Abstract :
The predetermination of the performance of a polyphase a-c. machine is greatly facilitated by the fact that at constant voltage and frequency its magnetic field is of constant intensity and rotating with uniform velocity. It is easy to form a mental picture of lines of force moving in space and being cut by conductors, which may be moving or stationary. Furthermore, the rate of cutting, and therefore the generated voltages, which form the basis for quantitative analysis, are readily determined by the relative motion of the flux and the conductors. Because of the ease with which a physical conception can be formed of a rotating magnetic field, the idea of considering a singlephase alternating field as made up of two oppositely rotating fields has been found very useful. In a paper entitled ``A Physical Conception of the Operation of the Single-phase Induction Motor´´ TRANSACTIONS A. I. E. E., 1918, p. 627), Mr. B. G. Lamme has given an excellent description of single-phase induction motor operation based on a conception of two oppositely rotating magnetic fields. From the discussion of Mr. Lamme´s paper, it appears to be the concensus of opinion that the method he uses furnishes the simplest and clearest physical conception of the single-phase motor. However, this is not the method usually employed in the quantitative analysis. Reference to text books will show that the mathematical treatment is usually based on the so-called ``cross field´´ theory.
