Coordinated Surge Arrester Deployment and Tower Footing Resistance Reduction for Transmission Lines in High-Lightning-Density Corridors

In corridors with high lightning ground flash density and unfavorable soil resistivity, backflashover remains a dominant outage mechanism for overhead transmission lines below 500 kV. The conventional reflex is to push tower footing resistance as low as possible. Yet field experience and simulation studies increasingly show that resistance reduction alone is neither universally achievable nor always economically rational. A coordinated strategy—selective surge arrester deployment combined with targeted, rather than absolute, footing resistance reduction—offers a more defensible engineering and economic outcome.

The physical basis for coordination is straightforward

 Tower footing impedance controls the amplitude of the lightning overvoltage that appears across the insulator string during a backflashover event. Lower impedance directly reduces that overvoltage. However, in soils with resistivity in the thousands of ohm-meters, driving resistance below a conventional threshold such as 10 Ω may require extensive counterpoise networks, deep-driven rods, or soil treatment, with diminishing returns and escalating cost. Simulation work on high-resistivity towers indicates that combined reduction measures can bring footing resistance below 10 Ω and cut trip-out rates by more than 50%, confirming that reduction works—but also that the effort required is highly site-dependent.

This is where line surge arresters change the design logic

 A surge arrester installed in parallel with the insulator string presents near-open-circuit impedance under normal voltage but transitions to low impedance when the voltage exceeds its threshold, clamping the phase-to-structure overvoltage before flashover can develop. In effect, the arrester does not require the tower footing to be an excellent conductor; it interrupts the voltage buildup that would otherwise drive backflashover. Studies on 110 kV, 220 kV, and 500 kV lines show that installing arresters on the two outer phases raises the backflashover withstand level by 59.15%, 63.1%, and 95.8%, respectively. Notably, when the allowable footing resistance was relaxed from 20 Ω to 25 Ω, adding just one additional insulator disc restored the original withstand level—demonstrating that the grounding requirement can be traded against other coordinated measures.

The practical implication is a shift from “lowest achievable resistance at every tower” to differentiated treatment. Towers with footing resistance already below roughly 10–15 Ω and moderate lightning exposure may require no arrester, or only single-phase protection. Towers where resistance remains above 30–50 Ω despite feasible reduction efforts, or where historical stroke density is concentrated, become priority candidates for two- or three-phase arrester installation. IEEE-oriented placement examples suggest that when footing resistance exceeds approximately 50 Ω, three arresters per structure may be needed to achieve performance improvement beyond 80%; below that threshold, partial phase protection can be sufficient depending on local stroke density. This tiered logic avoids the two failure modes of over-spending on marginal resistance reduction and under-protecting towers that remain electrically weak.

For grounding itself, the objective should be an effective impulse impedance compatible with the arrester-assisted protection level, not an arbitrary low-frequency target. Counterpoise wires remain the most established measure for high-resistivity soils, and their length can be optimized in conjunction with arrester placement rather than extended indiscriminately. Where construction access is constrained, vertical composite grounding or flexible graphite-based conductors can improve impulse dispersion without large excavation footprints. The key is to treat the grounding electrode and the arrester as parts of a single voltage-management system: the arrester limits the voltage that the grounding system must tolerate, and the grounding system limits the energy stress and residual voltage that the arrester must handle.

A coordinated design therefore begins with tower-by-tower characterization—footing resistance, soil resistivity, span geometry, and historical stroke density—rather than uniform retrofitting. Arrester quantities and phase configurations are then assigned where the marginal reduction in flashover risk per unit cost is highest, while grounding investment is concentrated on towers where a modest reduction meaningfully improves the arrester’s operating margin. This approach does not reject grounding improvement; it disciplines it. In high-lightning corridors, the most resilient and cost-effective outcome is rarely the lowest possible resistance everywhere, but the right combination of resistance control and active overvoltage clamping at the towers that need it most.