'O), and lime (CaO). It is inexpensive, has a low softening temperature, and is easy to form and process. However, its high alkali content makes it less suitable for electrical insulation applications. Recent advancements, including the addition of barium oxide (BaO), have improved its dielectric properties, making it more viable for certain insulator applications.

Applications: Soda-lime glass is generally used in regions where high-quality insulating materials are scarce. It is commonly employed in the production of insulators for power distribution and transmission, particularly in low and medium-voltage applications.

3. Lead Glass

Composition and Properties: Lead glass contains a significant amount of lead oxide (PbO), which lowers the softening temperature and makes the glass easier to shape and process. Lead glass also has good insulating properties, making it suitable for use in electrical components.

Applications: Lead glass is predominantly used in the production of vacuum tube glass, where its excellent insulation and ease of manufacturing are advantageous.

4. Borosilicate Glass

Composition and Properties: Borosilicate glass is characterized by its low alkali content, which is beneficial for electrical performance. It is easy to melt and process and offers excellent mechanical strength and resistance to thermal shock. These properties, combined with its superior insulation capabilities, make borosilicate glass an excellent choice for demanding applications.

Applications: Notable brands such as Pyrex (Pyrex) in the United States and Terex in Japan use borosilicate glass in their products. It is commonly used as an insulating material in communication devices, antenna insulators, and high-frequency insulators, where both mechanical strength and electrical performance are critical.

5. Alkali-Free Glass

Composition and Properties: Alkali-free glass is primarily used in the production of glass fibers for insulating coatings on power lines and other applications where high chemical stability and insulation performance are required. Unlike traditional glass fibers that contain high levels of alkali, which compromise their insulation properties, alkali-free glass offers superior electrical insulation and durability.

Applications: This type of glass is extensively used in the production of insulation coatings for electrical wires and cables, ensuring long-term stability and reliability in various electrical applications.

What causes the self-explosion of glass insulators?

Glass insulators are widely used in high-voltage power transmission due to their excellent electrical and mechanical properties. What causes the self-explosion of glass insulators?

1. Internal Stress Imbalance

One of the leading causes of glass insulator self-explosion is the imbalance of internal stress within the glass. During the manufacturing process, nickel sulfide (NiS) may be introduced into the glass composition. NiS undergoes a slow phase transformation over time, which can disrupt the internal stress equilibrium within the glass. This stress imbalance can eventually lead to spontaneous cracking or self-explosion of the insulator.

2. Effects of Electric Fields and Contamination

During operation, glass insulators are exposed to strong electric fields and environmental contaminants. These factors can cause localized, concentrated discharge on the insulator surface. Over time, this discharge can weaken the glass material, leading to self-explosion. The combination of electrical stress and surface contamination, especially in polluted environments, significantly increases the risk of this phenomenon.

3. External Mechanical Forces

Glass insulators are subject to various external mechanical forces, including gravity, wind, and the weight of accumulated ice. Over time, these forces can cause stress concentration at the junction where the iron foot connects to the glass. This stress concentration can lead to microcracks in the cemented joints, which may disrupt the internal stress balance of the glass and cause self-explosion.

4. Increased Leakage Current

Severe surface contamination on glass insulators can lead to an increase in leakage current. This elevated leakage current is one of the primary reasons for the concentration of self-explosions in glass insulators. The presence of iron powder or other metallic particles can exacerbate the increase in leakage current, further heightening the risk of self-explosion.

5. Design and Manufacturing Defects

Defects in the design and manufacturing process can also contribute to glass insulator self-explosion. Improper material selection, inadequate quality control during manufacturing, or design flaws can all lead to the production of insulators that are more prone to self-explosion. These defects can result in the introduction of impurities, improper stress distribution, or insufficient durability under operational conditions.

If you want to learn more, please visit our website Aerodynamic Glass Insulator.

What is the production process of glass insulators?

