MOTOR DRIVES AND APPLICATION

326. Design of motor drives. The proper design of motor drives for machines is very important. It involves not only the selection of a type and rating of motor but also the selection of a method of connecting the motor to the driven machine and the selection of control equipment. It is affected by power supply, driven-machine requirements, space limitations, safety and working conditions for opera- tors, initial cost and operating costs, production and quality of product, and surrounding conditions. The objective is to obtain a final installation which will be the best when all considerations are taken into account. The manner of attacking and the complexity of the solution of the problem depend upon the particular case. In some cases the limitations are so definitely fixed that they dictate only one answer. For instance, a machine requires a speed of 1600 rpm and full-load power of 24 hp with a very occasional peak of 28 hp and an average load of 20 hp. It is not necessary to maintain an absolutely fixed ratio of speed between driving and driven shaft. No speed control is required, but the speed should not vary by more than 10 percent with load changes. The starting-torque requirements are very light, but the power company will allow only exceptionally low starting currents. The power supply is 60 Hz, 230 V, three-phase. The machine is operated in a dry and clean location with normal temperatures. In this case there is no...