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Risk of Double Circuit Faults

The System Operator, acting reasonably and prudently in managing the outcomes of events that may cause cascade failure, identifies either directly or from advice received that the 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.

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.

ConditionCaused byAdvised byExample
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 - Lighting
- 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.