D.C. MACHINES . Working principle of D.C.Machine as generator and motor, constructional features, EMF equation of generator and simple problems, back emf and torque equation of DC motors, simple problems, types of DC motors, characteristics and applications, necessity of starter, 3-point starter.______________________________________________________________________A machine which works on direct current is defined as a D.C.Machine.

D.C.Machines are of two types. (i) D.C.Generator and (ii) D.C.Motor.

Sl.No. D.C. Generator D.C.Motor1 Definition:

A generator is a rotatingmachine which convertsmechanical energy intoelectrical energy

Definition:A motor is a machine which converts electrical energy into mechanical energy

2 Principle:Whenever a coil is rotated in a magnetic field an e.m.f. will be induced in this coiland is given bye=BlvSinθ volts/coil sidewhere, B=The flux density in Tesla, l=the active length of the coil side in meters, v=the velocity with which the coil is moved in meters/sec and θ is the angle between the direction of the flux and the direction of rotation of the coil side.

Principle:Whenever a current coil is placed under a magnetic field the coil experiences a mechanical force, and is given by F= BIlSinθ Newtons/coil side.Where, I is the current through the coil in ampere.

3 The direction of the emf induced is fixed by applying the Fleming’s right hand rule

The direction of the force acting is fixed by applying the Fleming’s left hand rule.

CONSTRUCTION OF A D.C.MACHINE.

Salient parts of a D.C.machine are: Field system (poles) Coil arrangement (armature)