There have always been pains and difficulties in the field of power transmission and transformation: failures still occur after passing the routine pre-test of MOAs, resulting in forced outages, and the low detection rate of latent faults has caused heavy losses. What is more difficult is that most of the MOAs are severely damaged after accidents, and it is difficult to study them. The reason is used to optimize the full life cycle management of MOA. This article describes a case in which partial discharge defects were detected in an MOA that passed the conventional test by HFCT partial discharge detection technology, proving the necessity of increasing the detection dimension of MOA technology. This study can reduce the forced outage rate of MOA, and provides a very valuable reference and guidance for MOA condition maintenance.