Testing Small Wind Turbine Generators - Renewable and ...

To ensure that connections remain secure throughout potentially vibration-prone testing,split-ring lock washers are used with every fastener.2.3 Drivetrain2.3.1 TheoryWhen the dynamometer is running, It is essential for both electrical machines andthe encoder to rotate exactly synchronously.If the generator alone turns at a differentdifferent angular velocity, the speed measurement developed by the encoder and digitalsignal processor will inaccurately reflect the true speed of the generator. Worse still, if theencoder and motor get out of sync the motor will stop turning smoothly, jerk to a halt, ormove erratically with potentially dangerous torque and current.Thus a belt and pully system would be inadequate. Belts can have a tendency to slip(suddenly losing traction) and creep (slowly advancing one pulley faster than another).Chain drive systems, however, guarantee sychronous motion by engaging discrete chainlinks on the teeth of a sprocket. As long as each sprocket has the same number of teeth andthe chain does not fail, the motion of each component will remain synchronous indefinitely.2.3.2 DesignThe generator shafts are designed for an attachment to be bolted on, compressed betweenthe thick main shaft and a nut on the thinner, threaded end of the shaft. The threadis an unusual metric size: 20 mm in diameter, with a 1.5 mm pitch. Thus to fit the shafts,flat sprockets with a 5/8” (15.9 mm) bore were machined on a lathe to have the required20 mm bore. Figure 2.6 shows a sprocket mounted on the generator shaft.The shaft of the optical encoder is 1/4”, far too small for any standard sprocket. Thisproblem was solved by increasing the diameter of the shaft with aluminum shaft couplings.These inexpensive units attach with set screws, and are adequate for the low torque appliedto the encoder. One coupling has an inside diameter of 1/4” and and outside diamter of12