We can see higher usage of electric motors in both home appliances as well as in the industrial sector. Electric motors have produced in various ways which suit specific requirements of people. They have designed to use in a wide range of capacities. From small devices such as electric motors, toys, clocks to giant machines like concrete mixers, such as cranes. Mainly these motors classify as direct current motors and alternating current motors according to their working condition. In this article, we are going to discuss the Alternating current motors.
Alternating current motors can classify as induction motors and synchronous motors. Both of these motors provide single-phase motors for small machines and three-phase motors for massive machines. Squirrel cage type motors are less expensive when compared to other motors since the simplicity of design. And also, maintenance and the repair of the motor is simple.
Induction motors use for fans, water pumps, compressors, etc. which work at a constant speed. Slip ring type or wound roto inductions motors are expensive. These can use for running machines like concrete mixers and cranes.
Synchronous motors can achieve constant speeds like 3000rpm, 1500 rpm, 1000 rpm. So, unlike Squirrel cage type induction motors, these motors can obtain the required speed ratios quickly. Therefore, these synchronous motors mainly use for devices. Such as clocks and timers and obtain the required speed ratios by the gear systems.
Three-phase induction motors
When we consider the three-phase induction motors, the rotating part is called the rotor, and the stationary part that supplies the alternating current is called the stator. The stator has three windings that can connect to a star or delta system. There are no windings in the rotor of a Squirrel cage type induction motor and have copper roto bars instead of that.
The stator of Three-phase induction motors
Usually motor converts electrical energy into kinetic energy. Three-phase induction motors Power supplies to the static stator windings.
As per the figure, 1.32 three-phase windings of three-phase induction motors have embedded into the slots that made of the laminated stator core. The core has made up of several layers of laminated sheet metal to reduce hurricane damage. If not when there may be a reduction of output power which can occur from the motor. Because there can be a power loss due to the vortex current, occur from magnetic flux. Edges of the three-phase windings and the common apex have connected to the terminal board. Figure 1.32 shows the position of the coil of the stator and the cross-section of the stator.
How Magnetic field occurs in a Three-phase induction motors
An alternating three-phase current supply to the static coils of a three-phase induction motor and the coil of the stator has coiled in such a way that to generate a rotating magnetic field.
The 1.33 figure shows the magnetic field of the stator corresponding to the alternating current supplied by an induction motor coiled to form two magnetic poles.
Figure 1.33 shows the direction in which the current flows in the static coils at the three cases, namely I, ii, iii, of the supplied three-phase current. Figure 1.33 also shows how the magnetic field exists according to Maxwell’s law of scrap when the current flows.
The direction of the magnetic field through the air space of the stator can use to determine the position of the North Pole and the South Pole according to the entry of magnetic field lines from the North Pole to the South Pole. When considering cases i, ii, iii, it shows that a rotating magnetic field has formed in the stator due to the supplied alternating current.
Experiments show that the magnetic field rotates in the opposite direction if any of the two phases in the static are interchangeable.