Transformer Working Principle-Types, Parts and Advantage

The working principle of the transformer is based on Faraday's law of electromagnetic induction. The three-phase power transformer is the main device of every power system. 

Considering the insulation part of the generator, the generation of electrical power is limited 11KV to 22KV, but to transmit power at a higher voltage level i.e 132KV or more is economical because of losses in lower voltage transmission is more and larger conductor size is required due to higher current. here we will see transformer working principle, types, parts, and advantages.

Every ac power transmission line starts with a three-phase electrical transformer and ends with it by stepping down 3 phase high voltage to usable level using a step-down type transformer i.e 415V for three-phase and 215V for single phase user.

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What is the transformer and its Working Principle?

The electrical transformer is a static piece device means it does not have any moving part in it. that's why the efficiency of it is high compared to other electrical machines.

The transformer basically transfers energy from one electrical circuit to another circuit through a magnetic field. Hence also called an electromagnetic energy conversation device. 

The circuit which transfers energy is called primary winding and which received energy refers as the secondary winding of a transformer which is further connected to the load.

Here mainly to Note that primary and secondary are not connected electrically to each other but connected magnetically.

Magnetic coupling allows transferring energy from a higher voltage level to a lower level or from low voltage to higher i.e energy transfer in either direction. 

The transformer converts voltage levels from one voltage to other voltage levels without a change in frequency or power.

Transformer Working Principle


Transformer works on the principle of Faraday's law of electromagnetic induction. According to Faraday's law, an emf is induced in a coil if it links to changing flux. 
When primary winding is fed with ac supply voltage " V1 " therefore an ac current " IФ " starts flowing through winding N1 turns.

Alternating MMF N1I creates alternating flux ϕ which starts flowing through the magnetic core and links to the secondary winding and induced voltage E2 in the secondary winding due to transformer action.

If a load is connected across secondary of X'mer, current starts flowing in secondary through the load.

Types of transformer

There are in general two types of transformer

Shell type and core type transformer These two types differ from each other in the manner in which winding wound on the magnetic core.


Core type

In core type, the magnetic core is built of laminations to form a rectangular frame and the windings are arranged concentrically with each other around the legs or limbs. 

The top and bottom horizontal portions of the core are called a yoke. The yokes connect the two limbs and have a cross-sectional area equal to or greater than that of limbs.

Each limb carries one-half of primary and secondary windings. The two windings are closely coupled together to reduce the leakage reactance. 
The low voltage winding is wound near the core and high voltage winding is wound over low voltage winding away from the core in order to reduce the amount of insulating materials required.

Shell Type


In shell-type, the windings are wound around the central limb and the flux travels through two side limbs and completes its circuit. 

The central limb carries total mutual flux while the side limbs forming a part of a magnetic circuit carry half the total flux. The cross-sectional area of the central limb is twice that of each side limbs

Step-up Transformer:

A transformer that changes voltage from a lower voltage to a higher voltage is called a step-up transformer. 

Step-up X'mer has more number of turn in secondary winding than primary hence voltage per turn increase, it increases voltage level, mostly use at generating station to transmit electrical power in transmission line at a higher voltage.

Step Down Transformer:

A transformer that lowers down voltage to utilization voltage called a step-down transformer, it reduced the voltage from higher to lower voltage level. It has less number of a turn on secondary winding compare to the primary winding.

It is used in a distribution network, where the transmission line end. mostly delta - star-connected windings, the primary is connected in delta and secondary is in star for deriving neutral point.

Note that step-down x'mer can be used as step-up transformer, in which secondary of a step-down x'mer becomes primary and primary of the step-down becomes secondary winding.

Step up or step down working operation of the transformer are decided after installation on site.

Parts of the transformer :

Magnetic core:

The magnetic core is made up of magnetic material like CRGO (cold-rolled grain-oriented steel). this material has high permeability. 

The core is a stack of thin silicon-steel lamination to reduce eddy current losses and separate from each other by using thin layers of varnish.

Winding :

Winding is made up of a copper conductor and wound on a magnetic core.
  • In a core-type transformer, most of the part of the core is surrounded by winding.
  • On the other hand in shell type transformer core surround a major part of the winding.
  • The advantage of the core type is it reduced core material but required more copper for winding
  • shell-type required less conductor material but more core material.
  • The vertical portion of the X'mer is called a limb and the horizontal portion is called a yoke.
  • 1 phase shell type x'mer has 3 limbs and winding wound on the central limb and core type has two limbs and winding wound on both limbs.

Conservator :


Transformer oil should not be allowed to come in contact with atmospheric air as it may take up moisture resulting reduction in the dielectric strength of the oil. also, air may cause acidity and sludging of oil. To prevent this transformer provided with a conservator.

The function of a conservator is to take up contraction and expansion of transformer oil during working without allowing it to come in contact with outside air. 
The conservator consists of an airtight metal drum-like structure fitted above the transformer top and connected with it by a pipe.

The main tank is completely filled with oil when cold. 
The conservator tank is partially filled with oil. So space for expansion of oil is provided and sludge formed remains in the conservator itself and does not go to the main tank.

Breather :

When temperature changes, the oil expands or contracts and there is a movement of air takes place. When the transformer cools down, the oil level goes down and the air is drawn inside. this process is known as breathing. 
The air, drawn in is passed through a breather for removing moisture from the air. 
The breather consists of a small vessel containing a silica gel crystal impregnated with cobalt crystal.

Advantages of transformer :

  • Used for stepping up or down supply voltage.
  • High efficiency compared to other electrical machines.
  • with the use of a x'mer, long-distance ac power transmission is possible.
  • Distribute power at high voltage.
  • Insulate circuits/establish separately derived circuits.
  • Provide 3-wire secondary circuits..
  • Provide electrostatic shielding transient noise protection.


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