Western Australia faces the unusual situation of having to transmit large quantities of power to the Perth region, from cogeneration and other on-site generation plants located at remote mines and industrial facilities. This raises its own electrical distribution problems, reports Drew Robb
In many regions, on-site power generation plays a secondary role in meeting electrical needs. It helps the host facility cut its utility bills and add to the area’s generating capacity, but most of the power comes from hydro or thermal plants built to serve the general public. Western Australia is a big exception; cogeneration and on-site power generation comprise the key elements of meeting that state’s rising power demands.
The state faces several challenges. In addition to the rise in per capita electrical consumption, Western Australia’s population is growing at an annual rate of 2%, and the economy at twice that rate. These combine to add about 120 MW to the demand every year. While it is turning to renewable resources, such as the 180 MW Emu Downs Wind Farm that opened in November 2006, the state is increasingly reliant on power generated at the area’s mines and foundries. Roughly half of the state’s 4000 MW of capacity currently comes from such facilities, and the newly restructured, independent power market gives facility owners even greater incentive to install on-site generators.
‘Supply of electricity to major loads is fully competitive with open access over the transmission system,’ says Patrick Peake, manager of system capacity for the Independent Market Operator, which handles the electricity market for the South West Interconnected Service (SWIS). ‘A significant number of independent power operators are now operating within the wholesale electricity market with a variety of generation types, sizes and fuels.’
Many of these sites, however, are far from the primary load centre in the capital city Perth. To make this arrangement work, therefore, requires significant beefing up of the grid to accommodate the long-range transmission from remote sites to the city. This also requires adding voltage support near Perth to avoid fluctuations and blackouts. But with these changes fully addressed, Western Australia can continue its move to more efficient cogeneration.
Planning for peak demand
Western Australia presents a dichotomy in terms of providing electricity. On the one hand, three quarters of the state’s population is nicely clustered around Perth. The rest of it, however, is scattered around the state’s remaining 2.6 million km2 at a density of around one person for every 5 km2. Further complicating the issue, much of the area’s electrical production and consumption takes place at the mines, refineries, mills and ports that dot the Western Australian landscape and drive much of its economic growth.
‘In planning for electrical demand, major loads such as mines and refineries are specifically identified and accounted for,’ says Peake.
This has put constraints on the SWIS, the grid carrying most of the load in Western Australia. According to Western Power’s Capital and Operating Expenditure Program for the South West Interconnected Networks, ‘the present supply/demand balance on the SWIS and the transmission system underpinning this are at a pivotal point in time. The SWIS system is approaching a time when it will be requiring significant additional capacity to maintain system security standards, and at the same time there is a need for new generation input to the network.’
Key mine/refinery power sources
According to data from the Western Australia Office of Energy, by the end of 2007 mines and refineries in the state had an installed generating capacity in excess of 2200 MW.
As of June 2006, SWIS had 3600 MW capacity with another 1100 MW scheduled to come on line by October 2008. This additional generation, however, is being installed at locations hundreds of kilometres away from the Perth load centre. To bridge the distance between generation and consumption requires stringing new transmission lines, as well as adding reactive power support near the city to stabilize the grid and prevent voltage collapse. Verve Energy’s 576 MW Pinjar plant near Perth, for example, has three GE Frame 6 gas turbines that are used as synchronous condensers, courtesy of clutches from SSS Gears of England.
Long distance electrons
While Perth used to generate most of its electricity locally, recent years have seen a shift. One factor driving this change is the location of available fuel. For example, the coal mines in the area around Collie are about 225 km south-east of Perth. The simple fact is that it is far cheaper to transmit the generated electricity from Collie to Perth than it is to move the coal to Perth and burn it there. So Verve Energy has an 800 MW and a 330 MW plant in Collie, and Griffin Power is bringing another 208 MW on line there late next year. Together, these plants account for nearly one third of the power carried over the SWIS grid.
Meanwhile, the 130 million litre per day Kwinana desalination plant that came fully on line last spring gets its power from the 180 MW Emu Downs Wind Farm, located about 200 km north of Perth at a spot where wind speeds peak at the same time of day that electrical demand spikes.
