INDUCTION MOTOR OPERATING PRINCIPLES

MOTOR OPERTATING PRINCIPLES;

  Instructor to read the write up

  And show cutaway view of the Induction motor

Induction Motor Operating Principles

Inside an Electric Motor An el­ectric motor is all about magnets and magnetism: A motor uses magnets to create motion. If you have ever played with magnets you know about the fundamental law of all magnets: Opposites attract and likes repel. So if you have two bar magnets with their ends marked "north" and "south," then the north end of one magnet will attract the south end of the other. On the other hand, the north end of one magnet will repel the north end of the other (and similarly, south will repel south). Inside an electric motor, these attracting and repelling forces create rotational motion. ­

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INSTRUCTORS INTRODUCTION;

Motor Operating Principles
                The three phase Induction motor or asynchronous motor is a type of alternating current motor where power is supplied to the rotor by means of electromagnetic induction. An electric motor converts electrical power to mechanical power in its rotor (rotating part). In an induction motor power is induced in the rotating device (rotor). The current in the primary side creates an electromagnetic field which interacts with the electromagnetic field of the secondary side to produce a resultant torque, thereby transforming the electrical energy into mechanical energy. Induction motors are widely used, especially polyphase induction motors, which are frequently used in industrial drives

                The induction motor does not have any direct power supplied into the rotor; instead, a secondary current is induced in the rotor. To achieve this, stator windings are arranged around the rotor so that when energised with a polyphase supply they create a rotating magnetic field pattern which sweeps past the rotor. This changing magnetic field pattern induces current in the rotor conductors. These currents interact with the rotating magnetic field created by the stator and in effect cause a rotational motion on the rotor.

                However for these currents to be induced the speed of the rotor must be less than the speed of the rotating magnetic field in the stator or else the magnetic field will not be moving relative to the rotor conductors and no currents will be induced. If by some chance this happens, the rotor typically slows slightly until a current is re-induced and then the rotor continues as before. This difference between the speed of the rotor and speed of the rotating magnetic field in the stator is called slip. It is unitless and is the ratio between the relative speed of the magnetic field as seen by the rotor (the slip speed) to the speed of the rotating stator field. Due to this, an induction motor is sometimes referred to as an asynchronous machine.

We will now watch three short videos on Motor Operating Principles;

Basic Operating Principles of an Induction Motor

Squirrel Cage Motor Operation Principles

Stator  Winding Connections