Hazard Assessment of Transient Step and Touch Potentials Caused by Shunt Capacitor Switching

Shunt capacitor switching can inject high magnitude, high frequency current transients into the substation ground grid. These current transients produce step and touch potentials that can affect personnel safety. In order to assess the hazards of such switching, measurements of transient step and touch potentials caused by shunt capacitor switching were made at BPA's 500-kV Ostrander Substation near Oregon City, Oregon. The testing was focused on whether or not it is safe for personnel to work on a de-energized group while an adjacent group is being switched. The presence of three grounded-wye, 388 MVAr shunt capacitor groups at this station allowed switching of a single capacitor group as well as back-to-back switching involving two capacitor groups. Measurements included high speed digital records of step potentials, touch potentials, potentials induced on control cables, and potentials with respect to remote earth. The data was analyzed to determine the influence of current limiting reactors, synchronous controlled closing, and peninsula grounding by E. J. Rogers et al. (1974) during shunt capacitor switching.