The Manufacturing Process of Glass Insulators: From Raw Materials to Finished Product

Glass insulators play a critical role in the safe and efficient transmission of electricity in high-voltage power lines. Their manufacturing process is both intricate and precise, ensuring that each insulator can withstand the rigors of its operational environment. In this article, we will explore the production process of glass insulators, from the selection of raw materials to the final inspection, highlighting the key steps that contribute to the quality and durability of the finished product.

1. Raw Materials Used in Glass Insulators

The primary raw materials used in the production of glass insulators are similar to those used in porcelain insulators, with the key difference being that the insulating component is made of glass rather than ceramic. The main ingredients include:

• Quartz Sand (SiO2): The primary source of silica, which forms the backbone of the glass structure.
• Feldspar: A group of aluminum silicates containing calcium, sodium, and potassium, which acts as a flux to lower the melting temperature of the glass.
• Limestone (CaCO3) and Dolomite (CaMg(CO3)2): Provide calcium and magnesium, which contribute to the chemical durability and mechanical strength of the glass.
• Soda Ash (Na2CO3) and Potassium Carbonate (K2CO3): These are used as fluxes to lower the melting point and act as clarifying agents to remove bubbles during the melting process.

The resulting toughened glass, which is a homogeneous silicate with a uniform microstructure, exhibits superior dielectric strength and excellent thermal stability, making it ideal for use in high-voltage environments.

2. Production Process of Glass Insulators

The production of glass insulators involves several crucial steps, each designed to ensure the final product meets stringent quality and performance standards.

2.1. Batching

Batching refers to the process of mixing the raw materials in precise proportions. The materials are typically mixed in a vertical shaft mixer, ensuring a uniform blend. The uniformity of this mix is essential for producing high-quality glass with consistent properties.

2.2. Melting and Fining

Once the raw materials are properly batched, they are subjected to high temperatures in a furnace to form a homogenous glass melt. The melting process involves heating the mixture to temperatures exceeding °C, which facilitates the formation of a uniform glass liquid. Fining, or the removal of gas bubbles from the molten glass, is an essential step to ensure the clarity and strength of the final product.

2.3. Pressing

After melting and fining, the molten glass is fed through a feeder system into a pressing stage. In this stage, the molten glass is shaped into insulator components using automated hydraulic presses. The molds used during this process dictate the shape of the insulator, while precise control over the amount of glass used ensures consistency across all insulators produced.

2.4. Toughening

Once the glass components are shaped, they undergo a toughening process, which involves controlled cooling. This process induces permanent compressive stress on the surface of the glass, greatly enhancing its strength and thermal stability. Equipment such as annealing ovens and toughening machines are used in this stage to achieve the desired surface stress.

2.5. Thermal Shock Testing

Toughened glass components are subjected to thermal shock tests to ensure their durability. This involves exposing the glass to rapid temperature changes to simulate the conditions the insulators will face in the field. A specialized nickel sulfide (NiS) treatment is also applied during this stage to eliminate the risk of spontaneous self-explosion, a critical quality measure that impacts the long-term reliability of the insulators.

2.6. Assembly

In the assembly stage, the glass components are combined with steel feet and caps using an assembly machine. This step involves the careful alignment of all parts to ensure coaxiality, which is crucial for maintaining the insulator's structural integrity and preventing premature failure in the field.

2.7. Inspection

Finally, each assembled glass insulator undergoes a rigorous inspection process. This includes a 50% tensile load test to verify mechanical strength, as well as measurements of the insulator's structural height to ensure it meets the required standards. Only insulators that pass these tests are approved for use.

Why Choose Us for Your Power Transmission Needs?

At the heart of every reliable power transmission system lies the quality and integrity of its components, and this is where our expertise shines. We are proud to be a leading provider of high-quality products for transmission lines, including electrical insulators, fittings, cables, conductors, and transmission towers. Our offerings are not just limited to supplying these essential components; we also provide custom design and manufacturing services tailored to meet the specific needs of your project, considering environmental factors, mechanical loads, and long-term performance.

Custom Solutions Tailored to Your Needs

We understand that every project is unique. That's why our team of engineers works closely with you to design and produce products that perfectly fit your requirements. Whether you need insulators that can withstand harsh environmental conditions or conductors designed for high-voltage transmission, we ensure that each product is manufactured to the highest standards and optimized for efficiency and durability.

Proven Expertise and Quality Assurance

With a proven track record in executing numerous power transmission projects across China, we bring a wealth of experience to the table. Our team comprises nearly a thousand skilled construction personnel who have successfully designed, built, and maintained transmission lines of various scales. We are committed to quality, ensuring that all our products are manufactured to meet international standards and subjected to rigorous testing.

Sustainable Solutions with Cost Efficiency

In today's world, sustainability and cost-efficiency go hand in hand. Our solutions are designed not only to meet the immediate needs of your project but also to offer long-term reliability that minimizes maintenance costs. By choosing us, you are investing in products and services that deliver consistent performance, reducing the need for frequent replacements and repairs, and ensuring that your transmission lines operate smoothly for years to come.

Comprehensive Service from Design to Construction

From initial design to final construction, we offer a comprehensive suite of services that ensures your project's success. Our experience in managing complex power transmission projects means we understand the challenges you face and can offer insights and solutions that streamline your operations. We are not just a supplier; we are a partner dedicated to the success of your project.

Let's Build a Reliable Future Together

When you choose us for your power transmission needs, you are choosing a partner who values quality, reliability, and customer satisfaction above all. Let us help you build a transmission system that stands the test of time, with products that are designed and manufactured with care, and services that are delivered with professionalism and expertise.

Contact us today to discuss your project requirements and discover how we can contribute to your success with our superior products and expert services. Together, we can create a power transmission network that is efficient, sustainable, and built to last.

Introduction

In the world of power transmission, high voltage insulators play a crucial role in ensuring the reliable and safe operation of electrical systems. They are designed to support and insulate electrical conductors from ground and other structures, preventing unwanted electrical discharges. This article provides a detailed comparison of various types of high voltage insulators, focusing on porcelain, glass, and composite insulators. By understanding their characteristics, advantages, and disadvantages, we can make informed decisions for their application in different environments.

Common High Voltage Insulators Performance Comparison

Common Faults

Disk Porcelain Insulator

Disk Glass Insulator

Rod Porcelain Insulator

Rod Composite Insulator

Semiconductor Glaze Insulator

Lightning StrikeHigh flashover voltage, may occur 'zero value', probability depends on the manufacturer, element damage may occur without arcing deviceHigh flashover voltage, elements may burst without arcing device, probability depends on the manufacturerDue to the installation of arcing horns, low flashover voltage, no element damage or breakdownSlightly lower flashover voltage, generally equipped with equalizing rings to prevent arc burn on the insulatorHigh flashover voltage, may occur 'zero value', probability depends on the manufacturer, element damage may occur without arcing devicePollutionPoor pollution resistance, double umbrella shape can improve self-cleaning performance, easy to adjust creepage distancePoor pollution resistance, anti-fog type can improve salt fog resistance, easy to adjust creepage distanceGood self-cleaning, poor salt fog resistance, cannot adjust creepage distanceHydrophobic surface, good anti-pollution flashover performance, generally no need to adjust creepage distanceKeeps surface dry under humid conditions, good anti-pollution flashover performance, generally no need to adjust creepage distanceBird DamageProtective measures requiredProtective measures requiredProtective measures requiredProtective measures requiredProtective measures requiredWind Deflection'Flexible' performance is good, resulting in small wind deflection.'Flexible' performance is good, resulting in small wind deflection.'Flexible' performance is good, resulting in small wind deflection.Flexible performance is relatively good, resulting in large wind deflection.'Flexible' performance is good, resulting in small wind deflection.String BreakageThe probability depends on the manufacturer.The probability is extremely low.The probability is low.The probability depends on the manufacturer.The probability depends on the manufacturer.DeteriorationThe deterioration rate depends on the manufacturer.There is basically no deterioration.There is no deterioration.The aging rate of silicone rubber and the 'creep' of the core rod depend on the manufacturer and usage conditions.The deterioration rate depends on the manufacturer.External ForceEasily damaged, with significant residual strength.Easily damaged, with significant residual strength.Easily damaged, potentially leading to rod breakage.Not easily damaged.Easily damaged, with significant residual strength.On-site Maintenance and InspectionHigh maintenance workload; double umbrella shape is easy to manually clean, but checking for 'zero value' is troublesome.Short cleaning cycles with high workload.Long cleaning cycles but difficult manual cleaning; any skirt damage requires immediate replacement.Maintenance is simple, but defect detection is difficult.

