Fig. 1,917.—Diagram of elementary transformer with continuous core and connections with alternator. The dotted lines show the leakage of magnetic lines. To remedy this the arrangement shown in fig. 1,918 is used.
Ques. How is the magnetic leakage reduced to a minimum in commercial transformers?
Ans. In these, and even in ordinary induction coils (the operating principle of which is the same as that of transformers) the magnetic leakage is reduced to the lowest possible amount by arranging the coils one within the other, as shown in cross section in fig. 1,918.
The Induced Voltage.—The pressure induced in the secondary winding will depend on the ratio between the number of turns in the two windings. For example, a transformer with 500 turns of wire in its primary winding and 50 turns in its secondary winding would have a transformation ratio of 10 to 1, and if it were supplied with primary current at 1,000 volts, the secondary pressure at no load would be 100 volts.
Fig. 1,918.—Cross section showing commercial arrangement of primary and secondary windings on core. One is superposed on the other. This arrangement compels practically all of the magnetic lines created by the primary winding to pass through the secondary winding.
EXAMPLE.—If ten amperes flow in the primary winding and the transformation ratio be 10, then 10 × 10 = 100 amperes will flow through the secondary winding.
Thus, a direct proportion exists between the pressures and turns in the two windings and an inverse proportion between the amperes and turns, that is: