Ideal Transformer

An ideal transformer is one which has no ohmic resistance and no magnetic leakage flux that means 100% flux passes through the core and links with the primary as well as with the secondary winding. It has no iron and copper losses. There are two purely inductive coils in the Ideal Transformer, which are wound on a core. As in Ideal transformer, there is no losses. Hence, the core of the transformer is free from the losses.

The resistance of the winding is zero, and there is no leakage reactance. The core of the transformer is infinitely permeable. It is an imaginary transformer and practically it is not possible for a transformer to behave as an ideal transformer. In an ideal transformer, there is no power loss. Therefore, the output power is equal to the input power.

Since E2 ∞ N2 and E1 ∞ N1, also E1 is similar to V1 and E2 is similar to V2

Therefore, transformation ratio will be given by the equation shown below
The primary and the secondary currents are inversely proportional to their respective turns.

Behavior and Phasor Diagram of Ideal Transformer

Consider an ideal transformer whose secondary side is open circuited that means the load is not connected in the secondary side of the transformer as shown in the figure below.
ideal-transformer-figureWhen the primary side is connected to the sinusoidal alternating voltage V1, a current Im known as magnetizing current flows through it. This current sets up the alternating flux ϕ or mutual flux ϕm in the core and magnetizes it. Hence, it is called Magnetizing current. The flux ϕm is proportional to the current Im and is in phase with it. As the primary coil is purely inductive the magnetizing current (Im) lags behind the applied voltage V1 by 90◦.

The above all discussion done is represented by the phasor diagram shown below.


Phasor Diagram of an Ideal Transformer

The alternating flux links with both the primary and the secondary winding. When it links with the primary winding, it produces self-induced emf E1 which is in the opposite direction to the applied voltage V1. Similarly, when this alternating flux links with the secondary winding it produces induced emf E2 known as mutually induced emf in the opposite direction to the applied voltage. Both E1 and E2 lags behind the flux ϕ by 90◦.

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