Why cannot use permanent magnets for large electricity generation as they donot require power to produce strong magnneticfield
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\$\begingroup\$ What use would a strong but stationary magnetic field be? \$\endgroup\$– Wouter van OoijenCommented Sep 11, 2015 at 15:27
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\$\begingroup\$ You mean like we already do? \$\endgroup\$– Ignacio Vazquez-AbramsCommented Sep 11, 2015 at 15:29
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\$\begingroup\$ @IgnacioVazquez-Abrams Grid generation is wound rotor sync machine not BLAC and there are valid reasons \$\endgroup\$– user16222Commented Sep 11, 2015 at 15:51
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3 Answers
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A magnetic field alone does not generate any electricity by itself. Energy can be converted from mechanical energy to electrical energy by means of a magnetic field.
This process is governed by Lorentz force and Faraday's law of induction
It is true though that a strong magnetic field improves the efficiency when converting mechanical energy into electrical energy.
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The value of the magnetic field is used also to control active and reactive power, if I remember correctly from my undergrad classes.
https://en.wikipedia.org/wiki/Alternator#Principle_of_operation
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\$\begingroup\$ There could be some truth to that as a factor, especially historically, but with modern power conversion electronics that could be solved in other ways if it were the primary issue. It isn't. \$\endgroup\$ Commented Oct 12, 2015 at 5:56
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\$\begingroup\$ So which is the primary issue? I doubt conversion electronics would handle the generation of active and reactive power in the 100+ MW range (he mentioned "large electricity generation") better than a simple DC current in the rotor, even if the issue with mechanical stress was not present (see next answer). \$\endgroup\$– FarOCommented Oct 12, 2015 at 12:25
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\$\begingroup\$ On the contrary, power conversion now makes things like DC long range transmission lines possible into the thousands of megawatts. \$\endgroup\$ Commented Oct 12, 2015 at 16:05
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Generating an electromagnetic field does not, by itself, require power. Permanent magnets are not batteries.
Variations can generate or require some energy, like moving masses in the gravitation field.
For high power applications, permanent magnets don't give strong enough fields, are more sensitive to thermal and mechanical stress, compared to windings.
