What is the difference between an AC generator and an Alternator?

Aren't both the same thing? Why then use different terminology?


Best Answer

  • edited May 5 Accepted Answer

    AC generators can be broadly referred to any type of electricity generator that generates electrical energy in Alternating Current (AC) form. So, in a way, yes, an Alternator is also an AC generator.

    A more appropriate term for an alternator is - AC synchronous generators.

    More specifically, in an alternator, the excitation winding (which produces magnetic field) is mounted on the Rotor shaft and the armature winding (which generates electrical current) is mounted on the Stator (stationary part of machine which surrounds the rotor). While in most of the other types of electrical generators, including DC generators, the excitation winding is stationary and the armature winding is mounted on the rotor shaft.

    So basically, you may distinguish it like - the magnetic field is stationary in generators, while it is rotating in alternators. Or the other way - the armature winding is rotating in generators, while it is stationary in alternators.

    So why the armature winding is stationary in an alternator?
    • At high voltages, it is easier to insulate the stationary armature winding, which may be as high as 11 kV or even more in some cases.
    • The generated high voltage output can be directly taken out from the stationary armature. Whereas for a rotary armature, there will be large brush contact drop at higher voltages, also the sparking at the brush surface will be a problem to look after.
    • If the field exciter winding is placed in the rotor, low voltage DC can be transferred safely to the exciter winding via slip-rings.
    • The armature winding can be braced well, to prevent deformation caused by high centrifugal force if it was in the rotor.

    Take it like this, all alternators are AC generators but NOT all AC generators can be alternators.

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