An experimental investigation of switching transients in a wind-collection grid scale model in a cable system laboratory

With the background of experience from field investigations in cable networks, multiple pre-strikes and re-ignitions are known to occur during switching operations, causing high frequency, steep fronted transient voltages and currents. Off-shore collection grids consist of vast amount of cables, with different length and connection points, which have low surge impedance compared with overhead lines. Consequently multiple pre-strikes and re-ignitions of switching apparatus with cables can cause transient overvoltages with higher time-derivatives than with overhead lines. The validation test circuits specified in the IEC standards developed for impulses due to fulmination on overhead lines do not consider the conditions of large cable grid and repetitive overvoltages due to switching. With the increase of cable grids and particularly wind parks, it has become important to characterize a collection grid cable system and the related transients during manoeuvres with different switching apparatus. The main contribution of this work is the experimental verification of the transient overvoltage phenomena in cable systems. An attempt is made to characterize this phenomenon in terms of number of re-ignitions, the magnitude and the rate of voltage step.