Step and Touch Potentials at Faulted Transmission Towers

The paper contains measurements and analyses of earth potential profiles at American Electric Power (AEP) 765 kV transmission towers and at an Ontario Hydro (OH) 500 kV test tower during staged fault tests. Measurements of the step and touch potentials for various tower grounding schemes are shown. The effectiveness of a special ground potential control (GPC) ring installed as part of the tower grounding to reduce step and touch potentials is demonstrated by measurements and supported by computer studies. The step and touch potentials are examined analytically for various GPC ring design parameters and for several two-layer soils.