With the increase of type test items for high-voltage switchgears

the operating conditions of power frequency test transformer become more complicated

and the requirements for its insulation performance become more stringent. In order to keep the power frequency test transformer in safe operating conditions and take reliable protective measures

clear judgments on the operating conditions should be made. In this paper

the steady state voltage and transient overvoltage stressed on power frequency test transformer and the protective measures used in power frequency withstand voltage test

combined voltage test and disconnector switching lower capacitive current test are introduced

and suggestions for researches on measurement and simulation of VFTO at the entrance of power frequency test transformer and on using ferromagnetic rings to suppressing VFTO are given. This paper provides with some reference values for power frequency test transformer design

selection

test standard revision and the lifetime study.