Judgment Standards for the Quality and Reliability of Insulators
Historically, insulators were primarily used on utility poles. With the advancement of technology, they evolved into strings of disc-shaped units suspended from high-voltage transmission towers. These units, typically made of glass or ceramics, are designed to increase creepage distance.
Insulators play two fundamental roles in overhead transmission lines: supporting the conductors and preventing current from returning to the ground. These functions must be guaranteed under all environmental and electrical load conditions. An insulator must not fail due to mechanical or electrical stresses; otherwise, the operational life and safety of the entire transmission line will be compromised.
1. Standards for Insulation Resistance
The quality of an insulator’s dielectric property is primarily measured by its insulation resistance:
- New Insulators: Insulation resistance should be ≥ 500 MΩ.
- In-Service Insulators: Insulation resistance should be ≥ 300 MΩ.
2. Classification of Insulation Deterioration
When resistance drops, the insulator is classified as follows:
- Low-Value Insulator: Insulation resistance is < 300 MΩ but > 240 MΩ.
- Zero-Value Insulator: Insulation resistance is < 240 MΩ.
Note: This resistance-based testing method is generally not applied to composite insulators.
3. Comparison: Glass vs. Porcelain Insulators
The choice between glass and porcelain often depends on maintenance strategies and environmental factors:
A. Durability and Aging
Glass insulators possess high surface mechanical strength, making them resistant to cracks. Their electrical strength remains consistent throughout their service life, and their aging process is significantly slower than that of porcelain. While porcelain defects often take years to manifest, glass insulator issues typically appear early in operation.
B. The “Self-Shattering” Advantage
One of the most significant advantages of toughened glass insulators is their “self-shattering” characteristic. Any internal damage or electrical failure will cause the glass to shatter spontaneously. This eliminates the need for expensive, periodic live-line preventive electrical testing because field personnel can easily identify damaged units through visual inspection.
C. Mechanical Safety
When a glass insulator shatters, the fragments near the steel cap and iron foot remain wedged in place. The residual mechanical strength of the remaining “stub” is sufficient to prevent the insulator string from breaking or the conductor from falling. Currently, the self-shattering rate is a critical quality metric and a key technical requirement in international power project bidding and tenders.
Taporel Insight: Whether choosing traditional glass/porcelain or modern composite insulators, maintaining the balance between mechanical load-bearing and electrical insulation is the key to a stable power grid.
