The document describes the key components and operating principles of DC dynamos and motors. It explains that a dynamo is a machine that converts mechanical energy to electrical energy or vice versa. The main parts are identified as the armature windings, field poles, and commutator. Generators use mechanical input to produce electrical output via electromagnetic induction. Motors use electrical input to produce mechanical output via the interaction of magnetic fields and current-carrying conductors. Various types of dynamos are described, along with factors that determine the magnitude of induced voltages and forces. Formulas are provided for calculating voltage, force, and torque.

1. DC Dynamos, Construction
and Armature Windings

2. Dynamo
• Symbol of power
• Defined as a rotating electrical machine that
converts mechanical energy into electrical
energy and vice versa.

3. Kinds of Dynamo
• Electric Generator
• Electric Motor

4. Generator
• It used to convert mechanical energy to
electrical energy.
• It is driven by a mechanical machine called
prime mover like steam turbine, gasoline
engine or an electrical motor.
• Generator action can take place when and
only when there is relative motion between
conductors wires and magnetic line of force.

5. Motor
• It used to convert electrical energy to
mechanical energy.
• It is supplied with electrical energy to
develops torque, tendency is to produce
rotation

6. Rotary Converters
• Electrical energy of one form is changed into
electrical energy to another form
• Usual arrangement is to change ac to dc

7. Frequency Converters
• Its function is to change AC electric energy at
one frequency into AC electric energy at
another frequency

8. Parts of a Dynamo
• Poles or an even set of electromagnet or
permanent magnets
• Laminated steel core containing current
carrying copper wires also known as armature
windings

9. Generator Figure

13. Motor

19. Armature Windings
• Wound on laminated steel cores of good
magnetic permeability
• Current developed is always AC regardless of
the type of motor or generator

20. Types of Armature
• Ring type
• Drum type

21. Commutator
• Is used as rotary switch in a certain type of
motor and generator that periodically reverses
the current direction between rotor and
extend circuit

22. Types of Commutator
• Split Commutator – used for DC output
• Slip commutator – used for AC output

23. Field Poles
• Used in all the types of DC generator and
motor , in an AC that are simple in
construction
• Always an even number of them and each one
consist of a laminated steel core rectangular in
cross section surrounded by one or more
copper coils

24. Types of DC Generator
• Series Generator
• Shunt Generator
• Compound Generator

25. Series Generator
• It has low resistance field winding of very few
turns of heavy wires placed in series in the
machine.
• its field winding called series field winding is
connected in series with the armature. It is
used for constant application like in series
street lighting.

26. Shunt Generator
• Its has comparatively high resistance field
winding of many turns of fine wire connected
in parallel with the machine

27. Types of Shunt Generator
• Self Excited– the excitation is produced by a
single winding connected to the positive and
negative brushes.
• Separately Excited - the excitation is produced
by a single winding connected to the positive
and negative brushes fed by another dc
generator.

28. Compound Generator
• It has two complete sets of windings for
excitation purposes
a. Shunt field
b. Series field

29. Types of Compound Motors
• Long shunt
• Short shunt

30. DC Generator and
motor principle

31. Principle of Generator Action
• The presence of magnetic line of force
• Motion of conductors cutting the flux
• Voltage generated

32. Principle of Motor Action
• The presence of magnetic line of force
• Conductor of electricity
• Power supply

34. Faraday’s Law of Electromagnetic
Induction
• It state that magnitude of the voltage induced
in a single turn of wire is proportional to the
rate of at which a conductor cuts magnetic
lines of force
• Eave = Φ / t x 10-8
• Eave = Φ / t

35. Factors Affecting magnitude of induced
EMF
• Flux density
• Active conductor length
• Relative linear velocity
• e = BLv sinɵ x 10-8
• e = BLv sinɵ

36. General Voltage Equation for DC
Generator
• Eg =
• Eg= total generated voltage in the armature, volts
• Ф = flux per pole, lines/pole or Maxwell’s/ pole
• P = no. of poles, an even no.
• N = speed of the armature conductors
• Z = total no. of active armature conductors
• a = no. of parallel paths in the armature

37. Problems
• Calculate the average voltage generated in a
moving conductor of it cuts a 2.6 x 106 Maxwell in
1/40 sec, in 1/80 sec.
• A magnetic coils produces 100,000 Maxwell with
2,000 turns and with current of 2A. The current is
cut off and the flux collapses in 0.01 sec. What is
the average voltage?
• The armature coil of a generator with 50
conductors on it rotates in a magnetic field with a
flux density 1.5 T. the effective area of the coil is
1000 square cm. If this coil is move across the
pole in 0.5 sec, determine the average emf
induced in the coil.

38. Commutation Process in a DC
Generator
• The process of the split-slip ring commutator
to change the direct current to alternating
current flowing in the armature conductor

39. Direction of Rotation
• Current flowing through the armature
conductor
• The polarity of fields

40. Factors affect the magnitude of
electromagnetic force F
• Magnetic field intensity
• Active length of the conductor
• Current flowing in the conductor
• F = BIL Newtons
• F = BIL/10 dynes
• F = BIL / 11300000 lb

42. Problems
• A six pole dc generator has an armature winding with 504 conductors
connected in six parallel paths. Calculate the generated voltage in this
machine if each pole produces 1 650 000 maxwells and the armature
speed is 1800 rpm. If the machine is modified to become two parallel
paths. At what speed should the machine be driven if it is develop the
same voltage as before the change, assuming all other conditions to
remained unchanged?
• Calculate the voltage generated by a four pole dc machine. Given the
following particulars: Number of slot in armature = 55; number of
conductor per slot = 4; flux per pole = 2620000 maxwells; speed = 1,200
rpm; numbers of parallel paths in armature = 2. find the generated if the
parallel paths is 4?
• A four pole machine generates 250 volts when operated at 1500 rpm. If
the flux per pole is 1850000 maxwells, the number of armature slots is
45, and the armature winding has two parallel paths, calculate the total
number of armature conductors and number of conductors in each slot.

43. • What is the frequency of the alternating voltage
generated in the armature conductors of 6poles 900
rpm, 8pole 750 rpm, 10 pole 500 rpm
• Calculate the force exerted by each conductor, 6 in
long on the armature of a dc motor when carries a
current of 90 amp and lies in a field intensity of which
52,000 lines per square inch. What is the torque
develop if it lies on an armature the diameter of which
is 9 in?
• The armature of a dc motor has 31 slots with 16
conductors in each slots only 68 percent of the
conductors lie directly under the pole faces, where the
flux density is uniform at 46,000 lines per square inch.
If the armature core diameter is 7.25 in., its length
4.25 in, and the current in each conductor is 25 amp.
Calculate the force exerted by the armature tending to
produce rotation and torque in lb-ft.

44. • How many poles are there in a generator in
which the armature frequency is 30 cps when
operating it a speed of 600 rpm?
• At what speed is an armature rotating in 12-pole
machine if the frequency in the armature
conductors is 50 cps
• A dc motor has an armature containing 192
conductors, 70 percent of which lie directly
under the pole faces at any given instant. If the
flux density under the poles is 52,000 lines per
square inch and the armature diameter and
length are 12 in and 4.5 inch respectively,
calculate the current in each armature
conductors for a torque of 120 lb-ft.