Although the Variable Input Electrical Generator (VIEG) has a wide range of potential applications, our primary focus is on the MW wind power market. We define this market as wind turbines generating in excess of 1 mega watt (MW).

Unique Geometry

Exro designed the RM5 series of the VIEG for high torque, low RPM applications such as wind turbines. Operating at low speed requires a very high pole count, and for the RM5 series we chose to achieve that by adding stacks down the length of the shaft, rather than take the traditional approach of increasing machine diameter. Our multi-stack approach provides a number of distinct advantages, the most obvious being a low diameter able to fit into most nacelles without major modification. In some instances this form factor is an advantage, particularly for turbine makers who want to upgrade a proven turbine design to direct-drive.

Fault Tolerance

With a conventional “ring generator”, a short or an open coil winding results in a hard down condition with no power generation. That’s not the case with the VIEG because our multi-stack configuration provides built-in redundancy. In the unlikely event of a shorted or open coil, the VIEG controller disconnects the faulted stack while leaving the others engaged to continue generating power (at reduced overall capacity).

Tailored Solution

At Exro, our design philosophy has always been to follow a modular approach with particular emphasis on ensuring that our design platform helps speed customization, reduce manufacturing costs, and simplify field maintenance.

Low Cut-In Speed

The VIEG was designed with a goal of minimizing both cogging torque and torque ripple. Lower cogging torque helps to reduce the cut-in speed at which a wind turbine begins to generate power and lower torque ripple helps to reduce noise and vibration during turbine operation. Our unique approach to magnetic balancing, within each stage and across multiple stages, led to a significant reduction in pole lock-up which in turn provided a significant reduction in both cogging torque and magnetic noise.

Cooling

Efficiency loss (1-η) ultimately becomes heat, and here the VIEG delivers a distinct advantage. RM5 series generators do not require a gearbox, and they operate at greater than 98% efficiency at peak, so overall heat generation in the nacelle is significantly reduced. In addition, our unique geometry doubles the cooling surface, so heat dissipation is greatly enhanced2. Despite these advantages, there is no getting away from the need for effective cooling, both to ensure the highest possible conversion efficiency and to protect against demagnetization. The choice of whether to cool a wind generator using air or liquid is dependent on site conditions. Liquid cooling is more costly to build and maintain, but air cooling simply isn’t enough in some instances. To address the problem, VIEG designers incorporate water cooling canals in the casting so that there is no impediment to deploying liquid cooling where required.

Reduced Weight

Bearings play a crucial role in all rotating machinery and this is particularly true in the drive-train of a large wind turbine. Rather than the typical two bearing design, Exro engineers designed a distributed bearing architecture which significantly reduces bearing load, drives down overall weight and enhances control over the airgap.

• Applications
• Renewables
• Gensets
• Vehicles
• Other