This part of NRS 039 covers the selection and application of gapless metal-oxide surge arresters for use in medium-voltage distribution systems to protect electrical equipment connected to these systems. The choice of the arrester and its application depend upon the Basic Insulation Level (BIL) of the system, and the equipment that is to be protected.
NOTE 1 The selection of protection methods against overvoltages is based upon economics, taking into account the assessed probability of an overvoltage exceeding withstand capacities and the effects of a disruptive flashover.
NOTE 2 The positioning of surge arresters on the low-voltage side of transformers is also recommended under certain conditions.
NOTE 3 A medium-voltage distribution system is considered to be a system that has a nominal voltage that exceeds 1 kV but does not exceed 44 kV.
NRS 039-1-1999 history
2008NRS 039-1-2008 Surge arresters for use in distribution systems Part 1: Guide for the application of gapless metal-oxide surge arresters
1999NRS 039-1-1999 Surge arresters for use in distribution systems Part 1: Guide for the application of gapless metal-oxide surge arresters