Event Categorisation

Under the Security Policy section of the Policy Statement, the system operator categorises credible events according to the nature of the control required to manage their effects.  This is determined periodically when we carry out a  credible event review, as detailed in the Policy Statement (see  clause 13.1).

The last credible event review was completed in 2014. We commenced the current review in 2017, which is to be completed by 2019.

For this review, we have adopted a new staged approach to our assessment. Details of this approach along with an assessment on what will be included in the current review is detailed in the following Credible Event Review Scope document.

Credible Event Review Scope [ pdf 805.43 KB ]

Response to Industry Feedback [ pdf 60.9 KB ]

Updated Event Categorisation

The completed assessments under the credible event review for the 2017-2019 period are detailed below. A summary of classifications effective from 1 October 2018 is available in the following document.

Summary of Event Classifications [ pdf 157.17 KB ]

Core Grid Busbars (voltage)

Transpower has completed assessment of all busbars connected to the core grid assessing impacts to equipment loading and related voltage issues. The final report and classifications can be viewed below along with the accompanying reports with results by grid zone. The categorisations are effective from 10 November 2017.

Participants were invited to comment on our report; a summary of feedback can be viewed below.

The following documents are available for your information:

Busbar Classification Review [ pdf 5.39 MB ]
Results GZ01 Northland [ pdf 1.06 MB ] Results GZ08 Wellington [ pdf 786.1 KB ]
Results GZ02 Auckland [ pdf 1.16 MB ] Results GZ09 Nelson [ pdf 935.31 KB ]
Results GZ03 Hamilton [ pdf 1.08 MB ] Results GZ10 Christchurch [ pdf 901.38 KB ]
Results GZ04 Edgecumbe [ pdf 1.41 MB ] Results GZ11 Canterbury [ pdf 689.08 KB ]
Results GZ05 Hawkes Bay [ pdf 781.46 KB ] Results GZ12 West Coast [ pdf 875.91 KB ]
Results GZ06 Taranaki [ pdf 1.07 MB ] Results GZ13 Otago [ pdf 985.06 KB ]
Results GZ07 Bunnythorpe [ pdf 1.22 MB ] Results GZ14 Southland [ pdf 1.1 MB ]
Summary of Industry Comments [ pdf 455.1 KB ]  

Interconnecting Transformers

Transpower has completed an assessment of all core interconnecting transformers, assessing impacts to equipment loading and related voltage issues. Following this review, participants were invited to provide feedback. 

The final report and classifications can be viewed below along with a summary of industry feedback.

The categorisations will come into effect on 1 October 2018.

The following documents are available for your information:

Interconnecting Transformer Classification Review [ pdf 1021.15 KB ]

Appendix 1 - North Island ICTs [ pdf 3.27 MB ]

Appendix 2 - South Island ICTs [ pdf 2.05 MB ]

Summary of Industry Submissions [ pdf 457.13 KB ]

For More Information

For questions regarding the Credible Event Review project please contact Bharti Patel.

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