Development of distributed on-line monitoring system for dielectric loss tangent of high voltage capacitive apparatus

This paper presents a distributed measuring system for on-line monitoring of dielectric loss factor tan delta, and capacitance of HV apparatus. The method employs the discrete Fourier transform (DFT) which is performed on the scaled down analog voltage and current signals obtained using digital signal processing (DSP) technology. The measuring unit of the on-line monitoring system takes a series of measures in the hardware circuit design to improve the effectiveness of the DFT algorithm. The lab test results of measuring unit show that the measuring unit has high precision of measurement based on the DFT method. Field tests at a regional substation to evaluate the insulation of two groups of 220 kV current transformer units using the developed system.