Condition evaluation of generator bars

Abstract

The condition evaluation of electric power equipment gained very much importance in the last years. Generally it forms the basis of maintenance strategy, risk evaluation and the decision over renewal or reinvestment. Dielectric measurements are a very important tool for the technical diagnosis of electric insulation systems like generator bars of rotating machines. Beside partial discharge and dissipation factor measurements the dielectric response of the electrical insulation system gives further information about the aging process and the condition of the insulation medium. The measurements and analysis of the polarization and depolarization current (PDC) are done in time domain and for the interpretation of the test results in the frequency domain the discrete Fourier transformation is applied. This paper should give a view to conventional dielectric measurements and the PDC analysis at insulation systems for rotating machines. Generator bars in resin rich and VPI technology were tested in different stadiums of age, mode of operation and load. For the results of the practical tests a mathematical model was found to show the correspondence to the existing models of the classical equivalent circuit of parallel and serial resistances and capacitances.