Impact of Tiwai exit

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Transpower, as System Operator, commenced analysis to determine system operation and security impacts of Tiwai’s exit following the initial announcement of a August 2021 closure. This work continues as planned following the announcement that the plant's operations will continue to the end of 2024. This webpage will be used to share the findings of our analysis as it becomes available.

Our Approach

To understand the impacts we are investigating the following:

  • Steady-state thermal limits under N-1 and N-1-1 conditions (Will be covered in the 2020 System Security Forecast)
  • Steady-state high voltage management under light load conditions (Will be covered in the 2020 System Security Forecast)
  • Steady-state voltage stability
  • Transient angular stability
  • Over frequency reserves
  • Small signal stability
  • Automatic under frequency load shedding (AUFLS) adequacy
  • Contingency and restoration planning:
    • Black start restoration process
    • Electrical islanding process
    • Regional contingency plans

Analysis Findings

Operational Impact Assessment, Tiwai Smelter Closure - Managing an HVDC bipole tripping [ pdf 2.46 MB ]

Links to Additional Information

Clutha and Upper Waitaki Lines Project Operational Information

System Security Forecast

Security of Supply Annual Assessment