I. Equipment Overview
The series resonance device is an important special power supply equipment in the modern high-voltage testing field. It utilizes the series resonance characteristics of the inductor and capacitor circuits, and can generate test voltages far higher than the power supply voltage with relatively smaller power supply capacity on the tested items. This device is mainly used for conducting AC withstand voltage tests on capacitive power equipment such as power cables, gas-insulated fully enclosed combined electrical equipment, generators, transformers, etc., and is the core tool for testing the insulation strength of power equipment.
Compared with traditional power frequency withstand voltage test equipment, the series resonance device has significant advantages in terms of volume, weight, power supply capacity requirements, and test safety. It has now been widely used in various high-voltage testing sites.
The working principle of the equipment is as follows: The variable frequency power supply adjusts the output frequency to gradually approach the inherent resonant frequency of the circuit; when the circuit reaches resonance, energy is efficiently exchanged between the reactor and the tested item, and the power supply only needs to supplement the active power loss of the resistance part in the circuit, significantly reducing the capacity requirement for the input power supply.
II. Core Components
A complete series resonance device consists of four core components, each with clear responsibilities and working together. The detailed introduction is as follows:
(1) Variable Frequency Power Supply
The variable frequency power supply is the core control component of the entire system. Its main function is to convert the power supply with power frequency into a sinusoidal wave power supply with adjustable frequency and voltage. Its conventional output frequency range is 20 to 300 hertz, and the frequency can be automatically or manually adjusted according to the capacitance parameters of the tested item, accurately tracking the resonant frequency of the circuit.
This component integrates multiple protective functions such as overcurrent, overvoltage, and overheating protection, and is equipped with a human-machine interface to facilitate operators to set the test parameters and monitor the test operation status in real time.
(2) Excitation Transformer
The excitation transformer is connected between the variable frequency power supply and the high-voltage circuit. It has two core functions: one is to boost the voltage, raising the output voltage of the variable frequency power supply to the required standard for the resonant circuit, providing excitation power for the resonant circuit; the other is to isolate, achieving electrical isolation between the high and low voltage sides to ensure the safety of the operators and measurement equipment during the test.
The excitation transformer does not need to bear the entire apparent power, only needs to supplement the active power loss of the circuit, so the equipment capacity is usually smaller and the structure is more streamlined.
(3) High-Voltage Reactor
The high-voltage reactor is the key inductive element of the resonant circuit, and can be combined with the capacitance of the tested item to form an LC series resonance structure. In practical applications, the device usually has multiple units of the same specification reactors, and can be flexibly used in series, parallel, or series-parallel combinations according to the voltage and capacitance parameters of the tested item.
The reactor adopts a core structure with air gaps, which can linearize the inductance and effectively avoid magnetic saturation problems, ensuring the stability of the test.
(4) Capacitive Voltage Divider
The capacitive voltage divider is connected in parallel to the tested item and is used to accurately measure the test voltage. The equipment consists of a high-voltage arm capacitor and a low-voltage arm capacitor, and the voltage division signal collected from the low-voltage arm can be directly transmitted to the measurement instrument or the variable frequency power supply control system to achieve voltage closed-loop regulation, while assisting in overvoltage protection.
III. Core Advantages of the Equipment
With its unique resonant boosting principle and modular structure, the series resonance device has extremely strong applicability in the field of high-voltage withstand voltage tests. The core advantages are as follows:
(1) Small size and light weight
This device eliminates the bulky voltage regulators and large power frequency transformers of traditional power frequency test equipment, relying on the resonant boosting principle to reduce the amount of ferromagnetic components. The overall weight is only one-fifth to one-tenth of that of traditional equipment, making it convenient to handle and suitable for outdoor, temporary construction site, and other working scenarios.
(2) Small power supply capacity requirement
When the circuit is in resonance, the input power supply only needs to supplement the active power loss, and the equipment capacity is only one-quarter of the apparent power of the tested item (Q is the quality factor). For example, when the quality factor Q is 50, a 15-kilowatt variable-frequency power supply can complete the cable withstand voltage test that a traditional equipment with a 750-kilowatt power capacity needs to carry out. This feature enables ordinary mains power to meet the large-scale high-voltage test requirements on site.
