By hvhipot 
Application and Advantages of Frequency Conversion Resonance
The frequency conversion resonance test is mainly used for on-site AC dielectric testing of large capacity electrical equipment, including medium and low voltage, high voltage, and ultra-high voltage GIS、 Motor stator, large transformer, capacitor, etc.
For the above electrical equipment, it is best to use power frequency for AC dielectric testing. However, the capacitance of the test object is relatively large, and the power required by the testing equipment is also high, making it impossible to conduct on-site testing. The series resonance test of variable inductance is only used for the dielectric performance test of the generator stator. In the 1970s, foreign power departments discovered that DC insulation testing was ineffective and dangerous for rubber and plastic insulation. Practice and research have shown that DC dielectric tests cannot effectively detect mechanical damage and other defects inside cable accessories under AC voltage. The ultra-low frequency (0.1Hz) AC test method is used, and although the equipment is small in size, it has limitations. Firstly, the current frequency and output waveform of 0.1Hz generated by the semi electronic and semi mechanical modes cannot achieve a sine wave with good equivalence; Secondly, the testing time requirement is 1 hHV Hipot Electric Co., Ltd., which results in low work efficiency; Meanwhile, the ultra-low (0.1Hz) dielectric test is only applicable to cables and cannot meet the requirements of the main insulation test for ultra-high voltage cables.
Composition of Series Variable Frequency Resonant System
The series variable frequency resonant system is achieved by changing the system inductance and test frequency to put the circuit in a resonant state. By adopting frequency conversion resonance technology, the power capacity and equipment weight are reduced, making it easier for on-site testing.
(1) Variable frequency power supply: adjustable frequency of 30~300Hz, 5, 10, 20, 50kVA.
(2) Excitation transformer: used to provide energy for inductive and capacitive resonance systems; Its characteristic is that the transformer core can be applied to a wide frequency voltage response. There are specifications such as 5, 10, 20, 50kVA, etc.
(3) Resonant reactor: Used for capacitor resonance of the same test object to obtain high voltage (or high current) reactors. The specifications are 30H/20kV/2A and 40H/40kV/3A. The number of reactors can be configured according to actual needs (from 1 to 3).
(4) Capacitive voltage divider: used to accurately measure the voltage applied to the terminals of the test object.
(5) Compensation capacitance: Due to the very small capacitance of large transformers and motors, it is necessary to increase the capacitance through compensation to ensure that the resonant frequency is within the range. However, cable testing is not necessary.