DC Generator - Working Principle - Construction - Parts of DC Generator - Types of DC Generator - Working of DC Generator - EMF Equation of DC Generator - Losses in DC Generator - Power Stages of DC Generator - Applications of DC Generator
What is a DC Generator?
A DC Generator is an Electrical Machine which converts Mechanical Energy into DC Electrical Energy. It mainly consists of armature, field coils which works as electromagnets in it. There are so many Parts of DC Generator which plays a significant role during its working. A DC Generator works on the principle of Faraday’s laws of electromagnetic induction. It provides DC Electrical Energy
which is used in many applications like DC transmission lines, heavy DC Power Supplies etc. So, lets discuss about the working principle of DC Generator
first and then we will move on to the construction of dc generator and will
study further more topics and details of dc generator below:
Working Principle of DC Generator
The working principle of dc generator is same as the faraday’s law
of electromagnetic induction and a simple loop generator/ loop generator. The working principle of DC generator is when the armature starts moving through the mechanical energy applied on its shaft then the armature coils produce an EMF. This EMF links with the field poles Due to magnetic flux and the current is generated in the field poles to provide DC on its output terminals/load terminals. For Further understanding let's move on to the Faraday's Laws of Electromagnetic Induction below:
Faraday’s Laws of Electromagnetic Induction
Basically, faraday’s law of electromagnetic induction is further divided into two slightly different laws and dc generator works on the Faraday's first law of electromagnetic induction. Both Faraday's Laws of electromagnetic induction are described below:
Faraday’s Laws of Electromagnetic Induction
Basically, faraday’s law of electromagnetic induction is further divided into two slightly different laws and dc generator works on the Faraday's first law of electromagnetic induction. Both Faraday's Laws of electromagnetic induction are described below:
Faraday’s First Law of Electromagnetic Induction
Faraday’s first law of electromagnetic induction states that “When a conductor cuts a magnetic flux, an EMF is induced in that conductor.” A Simple loop generator/loop generator is based on this law of electromagnetic induction.
Faraday’s Second Law of Electromagnetic Induction
Faraday’s second law of electromagnetic induction states that “The magnitude of generated EMF in a conductor(wire) is equal to the rate of change of flux linkage.”
The conversion of mechanical energy into electrical energy is based
on the faraday’s first law of electromagnetic induction and this law is used in
the construction of DC Generator. Without this law, DC Generator is not capable
to convert mechanical energy to DC electrical energy.
For further explanation of the Working Principle of DC Generator, lets move on to the Simple form of DC Generator named as Single loop Generator. This generator works exactly on the Faraday's First Law of Electromagnetic induction. This Loop Generator is described below in further more detail:
For further explanation of the Working Principle of DC Generator, lets move on to the Simple form of DC Generator named as Single loop Generator. This generator works exactly on the Faraday's First Law of Electromagnetic induction. This Loop Generator is described below in further more detail:
Single Loop Generator
A Loop
Generator / Simple Loop Generator is a basic concept of the DC
Generator. It is a conductor placed between the magnet bars.
These magnetic bars may be of permanent magnet or electro
magnet. The basic working of the simple loop generator is that
when the two wires, conductors or coils are placed between the magnet bars and
imagine the coil is rotating clockwise, the flux starts
changing its value and as a result EMF is induced in it.
Construction
A simple loop
generator is basically consists of two conductors or coils; two magnet bars and
two slip rings(which are insulated with each other and from
central shaft) and a normal wire for connection as required. The
rotating coil may be assumed as armature and the magnet bars
field magnets.
Working Principle
Assume that the coil
or the two conductors are rotating in a clock-wise direction. The coil has a
fixed position between the field and the flux linked with it starts changing
its value. As a result, EMF is induced in it and it is
proportional to the rate of change of flux linkage. When the coil
reaches at 90 degree in the process of rotating, the coil slides don’t cut the
flux and the flux move parallel between them. As a result, EMF is not induced
in the coil. As the coil continues its rotation, the amount increases to its
maximum and when the coil reaches again at 90 degrees then in this case maximum
EMF is induced in the coil this is because of the maximum flux is produced.
