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

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

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

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

《电路》（英文版）12-1 Three-phase voltages

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

Find the resonant frequency arallel resonance

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

sinusoidal voltage: V =V29 A sinusoidal current: I= We define the complex powerS=vi=V∠9,I∠-9 =V∠,-=V∠=+ jVI sin=P+j P=VIcos 9 --active(average) power

Example 1: If 0=4v2 cos\tV, Z=2/600Q2 Find p(t)and P. Solution: