electrical angle

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Electrical degreeA time interval equal to 1/360 of the time required for one complete cycle of alternating current. Mechanical rotation is often measured in degrees, 360° constituting one complete revolution. In describing alternating voltages and currents, the time for one complete cycle is considered to be equivalent to 360 electricaldegrees (360°) or 2&pgr; electrical radians. For example, if the frequency f is 60cycles per second (60 Hz), 360° corresponds to 1/60 second and 1 electrical degre

e to 1/21,600 second.

There is a definite relationship between electrical and mechanical degrees in rotating electric generators and motors. The illustration shows typical coil and angular relationships in a two-pole alternator. As the magnetic field in the machine moves relative to the coils in the armature winding, the coils are linked sequentially by the fluxes of north and south magnetic poles; two flux reversals induce one cycle of voltage in a given coil. Thus, in a two-pole machine 360° of electrical cycle corresponds to 360° of mechanical rotation, and an angle measured in mechanical degrees has the same value in electrical degrees. However, in a machine with more than two poles, one electrical cycle is generated per pair of poles per revolution. For example, a six-pole machine generates three cycles of vol

tage in each armature coil per revolution. In this case, each mechanical degreeis equivalent to 3 electrical degrees. In general, the relationship

below is valid, where p is the number of magnetic poles of either the rotor or the stator. It follows that the electrical angle between the centers of succeeding poles of opposite polarity is always 180 electrical degrees.

Coil and angular relationships in a two-pole alternatorThe concept of electrical degrees simplifies the analysis of multipolar machinesby allowing them to be analyzed on a two-pole basis. Furthermore, it permits trigonometry to be used in solving alternating-current problems.

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