When selecting a high-voltage test transformer, the following points should be mainly considered:

　　1) Voltage: Based on the requirements of the test object, first select a high-voltage test transformer with appropriate voltage, so that the rated voltage Un on the high-voltage side of the test transformer is higher than the test voltage Us of the tested object, i.e., Un>Us. Secondly, check whether the low-voltage side voltage required by the test transformer can match the on-site power supply voltage and the voltage regulator.

　　2) Current: The rated output current In of the high-voltage test transformer should be greater than the current Is required by the tested object, i.e., In>Is. The current required by the tested object can be estimated based on its capacitance, Is=Us w 

Cx, where Cx includes the capacitance of the test object and additional capacitance.

　　3) Capacity: Based on the rated output current and rated voltage of the test transformer, the capacity of the test transformer can be determined, i.e., P=UnIn.

　　According to the ministry standards, the voltage levels of test transformers in China include: 5, 10, 25, 35, 50, 100, 150, 300kV, etc.; capacity levels include: 3, 5, 10, 25, 50, 100, 150, 200kVA, etc.

　　Based on the calculation results, the required high-voltage test transformer can be selected by referring to the ministry standards. If there are special requirements, you can order test transformers with special specifications from the Sales Department of Wuhan Wugao Electric Testing Equipment Co., Ltd.

　　For example: For a distribution transformer with a voltage level of 10kV and a capacity of 1000kVA, and the test objects are basically of 10kV voltage level, a 50kV, 5kVA high-voltage test transformer can be selected, because the factory test voltage of a 10kV, 1000kVA distribution transformer is 35kV, and the AC test voltage is 30kV; at the same time, it can meet the test requirements of 10kV insulators and high-voltage switchgear (test voltage of 42kV) and the DC test of 10kV cables (DC voltage of 60kV, corresponding AC voltage of 42.83kV).

　　In terms of test capacity, for a 10kV, 1000kVA tested high-voltage test transformer, the capacitive current during charging is about 80~110mA at 30~35kV test, because 35kV×110mA<5kVA, so 5kVA can meet the requirements.

    Another example: For a 35kV, 2000~4000kVA transformer, when the test voltage is 72~85kV, the capacitive current is about 150~260mA; for 6000~8000kVA, it is about 300~420mA; for 10000kVA, it is about 800~1000mA, etc. At this time, the capacity of the selected test transformer must be greater than the capacity corresponding to the above capacitive current of the test object. Experience suggests that the capacity of the high-voltage test transformer is 5‰ of the capacity of the tested object (power transformer).