By Les Brand, Amplitude Consultants managing director and co-founder and Adam Peard, Amplitude Consultants manager of strategic and advisory services
The Australian transmission network has evolved over the last century to transmit power from the large, centralised generation sources to the major load centres in the Australian large and capital cities, as well as to the location of energy intensive industries. Power stations have tended to locate near fuel sources to reduce fuel transport costs, such as coal mines and gas supplies. This has created localised areas of significant generation which services load through high capacity AC transmission networks from these areas.
Grid-connected renewable generation sources, like wind and solar power stations, have differing needs in terms of fuel supply, geography and land availability. This often incentivises renewables to connect in different network locations requiring the transmission system to adapt, or requiring long and costly connection arrangements. With the relentless pace of new entrant renewable generation, it can be difficult for network augmentation to keep pace, and in certain locations constraints on generation output due to network limitations have become significant.
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Although the location of generation sources is becoming more diverse, system demand remains relatively localised and power still needs to get to the same locations. The NEM Renewable Energy Zones (REZ) are maturing, incentivising generation to cluster where fuel resource is favourable and in locations where high capacity network augmentation between the REZ and the bulk transmission system could be economic. This is not without its challenges though, as the bulk transmission system can then become the bottleneck, requiring extensive and costly augmentation with long lead times and considerable regulatory uncertainty.
Injecting REZ generation capacity directly into major demand centres seems a sensible option to explore, providing a bypass of existing and emerging bottlenecks in the transmission where management of future congestion risk is of major concern or in other words, creating a high-capacity parallel path to “shunt” power and offload the parallel transmission network.
One technology that could make this possible is High Voltage Direct Current (HVDC).
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HVDC is not a new technology. HVDC transmission has been in service around the world since the mid-1950s. Recent technological developments over the past few decades, including the development of Voltage Source Converters (VSC), have led to this technology being available for increasingly more applications, including operation in weaker networks and the long-distance transmission of renewable energy. VSCs inherently have the ability to generate and absorb reactive power, offering voltage control and stability capability for little or no additional cost, and the controllability of these HVDC systems provides the flexibility to control power flow across parallel AC transmission lines and respond quickly to outages experienced by those lines. Overseas, HVDC systems have been developed with control functions to emulate active power flow operation of an AC transmission line while providing the various other benefits of HVDC transmission and enhanced response in the case of network contingencies. HVDC transmission towers are typically smaller and therefore cheaper to build and offer better visual amenity than AC towers for the same power capacity. Other countries are exploring and implementing the conversion of AC transmission lines to HVDC systems to benefit from the higher power transfers possible without installing new transmission towers.
The implementation of such “transmission superhighways” could allow the bulk of the generation to get to the major load centres directly with lower losses, while leaving the parallel AC transmission network with less congestion to allow generation and loads to “tap in” along the way. This solution can be visualised as a highway bypass, allowing the bulk of traffic to bypass the area while still keeping the roads in and within the bypassed area available for local traffic to enter and leave with less congestion.
So, as we grow our transmission network to be ready for more renewable energy, the question has to be asked—is Australia ready for these HVDC transmission superhighways?