Use of a global earthing system to implement the safety requirements for protecting against indirect contacts in HV systems

The Belgian legislation on protection against indirect contacts in HV was introduced in 1983. These regulations are aimed at preventing accidents due to dangerous step voltages or touch voltages and the spread of high potential to areas with low potential and vice-versa. The safety philosophy was based on setting up a high-quality local earthing system, with active protection by interruption of the supply, completed, if necessary, with other passive safety measures. However, protection based solely on a local earthing system is not realistic. Various studies carried out in the period 1983-1990 demonstrated that the solution to the problem was present in the network itself. By making interconnections between a multitude of local earthing systems with protective conductors (which themselves frequently have an earthing effect, e.g. lead sheaths of paper/lead cables), a "global earthing system" is achieved. These studies show that such a system is capable of keeping touch voltages at a secure level. Document HD "Power installations exceeding AC 1 kV (DC 1.5 kV)" was drawn up by CENELEC Technical Committee 99X. Chapter 9, Earthing Systems, deals extensively with the problem of earthing systems, and thus also with protection against indirect contact in HV. At the international level, this document represented the first occasion that the principle of a global earthing system was treated in a normative document. Belgium has now completed the task of putting all these considerations into practice