By hvhipot 
HV Hipot Electric Co., Ltd. specializes in producing series resonance (also known as series resonance withstand voltage equipment). Next, we will share with you the voltage relationship during series resonance.
Voltage relationship during series resonance:
The voltages of each component during resonance are URO = RI O = US ULO = jω0LIO = jω0L U s R = jQUs UCO = j 1 ω0C o =− j 1 ω0C US R =− jQUS During resonance, the effective values of the inductor voltage and capacitor voltage are equal, both being Q times the applied voltage. However, the inductor voltage leads the applied voltage by 90 ° and the capacitor voltage lags behind it by 90 °, resulting in a total reactive voltage of 0. When the Q value of the circuit is high, the values of the inductor voltage and capacitor voltage will be much greater than the value of the applied voltage, so series resonance is also known as voltage resonance. Common test samples such as transformers, GIS systems, SF6 circuit breakers, current transformers, power cables, bushings, etc. are capacitive, while the reactors equipped in the system are inductive. During the test, the output frequency of the variable frequency power supply is first adjusted to cause series resonance in the circuit, and then the output voltage of the variable frequency power supply is adjusted under the condition of circuit resonance to achieve the test value of the sample voltage.
Due to the resonance of the circuit, a smaller output voltage of the variable frequency power supply can generate a higher test voltage on the test sample. In practical field applications, the high voltage and low voltage on the test sample follow the following formula: U test=QU excitation, where U test is the high voltage resonance test voltage, Q is the quality factor of the system series resonance, and U excitation is the output voltage of the excitation transformer. For example, assuming the quality factor Q of the system series resonance is 30, the excitation transformer selects a 16kV tap, and the rated input voltage of the excitation transformer is 400V. If the input voltage of the excitation transformer is 100V, the calculation steps for high voltage are as follows:
① Calculate the transformation ratio of the excitation transformer. The transformation ratio of the excitation transformer is N=the selected tap voltage of the excitation transformer/the rated input voltage, which is N=16kV/400V=16000/400=40
② Calculate the output voltage of the excitation transformer. The output voltage of the excitation transformer is equal to the input voltage of the excitation transformer multiplied by the transformation ratio of the excitation transformer, that is, U excitation=100V * 40=4kV
③ Calculate the high voltage resonance test voltage. The high voltage resonance test voltage is equal to the output voltage of the excitation transformer multiplied by the system quality factor, that is, U test=4kV * 30=120kV. Therefore, the final high voltage resonance test voltage of the system is 120kV.