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Basic Electrical Engineering
15ELE15/25
D
...
Machines:
Syllabus:
Working principle of D
...
Machine as a generator and a motor
...
Emf equation of
generator, relation between induced Emf and terminal voltage with an enumeration
of brush contact drop and drop due to armature reaction
...
C
...
Types of D
...
motors,
characteristics and applications
...
C
...
Introduction:
➢ The converters which are used to continuously translate an electrical input to a
mechanical output or vice versa are called as DC machines
...
Working principle of D
...
Machine as a generator and a motor:
Working principle of D
...
Machine as a generator:
➢ Whenever a coil is rotated in a magnetic field an Emf will be induced in this coil and
is given by e=B*l*v*Sinθ volts/coil side where, 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
...
Working principle of D
...
Machine as a motor:
➢ Whenever a current coil is placed under a magnetic field the coil experiences a
mechanical force, and is given by F= B*I*l*Sinθ Newton/coil side where, I is the
current through the coil
...
Construction of DC Machine:
Dept of EEE, SVIT
Basic Electrical Engineering
15ELE15/25
Salient parts of a D
...
Machine are:
(i)Field system (poles)
(ii)Coil arrangement (armature)
(iii)Commutator
(iv)Brushes
(v)Yoke
Yoke:
i) It serves the purpose of outermost cover of the D
...
machine
...
ii) It provides mechanical support to the poles
...
It provides a path of low reluctance for magnetic
flux
...
➢ It directs the flux produced through air gap to armature core, to the next pole
...
to achieve this, pole shoe has given a
particular shape
Field winding [F1-F2]:
➢ The field winding is wound on the pole core with a definite direction
...
As it helps in producing the magnetic field
i
...
exciting the pole as electromagnet it is called Field winding or Exciting winding
...
It consists of slots on its
periphery and the air ducts to permit the air flow through armature which serves
cooling purpose
...
➢ This needs rectifications in case of D
...
generator which is possible by device
called commutator
...
➢ Ball bearings are usually used as they are more reliable
...
Types of D
...
Armature Windings
Lap Winding
Wave Winding
In this winding all the coils carrying current in
In this winding all the pole groups of
the same direction are connected in series i
...
,
the coils generating emf in the same
coils carrying current in one direction are
direction
at
any
instant
of
time
connected in one series circuit and coils carrying
are connected in parallel by the brushes
...
2
...
Wave winding is also known as series
windings
...
3
...
The number of parallel paths is always equal
to the number of poles i
...
, A = P
...
e
...
4
...
The number of brushes required by this
winding is always equal to the number
winding is always equal to 2
...
5
...
The machine using wave winding does
requires equalizer rings for obtaining
require dummy coils to provide the mechanical
better commutation
...
6
...
Wave windings are used for high voltage and
voltage and high current machines
...
Dept of EEE, SVIT
Basic Electrical Engineering
15ELE15/25
Emf Equation of DC Generator:
For one revolution of the conductor,
Let, Φ = Flux produced by each pole in weber (Wb) and
P = number of poles in the DC generator
...
Now, according to Faraday’s law of induction, the induced emf of the armature conductor is
denoted by “e” which is equal to rate of cutting the flux
...
Here, Z = total numbers of conductor A = number of parallel paths
Then, Z/A = number of conductors connected in series
We know that induced Emf in each path is same across the line
Therefore, Induced Emf of DC generator E = Emf of one conductor × number of conductor
connected in series
...
e
...
➢ In general the method employed to connect field and armature winding has classify
into two groups
...
That means the field winding is electrically separated from the armature circuit
...
➢ The electromotive force that produced by generator at armature winding is supply to a
field winding (shunt field) instead of DC source from outside of the generator
...
They may be further classified as: a) DC Shunt generator
b) DC Series generator
c) DC Compound generator
...
Dept of EEE, SVIT
Basic Electrical Engineering
15ELE15/25
b) Series generator:
➢ The field winding and armature winding is connected in series
...
➢ Therefore, field winding conductor must be sized enough to carry the load current
consumption and the basic circuit
c) Compound generator :
➢
➢
The compound generator has provided with magnetic