Practical Applications of High-Voltage Insulators

Practical Applications of High-Voltage Insulators

High-voltage insulators are another cornerstone for ensuring the safe operation of power systems. Unlike surge arresters, which "actively divert current," the core function of insulators is "robust isolation."

I. Core Functions: Mechanical Support and Electrical Insulation

Insulators must simultaneously fulfill two core requirements:

Electrical Insulation: Under maximum operating voltage, lightning over-voltage, and switching over-voltage, they must effectively prevent current from flowing from the live conductor to the grounded structure (e.g., tower, crossarm) through their surface or interior.

Mechanical Support: They must withstand significant tensile, compressive, and bending forces from conductors, fittings, ice coating, etc., firmly securing the live conductor in place on overhead structures or equipment frameworks.

Simple Analogy: Insulators act like the "insulating skeleton" of power lines and equipment, needing both to bear weight and to "block current."

II. Primary Application Scenarios and Types

1.Transmission Lines (Largest Volume of Use)

21. Suspension Insulators (Disc Type): The absolute mainstay for high-voltage, extra-high-voltage (EHV), and ultra-high-voltage (UHV) transmission lines. They hang like strings of beads below the tower crossarm, connected in series via metal fittings to form "insulator strings."
21. Application: The number of units in a string is determined by voltage level and mechanical load (e.g., 500kV lines commonly use 28-32 discs). Used for suspending conductors on straight-line towers.
21. Pin/Post Insulators: Mainly used on lower-voltage lines (e.g., 35kV and below) to secure conductors to the top of poles.
21. Line Post Insulators: Act as part of the pole crossarm itself, integrating support and insulation for a compact design.
21. Long Rod Insulators: Used on tension, angle, or dead-end towers of lines, bearing the full tension of the conductor.

2. Substations / Converter Stations

 

21. Post Insulators: Widely used to support busbars, stationary contacts of disconnect switches, circuit breakers, and other live parts of equipment. They function like "insulating columns," providing stable ground insulation and mechanical support.
21. Transformer Bushings: Bring the high-voltage leads from the transformer's internal windings out through the tank wall while ensuring insulation from the tank (ground).
21. Circuit Breaker Bushings, Capacitor Bushings, etc.: Serve similar functions, acting as key insulating components for passing conductors through grounded enclosures.
21. Hollow Insulators (e.g., for GIS equipment): Used in gas-insulated switchgear, forming part of the enclosure while also insulating and supporting the internal high-voltage conductor from ground. They feature smooth surfaces and precise dimensions.

 

3. Electrified Railway Catenary Systems

Used as catenary cantilever insulators, tension insulators, etc., to support and insulate the contact wire, withstand dynamic forces from the pantograph, and resist severe pollution along railway lines.

4. Special Environment Applications

Polluted Areas (Coastal, Industrial): Use anti-fog/anti-pollution type insulators (e.g., suspension insulators with larger diameters and bell-shaped sheds, or silicone rubber composite insulators) to increase creepage distance and prevent flashover under damp, polluted conditions.

High-Altitude Areas: Use lengthened insulators to compensate for reduced insulation strength due to thin air.

Heavy Icing Areas: Use insulators with optimized shed profiles to minimize ice bridging or account for ice load in their design.

III. Insulator Materials and Technological Progress

Porcelain Insulators: Long history, stable performance, high mechanical strength, but heavy and prone to brittle fracture.

Toughened Glass Insulators: Feature "zero-value self-shattering" (they shatter upon losing insulating performance, facilitating visual detection during patrols), are easy to maintain, and have good arc resistance.

Composite Insulators (Polymer Insulators):

Key Application Advantages: Lightweight, high strength, excellent pollution flashover performance (hydrophobic surface). They have become the preferred choice for polluted areas. Constructed from silicone rubber sheds, a fiberglass reinforced plastic (FRP) core rod, and end fittings.

Wide Application: Extensively used in modern transmission lines, especially UHV lines, high-speed railway catenary systems, and urban grid upgrades.

 

IV. Key Considerations in Practical Application

 

Creepage Distance: Determined by the pollution level of the area, this is the minimum leakage distance required along the insulator surface, a critical parameter for preventing surface flashover.

Mechanical Strength Rating: Selected based on calculated loads from conductors, ice, wind pressure, etc., corresponding to specific mechanical failing load ratings (e.g., 70kN, 120kN, 210kN, 300kN).

Voltage Level Matching: The length of an insulator string or the height of a post insulator must meet the insulation requirements for the corresponding voltage level.

Environmental Durability: Must consider the aging effects of UV radiation, rain, acid rain, high temperature, and extreme cold on materials (especially composite insulators).

Monitoring and Maintenance:

Regular manual or drone patrols to inspect for damage, cracks, severe contamination, or flashover marks.

For porcelain/glass suspension insulators, use a zero-value detector or infrared thermography to identify "faulty units" (individual units that have lost insulating capability).

For composite insulators, check for loss of hydrophobicity, aging/cracking of sheds, and exposure of the core rod.

V. Summary: Synergistic Relationship with Surge Arresters

Insulators are the bones and joints, responsible for supporting the body (conductors/equipment) and isolating current (preventing "leakage").

Surge Arresters are the immune system, activating in emergencies when under severe attack from external "pathogens" (lightning overvoltage) to channel and neutralize the threat.

 

Surge arresters ensure transient overvoltages do not exceed the limits this insulation level can withstand.

 

The insulating performance of the insulators themselves (e.g., pollution flashover voltage) is also a key factor in determining the protective level of the surge arresters.

The application of high-voltage insulators runs through the entire process of power generation, transmission, transformation, distribution, and utilization. Their reliability is directly linked to the power grid's supply reliability and public safety. With advances in materials science and manufacturing processes, insulators are evolving towards higher strength, superior environmental resistance, and more intelligent monitoring capabilities.