When selecting the test transformer, the following points shall be considered:
(1) Voltage: according to the requirements of the test object, first select the test transformer with appropriate voltage, so that the rated voltage Un at 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 whether the low-voltage side voltage required by the test transformer can match the on-site power supply voltage and voltage regulator.
(2) Current: The rated output current In of the test transformer shall be greater than the current Is required by the tested object, that is, In>Is. The current required by the test object can be estimated according to its capacitance, Is=Us w Cx, where Cx includes the test object capacitance and additional capacitance.
(3) Capacity: According to the rated current and rated voltage output by the test transformer, the capacity of the test transformer can be determined, that is, P=UnIn.
According to the ministerial standards, the voltage levels of test transformers in China are: 5, 10, 25, 35, 50, 100, 150, 300 kV, etc; The capacity levels are: 3, 5, 10, 25, 50, 100, 150, 200kVA, etc.
According to the calculation results and the ministerial standards, the required test transformer can be selected. If there are special requirements, test transformers with special specifications can generally be ordered from the manufacturer.