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).
We commenced the current review in 2017. 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.
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The completed assessments under the credible event review for the 2017-2019 period are detailed below. A summary of classifications can be found in the following document.
Summary of Event Classifications [ pdf 786.67 KB ]
Core Grid Busbar Classifications due to Thermal and 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 classifications 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 ] |
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| 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 ] |
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Core Grid Busbar Classifications due to Frequency
Transpower has completed assessment and classification of all busbars connected to the core grid assessing impacts to frequency. The final report and classifications can be viewed below. The categorisations classifications are effective from 13 January 2019.
Participants were invited to comment on our report; a summary of feedback can be viewed below.
| Busbar Classification for Frequency [ pdf 1.67 MB ] |
| Summary of Industry Comments [ pdf 539.64 KB ] |
Interconnecting Transformer Classifications
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 classifications will come into effect on 1 October 2018.
The following documents are available for your information:
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Interconnecting Transformer Classifications – minor update 2021
The Credible Event Review takes place in a 5 yearly cycle. Minor updates to the existing reports may be required from time to time as the grid configuration changes between major review cycles.
Updated versions of the existing 2018 Interconnecting Transformer Classification reports are provided below. Changes to the original 2018 assessments have been highlighted in yellow.
The following changes have occurred:
- SFD T9 now replaces NPL T8
- A 50 Mvar reactor has been installed at KIK, impacting the light load calculation
- The OTA 110 kV bus is no longer split
- Correction of error in the costs KIK light load assessment
The classifications will come into effect on 01 January 2022.
The following documents are available for your information:
| Interconnecting Transformer Classification Review – minor update [ pdf 528.55 KB ] |
| Appendix 1 - North Island ICTs – minor update [ pdf 1.66 MB ] |
| Appendix 2 - South Island ICTs – minor update [ pdf 1.07 MB ] |
