The use of coal ash and plaster waste to improve grounding system

The main safety element to prevent operational failures in High Voltage Substations (HVS) is the grounding system (GS) consisting to conduct unwanted lightning strikes (failures) to the ground. When it is desired to build a GS on sandy soils (low electrical conductivity) it is necessary to add a product to the soil to adjust its electrical conductivity to safe levels, avoiding the burning of HVS’s equipment. There are some commercial products that can be dosed into the ground to increase its electrical conductivity prior installing GS. These products are made of non-renewable materials at relatively high cost. This study brings an innovation to conventional products. A new product (GRRA) is proposed, composed of two problematic residues from the industry: coal ash (CA) (fossil coal combustion) and plaster waste (PW) (construction and demolition). This novelty exposes a new alternative to dispose of these residues and a viable alternative to existing commercial products to improve the electrical conductivity of soils. First, a Mixture Design Methodology was used to estimate the CA and PW amount that should be added to the soil to achieve an acceptable electrical conductivity. Then, experimental tests were performed with the optimized mixture to determine its technical viability. Finally, a comparison of mixture was made, in terms of experimental results, with the products already available on the market. The optimum mixture mass composition was set in 70% coal ash, 15% sandy soil and 15% plaster waste. This mixture increased the soil electrical conductivity from 0.065 μS.cm-1 to 2792 μS.cm-1. The comparative study demonstrated the potential of replacing existing commercial products with the developed solution. [Display omitted] •The potential of using coal ash and plaster residues in grounding systems was investigated.•Mixture design was used to optimize mixing.•Mineral ash increased the electrical conductivity of the soil significantly.•The coal ash did not cause corrosion of the grounding system.