Maintenance is simple, and checking for 'zero value' is easy.

Porcelain Insulators

Porcelain insulators remain the most widely used type in power systems today. Made from high-strength porcelain, which is a mixture of quartz, feldspar, clay, and alumina, these insulators exhibit excellent mechanical and electrical properties. The porcelain surface is typically covered with a glaze to enhance its mechanical strength, water resistance, and surface smoothness.

Characteristics of Porcelain Insulators

Porcelain insulators are renowned for their excellent mechanical and electrical performance. Their broad range of products makes them versatile for various applications. However, they also have some drawbacks. Under polluted and humid conditions, their insulation performance can degrade rapidly when subjected to power frequency voltages, often resulting in local arcing and, in severe cases, flashovers. Furthermore, the uneven distribution of voltage across insulator strings or individual insulators can lead to corona discharge at high electric field concentrations, causing radio interference and accelerating the aging of the porcelain.

Types of Porcelain Insulators

Porcelain insulators are classified into two main types: ordinary type and anti-pollution type.

1. 1. Ordinary Type Insulators: These are used in general applications and are available in ball-type and slot-type connections.

   2. Anti-Pollution Type Insulators: These are further divided into double-shed, triple-shed, bell-type, streamlined (aerodynamic type), and large-diameter insulators. Compared to ordinary insulators, double-shed and triple-shed insulators have a larger creepage distance and smooth surfaces that accumulate less pollution, making them easier to clean manually.

      • Double-Shed and Triple-Shed Insulators: These have larger creepage distances and smoother surfaces, reducing pollution accumulation and facilitating manual cleaning.

      • Bell-Type Insulators: These have deeper sheds than ordinary insulators and smaller distances between sheds, making them more prone to pollution accumulation and harder to clean manually.

      • Streamlined Insulators: These have smooth surfaces that prevent pollution accumulation and are easier to clean manually. They offer certain advantages over ordinary or other anti-pollution insulators. However, their shorter creepage distance and lack of shed structures that can impede arc development limit their anti-pollution flashover performance.

      • Large-Diameter Insulators: In some regions, using streamlined insulators with larger shed diameters under cross-arms can help prevent ice flashovers and bird droppings flashovers.

Glass Insulators

• Environmental Stability and Production Efficiency

Glass insulators exhibit the same environmental stability as porcelain insulators. Their production process is straightforward and easily mechanized, resulting in high production efficiency. The primary components of glass insulators are acidic oxides such as SiO', B'O', and Al'O', combined with alkaline oxides like Na'O and K'O. These components are derived from raw materials like silica sand, feldspar, borax, calcium carbonate, and various other natural and industrial chemicals. Additionally, small amounts of auxiliary materials are added as clarifiers and reducing agents.

• Manufacturing Process and Mechanical Strength

After being melted and molded at temperatures above °C, the glass is annealed. Rapid cooling and tempering create a layer of permanent compressive stress on the glass surface, preventing the formation and propagation of micro-cracks. This significantly enhances the mechanical strength of the glass.

