Interview Questions for Power Personnel
System Specifications
 What is the generation capacity of the system (kW, MW?)?
 At what voltages does the system operate?
o Line voltages of those areas that have recently been affected by
tephra fall?
o Try to acquire a map outlining system circuits and assets.
 What sort of assets does the power company own (i.e. how many km of
lines, number of poles/towers, transformers, etc.)?
 What type of generators do you have (i.e. fossil, nuclear, renewable?
Diesel, oil, gas, steam, etc.?
o Have there been issues with the breakdown of control equipment
(e.g. switching cabinets, air conditioning/air cooling systems) due
to tephra penetration blocking air intakes and/or corrosion?
o Have portable generators been affected by the ashy conditions?
 What types of insulators are used on the system
(porcelain/glass/composite polymer)? Transmission? Distribution?
Specifications?
 What component within the system do you think is most vulnerable to
tephra contamination? What equipment is most valuable i.e. the hardest
to replace or fix?
Impacts
 Could you tell me the biggest problem(s) or impact(s) you receive
following a tephra fall event?
 Do outages occur during a) dry atmospheric conditions b) during rain c)
after rain?
 How much tephra (mm and/or volume) fell during outages? What colour
was it? Idea of grain size?
 Does most of the tephra get washed off after a light rain? After a heavy
rain? How much rain is needed to clean the insulators?
 What kind of rain initiates a fault (i.e. mist, dew, fog, rain, heavy rain,
etc.)?
 If possible, collect tephra samples from failed equipment, e.g.
transformers, insulators, bushings, conductors, etc. (to analyse ash
properties such as grain size).
 Do you experience outages due to the build up of pollution on insulators,
such as sea salt, industrial emissions, construction/mining operations,
fertilizers, guano, etc.? Do you think pre-existing contaminants played a
role in the recent power outages?
 Have you seen evidence of corrosion on metal apparatus or tracking on
insulation?
 Have you observed any abrasion of moving apparatus (e.g. transformer
cooling fans, air conditioning units, etc.) from tephra contamination?
 Do you experience power outages due to tephra-laden vegetation or other
objects falling onto power lines?
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Does tephra contamination cause concern for step-touch potentials in
ground resistivity of generation/substation/switchyard gravels (lowers
resistance)?
o If so, what safety measures (if any) are taken?
Have you ever had cascading failures (i.e. one circuit trips other loads)?
What are the common observations/perceptions surrounding the
cause(s) of failure?
Was there a period of time when impacts have been particularly bad or
frequent?
Mitigation Strategies
 What mitigation strategies are practised to combat tephra-induced power
failure (i.e. controlled outages, cleaning, RTV applications, etc.)?
 Do you regularly clean insulators/lines/poles/bushings of tephra or other
contaminants? Controlled outages or live line?
 Do you have any recommendations for combating the issue of power
system equipment failing while exposed to tephra fall?
 How do you combat the issue of remobilised tephra?
Request for Photos and/or Log Sheets
 Distribution equipment coated in tephra fall (note thicknesses).
 Damages caused by flashover (i.e. burn marks on insulators, wood poles,
transformers, etc.).
 Line maintenance (i.e. linesman performing replacement of insulators
due to tephra contamination).
 Logs with fault/time data?