ALTERNATOR: Construction - salient and non-salient pole type alternators -Principle of

operation -EMF equation – Load Characteristics of alternators -Voltage Regulation - Parallel

operation of Three Phase Alternators-Applications.

Construction - salient and non-salient pole type alternators

Definition of an Alternator
The synchronous generator or Alternator is a machine for converting the mechanical power
from a prime mover to an AC electrical power at a specific voltage and frequency.

Three-phase alternators are used because it has several advantages of distribution,

generation, and transmission. For bulk power generation large alternator is used in the
thermal, hydro and nuclear power station.

Alternator

An alternator consists of field poles placed on the rotating fixture of the machine i.e. rotor as
Shown. The rotor rotates in the stator.
The field poles get projected on the rotor body. The armature conductors are housed on the
stator.
An alternating three-phase voltage represented by aa’, bb’, cc’ is induced in the armature
conductors thus resulting in the generation of three-phase electrical power.

All modern electrical power generating stations use this technology for generation of three-
phase power, and as a result, the alternator or synchronous generator has become a subject of
great importance and interest for power engineers.

An alternator is basically a type of AC generator which also known as synchronous

generator.
The field poles are made to rotate at synchronous speed N s = 120 f/P for effective power
generation. Where, f signifies the alternating current frequency and the P represents the

number of poles.

In most practical construction of alternator, it is installed with a stationary armature

winding and a rotating field unlike in the case of DC generator where the arrangement is
exactly opposite.

This modification is made to cope with the very high power of the order of few 100
Megawatts produced in an AC generator contrary to that of a DC generator.

To accommodate such high power the conductor weighs and dimensions naturally have
to be increased for optimum performance. For this reason is it beneficial to replace
these high power armature windings by low power field windings, which is also
consequently of much lighter weight, thus reducing the centrifugal force required to
turn the rotor and permitting higher speed limits.

Principle of operation

The magnetic pole of the rotor is excited by the direct field current.

When the rotor rotates, the magnetic flux cut the stator conductor, and hence EMF induces in
them.

As the magnetic pole alternating rotating N and S, they induce an EMF and current in
armature conductor which first rotate in a clockwise direction and then in an anti-clockwise
direction.

Thus, generates the alternating current.

WORKING PRINCIPLE OF ALTERNATOR

The working principle of alternator is very simple. It is just like basic principle of DC
generator.
It also depends upon Faraday's law of electromagnetic induction which says the current is
induced in the conductor inside a magnetic field when there is a relative motion between that
conductor and the magnetic field.

For understanding working of alternator let us think about a single rectangular turn placed
in between two opposite magnetic poles as shown above. Say this single turn loop ABCD can
rotate against axis a-b. Suppose this loop starts rotating clockwise. After 90o rotation the side
AB or conductor AB of the loop comes in front of S-pole and conductor CD comes in front of
N-pole.

At this position the tangential motion of the conductor AB is just perpendicular to the
magnetic flux lines from N to S pole. Hence, the rate of flux cutting by the conductor AB is
maximum here and for that flux cutting there will be an induced current in the conductor AB
and the direction of the induced current can be determined by Flemming's right-hand rule. As
per this rule the direction of this current will be from A to B.
 At the same time conductor CD comes under N pole and here also if we apply Fleming right-
hand rule we will get the direction of induced current and it will be from C to D.

Now after clockwise rotation of another 90o the turn ABCD comes at vertical position as
shown below. At this position tangential motion of conductor AB and CD is just parallel to
the magnetic flux lines, hence there will be no flux cutting that is no current in the conductor.
While the turn ABCD comes from horizontal position to vertical position, angle between flux
lines and direction of motion of conductor, reduces from 90 o to 0o and consequently the
induced current in the turn is reduced to zero from its maximum value.

After another clockwise rotation of 90 o the turn again comes to horizontal position, and here
conductor AB comes under N-pole and CD comes under S-pole, and Fleming right-hand rule
is applied, and induced current in conductor AB, is from point B to A and induced current in
the conductor CD is from D to C. As at this position the turn comes at horizontal position
from its vertical position, the current in the conductors comes to its maximum value from
zero.

