Electric Machines Transformers Generators and Motors

Key learnings:
  • Electrical Machines Overview: Electrical machines are devices like transformers, generators, and motors that either convert electricity to mechanical power or vice versa.
  • Transformers: A transformer transfers electrical energy between two circuits without changing the frequency, crucial for regulating voltage levels in power distribution.
  • Generators: Generators convert mechanical energy to electrical energy, using electromagnetic induction, vital for producing electricity in power plants.
  • Motors: Motors convert electrical energy to mechanical energy, essential in applications from household appliances to industrial machines.
  • Operational Principles: The operation of these machines relies on electromagnetic principles, where electric currents and magnetic fields interact to produce or transform energy.

Electric machines, also known as electrical machines, are devices that use electrical energy. In these machines, the input, output, or both can be electricity.

Types of Electrical Machines

The electric machines are of three main types, transformer, generator, and motor.
Transformers: Transformers handle electrical power both as input and output, efficiently transferring energy between circuits without mechanical movement.
Electrical Generator: In a generator, the input is mechanical power and the output is electrical power.
Electrical Motor: In a motor, the input is electrical power and output is mechanical power.
electrical machinesElectrical Machines can also be categorized as static machine and dynamic machine.
The transformer represents a type of static electrical machine.
Both motors and generators are dynamic electrical machines.

Transformer: Transformer works on the principle mutual induction. There is an iron core which links windings of transformer. The flux in the core links both primary and secondary winding due to which voltage induced in the windings. The working principle of transformer can be described as follows. The alternating voltage is applied to the primary winding due to which magnetizing current flows through the primary winding and as a result magnetizing flux produced and concentrated in the closed low reluctance magnetic core path. This flux links with both primary and secondary winding. Voltage is self-induced in the primary winding and mutually induced in the secondary winding. Induced voltage per turn in both primary and secondary winding is the same. The voltage across the windings depends on the number of turns in the winding.

Transformers are categorized by voltage levels into step-up and step-down types. Step up transformer increase the voltage level, while step down transformer decrease it.

Depending on the uses transformers are categorised as power transformer, distribution transformer and instrument transformer.

Depending on the design criteria the transformer are categorised as two winding transformer and auto transformer.

Depending on the insulation system the transformers can be categorized as oil immersed transformer and dry type transformer.

Depending on the operating phase a transformer can be either single phase transformer and three phase transformer.

Three Phase transformer can also be single unit three phase transformer and multi-unit three-phase transformer.

When a conductor is moved in a magnetic field, emf is induced in the conductor. This is the principle of dynamically induced emf. Depending on that principle, all electrical generators work.

There are two types of generator – DC generator, AC generator or alternator.

DC Generator: In DC generator armature (assembly of conductors) is the rotor and electromagnetic poles are attached on the stator. When the rotor rotates in the stator alternating current is induced in the armature and collected through commutator segments attached to the shaft of the motor. The generated alternating current in the armature gets converted to direct current through commutator.

AC Generator: In an alternator, the armature is attached to the inner periphery of the stator. The electromagnet rotates in the stator. The electricity generated in the static armature is directly fed to the external circuit. The DC source supplies power to the rotor electromagnet through slip rings.

The electric motors can categorised as a DC motor or an AC motor.

DC Motor: these motors are fed by DC supply through commutator segments attached to the shaft of the motor. The motor rotates on basis of Fleming’s left hand rule. DC motor can be categorised as separately excited DC motor, shunt wound DC motor, series wound DC motor, compound wound DC motor.

There are two types of AC motor. Induction Motor and synchronous motor.

Induction Motors: These are further categorised as single phase induction motor and three phase induction motor. An induction motor can use a squirrel cage rotor or a wound type rotor.

In an induction motor, a rotating magnetic field is produced when electricity is supplied. This field interacts with the rotor conductors, inducing current due to the motion between the rotor and stator. The rotor then attempts to align with the magnetic field, causing it to rotate.

Synchronous Motor: In a synchronous motor, a rotating magnetic field is produced in the stator. Here rotor of the motor is an electromagnet and it is magnetically locked with the rotating magnetic field and hence the rotor rotates.

There are many others types of electric motors such as servo motor, stepper motor, hystersis motor etc.

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