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State the underlying principle of a transformer. How is the large-scale transmission of electric energy over long distances done with the use of transformers ? |
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Answer» Solution :Principle : When an alternating voltage is applied to the primary, the resulting current produces an alternating magnetic flux which links the secondary and induces an emf in it. (mutual induction) Derivation : The induced emf or voltages `epsilon_(s)`, in the secondary, with `N_(s)` turns is `epsilon_(0) = (-N_(s)d phi)/(dt)` The alternating flux `varphi`also induces and emf called BACK emf, in the primary .This is `epsilon_(p) = (-N_(p) d phi)/(dt)` But `epsilon_(s) = V_(s) gt epsilon_(p) = V_(p)` Therefore, `V_(s) = (-N_(s)d phi)/(dt)` and `V_(p) = (-N_(p) d phi)/(dt)` Hence `(V_(s))/(V_(p)) = (N_(s))/(N_(p))` If the transformer is assumed to be 100% efficient (no energy losses),the power input is equal to the power output and scenes `P = VI rArr V_(p)I_(p) = V_(s)I_(s)`, then `(V_(s))/(V_(p)) = (N_(s))/(N_(p)) = (I_(p))/(I_(s))` THELARGE scale transmission and distribution of electrical energy over long distances is done with the use of transformers the voltage output of the generator is STEPPED-up (so that the current is reduced and consequently, the `I^(2)R` loss is cut down). It is then TRANSMITTED over long distances to an area sub-station near the CONSUMERS there the voltage is stepped down. It is for the stepped down at distributing substations and utility poles before a power supply of 230 V reaches our homes. |
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