Transformer is an electronic device which converts alternating voltage from one value to the other value. It is composed of two coils, referred as primary coil and secondary coil. Both these coils are not connected electrically. These coils are either arranged side by side or one coil on top of the other coil. These coils are separated by air, iron-dust or iron. Figure depicts various transformer symbols based on these.
Working of transformer
A transformer works using concept called as electromagnetic induction. When AC is applied to the primary coil, it produces changing magnetic field. This field is passed through the secondary coil which induces changing voltage in the secondary coil. As per Lenz law, induced voltage in the secondary coil will have opposite polarity to the voltage in the primary coil.
Magnetic saturation of the core occurs in a transformer when too large current flows. Precausion is taken in the presence of DC component.
Secondary a.c. voltage/primary a.c. voltage = Number of turns in secondary coil/Number of turns in primary coil
In symbols, Vs / Vp= Ns / Np
The ratio Ns / Np is called turns ratio.
A transformer with two secondary coils will both step up and step down the primary voltage.
Power in primary = power in secondary
OR Vp X Ip = Vs X Is
In a perfect transformer, if Vs is double of Vp, Is will be half of Ip.
Actually, Is is always less than half of Ip because of energy losses due to following reasons:
• Resistance of copper wire
• Eddy currents
• magnetic field not passing completely through secondary coil
Transformer types are main transformer, audio frequency transformer and radio frequency transformer. Main transformers are used in Britain, which works at 50 Hz and primary voltage of 240V AC. The secondary windings may be step up or step down or will have one or more of each.
Audio frequency transformers are used to transfer maximum power from audio frequency output to the input of loudspeaker.
Radio frequency transformers will have adjustable iron dust core which forms part of tuning circuits in a radio. They are covered in a enclosure to avoid radiation to other circuits.
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