TRANSFORMERS CLASSIFIED AS PER OUTPUT

 There are two types of transformers on the basis of output obtained from the same. 

1.       1.Voltage step-up Type:

In this type of transformer, the voltage available at the secondary winding is greater than the voltage applied at the primary winding. Its secondary winding consists of a greater no. of turns in comparison to that of the primary winding.

        Let the transfer of electrical energy be 100% then

        Energy in primary= Energy in secondary

        Pp=Ps

        OR   Ip*Ep=Is*Es   

In this way, it is noted that by increasing the secondary’s voltage its current step-down transformer       as well.

2.       2.Voltage step-down Type:

In this type of transformer, the voltage available at the secondary winding is lesser than the voltage applied at the primary winding. Its secondary winding is lesser than the voltage applied at the primary winding. Its secondary winding consists of a lesser no. of turns in comparison to that of the primary winding. A voltage step-down transformer is a current step-up transfer as well. It is used in electric welding; electroplating etc. And for such purpose its size is made quite large.

TRANSFORMERS CLASSIFIED AS PER CORE

There are three types of transformers on the basis of core used between the windings:

1. Core type:

(a) Open core type:

In this type of transformer, the primary and secondary windings are wound on lathered paper spools of cylindrical or cubical shape. Laminated iron cores are fitted inside the spool. These types of transformer are almost out of use now.

(b) Closed Core type:

In this type of transformer L-shaped laminated cores are used which form a closed magnetic path. In this way the leakage of magnetic flux is greatly reduced in this type of transformer which increases the magnitude of electrical energy transferred.

2. Shell type:

In this type of transformer E and I-shaped laminated cores are used. The primary and secondary windings are wound one above the other on the central path of the core. In this way, the magnetic flux is divided into two parts at the center of core and covers both the windings all around. Most of the L.F. and A.F. transformers are of shell type.

3. Berry Type:

This is an improved form of a shell type of transformer. The main core of the transformer is cylindrical are both the winding wound on it. 8 to 10 shell joined to the main core cover the coil all around. In this way, the leakage of magnetic flux is minimized and the efficiency of the transformer is maximized. The transformer is used in special types of circuits.

TRONSFORMERS

A transformer is a static device which is used to transfer electrical energy from one circuit to the other. It works on the principle of mutual inductance. Since, there is no mutual inductance in D.C. circuits therefore, a transformer cannot work on D.C. and thus it can work only on A.C.

A transformer consists of two types of coils or windings:

1.       Primary:

                  The coil connected to the source of supply is called primary winding or only ‘primary’.

2.       Secondary:

                  The coil connected to the load is called secondary winding or only ‘secondary’.

                  A transformer has a single primary whereas it may have one or more secondaries.

          ADVANTAGES OF TRANSFORMERS

1.       The transfer of electrical energy takes place in a static mode and no part of the transformer moves at all. Hence, the transfer of electrical energy does not require any mechanical energy or any operator for looking after it.

2.       The transfer of electrical energy is almost peaceful, whereas in mechanical methods the operation of machines produces heavy noise.

3.       Since, the secondary circuit of the transformer rests isolated from the primary circuit; therefore, the use of a transformer in electronic equipments reduces the possibilities of a shock to the mechanic on touching the chassis etc.

4.       A transformer can increase or decrease either voltage or current as required and it is its main advantage.

5.       Since the transformer is a static device, therefore, its wear and tear is almost nil and it does not require much maintenance.

NON-INDUCTIVE COILS

Through the inductive is very useful property of a.c. circuits, but there are some electronic circuits in which the inductance is not desired at all. For example, when a wire wound resistor is used in a.c. circuits, it should have a non inductive winding. Besides, non-inductive coil the feeder line used for joining a transmitter or T.V. receiver to the antenna and the wire used for connecting indirectly heated filaments to the source of supply are designed to have minimum inductance. A twisted wire line of two parallel conductors’ line is used as feeder line.

INDUCTOR’S WINDING 

Various methods are used for winding the inductors so as to minimize the undesired capacitance between its turns. Principal winding methods are as follows:

1.       Solenoid-:

A solenoid is a single layered coil whose length is nearly 10 times of diameter.

2.       Toroid:

 It is a solenoid which is turned into a loop shape.

3.       Honeycomb Winding:

In this method the layers of winding take the shape of a honeycomb. The advantage of this method is this that the size of the coil can be made pretty small.

4.       Variometer:

A slight variation can be done with the help of dust or ferrite core in the inductance value of a coil but, when major variation is desired in the inductance value, a variometer is used. It consists of two coils wound on separate hallow cylindrical spools which are placed perpendicular to each other. When the two coils are perpendicular to each other, the inductance is minimum and when the two coils are parallel to each other, the inductance is maximum.

INDUCTORS

All conductors when carrying AC are supposed to have inductance. But, when a conducting wire is given the shape of a component by winding it like a coil, it is called as inductors. An inductor is commonly known as a choke. The word choke implies the meaning ‘to check’; hence, the component used for checking the flow of AC is called a choke. The main three types of chokes are as follows:

1.    Low frequency choke:

A choke designed to work in the frequency range of 50 to 60 Hz is termed as l.f. choke. It is made up to 100 henrys. It is used in the filter circuits of rectifiers for smoothing the pulsating D.C. Iron core is used in it.

2.    Audio frequency choke:

A choke designed to work in the frequency range of 20 to 20,000 Hz is termed as a.f. choke it offers a high impedance to a.f. currents but very low impedance to a.f. currents but a very low impedance to D.C. it is also made up to 100 henrys. It is used in impedance coupled amplifiers for coupling and in H.T.D.C. lines for blocking the flow of a.f. currents. Iron core is used in it also.

3.    Radio frequency choke:

A choke designed to work in the frequency range of 20 KHz and upwards is termed as r.f. choke. It is made to have a low inductance value of the order for micro-henrys.  Commonly, its inductance value does not exceed 125 mH. It offers high impedance for r.f. currents but very low impedance for a.f. currents and D.C. it is used in impedance coupled r.f. amplifiers for coupling and in H.T.D.C. lines for blocking the flow of r.f. currents.

      On the basis of core used, the types of chokes are as follows:

(a)    Air core type:

It is simply a coil of fine copper wire wound on a hollow cylindrical spool of an insulating material. It is made in the inductance range of the order of micro and Milli henrys; hence, it does not require an iron core.

(b)    Dust core type :

It consists of a core inside the coil. The core is made of iron dust and a suitable binding material. There are two advantages of using dust cores:
1.    It has relatively high inductance value.
2.    Dust core losses are less in comparison to iron cores.

(c)    Variable dust core type:

In this type of coil, threaded core and spool are used so that the inductance of the coil can be varied by screwing the core. More the core is inside the coil, more is the inductance of the coil. In the coils working at high frequencies, ferrite cores are used. Ferrite is a mixture of oxides of iron, barium and strontium.

Besides above explained types of inductors, many other types of inductors are also used in electronic circuit, e.g. voice coil of headphone or loudspeaker, current coil of moving coil meter, deflection yoke coil of a T.V. receiver etc.