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wsformer, r is less 1. Thus, (iii) The are to carry the high will have to Such wires will be, Alternating Current Circuits II 593, converting, ansformers, onvert high, ot in D.C.)., econdary',, One of the, P., N., nditions, we have, d the 'transformation ratio. In step-up transformer, r is more than 1; whereas in step-down, er number, voltage obtained across secondary, voltage applied across primary, no.of turns in secondary, no. of turns in primary, ag smaller, former, r1s fess than 1. ThuS, be the currents in the primary and the secondary at any instant and the energy losses be zero, then, power in the secondary power in the primary, V,xi,%3DV,x, %3D, that is,, N., when the voltage is stepped-up, the current is correspondingly reduced in the same ratio and vice-, Thus, the energy obtained from the secondary coil is equal to the energy given to the primary coil., Thuiously, a transformer is not a generator of electricity., Energy Losses in a Transformer : In practice, the power output of a transformer is less than the power, ut hecause of unavoidable energy losses. These losses are :, i) Copper Losses : As the alternating current flows through the primary and the secondary, heat is, developed inside the copper turns. This waste of energy is known as 'copper losses'., (ii Eddy Current Losses : Eddy currents are set up in the iron core of the transformer and generate, NA, MER, heat, with consequent loss of energy. To minimise these losses the iron core is laminated by making it of a, number of thin sheets of iron insulated from each other, instead of making it from one solid piece of iron., (iii) Hysteresis Losses During each cycle of A.C. the core is taken through a complete cycle of, magnetisation. The energy expanded in this process is finally converted into heat and is therefore wasted. This, 1OS Is minimised by using the core of a magnetic alloy for which the area of the hysteresis loop is a minimum., (iv) Flux Losses: The coupling of the primary and the secondary coils is never perfect. Therefore, the, whole of the magnetic flux generated in the primary does not pass through the secondary., On account of these losses, we have, ondary, When, etised, duced, rough, re, by, d emf, he efficiency of the transformer is given by, sume, olity of Transformers in Long-distance Power Transmission : If electric power generated at the, lay 2ation, say 22.000 W. be transmitted over long distances at the same voltage as required by consumers,, nd the, day's, 5 The current i flowing through the line wires will be very high (= 22,000/220 = 100A). Hence a large, or energy (i RA will be wasted as heat during transmission, R being the resistance of the line wires., 2., generating station., ) The line wires which are to carry the high current, will have to be made thick. Such wires will be