Power Generation

The most common disruptor of power at generation sites is controlled shut-down of HEP turbines to avoid accelerated wear of submerged components such as runner blades, labyrinth seals, wear rings, band seals, cheek plates and wicket gates. Even HEPs designed to cope with large volumes of sediment favor the bypass of ash-laden waters over continued operation of the plant, which involves the risk of damaging their turbines.

General Impacts:

• Flashover: Ash contamination of station and line insulators leading to flashover is the most common impact at power plants.
• Step/Touch Potential: ash may reduce the resistivity of ground gravel cover, reducing tolerable step and touch voltages.
• Disruption to Control Systems: ash ingress into heating, ventilation and air-conditioning (HVAC) systems can block intakes leading to reduced performance, and affecting dependent systems.
• Structural damage: Very thick ash deposits (>100 mm or 4 in) may create excessive loads on structures.
• Long span, low pitched roofs are typically the most vulnerable.
• When ash is wet, static loads may increase by up to 100%.
• Internal gutters: may block with ash, potentially leading to water ingress to indoor electrical equipment.

Hydroelectric Power Stations:

• Ash suspended in intake water can cause accelerated wear of hydroelectric turbines (e.g. runner blades, labyrinth seals, cheek plates and wicket gates).
• Hazard depends on volume of ash deposited in catchment, reservoir size, settling rate of ash, abrasiveness of ash.
• Even HEPs designed to cope with large volumes of sediment favor the bypass of ash-laden waters over continued operation of the plant, which involves the risk of damaging their turbines.
• Ash may also fill rain gauges in climate stations throughout river and reservoir catchments.

Thermal Power Stations:

There are few case studies to guide possible impacts or advice.
• Ash may block air intakes for gas turbines and boilers, or sub-aerial condenser systems causing blockages, abrasion and creating cleaning difficulties.
• Ashfalls have created airborne particle concentrations of up to 9 g/m³, several times higher than dust- or sand-storms.
• Mechanical seals may be vulnerable to abrasion and corrosion by ash.
• Fine ash ingested into gas turbines may cause accelerated wear or melt on turbine surfaces (similar to an aircraft turbine).
• Ash may contaminate exposed surface water cooling reservoirs, potentially blocking heat-exchange systems.

Insulator flashover at generation yards containing step-up transformers can cause cascading impacts. If power cannot be transmitted from a generation site due to contamination and subsequent flashover on transformation equipment (e.g. insulators and bushings), then the generated power cannot be transmitted to other sections of the system and the risk of brownout or blackout increases.

Ashfall is a hazard that could cause generation disruption or shutdown due to blockage of generator air intakes and off-site power resources (e.g. emergency lines or generators for back-up power). Similarly, some generation sites rely on heating, ventilation and air conditioning (HVAC) systems to keep sensitive electrical equipment at a maintained temperature (e.g. switching equipment and data centers). HVAC systems are vulnerable to ash damage (e.g. abrasion of moving parts such as fans), corrosion, and arcing of internal electrical components, and air filter blockage, especially if air intakes are horizontal surfaces, although these impacts have not been recorded.