In electrical substations, power/distribution transformers are pivotal components responsible for voltage regulation and power distribution. Despite their critical role, these transformers are vulnerable to various risks, notably partial discharge (PD), a phenomenon that predominantly affects oil-filled transformers. PD typically occurs within the interturn insulation and oil channels, leading to insulation degradation and potential transformer failure. This study introduces a predictive method for assessing PD occurrence by evaluating the peak electric field stress in high-voltage (HV) to high-voltage (HV) turn insulation and oil channels, quantified in V/mil, for a generic distribution oil-filled transformer. The methodology involves detailed analysis and measurement of the electric field stress within the transformer’s insulation system. Comparing these stress values against an internally developed partial discharge inception probability curve, one can estimate the likelihood of PD events. This comparative approach allows for the identification of critical stress points that are prone to PD, thereby facilitating early detection and intervention. The findings of this study aim to enhance the reliability and operational lifespan of power/distribution transformers by providing a robust predictive tool for PD. This early mitigation will help to prevent costly failures and ensure the continuous and efficient operation of electrical substations. Ultimately this approach will contribute to the development of more resilient power systems through improved transformer design for partial discharge.