Abstract: This paper presents a ‌partial discharge case‌ in a 10 kV switchgear at a 110 kV substation. Through comprehensive diagnostics employing ‌ultrasonic, transient earth voltage, ultra-high frequency, and acoustic imaging techniques‌, surface discharge defects were preliminarily identified near the ‌bushing wall penetrator‌ on phase B of the #1 main transformer's 10 kV switchgear. Subsequent disassembly of the busbar and bushing revealed ‌significant contamination deposits‌ and ‌observable discharge traces‌ on the busbar surface at the penetrator. The defects were successfully eliminated after treatment, thereby preventing a ‌forced outage event‌.