Fundamental Theory of Dielectric Breakdown Mechanisms in Eco-Friendly Transformer Insulation Fluids Under Nigerian Tropical Service Conditions

This research investigates the fundamental mechanisms of dielectric breakdown in biodegradable and eco-friendly transformer insulation fluids under the thermal, humidity, and contamination stresses characteristic of Nigerian tropical service conditions, making original theoretical and experimental contributions to the science of green insulating fluids for power transformer applications. The replacement of conventional mineral oil with natural and synthetic ester fluids in transformer insulation systems offers significant environmental and fire safety advantages and is gaining traction in Nigerian distribution transformer procurement, yet the dielectric breakdown mechanisms of these fluids under Nigerian tropical conditions remain insufficiently understood to support confident application in the Nigerian grid. The research employs a multi-scale theoretical approach combining molecular dynamics simulation to characterise breakdown initiation at the molecular level, finite element modelling of streamer propagation in curved electrode geometries representative of transformer winding insulation systems, and extensive experimental characterisation using IEC 60156 sphere-sphere gap breakdown testing, time-to-breakdown under ramp voltage, and partial discharge inception voltage measurement. Three fluids are investigated: conventional mineral oil, natural ester (rapeseed oil-based), and synthetic ester, both in new condition and after controlled accelerated ageing at 90 and 110 degrees Celsius simulating Nigerian service temperatures. Original theoretical contributions include a modified electron avalanche breakdown model that incorporates the higher viscosity and moisture absorption characteristics of ester fluids, explaining their experimentally observed higher AC breakdown strength but lower impulse breakdown strength relative to mineral oil. Keywords: dielectric breakdown, eco-friendly insulation, transformer fluid, tropical conditions, Nigeria.