186Fundamental Electrical and Electronic PrinciplesΦ1Φ1Φ2Φ2L1IaidingIL2L1IopposingIL2 Fig. 5.40 Mk L LM1 20 8 254025 3 henrymHso, mH.. The values for 11122L I and 12222L I have been calculated in part (a) and MII11123225 300 2558...mJ (i) For series aiding: WW078255836....11mJso, mJ Ans (ii) For series opposition: WW0782558045....11mJso, mJ Ans 5.23 The Transformer Principle A transformer is an a.c. machine, which utilises the mutual inductance between two coils, or windings. The two windings are wound on to When the coils are connected in series such that the two fl uxes produced act in the same direction, the total fl ux is increased and the coils are said to be connected in series aiding. In this case the total energy stored in the system will be increased, so the last term in the above equation is added, i.e. the sign applies. If, however, the connections to one of the coils are reversed, then the two fl uxes will oppose each other, the total fl ux will be reduced, and the coils are said to be in series opposition. In this case the sign is used. These two connections are shown in Fig. 5.40 .