When choosing a test transformer, the main points are considered:

(1) Voltage. According to the requirements of the test sample, the test transformer with the appropriate voltage is first selected, so that the rated voltage Un of the high voltage side of the test transformer is higher than the test voltage Us of the test object, that is, Un>Us. Secondly, check the low-voltage side voltage required for the test transformer to match the field supply voltage and voltage regulator.

(2) Current. The rated output current In of the test transformer should be greater than the current Is required by the test object, ie, In>Is. The current required for the test object can be estimated by its capacitance, Is = Us w Cx, where Cx includes the sample capacitance and the additional capacitance.

(3) Capacity. According to the rated current and rated voltage of the test transformer output, the capacity of the test transformer can be determined, that is, P=UnIn.