单回路网络-电力牵引交流传动系统课件.ppt

;Ohm’s Law for a Circuit Branch with an e.m.f. As will be recalled, for the potential of any point to be determined uniquely, it should be related to some reference, or datum, point. 分析：as…插入语，for…介词短语做目的状语。主句it指代any point ， reference point， datum point，这几个词组意思相同且为同位语。(同位语省译) 翻译：含一个电动势支路的欧姆定律 如前所述，要唯一地确定任一点的电位应该取定一个参考点(也就是基准点)。 ;If in the network shown in Fig.2.2(a) the reference or datum potential is φ2=constant=C, then, by definition, the potential at point 1’ will be higher than φ2 by an amount equal to the e.m.f. E (equation).;As already stated, the current in the external circuit, or generally in any passive element, is directed from a point at a higher potential a to a point at a lower potential b. Therefore the potential φ1= φa at point 1 is higher than the potential φ2 at point 2 。 ;also φ1’= φ1+RsI From Eqs.(1) and (2) it follows that φ1’= φ2+E=φ1+RsI Hence the current (eq.3) ;In the same vein, we may write an equation for the current in any branch of an arbitrarily complex circuit with any number of e.m.f.s and resistances and a specified P.D. across that branch (Fig.3.1). 同样，我们也可以对含有多个电动势和电阻、端电压已知的任意复杂的任一支路列出电流方程。;The current I in a branch containing an e.m.f. (an active branch) may be directed either from point a to point b, or the other way round. If the direction of current flow is not specified in advance, it should be assumed so that equation of the form Eq.(3) may be written. 对于包含有一个电动势的支路（即有源支路），电流I既可能从a流向b，也可能从b流向a。如果没有提前指定电流方向，就应该假设一个电流方向，以便写成式（3）的方程式。;Such an assumed direction is termed the positive reference direction and is denoted exactly as the actual direction by a hollow arrowhead or a current symbol with suitable subscripts. 这个假定的方向称为正参考方向，认为它准确地指示电流的实际方向，并用一个空心箭头或者带有合适下标的电流符号表示。;If the positive reference direction of I in the branch of Fig.3.1 is from a to b, the potential φb will be expressed in terms of φa thus (eq.) 如果图3.1中支路I的正参考方向是从a到b，那么电势φb可用φa来表示（公式）。;A minus sign in an answer obtained by Eq.(4) indicates an incorrec