Blue Corona Near Dry Type Transformer Bushings On Rainy Days: Causes And Fixes

Humid or rainy weather often reveals a puzzling sight around electrical equipment: a faint blue glow. When this glowing phenomenon appears near the bushings of a dry type transformer, it signals a specific electrical condition known as corona discharge. This visual effect happens when the intense localized electric field ionizes the moisture-heavy air surrounding the high-voltage components.

What Causes the Blue Glow?

The blue corona effect is primarily driven by high voltage stress interacting with environmental moisture.

• Air Ionization: The electric field strength exceeds the breakdown strength of the damp air.

• Moisture Accumulation: Rain and humidity lower the insulation resistance of the air, making it easier for the discharge to light up.

• Contaminants: Dust or salt buildup on the bushing surface accelerates the ionization process.

While a minor glow on a massive utility unit or a 225 kva dry type transformer might seem harmless initially, it indicates energy loss and potential insulation degradation over time.

How to Resolve and Prevent Bushing Corona

Ignoring this blue glow can lead to severe equipment failure. Systematic measures must be taken to reduce voltage stress.

1. De-energize and Clean: Safely shut down the system to wipe away dust, salt, and moisture from the bushings.

2. Inspect for Damage: Check the surface of a standard 150kva dry type transformer for micro-cracks or tracking marks.

3. Install Corona Rings: These rings redistribute the electric field gradient to prevent air ionization.

Regular maintenance ensures smaller units, like a 15kva dry type transformer, remain reliable during wet seasons.

Managing Single-Phase Systems

Special attention is required for isolated setups. A single phase dry type transformer operating in wet conditions is equally susceptible to localized stress if the bushings accumulate moisture.