(3) Pure output waveform
The series resonant circuit has excellent filtering capabilities, which can effectively suppress harmonic interference. The output voltage waveform distortion rate of the device is less than 1%, and it is a standard sine wave. It can avoid problems such as false breakdown of the tested item and distorted test data caused by waveform distortion, ensuring the accuracy of the test.
(4) Essential safety in the test process
The device has inherent safety attributes. If the tested item undergoes breakdown discharge, the resonant condition will be instantly disrupted, the circuit will quickly lose resonance, the test voltage will automatically decay and disappear, and there will be no destructive overcurrent or overvoltage commonly seen in traditional equipment. It can protect the tested item intact, ensure the safety of test personnel and supporting equipment, and reduce test risks.
(5) Wide adaptability
The reactor is designed in a modular way, allowing for flexible adjustment of series and parallel combinations. Combined with the adjustable parameters of the variable-frequency power supply, it can be adapted to different voltage levels and different capacitance parameters of the tested items. It can complete rapid tests for short cables and also meet the withstand voltage testing requirements for long cables, large generators, and other large-capacity equipment.
Four. Main application scenarios
The series resonant device is widely used in power systems, electrical equipment manufacturing, and research and testing fields. It is mainly used for AC withstand voltage tests on various capacitive electrical equipment. Typical application scenarios are as follows:
(1) AC withstand voltage test of power cables
Long-distance high-voltage cross-linked polyethylene cables have a large capacitance, and traditional power frequency test equipment requires an extremely large power capacity and bulky equipment. The series resonant device, with its small power capacity and high output voltage, becomes the recommended equipment for cable withstand voltage tests, suitable for cables of 10 kV, 35 kV, 110 kV and above voltage levels.
(2) On-site testing of gas-insulated fully enclosed combined electrical apparatus
This type of equipment has a relatively small capacitance, but has strict requirements for test voltage waveform and test safety factors. The series resonant device can output pure sine wave voltage, and its characteristic of automatically losing resonance after breakdown can avoid the expansion of internal faults in the enclosed equipment, making it suitable for on-site testing and detection.
(3) Withstand voltage tests of large generators and power transformers
The capacitance between the generator and transformer windings and the ground is large. Using the series resonant device, AC withstand voltage tests can be completed under low power input, reducing the occupation of factory power capacity and suitable for the factory inspection and operation maintenance tests of large electrical equipment.
(4) Other capacitive electrical equipment
In addition to the above equipment, this device can also be used for insulation withstand voltage tests of high-voltage busbars, bushings, current transformers, voltage transformers, and other electrical equipment, with a wide range of applicable types.
Five. Selection and configuration guidance
To match the test requirements and ensure the detection accuracy, when selecting the series resonant device, it is necessary to combine the parameters of the tested item and the test specifications for comprehensive judgment. The specific selection steps are as follows:
(1) Determine a higher test voltage
Based on the rated voltage of the tested item, strictly follow relevant national and industry standards, clearly define the higher voltage required for the test, and use this as the core basis for determining the voltage level of the device.
(2) Estimate the capacitance of the tested item
The capacitance of different electrical equipment varies greatly. Precise estimation of parameters is required to provide a reference for the configuration of the reactor: the capacitance of power cables is relatively large, with a conventional value of 0.2 to 0.4 microfarads per kilometer; the capacitance of gas-insulated fully enclosed combined electrical apparatus is small, ranging from several hundred picofarads to several nanofarads; the capacitance of generator windings is between the two.
(3) Calculate the required device capacity
The rated capacity of the device must meet the calculation formula: S ≥ (2πf C U²) × k. Where f is the test frequency, C is the capacitance of the tested item, U is the test voltage, and k is the safety margin coefficient, with a conventional value of 1.2 to 1.3. At the same time, the test frequency needs to be controlled and maintained within the standard allowable range of 20 to 300 hertz.
(4) Select a reasonable combination method for the reactor
The modular reactor supports three combination modes: series, parallel, and mixed. Series is used to increase the equipment’s withstand voltage level, while parallel is used to increase the output current capacity. It is recommended to choose a configuration scheme with flexible combinations to enable one set of equipment to be compatible with multiple test samples, thereby improving the cost-effectiveness of the equipment.
Post time: May-20-2026