Transmission & Distribution
Electrical networks are vulnerable to a number of impacts from ashfall:
- Insulator Flashover: Ash contamination of station and line insulators can lead to flashover.
- Flashover may occur with <3 mm (0.12 in) of ashfall provided a significant portion of the insulator creepage distance (>50%) is covered in wet ash
- This is the most common and widespread impact
- Loading Damage : ash accumulation may overload lines, weak poles and light structures, and cause additional tree-fall onto lines. Precipitation will exacerbate the risk:
- Loading damage typically occurs with >100 mm (4 in) ash accumulation " Induced tree fall from ash load may occur with thicknesses >10 mm (0.4 in)
- 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:
- Possible during any thickness of ashfall
- Earth Potential Rise : Ash may reduce the resistivity of substation ground gravel cover, reducing tolerable step and touch voltages.
- This has not been observed, but is theoretically possible.
Line breakage due to ash loading was observed following previous eruptions (e.g. Mt. St. Helens 1980, Rabaul 1994 and Chaiten 2008). Ash adherence to lines is highest during wet and freezing conditions, although this is a rarely observed impact. Many power companies are liable for maintaining acceptable clearance distances between trees and power lines on both public and privately owned property. Provided these distances are maintained, the power system should undergo no issues with ash contamination of nearby vegetation.
Download a poster on 'Ashfall Impact Advise for Power Plant Operators'.