The other factor is that, especially with the newly deregulated market in the state and split up of Western Power, there are more opportunities for cogeneration (combined heat and power) facilities at refineries that require process steam.
‘Cogeneration plants have a much higher efficiency than building separate plants to provide steam and electricity,’ says Peake. ‘Cogeneration has an efficiency of around 80%, whereas the best combined-cycle electricity generation plants operate at about 50% efficiency.’
The Pinjarra refinery
Over the past two years, for example, Alinta Energy (acquired by Babcock & Brown Power in August 2007) has brought two new 140 MW gas turbines on line at Alcoa’s alumina refinery in Pinjarra, well to the south of Perth. ‘The alumina refineries were initially built to meet their own power supplies with on-site generation, so were essentially neutral to the grid,’ says Peake. ‘More recently, at Worsley and Pinjarra, cogeneration plants have been built which supply steam to the host refinery and power to the grid.’
Bauxite ore conveyor at Pinjarra
Alcoa World Alumina Australia owns three refineries in Western Australia – Pinjarra, Wagerup and Kwinana – to process the bauxite mined at Huntly and Willowdale in the Darling Range. Together, these three plants process nearly one-sixth of the world’s alumina. Alcoa is conducting a AUS $550 million (US $509 million) upgrade to boost the energy efficiency and reduce emissions from Pinjarra. The plant uses about 90 MW of electricity, as well as consuming hundreds of tonnes of steam per hour. The project includes raising alumina production 17% to 4.2 million tonnes per year, but finances and environmental concerns also come into play. Part of the strategy, therefore, included installing a cogeneration facility, built by Alinta and now owned by Babcock & Brown Power.
Disaggregation in Western Australia
In April 2006, pursuant to the Electricity Corporations Act 2005, the Western Australia government split its electrical monopoly – Western Power – into four government-owned businesses. Verve Energy operates the five major power stations as well as wind farms, biomass and solar facilities. Horizon Power is a regional power corporation servicing about 30 towns and communities. Synergy is an energy retailer with more than 870,000 customers. There is also still a corporation going by the name Western Power, but this is a transmission and distribution company, not a successor to the original Western Power.
Bauxite mining at the Huntley Mine
‘Cogeneration power plants are highly efficient and are of interest to any kind of industry which is in need of process steam,’ says Wolfgang Steffens, general manager for power projects for Alinta Energy. Cogeneration in this case consists of combining the processes of generating steam and electricity in order to get the greatest return from the fuel burned. In addition to being more cost effective, it helps Alcoa reduce its greenhouse gas emissions by 270,000 tonnes per year. The plant has two 140 MW Mitsubishi gas turbine/generator sets – the first commissioned in 2006 and the second in 2007 – together with a heat recovery steam generator (HRSG). The exhaust from the turbine converts water into steam. Supplementary duct firing designed by Downer Engineering further raises the steam temperature. Babcock & Brown Power sells the electricity generated into the SWIS grid, while the 200–400 tonnes per hour of steam each unit produces is sold to Alcoa.
Clutches are designed to ensure synchronization between turbine and generator
‘Performance test results show an over-performance of the gas turbine, which means the unit exceeded the expectation,’ says Steffens. Based on this success, Alinta proposed adding another 350 MW at Alcoa’s plant in Wagerup, which lies to the south of Pinjarra. That dual-unit plant went live in 2007.
Building major power plants in locations like Pinjarra, Wagerup and Collie makes a lot of sense from a generation point of view, as it cuts fuel transport costs and extracts more usable energy per unit of fuel burned. However, it does raise significant problems with regard to power distribution. As the Western Energy expenditure report cited earlier describes it: ‘The bulk transmission network that underpins this generation capacity, allowing the reliable supply from the generation to the load centres, will consequently require a significant level of network investment to allow the system to accommodate the increased generating capacity and still achieve the performance levels specified in the Technical Code.’
