# Download Electric Motors Their Action Control and Application-First by Francis Bacon Crooker PDF

By Francis Bacon Crooker

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Same percentage of saturation represents the ratio between speed variation of a shunt motor and change of voltage V supplied to its terminals. 60 X 5 = the voltage increased 5 per cent, the percentage of ELECTRIC MOTORS, THEIR ACTION 30 AND CONTROL. At 100 per cent or complete saturation the saturation being 60. speed rises or falls exactly the same percentage as the voltage. On the other hand, at zero saturation or with low flux densities practically proportional to the excitation, the speed would be constant.

Rise being permissible) is 15 per cent greater (see p. 28 ohm. f. f. 2 volts. m. m. not material in most practical cases, as the change due to varying load may be 4 or 5 per cent as shown above. As already noted on page 22, the load may be and often is sud- cent, which is denly thrown off a motor when its armature is "hot," and conversely In each case it is rated load is often applied to a "cold" armature. merely a question of fact how warm the armature may be. But the variation in resistance tical effect Change upon is only 15 per cent and produces shown above.

The quantities involved in that equation are determined by the designer of a motor or generator, but all of them are not usually known to, or readily ascertainable Hence the following method is given data employs easily obtained by the simple tests already " indicated under the head of The Armature Resistance" on page 13. by, the user of the machine. because These it tests can readily be made after the machine is in practical service. In the armature circuit of any direct-current motor the applied voltage, F, overcomes three factors, namely, resistance drop, brush- V = I aR a + D b + (I a R a + D b ).