IEEE Power & Energy Magazine - September/October 2021 - 65

levels to co-optimize investment in transmission and generation.
For example, staging can be achieved by building a doublecircuit
tower but stringing a single circuit initially or through
the early acquisition of strategic easements for later stages. The
design can be enhanced by understanding long-term strategic
transmission development in the area so that staging of the
REZ development and costs can be optimized. Where REZs
can form part of interconnectors, the design should take this
into account to enable efficient interconnector development.
Number of Connections to the
Main Grid and Route Diversity
When a REZ reaches a certain critical capacity, it should connect
to the main transmission network with at least two connection
points. This looping allows for additional network reliability and
route diversity, which increases system resilience, for example,
to climate impact and bushfire risks. In recent years, the Australian
grid has been impacted by bushfires, resulting in multiple lines
out of service and reduced transfer capacity to major load centers.
Climate studies have demonstrated that extreme weather
occurrences will increase over time. When developing REZs,
risks such as these must be considered in the design.
The Network Design
AEMO's ISP highlighted that well-designed REZs should
consider the structure of the network needed to avoid the
application of constraints on generation to manage large
contingency events. For example, if single-easement radial
connections were applied to a large REZ, this would imply
a large single critical contingency size (possibly in excess of
the current largest single contingency size).
The contingency size is critical to the security of the
power system and the management of frequency within operating
standards. A looped or meshed integration of a REZ, if
designed well, could reduce the potential contingency size
and reduce or avoid potential operational limits that may otherwise
need to be applied to generation in the REZ.
Sharing Connection Assets
AEMO's ISP demonstrated that coordinating generator connections
at hubs, rather than connecting on a stand-alone
basis along transmission lines, may provide a more reliable
and cost-effective network connection. The hub connection
reduces capital expenditures by minimizing the duplication
of connection infrastructure. Adequate switching arrangements
to allow for outage flexibility will also minimize the
impact on the transmission network.
Adequate Network Capacity and Voltages
The long-term ultimate arrangement for transmission development
in the area can inform appropriate sizing and voltage
levels at relevant substations. In this way, costs can be optimized
through gains in economies of scale when executing
major construction projects. Most of the substation engineering,
procurement, and construction work can happen at one
september/october 2021
time. This limits the exponential costs of retrofitting expansions
that would otherwise be required in the future.
Through the ISP, AEMO identifies and refines REZ candidates
and prioritizes REZ developments with staging. This
approach results in a functional network design that integrates
REZs with the shared network.
First Steps Toward Implementation
AEMO's ISP identifies strategic investments in transmission
infrastructure and REZs, which, when coupled with low-cost
firming resources, will be the most cost-effective way to add
generation capacity and balance renewable resources. Since
the inaugural ISP in 2018, several individual REZ projects
have progressed through regulatory approval or been funded
by state governments. The New South Wales, Victoria, and
Queensland state governments have all committed to developing
REZs that are components of AEMO's ISP.
Australia's first expansion of the shared transmission network
to unlock a REZ is expected to be the Western Victoria
Transmission Network Project. Originating in the 2018
ISP, this 190-km project was rigorously assessed and will
deliver value to consumers by accessing high-quality wind
resources. Wind plants developed in this area are expected
to provide downward pressure on electricity costs by displacing
brown coal generation. In early 2021, this project
was undergoing environmental effects studies, planning
approvals, and easement acquisition.
Taking a different regulatory approach, the Central WestOrana
REZ Transmission Link project was recommended
in the 2020 ISP. This project gained strong support from the
New South Wales state government and local developers. State
Phase 1
* Development to Help Meet Regional
Energy Targets and Other Policies and/or
* Development Where There Is Good Access
to Existing Network Capacity With Good
System Strength
Phase 2
* Renewable Generation Development to
Replace Energy Provided by Retiring
Coal-Fired Generators That Is Supported
by the Actionable ISP Projects
Phase 3
* Renewable Generation Development to
Accompany Long-Term ISP Projects That
Are Being Created Specifically to Support
These REZ Modifications
figure 6. The REZ development phases. (Source: AEMO;
used with permission.)
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IEEE Power & Energy Magazine - September/October 2021

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