40th Question answer: high voltage winding side. Why Tappings are on High Voltage Side ? Normally the tappings are provided on high voltage (h.v.) winding due to following reasons, 1) A fine voltage regulation is possible with high voltage winding as it carries large number of turns. 2) The low voltage winding of the transformer carries large current. So if tappings are provided on low voltage side then then there are difficulties encountered in the interruption of high currents which makes its impracticable. 3) For the reasons of requirement of insulation, the low voltage (l.v.) winding is placed near the core while the l.v. winding is placed outside. Hence practically it is easier and simpler to provide tappings on high voltage winding. 4) In case of step down transformers, it is an added advantage to provide tappings on h.v. side. At light loads, the l.v. side voltage increases. It is required to decrease this voltage by adjusting the tapping on h.v. side to a position where number of turns are large. With large number of turns, the flux and flux density decreases. This results in reduction of core loss which increases transformer efficiency at light loads. 5) If the tappings are provided on the l.v. side then the exact voltage regulation may not be provided. This can be explained by considering an example of a transformer with rating 3 phase, 11 KV/415 V, delta/star connected which is designed for 15 volts/turn. The l.v. side voltage is 415/√3 = 240 V. The number of turns on l.v. side are 240/15 = 16. Minimum number of turns that can be tapped is one. Hence minimum possible voltage regulation with tappings on l.v. side is 15 V or 6.25 %. It can be seen that if a voltage regulation of 5 % is desired with this then it is not possible with tappings on l.v. side.
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Sir, i think 51th ans is 765kv but there is option in u r pdf, If, in exam options are given like A) 400kv B) 765kv C) both A and B D) neither A nor B Which is the correct ans.
