8/12/2019 AC and DC Generators and Motors

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8/12/2019 AC and DC Generators and Motors

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creating shaft torque in a rotating machine or force in a linear machine. The second role is to generatean electromotive force (EMF).

In the armature, an electromotive force is created by the relative motion of the armature and the field.When the machine acts in the motor mode, this EMF opposes the armature current, and the armatureconverts electrical power to mechanical torque, and power, unless the machine is stalled, and transfers

it to the load via the shaft. When the machine acts in the generator mode, the armature EMF drives thearmature current, and shaft mechanical power is converted to electrical power and transferred to theload. In an induction generator, these distinctions are blurred, since the generated power is drawn fromthe stator, which would normally be considered the field.

A growler is used to check the armature for shorts, opens and grounds.

Field poles

( electromagnetism ) A structure of magnetic material on which a field coil of a loudspeaker, motor,

generator, or other electromagnetic device may be mounted.

A field coil is an electromagnet used to generate a magnetic field in an electro-magnetic machine,

typically a rotating electrical machine s uch as a motor or generator . It consists of a coil of wirethrough which a current flows.

In a rotating machine, the field coils are wound on an iron magnetic core which guides the magnetic

field lines. The magnetic core is in two parts; a stator which is stationary, and a rotor , which rotates

within it. The magnetic field lines pass in a continuous loop or magnetic circuit f rom the stator through

the rotor and back through the stator again. The field coils may be on the stator or on the rotor.

The magnetic path is characterized by poles , locations at equal angles around the rotor at which the

magnetic field lines pass from stator to rotor or vice versa. The stator (and rotor) are classified by the

number of poles they have. Most arrangements use one field coil per pole. Some older or simpler

arrangements use a single field coil with a pole at each end.

Although field coils are most commonly found in rotating machines, they are also used, although not

always with the same terminology, in many other electromagnetic machines. These include

simple electromagnets through to complex lab instruments such as mass spectrometers and NMR

machines .

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