Updated: Jun 25
Transformer is used to transfer the power from primary side to secondary side by stepping up or down the voltage. The power at the input and output side is fairly remains constant. Transformer does not alter the frequency.
In ideal condition the input power must be equal to the output power after transfer of energy, however this condition is difficult to meet because transformer cannot be 100% efficient. Even, no machine is 100 % efficient. There is always some losses in the form of heat takes place in the machine. Therefore, an ideal transformer is hypothetical and can not be realized practically.
In a transformer the electrical energy is converted into magnetic energy and again the magnetic energy is converted into electrical energy. The magnetic energy is nothing but the flux which flows in the magnetic core of the transformer.
All the flux generated by the primary winding must linked to primary and secondary winding. This is possible only if there is no flux leakage in the core. This is an ideal condition. However, the some part of the flux leaks in the core which cause hysteresis loss. The leakage flux produces leakage reactance in a practical transformer. In an ideal transformer leakage reactance is zero.
A transformer has primary and secondary winding which is made of copper or aluminium. The copper or aluminium has certain resistance and copper loss (I2R) takes place in the transformer when current flows through its secondary winding. Zero copper loss can be possible if the resistance of both the winding is zero. This is imaginary condition. so, in an ideal transformer copper loss is zero.
In an ideal transformer core loss component of the current is zero, therefore the exciting or magnetizing current in phase with the magnetic flux. This is possible if the B-H or magnetization curve is linear.
In a practical transformer, the core loss component of current exist and therefore the exciting current is not in phase with the magnetic flux. The exciting current leads the magnetic flux by angle “α”. This angle is known as hysteric angle. In a practical transformer the B-H curve is not linear and it becomes flat with increase of magnetizing current.
From above phasor diagram, it is clear that practical transformer has core loss and therefore the exciting current is not in phase with the magnetic flux.
To summarize, the main difference between an ideal and practical transformer are as follows.
The core loss and copper loss of an ideal transformer is zero, whereas a practical transformer has finite core and copper loss.
The efficiency of an ideal transformer is 100%. The efficiency of the practical transformer depends on the loading and power factor and it can not be 100 % in any case.
There is no ohmic resistance drop in an ideal transformer so its voltage regulation is 0 %. The voltage regulation of a practical transformer is always more than 0%.
The flux generated in the primary gets fully linked to primary and secondary winding and there is zero flux leakage in an ideal transformer. In a practical transformer entire flux does not gets linked to both winding and some amount of the flux gets leaked.
An ideal transformer is hypothetical and can not be realized practically.