Hello learners. Welcome to this module on motor protection. Let's start with the topic, introduction to AC Motors. At the end of this topic, you should be able to list the classification of motors, explain the working principle of induction motor and synchronous motor. Let us begin with an introduction of the electric motor. Electrical energy is used to generate mechanical energy in an electric motor. It is generally done through the combination of magnetic fields with current-carrying conductors. An alternator or dynamo performs the reverse process of generating electrical energy from mechanical energy. There are two types of AC motors, induction motors, synchronous motors. These two categories are subdivided further based on phase, rotor type, and rotor magnetization. Let's discuss the induction and synchronous motor in detail. Induction motors make up roughly 70 percent to 80 percent of the industry alone. Motors are rated in horsepower or kilowatts, that is, one horsepower is equal to 746 watts. Let's see the working principle of the induction motor. A rotating magnetic field is produced when three-phase stator windings are powered by a three-phase supply. Consider a current-carrying rotor conductor in a stator generated magnetic field. As a result, all rotor conductors are subjected to mechanical force. Therefore, the mechanical force operates on all rotor conductors. The sum of mechanical forces on all rotor conductors produces a torque that tends to move the rotor in the same direction as that of a rotating magnetic field. The magnetic field's rotating speed is the synchronous speed, N_s. This field moves through the air gap and cuts the stationary rotor conductors, inducing EMF in it. The current begins to flow through the rotor conductors, because the rotor circuit is short-circuited. The rotor will never able to match the stator's field speed, in reality. There would be no rotor EMF, rotor current or torque, if the two were moving at the same speed. Slip is defined as the difference between the nominal synchronous speed, N_s, and the actual rotor speed, N. Application of induction motors. Squirrel cage induction motors are used in fans, blowers, centrifugal pumps, line shafting, conveyors, compressors, crushers, agitators, reciprocating pumps, shears, punch pressors, dice stamping. Slip ring induction motors are used in situations where high starting torque is required, such as in hoists, compressors, lifts, crushers, large ventilating fans, cranes, etc. Synchronous motors. The stator contains three-phase windings and is supplied with three-phase power. As a result, a three-phase rotating magnetic field is produced by stator winding. The rotor gets a DC supply. The rotating magnetic field produced by the stator winding locks with the rotor magnetic field to rotate at synchronous speed. The frequency of the supplied current now determines how fast the motor rotates. The frequency of the applied current controls the speed of the synchronous motor. A synchronous motor's speed can be computed as follows. N_s is equal to 120 into F by P. Applications of synchronous motors. Synchronous motors are used in a wide range of machines and devices, including water generated sets, synchronous clocks, stroboscopic devices and timing devices, fans and blowers, and centrifugal pumps, as well as vacuum pumps. They are also found in textile and paper mills, as well as pulp grinding operations. Transmission line voltage regulation makes considerable use of synchronous motors as power factor collectors, phase advancers, and phase modifiers. Let us summarize all that you have learned. Explain the working principle of induction motor and synchronous motor. Listed the application of induction motor and synchronous motor.
