Murraylink: Australia's Longest Underground HVDC Transmission Link

Overview

Murraylink is a high voltage direct current (HVDC) electricity transmission link located in Australia, designed to interconnect the state electricity grids of South Australia and Victoria. The infrastructure spans from Berri in South Australia to Red Cliffs in Victoria, serving as a critical corridor for power exchange between the two regions. Commissioned in 2002, the project was developed by TransEnergie Australia, which operated as a subsidiary of Hydro-Québec during the construction phase. The system is recognized for its engineering scale, holding the distinction of being the world's longest underground transmission system. The initial investment for the project exceeded A$177 million, reflecting the complexity of deploying extensive subterranean HVDC infrastructure across state boundaries.

The operational and ownership structure of Murraylink has evolved since its inception. While APA Group currently serves as the operator, the ownership interests were reorganized in December 2008. At that time, ownership was transferred to the Energy Infrastructure Investments Group (EII). The equity distribution within EII includes APA holding a 19.9% stake, Marubeni holding 49.9%, and Osaka Gas holding 30.2%. Prior to this consolidation, the asset was sold to the APA Group in March 2006 for A$153 million. This transaction marked a shift from the original developer to a diversified ownership model that continues to manage the asset while maintaining APA's operational role. The system remains operational, continuing to facilitate energy transfer between the South Australian and Victorian grids.

Technical Specifications and Operation

Murraylink utilizes high voltage direct current (HVDC) technology to transmit electricity between the South Australian and Victorian grids. The system is characterized by its extensive use of underground cabling, a design choice that distinguishes it from many overhead transmission lines. According to available records, Murraylink is believed to be the world's longest underground transmission system. The infrastructure connects the Berri substation in South Australia to the Red Cliffs substation in Victoria, facilitating cross-border power flow. The project was constructed by TransEnergie Australia, which operated as a subsidiary of Hydro-Québec at the time of development. The total construction cost exceeded A$177 million, reflecting the complexity of laying long-distance underground cables across varying terrain. The system was commissioned in 2002, establishing a critical link for energy exchange between the two states. The technical architecture relies on HVDC Light technology, which employs insulated-gate bipolar transistor (IGBT) converters. This technology allows for efficient power control and flexibility in managing load fluctuations between the two grid systems. The bipolar configuration of the cables enhances reliability, allowing for continued operation even if one pole experiences a fault. The 150 kV operating voltage is optimized for the distance and capacity requirements of the link. The 220 MW capacity enables significant power transfer, supporting both peak demand and renewable energy integration in the region. The underground nature of the cables minimizes visual impact and land use compared to traditional overhead lines, although it requires specialized maintenance and monitoring systems. The system's design reflects the engineering priorities of the early 2000s, focusing on reliability and efficient long-distance power transmission. The use of HVDC Light technology was a strategic choice, offering advantages in terms of converter station size and operational flexibility. The infrastructure continues to play a vital role in the Australian energy landscape, connecting major generation and consumption centers. The technical specifications of Murraylink demonstrate the application of advanced power electronics in long-distance transmission. The system's ability to handle 220 MW of power over 176 kilometers of underground cable is a testament to the effectiveness of the chosen technology. The ongoing operation of Murraylink highlights the durability and efficiency of the HVDC Light system in a real-world application. The technical details of the system are critical for understanding its role in the broader Australian grid infrastructure. The use of IGBT converters allows for precise control of power flow, enhancing grid stability. The bipolar design provides redundancy, ensuring that power can still be transmitted even during partial system failures. The 150 kV voltage level is suitable for the distance and capacity of the link, balancing efficiency and cost. The underground cables are protected by specialized insulation and sheathing to withstand environmental stresses. The system's technical performance has been monitored since its commissioning in 2002, providing valuable data on the long-term reliability of HVDC Light technology. The infrastructure supports the integration of diverse energy sources, including renewable generation, into the state grids. The technical specifications of Murraylink are a key factor in its operational success and continued relevance in the Australian energy sector.

How does the HVDC Light technology work?

Murraylink utilizes high voltage direct current (HVDC) Light technology, a system designed to efficiently transmit electricity over long distances by converting alternating current (AC) from the source grid into direct current (DC) for transmission, and back into AC at the receiving end. This conversion process is managed by voltage-source converter (VSC) stations located at each terminal of the link. The core of these converters relies on insulated-gate bipolar transistors (IGBTs), which act as high-speed electronic switches. By rapidly turning these transistors on and off, the system can precisely control the flow of power and the voltage levels, allowing for stable transmission even when the connected AC grids are not perfectly synchronized.

Voltage-Source Converter Operation

The voltage-source converter system differs from traditional line-commutated converters by using self-commutated devices like IGBTs. In the Murraylink configuration, the AC electricity from the South Australian grid at Berri is fed into the converter station, where the IGBTs rectify the power into DC. This DC power travels through the underground cables to the Red Cliffs terminal in Victoria. There, a second set of converters inverts the DC back into AC, matching the frequency and phase requirements of the Victorian grid. The use of IGBTs allows for independent control of active and reactive power, providing enhanced flexibility and stability to the interconnected systems. This technology is particularly suited for underground cable systems, as it helps mitigate capacitive charging currents that can affect efficiency over long distances.