The result is that
when the coil rotates from 90 to 180 degrees, the flux increases gradually and
the rate of change of flux linkage decreases.
When the coil rotates
from 180 to 360 degrees the variation occurs in the magnitude of the EMF.at
first EMF remains similar on the middle position EMF reaches to its maximum and
at the end minimum EMF is produced.
Conclusion
Remember that the
current produced in the coils is alternating and we get this
current rectified by the split rings. Hence it is
cleared that the armature of the DC Generator also
provides Alternating Voltages.
Construction of DC Generator
The construction of dc generator mainly consists of a yoke/main cover, pole cores, field coils, armature, windings etc. Each part of
dc generator has its own importance according to its working and function so
these parts are described below in further detail and explanation:
Parts of
DC Generator
DC generator consists of the following main parts:
- Yoke/Main Cover : Yoke is the main cover of the DC Generator made up of iron or any other material
- Pole Cores : Pole Cores are used as field magnets. These are used to spread out the flux in the air gap and it is also used to support the exciting coils.
- Field Coils : Field coils are the coils of a conductor wounded across the pole core. When current is passed through these coils the poles reacts as an electromagnet and magnetic flux is produced in it.
- Armature Core : Armature core is cylindrical or drum shaped and is built up of circular steel sheets or laminations. It is set to the shaft.
- Armature Winding : The armature windings are in a wound form. These windings are insulated from each other and normally copper winding are generally used in it.
- Commutator : The commutator provides a collection of currents from the armature winding or conductors. It converts the alternating current which is induced in the armature conductors into direct current (DC).
- Brush Gear : Brush gears holds heavy carbon brushes and are used to transfer huge amount of excitation current from it to the terminal junction.
- Capacitor : Capacitor is a basic component of DC Generator which is used to remove some fluctuations and filters the DC output supply from its output terminals.
- Load Junction : Load junction of a dc generator consists of the two output terminal wires negative and positive which are installed in the terminal box to provide the load current and are used to connect the load supply on it.
- Terminals : In some modified DC Generators, the manufacturers provide an easy junction for the load and the manufacturers provide the two wires which are already connected to the load junction and these two wires are assembled and installed in the main cover or yoke of the DC Generator to connect directly to the load connection.
- Suppressor Box : A Suppressor box is used to reduce the irrelevant and unwanted noise of a high KV rated DC Generators.
- Terminal Cover : Terminal cover is a cap which protects the joints of the DC generator terminals and the load terminals and this cover is also used for safety measures to prevent from electric shock and fire.
- Carbon Brushes : In DC generator, Carbon brushes are used to collect current from the commutator and then transfer to its main contacts.
- Bearings : Bearings are used to rotate shaft very easily. Usually ball bearings are frequently used in heavy machines due to its flexibility.
- Bearing Support Head : Bearing support head looks like the shape of bearing and it holds the bearing in its case to provide support and alignment and it is fixed to straight the bearing.
- Shaft : A Shaft of a DC Generator is a mechanical component. It consists of a mild steel and it provides torque and rotation.
- Shaft Spline : Shaft spline is a small component installed on a shaft sometime it is fixed on a shaft and sometimes it comes in variable form. A shaft spline consists of teeth and in a circular form and is used for coupling/joining the other shaft to it for mechanical input for DC Generator.
- Clamps : Clamps are used to hold the load wires tightly and make the load terminals safe and clean.
- Window Strap : Window strap is basically a net made up of iron and it is connected to the yoke and it is used to provide air gap to the DC Generator for the purpose of cooling.
- Retaining Cap : Retaining cap are made up of alloy of a non-magnetic steel and is tighten on the shaft to provide support to the shaft against centrifugal forces during rotation.
- End Cover : End cover is a part of yoke and it covers from the end of DC Generator with the help of bolts and it is used to protect the generator from its end.
