as the ratio of the useful output power to the input power . Thus η = Output power Input power % ( . ) Transformers are highly efficient devices having their efficiency in the range of – %. Various energy losses in transformers will not allow them to be % efficient.
. . Energy losses in a transformer Transformers do not have any moving parts so that its efficiency is much higher than that of rotating machines like generators and motors. But there are many factors which lead to energy loss in a transformer.
i) Core loss or Iron loss This loss takes place in transformer core. Hysteresis loss (Refer section . ) and eddy current loss are known as core loss or Iron loss. When transformer core is magnetized and demagnetized repeatedly by the alternating voltage applied across primary coil, hysteresis takes place due to coil.
This means that rate at which magnetic flux changes through each turn is same for both primary and secondary coils. As a result of flux change, emf is induced in both primary and secondary coils. The emf induced in the primary coil or back emf ε p is given by ε p p N d dt =− Φ But the voltage applied v p across the primary is equal to the back emf. Then v N d dt p p =− Φ ( .
) The frequency of alternating magnetic flux in the core is same as the frequency of the applied voltage. Therefore, induced emf in secondary will also have same frequency as that of applied voltage. The emf induced in the secondary coil ε s is given by ε s s N d dt =− Φ where N p and N s are the number of turns in the primary and secondary coil respectively. If the secondary circuit is open, then ε s = v s where v s is the voltage across secondary coil.
v s s N d dt =− Φ ( . ) From equations ( . ) and ( . ), v v s p s p K ( .
) This constant K is known