Overhead-line parameters for circuit-breaker application

The paper presents the results of a comprehensive series of measurements and calculations by a collaborative committee aimed at determining values of overhead-line parameters (particularly for lines 1¿8 km long), significant in circuit-breaker application. Line models used in the calculations are discussed, as are refinements made to the models as the work progressed to give a final accuracy of calculation within ±5%. Measurement techniques are described, and the results of surge impedance and 50 Hz inductance and resistance measurements presented. Typical values calculated for the CEGB standard 275 kV and 400 kV lines are given, together with the effect of varying parameters such as frequency, line height and earth resistivity. A particular study was made of the effect of high tower-footing resistance, which was found to increase the 50 Hz inductance per unit length for the shorter line lengths. High footing resistance of the sending-end tower also increases surge impedance, but this is of no importance in practice. From a circuit-breaker viewpoint, the effect of subconductors touching due to attraction under short circuit is shown to be significant, since it increases the rate of rise of transient recovery voltage.