Johnny Wardman

Potential impacts from tephra fall to electric power systems: a review and mitigation strategies

Modern society is highly dependent on a reliable electricity supply. During explosive volcanic eruptions, tephra contamination of power networks (systems) can compromise the reliability of supply. Outages can have significant cascading impacts for other critical infrastructure sectors and for society as a whole. This paper summarises known impacts to power systems following tephra falls since 1980. The main impacts are (1) supply outages from insulator flashover caused by tephra contamination, (2) disruption of generation facilities, (3) controlled outages during tephra cleaning, (4) abrasion and corrosion of exposed equipment and (5) line (conductor) breakage due to tephra loading. Of these impacts, insulator flashover is the most common disruption. The review highlights multiple instances of electric power systems exhibiting tolerance to tephra falls, suggesting that failure thresholds exist and should be identified to avoid future unplanned interruptions. To address this need, we have produced a fragility function that quantifies the likelihood of insulator flashover at different thicknesses of tephra. Finally, based on our review of case studies, potential mitigation strategies are summarised. Specifically, avoiding tephra-induced insulator flashover by cleaning key facilities such as generation sites and transmission and distribution substations is of critical importance in maintaining the integrity of an electric power system.

Influence of volcanic ash contamination on the flashover voltage of HVAC outdoor suspension insulators

High voltage station and line insulators are vulnerable to volcanic ash-induced flashover, yet little quantitative data exists on the environmental, volcanological and electrical parameters most influential in reducing their flashover voltage. This paper presents the results from clean-fog rapid flashover tests for 5 different suspension insulators of ceramic, non-ceramic, or RTV-coated design under different environmental and volcanic ash contamination scenarios. Results suggest that moderate accumulations (up to 3 mm) of volcanic ash can accumulate on insulator surfaces without critically reducing the flashover voltage, provided >40% of the creepage distance remains clean and dry. Composite polymer insulators have higher dielectric strength than ceramic equivalents under light to heavy pollution severities, however, all insulators tested here perform comparably when critically contaminated (i.e. both top and bottom surfaces coated in ash). Based on these and other findings, some basic discussion of optimal insulator selection in ashy environments is provided.

Volcanic ashfall preparedness poster series: a collaborative process for reducing the vulnerability of critical infrastructure

Volcanic ashfall can be damaging and disruptive to critical infrastructure including electricity generation, transmission and distribution networks, drinking-water and wastewater treatment plants, roads, airports and communications networks. There is growing evidence that a range of preparedness and mitigation strategies can reduce ashfall impacts for critical infrastructure organisations. This paper describes a collaborative process used to create a suite of ten posters designed to improve the resilience of critical infrastructure organisations to volcanic ashfall hazards. Key features of this process were: 1) a partnership between critical infrastructure managers and other relevant government agencies with volcanic impact scientists, including extensive consultation and review phases; and 2) translation of volcanic impact research into practical management tools. Whilst these posters have been developed specifically for use in New Zealand, we propose that this development process has more widely applicable value for strengthening volcanic risk resilience in other settings.

Volcanic ash contamination: limitations of the standard ESDD method for classifying pollution severity

The pollution severity of airborne contamination on high voltage insulation has traditionally been quantified by calculating the contaminants equivalent salt deposit density (ESDD). Volcanic ash is a rare but severe form of airborne pollution, and the high conductivity of wet volcanic ash (often >1.3 × 10-4 S/cm) can cause pollution-induced insulator flashover. This paper presents the ESDD and non-soluble deposit density (NSDD) for four different fresh volcanic ash samples and two ash proxies measured at different thicknesses using a standardised plate test. Results show that there is a log-linear increase of ESDD with increasing NSDD. Tests indicate that a 3 mm thick deposit (NSDD between 158 and 231 mg/cm2) of fresh volcanic ash yields an ESDD between 0.02 and 0.7 mg/cm2, suggesting that ash can have high contamination severity and therefore potential to cause pollution-induced insulator flashover. Whilst the ESDD/NSDD method provides direct analysis of the ionic content of a contaminant, the procedure is time consuming, cannot accommodate the high NSDD of volcanic ash for site pollution severity classification and does not account for changes in the contaminants electrical conductivity under different environmental, chemical and physical conditions. Given these limitations, this study proposes an alternative, simple yet more comprehensive technique for investigating the electrical properties of volcanic ash by means of direct resistivity analysis.