Example of capacity selection calculation method for high voltage test transformer. High voltage test transformer is suitable for insulation strength tests under power frequency or DC high voltage on various high-voltage electrical equipment, electrical components, and insulating materials in power systems, industrial and mining enterprises, scientific research departments, etc. It is an essential important equipment in high voltage tests.

  1) Voltage: According to 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 test 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 test object, i.e., In>Is. The current required by the test 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 current and rated voltage output by the test transformer, the capacity of the test transformer can be determined, i.e., P=UnIn.

  According to the ministry-issued 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, refer to the ministry-issued standards to select the required high voltage test transformer. 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.

  Example 1: For a distribution transformer with a voltage level of 10kV and a capacity of 1000kVA, and the test objects are basically at the 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 for 10kV insulators and high-voltage switchgear (test voltage of 42kV) and DC tests for 10kV cables (DC voltage of 60kV, corresponding AC voltage of 42.83kV).

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

  Example 2: 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 capacitive current of the above test objects. Experience suggests that the capacity of the high voltage test transformer is 5‰ of the capacity of the test object (power transformer).