Selection of the pole number of induction machines for variable speed applications

An effort is made to identify the important second-order effects of the pole number on the motor parameters and performance by comparing two-pole and four-pole motors of the same overall outside dimensions. The tradeoffs involved in the pole number selection are pointed out, and it is shown that many of the issues are quite similar to those faced in the design of DC machines. This realization can provide useful guidance in comparing machines of different pole number. The absence of a breakdown torque in DC machines is shown to be the major distinction between DC and induction machines in regard to selecting the pole number. A sample design is presented comparing a two-pole and four-pole motor to illustrate and support the analysis results and discussion. Some general conclusions concerning pole number selection are also presented