Power grid main characteristics
The National Electricity Market (NEM) is an interconnected electricity market linking five regional market regions (namely, Queensland, New South Wales (including the Australian Capital Territory), Victoria, South Australia, and Tasmania). The NEM operates on one of the world’s longest interconnected power systems of around 5,000 kilometres. It has a total connected generation capacity of more than 50,000 MW.
In the NEM, wholesale electricity generation is transported via high-voltage transmission lines to electricity distributors, who deliver it to homes and businesses. The transport of electricity from generators to consumers is facilitated through a “pool”, or spot market, where output is aggregated and scheduled at five-minute intervals to meet demand.
Victorian Declared Wholesale Gas Market (DWGM) arrangements apply to the Victorian Declared Transmission System (DTS), which transports gas to the majority of Victoria’s households and businesses. More than 1.9 million Victorian customers consume more than 202 PJ a year – Australia’s highest residential gas usage.
The Short Term Trading Market (STTM) is a wholesale market designed to facilitate short-term gas trading using market-driven, short-term (daily) prices. The STTM allows market participants to purchase any additional gas supply they need, on top of their contractual arrangements. The STTM operates at demand hubs located in Adelaide, Sydney and Brisbane, which act as transfer points through which gas is transmitted and delivered to distribution networks.
Major incidents & preventive measures
Tropical Cyclone Yasi
On 3 February 2011, Tropical Cyclone Yasi crossed the north Queensland coast, causing extensive damage to the local 132 kV transmission and distribution networks, and the loss of supply to a number of substations. However, the 275 kV transmission network remained intact and the power system in a secure operating state. Restoration of the 132 kV transmission network was completed by 11 February 2011.
Victoria experienced extreme weather conditions on Saturday 7 February 2009. Bushfires and lightning caused seven major transmission lines to trip out of service, leading to the separation of the Victoria and New South Wales regions.Following the bushfires, AEMO (then the National Electricity Market Management Company (NEMMCO)) found that protection systems on the power system operated correctly to protect the assets and ensure safety under very extreme conditions. Restoration of the power system was carried out according to the asset owner’s restoration policy, however care had to be taken when restoring transmission lines as firefighting crews were present.NEMMCO found that while its power system operators faced a number of challenges when managing power system security on 7 February 2009, including simultaneous outages of a number of key Victorian transmission lines, resulting in significantly reduced transmission network capability, actions taken to manage power system security were appropriate.