PURPOSE:To equalize magnetic flux density of all steel cores, by making sectional area of a side leg on the other side larger than that of a side leg on the side where a winding is wound. CONSTITUTION:Side legs 2A and 2B are provided on both sides of main legs 1A and 1B, and these main legs and side legs are magnetically combined by a top yoke 3A and a bottom yoke 3B. Low-pressure windings 4A and 4B and high-pressure windings 6A and 6B are respectively wound coaxially on the main legs 1A and 1B. And an exciting winding 7 and a tap winding 8, which is excited by the winding 7, are coaxially wound on the side leg 2A on one side. In thus constituted transformer, sectional area of the side leg 2B is made larger than that of the side leg 2A in accordance with amount of magnetic flux. It is possible, by doing so, to equalize magnetic flux density of the side leg 2B being under load to the magnetic flux of the main legs 1A and 1B and also of the side leg 2A. And therefore, it is possible thereby to eliminate unbalance of thermal expansion in a steel core and to prevent unbearable thermal strees from being applied onto the steel core.
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