Modelling of Flashover on Insulator Strings of Overhead Lines Due to Lightning Overvoltages

The flashover occurrence on insulator string depends on various parameters such as grounding resistance, lightning current parameters, flashover performance of insulator string, weather conditions, etc. A crucial parameter in describing the dielectric strength of insulator strings is the critical flashover voltage (CFO), which represents the peak value of the impulse voltage at which there is a 50% probability for flashover occurrence. For flashover modelling, U-t curves, integration-based and physical models can be used. Conducting tests on equipment with various non-standard voltage waveforms is not practical, so analytical methods are employed to predict insulation behaviour under non-standard waveforms that occur in reality. U-t curves are rarely used due to significant deviations in flashover voltage values. In this paper, integration-based and physical models are developed in electromagnetic transients (EMT) software according to CIGRE recommendations for insulator strings of various voltage levels. To verify the accuracy of calculations, the obtained U-t flashover curves are compared with measurements performed in the HV laboratory. The influence of changes in front and time-to-half durations on the critical flashover voltage is observed. The developed models are used for several simulations on 110 kV overhead line to observe the behaviour of developed models depending on various network parameters and lightning current parameters.