Staged fault test evaluation of high-voltage equipment maintenance safety grounding at a large hydro-electric powerplant

The effectiveness of temporary personal protective safety grounding for high-voltage equipment is investigated with staged fault tests conducted by the Bureau of Reclamation at the Hoover hydroelectric powerplant, Nevada, USA. Several equipment work site grounding configurations were constructed with personal protective ground cables connected to a 16.5 kV, 115 MVA generator bus. The bus was faulted, causing high current to flow in the ground cables at the work site. Instrumentation recorded selected worker contact voltages and body currents during the faults. Measured ground cable fault voltage drop is examined and shown to contain both resistive and reactive voltage drop components, with the reactance component becoming significant at high current. An approach for the prediction of ground cable composite fault voltage drop, worker exposure voltage and the dependence of both upon work site grounding geometry is provided.