Electrical machine

Introduction:

An electrical machines  is a device which converts mechanical energy into electrical energy or vice versa. Electrical machines also include transformers, which do not actually make conversion between mechanical and electrical form but they convert AC current from one voltage level to another voltage level.

Generator:

A generator is an electrical machine which converts mechanical form of energy into electrical form. Generator works on the principle that whenever a conductor moves in a magnetic field, an emf gets induced in the conductor. This principle is called as generator action.
Generators have generally two basic parts named "Stator" and "Rotor". Mechanical energy is provided to the rotor of a generator by means of a prime mover (i.e. a turbine). Turbines are of different types like steam turbine, water turbine, wind turbine etc. Mechanical energy can also be provided by IC engines or similar other sources.
To learn more about how generators work, read the following articles.

• AC Generator (converts mechanical energy into Alternating Current (AC) electricity)
• DC Generator (converts mechanical energy into Direct Current (DC) electricity)

AC generator

An AC generator converts mechanical energy into alternating current electricity. Because power transferred into the field circuit is much less than power transferred into the armature circuit, AC generators nearly always have the field winding on the rotor and the armature winding on the stator.

AC generators are classified into several types.

• In an induction generator, the starter magnetic flux induces currents in the rotor. The prime mover then drives the rotor above the synchronous speed, causing the opposing rotor flux to cut the stator coils producing active current in the stator coils, thus sending power back to the electrical grid. An induction generator draws reactive power from the connected system and so cannot be an isolated source of power.
• In a Synchronous generator (alternator), the current for the magnetic field is provided by a separate DC current source.

DC generator

An electric generator is a machine that converts mechanical energy into electrical energy. An electric generator works based on the principle that whenever conductor cuts the magnetic field, an emf is induced which will cause the current to flow if conductor circuit is closed. Take the working of Simple loop Generator as an example.

Motor:

A motor is an electrical machine which converts electrical energy into mechanical energy. When a current carrying conductor is placed in a magnetic field, the conductor experiences a mechanical force and this is the principle behind motoring action.
Just like generators, motors also consists two basic parts, stator and rotor. In a motor, we give electric supply to both the stator and rotor windings which causes a mechanical force between the stator and rotor. This force causes the rotor to rotate.
To learn more about electric motors, read the following articles.

AC motors: (i) Induction motors and (ii) Synchronous motor

DC motors: (i) Brushed DC motor and (ii) Brushless DC motor

AC motor

An AC motor converts alternating current into mechanical energy. It commonly consists of two basic parts, an outside stationary stator having coils supplied with alternating current to produce a rotating magnetic field, and an inside rotor attached to the output shaft that is given a torque by the rotating field. The two main types of AC motors are distinguished by the type of rotor used.

• Induction (asynchronous) motor, the rotor magnetic field is created by an induced current. The rotor must turn slightly slower (or faster) than the stator magnetic field to provide the induced current. There are three types of induction motor rotors, which are squirrel-cage rotor, wound rotor and solid core rotor.
• Synchronous motor, it does not rely on induction and so can rotate exactly at the supply frequency or sub-multiple. The magnetic field of the rotor is either generated by direct current delivered through slip rings (exciter) or by a permanent magnet.

DC motor

The brushed DC electric motor generates torque directly from DC power supplied to the motor by using internal commutation, stationary permanent magnets, and rotating electrical magnets. Brushes and springs carry the electric current from the commutator to the spinning wire windings of the rotor inside the motor. Brushless DC motors use a rotating permanent magnet in the rotor, and stationary electrical magnets on the motor housing. A motor controller converts DC to AC. This design is simpler than that of brushed motors because it eliminates the complication of transferring power from outside the motor to the spinning rotor. An example of a brushless, synchronous DC motor is a stepper motor which can divide a full rotation into a large number of steps.

Transformers:

Transformers do not actually make conversion between mechanical and electrical form, but they transfer electric power from one circuit to another circuit. They can decrease or increase the voltage while transferring the power without changing the frequency, but with the corresponding increase or decrease in the current. Transformers also belong to electrical machines.
Step up transformers increases the voltage level from primary to secondary but with the corresponding decrease in the current and vice versa.




There are three types of transformers

1. Step-up transformer
2. Step-down transformer
3. Isolation transformer

There are four types of transformers based on structure

1. core type
2. shell type
3. power type
4. instrument type