machines

MACHINES??

What is a Machine??

Any device that reduces human efforts & time in doing a particular work can be termed as a machine.

Electrical Machines??When we talk about electrical machines we

are restricting ourselves to:-1)AC Machine, (Transformers, Induction

machine, Synchronous Machine etc.)

2)DC Machine, (DC Generators , DC Motors.)

DC MACHINEMotor: The device which converts electrical

energy into mechanical energy is called a motor.

Generator: The device which converts mechanical energy into electrical is called a generator.

Basic Principal of Generators Faradays law of electromagnetic induction

states that when a conductor or a coil is rotated in a magnetic field an emf is induced, and if the

coil form a closed loop, currents starts to flow in it.Generator always works on Fleming’s right hand rule.

Basic Principal of Motors If a conductor carrying current is placed in a

magnetic field force is act on the conductor.

Motors works on fleming’s left hand rule.

Construction of Dc machine

•Stator is the static part of machine

•Rotor is the rotating part of machine

Constructional features A dc machine works as a DC generator when it is driven by a prime mover.

The same machine works as a DC motor when electrical energy is supplied to it.

Main parts of DC Machine

Static parts of dc machine

Frame or yoke : yoke made of cast steel. Outer framed machine – protection Provide the flux path.

Pole : Pole is made of laminated steel sheet Pole houses the field winding.

Field winding : It is cupper wire winding It is responsible for set up of a field in which

armature rotate.Pole shoe :

Face of the pole. Concave shape Distribute the main flux

INTERPOLE :To neutralize the effect of armature reaction in the space in between two main poles, smaller poles, called interpoles .

Rotating partsThe rotating part of the DC machine is also

known as armature. Shaft :The Shaft houses the cylindrical

armature. Prime mover is case of generator & load in case of motor is connect with the shaft.

Commutator& brushes: 1)Convert A.C. of armatures in to DC output

in generator . 2)In motor it convert DC supply into AC.

Commutator which rotates with the armature is made from a number of wedge-shaped hard drawn copper bars or segments insulated from each other and from the shaft.

Current is collected from the armature winding by means of two or more carbon brushes, mounted on the Commutator.

Complete View of Machine

Armature core made of laminated steel to reduce the eddy current losses in core.

Slots are stamped on the periphery of the armature. The armature slots house the armature winding.

Armature conductors in the slots are secured in their places by hard wooden wedges or fiber glass wedges.

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