Journal of Engineering Science and Technology Vol. 10, No. 6 (2015) 811 - 826 © School of Engineering, Taylor’s University 811 BEHAVIOUR OF BACKFILL MATERIALS FOR ELECTRICAL GROUNDING SYSTEMS UNDER HIGH VOLTAGE CONDITIONS S. C. LIM 1, *, C. GOMES 2 , M. Z. A. A. KADIR 2 , G. NOURIRAD 2 , Z. A. MALEK 3 1 School of Engineering, Taylor’s University, Taylor's Lakeside Campus, No. 1 Jalan Taylor's, 47500, Subang Jaya, Selangor DE, Malaysia 2 Center of Excellence on Lightning Protection (CELP) Department of Electrical and Electronics Engineering, Universiti Putra Malaysia 3 Institute of High Voltage & High Current (IVAT), UTM, Malaysia *Corresponding Author: ChunLim.Siow@taylors.edu.my Abstract Backfill materials like Bentonite and cement are effective in lowering grounding resistance of electrodes for a considerable period. During lightning, switching impulses and earth fault occurrences in medium and high voltage networks, the grounding system needs to handle extremely high currents either for a short duration or prolonged period respectively. This paper investigates the behaviour of bentonite, cement and sand under impulse and alternating high voltage (50Hz) conditions. Fulguritic-formation was observed in all materials under alternating high voltage. The findings reveal that performance of grounding systems under high voltage conditions may significantly change from the outcomes anticipated at design stage. Keywords: Grounding, Backfill materials, Bentonite, High voltage experiment, resistance, Fulgurites. 1. Introduction Backfill materials have extensive application in the field of construction as well as electrical grounding. In the former, backfill materials are mostly used in filling remaining voids after any excavation or construction work whereas in the latter it is used especially when the soil resistivity of the area where grounding systems are installed is extremely high. The main purpose of introducing backfill materials into the intended soil for the two aforementioned cases is different. In the former it is to maximise soil compaction, thus backfill materials serve to address