Interview Questions for Power Personnel

System Specifications

  • What is the generation capacity of the system (kW, MW?)?
  • At what voltages does the system operate?
  • Line voltages of those areas that have recently been affected by tephra fall?
  • 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.?
  • Havethere 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?
  • 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?
  • Does tephra contamination cause concern for step-touch potentials in ground resistivity of generation/substation/switchyard gravels (lowers resistance)?
  • 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?