Permanent magnet generator
In addition to the excitation generator mentioned above, there is also a type of permanent magnet generator in the generator set. The biggest difference between it and the excitation generator is that its excitation field is generated by permanent magnets. The permanent magnet is both a magnetic source and a component of the magnetic circuit in the motor. The permanent magnet generator rotor adopts steel structure, and the surface is embedded with permanent magnets in sequence. The surface of the rotor has strong magnetic flux, light weight, small volume and no contact. The only wear part of the whole machine is the bearing.
In addition, in the case of the same power level, the permanent magnet of the permanent magnet generator in the direct-axis magnetic circuit has a small magnetic permeability, and the direct-axis armature anti-reactance Xad is much smaller than that of the electric-excited synchronous motor, and thus the voltage adjustment rate. It is also smaller than the electric excitation synchronous motor, and the output waveform is close to a sine wave. The output voltage is stable, the line voltage distortion is small, and the output voltage waveform is good.
The permanent magnet rotor structure eliminates the excitation power required to generate the rotor magnetic field and the mechanical loss of friction between the carbon brush and the slip ring, so that the efficiency of the permanent magnet generator is greatly improved. Ordinary excitation generators have an average efficiency of only 65% over the rated speed range and permanent magnet generators with up to 83%.