Interference Currents in 380 and 150 KV Substations

We discuss the interference in high-voltage (HV) substations which results from switching operations, from an (inadvertent) breakdown or from a direct or nearby lightning stroke. In case of switching operations the initial power level of the disturbance is of the order of V²/Z0, where V can be the amplitude of the phase voltage, and where Z0 is the characteristic impedance of the HV circuit. A ns-fast rising wavefront runs through the HV circuit; after reflections in or near the substation high frequency (hf) waves are resulting. One expects that the disturbances will be more severe for higher voltages or lower impedances Z0 (in closed gas insulated substations (GIS), about 75 Ω, versus open air substations, about 300 Ω).