Why is transformer called as a Constant Flux Machine?

Transformer is a device that is used for changing voltage levels in a power system. Basically, Transformer is a device that transfers electrical power from one electrical circuit to another electrical circuits. It uses the principle of mutual induction or electromagnetic induction to transfer electrical energy between coils without a metallic connection.

Transformer – A Constant Flux Machine

Let us understand this with a simple concept, we know that in an electrical circuit, there is a flow of charge in it. So, current is produced due to the flow of charges. Similarly, in the case of a transformer, there is the flow of flux (φ) in the core.

Transformer is generally called as ‘Constant flux machine’. The reason behind this is that Transformer works on the principle of electromagnetic induction, so there is a flow of flux in the core.

Let us see with the diagrammatic representation, Why Transformer is referred to as a constant flux machine?

In the transformer, there are two winding, first one is called as a primary winding and the second is the secondary winding. When the secondary is loaded, the secondary current I₂ is set up. The magnitude and phase of I₂ w.r.t V₂ is determined by the characteristics of load.

i) When the load is resistive, the current I₂ is in phase with V₂ .

ii) When the load is inductive, the current lags .

iii) When the load is capacitive, the current leads.

Let us understand the concept, with the help of diagrams.

In fig. a) :- When there is no load, the secondary of transformers is open, secondary current I₂=0. So, no-load primary current Io produces mmf N₁I_o which sets up its own flux φ_m in the core.

Fig.b) :- In fig, b) when load is connected at the secondary of transformer, emf E₂ = V₂ circulates current around I₂ in the secondary winding. The I₂ current sets up its own mmf N₂I₂ and flux φ₂ whose direction is opposite to the φ_m. ( By Lenz’s law) . Hence φ_m reduces.

Fig.c) : As φm reduces, primary self-induced emf E₁ also reduces. But primary voltage V₁ is constant, so to make E₁=V₁, primary draws additional current I₂‘. This I₂‘ sets up its own mmf N₁I₂‘ and own flux φ₂‘.

This φ₂‘ and φ₂ are equal in magnitude but they are opposite in direction. So, they cancel out each other. Now, only one flux (φ_m) remains in the core of transformer.

In the Fig. (d) The flux φ_m is the constant flux that remains in the core irrespective of load from no load to full load conditions, φ_m remains constant.

Therefore, the transformer is called as ‘Constant Flux Machine’ .

In this way we understand that why the transformer is also called as ‘Constant Flux Machine’.

Simple !!!