Transients of Restriking Voltage on Overhead-Line Systems

This report examines data relating to the parameters governing transients of restriking voltage on 132-kV overhead-line systems. From these data, which were obtained partly by short-circuit tests at full voltage and partly by low-voltage measurements, it is concluded that for most calculations relating to transients of restriking voltage in such networks, it is justifiable to use the power-frequency parameters of inductance and capacitance, and to neglect losses. In the network examined, rates of rise of voltage at the clearance of the first phase of a 3-phase fault under normal working conditions ranged from 600 to 4350 volts per microsecond at different points, the former relating to a circuit-breaker fed through a long line, the latter to a circuit-breaker adjacent to the transformer through which it is supplied. It is show in this report that at the start and during clearance of short-circuits, there may exist transient oscillatory currents of a few kilocycles frequency and quite large amplitude. These currents had quite an appreciable effect on the transients of restriking voltage observed in the short-circuit tests discussed: but it is concluded that their effect will be small under normal working conditions, since power-frequency fault currents will then be considerably larger in relation to the oscillatory currents.