Advantages of HVDC Light Technology

The adoption of HVDC Light technology for Murraylink offers several operational advantages. The system can transmit power in either direction, allowing for flexible energy trading between South Australia and Victoria. Additionally, the IGBT-based converters enable fast response times to grid disturbances, improving overall system reliability. The technology also supports the connection of weaker grids, as it can provide voltage support and frequency regulation. These features make HVDC Light an effective solution for linking regional electricity networks, enhancing energy security and facilitating the integration of diverse power sources across state boundaries.

What limits the transmission capacity during peak demand?

Construction and Corporate History

Murraylink was constructed by TransEnergie Australia, a subsidiary of the Canadian utility Hydro-Québec. The project involved laying a high voltage direct current transmission link between Berri in South Australia and Red Cliffs in Victoria, connecting the two state electricity grids. The construction resulted in what is believed to be the world's longest underground transmission system. The total cost of the project exceeded A$177 million.

Corporate Ownership Timeline

Following its commissioning in 2002, the asset changed hands in March 2006 when it was sold to the APA Group for A$153 million. In December 2008, ownership of Murraylink was transferred to the newly formed Energy Infrastructure Investments Group, while the APA Group continued to serve as the operator. The ownership structure of the Energy Infrastructure Investments Group consists of APA holding 19.9%, Marubeni holding 49.9%, and Osaka Gas holding 30.2%.

Ownership Structure and Investment

The ownership structure of the Murraylink transmission asset underwent a significant reorganization several years after its initial commissioning. While the infrastructure was originally constructed by TransEnergie Australia, a subsidiary of Hydro-Québec, and subsequently sold to the APA Group in March 2006 for A$153 million, the long-term investment vehicle was established later. This corporate restructuring separated the operational management from the equity ownership, allowing for a diversified investment portfolio while maintaining consistent technical oversight.

Equity Breakdown of Energy Infrastructure Investments Group

The Energy Infrastructure Investments Group was structured to combine Australian operational expertise with significant Japanese capital investment. The ownership stakes within EII are distributed among three primary entities, reflecting a strategic partnership designed to leverage regional market knowledge and international financial stability. The APA Group retains a 19.9% equity share in the group. Despite holding a minority stake compared to its Japanese partners, APA’s role remains central to the asset’s day-to-day management.

The largest shareholder in the Energy Infrastructure Investments Group is Marubeni, which holds a 49.9% ownership interest. Marubeni, a major Japanese general trading company (sogo shosha), provides significant capital backing and strategic market access. The third partner is Osaka Gas, which holds a 30.2% stake in the group. Osaka Gas, a prominent urban gas utility in Japan, brings energy sector specialization and long-term investment horizons to the Murraylink asset. Together, these three entities form the complete ownership structure of EII, with the percentages summing to the total equity of the investment vehicle.

Continuity of Operational Management

A critical aspect of the 2008 ownership transfer was the continuity of operational responsibility. While the equity ownership shifted to the joint venture structure of EII, the APA Group continued to serve as the operator of the Murraylink transmission link. This arrangement ensures that the technical expertise and grid management capabilities originally developed by APA during the initial acquisition phase remain intact. The separation of ownership (EII) and operation (APA Group) allows for specialized focus: EII manages the financial performance and strategic investment decisions, while APA handles the engineering, maintenance, and grid integration aspects of the high voltage direct current link between Berri, South Australia, and Red Cliffs, Victoria. This dual structure has provided stability to the asset since its commissioning in 2002, supporting its status as a critical interconnector between the two state electricity grids.

Why it matters

Murraylink holds a distinct position in global energy infrastructure as the world's longest underground transmission system. This distinction is significant for high voltage direct current (HVDC) engineering, demonstrating the viability of subterranean corridors for interconnecting major power pools over extended distances. The link connects the electricity grids of South Australia and Victoria, specifically running between Berri and Red Cliffs. By bridging these two state systems, Murraylink provides a critical conduit for power exchange, enhancing the reliability and flexibility of the broader Australian National Electricity Market. The underground nature of the line minimizes visual and spatial impacts compared to overhead alternatives, a factor that contributed to its selection despite the higher initial capital expenditure.

Financial and Operational Context

The project represented a substantial financial commitment for its era, costing more than A177millionuponcommissioningin2002.ThisinvestmentwasundertakenbyTransEnergieAustralia,asubsidiaryofHydro−Queˊbec,whichservedastheprimarybuilder.ThefinancialstructureofMurraylinkevolvedshortlyafteritsoperationaldebut.InMarch2006,theassetwassoldtotheAPAGroupforA153 million. This transaction marked a shift in ownership strategy, aiming to optimize returns on the infrastructure asset. Subsequently, in December 2008, ownership was transferred to the Energy Infrastructure Investments Group (EII). Under this structure, APA Group retained a 19.9% stake, while continuing to serve as the operator. The remaining ownership was divided between Marubeni, holding 49.9%, and Osaka Gas, holding 30.2%. This diversified ownership model reflects the strategic importance of Murraylink to both domestic and international energy investors. The continued operation by APA Group ensures technical continuity, leveraging their expertise in HVDC transmission management. The link remains operational, fulfilling its role as a key interconnector between the two states. Its existence supports grid stability and facilitates the flow of electricity from generation-rich areas to demand centers, underscoring the long-term value of the initial A$177 million investment.

See also

• Devils Gate Dam and Power Station
• Kurnell Refinery: History, Operations and Decommissioning
• Liapootah Dam and Power Station: Infrastructure on the Nive River
• Koombooloomba Hydro Power Station
• Taryn Lane: Community Wind Energy Leadership in Australia