FAQ

The purchase quantity of insulators depends on multiple core factors:
 
  • Project scale: The total length of transmission lines, the number of towers/poles, and the number of circuits (single-circuit, double-circuit, etc.) directly determine the base demand.
  • Installation configuration: The number of insulators per string (e.g., 10 units for 110kV lines, 20+ units for 500kV lines), and the number of strings per tower (suspension strings, tension strings, jumper strings).
  • Spare ratio: Industry practice usually requires a 3%–5% spare quantity to cover loss, damage during transportation and installation, and future maintenance replacement.
  • Type differentiation: Different insulator types (porcelain, glass, composite) for different scenarios (outdoor, coastal, polluted areas) need separate quantity calculation.
Use this formula for preliminary calculation:
 
Basic quantity = (Number of towers × Number of insulator strings per tower × Number of insulators per string) + Spare quantity
 
 
  • Example: A 110kV single-circuit transmission line with 50 towers, 2 suspension strings per tower, 10 insulators per string, and 3% spare ratio.
     
    Basic quantity = (50 × 2 × 10) = 1000 units
     
    Spare quantity = 1000 × 3% = 30 units
     
    Total purchase quantity = 1030 units
Yes, most manufacturers set MOQs for insulators, which vary by type and specification:
 
  • Standard insulators (common voltage levels like 10kV, 35kV, 110kV): MOQ is usually 50–200 units per type.
  • Customized insulators (special specifications for polluted areas, high-altitude regions): MOQ is higher, generally 200–500 units per type, due to mold opening and production line adjustment costs.
  • Wholesale for large projects: MOQs can be waived if the total order volume is large enough (e.g., 10,000+ units).
Yes, for long-term operation of power lines, it is recommended to reserve a 1%–2% annual maintenance quantity based on the total installed insulators.
 
  • These reserved insulators are used to replace aging, broken, or faulty insulators during regular inspections (e.g., glass insulators with self-explosion, composite insulators with sheath aging).
  • It is advised to purchase maintenance insulators in batches every 2–3 years to ensure consistency with the existing insulator model and performance.
  • Visual inspection: Check insulators for cracks, chips, bubbles (porcelain/glass types), or sheath damage (composite types). Reject any insulator with obvious defects.
  • Cleaning: Wipe the surface of insulators with a clean cloth to remove dust, dirt, or oil stains. For insulators used in polluted areas, clean them with a neutral detergent and dry thoroughly.
  • Tool preparation: Prepare matched hardware (clevises, ball sockets, pins, clamps), torque wrenches, and lifting tools. Ensure all hardware components are galvanized and free of rust.
  • Parameter confirmation: Verify that the insulator type, rated voltage, and mechanical strength match the design requirements of the transmission line or electrical equipment.
  • Over-tightening hardware: Excessive torque on bolts or pins may crack the insulator cement or damage the composite sheath.
  • Ignoring locking devices: Forgetting to install cotter pins or spring washers will cause the pins to fall off during operation, leading to string disconnection.
  • Mixing different types/specifications: Do not assemble insulators of different voltage levels, materials, or manufacturers in one string, as this will cause uneven stress and insulation failure.
  • Rough handling: Dropping or dragging insulators during assembly can cause hidden internal cracks that are not visible to the naked eye.
  • Porcelain/glass insulators:
    • Visual inspection: Look for cracks, self-explosion (glass insulators have self-explosion characteristics), or loose cement bonding between the insulator body and fittings.
    • Test: Use a spark gap tester or insulation resistance meter to detect zero-value or low-value insulators (zero-value insulators cannot bear voltage and need to be replaced immediately).
     
  • Composite insulators:
    • Check for sheath aging, cracking, or shedding, core rod exposure, or end fitting corrosion.
    • Use an ultrasonic detector or infrared thermal imager to detect internal defects that are not visible on the surface.
  • Porcelain insulators: 20–30 years under normal operating conditions.
  • Glass insulators: 25–35 years (self-exploded insulators are replaced individually, no need for batch replacement if the overall performance is good).
  • Composite insulators: 15–20 years (affected by sheath aging and core rod degradation).
  • Batch replacement conditions: When the failure rate of insulators in a line exceeds 5%, or when the insulation performance of most insulators drops below the design standard after testing, batch replacement is recommended.