Common Insulator Failures and Preventive Measures

Insulators are specialized insulating components that serve a dual purpose in overhead transmission lines: supporting conductors and preventing current grounding. They are installed at connection points between utility poles/towers and conductors, and between substation structures and power lines. Based on dielectric materials, insulators fall into three categories: porcelain, glass, and composite. Analyzing common insulator failures and maintenance strategies aims to prevent insulation failure caused by environmental and electrical load variations, which generate electromechanical stresses that compromise power line performance and lifespan.

​Failure Analysis​

Insulators, continuously exposed to the atmosphere, are susceptible to various failures due to lightning strikes, contamination, bird interference, ice/snow, extreme heat/cold, and elevation differences.
• ​Lightning Strikes:​​ Transmission corridors often traverse hills, mountains, open areas, or polluted industrial zones, where lines are prone to lightning-induced insulator puncture or explosion.
• ​Bird Interference:​​ Research indicates a significant portion of flashover incidents stem from bird activity. Composite insulators exhibit higher susceptibility to bird-related flashovers compared to porcelain or glass types. Such incidents predominantly occur on 110 kV and higher transmission lines; urban distribution networks (≤35 kV) experience fewer cases due to lower bird populations, reduced voltage levels, smaller air gaps for breakdown, and effective prevention by insulator sheds without grading rings.
• ​Grading Ring Failures:​​ High electric field concentration near insulator end-fittings necessitates grading rings on 220 kV+ systems. However, these rings reduce clearance distance, lowering withstand voltage. During severe weather, low corona inception voltage at ring mounting bolts can induce corona discharge, compromising string safety.
• ​Contamination Flashovers:​​ Conductive pollutants accumulate on insulator surfaces. Under humid conditions, this contamination drastically reduces insulation strength, leading to flashovers during normal operation.
• ​Unknown Causes:​​ Many flashovers lack clear explanations, e.g., zero-resistance porcelain insulators, shattered glass insulators, or composite insulator tripping. Despite inspections, causes remain undetermined. These incidents typically share traits: occurring overnight (especially during rain) and often allowing successful auto-reclosing post-fault.

​Preventive Measures​

• ​Lightning Protection:​​ Address root causes (short dry-arc distance, single-point grading rings, excessive grounding resistance) by installing extended composite insulators, dual grading rings, and improving tower grounding.
  • ​Bird Damage Prevention:​​ Deploy bird barrier nets, anti-bird spikes, or protective covers on high-risk line sections.
  • ​Grading Ring Mitigation:​​ Use insulators with equal-sized sheds meeting technical spacing requirements. Increase creepage distance where necessary to reduce ice/snow flashovers. Conduct regular inspections and random tests (mechanical strength, electrical performance, aging assessment) across diverse regions/environments to prevent strength degradation, swing resistance loss, or shed aging issues.
  • ​Contamination Control:​​
  o ​Regular Cleaning:​​ Clean all insulators before peak contamination seasons; increase frequency in heavily polluted areas.
  o ​Enhanced Creepage Distance:​​ Boost insulation levels by adding insulator discs or using anti-fog designs. Field experience confirms anti-fog insulators' effectiveness in severely polluted zones.
  o ​Silicone Coatings:​​ Apply anti-pollution coatings (e.g., ceresin wax, paraffin, silicone-based materials) to improve contamination resistance.
  • ​Unexplained Flashovers:​​ Perform comparative tests on new insulators (same model) and in-service units (>3 years), including power-frequency dry flashover and mechanical failure tests. Conduct aging evaluations periodically. Implement scheduled cleaning, timely ESDD (equivalent salt deposit density) measurements, and incorporate new anti-aging agents during replacements.
  • ​General Maintenance:​​ Prohibit personnel from stepping on insulators or scraping them with sharp tools to extend service life.