Transformer as a Constant Flux Device ( Transformer on LOAD )

Transformer ON Load

• When the supply voltage V₁ is given to the transformer primary winding, primary current I₁ flows through the winding which produces maximum flux F_m in the core. 
• When the secondary winding of the transformer is loaded, the secondary current I₂ flows through it. 
• However the phase of current I₂ with respect to secondary voltage V₂ depends upon type of load. i.e. inductive, capacitive or resistive load. 

• The secondary current I₂ sets up its own mmf N₂I₂ and its own flux F₂ which opposes the main or primary flux F_m. 
• Therefore the resultant flux and primary induced emf is also decreased.

        Resultant flux F = F_m – F₂

• The supply system draws more current from the primary winding due to difference between supply voltage V₁ and induced emf E₁ increases until the original value of flux or main flux F_m is obtained.
• Let the additional primary current be I₂'. 
• This current is equal in magnitude with I₂  but anti phase with I₂. This current I₂' is known as reflected load current. 
• The current I₂' sets up flux F₂' in magnitude. 
• Therefore the mmf N₁I₂' and mmf N₂I₂ cancel each other. 
• We can say that the magnitude and phase of load component of primary current depends upon the type of load. 
• The net flux passing through the core remains constant whatever the load conditions if we neglect primary and secondary leakage fluxes. From the above discussion 

       F₂' = F₂

       N₁I₂' = N₂I₂

       I₂' = ( N₂ / N₁ ) I₂ = K I₂ …………… ( 1 )

Therefore the primary current consists of vector addition of two current
( 1 ) No load current I₀
( 2 ) Reflected load current component I₂'

Primary current I₁ = I₀ + I₂’…………….( 2 )
Figure B shows the vector diagram of transformer under different load conditions. In this diagram total voltage drops of both winding are neglected therefore

       V₁ = E₁ and V₂ = E₂

Vector Diagram For Lagging power factor

The vector diagram shows that the secondary current I₂ lags behind the load voltage by angle F₂.

Vector Diagram For Unity power factor

• The vector diagram shows that the secondary current I₂ is in phase with the load voltage. 
• It means that the phase angel between V₂ and I₂ is equal to zero.

Vector Diagram For Leading power factor

• The vector diagram shows that the secondary current I₂ leads the load voltage V₂ by angle F₂.  

What is Demagnetizing MMF? Describe its function.

• The mmf sets up by the load current in the secondary winding is known as demagnetizing mmf ( N₂I₂ ). 
• Its function is to reduce main flux F_m.

The transformer is a constant flux device, isn’t it?

• Yes, the core flux in the transformer remains constant whatever the load condition if we neglect leakage flux in the primary as well as secondary winding.

You may also like :

VIDYUT PRAVAY –Its Amazing !

Compare –Intrinsic Semiconductor and Extrinsic Semiconductor

Define : Low voltage, Medium voltage and High voltage

Do you know –Ideal current source means?