Let us now define resonance. In a two-terminal electrical network containing at least one inductor and one capacitor, resonance is the condition which exists when the input impedance of the network is purely resistive

Find the resonant frequency arallel resonance

Example 2: Find the three inductance appearing in the T equivalent of the transformer shown in Fig., if L2=4H and the input inductance at A-B is 6H with C-D open-circuited, and 2H with C-D short-circuited

《电路》（英文版）12-1 Three-phase voltages

A A--connection three-phase sources a, b, c--line ter min als

The readings of three watt-meters Ax =v an+lnx vBx=vbn+lnx vc=von+v Nx (UANia tUBvibB+Uvicdt+l(uN(ia tibB +ic)dt T Jo aNaA foBNLbB +Uvic)dt The sum of the average powers taking by the three-phase loads

Let us add and subtract on the right side of I2 we have

the short-circuit input impedance I12=0 the short-circuit forward current gain I1V2=0 Let 1=0 he open-circuit reverse voltage gain I1=0 the open-circuit output admittance

13-6 Interconnection of two-ports 1. Series connection

13-8nic(Negative-impedance- converter(负阻抗变换器))