This document discusses the power stages in DC generators and motors. It explains that in a DC generator, the input mechanical power minus losses equals the electrical power output, and the efficiencies can be calculated at each stage. A DC motor operates similarly but converts electrical power to mechanical power output. It also describes the basics of how DC motors work using Fleming's left hand rule, the production of back EMF, different types of DC motors, sources of losses in DC motors, and methods for testing DC machines.

1. D.C. Machine

2. Power Stages in D.C. Generator
Stage A Stage B Stage C

3.  Input (B.H.P x 735.5) – Iron & Friction loss
= Electrical Power Developed in Armature
(E*Ia)
 Electrical Power Developed in Armature
(E*Ia) – Copper Loss = Net output (Vt * IL)
 Mechanical Efficiency = Stage B / Stage A
= E*Ia / (B.H.P x 735.5)
 Electrical Efficiency = Stage C / Stage B
= Vt*IL / E*Ia
 Overall Efficiency = Stage C / Stage A
= Vt*IL / (B.H.P x 735.5)

4. Example

6. D.C. Motor
Introduction:
 Similar construction to D.C. Generator.
 Infect D.C. machine can be work as generator
or motor.
 Motor converts electrical energy in to
mechanical energy.
 Generator converts mechanical energy in to
electrical energy.

7.  When a current carrying conductor is placed
in a magnetic field, the conductor experiences
the force.
 The direction of force depends on the
direction of magnetic field and also depends
upon direction current in the conductor.

8. Fleming’s Left Hand Rule
 The direction of force is also decided by
applying Fleming's left hand rule.
 Thumb and first two fingers are use to explain
this rule.

9. Working Principle of D.C. Generator:
 It works on principle that, When current carrying
conductor is kept in magnetic field, a force is
produce on the conductor in define direction.
 When field winding carries the current (main flux
production) similarly the armature also carry the
current.
 If the main flux is downwards from ‘N’ to ‘S’ pole
and armature current having direction (.) in
upper conductor and (+) in the bottom
conductor, then applying Fleming’s left hand rule
the direction of the force on the upper conductor
is towards right and on bottom conductor
towards right. (as seen in next Fig.)

10.  This two equal and opposite forces produces
a ’Torque’ and thus motor starts working in
clockwise direction as seen in fig.
 Magnitude of this force is given by,
Force, F = B.I.L
Where,
B = Flux density of the field
I = Current in the conductor
L = Length of the conductor

11. Back EMF (Eb)
 Also called counter EMF.
 The term back electromotive force, or just back-EMF,
is most commonly used to refer to the voltage that
occurs in electric motors where there is relative
motion between the armature of the motor and the
magnetic field from the motor's field magnets, or
windings.
 In a motor using a rotating armature in the presence
of a magnetic flux, the conductors cut the magnetic
field lines as they rotate. This produces a voltage in the
coil; the motor is acting like a generator (Faraday's law
of induction) at the same time it is a motor. This
voltage opposes the original applied voltage;
therefore, it is called "back-electromotive force“.

12. Types of D.C. Motor
 D.C. Shunt Motor:
 D.C. Series Motor:

13.  D.C. Compound Motor:
 Long Shunt Compound Motor:

14. Losses in D.C. Motor
 Iron Loss/ Core Loss:
1. Hysteresis Loss
2. Eddy Current Loss
 Copper Loss:
 Mechanical Loss:
1. Friction Loss
2. Wind Loss

15. Power Stage for D.C. Motor

16. Example

18. Testing O D.C. Machine
 In order to check performance such as efficiency,
regulation, losses, change in speed, condition of
commutation, temperature rise etc.
1. Direct method of testing:
 Machine directly connected with load/pulley and
break arrangement.
2. Indirect method of testing:
 No Load test data obtain and parameters
calculate.
3. Regenerative method of testing: