The variable frequency series resonance test device operates on the principle of series resonance, using an excitation transformer to excite the series resonance circuit, adjusting the output frequency of the variable frequency controller so that the circuit inductance L and the test product C resonate in series, and the resonance voltage is the voltage applied to the test product. The variable frequency resonance test device is widely used in industries such as electric power, metallurgy, petroleum, and chemical engineering, and is suitable for large-capacity, high-voltage capacitive test products. The series resonance withstand voltage device mainly consists of a variable frequency controller, an excitation transformer, a high-voltage reactor, and a high-voltage voltage divider. The variable frequency controllers are divided into two major categories: those with 20KW and above are console type, and those below 20KW are portable box type; it is composed of a controller and a filter. The main function of the variable frequency controller is to convert the 380V or 200V power frequency sinusoidal AC power with fixed amplitude and frequency into a sinusoidal wave with adjustable amplitude and frequency, and provide power for the entire set of equipment.