An ideal transformer cannot be physically exist, however its study provides a very useful information in the analysis of practical transformer. A transformer is said to be ideal if its output power is equal to input power. In other words, it does not have any losses and its efficiency is 100% . In this article, we will discuss some of the properties which needs to be satisfied to consider a transformer as an ideal transformer.
Infinite Permeability:
Permeability is defined as the measure of ability of material to support the formation of magnetic field within itself. This simply means that if permeability of core material is high, less magnetizing current(magnetomotive force) is required to establish the flux in the core. Moreover, if the permeability of core is infinity, magnetizing current needed to establish the flux in the core is almost zero. In case of ideal transformer, core has infinite permeability due to which the magnetizing current required is zero.
Explanation:
In order to understand, let us consider the BH curve
as shown below. The area cover under the BH loop is nothing but hysteresis loss (fig:1). If the BH curve gets narrower until the area cover under the BH loop is become zero , hysteresis loss becomes zero(which is the ideal case). Now, the obtained slope is nothing but permeability(
). This slope tells us that how much amount of magnetomotive force (current)is needed to obtain the required flux
for given core (fig:2).
If the permeability of core material is infinity, we have a BH curve almost along vertical axis as shown below. This vertical BH curve tell us that in order to setup a flux in the core, the current required for magnetizing the transformer core is zero which is the characteristic of ideal transformer. Hence we can say that in the case of ideal transformer, permeability ( ) of transformer core is infinity and we have a B-H curve along the vertical axis (shown below).
Core Saturation:
One more characteristic of ideal transformer is that core of the transformer doesn’t saturate. In other words, permeability is going to be infinite for all values of Bsat (core saturation).
Explanation:
BH vertical curve tells another important point of ideal transformer. As we know that for every type of core material, there is a value of flux density (B) beyond which the flux will not increase with the increase of magnetomotive force (current) and saturates. It loses its magnetization properties (it doesn’t act like a magnetic material)after a particular value. However, if Bsat tend towards infinity, then we will have a magnetization curve which is a vertical axis curve as shown below. This simply means that the core of transformer will never saturate which is the characteristic of ideal transformer.
No Eddy Current Losses :
Eddy current losses in the ideal transformer is zero. In other words, resistivity of the core material is infinity in case of ideal transformer.
Explanation:
When flux flows in the core of transformer, current is going to be induced in the core material (since core of transformer is conducting material). This current I is going to produce
loss in the core material which is known as eddy current losses. If the resistivity of core material is increased, eddy current loss is going to be reduced. Moreover, if the resistivity of core material is infinity, there will no flow of eddy current which means that eddy current losses are zero (characteristics of ideal transformer).
Winding Resistance:
Resistance of primary and secondary winding is zero in case of ideal transformer.
Explanation:
Normally, copper coils are wound on the core material has finite resistance. Hence there is going to be loss. If the resistance of coil windings is zero, there will be no copper loss. For an ideal transformer, both primary and secondary windings have zero resistance and they are purely inductive.
No Leakage Flux:
Leakage flux in the ideal transformer is zero.
Explanation:
When current flows through the primary and secondary coils, it produces magnetic flux. However, some part of the flux produced by the primary current doesn’t link with the secondary winding. Similarly, secondary current produces some flux which doesn’t link with the primary winding. Hence the flux which links only one winding is called leakage flux. For an ideal transformer, all the flux produced in the core of transformer must links with both (primary and secondary) windings. In that case leakage flux is zero which is the characteristics of ideal transformer.
The above mentioned are the characteristics of ideal transformer. In an ideal transformer, there will be absolutely no losses. Input power given to the primary of transformer will be equal to its output power at the secondary side. In simple words, if there is no load connected across the secondary, no current is required from the supply to set up flux in the core. The flux itself setup in the core and will induce an emf at the secondary side according to its turn ratio. Moreover, the secondary emf induced has no losses since the hysteresis, eddy current and copper losses are zero. In simple words, power loss in the ideal transformer is zero and efficiency is 100%.