|State||New South Wales|
|Owner||Energy Infrastructure Investments|
|Manufacturer of conductor/cable||ABB|
|Manufacturer of substations||ABB|
|Type of current||Light HVDC|
|Total length||59 km (37 mi)|
|Power rating||180 MW|
|AC Voltage||110 kV (Bungalora), 132kV (Mullumbimby)|
|DC Voltage||±80 kV|
|No. of circuits||3|
Terranora interconnector (formerly named Directlink) is a high voltage direct current electricity transmission line between Mullumbimby, New South Wales ( ) and Bungalora, New South Wales ( ) in Australia. It is one of the two interconnections used to trade electricity between New South Wales and Queensland (the other one is the Queensland – New South Wales Interconnector). For environmental protection reasons it is implemented as underground cables.
The interconnector was developed by a joint venture of NorthPower (later Country Energy), TransÉnergie–a subsidiary of Hydro-Québec, and Fonds de solidarité FTQ. 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 the first time that transmission systems of New South Wales and Queensland were linked. The construction cost 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 completed 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 on 10 March 2006.
Terranora interconnector is a 59-kilometre (37 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 to a 132 kV alternating current transmission grid and in Queensland to 110 kV alternating current transmission grid.
The total rating of the interconnector is 180 MW minus transmission losses. The maximum net electricity flow (taking into account transmission losses) is around 170 MW. If one pair of cables malfunctions, the available capacity is around 115 MW. If 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 in the New South Wales direction is the thermal ratings of the Terranora–Mudgeeraba 110 kV lines and Mullumbimby–Dunoon 132 kV lines, and for flow in the Queensland direction is the thermal ratings of the 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. 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.
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