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)


2/22

17-04-2011

2

ElectricalMachines

DCMachines

DC Motor

DC

Generator

AC

Machines

AC Motor

Alternator

Transformer


3/22

17-04-2011

3


4/22

17-04-2011

4


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.


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


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


8/22

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


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


10/22

17-04-2011

10

17-04-2011


11/22

17 04 2011

11

17-04-2011


12/22

17 04 2011

12

17-04-2011


13/22

13


14/22

17-04-2011


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.


16/22

17-04-2011


17/22

17

17-04-2011


18/22

18

17-04-2011


19/22

19

Faradays Law of Electromagnetic Induction

17-04-2011


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


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


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.

Documents

EMFT in electrical machine