An ideal transformer is a useful approximation of a very tightly coupled transformer in which the coefficient of coupling is almost unity and both the primary and secondary inductive reactance are extremely large in comparison with the terminating impedance

A current i at Li produces an open circuit voltage u,at L2s dyal

Find the resonant frequency arallel resonance

①主电路保护的设置 这里所讲的保护，主要是针对电源变换装置里 的器件，需要保护的状态包括：过电压、过电流、 过热等

Frequency characteristics(Xi, xc,x,z, y, o vs o Z=R+A=R+(L+Xc)=R+ilo I

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

We assume=Im cos(t+a)i=Im cos(ot+B) The phase angle by which the voltage leads

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

《电路》（英文版）9-1 Instantaneous power