Means current is circulating in the close turn from point B to A, from A to D, from D to C
and from C to B, provided the loop is closed although it is not shown here. That means the
current is in reverse of that of the previous horizontal position when the current was
circulating as A → B → C → D → A.
While the turn further proceeds to its vertical position the current is again reduced to zero. So
if the turn continues to rotate the current in turn continually alternate its direction. During
every full revolution of the turn, the current in turn gradually reaches to its maximum value
then reduces to zero and then again it comes to its maximum value but in opposite direction
and again it comes to zero. In this way, the current completes one full sine wave cycle during
each 360o revolution of the turn. So, we have seen how an alternating current is produced in a
turn is rotated inside a magnetic field. From this, we will now come to the actual working
principle of alternator.

If one stationary brush on each slip ring is connected and If two terminals of an external load
is connected with these two brushes, an alternating current is produced in the load. This is an
elementary model of alternator.

THE BASIC OPERATIONAL PRINCIPLE OF A PRACTICAL ALTERNATOR

Generally the practical construction of alternator is armature conductors are stationary and
field magnets rotate between them.
The rotor of an alternator or a synchronous generator is mechanically coupled to the shaft or
the turbine blades, which being made to rotate at synchronous speed Ns under some
mechanical force results in magnetic flux cutting of the stationary armature conductors
housed on the stator.
As a direct consequence of this flux cutting an induced emf and current starts to flow
through the armature conductors which first flow in one direction for the first half cycle and
then in the other direction for the second half cycle for each winding with a definite time lag
of 120o due to the space displaced arrangement of 120 o between them. This particular
phenomenon results in three phase power flow out of the alternator which is then transmitted
to the distribution stations for domestic and industrial uses.
 In addition to these, armature winding of alternator can also integral slot winding and
fractional slot winding.
Construction of Alternator

There are mainly two types of rotor used in construction of alternator,

1. Salient pole type.
2. Cylindrical rotor type (or) non-salient pole rotor
Salient Pole Type
The term salient means protruding or projecting.

The salient pole type of rotor is generally used for slow speed machines having large
diameters and relatively small axial lengths.

The poles, in this case, are made of thick laminated steel sections riveted together and
attached to a rotor with the help of joint.

An alternator as mentioned earlier is mostly responsible for generation of very high electrical
power. To enable that, the mechanical input given to the machine in terms of rotating torque
must also be very high.
This high torque value results in oscillation or hunting effect of the alternator or synchronous
generator, to prevent these oscillations from going beyond bounds the damper winding is
provided in the pole faces as shown

The damper windings are basically copper bars short-circuited at both ends are placed in the
holes made in the pole axis.
When the alternator is driven at a steady speed, the relative velocity of the damping winding
with respect to the main field will be zero.
But as soon as it departs from the synchronous speed there will be relative motion between
the damper winding and the main field which is always rotating at synchronous speed.
This relative difference will induce the current in them which will exert a torque on the field
poles in such a way as to bring the alternator back to synchronous speed operation.
 The salient feature of pole field structure has the following special feature-
1. They have a large horizontal diameter compared to a shorter axial length.
2. The pole shoes covers only about 2/3rd of pole pitch.
3. Poles are laminated to reduce eddy current loss.
4. The salient pole type motor is generally used for low-speed operations of around 100 to
400 rpm, and they are used in power stations with hydraulic turbines or diesel engines.
Salient pole alternators driven by water turbines are called hydro-alternators or hydro
generators.

Cylindrical Rotor Type

The cylindrical rotor is generally used for very high speed operation and employed in steam
turbine driven alternators like turbo generators.

The machines are built in a number of ratings from 10 MVA to over 1500 MVA. The
cylindrical rotor type machine has a uniform length in all directions, giving a cylindrical
shape to the rotor thus providing uniform flux cutting in all directions.

The rotor, in this case, consists of a smooth solid steel cylinder, having a number of slots
along its outer periphery for hosting the field coils.

The cylindrical rotor alternators are generally designed for 2-pole type giving very high speed

of

Or 4-pole type running at a speed of

Where, f is the frequency of 50 Hz.

The cylindrical rotor synchronous generator does not have any projections coming out from
the surface of the rotor, rather central polar area is provided with slots for housing the field
windings as we can see from the diagram above.

