(3)功率平衡式 电动机从电源输入的电功率为 P=U·I=[Ea+l(R+R2)l+U·Ir Eala+la(ra+ ra)+ul= Pem pcua t pcuf Pn=Eln=Mmn·2=(M2+M)·g=P2+p2 60 Po=pfe t pmec t pad（3）功率平衡式 电动机从电源输入的电功率为：   a a a a f em cua cuf a a a a f E I I R R U I P p p P U I E I R R I U I = + + + = + + =  = +  +  +    ( ) ( ) 2 1 f e mec a d p = p + p + p 0 2 0 2 0 P E I M (M M ) P p em = a a = em  = +  = +  =  n 60 2