Rare Earth Permanent Magnet Generators Background Information

Presently regular engine-generators in the market have these problems:
1. Regular engine-generators also named excitation generators have a stator with a winding and a rotor with an excitation winding. When the rotor rotates at high speed driven by the gasoline engine the stator winding generates the electrical power. Generally the excitation winding connects to the external circuits and automatic voltage regulator by slip-ring brushes. The output voltage is automatically regulated according to the load to minimize voltage fluctuations. In addition to difficulties in maintenance and a higher failure rate the main shortcoming is the high output voltage distortion up to 15% and as high as 30%. This is unsuitable for sensitive electrical equipment such as communication equipment meters and instruments numerical controlled equipment and computers and so on.
2. The efficiency of the regular engine-generators is quite low. When used with resistive loads such as illumination or electric heater the efficiency is only around 70%-75%. With inductive load (power tools, air conditioner, computer, electrical appliance with transformer, etc), the efficiency is even lower, less than 50%. For this reason, a factory-assembled Yamaha 2700 generator set is unable to start a 2HP (1.5KW) air conditioner.

The Rare Earth Permanent Magnet Generators were developed to resolve these two problems. Their stators are similar to those of regular engine-generators but in their rotors the excitation winding are replaced by a carefully designed rare-earth permanent magnet with ultra-high magnetic field. This design provides the Rare Earth Permanent Magnet Generators with the following main advantages:
1. The waveform of its output voltage and current are absolute sine waves similar to the AC electric waveform in a home. The distortion rate is less than 4%. As such it cannot only be used in a home but also by sensitive equipment like communication and numerical controlled equipment and computers and so on.
2. The efficiency of the generator is very high generally around 85%-90%, 15%-20% higher than ordinary excitation generators in the market reducing significant amount of energy consumption. Take the 3KW PS3800 as example its engine power can be lowered to 6.5HP from 8HP greatly reducing the volume and weight of the generator. As expected the smaller engine horsepower means less fuel consumption. For this reason the Rare Earth Permanent Magnet Generators can also be called an energy saving product.
3. The Rare Earth Permanent Magnet Generators have excellent reliability. Since the rotor excitation winding and slip-ring brushes are all eliminated and the rotor is a solid magnet they can be driven at much higher speed for higher efficiency while maintaining reliable operation and low failure rate.
4. The Rare Earth Permanent Magnet Generators have inherent tough starting performance and overloading capability especially for inductive loads such as air-conditioners, computers, and power tools. The 3KW PS3800 can start and run a Toshiba 3HP (2.2KW) board air conditioner that is impossible for ordinary excitation generators. Even the factory-assembled Yamaha frequency conversion generator set fails to start because the huge starting current trips the circuit breaker.

The two shortcomings of rare permanent generators are:
1. The higher cost of the high-performance Rare-earth permanent magnet that has up to 10 times higher field strength. However the benefits of REPM technology more than offsets the higher cost.
2. The Rare-earth permanent magnetic field on the rotator is hard to regulate. It is difficult to maintain constant voltage with changing load. This problem has been resolved. When the load varies the output voltage variation is kept under 8% safely within the 10% limit of industrial standard.

Currently some manufacturers are producing other kind of excitation generators called frequency conversion generators. These generators run at higher speed to generate AC electricity with frequency much higher than 50Hz (60Hz). The AC electricity is rectified into DC electricity. Subsequent inversion converts the electricity as single-phase 50Hz (60Hz) AC electricity. Though this type is generator features stable voltage high efficiency and good waveform it has high production cost poor overload capability and poor starting performance for inductive load.

Compared with regular excitation generators Rare Earth Permanent Magnet Generators have excellent output waveform good inductive load starting performance superb efficiency and outstanding reliability.

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