Abstract: The problem that the contact of the handcart switch cabinet heats has long interfered with the safe and stable operation of the power grid.Due to the unqualified installation technology,the different professional quality of the operators and the poor design,the contact error between the dynamic and static contacts of the switch cabinet often exceeds the standard value.Poor contact between dynamic and static contacts leads to a gradual increase in contact resistance,which may eventually lead to a burnout due to heat,insulation breakdown and even tripping accidents.With a tripping fault of main transformer as an example,the causes and countermeasures of the fault are discussed.