D-C Dynamic Braking of Squirrel-Cage Induction Motors [includes discussion]

A rational method is given for estimating the torque speed curves of squirrel-cage motors during dynamic braking. An expression for average torque and one for peak torque are also developed. Results of the use of these are compared to results by previously published methods, with generally favorable conclusions. It is shown that squirrel-cage copper losses resulting from air-gap flux harmonics are much reduced at speeds below one-tenth of synchronous speed, with a consequent reduction of apparent rotor resistance. It is also inferred that inductor-generator action accounts for 20 to 30 per cent of the torque in the region of maximum torque. This paper is presented because no such rational method has yet been published and also because it is felt that the subject is timely in view of the increasing requirement of accuracy in the engineering of industrial controls.