AC electric motors, especially three-phase induction motors, are designed to be simpler and stronger than DC motors. Three-phase induction motors with squirrel cage rotors are more advantageous than winding rotor motors because they are constructively simpler, faster to connect to the network and cheaper because the existing collector in the coiled rotor is sensitive and expensive. This type of machine is applied in all places where there is danger of explosion, https://www.mrosupply.com/synchronous-belts/1244919_92741090_gates-rubber/ as it does not produce sparks. The MIT presents as a disadvantage the power factor of less than one, and are generally even lower in the small power engines.
If we compare a DC motor and a three-phase induction motor (MIT), both with the same power, the AC motor will be smaller in size, 20 to 40% less in mass than the DC motor. This explains why MIT has a lower acquisition and maintenance cost than the DC motor. Three-phase induction motors with winding rotor are used when starting and frequent stops are required, which requires a larger initial torque and also allows the speed control with rheostats.