2.41. Which transformer would you expect to be the heavier, a 25-Hz unit or a 60-Hz unit of identical voltampere rating and identical secondary voltage rating? Explain.
Ans. From (2.9) it follows that 25-Hz transformer requires a greater flux as compared to a 60-Hz. This implies a greater core cross section for the 25-Hz transformer (for the same Bmax). Hence the 25-Hz transformer is heavier.
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2.42. A transformer is rated 1-kVA, 240-V/120-V, 60-Hz. Because of an emergency, this transformer has to be used on a 50°Hz system. If the flux density in the transformer core is to be kept the same as at 60 Hz and 240 V: (a) What voltage should be applied at 50 Hz? (b) What is the voltampere rating at 50 Hz? Ans. (a) 200 V; (b) 0.833 kVA