Medium-frequency transformers (MFTs) utilized in SSTs typically face mixed-frequency stresses, which is a superimposed electric stress of two different frequencies. Although it is a new concern for MFTs’ insulation design, the test environment for them has been limited. This paper aims to fill this gap by proposing a test setup dedicated to mixed-frequency stresses. A battery-powered square-wave source is developed to be connected in series with an existing insulation test setup to emulate the stress, achieving a wide test condition including the dv/dt. The details of the design are given, and the key operation is verified in the experiment.
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