Transgrid PADR: Maintaining reliable supply to the North West Slopes area

Market Network Service Provider
StageProject Assessment Draft Report
ConvenorAEMO NSP
Accepting submissions?No

Transgrid has recently published a Project Assessment Draft Report (PADR) for maintaining reliable supply to the North West Slopes area in Northern NSW. 

As set out in Transgrid’s 2021 Transmission Annual Planning Report (TAPR), the latest forecasts indicate that electricity demand is expected to increase substantially in the North West Slopes area going forward. This is mainly due to a number of substantial industrial loads that are anticipated to connect, as well as underlying general load growth in Narrabri and Gunnedah.

Schedule 5.1.4 of the National Electricity Rules (NER) requires Transgrid to plan and design equipment for voltage control to maintain voltage levels within 10 per cent of normal voltage. The NER also requires the power system to be operated in a satisfactory operating state, which requires voltages to be maintained within these levels, both in normal operation and following any credible contingency event. 

Transgrid has undertaken planning studies that show that the current North West Slopes network will not be capable of supplying the forecast increases in load in the area without breaching the NER requirements and that voltage-limited constraints will have to be applied in the 132 kV supply network if action is not taken. Moreover, in addition to the voltage constraints identified, our planning studies show that the increased demand will also lead to thermal constraints, particularly during times of low renewable generation dispatch in the region. 

If the longer-term constraints associated with the load growth are unresolved, it could result in the interruption of a significant amount of electricity supply under both normal and contingency conditions due to voltage and thermal limitations in the area. 

The PSCR and accompanying non-network Expression of Interest (EOI) were released in April 2021. Transgrid did not receive any submissions directly to the PSCR, however two parties responded to the EOI. Both parties requested confidentiality, so none of the material has been reproduced in the PADR or on Transgrid’s website.

While there have been no material changes to the network options since the PSCR, the non-network options have been refined to reflect:

  • responses to the EOI, resulting in two new options being included that utilise Battery Energy Storage Systems (BESS) as put forward by proponents; and
  • revised demand forecasts since the PSCR, which has led to the non-network components being resized and slightly rescoped.

The results of the PADR assessment find that the options involving non-network solutions in the short-term are preferred over those based solely on network components. This is due to these options being assumed to be able to be commissioned approximately one to three years before the network options, which allows them to avoid substantial additional unserved energy in those early years. 

We will therefore be focussing, internally and with third party proponents of non-network solutions, to firm up the assumed commissioning dates (and costs) for all options between now and the Project Assessment Conclusions Report (PACR), and to ensure that the assumed option timing is realistic in all cases.

At this stage of the RIT-T, the preferred option therefore involves a non-network solution in the short-term as well as the installation of a third 132/66kV transformer at Narrabri 132/66kV substation. The non-network solutions are not considered to be long-term standalone solutions and, instead, defer or avoid the rebuilding of line 969 as a double-circuit line and upgrading the 9UH line between Narrabri and Boggabri East.

Transgrid welcomes written submissions on materials contained in the PADR. Submissions are due on 7 April 2022. 

In accordance with the requirements of the Rules, a summary of the PADR is made available on the AEMO website. A copy of the PADR can be obtained from Transgrid’s website or by emailing

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