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Anna University Previous Year Questions on Transformers In this post, we collected some of the questions on transformers (semester-III)  asked in anna university previous year semester exams. We are sure that they will help you to prepare for your technical interview. [1] Why transformers rated in KVA instead of KW? The copper loss (I2R) in the transformer depends on the current I through the winding while the iron or core loss depends on the voltage V as frequency of operation is constant. None of these losses depend on the power factor (cosφ) of the load. Hence losses decide the temperature rise and hence the rating of the transformer. As losses depends on V and I only, the rating of the transformer is specified as a product of these two parameters VxI. Thus the transformer rating is in kVA and not in kW. [2] Why is the efficiency of transformers more than that of other rotating machines? There are no moving parts in transformer hence the friction and mechanical losses are absent...