Types of Electrical Machines

TYPES OF ELECTRICAL MACHINES

Electrical machines are classified as AC machines and DC machines.

Types of DC machines

                                                                                  DC Generator

                                                                                  DC Motor

Types of AC machines

                                                 i.      Transformers

a.    (a)Single phase

b.   (b) three phase

                                               ii.      Alternators

                                            iii.      Synchronous motor

                                            iv.      Induction motor

a.    (a)Single phase

b.   (b) three phase

1. APPLICATIONS OF DC MOTOR

Shunt: driving constant speed, lathes, centrifugal pumps, machine tools, blowers and fans, reciprocating pumps

          Series: electric locomotives, rapid transit systems, trolley cars, cranes and hoists, conveyors

          Compound: elevators, air compressors, rolling mills, heavy planners.

2. CHARACTERISTICS OF DC MOTORS

To select the electric motor for a particular purpose it is necessary to know the characteristics of electric motors. Hence the performance of DC motor can be judged from its characteristics curves.

Ø                         Electrical characteristics

                             Torque / Armature current characteristics

                             Speed / Armature current characteristics

Ø                         Mechanical characteristics

                             Speed / Torque characteristics

3. TYPES OF ELECTRIC BRAKING

There are three types of electric braking namely,

Ø                       Rheostatic or Dynamic braking

Ø                       Plugging or counter current braking or reverse current braking

Ø                       Regenerative braking

REGENERATIVE BRAKING

Ø               In the regenerative braking operation, the motor operates as a generator, while it is still connected to the supply here, the motor speed is grater that the synchronous speed.

Ø               Mechanical energy is converter into electrical energy, part of which is returned to the supply and rest as heat in the winding and bearing.

DYNAMIC BRAKING

Ø               In this method of breaking, the motor is disconnected from the supply, the field connections are reversed and motor is connected in series with a variable resistance R.

PLUGGING

                The plugging operation can be achieved by changing the polarity of the motor there by reversing the direction of rotation of the motor.

                 This can be achieved in ac motors by changing the phase sequence and in dc motors by changing the polarity