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).

We have recently commenced a credible event review. For this and subsequent reviews we are adopting a staged approach to our assessment.   We will assess assets by class, rather than carry out a complete assessment of all assets (our previous approach).  As each asset class or event category is assessed, classifications will be updated on this website following normal consultation process. These classifications will come into effect once they have been incorporated and published in the Policy Statement.

A draft plan of our staged approach can be found below. This will be updated when a more detailed plan is finalised.

Draft Plan [ pdf 483.39 KB ]

In 2015 an interim policy was established for 220kV interconnecting transformers and busbars connected to the core grid. The interim policy (set out below) will be updated as these assets are progressively reviewed, where necessary change is identified.  

Interim Policy

Following the double circuit outage at Manapouri on the 16th May 2015 the system operator reviewed its extended contingent event policies.  The system operator identified the need to review the classification of interconnecting transformers and core grid busbars as extended contingent events and initiated a project to complete the review and to operationalise management processes if required.

Core Grid Busbars

The interim policy for core grid busbars will continue to apply until a review is completed. The policy is set out below with immediate effect:

  1. The system operator will not (subject to the exception below) actively monitor and manage ECE risks presented by core grid busbars.  The system operator will, therefore, not manage pre-contingently for the loss of a core grid bus bar during any outage, including single circuit or double circuit outages.
  2. ECE risks posed by a Manapouri busbar relating to frequency, will be managed during both normal (all equipment in service) and outage scenarios (consistent with the existing policy).
  3. No other core grid busbars will be managed in relation to frequency.

Interconnecting Transformers

The interim policy for interconnecting transformers will continue to apply until a review is completed. This is set out below with immediate effect:

The interim policy effectively classes a number of ICT’s on the system as CE risks.  Remaining ICT’s will continue to be classed as ECE risks and will only be managed post contingently.

  • The ICTs classed as a CE risk during the interim period are:

HAM T6 T9

HAY T1 T2 T3

HEN T1 T2

ISL T3 T6 T7

KIK T2

MDN T5 T6

NPL T8

OTA T2 T3 T4 T5

RDF T3 T4 (for asset protection reasons)

SFD T10

STK T7

TRK T2 T3

WIL T8

 

 

  • The ICTs classed as an ECE risk during the interim period (and only to be managed post-contingently) are:

ALB T4

BPE T1 T2 T3

BRY T5 T6

CML T5A T5B T8

CUL T22 T23

DOB T11 T12

EDG T4 T5

HWB T4 T6

INV T1

KAW T12 T13

KMO T2 T4

MPE T1 T2

PEN T6 T10

ROX T10

STK T3

WPR T12 T13

WTK T23 T24

 

Updated Event Categorisation

The completed assessments under the credible event review for the 2017-2019 period are detailed below. These classifications will take effect once they have been incorporated and published in the Policy Statement. When this occurs, the effective date will be published on this website.

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.

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

he following documents are available for your information/comment:

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 ]  

For questions regarding the interim policy please contact Scott Avery

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

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