• How Permanent Magnet Generators Work?

    Permanent magnet generators are superior alternatives to traditional induction motors that can be coupled with turbines, diesel generators and used for hybrid vehicles. One of the biggest benefits of permanent magnet generators is that these do not require definite environmental conditions to work properly which allows them to be used for wind energy and water energy projects.

    At the core of the working mechanism of PM generators are powerful magnets. When the magnets rotate around conducting wires, it creates electricity (Faraday’s Law od Electromagnetic Induction ).Since the Permanent Magnet does not need to be exited by providing it with additional power its efficiency is enhanced by at least 33%.

    The powerful magnets in the standard PM generators are able to run for more than 25 years. The magnets used in these generators are specially constructed and certified for long term usage and once installed can work for years without needing replacement.


    Benefits of Using Permanent Magnet Generators

    With the rising cost of electricity, more and more people are looking for alternative sources of energy and permanent magnet generators fit the bill perfectly. These generators can also reduce the strain on the environment as these do not use any non-renewable sources of energy for producing electricity when coupled with renewable sources. Also, there is no harmful waste material production from the use of PM generators. Environment experts recommend the use of permanent magnet generators as these can reduce the impact of pollution by up to 50%.


    Advantages of Permanent Magnet Generators

    Low RPM Generators

    Traditional generators need to revolve at 1800 revolutions per minute to generate power. This requires a great expenditure of energy to produce a feasible amount of power. With low RPM generators, there is the advantage of power production at low revolutions per minute. The low RPM generator starts producing power at a single RPM. There are several advantages associated with a low RPM generator in terms of performance, reliability and life of the equipment. The low rpm permanent magnet generator uses powerful neodymium magnets that create a permanent magnetic field around the conducting coils. Below mentioned are some advantages of low RPM PMG.


    Low Comparative cost:  These generators not only provide higher efficiency than traditional alternators but they and have relatively high upfront capital costs. However they work out to be much more economical than other generators over a longer period of time due to much higher energy efficiency which translates to substantially lower running cost per watt of energy produced and negligible maintenance cost.


    Low maintenance: The permanent magnet generators don’t require extensive maintenance as these are designed to operate in an optimum manner. The neodymium magnets used in these generators have a high working temperature which ensures that these magnets will not demagnetize very soon and continue to provide services for a long time to come.


    Reliable Power Output: The permanent magnet generators are a highly reliable source of power as they work at low speeds which leads to less wear and tear of various parts of the generators. As there are no slip rings used in these generators, these are simple to maintain and ideal for power production for a longer duration of time.


    Different Sizes:

    These generators are available in different sizes and capacities that allow users to choose one that meets their requirements and budget. Whether a permanent magnet generator is coupled with a wind turbine for a small business facility or for power needs of a small house, these generators are perfect for all applications.


    HIGHER EFFICIENCY : Besides being able to produce desired power at low RPM the PMG does away with the need for using Gear boxes in wind mills and hyrdo power generation thus bring the mechanical losses to nearly zero.

    Permanent Magnet Generators: Price vs. RPM

    Permanent magnet alternators can be operated at different speeds or RPM ( ranging from 25 RPM to 3000 RPM ). Thus there are alternators working at low rpm and others at high rpm. The RPM of the PMG depends on the application for these alternators have applications in various fields like wind turbines, hydro-kinetic energy and other renewable energy devices. For example, vertical axis permanent magnet wind generators require very low rpm for direct drive applications. But there is a compensating factor when reducing the speed, which is price.

    The price of an alternator is inversely proportional to the rpm of the permanent magnet alternator. As we go on reducing the rpm of the alternator keeping the power output fixed, the price increases. As the speed decreases, the alternator becomes physically larger in size. This is because reducing the speed leads to an increase in the number of poles which in turn increases the material consumption of the device. The device becomes bigger because of overall volume increase. The diameter or the length has to be increased since total flux needs to be increased at lower rpm to match the conductors. More copper and magnets are required.

    Permanent Magnet Alternators: Voltage and RPM

    It is important for the customers as well as the manufacturers to know the voltage and rpm specifications of the product. But exactly how are they related?

    Simply said, voltage generated in an alternator is directly proportional to the speed of the generator or the prime mover; E = K x Flux x speed x turns

    Which implies that the voltage and RPM are directly proportional.

    Which means that on doubling the rpm of the generator the voltage is doubled.

    Example : A PMG designed at 300 RPM , 440 Volts if operated at 600 RPM the voltage would be 880 volts and at 150 RPM the voltage would be 220 volts.


    Permanent Magnet Alternators: Frequency and RPM

    Another important thing to keep in mind is the frequency for the FREQUENCY , RPM and Number of POLES are related by the formula given below

    Number of Poles = (120 X Frequency) / RPM

    Which means that RPM AND FREQUENCY are directly related

    Which implies that increasing or decreasing the RPM increases or decreases the frequency proportionally.

    Example : A PMG designed at 300 RPM , 50 Hz, if operated at 600 RPM will produce a frequency of 100 Hz and at 150 RPM the frequency would be 25 Hz.

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