What is an electric machine?
An electrical machine is a device that converts mechanical energy into electrical energy or mechanical energy to electric energy. These machines which are operated in relation to electrical energy are called electric machines. In electrical machines, input or output or both can be electricity. An electric machine consumes electric energy to do specific work in operation. The most common machine type is the induction motor.
Types of Electrical Machines
The electric machines are of three main types:
Electrical Transformer: In a transformer, both input and output are electrical power.
Electrical Generator: In the generator, the input is mechanical power and the output is electrical power.
Electrical Motor: In a motor, the input is electrical power and we get the output as mechanical power.
BASIC FEATURES OF ELECTRIC MACHINES
The basic structural features of a machine are:
• Stator – The stator consists of the field winding. The stator and the rotor constitute the magnetic circuit or core of the machine.
• Rotor – It carries the armature winding. The armature is the load-carrying of the instrument. It is cylindrical in shape.
• Armature Winding – This winding rotates in the magnetic field which is set up at the stationary winding. An armature winding is a continuous winding. It has no beginning or end.
• Field Winding – This system may be an electrical winding or a permanent magnet and which is located on the stator.
• Commutator – The coils on the armature are terminated and interconnected which are comprised of a number of bars. These bars are insulated. The commutator rotates with the rotor and serves to rectify the induced voltage and the current in the armature both of which are A.C.
• Brushes – These are conducting carbon graphite spring made to ride on the commutator. It acts as an interface between the external circuit and the armature winding.
• Poles – The field winding placed in poles. The number of which is determined by the voltage and current ratings.
• Slot/Teeth – The main function of the slot is mechanical support, protection from abrasion and electrical insulation. We have non-conducting slot liners which are placed between the coils and the slot walls. This magnetic material between the slots is called teeth.
Michael Faraday proved that when we pass a current through a conductor freely suspended in a fixed magnetic field, it creates a force that causes the conductor to move. If the conductor in place of the magnet is constrained then the magnet creating the field will move relative to the conductor.
The force created by the current, known as the Lorentz force, acts between the current conductor and the magnetic field, or the magnet creating the field.
The magnitude of the force on the conductor is given by:
F = BLI
Where F is the force experienced on the conductor, L is the length of the conductor and I is the current flowing through the conductor
Faraday also proved that the converse is true – moving a conductor through a magnetic field, or moving the magnetic field relative to the conductor, causes a current to flow. The magnitude of the EMF generated in this way is:
E = BLv
The motor and the generator effects take place simultaneously.
When we pass the current through a conductor in the magnetic field it causes the conductor to move through the magnetic field. When the conductor starts moving it becomes a generator creating. A current flows through the conductor in the opposite direction to the applied current. The motion of the conductor exerts a “back EMF” which opposes the applied EMF.
The magnetic field is provided by the stator. The stator is a permanent magnet however in the many of the electrical machines the magnetic field is provided by coils that wound around the stator poles.
ELECTRIC MACHINE DRIVES AND POWER SYSTEM
An electrical drive is a form of machine equipment used to convert electrical energy into mechanical energy and provide electrical control of the processes. The system used for motion control is called an electrical drive. The speed is changed by changing the frequency of the electrical supply to the motor.
An electric power system is a network of electrical equipment used to supply, transfer, and consume electric power. An example of an electric power system is the grid that provides power to an extended or a large area. Electric power is defined as the rate at which electrical energy is consumed in an electric circuit.