Computer based on-line diagnostics of insulation quality of high voltage apparatus
The safe and reliable operation of a power system is directly related to the insulation condition of high voltage apparatus in service, which may age and deteriorate under normal operating conditions. Therefore, the detection of insulation quality of high voltage apparatus is important. This task can be implemented advantageously by the measurement of dissipation factor and capacitance using on-line digital methods, since these methods require no service interruption thus resulting in low labor cost. Moreover, on-line measurements under operating voltage are more helpful in the assessment of the status of the insulation. In this work, a computer-aided system for on-line monitoring dissipation factor and capacitance was developed based on a method, which employs the Discrete Fourier Transform (DFT). The DFT is performed on the scaled down analog voltage and current signals obtained using a Digital Storage Oscilloscope (DSO) board, and results are displayed using the graphic user interface which is implemented with software Labview. To optimize system performance, software simulation and laboratory tests were carried out. Based on the results, optimal values of measurement parameters have been suggested. Field tests were conducted at Manitoba Hydro's Dorsey station to evaluate the insulation of a 230KV current transformer unit using the developed system.