Wind Mill Designing with Permanent Magnet Generators – I
A very important aspect of installing a wind mill is the shape of its blades. There are different materials from which the blades are made. A short note on blade design is presented to give a basic idea about this factor.
Blade design
The ratio between the speed of the blade and wind speed is called tip speed ratio. High efficiency 3-blade-turbines have tip speed/wind speed ratios of 6 to 7. Modern wind turbines are designed to rotate at varying speeds. Low inertia is achieved by the use of aluminum and composite materials in the blade design. Hence the blades start rotating quickly.
The speed and torque at which a wind turbine rotates must be controlled for several reasons;
1. For keeping the generator within the speed and torque limits
2. To optimize the aerodynamic efficiency of the rotor in light winds.
3. To keep the rotor and hub within their centrifugal force limits. The centrifugal force from the spinning rotors increases with the square of the rotation speed, which makes this structure sensitive to over speed.
4. To keep the rotor and tower within their strength limits. Because the power of the wind increases as the cube of the wind speed, turbines have to be built to survive much higher wind loads (such as gusts of wind) than those from which they can practically generate power.
5. To facilitate maintenance. Since it is dangerous to have people working on a wind turbine while it is active, it is sometimes necessary to bring a turbine to a full stop.
6. To reduce noise. As a rule of thumb, the noise from a wind turbine increases with the fifth power of the relative wind speed.
* When you gather all these basic information regarding the designing of the wind mill, send us the requirements and the conditions and the skilled and experienced R&D heads at PM generators Ltd. will design an alternator which will match the mechanical power output as per the alternator requirement. PM Generators Ltd. will work on the provided specifications and develop a customized design which will suit your requirements to the fullest.
