It takes more than a tall tower and a few huge blades to make a wind turbine go. Hundreds of different components are required, such as gearboxes, generators, shafts, bearings, sensors, motors and controllers. And, all those components, which are typically housed in a large nacelle, must be able to withstand constant vibration and temperature extremes.
“Manufacturers of turbines are in a very tough business,” says Mike Nager, industry marketing manager-Americas at Phoenix Contact Inc., which supplies transient suppression products to limit potential damage caused by lightning. “On one hand, the application requirements are demanding since these machines are often located in remote areas, experience high vibration and wide temperature fluctuations.
“The components used within the turbines must be able to perform in these conditions-something that requires extensive design and manufacturing expertise, and eliminates lesser products from consideration,” claims Nager. “[Space constraints also pose unique challenges to engineers]. The space available to dedicate to surge arresters is tight, so even though they have to channel very large energy levels, it has to be done in a product that is as small as possible.
“On the other hand, electricity produced from wind is still perceived to be quite expensive when compared to traditional generation technologies, and the cost pressures on reducing to the price of the machine is intense,” adds Nager. “The complexity of a wind turbine can be compared to that of a jet plane where high-precision components are needed-but at a relatively low price.”
Blade control systems are a critical component in all wind turbines. For instance, a pitch system is used to control the rotation of the blades. “This is necessary to control the speed of the turbine and to safely feather the blades in adverse weather conditions,” says Mauro Gnecco, North American wind market manager at Moog Industrial Group. The company’s PITCHmaster II servodrive, which is housed in a wind turbine’s rotating hub, supplies critical information about rotor speed, rotor position and vibration.
Hydraulics also plays an important role in motion control. Blade pitch control, primary braking and secondary braking (for both the rotor and the azimuth) are some of the main applications of hydraulics in a wind turbine.
“Each of these applications uses a hydraulic power pack (HPU) of varying complexity, size and capacity to drive an actuator,” says Brad Nicol, an applications engineer with the hydraulic pump div. of Parker Hannifin Corp. “HPUs typically consist of components such as pumps, valves, sensors, tanks, electric motor and hydraulic fittings.
“Linear actuators (hydraulic cylinders) are used for blade pitch, as well as the service brake on a turbine,” Nicol points out. “An azimuth (yaw) drive employs a rotary actuator (hydraulic motor) and the secondary brakes, both for azimuth and rotor functions, employ hydraulic brake calipers. Some turbine manufacturers are also considering the use of hydrostatic transmissions as part of the system to transfer power from the turbine rotor to the generator.”
Every component used in a wind turbine must perform flawlessly, because downtime and service can be quite expensive. According to Nicol, all products must “meet or exceed reliability standards, reduce service intervals and downtime, and maximize profitability for the asset owner. Special testing and documentation is often required. The corrosion protection for the systems is similar to what we use with our marine customers.”
“Reliability is key,” adds Gnecco. “The life expectancy for a wind turbine is 20 years. Design through supply chain development [must] tie together to provide a system that [meets those] demanding needs.
“The wind power industry is reaching maturity very quickly, and the slow economy of the past year has given manufacturers the opportunity to analyze their processes and optimize their designs,” explains Gnecco. “The wind market will offer suppliers similar challenges already experienced in the automotive industry . . . [such as] integration of the supply chain in the manufacturing process, attention to reliability, lead time and cost. Also, we see the physical proximity of manufacturing as a key element for a qualified offering to wind turbine manufacturers.”
Moog’s products are built to order. Manufacturing engineers use lean concepts to eliminate waste, in addition to statistical techniques to monitor and control key process attributes.
“Our internal processes utilize practices that reduce operator fatigue and error,” says Gnecco. “Tools such as pneumatic torque drivers with SPC output are being considered.”