Abstract- Results of Frequency Domain Spectroscopy measurements are known to be largely influenced by insulation conditions, predominantly moisture ...
2009 Annual Report Conference on Electrical Insulation and Dielectric Phenomena
Deriving an Equivalent Circuit of Composite Oil Paper Insulation for Understanding the Frequency Domain Spectroscopic Measurements F. Meghnefi1,2, I. Fofana1,2, H. Hemmatjou1,2 and M. Farzaneh2
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Canada Research Chair on Insulating Liquids and Mixed Dielectrics for Electrotechnology (ISOLIME), University of Quebec at Chicoutimi, Qc, Canada 2 International Research Centre on Atmospheric Icing and Power Network Engineering (CenGivre), University of Quebec at Chicoutimi, Qc, Canada dielectric test results are only possible with a clear understanding of the physical behavior of the insulation system in response to moisture and temperature. A circuit model, based on the principles of linear dielectric response has been derived. The measurement has been performed under controlled temperatures and moisture content in the paper. The values of the model parameters have been identified from the dielectric tests on the laboratory made bushing. Since the dielectric parameters values are geometry dependent, poles, calculated from resistances and capacitances, were used as they are independent of the geometry. A correlation has been developed between the physical condition of the insulation and the equivalent model parameters that enable a clear and transparent interpretation of the dielectric test results. The feasibility of using poles to assess insulation condition is discussed.
Abstract- Results of Frequency Domain Spectroscopy measurements are known to be largely influenced by insulation conditions, predominantly moisture content and temperature. In this paper, the dielectric behaviour of a composite oil paper insulation system has been explained from the properties of Debye basic model. The measurement has been performed at controlled temperatures and moisture content in the paper. The equivalent circuit parameters of a laboratory made oil paper condenser bushing model were obtained using a non-linear optimization procedure. Since the dielectric parameters values are geometry dependent, poles, calculated from resistances and capacitances, were used as they are independent of the geometry. It was shown that the poles can be regarded as parameters able to be used for insulation condition assessment.
I. INTRODUCTION Power transformers are considered capital investments in the infrastructure of every country in the world. They are the “heart” of any electric power distribution and transmission systems and it is essential that they function properly. Increasing requirements for appropriate tools to diagnose power systems insulation non-destructively and reliably in the field drive the development of diagnostic tools like Time domain measurement based on Polarization/Depolarization Current measurements, Recovery Voltage measurements and Frequency Domain Spectroscopic measurements, over the last decades [1-5]. Frequency Domain Spectroscopy (FDS) measurement techniques provide indication of the general ageing status and moisture content of the oil-paper insulation of transformer. 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 (H’) and imaginary (H’’) parts of the dielectric permittivity as well as the dissipation factor (tanG) 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 [1-5]. However, the results of these tests are severely influenced by several factors, predominantly moisture content and temperature [1-5]. A better understanding and analysis of the
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II. EXPERIMENTAL SETUP A laboratory oil paper condenser model (Fig. 1) has been designed to perform these investigations. Terminals Box containing paper samples for Karl Fisher titrations OIP condenser
Fig. 1. Overview of the OIP condenser Model.
The object model was constructed by wrapping a conductor with cellulose paper and aluminium foils. Cellulose paper used was a Diamond Pattern Paper (DPP), manufactured by Weidmann [6] having a thickness dlayer = 0.125 mm and a dielectric value VB,layer = 8.5 kV, performed according to ASTM D-202, Section 143.
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The moisture content of the cellulose paper, when delivered, was measured to ~6% using Karl Fisher coulometer. The oil paper condenser model was carefully dried under vacuum (