• Limitations in Design and Anti-Pollution Performance

However, due to the limitations of the manufacturing process, glass insulators cannot achieve increased creepage distances through double-shed or triple-shed designs like porcelain insulators. To achieve larger creepage distances in anti-pollution glass insulators, deep ridges must be added to the undersides of the sheds. In areas with severe dust pollution, the deep ridges of the bell-shaped sheds have poor self-cleaning capabilities and are difficult to clean manually, resulting in severe fouling of the undersides and a significant reduction in pollution flashover resistance.

Characteristics of Glass Insulators

Glass insulators have several notable characteristics:

• Uniform Voltage Distribution: The dielectric constant of glass is between 7 and 8, higher than porcelain's dielectric constant of 5 to 6, giving glass insulators a larger main capacitance.
• Self-Cleaning Ability: They are easy to clean and maintain good anti-pollution performance.
• Arc Resistance: They have excellent arc resistance.
• High Mechanical Strength: The mechanical strength of tempered glass can reach 80-120 MPa, which is 2-3 times that of ceramics. The mechanical properties remain stable over long-term operation.
• Ease of Inspection: Due to the transparency of glass, it is easy to detect small cracks and internal damage during visual inspections.
• Zero or Low-Value Self-Destruction: Glass insulators can self-destruct when they reach zero or low values, making it easy to identify potential hazards without manual testing.
• Slow Aging Process: They exhibit a slow aging process.

Drawbacks of Glass Insulators

• Fragility: The skirts can crack more easily under external forces, leading to a higher damage rate compared to porcelain insulators.
• Early Self-Destruction Rates: Glass insulators have a relatively high early self-destruction rate. Self-destroyed remnants must be replaced promptly to prevent the internal glass from becoming damp and fusing, which can lead to broken strings and line failures.

Composite Insulators

Composite insulators generally consist of three main parts: the shed and sheath, the fiberglass core rod, and the metal end fittings. The shed and sheath are typically made from organic synthetic materials such as high-temperature vulcanized silicone rubber or ethylene propylene rubber. The core rod is usually a composite material made of fiberglass as the reinforcing material and epoxy resin as the matrix. The end fittings are commonly made from carbon steel or structural carbon steel with a hot-dip galvanized coating on the surface. The core rod and the shed/sheath each bear mechanical and electrical loads, respectively, thus combining the advantages of the superior weather resistance of the shed/sheath material and the excellent tensile mechanical properties of the core rod material. Silicone rubber is currently the best material for the shed and sheath of composite insulators due to its unique hydrophobic transfer properties, which are crucial for its successful use in polluted areas.

Characteristics of Composite Insulators

• Lightweight and Compact: Composite insulators are lightweight and compact, with their weight being only 10%-15% of porcelain or glass insulators, making them easier to install, replace, and transport.
• Rod-Shaped Structure: The distance between the internal and external electrodes is almost equal, which generally prevents internal insulation breakdown and eliminates the need for zero-value detection.
• Strong Hydrophobicity: The insulator surface exhibits strong hydrophobicity, providing excellent anti-pollution performance, extending the cleaning cycle, and significantly reducing labor intensity.

Drawbacks of Composite Insulators

• Short Operation Time: Composite insulators have a relatively short operational history, and their service life is yet to be fully determined.
• Poor Bending and Torsional Resistance: They have poor resistance to bending and torsion. When subjected to significant lateral pressure, they are prone to brittle fracture.
• Low Shed Strength: The strength of the sheds is low, making them susceptible to damage from stepping or collision.
• Cleaning Difficulties: Accumulated dirt is difficult to clean, and over time, the hydrophobicity of the surface may gradually diminish.
• Interface Issues: Multiple bonding interfaces exist between the core rod and sheath, sheath and sheds, core rod and metal end fittings, and metal end fittings and sheds. If air or moisture is not completely expelled from these interfaces during assembly, bubbles or moisture can remain. Under the influence of a strong electric field, these will initially discharge and carbonize, gradually expanding until forming a conductive path that leads to breakdown.

