Terranora interconnector (formerly named Directlink) is a high voltage direct current electricity transmission line between Mullumbimby, New South Wales

Mullumbimby, New South Wales

Mullumbimby is a town in the Northern Rivers region of New South Wales, Australia in Byron Shire, and is colloquially referred to as The Biggest Little Town in Australia. It lies at the foot of Mount Chincogan in the Brunswick Valley about from the sea...

 (28°34′15"S 153°27′8"E) and Bungalora, New South Wales (28°15′20"S 153°28′20"E) in Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

. It is one of the two interconnections used to trade electricity between New South Wales

New South Wales

New South Wales is a state of :Australia, located in the east of the country. It is bordered by Queensland, Victoria and South Australia to the north, south and west respectively. To the east, the state is bordered by the Tasman Sea, which forms part of the Pacific Ocean. New South Wales...

 and Queensland

Queensland

Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...

 (the other one is Queensland – New South Wales Interconnector). For environmental protection reasons it is implemented as underground cables.

History

The interconnector was developed by a joint venture of NorthPower (later Country Energy

Country Energy

Country Energy is a retail subsidiary of Origin Energy. The corporation was formally owned by the Government of New South Wales. It provides natural gas and electricity to retail customers in New South Wales, Victoria, Queensland, South Australia and the Australian Capital Territory.-History:On 1...

), TransÉnergie–a subsidiary of Hydro-Québec

Hydro-Québec

Hydro-Québec is a government-owned public utility established in 1944 by the Government of Quebec. Based in Montreal, the company is in charge of the generation, transmission and distribution of electricity across Quebec....

, and Fonds de solidarité FTQ

Fonds de solidarité FTQ

The largest labour-sponsored fund in Canada, the Fonds de solidarité FTQ is a Québec development capital organization whose overriding mission is to invest in local businesses to further the economic development of all the regions of...

. The reason behind the interconnector was the power shortage in Southern Queensland and surplus capacities in New South Wales. It was commissioned in December 1999 and it started operations in April 2000. It was for the first time to link transmission systems of New South Wales and Queensland. The construction costed US$70 million.

In December 2006, it was announced that the cable will be purchased by Australian Pipeline Trust, a part of APA Group, for US$133 million. The transaction was closed in February 2007. In December 2008, ownership of the interconnector was transferred to the Energy Infrastructure Investments Group, although APA Group remained the operator.

Originally, the interconnector operated as a market network service. However, on 6 May 2004 an application to convert it to a regulated network service was submitted. The application was approved by the Australian Energy Regulator

Australian Energy Regulator

The Australian Energy Regulator is the regulator of the wholesale electricity and gas markets in Australia. It is part of the Australian Competition and Consumer Commission and enforces the rules established by the Australian Energy Market Commission....

 on 10 March 2006.

Technical description

Terranora interconnector is a 59 kilometres (36.7 mi) bipolar HVDC cable route. The system has three static inverters at each terminal, and three pairs of bipolar transmission cables. Each pair of cables operates at +/-80 kV and transmits 60 MW. In New South Wales it is connected with a 132 kV alternating current

Alternating current

In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....

 transmission grid and in Queensland with 110 kV alternating current transmission grid.

The total rating of the interconnector is 180 MW minus transmission losses. The maximum net electricity flow (taking account transmission losses) is around 170 MW. In the case of disfunctioning of one pair of cables, the available capacity is around 115 MW. It two pairs of cables are out of service, the capacity is around 57 MW. However, in some cases for a limited time period the interconnector has operated in an overloading mode for up to 250 MW. The limiting factor for flow to New South Wales direction is the thermal ratings of Terranora–Mudgeeraba 110 kV lines and Mullumbimby–Dunoon 132 kV lines, and for flow to Queensland direction is the thermal ratings of Lismore–Dunoon 132 kV lines.

HVDC was chosen for this project for reasons of low environmental impact of the transmission line, and the ability of the IGBT transistor converter stations at each end to accurately control both real and reactive power

AC power

Power in an electric circuit is the rate of flow of energy past a given point of the circuit. In alternating current circuits, energy storage elements such as inductance and capacitance may result in periodic reversals of the direction of energy flow...

. Individual water-cooled IGBT modules are rated at 2.5kV and 500 A, with multiple units connected in series to achieve the required voltage rating.