A new form of crane-hoist control using a 3:1 pole-changing induction motor

The basic practical requirements of crane-hoist drives are summarized and the latest developments, including closed-loop control methods, in satisfying such requirements with a.c. drives are discussed. In particular, the paper investigates the suitability of an economical design of a 3:1 pole-changing induction motor for crane-hoist drives. In conjunction with a single-phase auto-transformer, the pole-changing motor enables the best use to be made of d.c. and a.c. dynamic braking, which further assists in reducing the energy dissipation in the motor circuits as well as reducing the number and size of the secondary-circuit resistors and contactors. It is shown that the performance characteristics are such as to satisfy crane-hoist requirements without undue complexity of the complete equipment.