Lecture 121 EEE 302 Electrical Networks II Dr. Keith E. Holbert Summer 2001

Lecture 122 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 123 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 v 1 i 1 + v 2 i 2 = 0 = p 1 + p 2 An ideal transformer is very tightly coupled (k  1)

Lecture 124 Defining the turns ratio, n=N 2 /N 1, provides the frequency domain equations for an ideal xformer NOTE: these equations require I 2 in the reverse direction (see Fig )---against dot convention Each change of voltage or current with respect to the dot introduces a negative sign in the corresponding equation Ideal Transformer

Lecture 125 Ideal Transformer I1I1 + – V1V1 I2I2 + – V2V2 1:n ZLZL

Lecture 126 Class Examples Extension Exercise E11.6 Extension Exercise E11.7

Lecture 127 Thevenin Equivalent Circuit Thevenin's theorem may be used to derive equivalent circuits for the transformer and either its primary or secondary circuit

Lecture 128 Class Examples Extension Exercise E11.9