Other Common High Voltage Insulators

1. Rod-Shaped Porcelain Insulators

• Development and Characteristics

Rod-shaped porcelain insulators were developed based on the advantages and disadvantages of suspension insulators, evolving from double-shed solid insulators. They retain the electrical stability of porcelain and eliminate the drawback of the head section's breakdown distance being much shorter than the air flashover distance in disc-type suspension porcelain insulators. Additionally, they modify the complex stress structure of the cap-and-pin design.

• Performance and Advantages

Rod-shaped insulators exhibit excellent anti-pollution and self-cleaning properties. Under identical length and pollution conditions, their electrical strength is 10-25% higher than that of porcelain disc insulators. Due to the absence of metal fittings between the insulator sheds, the creepage distance is effectively increased by 20% compared to disc-type insulator strings of the same insulation length.

Rod-shaped porcelain insulators are non-breakdown structures, preventing the drop-off accidents caused by the cracking of porcelain insulator steel caps. They also reduce radio interference levels and eliminate zero-value or low-value insulator issues, thus removing the need for insulator testing, maintenance, and replacement.

• Global Leadership and Advancements

Japan and Germany currently lead the world in the quality of rod-shaped insulators, with the average annual failure rate of German-produced insulators being only 0.%. In recent years, China has also made advancements in the production of rod-shaped insulators, developing and producing high-strength rod-shaped insulators suitable for 500kV voltage levels, which are now operational on transmission lines in East China.

• Operational Performance

Surveys of 500kV line operations show that the surface salt density of rod-shaped porcelain insulators after two years without cleaning ranges from 0. to 0. mg/cm². In contrast, the salt density of XWP-160 porcelain insulators at the same location (cleaned six months prior) was measured at 0.014 to 0.036 mg/cm². Operating departments report that the surface of rod-shaped porcelain insulators remains clean on the upper side and free from scaling on the bottom after two years, whereas double-shed disc-type insulators show significant scaling on the bottom.

• Limitations and Considerations

However, rod-shaped porcelain insulators are composed of several sections connected in series (typically three sections for 500kV lines), with grading rings or arcing horns installed between sections. Each section's distance is shorted by approximately 30 cm, resulting in a shorter dry arc distance compared to other insulators of the same length. Additionally, the installation of inter-section protection rings increases the string length, potentially requiring larger tower windows, revealing a weakness of rod-shaped porcelain insulators compared to composite insulator strings.

For high-voltage lines with long strings, the economic design of towers and corridor width constraints may limit the use of rod-shaped porcelain insulators. Comparatively, rod-shaped porcelain insulators are more advantageous for strain towers. However, their heavy section weight complicates transport in mountainous areas, and they are prone to damage. Currently, there is limited operational experience, and their electrical performance during operation cannot be tested, and they are more expensive.

2. Semiconductor Glaze Insulators

Semiconductor glaze insulators are a new type of insulator with a semiconductor glaze coating on the surface. The power loss from this semiconductor glaze raises the surface temperature above the ambient temperature, preventing moisture formation from fog and severe pollution. This improves the power frequency insulation strength of polluted insulators in humid environments. The antimony-tin semiconductor glaze insulators developed in China have achieved promising results.

3. Porcelain Composite Insulators

Porcelain composite insulators feature a silicone rubber composite sheath attached to the surface of porcelain discs, utilizing the hydrophobicity of silicone to enhance anti-pollution capabilities. Porcelain composite insulators are a combination of traditional porcelain and modern composite materials, aiming to leverage the advantages of both materials. The silicone rubber sheath provides superior hydrophobicity, which is essential for maintaining high performance in polluted environments. This combination aims to mitigate the limitations of each material when used independently, offering a more robust solution for high-voltage insulation applications.