The field coils are so arranged around these poles that flux density is maximum on the polar
central line and gradually falls away as we move out towards the periphery. The cylindrical
rotor type machine gives better balance and quieter-operation along with lesser windage
losses.

Salient Pole Rotor Vs. Non-Salient Pole Rotor

https://www.electricaleasy.com/2014/03/salient-pole-rotor-vs-non-salient-pole.html

Rotors of an electrical machine are classified as: (i) Salient pole rotors and (ii) Non-salient
pole rotors.

Salient Pole Rotor

In salient pole type of rotor consist of large number of projected poles (salient poles)
mounted on a magnetic wheel.

Construction of a salient pole rotoris as shown .

The projected poles are made up from laminations of steel. The rotor winding is
provided on these poles and it is supported by pole shoes.

 Salient pole rotors have large diameter and shorter axial length.
 They are generally used in lower speed electrical machines, say 100 RPM to 1500
RPM.
  As the rotor speed is lower, more number of poles are required to attain the required
frequency. (Ns = 120f / P therefore, f = Ns*p/120 i.e. frequency is proportional to
number of poles). Typically number of salient poles is between 4 to 60.
 Flux distribution is relatively poor than non-salient pole rotor, hence the generated emf
waveform is not as good as cylindrical rotor.
 Salient pole rotors generally need damper windings to prevent rotor oscillations during
operation.
 Salient pole synchronous generators are mostly used in hydro power plants.

Non-Salient Pole (Cylindrical) Rotor

Non-salient pole rotors are cylindrical in shape having parallel slots on it to place rotor
windings. It is made up of solid steel.

The construction of non-salient pole rotor (cylindrical rotor) is as shown .Sometimes,

they are also called as drum rotor.

 They are smaller in diameter but having longer axial length.

 Cylindrical rotors are used in high speed electrical machines, usually 1500 RPM to
3000 RPM.
 Windage loss as well as noise is less as compared to salient pole rotors.
 Their construction is robust as compared to salient pole rotors.
 Number of poles is usually 2 or 4.
 Damper windings are not needed in non-salient pole rotors.
 Flux distribution is sinusoidal and hence gives better emf waveform.
  Non-salient pole rotors are used in nuclear, gas and thermal power plants.

Single Phase Armature Winding

Single phase armature winding can be either concentrated or distributed type.

Concentrated Armature Winding

The concentrated winding is employed where the number of slots on the armature is equal to
the number of poles in the machine. This armature winding of alternator gives maximum
output voltage but not exactly sinusoidal.

The most simple single-phase winding is shown below in the figure-1. Here, number poles =
the number of slots = number of coil sides. Here, one coil side is inside one slot under one
pole and the other coil side inside other slots under next pole. The emf induced in one coil
side gets added to that of adjacent coil side.

This arrangement of an armature winding in an alternator is known as skeleton wave

winding. As per the fig-1, coil side-1 under N-pole is connected to coil side-2 under S-pole at
the back and coil side-3 at the front and so on. The direction of induced emf of coil side-1 is
upward and emf induced in coil side-2 is downward. Again as coil side-3 is under N-pole, it
will have emf in the upward direction and so on. Hence total emf is the summation of emf of
all coil sides. This form of armature winding is quite simple but rarely used as this requires
considerable space for end connection of every coil side or conductor. We can overcome this
problem, some extent by using multi turns coil. We use the multi-turn half coiled winding to
get higher emf. Since the coils cover only one half of the armature periphery thus, we refer
this winding as Half coiled or Hemi - tropic winding. Figure - 2 shows this. If we distribute
the all coils over the whole armature periphery, then the armature winding is referred as
whole coiled winding.

Fig
ure 3 shows a double layer winding, where we place one side of each coil on the top of
armature slot, and another side in the bottom of the slot. (Represented by dotted lines).

Distributed Armature Winding of Alternator

For obtaining smooth sinusoidal emf wave from, conductors are placed is several slots under
single pole. This armature winding is known as distributed winding. Although distributed
armature winding in alternator reduces emf, still it is very much usable due to following
reason.
1. It also reduces harmonic emf and so waveform is improved.
2. It also diminishes armature reaction.
3. Even distribution of conductors, helps for better cooling.
4. The core is fully utilized as the conductors are distributed over the slots on the armature
periphery.
Lap Winding of Alternator
Full pitched lap winding of 4 poles, 12 slots, 12 conductors (one conductor per slot)
alternator is shown below. The back pitch of the winding is equal to the number of
conductors per pole, i.e., = 3 and the front pitch is equal to back pitch minus one. The
winding is completed per pair of the pole and then connected in series as shown in figure - 4
below.
Wave Winding of Alternator
Wave winding of the same machine, i.e., four poles, 12 slots, 12 conductors is shown in the
figure-e below. Here, back pitch and front pitch both equal to some conductor per pole.

