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The core of a 25-kVA, 1200/550 V, 60-Hz, 1-ph, core type transformer has a cross-section of 50 cm × 50 cm. Find:i. the number of H.V. and L.V. turns per phaseii. the e.m.f. per turn if the maximum core density is not to exceed 1.5 Tesla. Assume astacking factor of 0.8.iii. Explain what will happen if its primary voltage is increased by 15% on no-load. |
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Answer» Given, f = 60Hz Bm = 1.5 tesla A = 2500 cm2 E1 = 1200 v E2 = 550 v Induced emf is equation \(E_1 = 4.41 \,f\,N_1\,\phi _m\) ......(i) \(E_2 = 4.41 \,f\,N_2\,\phi _m\) ......(ii) where N1 - number of turn in primary winding high voltage N2 - number of turn in secondary winding low voltage \(\phi_m = B_m\times A\) Then \(E_1 = 4.44 \,f\,N_1\,B_m\,A\) \(N_1 = \frac{E_1}{4.44 f B_mA}\) \(N_1= \frac{1200}{4.44 \times60\times 1.5 \times2500\times10^{-4}}\) \(N_1 = \frac{1200}{99.9}\) N1 = 12.01 turns Similarly \(N_2= \frac{E_2}{4.44 \times60\times 1.5 \times2500\times 10^{-4}}\) \(N_2 = \frac{550}{99.9}\) N2 = 5.50 turns Low voltage side turn N2 = 5.50 turns High voltage side turn N1 = 12.01 turns |
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