Insulator Flashover
Insulator flashover across a string of 3 glass insulators, which have been coated with 3mm of wet volcanic ash. Flashover occurred at ~80kV, about 30% lower than if insulators were clean.
Volcanic ash is a potentially highly disruptive form of contamination capable of causing insulator flashover across station and line insulators. Ash-induced insulator flashover is a disruptive electrical discharge over the surface of solid insulation caused by the high conductivity of volcanic ash when it becomes wet (e.g. from light rain conditions such as dew, fog, light rain, etc.).
The flashover voltage of ceramic and non-ceramic insulators is influenced by a number of factors.
Flow chart illustrating the many variables influencing ash-induced insulator flashover.
The dielectric strength of ceramic insulators under critical ash contamination (complete surface coverage) is ~10 kV/unit or 30 kV per metre of creepage distance. It is estimated that 1 mm (1/32 in) thickness coverage of ≥40% of insulator creepage distance in wet ash is critical, and will lead to flashover problems.
The dielectric strength of non-ceramic (e.g. composite polymer, silicone rubber, etc.) insulators is higher than ceramic equivalents under volcanic ash contamination (recent literature suggests 35 kV per metre of creepage distance). Thus, non-ceramic insulators are the optimal choice of insulation in ashy environments.
Standard Glass - Common insulators used on power transmission circuits, contaminated by volcanic ash.
Standard Porcelain - Common insulators used on power transmission circuits, contaminated by volcanic ash.
Aero Glass- Common insulators used on power transmission circuits, contaminated by volcanic ash.
Composite - Common insulators used on power transmission circuits, contaminated by volcanic ash.
HVAC Insulator Dielectric Strength
Pollution performance curves for different ceramic and non-ceramic insulators. The pink shaded area represents an Ave. ESDD/NSDD 0.02/10.7 – 0.04/19.1 mg/cm2; yellow represents an Ave. ESDD/NSDD 0.1/60 – 0.3/106 mg/cm2; purple an Ave. ESDD/NSDD 0.3/113 – 0.6/218 mg/cm2