Concentric or Spiral Winding

This winding for the same machine, i.e., four poles 12 slots 12 conductors alternator is shown
in the figure-f below. In this winding, the coils are of different pitches. The outer coil pitch is
5, the middle coil pitch is 3, and inner coil pitch is one.
Poly Phase Armature Winding of Alternator
Before discussing poly phase armature winding of alternator, we should go through some
of the related terms for better understanding.

Coil Group
It is product of number of phases and number of poles in a rotating machine. Coil group =
number of poles × the number of phases.

Balanced Winding
If under each pole face, there are an equal number of coils of different phases, then the
winding is said to be balanced winding. In balanced winding, coil group should be an even
number.

Unbalanced Winding
If the number of coils per coil group is not a whole number, the winding is known as
unbalanced winding. In such case, each pole face contains unequal of coils of different phase.
In two-phase alternator, two single-phase windings are placed on the armature by 90
electrical degrees apart from each other. In case of three phase alternator, three single-phase
windings are placed on the armature, by 60 degrees (electrical) apart from each other. The
figure below represents, a Skelton 2 phase 4 pole winding two slots per pole. The electrical
phase difference between adjacent slots = 180/2 = 90 degree electrical).

Poi
nt a and b are starting point of the first and second phase winding of two, phase alternator. a’
and b’ are finishing point of first and second phase wining of the two-phase alternator,
respectively. The figure below represents a Skelton 3 phase 4 pole winding, three slots per
pole. The electrical phase difference between, adjacent slots is 180/ 3 = 60 degree (electrical)
a, b and c are starting point of Red, Yellow, and blue phases and a’, b’, and c’ are the
finishing points of same Red, Yellow and Blue phases of the three-phase winding.

Say
red phase winding starts at slot no 1 and ends over slot no 10. Then yellow winding or second
winding starts at slot no 2 and ends over slot no 11. Third or blue phase winding starts at slot
no 3 and ends at slot no 12. The phase difference of induced emfs, in red phase and yellow,
yellow phase and blue phase and blue phase and red phase winding respectively by 60
degrees, 60 degree and 240 degrees (electrical respectively). Since in three phase system, the
phase difference between red, yellow and blue phase is 120 degree (electrical). This can be
achieved by revering yellow phase (second winding) winding as shown in the figure above.

Figure- below represents 4 pole, 24 slot, single layer, full pitched 3 phases distributed
winding. No of slot per pole per phase _______________________ The phase difference
between emfs induced in the conductors, of two adjacent slots is _________ Hence,

Slots No: 1, 2, 7, 8, 13, 14, 19, and 20 for R phase

Slots No: 5, 6, 11, 12, 17, 18, 23 and 24 for Y phase

Slots No: 3, 4, 9, 10, 15, 16, 21 and 22 for B phase

The figure below shows three phase full pitched double layer lap winding. Each winding is
spaced 120 electrical degrees from two adjacent winding. This winding has 12 slots per pole
per phase. Since the winding is the full pitched coil, so the pitch of each. The coil is 12 slots.
Since one pole presents 180 electrical space degrees, so the slots pitch corresponding to
180/12, i.e., 15° (electrical). In a fractional pitch winding, we make the coil span less than
 180 degrees electrical space degrees. In the figure above a coil instead of having a pitch of 12
slots now has a pitch of 10 slots so that its spread is no longer equal to pole pitch. There are
two types of coil span. The first one is full pitched coil where two sides of the coil are 180
degrees (electrical) apart. In full pitched coil when one side of the coil is under N pole, the
other side is in the corresponding position, under S pole. The induced emfs on two opposite
side of coil differ by 180 degrees (electrical). Hence the resultant, emf of the coil, is just
arithmetic sum of these two emfs. The second one is the short-pitched coil, where, two
opposite side of a coil is not exactly 180 degree (electrical) it is less than that. In this case, the
phase difference between emf of two coil side is also less than 180 degree (electrical). Hence,
the resultant emf of the coil is not a simple arithmetic sum of two emfs, but it is the vector
sum of two emfs. Hence, resultant emf of a short-pitched coil is always less than that of a full
pitched coil. But still, we preferably use short pitched coil because short pitched coil reduces
or elements harmonics from waveforms.

