EMFT in electrical machine
-
Upload
aditya-gupta -
Category
Documents
-
view
226 -
download
3
Transcript of EMFT in electrical machine
-
8/7/2019 EMFT in electrical machine
1/22
17-04-2011
1
By: Aditya Gupta(09BEE004)
Manish Kumar Singh(09BEE029)
-
8/7/2019 EMFT in electrical machine
2/22
17-04-2011
2
ElectricalMachines
DCMachines
DC Motor
DC
Generator
AC
Machines
AC Motor
Alternator
Transformer
-
8/7/2019 EMFT in electrical machine
3/22
17-04-2011
3
-
8/7/2019 EMFT in electrical machine
4/22
17-04-2011
4
-
8/7/2019 EMFT in electrical machine
5/22
17-04-2011
5
An electric motor is a machine which converts electrical energy into mechanical energy.
Principle:
It is based on the principle that when a current-carrying conductor is placed in a magneticfield, it experiences a mechanical force whose direction is given by Fleming's Left-hand rule
and whose magnitude is given by
Force, F = B I l newton
Where B is the magnetic field in weber/m2.
I is the current in amperes and
l is the length of the coil in meter.
The force, current and the magnetic field are all in different directions.
-
8/7/2019 EMFT in electrical machine
6/22
17-04-2011
6
If an Electric current flows through two copper wires that are between the poles of a
magnet, an upward force will move one wire up and a downward force will move the otherwire down.
Force in a DC Motor Field in a DC Motor
-
8/7/2019 EMFT in electrical machine
7/22
17-04-2011
7
The loop can be made to spin by fixing a half circle of copper which is known as
commutator, to each end of the loop. Current is passed into and out of the loop by
brushes that press onto the strips. The brushes do not go round so the wire do not gettwisted. This arrangement also makes sure that the current always passes down on
the right and back on the left so that the rotation continues. This is how a simple
Electric motor is made.
17 04 2011
-
8/7/2019 EMFT in electrical machine
8/22
17-04-2011
8
First Law :Whenever the magnetic flux linked with a circuit changes,an e.m.f. is always induced in it.
orWhenever a conductor cuts magnetic flux, an e.m.f. is induced inthat conductor.
Second Law :The magnitude of the induced e.m.f. is equal to the rate of change
of flux linkages.
17 04 2011
-
8/7/2019 EMFT in electrical machine
9/22
17-04-2011
9
Principle :It is based on the principle of production of dynamically (or motionally)
induced e.m.f (Electromotive Force). Whenever a conductor cuts magneticflux, dynamically induced e.m.f. is produced in it according to Faraday'sLaws of Electromagnetic Induction. This e.m.f. causes a current to flow ifthe conductor circuit is closed.
Hence, the basic essential parts of an electric generator are :1. A magnetic field and2. A conductor or conductors which can so move as to cut the flux.
17 04 2011
-
8/7/2019 EMFT in electrical machine
10/22
17-04-2011
10
17-04-2011
-
8/7/2019 EMFT in electrical machine
11/22
17 04 2011
11
17-04-2011
-
8/7/2019 EMFT in electrical machine
12/22
17 04 2011
12
17-04-2011
-
8/7/2019 EMFT in electrical machine
13/22
13
-
8/7/2019 EMFT in electrical machine
14/22
17-04-2011
-
8/7/2019 EMFT in electrical machine
15/22
15
Principle :
A.C. generators or alternators (as they are usually called) operate on theSame fundamental principles of electromagnetic induction as D.C.generators.Alternating voltage may be generated by rotating a coil in the magnetic fieldor by rotating a magnetic field within a stationary coil. The value of thevoltage generated depends on :
1. The number of turns in the coil.2. Strength of the field.3. The speed at which the coil or magnetic field rotates.
-
8/7/2019 EMFT in electrical machine
16/22
17-04-2011
-
8/7/2019 EMFT in electrical machine
17/22
17
17-04-2011
-
8/7/2019 EMFT in electrical machine
18/22
18
17-04-2011
-
8/7/2019 EMFT in electrical machine
19/22
19
Faradays Law of Electromagnetic Induction
17-04-2011
-
8/7/2019 EMFT in electrical machine
20/22
20
A transformer is a static piece of apparatus by means of which electric power in one
circuit is transformed into electric power of the same frequency in another circuit. It
can raise or lower the voltage in a circuit but with a corresponding decrease or
increase in current.
In brief, a transformer is a device that1. Transfers electric power from one circuit to another.2. It does so without a change of frequency.3. It accomplishes this by electromagnetic induction and4. Where the two circuit are in mutual inductive influence of eachother.
17-04-2011
-
8/7/2019 EMFT in electrical machine
21/22
21
In it's simplest form it consist of, two inductive coils which are electrically separated
but magnetically linked through a path of low reluctance. If one coil (primary) is connected tosource of alternating voltage, an alternating flux is set up in the laminated core, most of which
is linked with the other coil in which it produces mutually-induced e.m.f. (according to
Faraday's Laws of Electromagnetic Induction. If the second coil (secondary) circuit is closed, a
current flows in it and so electric energy is transferred (entirely magnetically) from the first
coil to the second coil.
17-04-2011
-
8/7/2019 EMFT in electrical machine
22/22
22
DC motor: It uses the principle that a current carrying coil placed in a magnetic field
experiences a torque
DC generator: It is based on the fact that a voltage is induced in a conductor placed in a
magnetic field, the voltage induces a current if the circuit is complete and the direction of
current is such that it opposes the cause which produces the voltage.
AC motor: It uses the same principle as dc motor but the current used here is alternating,
differs only in construction.
AC generator: Same as the dc generator , the only difference is the construction and the
nature of current induced.
Transformer: It uses the principle that an alternating current carrying coil produces a varying
magnetic field and this causes a sinusoidal voltage to be induced in a nearby coil magnetically
coupled to it.