Footing Resistance Design for Reliable OHL Lightning and Fault Protection

Medium-voltage (MV) overhead lines supplying critical industrial loads are increasingly exposed to lightning-induced overvoltages, switching transients, and adverse environmental conditions. Although overhead ground wires, surge arresters, and conventional protection schemes are widely applied, repeated failures continue to occur in practice, often despite correct insulation coordination and relay operation. Post-event investigations frequently identify inadequate grounding performance, particularly excessive structure footing resistance, as a dominant contributor. Existing standards recognize the importance of grounding for lightning performance but treat footing resistance primarily as a prescriptive constraint rather than a performance-based design variable . This paper presents a structured methodology for selecting optimal footing resistance values for MV overhead line applications. The approach integrates insulation withstand levels and critical flashover voltages (CFOs), site-specific lightning exposure and shielding failure probabilities, surge arrester characteristics and protection coordination, and soil resistivity-based grounding system design. Probabilistic lightning performance assessment is combined with deterministic electromagnetic transient (EMT) simulations using PSCAD/EMTDC and ATP-EMTP to quantify the influence of footing resistance on flashover risk, surge voltage levels, and transient current return paths. An industrial case study demonstrates how elevated footing resistance and unfavorable grounding topology led to repeated faults, cumulative equipment stress, and initial misdiagnosis on a 34.5 kV feeder, despite the presence of overhead ground wires and correctly operating protection systems. The results show that treating footing resistance as a primary design parameter, rather than a post-construction compliance check, can prevent misdiagnosis, reduce downtime, and significantly improve lightning resilience. While assumptions related to soil modeling accuracy and data availability are acknowledged, the methodology is applicable to MV distribution systems and can be extended to other voltage levels with appropriate adaptation.