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Although not very apparent, the rate of rise of the line oscillation is higher for the shorter line lengths due to the higher interrupted fault currents, although the lower surge impedances reduce this effect. These slf transients have been combined with a source trv envelope in Fig. 4 to show the overall effect of different short-line faults. In this illustration the same basic source trv is used for all the slf conditions and modified according to IEC 56-2. From Fig. 4 it can readily be seen that the higher rate of rise of trv occurs with the shorter line lengths to the fault location although the initial voltage peaks are lower.

From Table 1 the first and last pole to clear surge impedances ZL 1 and zL 3 are calculated to be 299 and 322 ohms respectively. 39 SHORT LINE FAULT The equivalent surge impedances from the modal analysis for the same line conditions lie between the 1st/4th pole impedances and the 3rd/6th pole impedances respectively. Thus it can be seen that the single value of surge impedance derived from the sequence parameters represents an average value for the line. For some particular studies the average value may be insufficient if the conductor location on a tower is considered to be significant.

Possible effects of the behavior of arc roots on the interruption process will be discussed in the paper by Mentel. 2. Important Arc Characteristics Before describing the extinction 16 process, we summarize some experimental results 15 ' for an arc in the configuration shown in Fig. 10. Two arc segments must be dis- tinguished . In the area between the two nozzle throats there exists an approximately parabolic (see Fig. 10) axial pressure distribution, which results in a cylindrical arc (dT /dz = 0).