Effect of micro-nano additives on breakdown, surface tracking and mechanical performance of ethylene propylene diene monomer for high voltage insulation

Ethylene propylene diene monomer (EPDM) is a polymer widely used for insulation in high voltage outdoor insulators and cables. It is well accepted that appropriate addition of micron particles to form a composite can enhance its insulation performance. This work reports improvement on the dielectric breakdown strength, tracking failure time, mechanical properties and volume resistivity of EPDM composites co-filled with boron nitride (BN) micron and nano–particles. Test specimens were fabricated by melt-blending and hot press techniques. AC breakdown tests were performed as per IEC60243-1 Standard. The tracking test was performed following IEC 60587 Standard and volume resistivity measurement as per ASTM D257. Experimental results show improvement in electrical properties with increasing particle loading up to a certain dosage but enhancement in the mechanical properties is observed up to 30 wt% particles addition. The co-filled composite exhibits considerably higher dielectric breakdown strength (89.24 kV/mm) and volume resistivity (~ 5.0 × 10¹⁵ Ω cm) relative to Micro-20 wt%. The tracking failure time of the co-filled is much improved due to excellent resistance against dry band arcing and thermal accumulation in the discharge region. Moreover, co-filled composites show improvement in mechanical properties as compared to the micron–filled counterparts. The improved thermal conductivity, better thermal stability and overall higher surface area of the particles are possible factors which impart better performance to the co-filled composites.