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UNIT-IV
DC GENERATOR
Introduction:
The electrical machines deals with the energy transfer either from mechanical to electrical form
or from electrical to mechanical form, this process is called electromechanical energy conversion.
An electrical machine which converts mechanical energy into electrical energy is called an
electric generator while an electrical machine which converts electrical energy into the
mechanical energy is called an electric motor. A DC generator is built utilizing the basic principle
that emf is induced in a conductor when it cuts magnetic lines of force. A DC motor works on the
basic principle that a current carrying conductor placed in a magnetic field experiences a force.
Working principle:
All the generators work on the principle of dynamically induced emf. The change in flux
associated with the conductor can exist only when there exists a relative motion between the
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conductor and the flux. The relative motion can be achieved by rotating the conductor w.r.t flux
or by rotating flux w.r.t conductor. So, a voltage gets generated in a conductor as long as there
exists a relative motion between conductor and the flux. Such an induced emf which is due to
physical movement of coil or conductor w.r.t flux or movement of flux w.r.t coil or conductor is
called dynamically induced emf. Whenever a conductor cuts magnetic flux, dynamically induced
emf is produced in it according to Faraday‟s laws of Electromagnetic Induction. This emf causes
a current to flow if the conductor circuit is closed.In a practical generator, the conductors are
rotated to cut the magnetic flux, keeping flux stationary. To have a large voltage as output, a
number of conductors are connected together in a specific manner to form a winding. The
winding is called armature winding of a dc machine and the part on which this winding is kept is
called armature of the dc machine. The magnetic field is produced by a current carrying winding
which is called field winding.The conductors placed on the armature are rotated with the help of
some external device. Such an external device is called a prime mover. The commonly used
prime movers are diesel engines, steam engines, steam turbines, water turbines etc. The purpose
of the prime mover is to rotate the electrical conductor as required by Faraday‟s laws The
direction of induced emf can be obtained by using Flemings right hand rule. The magnitude of
induced emf = e = BLV sin = Em sin. The nature of the induced emf for a conductor rotating
in the magnetic field is alternating. As conductor rotates in a magnetic field, the voltage
component at various positions is different. Hence the basic nature of induced emf in the armature
winding in case of dc generator is alternating. To get dc output which is unidirectional, it is
necessary to rectify the alternating induced emf. A device which is used in dc generator to
convert alternating induced emf to unidirectional dc emf is called commutator.
Construction of DC machines: A D. C. machine consists of two main parts
1. Stationary part: It is designed mainly for producing a magnetic flux.
2. Rotating part: It is called the armature, where mechanical energy is converted into
electrical (electrical generate) or conversely electrical energy into mechanical (electric
into)
Parts of a Dc Generator:
The stationary parts and rotating parts are separated from each other by an air gap. The
stationary part of a D. C. machine consists of main poles, designed to create the magnetic flux,
commutating poles interposed between the main poles and designed to ensure spark less
operation of the brushes at the commutator and a frame / yoke. The armature is a cylindrical body
rotating in the space between the poles and comprising a slotted armature core, a winding inserted
in the armature core slots, a commutator and brush
Yoke:
jntuworldupdates.org Specworld.in
UNIT-IV
DC GENERATOR
Introduction:
The electrical machines deals with the energy transfer either from mechanical to electrical form
or from electrical to mechanical form, this process is called electromechanical energy conversion.
An electrical machine which converts mechanical energy into electrical energy is called an
electric generator while an electrical machine which converts electrical energy into the
mechanical energy is called an electric motor. A DC generator is built utilizing the basic principle
that emf is induced in a conductor when it cuts magnetic lines of force. A DC motor works on the
basic principle that a current carrying conductor placed in a magnetic field experiences a force.
Working principle:
All the generators work on the principle of dynamically induced emf. The change in flux
associated with the conductor can exist only when there exists a relative motion between the
jntuworldupdates.org Specworld.in
, Smartzworld.com Smartworld.asia
conductor and the flux. The relative motion can be achieved by rotating the conductor w.r.t flux
or by rotating flux w.r.t conductor. So, a voltage gets generated in a conductor as long as there
exists a relative motion between conductor and the flux. Such an induced emf which is due to
physical movement of coil or conductor w.r.t flux or movement of flux w.r.t coil or conductor is
called dynamically induced emf. Whenever a conductor cuts magnetic flux, dynamically induced
emf is produced in it according to Faraday‟s laws of Electromagnetic Induction. This emf causes
a current to flow if the conductor circuit is closed.In a practical generator, the conductors are
rotated to cut the magnetic flux, keeping flux stationary. To have a large voltage as output, a
number of conductors are connected together in a specific manner to form a winding. The
winding is called armature winding of a dc machine and the part on which this winding is kept is
called armature of the dc machine. The magnetic field is produced by a current carrying winding
which is called field winding.The conductors placed on the armature are rotated with the help of
some external device. Such an external device is called a prime mover. The commonly used
prime movers are diesel engines, steam engines, steam turbines, water turbines etc. The purpose
of the prime mover is to rotate the electrical conductor as required by Faraday‟s laws The
direction of induced emf can be obtained by using Flemings right hand rule. The magnitude of
induced emf = e = BLV sin = Em sin. The nature of the induced emf for a conductor rotating
in the magnetic field is alternating. As conductor rotates in a magnetic field, the voltage
component at various positions is different. Hence the basic nature of induced emf in the armature
winding in case of dc generator is alternating. To get dc output which is unidirectional, it is
necessary to rectify the alternating induced emf. A device which is used in dc generator to
convert alternating induced emf to unidirectional dc emf is called commutator.
Construction of DC machines: A D. C. machine consists of two main parts
1. Stationary part: It is designed mainly for producing a magnetic flux.
2. Rotating part: It is called the armature, where mechanical energy is converted into
electrical (electrical generate) or conversely electrical energy into mechanical (electric
into)
Parts of a Dc Generator:
The stationary parts and rotating parts are separated from each other by an air gap. The
stationary part of a D. C. machine consists of main poles, designed to create the magnetic flux,
commutating poles interposed between the main poles and designed to ensure spark less
operation of the brushes at the commutator and a frame / yoke. The armature is a cylindrical body
rotating in the space between the poles and comprising a slotted armature core, a winding inserted
in the armature core slots, a commutator and brush
Yoke:
jntuworldupdates.org Specworld.in
