What are the different types of Resonant system with Variable Frequency

　　What are the different types of Resonant system with Variable Frequency? 　　1)For XLPE cross-linked high-voltage cables and GIS AC withstand voltage,the IEC standard specifies that non-power frequency withstand voltage can be used,with a frequency range of 20Hz to 300Hz.There are also relevant test standards in China,with a general frequency range between 30Hz and 300Hz.Therefore,for the AC withstand voltage test of these devices,variable frequency series resonant test equipment can be used.Variable frequency series resonant test equipment generally consists of the following main parts:variable frequency power supply(used to generate the non-power frequency power required for the test),excitation transformer,reactor(divided into fixed and adjustable types),and capacitive voltage divider(used to test the test voltage).According to the tuning method,it can be further divided into frequency tuning,inductance tuning,and frequency-inductance tuning.

　　2)For the AC withstand voltage of the stator of a generator,due to the relatively weak insulation of the stator winding insulation,if a too high frequency is used for the AC withstand voltage test,the insulation of the winding is easily damaged due to the polarization and heating caused by the high frequency.If a low frequency is used for the test,it cannot reflect the normal working state of the stator,and good test results cannot be obtained.Therefore,for the withstand voltage test of the generator stator,the power frequency is generally used.The definition of power frequency in relevant domestic standards is generally 45Hz to 55Hz.The tuning methods of the power frequency series resonant withstand voltage equipment theoretically consist of inductance tuning and capacitance tuning.Inductance tuning usually adjusts the iron core air gap of the adjustable reactor to smoothly adjust the inductive reactance value continuously,which is more convenient to operate.Capacitance tuning not only requires bulky capacitors,but the capacitance cannot be continuously adjusted,so it is not very suitable for on-site operation.Therefore,the tuning is generally carried out by adjusting the inductance,hence it is also called power frequency series resonant inductance tuning.