The working principle of the variable-frequency series resonance test device

The variable frequency series resonance test device is a high-precision detection equipment widely used in the insulation testing of power equipment. It generates high voltage through a resonant circuit composed of inductors, capacitors and resistors at a specific frequency, thereby conducting withstand voltage tests and local discharge detection on power equipment. Due to its advantages such as high testing efficiency, low energy consumption and minimal damage to the test samples, this device has become an important equipment in the high-voltage testing field.
The core working principle of the variable-frequency series resonance test device is based on the characteristics of the resonant circuit. When the frequency of the AC power supply is the same as the inherent frequency of the LC circuit, the circuit undergoes series resonance. At this time, the circuit impedance is the smallest and the current is relatively large, thereby generating the required high voltage on the test sample. The device adjusts the output frequency through the variable-frequency power supply to match the inherent frequency of the circuit, achieving the resonant state. Near the resonant point, even if the input voltage is low, a voltage several times higher than the input can be obtained on the test sample. This is precisely the key to the device’s ability to efficiently generate high voltage.
This device is mainly composed of a variable frequency power supply, an excitation transformer, a resonant reactor, a voltage divider, and a control system. The variable frequency power supply is responsible for generating adjustable-frequency alternating current; the excitation transformer raises the power supply voltage to an appropriate level; the resonant reactor and the test specimen capacitor form a resonant circuit; the voltage divider is used to measure the output voltage; the control system realizes automatic frequency tracking and protection functions. The various components work together to ensure the safety and reliability of the test process.
The working process of the variable frequency series resonance test device can be divided into four stages: Firstly, the parameter setting stage, where the resonant frequency and the parameters of the reactor are determined based on the capacitance of the test sample and the required test voltage; Secondly, the frequency scanning stage, in which the output frequency of the variable frequency power supply changes from low to high to find the resonance point; Then, the voltage stabilization control stage, where the power supply output is adjusted under the resonant state to stabilize the voltage of the test sample at the set value; Finally, the test completion stage, where the voltage is gradually reduced and the test data is recorded. The entire process is automatically completed by the intelligent control system, which is simple to operate and highly accurate.
Compared with traditional power frequency withstand voltage test equipment, the variable frequency series resonance test device has significant advantages. Its output voltage waveform is close to a sine wave, which is more in line with the actual operating conditions; because it operates in a resonant state, the required power supply capacity is only 1/Q of the test sample capacity (Q is the quality factor), significantly reducing energy consumption; at the same time, the device is small in size and light in weight, making it convenient for on-site use. These features make it particularly suitable for on-site tests of capacitive test samples such as large power transformers, GIS equipment, and cables.
In practical applications, the selection of several key parameters for the variable frequency series resonance test device requires special attention. The test frequency is usually within the range of 30-300Hz. An excessively high frequency may lead to an increase in dielectric loss, while a too low frequency will affect the test efficiency. The selection of the quality factor Q should take into account both voltage gain and bandwidth, typically ranging from 20 to 80. The adjustment of the output voltage should be smooth and slow to avoid causing impact on the test sample. Additionally, the device should have complete protection functions, such as overvoltage, overcurrent, and flashover protection, to ensure the safety of the test.
As power equipment continues to evolve towards higher voltages and larger capacities, the technology of variable frequency series resonance test devices is also constantly innovating. Modern devices generally adopt digital control technology, enabling functions such as automatic frequency tracking, automatic parameter matching, and automatic data recording; some high-end products even integrate a partial discharge detection system, capable of simultaneously conducting withstand voltage tests and partial discharge detection; the application of wireless transmission technology makes remote monitoring and operation possible. These technological advancements have significantly enhanced the testing capabilities and ease of use of the devices.
The variable-frequency series resonance test device plays an irreplaceable role in the preventive tests of the power system. By conducting regular withstand voltage tests on power equipment, insulation hazards can be promptly identified and accidents prevented. This device is not only applicable to the factory tests of new equipment but is also widely used in the preventive maintenance of operating equipment. With the advancement of smart grid construction, the requirements for power equipment condition monitoring are becoming increasingly higher, and the application prospects of the variable-frequency series resonance test device will be even broader.
When using the variable frequency series resonance test device, strict adherence to the operating procedures is mandatory. Before the test, carefully inspect the wiring to ensure that all components are connected correctly; during the test, closely monitor parameters such as voltage and current, and stop immediately if any abnormalities are detected; after the test, fully discharge the equipment to ensure safety. At the same time, operators should receive professional training to familiarize themselves with the device’s principles and operation procedures, and possess the ability to handle emergencies. Only by following the procedures can the device’s performance be fully utilized and ensure the reliability of the test results.
The variable-frequency series resonance test device represents the development direction of high-voltage testing technology. Its working mode based on the resonance principle not only improves the testing efficiency but also reduces the potential damage to the test sample. With the application of new materials and new technologies, the future devices will develop in the direction of higher precision, greater intelligence, and greater portability, providing more reliable guarantees for the safe operation of power equipment.