What is an electric motor
An electric motor is an electromechanical device that does the conversion of electrical energy into mechanical energy. This mechanical energy is used to rotate pump impeller, fan, blower, drive compressors, and lift materials. The generation of the force in an electric motor is done by the motor’s magnetic field and the winding currents. Electric motors can be powered by a direct current source, such as batteries, motor vehicles, or rectifiers. It can also be power by using AC sources such as a power grid, inverters, or generators. General-purpose motors with standard dimensions and characteristics can provide required mechanical power for industrial use. Electric motors can provide rotary force.
How does an Electric motor work and what is its working principle
If a current-carrying conductor is placed in a magnetic field then it would experience a mechanical force and the electric motor works according to this principle. It can be explained by Flemings’ left-hand rule, so when a rectangular coil is placed in a magnetic field and a current is passed through it, a force acts on the coil which rotates it continuously. So when the coil rotates a shaft attached to it also rotates. The stationary outer part of the motor is called a stator and the important part of this is a large magnet and its north and south-pole is shown in the above diagram. The rotor is the rotating inner part of the motor it consists of a coil of wire wrapped around an iron core and the core and a device is called a commutator, which is attached to an axel that is free to rotate.
The two ends of the wire in the coil is connected to the two sides of the commutator. These two sides are conductors and they are separated by strips of the insulator. Two brushes are used to connect the commutator to two electrical terminals. When the terminals are connected to a suitable battery, then the electricity will flow through the coil on the rotor and the rotor becomes a magnet. The top of the rotor is repelled by the north pole of the stator and attracted to the south pole of the stator. The like magnetic poles repel and unlike poles attract. The bottom of the rotor is repelled by the south pole of the stator and attracted to the north-pole, and these magnetic forces all combined to make the rotor rotate clockwise. When the brushes make contact with the opposite side of the commutator, then electricity flows through the coil in the opposite direction so the poles on the rotor are reversed. Now the poles are attracted to the opposite sides of the stator so the rotor will continue to rotate clockwise.
Preventive maintenance of motor
What are the factors that influence the efficiency of electric motor
- Age
- Capacity
- Speed and Type
- Temperature
- Rewinding
- Load
What are the types of electric motors
DC motors – shunt, separately excited, series, permanent magnet and compounded
AC motors - induction motors and synchronous motors
Other motors
- Stepper motor
- Brushless DC motor
- Hysteresis motor
- Reluctance motor
Hysteresis motor
Hysteresis motor is a type of synchronous motor, it works on the principle of hysteresis losses induced in the rotor. It can operate both in a single and three-phase supply. This motor has a smooth vibration-free operation, lower noise, and constant torque. It is a single-phase motor whose operation is depended upon the hysteresis effect. When the stator is energized it produces a rotating magnetic field. The main and auxiliary windings must be supplied continuously at the start and in running conditions in order to maintain the rotating magnetic field. The rotor will start to rotate due to eddy current torque and hysteresis torque and when the speed is near to the synchronous speed the stator pulls the rotor into synchronism. Due to the hysteresis effect, the rotor pole axis lags behind the axis of the rotating magnetic field and because of this, the rotor pole gets attracted to the moving stator pole. Thus rotor gets subjected to the torque called hysteresis torque. Hysteresis torque will be higher in the case of higher residual magnetism. High residual magnetism will ensure the continuous magnetic locking between the stator and the rotor. Due to the presence of hysteresis torque, the rotor runs at synchronous speed.
Reluctance motor
In this motor, torque is generated through magnetic reluctance. It has the conventional split-phase stator and a centrifugal switch for cutting out the auxiliary winding. When the stator winding is energized the revolving magnetic field exerts reluctance torque on the unsymmetrical rotor tending to align the salient pole axis of the rotor with the axis of the revolving magnetic field. Reluctance motors are classified into a variable and synchronous motor.