Transient torques in squirrel-cage induction motors, with special reference to plugging

WHEN a squirrel-cage motor is switched in any way, whether while running or at rest, transient torques, which are usually several times the steady-state torque, occur and must be considered in design. It was desired to obtain a general semi-quantitative view of these torques by considering a limiting case which is accessible analytically with the expectation that a simple rule would be apparent for estimating the magnitude of these torques from design data. No such rule was found, and we must be content to exhibit limiting transient torque curves for certain types of motors in the commercial range and to provide accurate formulas for calculating such limiting torques for types not considered here. The limiting case studied involves the following assumptions: