Inductive power frequency series resonant withstand voltage test device

1、 Core Definition and Technical Principles

The power frequency withstand voltage test is a mandatory item for the factory delivery, handover, and preventive testing of electrical equipment. Its core requirement is to apply a sine high voltage that is consistent with the operating frequency of the equipment, and simulate the insulation withstand capacity of the equipment under long-term operating conditions. The core definition of the inductive power frequency series resonant withstand voltage device refers to a specialized test device that adjusts the inductance parameters of the adjustable reactor manually or electrically to make the inductance impedance in the series circuit equal to the equivalent capacitance impedance of the test object, thereby achieving series resonance at the power frequency and outputting high-power high voltage with a low-power power supply. Its core value lies in utilizing the resonance energy amplification effect, breaking through the dependence of traditional equipment on power capacity, and ensuring that the test waveform is highly consistent with the actual operating voltage.

The technical principle is based on the electrical characteristics of series resonance: the device consists of a series circuit consisting of a power supply, an excitation transformer, an adjustable reactor, a test object (equivalent capacitance), and a measurement and control system. The power supply provides initial low-voltage electrical energy, which is input into the circuit after being boosted by the excitation transformer; By adjusting the iron core air gap or winding turns of the adjustable reactor through mechanical structure, the inductance of the circuit is changed. When the inductance (XL) is equal to the capacitance impedance (XC) of the test sample, the total impedance of the circuit drops to a small value and becomes purely resistive. At this time, the circuit current reaches its peak, forming series resonance. In resonance state, the voltage at both ends of the test sample is Q times the excitation voltage (Q is the quality factor, usually 30-100), achieving the effect of "small power source generating high voltage"; At the same time, the voltage and current are in phase, with a power factor of approximately 1 and reactive power loss. This not only reduces the capacity requirements for the power supply, but also ensures the sinuosity of the output voltage waveform, avoiding additional damage to the insulation of the test sample caused by harmonics.

2、 Core Structure and Design Highlights

The inductive power frequency series resonant withstand voltage device adopts a modular integrated design, and the various components work together to form a complete testing chain. The core components include five functional modules. The power supply module provides stable 50Hz/60Hz low-frequency power to the system. The input voltage supports AC380V or AC220V, and the output power is configured as 10-500kW according to the test requirements. Some models support generator power supply and are suitable for on-site scenarios without external power supply; The excitation transformer module achieves voltage matching and electrical isolation, raising the power frequency supply voltage to 1-10 kV to provide safe excitation for high-voltage circuits. Its iron core is made of high permeability silicon steel sheets to reduce no-load losses; The adjustable reactor module is the core tuning component, which adopts a dry-type structure encapsulated in epoxy glass cloth tube. It is driven by a stepper motor to adjust the air gap of the iron core through a mechanical mechanism. The inductance adjustment range is 5-1000mH, and the adjustment accuracy is ± 1%, ensuring fast matching of test samples with different capacitance values; The capacitive voltage divider module is connected in parallel to both ends of the test sample, using high-precision capacitive voltage division principle. The voltage division ratio error is ≤ 0.5%, and real-time high-voltage signals are collected and fed back to the control system, with overvoltage protection function; The intelligent measurement and control module is equipped with a 10 inch touch screen, which integrates automatic tuning, data acquisition, curve display, and report generation functions, and supports remote operation and data storage.

The design highlights are mainly reflected in three aspects: firstly, excellent waveform quality. By optimizing the reactor core structure and power filter circuit, the output voltage waveform distortion rate is ≤ 1%, far exceeding traditional test transformers and meeting the strict requirements of power frequency testing for waveforms; The second is efficient and precise tuning, using the "mechanical tuning+intelligent matching" algorithm. The system can automatically identify the capacitance range of the test sample, quickly calculate the optimal inductance parameters, tune for ≤ 60 seconds, and achieve a resonance point capture success rate of ≥ 99.5%; The third is comprehensive safety protection, with a triple mechanism of overvoltage, overcurrent, and flashover protection. When the insulation of the test sample breaks down, the circuit immediately loses resonance, and the current instantly drops to a safe value without the risk of restoring overvoltage. At the same time, the high-voltage area is equipped with sound and light warning and interlocking protection to ensure the safety of operators.

3、 Core functions and significant advantages

The device's functional design is closely aligned with on-site testing requirements, combining professionalism and practicality. The core testing functions include: the power frequency withstand voltage test can output high voltage from 0-500kV, support voltage holding for any duration from 1-9999s, and meet the testing standards of different equipment; The automatic tuning function can automatically adjust the inductance and match the resonance according to the parameters of the test sample, without the need for manual repeated debugging; The data processing function displays real-time parameter curves such as voltage, current, and power factor, automatically calculates quality factor and test results, and generates electronic reports that comply with DL/T849.6-2004 standards; Multi mode operation supports both fully automatic and manual modes, suitable for operators with different skill levels and complex testing scenarios.

Compared to traditional power frequency test transformers, its advantages are extremely prominent: firstly, it has low power capacity requirements. When testing a 1km 110kV cable, only a 50kW power supply is needed to replace a 2000kVA traditional test transformer, greatly reducing on-site power supply pressure; Secondly, it has strong portability, with lightweight design of core components and a single weight of ≤ 60kg. It is equipped with mobile rollers and specialized lifting structures, making it suitable for transportation and layout in complex environments such as substations and wind power sites; Thirdly, it has a wide range of adaptability. By replacing the reactor module and excitation transformer, it can meet the testing needs of various equipment such as 6-500kV cables, 35-500kVGIS, and 10-500kV transformers; Fourthly, it has low operating costs, low reactive power loss in resonance state, energy consumption only 1/30-1/100 of traditional equipment, and simple equipment maintenance, with a service life of over 15 years.