Investigation of insulating properties of crushed-stone on the conditions it should perform as a security element in electrical systems

Abstract

The authors investigate the effective insulating properties of the types of crushed stones usually employed in Brazilian substations in the frequency range of the most important occurrences at electric power systems (from normal conditions to transients associated with atmospheric discharges). The measurements consider several humidities of the material. The influence of impregnating water resistivity is evaluated in the range of values actually found for rain water. In the frequency range investigated, only the values found for the condition of entire immersion of the material into water presented values of resistivity lower than 3000 Omega -m, which is generally adopted by the Brazilian utility companies in their projects.<>