What is the function of oil in transformer electrical performance?

Oil improves electrical performance by increasing dielectric strength, reducing electric field intensity in critical gaps, and suppressing partial discharge by filling voids. It also stabilizes insulation temperature, which strongly affects dielectric properties and aging rate. By keeping cellulose insulation drier and cooler, oil supports higher reliability and better withstand capability under transients. Oil also provides a medium for diagnostic gases, enabling DGA to detect electrical stress and overheating issues early, which supports proactive maintenance and reduced outage risk.