Integral Slot and Fractional Slot Winding

When the number of slots per pole per phase is an integer, the winding is the integer slot
winding but when the number slots per pole per phase is fractional number the winding we
refer as fractional slot winding. Fractional slot winding is practicable only with the double
layered winding. It limits the number of parallel circuits available because phase group under
several poles must be connected in series before a unit is formed and the widening respects
the pattern to give the second unit that can be put in parallel with the first.
PARALLEL OPERATION OF ALTERNATOR
In alternator, an EMF is induced in the stator (stationary wire) with the influence of rotating
magnetic field (rotor) due to Faraday’s law of induction.
Due to the synchronous speed of rotation of field poles, it is also known as synchronous
generator.
If the AC power systems are to be interconnected for efficiency, the alternators should also
have to be connected in parallel. There will be more than two alternators connected in parallel
in generating stations.
Condition for Parallel Operation of Alternator
There are some conditions to be satisfied for parallel operation of the alternator. Before
entering into that, we should understand some terms which are as follows.

 The process of connecting two alternators or an alternator and an infinite bus bar system in
parallel is known as synchronizing.
 Running machine is the machine which carries the load.
 Incoming machine is the alternator or machine which has to be connected in parallel with
the system.
 The conditions to be satisfied are

1. The phase sequence of the incoming machine voltage and the bus bar voltage should be
identical.
2. The RMS line voltage (terminal voltage) of the bus bar or already running machine and the
incoming machine should be the same.
3. The phase angle of the two systems should be equal.
4. The frequency of the two terminal voltages (incoming machine and the bus bar) should be
nearly the same. Large power transients will occur when frequencies are not nearly equal.
Departure from the above conditions will result in the formation of power surges and current.
It also results in unwanted electro-mechanical oscillation of rotor which leads to the damage
of equipment.

General Procedure for Paralleling Alternators

The figure below shows an alternator (generator 2) being paralleled with a running power
system (generator 1). These two machines are about to synchronize for supplying power to a
load. Generator 2 is about to parallel with the help of a switch, S1. This switch should never
be closed without satisfying the above conditions.

1. To make the terminal voltages equal. This can be done by adjusting the terminal voltage of
incoming machine by changing the field current and make it equal to the line voltage of
running system using voltmeters.
2. There are two methods to check the phase sequence of the machines. They are as follows
 o First one is using a Synchroscope. It is not actually check the phase sequence but it is
used to measure the difference in phase angles.
o Second method is three lamp method (Figure 2). Here we can see three light bulbs are
connected to the terminals of the switch, S1. Bulbs become bright if the phase difference
is large. Bulbs become dim if the phase difference is small. The bulbs will show dim
and bright all together if phase sequence is the same. The bulbs will get bright in
progression if the phase sequence is opposite. This phase sequence can be made equal
by swapping the connections on any two phases on one of the generators.

3. Next, to check and verify the incoming and running system frequency. It should be nearly
the same. This can be done by inspecting the frequency of dimming and brightening of
lamps.
4. When the frequencies are nearly equal, the two voltages (incoming alternator and running
system) will alter the phase gradually. These changes can be observed and the switch, S1
can be made closed when the phase angles are equal.
Advantages of Parallel Operating Alternators
 When there is maintenance or an inspection, one machine can be taken out from service
and the other alternators can keep up for the continuity of supply.
 Load supply can be increased.
 During light loads, more than one alternator can be shut down while the other will operate
in nearly full load.
 High efficiency.
 The operating cost is reduced.
 Ensures the protection of supply and enables cost-effective generation.
  The generation cost is reduced.
 Breaking down of a generator does not cause any interruption in the supply.
 Reliability of the whole power system increases.
EXTRA POINTS

