Question

thoroticaly,the coluping between 2coil is never perfect ,why?​

Answer 1

Explanation:

Leakage Flux – There is never perfect coupling between primary and secondary coils. ... The magnetic flux that is not common to both windings is called leakage flux. Due to leakage flux, self-induction occurs in the primary coil, and some inductive voltage opposing the supply voltage is induced on the primary coil.

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Answer 2

Answer:

Leakage Reactance – There is some small amount of leakage inductance in both windings. This inductance causes some reactance on both coils, which is called leakage reactance. The leakage reactance acts as unwanted inductances connected in series to transformer coils. Due to these leakage inductances, there is some voltage drop on both coils. The voltage drop increases as the current through the transformer coils is increased, and more power is drawn at the secondary.

Coil Resistance – The coils have some resistance, which serves as the internal resistance of the transformer. These internal resistances appear at both coils and act as series resistance to transformer coils. Due to internal resistances, there is a secondary voltage drop on both coils.

Stray Capacitance – Stray capacitance appears on transformer coils due to slightly different voltage levels of coil turns. These capacitances appear on both coils and are modeled as parallel capacitors to coils. At low frequencies, stray capacitance does not have any significant effect, but at high frequencies, this capacitance can resonate with leakage inductance. This changes the expected behavior of the transformer near the resonant frequency.

Mutual Capacitance – There is also some capacitance between the two transformer coils. This is modeled as a mutual capacitance connected between transformer coils. There is also some mutual capacitance between the coils and the core, coils and the shield, and coils and the chassis.

Core Losses – There are internal (power) losses due to eddy currents and hysteresis in the transformer core. To minimize these losses, the core is often laminated into sheets so that that circular eddy currents could be avoided.

Explanation: