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.
Fig. (a)
Fig. (b)
Fig. (c)
Fig. (d)
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 N1Io which sets up its own flux φm 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 φm. ( By Lenz’s law) . Hence φm 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 (φm) remains in the core of transformer.
In the Fig. (d) The flux φm is the constant flux that remains in the core irrespective of load from no load to full load conditions, φm 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 !!!
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