In addition to requiring additional transmission lines, it raises the need for reactive power to provide voltage support on the network. Components of AC systems produce and consume both real and reactive power. Real power accomplishes useful work and is a product of the voltage and current. The voltage and current, although operating on the same frequency, are not in phase with each other. There is, however, an average power level which is measured in volt-amperes or watts.
Reactive power is measured in volt-amperes reactive (var) which expresses the maximum value over a cycle, rather than the average. The var can be positive or negative, depending whether the current peaks before or after the voltage. Although reactive power doesn’t perform actual work, it is needed to provide voltage support and system reliability. Consuming reactive power lowers the voltage, while supplying it raises the voltage. In addition to preventing catastrophic voltage collapses, it also increases transmission efficiency, boosting the amount of real power that can be transmitted over a line.
Generators can produce both real and reactive power. Real power travels well over long distances, which is a major reason why AC is used rather than DC power. Reactive power, on the other hand, does not travel over long distances, so the generators at Pinjarra, Collie, Wagerup and Emu Downs cannot provide the reactive power needed to support voltage levels in Perth. Western Power described the situation in its 2006 Transmission and Distribution Annual Planning Report: ‘Firstly, the four 330 kV transmission lines between the south-west generation sources and the Perth metropolitan area are all around 200 km long. 330 kV lines of this length can transfer no more than 500 MW of power each before voltage stability limits begin to constrain their power transfer capacity. To maintain stable and secure network operation at loading levels above 500 MW, reactive power support is needed.’
The reactive power could normally be supplied by generators within the city. However, the remote generators are more efficient and so are replacing the ones in Perth. As Western Power’s report states: ‘Most usually, this displaced generation is located near to the Perth metropolitan area and, due to its proximity to the load, it would normally provide dynamic reactive power support to stabilize the network during faults. When this generation is displaced, the reactive power support normally provided by it needs to be sourced from elsewhere.’
Western Power and the SWIS have therefore been taking actions to add transmission lines and reactive power sources. According to the SWIS expenditure report: ‘In 2004/05 and 2005/06 investment increased to construct the KEM-KW 91 330 kV transmission line, to establish Guildford Terminal and to provide reactive power support to the network to accommodate new generators at Kemerton, Pinjarra and Walkaway.’
One action that Western Power took last year to address this issue was to modify some of its generators to provide the needed reactive power by operating as synchronous condensers – generators that are synchronized to the grid and providing the reactive power needed to stabilize the grid.
Reactive power support
Verve Energy, the company that took over Western Power’s generating assets, owns a 576 MW plant in Pinjar, a town at the northern end of the Perth metropolitan area. The Pinjar Gas Turbine Power Station contains nine General Electric Frame 6 gas turbines. These turbines are normally idle, but can be brought on line in 15 minutes when power demand rises. These types of generators are ideal for use as synchronous condensers: they are idle most of the time and they are located near the city. Western Energy, when it installed the generators nearly 20 years ago, ordered three of them with clutches from SSS Gears.
The clutches are designed so that when the turbine is moving faster than the generator, the clutch automatically engages and the turbine drives the generator. Then, once the generator is up to speed and synchronized to the grid, the turbine shuts down and the clutch automatically disconnects the turbine from the generator. The generator then continues spinning using power from the grid and providing dynamic reactive power. Not having to keep the turbine spinning as well cuts down power and maintenance costs.
Given the increasing need for reactive power in Perth, last year three more of the generators were retrofitted with size 194T SSS clutches which were incorporated in the load gear made by Flender Graffenstaden in Strasbourg, France. ‘That was due to modelling done by Western Power indicating that the system required them to operate as synchronous condensers,’ says Peter South, Manager of Verve Energy’s Gas Turbines Branch.
More work still needs to be done to provide both the real and reactive power in Western Australia. The government’s recent proposal to ban incandescent light bulbs doesn’t come close to offsetting rising demand in other areas. This year the Boddington Gold Mine will pull another 180 MW out of the grid, which, Peake says ‘represents about a full year’s load growth’ for the entire SWIS system. But by addressing the interconnected issues of generation, transmission, distribution and voltage support, this growth can be accommodated without compromising power quality and reliability.
Drew Robb is a US-based writer on energy.