Clutha and Upper Waitaki Lines Project Operational Information Q & A


Questions and Answers

We have listed below common questions we have received from industry along with our responses.  We will continue to update this section and share with participants any updates.

Number Description

What is meant by enabling works and will this result in any rating changes?

Grid Owner Response 12 August 2020

The enabling works are a thermal upgrade of the Cromwell-Twizel section of the Roxburgh-Twizel line. At the completion of these outages there will be some additional capacity on these lines.  Confirmation of these new ratings will be provided in due course.


Will the thermal upgrade work on Cromwell-Twizel be completed prior to the outages for the reconductoring work on the Naseby-Roxburgh circuit in January 2021?

Grid Owner Response 19 August 2020

Yes, we are planning to complete all thermal upgrade work on the Cromwell-Twizel circuits prior to this Naseby-Roxburgh outage. The planned uprated capacity of these CML-TWZ circuits is detailed in the CAN issued 18th August.

Given the recall times for the reconductoring outages (Naseby- Roxburgh and Livingstone-Naseby) are 2-3 weeks, and Naseby will be on N-security during the Roxburgh-Livingstone outages needed, is there anything we can do to restore Naseby quicker in the event of a loss of supply?

Grid Owner Response 22 September 2020

If there is a fault in the remaining circuit during the outages, it’s likely that our focus will be on restoring the faulted circuit rather than recalling the circuit out of service for reconductoring (simply given the recall times).  However, we will consider these situations as part of our contingency planning. One option may be to ensure we have sufficient maintenance crews closer to the vulnerable circuit.


During the HVDC 2020 outages earlier this year, one remaining section of reconductoring of the HVDC line was held off until a future HVDC outage.  Will this work be completed during these CUWLP outages?

Grid Owner Response 22 September 2020

This work on the final section of the HVDC line will be programmed to fit within scheduled HVDC outage windows in 2023 and 2024.


When will Aviemore-Benmore Special Protection Scheme (SPS) be completed?

Grid Owner Response 22 September 2020

We are progressing the design work for the SPS and currently looking to install winter time next year however this will be reliant on design complexity and outage availability.  We are happy to update at next briefing.


Question: Were the published transfer limits based on as assumption of standard 15-min offload times?

System Operator Response 22 September 2020

The published assessment used our standard security criteria, which assumed a standard 15-min offload time, where this limited the transfer.


Questions on a double-circuit events (trippings):

Is the double circuit event only a risk during the construction period?

System Operator Response 22 September 2020

The double circuit tripping is a risk during severe weather events, but given the duration of the outages we are looking closely at the implications and management.


What are the implications of a double circuit contingency during the reconductoring outages on Naseby- Roxburgh and Livingstone-Naseby?

System Operator Response 22 September 2020

We will apply a pre-contingent constraint across the two circuits to manage the risks of a double circuit tripping. This is required to manage system frequency should a tripping occur. We have ongoing work to confirm these constraints.


Will you publish information on this, and if so when, and will you update NZGB?

System Operator Response 22 September 2020

Yes, we will publish our information. We are working on it now, but cannot commit to a date. We aim to have it completed as much in advance as possible. Consideration will be given to including these constraints in NZGB. This will only be required if the resulting generation capacity reduction is larger than any of the existing risks considered in NZGB.