Research On Defect Detection Method Of Dry-type Air-core Reactor Based On SFRA

As a key equipment for achieving reactive power compensation and maintaining power quality in the power system,the normal operation of dry-type air-core reactors(DAR)is crucial for the stable operation of the power system.At present,DAR defect detection methods have certain limitations,limited to some physical detection methods,such as inter turn detection and infrared temperature measurement technology,and are only applicable to certain fault situations,such as inter turn short circuits and largescale faults.Although these methods can serve as a basis for fault analysis,it is difficult to achieve early fault detection.Therefore,this article proposes a defect detection method for dry type air-core reactors based on swept frequency response method.This method utilizes the high-frequency sensitivity of capacitor parameters to design a method for detecting and judging capacitor parameters of reactors,in order to achieve overall judgment of the working condition of reactor windings.Firstly,the principle and implementation method of defect detection based on sweep frequency response method were analyzed.Using high-frequency as the design environment,based on the characteristics of DAR structure and combined with other calculated values,a corresponding distributed equivalent circuit model is designed to complete parameter theoretical derivation,specifically involving the calculation of coil to ground stray capacitance,interlayer capacitance,composite resistance,winding coil self inductance and mutual inductance.Secondly,a calculation programming method based on node numbering method was designed,which can quickly obtain the equivalent circuit node voltage of DAR high-frequency distribution,and conduct a detailed analysis of the electrical quantity problem of reactors with any number of encapsulation layers.On the basis of this research method,it was found that there are significant differences in the voltage drop distribution of reactors under different frequency conditions.At low frequencies,the voltage drop of the reactor is evenly distributed;At high frequencies,it is distributed in proportion to the capacitance,and the main voltage drop is located in the front section of the impedance section.At the same time,it is also possible to detect synchronous changes in the frequency response curves of the upper and lower arm currents in the resonant range,namely high peaks,where the current is more sensitive to fluctuations in capacitor parameters.This feature can be used to achieve the accuracy of parameter fluctuations.Subsequently,in the simulation study of a certain type of DAR winding,the fluctuation of capacitance parameters in the high-frequency sweep frequency range was simulated using the presence or absence of local water as a variable.Based on the results,the allowable sweep frequency range was determined,and the optimal measurement terminal was given.Finally,a set of insulation defect detection device was designed,and the feasibility and reliability of the method were verified through experiments based on the verified frequency scanning range and simulation data.The research and development process of the device was introduced in detail,including theoretical analysis,hardware design,software design,and device testing.Considering the variability of subsequent experimental applications,the output parameters of this device have a certain margin of error.The output performance of this device includes generating a scanning excitation signal with an amplitude of 100 m V-7 V and a frequency of 1 k Hz to 8 MHz.We have built a DAR experimental platform to simulate local water ingress at different axial positions of the winding and study the changes in frequency response curve characteristics at different positions.In the device validation test,it was found that the response of the frequency response curve varied with the location of local water inflow,and the frequency response curve can reflect normal and abnormal states.The experimental results indicate that the proposed method has high feasibility.