Risk of Double Circuit Faults

The Transpower as system operator identifies that a situation warrants a double circuit tripping be treated as a single risk and actions this in accordance with the Risk Management Policies in the Policy Statement.

Acting reasonably and prudently to manage the outcomes of events that may cause cascade failure, we identify either directly or from advice received from others that the situation warrants a double circuit tripping be treated as a single risk and actions these in accordance with the Risk Management Policies in the Policy Statement.

The following table lists indicative environmental conditions that may create a high likelihood of simultaneous double circuit tripping of both transmission circuits of a double circuit line and will be treated as a single contingent event. This list may not be exhaustive and will not limit the definition of the contingent event.

Condition Caused by Advised by Example
Historical
  • Trippings due to electrical storms
  • Transient events
  • System Operator from historical events
  • Based on information held by the System Operator.
Pollution
  • Dust
  • Dirt
  • Salt
  • Industrial
  • Birds
  • Smoke
  • Fire
  • Asset Owner or participant
  • Pollution build up on an asset due to any of the identified causes.
  • A fire near or passing through both sets of conductors of a double circuit line.
Weather
  • Lightning
  • Flooding
  • Wind
  • Conductor clashing
  • Asset Owner or participant
  • Local conditions along transmission line route places the asset at risk.
  • Conductor clashing can occur due to ice or snow unloading.
Natural Disaster
  • Earthquake
  • Volcanic activity
  • Tsunami
  • Storm surge
  • River erosion
  • Landslides
  • Asset Owner or participant
 
Other
  • Vehicle accident
  • Aircraft
  • Vandalism
  • Terrorism
  • Animals
  • Machinery
  • Asset Owner or participant
  • Any one of the identified causes could place the transmission line at risk.

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