APPLICATION OF AMPLITUDE-PHASE ANALYSIS OF MAGNETIZING CURRENT TO DIAGNOSE CURRENT TRANSFORMERS DAMAGES
THE PURPOSE. To develop the method for diagnosing faults in current transformer windings and magnetic core. To determine the mathematical processing method of the instrument transformer magnetizing current for effective diagnostics. To determine the criterion for the fault detection. METHODS. To analyze the harmonic composition of the magnetizing current, digital signal processing was used, including digital filtering and Fourier series expansion. To study the magnetizing current of a current transformer with damages of different severity, a series of field tests was carried out. RESULTS. The existing methods for current transformers diagnostics are considered, their advantages and disadvantages are described. A method for detecting damage in a current transformer by analyzing the ratio of amplitudes and initial phases of the fundamental and higher harmonics of its magnetizing current is proposed. Obtaining the necessary data can be carried out during the scheduled work on checking the excitation characteristic of the transformer using the RETOM-51(61) device. Various types of current transformers were tested in order to find a diagnostic criterion fitting for current transformers of different construction. CONCLUSION. As a result of the experimental data analysis, recommendations were formed on how to use the proposed method: it is recommended to oscillography the instantaneous values of the magnetizing current during magnetizing characteristics test for several points of the linear and nonlinear parts of the excitation curve. To detect a damage, it is enough to find at least 10% deviation of the phase or amplitude of the complex phasor at one or more points of the excitation curve. The phasor mentioned is determined by the ratio of the magnetizing current harmonic components. Application of the described method will make it possible to reliably identify internal faults of current transformers without significant complication of diagnostic equipment.