Three generator designs serve many turbines

ABB says it has developed permanent magnet (PM) generators for applications that call for direct drives, and medium and high-speed. The electrical performance of individual generators can be tweaked for best performance in cooperation with the wind-turbine OEM. For a closer look:

A low-speed gearless design works best in direct-drive applications. The turbine and generator form a compact and structurally integrated unit. The design is said to give free access to all parts for easy installation and maintenance. The simple and reliable low-speed rotor without separate excitation or cooling system results in minimum wear, reduced maintenance requirements, lower life-cycle costs, and a long lifetime.

A medium speed PM generator provides a compact low-speed system. The turbine main bearing and PM generator combined with a single-stage gear box to work at high efficiency and require little maintenance. This design features a simple and reliable low-speed generator rotor without separate excitation or cooling systems. The designs result in less wear, reduced maintenance requirements, lower life cycle costs, and a long lifetime.

And the third design arrangement is a high-speed PM generator similar to a doubly-fed version with even smaller space requirements. It is said to package high power in a small size. Its typical speed range is from 1,000 to 2,000 rpm using a 6 or 8-pole generator. Other pluses are a mechanically identical design to mainstream equipment but without slip rings.

ABB also offers wind turbine generators in conventional synchronous versions.

Efficient generator stays cool and does not cog

Clean Energy Technologies, Calgary, Alberta, Canada  is said to have developed a generator for wind turbines that is more efficient than existing designs. The company’s Axial Flux Permanent Magnet (AFPM) generators work at high efficiencies and produce more power at lower wind speeds due to a coreless design. The generators eliminate traditional cogging issues which makes them well suited for wind-turbine applications.

Traditional or radial-flux permanent magnets (RFPM) orient the magnetic flux outward or radially from the turbine shaft while the AFPM design works by orienting the magnetic flux along the axis of the turbine shaft. A coil wraps around a disc at the center axis. Magnetic discs then rotate on the sides of the coil disc and generate electricity. This kind of power generation is said to be ideal for wind power applications because its initial operating torque (cut-in speed) is lower than existing RFPM methods.

AFPM power generation divides into inner and outer classifications. With an inner configuration, only the magnetic disk rotates while the generator housing remains fixed. In the outer configuration, the whole generator body rotates by fixing the magnetic disk to the body. Application requirements determine the configuration.

There is another consideration. A generator producing electricity also produces heat. As the heat increases, efficiency decreases. To solve this problem, Clean Energy generators are liquid cooled. This significantly reduces, says the company, the wear that high temperatures cause, and thus improves the generator’s life-span. The table compares a few details of the competing designs.

Generators and services for wind turbines

Electrical design firm Potencia developed a 5 kW wind turbine in 1975 but has evolved as a designer and supplier of generators for the wind-turbine industry. The company has since developed 500 kW induction generators, and 750 kW doubly-fed wound-rotor generators in the 90′s. More recently, the Mexico-based company has developed permanent-magnet generators for multi-megawatt turbines for Clipper Windpower, Carpinteria, Calif.
Potencia says it has manufactured generators classified as induction, wound rotor, salient pole, and permanent magnet, and that its custom generators can meet any specification. The firm adds it is aware of the need for high-reliability in equipment and so guarantees a lowest temperature-rise and highest efficiency for its units. The generators are manufactured with U.S. materials and dollar-based competitive prices with shipping to any place in North American.

The company also refurbishes several generator designs. The tables list a few specs for a new Leroy Somer, wound-rotor generator in a 660kW unit, and then performance figures for before and after it was refurbished.

A few specs for a Leroy Somer generator

Performance figures for before and after rebuilding the generator

Gearbox, generator, and controls in one package

GE Drivetrain Technologies, a unit of GE Transportation, Erie, Pa, says the company has launched a wind generator and control systems division to serve wind turbine owners around the globe.

The new company will immediately offer doubly-fed induction and permanent magnet generators in the 2 to 6 MW power range. The company produces more than 3,000, 2 MW and greater generators annually and has sold more than one million generators and motors globally. The company says these generators have been proven reliable in extreme environments in applications as diverse as railway locomotives, mining trucks, and off shore drilling rigs.

“Our objective is to apply GE Transportation’s capability to advance the state of the art in wind energy generation technology,” says GE Drivetrain Business Leader Prescott Logan. “GE Transportation’s global supply chain, including existing generator-manufacturing facilities in Erie, Pa. and Monterrey, Mexico creates near-term production capability.”