Inductive variable frequency series resonant withstand voltage test device

The AC withstand voltage test is a mandatory test item for testing the insulation withstand capability of electrical equipment, and the core definition of the inductive variable frequency series resonant withstand voltage device refers to changing the inductance by electrically adjusting the air gap of the reactor core, and adjusting the frequency with the help of the variable frequency power supply

1、 Core Definition and Technical Principles

The AC withstand voltage test is a mandatory test item for testing the insulation withstand capability of electrical equipment, and the core definition of the inductive variable frequency series resonant withstand voltage device refers to an integrated testing device that changes the inductance by electrically adjusting the air gap of the reactor core, and adjusts the frequency with the variable frequency power supply to make the inductance (XL) in the circuit equal to the capacitance (XC) of the test object, thereby generating high voltage at both ends of the test object. Its core value lies in utilizing the resonance effect to achieve ultra-high voltage output with a power supply power of only 1/Q of the test capacity (Q is the quality factor).

The technical principle is based on the energy amplification characteristics of series resonance: the device is provided with an initial low-frequency sine wave voltage by a variable frequency power supply, which is boosted by an excitation transformer and input into a series circuit; In the circuit, an adjustable reactor and the test object (equivalent to a capacitor) form an LC series structure. The inductance is changed by adjusting the air gap of the reactor core through a mechanical mechanism, and the output frequency is fine tuned by the variable frequency power supply. When XL=XC, the total impedance of the circuit drops to the pure resistance value (Z=R), and the current reaches its peak value; At this time, energy oscillation is formed between the reactor and the test sample, and the voltage at both ends of the test sample is Q times the excitation voltage of the power supply (usually Q=30-100), achieving the effect of "small power supply producing high voltage". In resonance state, voltage and current are in phase, with a power factor of 1 and reactive power loss, which not only improves testing efficiency but also reduces energy consumption.

2、 Core Structure and Design Highlights

The inductive variable frequency series resonant withstand voltage device adopts a modular integrated design, with each component working together to form a complete testing chain. The core components include five major modules. The variable frequency power module serves as the control core, outputting sine waves with adjustable frequencies of 30-300Hz, with distortion ≤ 1%, and achieving precise frequency control through DSP chips; The excitation transformer module achieves voltage matching and isolation, raising the voltage of the variable frequency power supply to 1-10 kV to ensure safe isolation between the high-voltage circuit and the low-voltage control system; The adjustable reactor module is the core tuning component, packaged in epoxy glass cloth tube. The air gap of the iron core is adjusted by a stepper motor, and the inductance adjustment range reaches 10-1000mH with an adjustment accuracy of ± 1%; The capacitive voltage divider module is connected in parallel to both ends of the test sample, with a voltage divider ratio error of ≤ 0.5%. It collects high voltage signals in real time and feeds them back to the control system, with overvoltage protection function; The intelligent measurement and control module is equipped with a 10 inch touch screen, integrating automatic tuning, data storage, and report generation functions, and supporting remote operation.

The design highlights are mainly reflected in three aspects: firstly, precise and efficient tuning, adopting the strategy of "coarse sensing+fine frequency modulation", tuning time ≤ 30 seconds, resonance point capture success rate ≥ 99.5%, and adapting to complex samples with large capacitance variation range; The second is safety protection, which has a triple mechanism of overvoltage, overcurrent, and flashover protection. When the test sample breaks down, the circuit current instantly drops to 1/Q, the arc is immediately extinguished, and there is no risk of restoring overvoltage; Thirdly, it has excellent portability, with lightweight design of core components and a single weight of ≤ 50kg. It is equipped with mobile rollers and suitable for transportation in complex environments such as substations and wind power sites.

3、 Core functions and significant advantages

The function of the inductive variable frequency series resonant withstand voltage device meets the requirements of on-site testing, with both professionalism and practicality. The core testing functions include: AC withstand voltage testing can output high voltage from 0-500kV, support any duration of withstand voltage from 1-9999s, waveform distortion rate ≤ 2%, and meet the testing standards of different equipment; The automatic tuning function can automatically calculate the resonant frequency range based on the capacitance of the test sample, and complete the matching of inductance and frequency with one click; The data processing function displays real-time voltage, current, and frequency curves, automatically calculates the quality factor, and generates test reports that comply with DL/T849.6-2004 standards; Multi mode operation supports three operating modes: fully automatic, manual, and semi-automatic, suitable for operators with different skill levels.

Compared to traditional testing equipment, its advantages are extremely prominent: firstly, it has low power capacity requirements. When testing a 2-kilometer 110kV cable, only a 30kW power supply is needed to replace a 1500kVA traditional testing transformer; Secondly, the output waveform is of high quality, with a sine degree far exceeding that of the power frequency equipment, to avoid damage to the insulation of the test sample caused by harmonics; Thirdly, it has a wide range of adaptability and can meet various equipment testing requirements such as 6-500kV cables, 35-500kVGIS, 10-500kV transformers, etc. through module combinations; Fourthly, it has strong on-site adaptability, with a working temperature range of -10 ℃ -40 ℃, supporting generator power supply without external power supply, and is suitable for remote wind and photovoltaic power station scenarios.