Risk of double circuit faults

As system operator we identify situations that 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.

Risk of double circuit faults

System Operator