The reactor of the series resonant frequency conversion test device and the reactance of the test object cancel each other out



The series resonant frequency conversion test device (often referred to as series resonance, frequency conversion resonance, or AC withstand voltage test device) is a "heavyweight" test equipment used in the power system for insulation performance testing of high-voltage electrical equipment. It is specifically designed to solve the problem that traditional test equipment is bulky and requires excessive power supply capacity when conducting AC withstand voltage tests on large-capacity, high-voltage capacitive test objects (such as long cables and large transformers) on site.

⚡ Core Working Principle

The series resonant frequency conversion device cleverly utilizes the principle of series resonance (LC resonance) in physics. Its core working process is as follows:

Frequency conversion power supply excitation: The device first converts the power frequency (50Hz) AC power into a sinusoidal wave output with adjustable frequency and voltage (typically between 30Hz and 300Hz).

Finding the resonance point: By adjusting the output frequency of the frequency conversion power supply, the high-voltage reactor (inductance L) in the circuit and the test object (capacitance C) undergo series resonance. When the frequency satisfies the formula f = 1/(2π√LC), the circuit reaches a resonant state.

Voltage multiplication output: In the resonant state, the reactance of the reactor and the test object cancel each other out, leaving only a small resistance in the circuit, thereby generating a large current. This strong current induces the required high voltage on the test object.

Quality factor (Q value) effect: The ratio of output voltage to input voltage is called the quality factor (Q value), and the Q value of high-quality equipment is usually between 30 and 80. This means that if 1000V is input, a high voltage of 30000V to 80000V can be obtained on the test object, greatly reducing the requirement for on-site power supply capacity.