MOTOR WITH EQUAL MAGNETIC ENERGIES IN FIELD AND ARMATURE.
Let it be assumed that the energy as represented in the magnetism in the
field of a given rotating field motor is ninety and that of the armature
ten. The sum of these quantities, which represents the total energy
expended in driving the motor, is one hundred; but, assuming that the
motor be so constructed that the energy in the field is represented by
fifty, and that in the armature by fifty, the sum is still one hundred;
but while in the first instance the product is nine hundred, in the
second it is two thousand five hundred, and as the energy developed is
in proportion to these products it is clear that those motors are the
most efficient--other things being equal--in which the magnetic energies
developed in the armature and field are equal. These results Mr. Tesla
obtains by using the same amount of copper or ampere turns in both
elements when the cores of both are equal, or approximately so, and the
same current energizes both; or in cases where the currents in one
element are induced to those of the other he uses in the induced coils
an excess of copper over that in the primary element or conductor.
[Illustration: FIG. 67.]
The conventional figure of a motor here introduced, Fig. 67, will give
an idea of the solution furnished by Mr. Tesla for the specific problem.
Referring to the drawing, A is the field-magnet, B the armature, C the
field coils, and D the armature-coils of the motor.
Generally speaking, if the mass of the cores of armature and field be
equal, the amount of copper or ampere turns of the energizing coils on
both should also be equal; but these conditions will be modified in
different forms of machine. It will be understood that these results are
most advantageous when existing under the conditions presented where the
motor is running with its normal load, a point to be well borne in
mind.