Tests with High Lightning and Switching Impulse Voltages
Lightning impulse (LI) over-voltages and switching impulse (SI) over-voltages are caused by direct or indirect lightning strokes or even by switching operations in electric power systems, respectively. They cause transient stresses to the insulations, much higher than the stresses due to the operational voltages. Therefore, insulations must be designed to withstand LI and SI over-voltages, and the correct design has to be verified by withstand testing using LI test voltages , respectively, SI test voltages . This chapter deals with the generation of aperiodic and oscillating LI and SI impulse voltages and the requirements for their application in HV tests. Special attention is given to the interactions between the LI/SI generator and the test object. The deviations from the standardized impulse shape, e.g. by an over-shoot on the LI peak, are analysed, and the evaluation of recorded pulses according to IEC 60060-1:2010 and IEEE St. 4 (Draft 2013) is described. This is completed by the description of components and of the procedures for the correct measurement of LI/SI test voltages. Also the measurement of the test currents in LI voltage tests and the PD measurement at SI, LI and VFT test voltages are included.