Abstract:
Transformer is a cornerstone of electrical power systems, and the most problems occur in
it is related to the defects and weakness of the insulation systems. This study aims to
contribute to the understanding of the electric field in influencing the breakdown
mechanisms of insulating oil in transformers. It investigates the impact of field non uniformity on breakdown voltage, partial discharge in mineral oil (MO) under AC voltage
by considering three different electrode configurations: 1) plane-plane (P-P), 2) needle needle (N-N), and 3) plane-needle(P-N). In addition, Fourier Transform Infrared (FTIR)
spectroscopy is employed to analyze the chemical changes in tested MO samples after
exposure to the applied AC voltage under above mentioned three configurations. Also,
Weibull statistical analysis is conducted to confirm breakdown voltage conformity across
AC setup at a 1.5mm gap in which plane-plane and needle-needle (tip radius= 0.5µm)
configurations are identified as quasi-uniform fields with higher AC breakdown voltage
(AC-BDV) compared to the plane-needle geometry. Therefore, plane-needle configuration
created the highly non-uniform electric field, thereby diminishing the dielectric strength of
the tested oil. The impact of electrode configuration on field uniformity is further
highlighted by partially resolved partial discharge (PRPD) patterns. Partial discharge
analysis primarily examines variations in charge intensity along the edges of plane
electrodes and the sharpness of needle tips. Surprisingly, the analysis reveals that the plane plane configuration setup exhibits the highest partial discharge charge intensity compared
to other configurations. The FTIR analysis of the tested oil confirms changes in chemical
composition and the degradation of MO samples following exposure to the applied AC
voltage under 1,2 and 3 electrode configurations. The chemical degradation of the mineral
oil tested through FTIR notices the higher chemical deterioration and furan formation in
the plane-plane configuration while almost similar trend is noticed for needle-plane and
needle-needle configurations.
