EEE 302 Electrical Networks II

EEE 302Electrical Networks II Dr. Keith E. Holbert Summer 2001 Lecture 12

Ideal Transformer For an ideal transformer (which is coupled with good magnetic material so that the core permeability and winding conductivities are assumed infinite, and it is therefore lossless) the time domain relations are where both currents are entering the dots on the positive terminal. Lecture 12

Ideal Transformer • Note that the two equations above can be combined to show that the power into the ideal transformer is zero, and it is therefore lossless v1i1 + v2i2 = 0 = p1 + p2 • An ideal transformer is very tightly coupled (k1) Lecture 12

Ideal Transformer • Defining the turns ratio, n=N2/N1, provides the frequency domain equations for an ideal xformer • NOTE: these equations require I2 in the reverse direction (see Fig. 11.13)---against dot convention • Each change of voltage or current with respect to the dot introduces a negative sign in the corresponding equation Lecture 12

Ideal Transformer I1 I2 1:n + + ZL V1 V2 – – Lecture 12

Class Examples • Extension Exercise E11.6 • Extension Exercise E11.7 Lecture 12

Thevenin Equivalent Circuit Thevenin's theorem may be used to derive equivalent circuits for the transformer and either its primary or secondary circuit Lecture 12

Class Examples • Extension Exercise E11.9 Lecture 12

EEE 302 Electrical Networks II