• Summary
• Design
• Build

Overview:
C-GEN is a lightweight permanent magnet (PM) generator, which has been developed by the University of Edinburgh since 2005 with funding from Scottish Enterprise & The Carbon Trust. The main applications for this technology are in wind, wave and tidal current energy converters. Since 2005 several prototypes have been design, built and successfully demonstrated – 20kW, 100rpm rotary generator tested in the lab; 1kW linear prototype in the lab; 15kW, 150rpm rotary generator installed on a 15kW wind turbine (Figure 1) 50kW(peak) linear generator for direct drive wave energy converters (Figure 2) to be tested at TUV NEL in Scotland.

Figure 1: C-Gen generator on wind turbine

Figure 2: Linear C-Gen generator at NEL

The benefits of the C-GEN technology are:

• 50 % lighter compared to conventional direct drive PM generators.
• No magnetic attraction forces between moving and stationary parts.
• Reduced system cost.
• Modular design.
• More scaleable at multi-MW.
• Manufacture and assembly: safer, easier & cheaper.
• Reduced cost of Installation.
• No cogging torque.
• More easily transported.
  

NGenTec Ltd was spun out of the University of Edinburgh to commercialise C-GEN technology. An exclusive royalty free licence was signed in November 2009 covering all patents filed, know-how, design tools developed and access to all prototypes built.

Technology Description
In a conventional PM machine steel exists in the rotor, and the coils are embedded in a steel structure, so that significant magnetic attraction forces exist. In order to overcome these attraction forces and maintain a small physical clearance between moving and stationary sections a very large structure is required, which accounts for more than 60% of the total mass in a direct drive generator. The innovation in C-GEN lies in the use of a PM c-core arrangement and air-cored coil as shown in Figure 3. A number of these c-cores are mounted circumferentially to produce a rotary generator. A linear module is shown in Figure 4. By mounting the PMs onto the c-core, the attraction forces are reacted by the c-core structure rather than at the shaft several metres away. An air-cored coil contains no steel, so that when it is inserted into the c-core as shown there are no magnetic attraction forces. Hence the support structure for the generator only needs to support the mass of the c-cores and coils, and does not have to overcome any magnetic attraction forces

Figure 3(a): Permanent Magnet (PM) c-core and air-cored coil (b): Coil inserted into PM c-core module

Figure 4: Single linear module and small linear prototype

A single linear module as shown in Figure 4 is completely self supporting with an integrated bearing housing. Designs of C-GEN show that it will be 50% lighter than existing conventional PM generator technology. Assembly of a C-GEN generator is easier than with a conventional PM generator machine because there are no magnetic attraction forces. Both the large rotary prototypes and the 50kW linear prototype were assembled by hand with the aid of an engine hoist with a 500kg maximum lift, as can be seen in Figure 5

Figure 4: Single linear module and small linear prototype

Dr. Markus Mueller
NGenTec Ltd & University of Edinburgh.
Email:Markus.Mueller@ed.ac.uk
Tel: +44 131 650 5602
Mob; +44 781 383 4056
www.ngentec.com