insulators in power transmission lines play core roles in mechanical support and electrical insulation. Currently, porcelain insulators, glass insulators and composite insulator strings are the three mainstream types. Long rod porcelain insulators are still in service but being gradually replaced by composite strings, with no new installations.
Each type has unique physical and electrical properties due to different materials and manufacturing processes.
1. Porcelain Insulators
Made of electrical porcelain sintered from quartz, feldspar and clay, with a hard glaze on the surface.
Mechanical Properties
High mechanical strength and excellent aging resistance; mechanical performance barely degrades under long-term tension and pressure.
Electrical Properties
Stable insulation performance. However, internal deterioration and zero-value breakdown are not visually detectable, requiring regular zero-value testing.
Main Disadvantages
- Zero-value insulators (loss of insulation with no visible damage) require regular testing, increasing workload.
- Poor pollution resistance: Hydrophilic surface easily causes pollution/ice flashover in heavily polluted/icy areas; PRTV coating can improve performance.
- Heavy weight, making transportation and installation difficult.
2. Glass Insulators
Made of high-strength tempered glass.
Mechanical Properties
High tensile strength due to high-strength tempered glass.
Electrical Properties
Unique zero-value self-shattering: Glass discs automatically shatter and fall off when internal defects or insulation breakdown occur, enabling easy visual inspection and replacement without regular zero-value testing.
Main Disadvantages
- Certain self-shattering rate, prohibited in substations, power plants and urban areas with pedestrian traffic.
- Vulnerable to impact damage in heavy ice and severe hail areas.
- Hydrophilic surface with pollution resistance similar to porcelain insulators; PRTV coating is applicable.
3. Composite Insulator Strings
Composed of fiberglass epoxy resin core rod, silicone rubber sheds and end fittings.
Mechanical Properties
Extremely high tensile strength (core rod: 2-3 times that of ordinary steel) and compact structure.
Electrical Properties
High voltage withstand strength; no internal zero-value faults due to non-breakdown structure.
Core Advantage: Excellent Pollution Resistance
Silicone rubber has superior hydrophobicity and hydrophobic migration. Silicone oil permeates contaminated surfaces, forming isolated water droplets (lotus leaf effect) without conductive water film, ideal for heavily polluted and coastal areas.
Main Disadvantages
- Prone to material aging: Silicone rubber hardens, cracks and loses hydrophobicity under long-term UV, corona and acid rain.
- Poor tear and bird-pecking resistance.
- Internal damage is hard to detect visually, possibly leading to brittle fracture.
4. Long Rod Porcelain Insulators
Made of inorganic minerals (quartz, feldspar, clay, etc.) sintered at over 1300℃.
Mechanical Properties
High mechanical strength for extreme tensile loads; high rigidity and low deformation compared with composite insulators.
Electrical Properties
100% non-breakdown: Solid porcelain rod structure with no penetrating metal fittings; breakdown distance equals external flashover distance, avoiding internal breakdown (zero-value fault).
Excellent aging resistance: Inorganic material is permanent, with strong UV and climate corrosion resistance.
Main Disadvantages
- High brittleness and poor impact resistance: Prone to fracture or micro-cracks from impact during transportation, installation or operation.
- Structural risk of fracture-induced falling: Single rigid structure; fracture leads to total load loss and potential line drop (unlike multi-piece disc insulators).
- Heavy weight increases construction difficulty; winch machines are required for tower replacement.
- Arcing horns at both ends form short air gaps, easily causing lightning-induced tripping (critical flaw).
Post time: 2026-05-14
