ABSTRACT
The synchronous generator is the most popular machine used to generate electricity in power plants. Worldwide, over 98% of all electric power is generated by the synchronous generators. The machine has excitation circuit connected to the rotor. For small-sized generators, the excitation is produced by ferrite permanent magnetic material. This is the most economic design for fractional horsepower generators that do not experience repeated surges in stator currents (repeated surges can demagnetize the rotor). In better designs, the rotor is made of rare earth permanent magnetic material such as the samarium-cobalt to produce stronger magnetic fields. One great advantage of generators built with rare earth material is their high power/volume ratios that make them small in size and weight. The strong rare earth permanent magnetic material allows designers to build generators as large as 1.0 MW. Another advantage is that the rare earth permanent magnet cannot be easily demagnetized, so it can be used for applications where heavy currents and surges in currents are expected. Because of these advantages, the rare earth permanent magnetic synchronous generator is used in wind turbine.
