A Study Of Wind Powered Turbine Generation

iii)    Supporting Arm Vibration And Deflection
The rotor vibration might build up if the rotor rpm is operated constantly at fixed rpm that coincide with the structure nature frequency. The rough estimate frequency is made by assuming the support arm as a spring while the other handing components are rigid mass and the supporting components as fixed support. This will not provide the real structure natural frequency but just as a comparison of how stiff this part of structure is, compared to the other parts. The pair of flat plates support arm will have the possibility to act like a single beam which will be very stiff.
Cantilevered beam Vibration Formula

iv)    Shaft Bending Stress and Vibrating
The vibration of the shaft at hub position was analyzed as an overhanging had with simple support beam with the rotor as a lumped mass load. This shaft in question is supported by a pair of bearing.
Deflection of hub

v)    Pipe Bending Stress, Deflection and Vibration
The pipe supports the shaft so it will also experience the centrifugal force from the rotor imbalance. The pipe is very stiff with very high frequency and so in the vibrating calculation / estimation, the frame was assumed to be a fixed support while the pipe as a cantilever  supporting the rotor mass.
vi)    Bearing Size Selection
The bearing size should be as small as possible partly to reduce loss but most importantly to reduce torque loss at start up.
4.1    SYSTEM DESIGN
Here there are two basic arrangements in respect to the system design namely:
i)    Constant speed constant frequency (CSCF) system
ii)    Variable speed constant frequency (VSCF) system
i)    Constant speed constant frequency (CSCF) system: Is where the rotor speed is held constant by continually adjusting blade pitch and or generator electrical characteristics.
ii)    Variable speed constant frequency (VSCF) system: Is where the rotor speed is allowed to vary in proportion with the power resulting in maximum conversion factor for most of the operating zone.
In the variable speed constant frequency alternators, the rotor is meant to rotate freely at the wind speed. The actual speed of rotation is determined by these speed/load characteristics of both wind rotor and the generator. The rotor speed determines the efficiency of conversion from wind energy to mechanical energy. At a particular ratio the conversion factor K1 is maximum and the efficiency of conversion from wind energy to mechanical energy is optimum.
Since a constant frequency is needed from a variable speed machine an additional circuit is necessary. A solid state electronic circuit is required to rectify the instantaneous power output d.c power and another circuit comparing chopper is used to invert the d.c power back again to a.c at a given constant frequency (say 50Hz). These additional circuiting makes the VSCF system more complex and of course more cost effective.