New diagnostic techniques for large utility generators

Abstract

For many years the diagnostic techniques used for the assessment of the insulation condition of high voltage generators was based on the determination of several traditional dielectric parameters. The detection of partial discharge activity in the insulation can give a closer knowledge of the defects in stator winding insulation. In the past few years digital techniques for the acquisition of the partial discharge signals have been developed. The statistical processing of this data allows a better understanding of the phenomena in the insulation. In this paper a digital implementation of a method for the measurement of partial discharges is shown. Conventional digital oscilloscopes can be used as an interesting alternative instead of using expensive dedicated electronics. A software package has been developed for the statistical analysis of the discharges. In the past few years new parameters have been used. The software calculates these parameters from the statistical analysis in order to make a more precise diagnostic of the insulation condition. The system has been used during field tests in different types of generators and also in laboratory tests. The calibration of the measuring system and its related problems are discussed. Electronic pulse generators are commonly used for the calibration of the system but in complex systems many new problems arise. The reflection and attenuation of pulses make it difficult for the system to correctly detect the discharges.