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Starting Torque of a Squirrel-Cage Motor

9.3. Starting Torque of a Squirrel-Cage Motor. The squirrel-cage rotor resistance is fixed and small as compared to its reactance which is very large especially at start (because at standstill the frequency of rotor current is equal to that of supply frequency). Hence, the starting current I2 of the rotor, though very large in magnitude, lags by a very large angle behind E2; consequently the starting torque per ampere is very poor. It is roughly 1.5 times the full-load torque although the starting current is 5 to 7 times the full-load current. Thus such motors are not suitable for applications where these have to be started against heavy loads.