Yoke/Main
Cover
Yoke is the main cover of the DC
Generator made up of iron or any other material. It provides a
mechanical support for the poles. It acts as a protecting
cover for the whole machine. It also carries the magnetic
flux produced by the poles. These yokes are
made up of cast iron and for large machines cast steel or
rolled steel is used.
Pole Cores
Pole
Cores are used as field magnets. These are used to spread
out the flux in
the air gap and it is also used to support the exciting
coils. Pole cores are the solid piece and are made up of cast iron or
cast steel. In modern age pole cores are made up of thin laminations of
enameled steel. The thickness of lamination is from 1 milli
meter to 0.25 milli meter. The laminated poles are more secured than
the solid
piece pole cores.
Field Coils
Field
coils are the coils of a conductor wounded across the pole core. When
current is passed through these coils the poles reacts as an electromagnet and magnetic
flux is produced in it.
Field
coils are the coils of a conductor wounded across the pole core. When
current is passed through these coils the poles reacts as an electromagnet and magnetic
flux is produced in it.
Armature Core
Armature core is cylindrical or drum shaped and is built
up of circular steel sheets or laminations. It is
set to the shaft. The slots are punched on its outer side. In small
machines or motors the armature slots are set directly
to the shaft. These laminations are used for the
cooling purposes for the armature and to reduce the eddy
current losses and voltage drops. The circular stampings or slots are
cut out in one piece.
Armature core is cylindrical or drum shaped and is built
up of circular steel sheets or laminations. It is
set to the shaft. The slots are punched on its outer side. In small
machines or motors the armature slots are set directly
to the shaft. These laminations are used for the
cooling purposes for the armature and to reduce the eddy
current losses and voltage drops. The circular stampings or slots are
cut out in one piece.
Armature
Winding
The armature windings are in a wound form. These windings are
insulated from each other and normally copper winding are generally used in it.
These conductors or winding is placed in the armature slots which are lined
with insulation.
Commutator
The commutator provides a collection of currents from
the armature winding or conductors. It converts
the alternating current which is induced in the armature
conductors into direct current (DC). It is a cylindrical
shaped and have wedge shaped segments. These segments
are insulated from each other. The number of segments are
equal to the number of armature coils. Each segment is
connected to the armature conductor through riser or strip.
These segments have V-grooves to prevent from centrifugal
forces.
Brush
Gear
Brush gears holds heavy carbon brushes and are used to
transfer huge amount of excitation current from it to the terminal junction.
Normally these are used in Highly Rated DC Generators. The brush gear is used
to change its position according to the requirement either you want small
output current or either you want maximum current and the most important use
case of the brush gear is to adjust the carbon brushes in different direction
to get maximum DC output from the DC Generator.Capacitor
Capacitor is a basic component of DC Generator which is used to remove some fluctuations and filters the DC output supply from its output terminals. It provides smoothness in output voltage and provides constant voltage.
Load
Junction
Load junction of a dc generator consists of the two output terminal wires negative and positive which are installed in the terminal box to provide the load current and are used to connect the load supply on it. This junction is very strong and the two wires are connected to the commutator from which they take DC in it and then provide it on its junction for the load connection.
Terminals
In some modified DC Generators, the manufacturers provide an easy junction for the load and the manufacturers provide the two wires which are already connected to the load junction and these two wires are assembled and installed in the main cover or yoke of the DC Generator to connect directly to the load connection.
Suppressor
Box
A Suppressor box is used to reduce the irrelevant and unwanted noise of a high KV rated DC Generators. This box consists of various valves and some other filters like some holes, iron rings, resistive net etc. Which are used to reduce the noise from the generator.
Terminal
Cover
Terminal cover is a cap which protects the joints of the DC generator terminals and the load terminals and this cover is also used for safety measures to prevent from electric shock and fire.
Carbon
Brushes and Bearings
In DC generator, Carbon brushes are
used to collect current from the commutator and then transfer to its main contacts. These brushes are commonly made up
of carbon and graphite. These brushes are rectangular
shaped. These brushes are mounted on the brush holders and
the brush holder is mounted on a spindle.
These brushes remain joined with the commutator by
a spring. A flexible copper pigtail is mounted on the top of
the carbon brushes which convey current from the brushes to the holder.
Bearings are used to rotate shaft very easily.
Usually ball bearings are frequently used in heavy
machines due to its flexibility. Ball bearings work
very efficiently in heavy machines. The balls and rollers of ball
bearings are packed in hard oil.
Bearing
Support Head
Bearing support head looks like the shape of bearing and it holds the bearing in its case to provide support and alignment and it is fixed to straight the bearing and it provides the complete support in a required direction to provide uninterruptible function.
Shaft
A Shaft of a DC Generator is a mechanical component. It consists of a mild steel and it provides torque and rotation. It is prototype and long and it is used for coupling in DC Generator to provide mechanical energy.
Shaft
Spline
Shaft spline is a small component installed on a shaft
sometime it is fixed on a shaft and sometimes it comes in variable form. A
shaft spline consists of teeth and in a circular form and is used for
coupling/joining the other shaft to it for mechanical input for DC Generator.
Clamps
Clamps are used to hold the load wires tightly and
make the load terminals safe and clean.
Window
Strap
Window strap is basically a net made up of iron and it
is connected to the yoke and it is used to provide air gap to the DC Generator
for the purpose of cooling and it provides a better temperature for cooling.
Retaining
Cap
Retaining cap are made up of alloy of a non-magnetic
steel and is tighten on the shaft to provide support to the shaft against
centrifugal forces during rotation.
End Cover
End cover is a part of yoke and
it covers from the end of DC Generator with the help of bolts and it is used to
protect the generator from its end.
Winding Element and Conductor in Armature
There should be two types of windings
enrolled on armature of dc generator. These two windings either single turn
coil or a multi turn coil. A single turn coil has two conductors and
multi turn coil has so many conductors. The conductors are placed in the slots
of the armature. The side of the coil is known as winding element.
Pole pitch
Pole pitch is the distance between the two head to head poles in dc generator and it is the division between the number of conductors of armature winding and poles of DC generator. For example: if there are 60 conductors and 4 poles then 60/4 equals to 15 and this 15 is the pole pitch.
Coil pitch
Coil pitch is the distance between the
two sides of a coil. If the coil pitch and the pole pitch are
equal to each other then the coil span will be 180 degrees and the coil sides
will be arranged under opposite poles and maximum EMF will produced in the coil
sides and then we will use the term that the winding is full pitched.
Pitch of winding
It is the distance between the two turns
of a conductor. The pitch of the winding is denoted by Y. The formula to find
the pitch of winding is given below:
Y = Yb – Yf For Lap Winding
Y= Yb + Yf For Wave Winding
Here YB is the back pitch and
the YF is the front pitch which are defined below:
Front Pitch
It is the number of armature conductors
covered by a coil on the front of an armature is called the front pitch.
It is the distance between the first conductor of a coil and the second
conductor of a next coil which are connected together at the end of the
commutator. For example: element 8 is connected to the element number 3 so the
front pitch YF will be
8 – 3 = 5.
Back Pitch
It is the distance between the two
conductors of a coil in armature which are connected to each other on the back
side of armature. It is denoted by YB. For example: element 8 is connected
to the element 1 on the back side of the armature so the back pitch will be
8 – 1 = 7.
Resultant Pitch
It is the distance between the two coils
wounded on the armature. This distance starts from the starting point of the
first coil and ends at the starting point of the other coil wounded in the
armature. It is denoted by YR.
Commutator Pitch
It is the distance between the two
conductors from where these two conductors are connected to the commutator
bar/segment. It is denoted by YG.
Single Layer Winding
It is a coil which consists of a single
conductor or a coil of single conductor wounded on the single armature slot.
Double Layer Winding
In this winding, a coil consists of
single conductor and one side of each coil (first half) is placed on the armature
slot where the other half of the coil is already placed on that slot. It means
that every slot of armature consists of their first halfs of two coils and so
on. The upper halfs of the coils are placed in the odd numbered slots of the armature
whereas the lower halfs of the coils are placed on the even numbered slots of
armature.
