OHL Work Safety. Use of EMT to Design the Protocol for Setting Up Temporary Grounding Protection

This paper explains how a maintenance safety protocol was designed for a double-circuit overhead line section equipped with a New-Concept Overhead Line tower (NCLA) on a double circuit 400 kV OHL in France. Operators work in a safe zone by installing a Temporary

Protection Ground (TPG) and, when required, Equipotential Bonding (EB). The protocol addresses one key constraint: limiting the current that could transfer through the worker during a remote lightning strike.

Because of the NCLA tower geometry, the dedicated TPG can be longer than on conventional towers, yet it must remain easy to handle and install. Its design is checked against three requirements: withstand short-circuit stresses, remain light enough for handling, and minimize the risk of heart fibrillation for an operator working in the Work Zone during distant lightning.

The article focuses on verifying this last requirement.

The method relies on EMT simulations that represent the line, towers, terminations, bonding paths, and the operator. For each configuration, the analysis evaluates the current that could flow through the operator, quantifies the risk with the corresponding specific energy and compares it with the thresholds depicted in the IEC 60479-2 standard. To turn modelling into practical rules, the study examines 6 scenarios: whether a bonding path exists in parallel to the operator, alternative TPG connection layouts, lightning location relative to the Work Zone, the value of adding a conventional TPG on neighboring lattice towers, the role of the shield wire, and the influence of lightning current magnitude.

The study confirms that a dedicated NCLA TPG can be used under remote-lightning conditions without installing additional TPG on the towers framing the Work Zone, provided that reliable electrical contact is ensured between the work ladders and the phase conductors.