Just 220 kilometres north of Adelaide, heading towards Broken Hill on the Barrier Highway, lies some of the most rugged, windswept and rain-drenched land in South Australia. The area around Hallett is home to what will be Australia’s largest wind farm, pumping enough renewable energy into the grid to support the electricity needs of 60,000 average Australian households per year.

Scheduled for completion in the first half of 2008, Suzlon Energy Australia (SEA) was awarded the contract by AGL Energy to build the 14 kilometre stretch of 45 turbines on the Brown Hill ridge. When commissioned, Suzlon’s turbines will have a total capacity of 94.5 megawatts (MW) – 3.75 MW more than the country’s largest operational wind farm at Wattle Point on the state’s Yorke Peninsula.

SEA has contracted Schneider Electric to provide customised kiosk substations at the base of each turbine. “We’ve worked with Schneider to design the kiosk substation,” says SEA Chief Operations Officer Chris Judd. “They have done this sort of thing [wind farms] before, but not at the voltage rating we need or with the combination of equipment. We are using various components, including low and medium voltage switching gear.”

Schneider Electric National Business Development Manager Joe Riitano explains the configuration. “The wind turbines at Hallett Wind Farm generate 690 volts, which flows into the switchgear in the kiosk. The power is then feed into a 2.5 megavolt ampere (MVA) transformer, which boosts the voltage from 690 volts to 33 kilovolts (kV). The 33 kV end of the transformer is protected by Schneider Electric DVCAS circuit breakers. So, under the one enclosure we have 690 volt switchgear, a 2.5 MVA transformer, and 33 kV MESA switchgear.”

“Because of the size of the wind farm, the energy losses are much smaller at 33 kV than at lower voltages,” says Mr Riitano. And at the higher voltage, cables with smaller conductors can be used. “With the price of copper and aluminium, which are the most common conductors used for cables, it’s more economical to go with the higher voltage.”

High availability

Suzlon Energy Electrical Engineering Manager Serel Ogten says the 33 kV MESA switchgear is specifically designed for wind farm applications.

“The additional switches provide more functionality than has traditionally been available in wind farm applications. Before now, wind farms were not able to isolate turbines within a string; so an underground cable failure anywhere along the string would shut down all turbines until repairs were complete. With the Schneider switchgear, if we have, for example, a string of 12 turbines and we have a cable failure at turbine three, we can continue to operate nine turbines.”

The Schneider Electric 33 kV switchgear supplied also uses circuit breaker (CB) protection for the transformer. Ferroresonance, or unstable high voltage, typically causes equipment to fail, so CB protection is a way of minimising down time.

“CB protection was the preferred solution,” says Mr Ogten, “as it helps to mitigate ferroresonance, which can occur with oil-immersed fused transformer protection. It ensures that all three phases trip during a fault and helps to mitigate switching delays between phases.

Windproof enclosures

The size and location of the Hallett Wind Farm imposed some unique constraints for Schneider Electric to work within. The design of the enclosure has been carefully considered to make sure it can withstand high winds.

Mr Riitano explains that on a normal kiosk substation, there are two doors at either end. “At a wind farm, if you open one of these doors it acts like a sail. So in designing the enclosure, we have reduced the size of the doors, we increased the number of doors – six instead of two. We also used a thicker gauge of material to create a stronger, sturdier enclosure.”

Citect, a subsidiary of Schneider Electric, has been working closely with the parent company to design, implement, and commission the wind farm’s SCADA system. The CitectSCADA product offers a host of connectivity options. Not only will the SCADA system need to communicate to standard field devices via DNP3, Modbus, OPC and IEC60870-5-103 protocols, but it will also need to connect to proprietary wind turbine control systems, meteorological stations and the National Electricity Market Management Company system.

The SCADA system also spells good news for AGL operations staff. While the wind farm will be controlled on site at Hallett, the SCADA system will allow AGL staff to remotely monitor and control the wind farm from the comfort of their less-exposed operations centre at Mount Beauty in Victoria.