Murraylink

The Murraylink HVDC project is a significant underground power transmission system connecting the electricity grids of Victoria and South Australia. When it was commissioned in 2002, it was the world's longest underground power transmission system, spanning approximately 180 kilometers between Berri in South Australia and Red Cliffs in Victoria.

Technical Specifications

Murraylink utilizes 3-level Voltage Source Converter (VSC) technology developed by ABB (now Hitachi Energy). The link operates in a symmetrical monopole configuration, consisting of two HVDC cables buried underground. The system has an operating voltage of ±150 kV DC and a transmission capacity of 220 MW.

The converter stations at each end of the link employ insulated-gate bipolar transistors (IGBTs) to convert electricity between alternating current (AC) and direct current (DC). These stations connect to the local AC grids at different voltages: 220 kV at Red Cliffs in Victoria and 132 kV at Berri in South Australia.

Power Flow and Reactive Power Control

Murraylink allows bidirectional power flow between the two states, with the Australian Energy Market Operator (AEMO) determining the transmission through its central dispatch process. The system can provide reactive power support to the AC networks, with a range between +140 MVAr and -150 MVAr at each end. This capability is particularly important for supporting the weak Berri network at the edge of the South Australian system.

Cable System

The HVDC Light transmission system comprises extruded, oil-free cables buried in the ground. The total length of DC cable used in the project exceeds 360 km, with each cable being a single core design.

Converter Stations

The converter stations at Red Cliffs and Berri contain various components, including transformers, phase reactors, AC filters, and cooling systems. The stations use a three-level VSC topology, which requires harmonic filters to smooth the sinusoidal AC voltage waveform produced by the high-frequency pulse-width modulation (PWM) switching.

Environmental and Engineering Considerations

The choice of VSC-based HVDC technology for Murraylink was influenced by several factors, including the ability to use buried cables in existing rights-of-way, reactive power control capabilities, compact converter station layout, and a modular, factory-tested design allowing for rapid field testing and commissioning.

Performance and Limitations

While Murraylink is rated at 220 MW, its actual operating capacity can be constrained during periods of high demand due to limitations in the transmission infrastructure at either end. These constraints relate to thermal overload of transformers or transmission lines in the Riverland area and western Victoria.

Recent Developments

As of 2022, there have been discussions about upgrading the Murraylink system. One option under consideration is replacing the current IGBT-based converters with more modern Modular Multi-level Converter (MMC) technology. This upgrade could potentially reduce losses, improve reliability and thermal performance, and future-proof the HVDC system.

The Murraylink project has received several Australian state and national awards for both environmental and engineering excellence, highlighting its innovative approach to power transmission and its importance in the Australian electricity market.