Ideal Transformers

What is Ideal Transformer

An ideal transformer is one which has no losses in it. An ideal transformer is completely an imaginary transformer, Though Ideal transformer doesn't exist in this world, the study is made to better understanding of actual transformer. Ideal transformer winding have no ohmic resistance and there is no magnetic leakage. Simply, an ideal transformer consists of two coils which are purely inductive and wound on a loss-free core.

Ideal Transformer on NO LOAD

Consider an ideal transformer whose primary is connected to a sinusoidal alternation voltage source s and whose secondary is opened. Under this condition, when the sinusoidal voltage s is turned ON, the primary draws a current from the source to build up a emf(self induced) which is equal and opposite to the applied voltage source s. Since the coils are purely inductive and there is no load, the primary draws the magnetising current I_μ from the applied voltage source s to magnetise the core. This alternating magnetising current I_μ produces an alternating flux Φ which is proportional to the current and hence is in phase with it. This changing flux is linked with both the windings. Due to this changing flux an emf (e₂) is induced in the secondary side called mutually induced emf This mutually induced emf (e₂) acts very much similar to the self induced emf (e₁) ie) in phase and opposite to the applied voltage v₁ Here, the magnitute of the mutually induced emf is proportional to the rate of change of flux and the number of secondary turns.

Ideal Transformer ON LOAD

Consider an Ideal transformer whose secondary is loaded. When the secondary is loaded, secondary current I₂ is set up as it forms a closed circuit. The magnitude of I₂ is determined by the characteristic of the load. Due to the current I₂, the flux Φ₂ is set up which opposes to the primary flux Φ, which is due to I_o. The opposing secondary flux Φ₂ weakens the primary flux for a very short time and primary back emf E₁ tends to reduce. At that particular time, V₁ > E₁ and hence causes more current(I'₂) to flow in the primary winding. This current I'₂ is also known as load component of primary current. I'₂ current is in phase and opposition to current I₂ in the secondary winding. Similarly the flux Φ'₂ opposes Φ₂ in the same direction with equal magnitude. Thus, the secondary current I₂ get neutralized immediately by additional primary current I'₂.

Ideal transformer NO LOAD vs Ideal Transformer ON LOAD

NO LOAD Ideal Transformer	ON LOAD Ideal Transformer
Net Flux passing through the core is approximately equal to ON load ideal transformer	Net Flux passing through the core is approximately equal to NO load ideal transformer
I2 = 0	I2 α to load
Core loss is same as ON load Ideal transformer	Core loss is same as NO load Ideal transformer
Primary current = I0	Primary current = I0 + I'2