Electric Machines Transformers Generators and MotorsPublished on 23/10/2018 and last updated on 30/10/2018
Types of Electrical MachinesThe electric machines are of three main types, transformer, generator, and motor. Electrical Transformer: In the transformer, both input and output are electrical power. 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 Machines can also be categorized as static machine and dynamic machine. The transformer is an example of static electrical machine. Motor and generator both are dynamic electrical machine.
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.
Depending on the voltage level there are two types of transformers, step up transformer and step down transformer. Step up transformers are for increasing the voltage level of electricity. Step down transformers are for decreasing voltage level of electricity.
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.
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 alternator 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 be categorised as - DC motor, 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 also be squirrel cage rotor type and wound rotor type. In an induction motor rotating magnetic field is produced when the motor is supplied by electricity. This rotating magnetic field interacts with the rotor conductors and due to which current gets induced the conductors. The induced current through the rotor conductors is caused due to relative motion between rotor and stator. To reduce the cause of induced current, the rotor tries to catch the rotation of the magnetic field. As a result, the rotor rotates.
Synchronous Motor: In synchronous motor, 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.