06_dielectrciresponse_hvmachine - IEEE Transactions on...

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IEEE Transactions on Dielectrics and Electrical Insulation Vol. 13, No. 1; February 2006 1070-9878/06/$20.00 © 2006 IEEE 383 Dielectric Response Studies on Insulating System of High Voltage Rotating Machines M. Farahani, H. Borsi and E. Gockenbach University of Hannover, Schering-Institute Callinstr. 25A, D-30167, Hannover, Germany ABSTRACT A significant method to characterize the electrical properties of materials and to evaluate the condition of the insulating systems is the dielectric response study which can be done in the time or frequency domain. The dielectric response measuring results can be affected by different parameters like measuring voltage, temperature, water content and aging condition of insulating system. In this work numerous measurements are presented, thus to understand, how the dielectric response measurement results at the insulating system of high voltage rotating machines can be affected by these parameters in the time and frequency domain. Because of the importance of the dielectric response application as a non-destructive diagnostic method the possibilities and limitations of this method to reflect the deterioration processes due to thermal and electrical stress were also investigated. In addition the possibility to transfer the measuring data from the time to frequency domain was investigated and the calculated and measured data were compared. For the test object actual stator bars were used that were manufactured with epoxy VPI technology. Index Terms — Rotating machine insulation, dielectric measurement, polarization, fault diagnosis, aging, moisture. 1 INTRODUCTION THE importance of dielectric response studies lies in the fact, that they allow the characterization of electrical properties of the material and especially the calculation of the real ( ε ’) and imaginary ( ε ’’) parts of the dielectric permittivity [1] as well as the dissipation factor (tan δ ) and capacitance (C) at different frequencies. The dielectric response analysis can be used for different purposes in electrical power engineering like development of new insulating materials, qualification of insulating systems after production or for diagnostic of high voltage (HV) apparatus in a non-destructive manner. Because of the steadily increasing age of expensive HV components and increasing requirement for the development and application of improved diagnostic methods, most recent attention has been directed at the application of the dielectric response analysis to evaluate the condition of the electrical insulation systems. The traditional dissipation or power factor measurement, which is conducted during standardized tests for many power apparatus, is a single frequency dielectric response measurement where the test voltage frequency is the power frequency for which the equipment is designed. The power factor at a single frequency is, however, sometimes insufficient to quantify even strong changes in the dielectric properties of a complex system [2, 3]. Therefore
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This note was uploaded on 06/11/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.

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06_dielectrciresponse_hvmachine - IEEE Transactions on...

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