Effect of shielded distribution cable on very fast transients

Fast transients in power systems can be generated by switching of vacuum an d SF6 insulated devices as well as by solid state devices such as those use d in variable speed drives. Transients with ns risetimes can be generated w hich, in a cable-connected system, propagate down the cable to inductive de vices such as motors and transformers, In general, the amplitude of such su rges is not out of the ordinary; however, the very short risetime can cause unacceptable voltages across the first turn of an inductive device. A cabl e with high frequency loss does not generally decrease the amplitude of suc h surges appreciably but can lengthen the risetime substantially by absorbi ng high frequency energy from the surge. This reduces the voltage across th e first turn of inductive devices and thereby protects them from damage and failure caused by such surges. In the present contribution, we quantify th e high frequency losses and effect thereof on very fast transients for four types of shielded, 15 kV distribution cable, three made from various EPR c ompounds and one made from TR-XLPE.