Study on Interturn Defect Diagnosis of Dry-Type Air-Core Reactor Based on FRA

The dry-type air-core reactor play a crucial role in the operation of the power grid, but they are prone to defects and faults due to the influence of the working environment. Frequency domain response analysis (FRA), based on non-invasive measurements, can obtain impedance spectrum information and achieve defect diagnosis of electrical equipment. Therefore, this article aims to address the challenges of diagnosing and warning of defects in dry resistance, and designs an on-site detection device for dry resistance defect diagnosis based on FRA. A high-frequency square wave inverter signal excitation device was constructed based on a new switching device SiC MOSFET. Combined with an RC pseudo trapezoidal wave modulation circuit to suppress and absorb transient spikes, a pseudo trapezoidal wave signal output with a frequency of up to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{1 0 ~ M H z}$</tex> and a maximum output voltage of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{8 0 0}$</tex> Vpp was achieved, solving the problems of low voltage and signal attenuation at high frequencies. Finally, typical test samples of 66 kV reactors were set with defects and faults such as interturn short circuit, insulation moisture, and overheating aging. The device developed in this paper was used for detection, and the results showed that the effective identification accuracy of offset could reach 1 %. On site fault diagnosis was conducted on the dry-type air-core reactor that exited after a turn to turn short circuit fault in a 500 kV substation, and the diagnosis results were consistent with the reactor defect. This proves that the insulation diagnostic device developed in this article can be applied to the defect diagnosis of onsite dry-type air-core reactors.