Key Differences Between Alternator & Generator

1. An alternator is a machine which converts the mechanical energy from a prime mover into
the AC, whereas the generator converters the mechanical energy from the prime mover into
an AC or DC.
2. The alternator induces the AC, whereas the generator causes both the AC and DC power.
The generator produces the alternating current which is converted into DC by the help of the
commutator.
3. The alternator has a rotating magnetic field, whereas the generator has a rotating magnetic
field for the high voltage generation and low voltage stationary magnetic field is used.
4. The alternator takes input supply from the stator whereas the generator takes input supply
from the rotor.
5. The armature of an alternator is stationary, and in the case of the generator, it is rotating.
6. The output EMF of the alternator is variable, and the output voltage of the generator is
constant.
7. The alternator has a wide range of RPM whereas the generator has a narrow range of RPM
(rotation per minute).
8. The alternator does not charge the completely dead battery whereas the generator charges
the dead battery.
9. The output of the alternator is higher than that of the generator.
The alternator is smaller in size and requires less space whereas the generator requires large
space.

https://circuitglobe.com/difference-between-alternator-and-generator.html

Comparison Chart
Basis for
Alternator Generator
Comparison

Definition A machine that A machine that changes

converts the mechanical energy into
mechanical energy electrical energy (AC or
into AC electrical DC).
power.

Current Induces alternating Generate both AC & DC.

current

Magnetic Field Rotating Stationary

Basis for
Alternator Generator
Comparison

Input Supply Takes from stator. Takes from rotor.

Armature Stationary Rotatory

Output EMF Alternating Constant

RPM (Rotation per Wide Range Narrow Range

minute)

Dead Battery Do not charge charge

Output Higher Lower

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Difference Between Synchronous Motor And Induction Motor
AC motors can be divided into two main categories - (i) Synchronous motor and
(ii) Asynchronous motor. An asynchronous motor is popularly called as Induction motor.
Both the types are quite different from each other. Major differences between a synchronous
motor and an induction motor are discussed below.
Constructional Difference
 Synchronous motor: Stator has axial slots which consist stator winding wound for a
specific number of poles. Generally a salient pole rotor is used on which rotor winding is
mounted. Rotor winding is fed with a DC supply with the help of slip rings. A rotor with
permanent magnets can also be used.

Synchronous motor

 Induction motor: Stator winding is similar to that of a synchronous motor. It is wound

for a specific number of poles. A squirrel cage rotor or a wound rotor can be used. In
squirrel cage rotor, the rotor bars are permanently short-circuited with end rings. In
wound rotor, windings are also permanently short-circuited, hence no slip rings are
required.

Induction motor
Difference In Working
 Synchronous motor: Stator poles rotate at the synchronous speed (Ns) when fed with a
three phase supply. The rotor is fed with a DC supply. The rotor needs to be rotated at a
speed near to the synchronous speed during starting. If done so, the rotor poles get
magnetically coupled with the rotating stator poles, and thus the rotor starts rotating at the
synchronous speed.
 Synchronous motor always runs at a speed equal to its synchronous speed.
i.e. Actual speed = Synchronous speed
or N = Ns = 120f/P
 Learn more about working of a synchronous motor here.
 Induction motor: When the stator is fed with two or three phase AC supply, a Rotating
Magnetic Field (RMF) is produced. The relative speed between stator's rotating magnetic
field and the rotor will cause an induced current in the rotor conductors. The rotor current
gives rise to the rotor flux. According to Lenz's law, the direction of this induced current
is such that it will tend to oppose the cause of its production, i.e. relative speed between
stator's RMF and the rotor. Thus, the rotor will try to catch up with the RMF and reduce
the relative speed.
 Induction motor always runs at a speed which is less than the synchronous speed.
i.e. N < Ns
 Learn more about working of induction motor here.

Other Differences
 Synchronous motors require an additional DC power source for energizing rotor winding.
Induction motors do not require any additional power source.
 Slip rings and brushes are required in synchronous motors, but not in Induction motors
(except wound type induction motor in which slip ring motors are used to add external
resistance to the rotor winding).
 Synchronous motors require additional starting mechanism to initially rotate the rotor
near to the synchronous speed. No starting mechanism is required in induction motors.
 The power factor of a synchronous motor can be adjusted to lagging, unity or leading by
varying the excitation, whereas, an induction motor always runs at lagging power factor.
 Synchronous motors are generally more efficient than induction motors.
 Synchronous motors are costlier.
https://youtu.be/gQyamjPrw-U

An alternator is an electrical machine which converts mechanical energy into alternating

electric energy. They are also known as synchronous generators.

