Prediction of surge response of a symmetrically excited three-phase line,and comparison with experimental results

The traveling-wave response of a 33-kV, flat-spaced three-phase line to symmetrically impressed double-exponential-surge excitation was predicted from Carson´s equations. The following modified asymptotic approximation was derived for the propagation functions of the two symmetrical-type natural modes. rAn= s√µ0ε0+ b1√s+η+b2Here η = 2(b2b1)²if b2< 0 (high-loss mode); η = 0 if b2> 0 (low-loss mode). The approximate voltage transform in terms of γAnhas a closed-form inverse. Numerical integration was used to compute a corrective voltage term. Predicted results for distances from 0.8 miles to 7.98 miles from the source compared favorably with earlier oscillograms for voltages below the corona-onset level.