An ideal transformer is one which has no losses (no iron loss and no copper loss) and no leakage flux i.e. all the flux produced by the primary winding is linking with the secondary winding.
 
In actual practice, it is impossible to make such a transformerbut to understand the concepts of transformer it is better to start with an ideal transformer and then extend to a practical transformer. In this article I am discussing the ideal transformer on load.
 

 
Consider an ideal transformer whose secondary is open as shown in the figure. When it is connected to AC supply voltage V₁ a current I_m flows through its primary winding.
 
Since the resistance of the primary coil is zero (i.e. it is purely inductive) the current I_m lags behind the applied voltage V₁ by 90^o. The losses are zero (as assumed) and no load is applied to the transformer, therefore, the magnitude of current I_m will be very small.
 
This current is called magnetizing current I_m as it produces flux φ in the core. Because flux is produced by I_m hence it is in phase with I_m.
 
This alternating flux links with both secondary and primary windings. When this flux links with secondary winding it produces mutually induced EMF E₂ in the secondary winding. When this flux links with primary winding it produces self-induced EMF E₁ in the primary winding.
 
Both the EMFs (E₁ and E₂) oppose the cause (applied voltage V₁) producing it (as per Lenz’s law). Hence these are shown in opposite direction in the phasor diagram.
 
V₁ = primary applied voltage
E₁ = self-induced EMF in the primary winding
E₁ = V₁ (because it is an ideal transformer with no resistance and reactance on primary side)
 
E₂ = mutually induce EMF on the secondary side
V₂ = secondary terminal voltage
V₂ = E₂ (because at no load I₂ is zero)
 
I₁ = I_m, magnetizing current on primary side
I₂ = 0 (no load)
 

Ideal Transformer on Load

 
When a load is applied to the secondary side of an ideal transformer, a finite value of secondary current (I₂) starts flowing. The magnitude and phase of secondary current, I₂ w.r.t. secondary terminal voltage, V₂ depends upon the nature of the load.
 
If the load is resistive, I₂ is in phase with V₂.
If the load is inductive (R-L) type, I₂ lags V₂ by some angle φ₂.
If the load is capacitive (R-C) type, I₂ leads V₂ by some angle φ₂.
 
When I₂ flows, it sets up its own MMF (N₂I₂) and hence creates its own flux φ₂.
 
However, φ₂ opposes the main flux φ_m setup by magnetizing current (as per Lenz’s law).
 
This momentarily weakens the main flux φ_m and therefore primary back EMF E₁ tends to decrease. Due to the reduction in E₁, the difference between V₁ and E₁ increases and the additional primary current I₂’ starts flowing. The I₂’ component of primary current is called load component of the primary current.

The current component I₂’, sets up an MMF N₁I₂’ to counter the effect of secondary produced MMF N₂I₂
 
i.e N₁I₂’ = N₂I₂
or I₂’ = N₂I₂ / N₁ = KI₂
 
and it is 180^o out of phase with I₂. The net primary current I₁ is phasor sum of I₂’ and I_m (because I_w is zero in an ideal transformer).
 
Thus due to load on the secondary side, the primary current of the transformer increases to supply the additional power to the load.
 
Since, winding resistance of an ideal transformer is zero, therefore, its voltage regulation will be zero and its efficiency will be 100%.

Phasor Diagrams of Transformer on Load

• Ideal Transformer
• Construction of Three Phase Transformer
• Types of Transformers
• Equivalent Resistance and Reactance of Transformer
• Equivalent Circuit of Single Phase Transformer
• Power Loss in a Transformer
• Open Circuit Test of Single Phase Transformer
• Short Circuit Test on Single Phase Transformer
• Transformer Efficiency
• Regulation of Transformer
• Autotransformer
• Instrument Transformers
• Polarity of Transformer Windings
• Significance of Vector Group of Transformer
• Buchholz Relay Construction | Working
• Why current transformer secondary should not be opened
• Dielectric Strength Test of Transformer Oil
• Transformer Moisture Removal Process

© https://www.yourelectricalguide.com/ ideal transformer on load.