How does an AC generator work?

The working principle of an alternator or AC generator is similar to the basic working
principle of a DC generator.
Above figure helps you understanding how an alternator or AC generator works.
According to the Faraday's law of electromagnetic induction, whenever a conductor moves in
a magnetic field EMF gets induced across the conductor. If the close path is provided to the
conductor, induced emf causes current to flow in the circuit.

Now, see the above figure. Let the conductor coil ABCD is placed in a magnetic field. The
direction of magnetic flux will be form N pole to S pole. The coil is connected to slip rings,
and the load is connected through brushes resting on the slip rings.

Now, consider the case 1 from above figure. The coil is rotating clockwise, in this case the
direction of induced current can be given by Fleming's right hand rule, and it will be along A-
B-C-D.

As the coil is rotating clockwise, after half of the time period, the position of the coil will be
as in second case of above figure. In this case, the direction of the induced current according
to Fleming's right hand rule will be along D-C-B-A. It shows that, the direction of the current
changes after half of the time period, that means we get an alternating current.
Construction of AC generator (alternator)

Salient pole type alternator

Main parts of the alternator, obviously, consists of stator and rotor. But, the unlike other
machines, in most of the alternators, field exciters are rotating and the armature coil is
stationary.

Stator: Unlike in DC machine stator of an alternator is not meant to serve path for magnetic
flux. Instead, the stator is used for holding armature winding. The stator core is made up of
lamination of steel alloys or magnetic iron, to minimize the eddy current losses.

Why armature winding is stationary in an alternator?

 At high voltages, it easier to insulate stationary armature winding, which may be as
high as 30 kV or more.
 The high voltage output can be directly taken out from the stationary armature.
Whereas, for a rotary armature, there will be large brush contact drop at higher
voltages, also the sparking at the brush surface will occur.
 Field exciter winding is placed in rotor, and the low dc voltage can be transferred
safely.
 The armature winding can be braced well, so as to prevent deformation caused by the
high centrifugal force.
Rotor: There are two types of rotor used in an AC generator / alternator:
(i) Salient and (ii) Cylindrical type

1. Salient pole type: Salient pole type rotor is used in low and medium speed alternators.
Construction of AC generator of salient pole type rotor is shown in the figure
above. This type of rotor consists of large number of projected poles (called salient
poles), bolted on a magnetic wheel. These poles are also laminated to minimize the
eddy current losses. Alternators featuring this type of rotor are large in diameters and
short in axial length.
 2. Cylindrical type: Cylindrical type rotors are used in high speed alternators, especially
in turbo alternators. This type of rotor consists of a smooth and solid steel cylinder
havingg slots along its outer periphery. Field windings are placed in these slots.
The DC suppy is given to the rotor winding through the slip rings and and brushes
arrangement.

Connecting an alternator in grid is called as synchronization of alternator, read more about it

at the link.

https://www.electricaleasy.com/2014/02/AC-generator-alternator-construction-working.html

EMF Equation of Alternator

Let,
  𝑃 = Number of poles
 φ = Flux per pole in webers
 𝑁 = Rotor speed in RPM
 𝑓 = Frequency of the induced EMF in Hz
 𝑍 = Number of conductors in series per phase
 𝑇 = Number of coils or turns per phas𝑒
As the flux per pole is φ, hence, in one revolution, each stator conductor cut a flux of,
VOLTAGE REGULATION

The voltage regulation of an alternator or synchronous generator is defined as the rise in the
terminal voltage when the load is decreased from full-load rated value to zero. The speed
and field current of the alternator remain constant.
In other words, the voltage regulation of the alternator can be defined as the change in
terminal voltage from no-load to full load rated value divided by the full-load rated voltage
APPLICATIONS OF ALTERNATOR
An alternator is mainly used for converting
mechanical energy into electrical energy
in various applications such as:
 In automobiles
 In locomotives
 Power generation plants
 In Marine and navy boats
 Radiofrequency transmission