Salient and Non Salient Pole Generators

What is Alternator?
An alternator is defined as a machine or generator which produces AC
(Alternating Current) supply and it converts mechanical energy into electrical
energy, so it is also called an AC generator or synchronous generator. There
are different types of alternators based on applications and design. The
Marine type alternator, Automotive type alternator, Diesel-electric locomotive
types alternator, Brushless type alternator, and Radio alternators are the types
of alternators based on the applications. The Salient Pole type and Cylindrical
rotor type are the types of alternators based on the design.
Construction of an Alternator
The main components of an alternator or synchronous generator are rotor and
stator. The main difference between rotor and stator is, the rotor is a rotating
part and stator is not a rotating component means it is a stationary part. The
motors are generally run by rotor and stator.

The stator word based on the stationary and the rotor word based on the
rotating. The construction of the stator of an alternator is equal to the
construction of the stator of an induction motor. So induction motor
construction and synchronous motor construction are both are same. Thus the
stator is the stationary part of the rotor and the rotor is the component that
rotates inside of the stator. The rotor is located on the stator shaft and the
series of the electromagnets arranged in a cylinder causing the rotor to rotate
and create a magnetic field. There are two types of rotors they are shown in
the below figure.
Salient Pole Rotor
The meaning of the salient is projecting outward, which means the poles of
the rotor are projecting outward from the center of the rotor. There is a field
winding on the rotor and for this field winding will use DC supply. When we
pass the current through this field winding N and S poles are created. The
salient rotors are unbalanced so the speeds are restricted. This type of rotor
used in hydro stations and diesel power stations. The salient pole rotor used
for low-speed machines approximately 120-400rpm.
Cylindrical Rotor
The cylindrical rotor is also known as a non-salient rotor or round rotor and
this rotor is used for high-speed machines approximately 1500-3000 rpm and
the example for this is a thermal power plant. This rotor is made up of a steel
radial cylinder having the number of slots and in these slots, the field winding
is placed and these field windings are always connected in series. The
advantages of this are mechanically robust, flux distribution is uniform,
operates at high speed and produces low noise.
An AC motor comes in many shapes and sizes, but we can’t have an AC
without a rotor and stator. The rotor is made up of a cast iron and the stator is
made up of silicon steel. The prices of the rotor and stator depend on the
quality.
Working Principle of Alternator

All the alternators work on the principle of electromagnetic induction.
According to this law, for producing the electricity we need a conductor,
magnetic field and mechanical energy. Every machine that rotates and
reproduces Alternating Current. To understand the working principle of the
alternator, consider two opposite magnetic poles north and south, and the flux
is traveling between these two magnetic poles. In the figure (a) rectangular
coil is placed between the north and south magnetic poles. The position of the
coil is such that the coil is parallel to the flux, so no flux is cutting and
therefore no current is induced. So that the waveform generated in that
position is Zero degrees.
If the rectangular coil rotates in a clockwise direction at an axis a and b, the
conductor side A and B comes in front of the south pole and C and D come in
front of a north pole as shown in figure (b). So, now we can say that the
motion of the conductor is perpendicular to the flux lines from N to S pole and
the conductor cuts the magnetic flux. At this position, the rate of flux cutting by
the conductor is maximum because the conductor and flux are perpendicular
to each other and therefore the current is induced in the conductor and this
current will be in maximum position.
The conductor rotates one more time at 900 in a clockwise direction then the
rectangular coil comes in the vertical position. Now the position of the
conductor and magnetic flux line is parallel to each other as shown in figure
(c). In this figure, no flux is cutting by the conductor and therefore no current is
induced. In this position, the waveform is reduced to zero degrees because
the flux is not cutting.
In the second half cycle, the conductor is continued to rotate in a clockwise
direction for another 900. So here the rectangular coil comes to a horizontal
position in such a way that the conductor A and B comes in front of the north
pole, C and D come in front of the south pole as shown in the figure (d). Again
the current will flow through the conductor that is currently induced in the
conductor A and B is from point B to A and in conductor C and D is from point
D to C, so the waveform produced in opposite direction, and reaches to the
maximum value. Then the direction of the current indicated as A, D, C and B
as shown in figure (d). If the rectangular coil again rotates in another 900 then
the coil reaches the same position from where the rotation is started.
Therefore, the current will again drop to zero.
In the complete cycle, the current in the conductor reaches the maximum and
reduces to zero and in the opposite direction, the conductor reaches the
maximum and again reaches zero. This cycle repeats again and again, due to
this repetition of the cycle the current will be induced in the conductor cont.sly.
This is the process of producing the current and EMF of a single-phase. Now
for producing 3 phases, the coils are placed at the displacement of 1200 each.
So the process of producing the current is the same as the single-phase but
only the difference is the displacement between three phases is 1200. This is
the working principle of an alternator.
Characteristics
The characteristics of an alternator are
1. Output Current with Speed of Alternator: The output of the current

reduced or decreased when the alternator speed reduced or
decreased.
2. The efficiency with Speed of Alternator: Efficiency of an alternator
is reduced when the alternator runs with low speed.
3. Current Drop with Increasing Alternator Temperature: When the
temperature of an alternator increased the output current will be
reduced or decreased.
Applications
The applications of an alternator are
● Automobiles
● Electrical power generator plants
● Marine applications
● Diesel electrical multiple units
● Radiofrequency transmission

Salient and Non Salient Pole Generators

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What is Alternator?

An alternator is defined as a machine or generator which produces AC

(Alternating Current) supply and it converts mechanical energy into electrical

energy, so it is also called an AC generator or synchronous generator. There

are different types of alternators based on applications and design. The

Marine type alternator, Automotive type alternator, Diesel-electric locomotive

rotor type are the types of alternators based on the design.

motors are generally run by rotor and stator.

Salient Pole Rotor

for low-speed machines approximately 120-400rpm.

advantages of this are mechanically robust, flux distribution is uniform,

operates at high speed and produces low noise.

An AC motor comes in many shapes and sizes, but we can’t have an AC

Working Principle of Alternator

According to this law, for producing the electricity we need a conductor,

therefore no current is induced. So that the waveform generated in that

position is Zero degrees.

If the rectangular coil rotates in a clockwise direction at an axis a and b, the

current will be in maximum position.

induced. In this position, the waveform is reduced to zero degrees because

the flux is not cutting.

In the second half cycle, the conductor is continued to rotate in a clockwise

conductor A and B is from point B to A and in conductor C and D is from point

D to C, so the waveform produced in opposite direction, and reaches to the

maximum value. Then the direction of the current indicated as A, D, C and B

Therefore, the current will again drop to zero.

the working principle of an alternator.

1. Output Current with Speed of Alternator: The output of the current

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