Transformer—Transformer is a device which converts low alternating voltage at high alternating current into high alternating voltage at low alternating current and vice versa. It does not work on D.C.
Principle—It works on the principle of “mutual induction”. It states that if magnetic changes in primary coil then EMF is induced in secondary coil and vice versa.
Construction
Working
In a transformer these are two types of coil :
Primary and Secondary. Primary coil is attached with input whereas secondary coil is connected to output. Through induction alternating voltage may be increased or decreased. It works on the “Coupling Method”. Theory
According to law of Faraday
Flux changes in the coil is directly proportional to the no. of turns in the coil
eqn is called working theory of a Transformer upto here only
Ns/Np is called Transformation Ratio
It is represented by k
K = Ns/Np …(vi)
If K > 1, then transformer is step-up Transformer.
If k < 1, then transformer is step-down Transformer.
Types of Transformer
Step-up Transformer—A transformer is said to be step-up if low alternating voltage at high alternating current is converted into high alternating voltage at low alternating current. In a step-up transformer, no. of turns in secondary coil is larger than no. of turns is primary coil.
i.e. Ns > Np
Step-Down Transformer—Transformer is said to be step-down transformer if it converts high alternating voltage at low alternating current into low alternating voltage at high alternating current. Number of turns in a primary coil is larger than no. of turns in a secondary coil.
i.e. Ns > Np
Uses of Transformer
(i) A step-down transformer is used for the purpose of obtaining large electric current for electrical welding.
(ii) A step-down transformer is used in the Induction-furnace for melting the metals.
(iii) A step-up transformer is used for the production of X-ray.
(iv) Transformer are used in voltage-regulator and stabilizer.
(v) Small transformer are used in radio-sets, television,telephones and loud speakers.
Different Types of loses in transformer
Flux loss—The linkage of primary to secondary coil is neither ideal nor perfect. Hence, whole of the magnetic flux produced in primary coil never gets linked up with the secondary coil. Hence some of the energy is lost in the form of flux, known as flux loss.
Copper loss—Due to resistance of the windings in primary and secondary coil, it opposes the current to pass through it when current passes through the coil heat is produced. Due to heat, energy is lost which is called ‘copper loss’.
Iron loss—Due to the variation in magnetic flux, eddy current is produced in the core of a transformer. When current passes through resistance, small heat is produced due to Eddy current. Hence small amount of energy is lost due to heat, known as Iron loss.
Hysteresis loss—The alternating current passed through the coil which is magnetic in behaviour. During each cycle of AC, magnelisation and demagnetisation is the result. Due to this hysteresis loop, energy is lost which is called Hysteresis loss.
Humming loss—When alternating current is passed through the core of wise, it starts vibrating. Due to vibration, sound is produced, hence same amount of energy is lost in the form of sound, which is called ‘Humming loss’.
Efficiency
Efficiecny the ratio of output powr to the input power Mathematically it can be written as :
Due to different types of losses, such as flux loss, copper loss, Iron loss, hysteresis loss and humming loss, output power is always less than input power.
Conclusion : Efficiency of a transformer is always less than 100%