Lap Winding
In lap windings, the front pitch and the
back pitch are equal to each other. Both pitches should be in odd arrangement.
By this an emf is increased and more energy is produced in the armature coils.
Wave Winding
Wave windings is a process of winding in
armature in which we use only one conductor on the armature slots and we fill
the armature slots with so many turns of a single conductor and when the first slot
of the armature is filled then we receive the first end of the conductor and
the second end of that conductor and then placed these two conductors on the
same segment of the commutator. In this winding, the segments of the commutator
are equal to the number of coils.
Types of DC Generator
DC generators are classified into two
different types which are described below:
Separately Excited DC Generators
As described from its name that
these DC Generators are those generators whose field magnets are
excited/energized with a separate source of DC as shown in figure below:
Self-Excited DC Generators
Self-excited dc generators are those generators whose field magnets are excited/energized by
the dc generator’s own producing current. The flux is present in poles through
residual magnetism so that a current is produced in it and it energizes the
field magnets of dc generator. These self-excited generators are further
divided into its three types which are described below:
Shunt Type DC Generators/Shunt Wound DC Generators
In these type of dc generators, the field winding is connected in parallel with the armature and this field winding is connected to the supply as shown in figure below:
Series Type DC Generator/Series Wound DC Generators
In this type of dc generators, the field winding is connected in series with the armature. It consists of few turns of thick wire and carries full load current. These generators are also called as special purpose dc generators and are used as voltage boosters in many places.
Compound DC Generator/Compound Wound DC Generators
Compound dc generators are further divided into its two types which are explained below:
Short Shunt Compound DC Generator
Short shunt compound dc generators are those generators in which the shunt field winding is connected in parallel with the armature and the series field winding is connected in series with the armature as shown in figure below:
Long Shunt Compound DC Generator
Long shunt compound dc generators are those generators in which shunt field winding is connected in parallel connection with the armature and series field winding whereas the series field winding is connected in series with the armature of dc generator.
EMF Equation of DC Generator
Let
Φ = flux per pole in weber
Z = total number of armature
conductors
P = no of pole in a generator
A = no of parallel paths in an
armature
N = rotation of armature in rpm
E = EMF induced in armature
Then,
Losses in DC Generator
Every electrical machine which
consume electric supply has many losses during its operation and so many
electric power is wasted. In dc generator, there are so many kinds of losses
occurred during its operation these losses are iron losses, hysteresis losses, eddy current losses, copper losses etc. These losses are mentioned below:
Iron Losses/Core Loss
These losses are occurred due to
the iron core and magnetic flux produced in field poles and these
losses are called iron losses/core losses. Iron loss consist of two losses
which are described below:
Hysteresis Loss
This loss is occurred due to the
changing magnetization of the armature core and this magnetization reverses the
polarity which causes the opposite flux and this flux starts wasting.
Eddy Current Loss
Due to the rotation of the armature
core it also cuts the magnetic flux and EMF is induced in the body
of core. This current has low value and this current is known as eddy current
and due to the wastage of eddy current so this is known as eddy current loss.
Copper Loss
Copper losses are not produced if
we use standard conductor/conducting material in the winding but sometimes a
material is not good for conduction and it takes so many power and current
cannot flow easily through this conductor. So, these are called copper losses.
Mechanical Losses
These losses are friction losses
at bearings and commutator and air friction loss in rotating armature.
Stray Losses
The addition of Magnetic losses
and mechanical losses are known as stray losses.
Power Stages of DC Generator
There are many power stages of a
DC Generator and these stages are shown below:
Efficiencies of DC Generator
The efficiencies of a dc generator are given below:
Mechanical Efficiency
Electrical Efficiency
Commercial/Overall Efficiency
Applications of DC Generator
There are so many applications of DC Generator and some of these applications are mentioned below:
- Separately excited dc generators are used as boosters and in the process of electroplating and as a regulator etc.
- Compound dc generators are used as power supply of welding machines.
- DC generators are also used to reduce the voltage drops in feeders.
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