Research on Identification of Encapsulation Defects in Dry-Type Air-Core Reactor Based on Differential Impedance Spectrum

The identification of encapsulation defects in dry-type air core reactors is of great significance for the operation and maintenance of the power grid. The traditional impedance spectrum encapsulation defect detection method has limitations, such as high testing frequency and severe voltage signal attenuation, which results in a large oscillation range near the resonance peak point of the impedance spectrum and high peak values of interference peaks, affecting identification accuracy. Therefore, this paper proposes a method for identifying the encapsulation defects of reactors based on the differential impedance spectrum. Firstly, build an equivalent simulation model based on the changes in the distribution parameters of reactors with encapsulation defects. Then, obtain the fundamental frequency impedance spectrum of the reactor based on non-sinusoidal excitation. Discretize the fundamental frequency impedance spectrum and extend it to the desired frequency band to obtain the full frequency discrete impedance amplitude matrix and frequency matrix. Using differential numerical analysis methods, obtain the slope matrix of the impedance amplitude spectrum. Finally, the proposed method is verified to obtain differential impedance amplitude spectra of different types and locations of encapsulated defects, including interturn short circuits and insulation moisture. Identification criteria for differential impedance amplitude spectra of encapsulated defects are established. Compared with traditional identification methods, this method can reduce the oscillation range of interference peaks in the impedance amplitude spectrum near the resonance peak point, and lower the oscillation peak of interference peaks. As a result, the accuracy of package identification for reactors has been improved.