Electromechanical Energy Conversion

Today, electrical energy is the most widely used form of energy for performing several industrial, commercial and domestic functions such as pumping water, fans, coolers, air conditioning, refrigeration, etc. Since, most of processes require the conversion of electrical energy into mechanical energy. Also, the mechanical energy is converted into electrical energy. Hence, this clears that we need a mechanism to convert the electrical energy into mechanical energy and mechanical energy into electrical energy and such a mechanism is known as electromechanical energy conversion device.

Electromechanical Energy Conversion Device

Thus, a device which can convert electrical energy into mechanical energy or mechanical energy into electrical energy is known as electromechanical energy conversion device. The electric generators and electric motors are the examples of electromechanical energy conversion device.

In any electromechanical energy conversion device, the conversion of electrical energy into mechanical energy and vice-versa takes place through the medium of an electric field or a magnetic field. Though, in most of the practical electromechanical energy conversion devices, magnetic field is used as the coupling medium between electrical and mechanical systems.

The electromechanical energy conversion devices can be classified into two types −

• Gross motion devices (like motors and generators)
• Incremental motion devices (such as electromagnetic relays, measuring instruments, loudspeakers, etc.)

When the electromechanical energy conversion takes place from electrical energy to mechanical energy, the converter is known as motor. Whereas, when the conversion takes place from mechanical energy to electrical energy, the device is known as generator.

In the electrical machines, conversion of energy from electrical to mechanical or from mechanical to electrical results following two electromagnetic phenomena −

• When a conductor moves in a magnetic field, an EMF is induced in the conductor.
• When a current carrying conductor is placed in a magnetic field, a mechanical force acts on the conductor.

These two effects occur simultaneously whenever energy conversion takes place from electrical to mechanical or vice-versa.

In motoring action, electric current flows through the conductors placed in a magnetic field due to which a force is produced on each conductor. The conductors are placed on a rotor, which is free to move. Therefore, an electromagnetic torque is produced on the rotor so that the rotor starts rotating at some speed.

The torque produced on the rotor is transferred to a shaft of the rotor and hence it can drive a mechanical load. Since the conductors are rotating in a magnetic field, thus an EMF is also induced in each conductor.

In generating action, in this case the rotor is driven by a prime mover. An EMF is induced in the rotor conductors due to which a current will flow and deliver electric power to the load. In addition to this, the current flowing through the conductors will interact with the magnetic field to produce a reaction torque, which will tend to oppose the torque developed by the prime mover.

Principle of Conservation of Energy

The principle of conservation of energy states that "the energy can neither be create not destroyed. It can only be converted from one form to another".

In an electromechanical energy conversion device, the total input energy is equal to the sum of following three components −

• Energy dissipated,
• Energy stored, and
• Useful output energy.

Hence, the principle of electromechanical energy conversion is based on the following two equations −

The energy balance equation or energy transfer equation for motoring action can be written as −

$$\mathrm{[Electrical \:energy \:input] \:=\: [Energy \:disipated\: in \:electrical \:losses] \:+ \:[Energy \:stored\:\:in\:coupling\: medium]+[Mechanical\:energy \:output]}$$

Where,

• The electrical energy input is the electricity supplied from the main supply.
• Energy stored is equal to sum of the energy stored in the magnetic field and in the mechanical system in the form of potential and kinetic energies.
• The energy dissipated is equal to sum of energy loss in electric resistance, energy loss in magnetic core (hysteresis loss + eddy current loss) and mechanical losses (windage and friction losses).

The energy balance equation or energy transfer equation for generating action can be written as −

$$\mathrm{[Mechanical \:energy \:input] \:=\: [Electrical\:Energy\:Output]+[Energy \:stored\:\:in\:coupling\: medium] \:+\: [Energy \:disipated]}$$

Where, the mechanical energy input is the mechanical energy obtained from a turbine, engine, etc. to turn the shaft of the generator.