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Turns Ratio
Figure 1    Core-Type Transformer

Electrical Science Volume 4 of 4
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Transformers TRANSFORMER THEORY Efficiency Efficiency of a transformer is the ratio of the power output to the power input, as illustrated by Equation (13-3). (13-3) Efficiency Power  Output Power  Input PS PP x  100 where PS   =    power of secondary PP   =    power of primary Theory of Operation A transformer works on the principle that energy can be transferred by magnetic induction from one  set  of  coils  to  another  set  by  means  of  a  varying  magnetic  flux.    The  magnetic  flux  is produced by an AC source. The  coil  of  a  transformer  that  is  energized  from  an  AC  source  is  called  the  primary  winding (coil), and the coil that delivers this AC to the load is called the secondary winding (coil) (Figure 1). In Figure 1, the primary and secondary coils are shown on separate legs of the magnetic circuit so that we can easily understand how the transformer works.   Actually, half of the primary and secondary coils are wound on each of the two legs, with sufficient insulation between the two coils  and  the  core  to  properly  insulate  the  windings  from  one  another  and  the  core.     A transformer wound, such as in Figure 1, will operate at a greatly reduced efficiency due to the magnetic leakage.   Magnetic leakage is the part of the magnetic flux that passes through either one  of  the  coils,  but  not  through  both.    The  larger  the  distance  between  the  primary  and secondary windings, the longer the magnetic circuit and the greater the leakage. Rev. 0 Page 3 ES-13







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