TY - JOUR A1 - Schober, Fabian A1 - Küchler, Andreas A1 - Krause, Christoph T1 - Oil conductivity – an important quantity for the design and the condition assessment of HVDC insulation systems JF - FHWS Science Journal N2 - HVDC (high voltage direct current) transmission is a very effective way of power transmission and it is necessary to supply the worlds growing amount of energy. In HVDC equipment the major insulating materials are oil and pressboard. Oil conductivity is an important quantity for the design, the diagnosis and the condition assessment of HVDC insulation systems. Unfortunately, insulating oil has a strongly nonlinear conductivity which depends on various parameters (field strength, temperature, water content and ageing) and is time-dependent because of charge carrier drift processes. Measuring methods are required to provide the information necessary for the condition assessment of HVDC systems. Therefore, measurements of new and aged oils are compared and taken into account for a diagnosis of oil-filled HVDC insulation systems. Furthermore, today’s standards are analyzed and compared to the so called PDC method. Relations between initial and steady-state conductivities at different temperatures, field strengths and for various oil types are presented and consequences for the condition assessment of insulation systems are discussed. KW - Electromobility KW - Energy Engineering KW - HVDC transmission KW - converter transformer KW - insulation Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:863-opus-463 VL - 1 IS - 2 SP - 59 EP - 78 CY - Würzburg ER - TY - CHAP A1 - Krieg, Andreas A1 - Lala, Gjergj A1 - Schober, Fabian A1 - Wiener, Johannes A1 - Paulus, Johannes A1 - Küchler, Andreas A1 - Zink, Markus H. A1 - Liebschner, Marcus T1 - FEM model for describing the dielectric behavior of oil-impregnated pressboard under DC stresses T2 - Papers of 33rd International Scientific Conference "Science in Practice" N2 - According to the worldwide growing demand for electric energy, it is necessary to construct safe and efficient power systems. HVDC (high voltage direct current) applications become more and more important due to larger distances for the energy transportation and the increasing demand for reactive power transportation. Appropriate insulation materials, i.e. mineral oil and pressboard, are widely used in HVDC components, mainly in power transformers though the knowledge about dielectric behavior of oil-impregnated pressboard under DC stresses in time domain is not sufficient. In this paper, a Finite Element Method (FEM) model is presented to describe the electrical conduction behavior of the material by separate consideration of mineral oil and pressboard. With this model the electric potential distribution under DC stress was simulated to analyze polarization and electrical conduction. The model parameters volume ratio as well as angle variations of FEM model are investigated and their influences on the current through the model are evaluated. Furthermore, geometrical and physical parameters are estimated and the results are compared to currents that are measured on oil-impregnated pressboard samples in time domain. KW - electrical conduction KW - FEM simultation KW - HVDC KW - polarization KW - oil-impregnated pressboard Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:863-opus-2609 SP - 62 EP - 66 ER - TY - CHAP A1 - Targitay, Deniz A1 - Roth, Lisa A1 - Zink, Markus H. A1 - Küchler, Andreas A1 - Bier, Markus A1 - Kobus, Maja A1 - Geißler, Michael A1 - Schlittler, Balz T1 - An FEM simulation model of oil-pressboard insulating systems for HVDC transformers T2 - 23rd International Symposium on High Voltage Engineering (ISH 2023) N2 - In this contribution, a simulation model for the description of the nonlinear dielectric behaviour of an insulation system composed of mineral oil and oil-impregnated pressboard is presented. The model was verified by comparing the simulation results with electric field and current measurements. At the outset, the ideal case, where a homogeneous initial charge carrier distribution according to the definition of ohmic conductivity is present, is analysed to establish the preliminary foundations pertaining to a typical measurement. Following that, the influence of distinct charge carriers on the measured quantities are investigated by altering their parametrisations. In contrast to the ideal case, a real measurement reveals a current trend, that can be explained by an excess amount of initial charge carriers related to the oil-impregnated pressboard layers. Potential possibilities to the origin of the surplus are discussed. Furthermore, it is shown that the dissociable and intrinsic charge carriers alone can reconstruct the measured quantities in terms of the transient behaviour. This points out that, for the field strength studied here ( E ≤ 1 kV/mm ), the charging of the highly resistive pressboard barriers is dominated by the dissociation of charge carriers in the oil gaps. KW - Mineral oil KW - Oil-impregnated pressboard KW - Poisson-Nernst-Planck theory KW - Ion drift KW - Electric current Y1 - 2023 UR - https://doi.org/10.1049/icp.2024.0488 PB - Institution of Engineering & Technology ER -