Marcin Szewczyk

New Concept for VFTO Attenuation in GIS with Modified Disconnector Contact System

This paper investigates on a new concept for very-fast transient overvoltages (VFTOs) attenuation in gas-insulated switchgear (GIS). The concept, first introduced by the authors in this paper, involves modification of the GIS disconnector contact system in order to dissipate the VFTO energy in damping elements placed inside the GIS busbar conductor. The concept is an alternative to the state-of-the-art method where magnetic rings are placed in the space between the GIS conductor and the enclosure. The proposed arrangement has no impact on the damping element on the dielectric design of the GIS busbar, and it highly reduces the impact on the GIS thermal design. This paper presents analyses which show feasibility of the concept, through 1) principles which govern voltage conditions inside the GIS busbar and 2) full-Maxwell finite-element method electromagnetic simulations of VFTO attenuated with the use of the proposed concept.

High-Frequency Model of Magnetic Rings for Simulation of VFTO Damping in Gas-Insulated Switchgear With Full-Scale Validation

Nanocrystalline magnetic rings have been experimentally proven for effective damping of very fast transient overvoltages (VFTOs) in gas-insulated switchgear (GIS). The application of any damping solution in a specific GIS setup (rated voltage, GIS arrangement) requires simulation-based design, which, in turn, requires reliable models with proven accuracy in demanding high-frequency and high-current VFTO conditions. This paper presents a new model of a magnetic ring, employing full frequency-dependent characteristics of the rings complex impedance, as well as the dedicated approach on modeling the saturation effect of the material magnetization characteristics. The saturation effect is modeled by a bypassing branch, activated at a certain saturation current value calculated according to the specific magnetic material properties and for the VFTO main frequency component. The model was implemented in Electromagnetic Transients Program simulation software and validated experimentally in a full-scale 550-kV GIS test setup. The validation proved the applicability of the model for the assessment of VFTO damping effectiveness with the use of nanocrystalline magnetic rings and, thus, for the design of a particular magnetic-based damping solution in a specific GIS setting.

Advanced Modeling of Magnetic Cores for Damping of High-Frequency Power System Transients

This paper presents a novel approach to modeling magnetic cores for high-frequency transient analyses in power system applications. A method is presented to obtain a frequency-dependent, nonlinear equivalent circuit model of magnetic cores, suitable for simulations of transients in high-frequency and high-current conditions. The model can be used in any Electromagnetic Transients Program (EMTP)-like simulation software for power system transient analyses and hardware design of transient mitigation solutions. The model has been developed based on the frequency characteristics of the complex impedance of a magnetic core, measured for different operating points on the magnetization curve. Based on the measured characteristics and on some basic material properties, a nonlinear equivalent model composed of a set of lumped elements was established. The presented method is generic; however, the results are presented for a magnetic core of nanocrystalline type and the model implementation is shown in EMTP simulation software. The exemplary model is dedicated for the frequency range f = 1 kHz ÷100 MHz, and for the current range I = 0 ÷ 10 kA. The model accuracy was validated with selected measurement results, and the accuracy of the method is thoroughly discussed.

Modeling of Repetitive Ignitions in Switching Devices: Case Studies on Vacuum Circuit Breaker and GIS Disconnector

Repetitive ignitions of electric arc during switching operation may result in generating Fast and Very Fast Transients (FT and VFT) and thus require analyses to ensure reliable system operation. The paper presents a common approach for modeling and simulation of such phenomenon for two types of switching devices: Vacuum Circuit Breakers (VCB) and GIS disconnectors. In each case, the associated (VFT) are modeled with the use of a case-specific Breakdown Voltage Characteristic (BDV), characterizing the switching process, and with the use of case-specific power system conditions. Two case studies are presented. For Vacuum Circuit Breaker, a switching operation of un-loaded transformer is presented. For GIS disconnector, switching of short bus-bar during the disconnector type testing is presented.

Quantitative Analysis of High-Frequency Material Properties in Thin-Ribbon Magnetic Cores

This paper presents quantitative analysis of material properties of magnetic cores wound of thin magnetic tape. Self-consistent model of penetration depth was proposed to include skin effect in calculation of magnetic material parameters. The model was used to extract geometry-independent material parameters based on which quantitative analysis of the material complex permeability was presented. The model is based on the magnetic cores frequency-dependent complex impedance (measured) and on selected basic material parameters (typically provided by manufacturers). The approach is demonstrated on a practical example, in which frequency-dependent saturation current of the magnetic cores was calculated based on the extracted geometry-independent material parameters. The results are presented for three types of nanocrystalline cores, in a frequency range from 1 kHz to 100 MHz.

Investigation on circuit breaker influence on transient recovery voltage

As Hammarlund stated in (1946), transient recovery voltage (TRV) investigation can never be finished completely, as the progress of circuit breaker construction and network design goes on. The most common approach to TRV investigation is concerning the so called prospective TRV, in which an assumption of neglecting interaction between circuit breaker itself and the inherent system recovery voltage is being made. However, it still seems to be worthy to investigate how circuit breaker affects TRV. In presented paper such an influence is being investigated in some detail, with use of black- box Habedank circuit breaker model (U. Habedank, 1993), in exemplary MV large industrial network (Z. Ciok et al., 1996). The influence of reactance of inductive fault current limiter as well as distance to fault in short line fault condition on rate of rise of recovery voltage has been investigated. The investigation has been made by means of simulation performed using Matlab/Simulink programme.

Damping of VFTO in Gas-Insulated Switchgear by a New Coating Material

Several methods of attenuation of very-fast transient overvoltages (VFTOs) in gas-insulated switchgear (GIS) are under development. An approach that is currently gaining high attention among researchers is based on the application of magnetic cores dissipating the energy associated with VFTO due to eddy current losses and magnetic hysteresis losses. This paper presents an advancement in this approach by introducing a new material type (denoted in this paper as “nanoflakes”). This new material comprises macro pieces of nanocrystalline ribbons (with the size ranging in square millimeters), acquired from crumbled nanocrystalline cores of a standard design. The material is characterized by relatively high magnetic permeability, poor electrical conductivity, and high saturation flux level. The material is suitable for application as a coating layer applied to the surfaces of an inner and/or an outer GIS conductor, as a fill-in material in the GIS shielding elements, or as a standard shaped core. This paper presents the material major features, outlines its development process, and reports on validation of the material effectiveness in real VFTO conditions. The validation is based on the measurement of VFTO attenuation in a full-scale 550 kV GIS test setup.

Full-Maxwell Simulations of Very Fast Transients in GIS: Case Study to Compare 3-D and 2-D-Axisymmetric Models of 1100 kV Test Setup

Development and type testing of gas-insulated switchgear (GIS) disconnectors are supported with the simulation-based analyses of very fast transients (VFTs) that are associated with the disconnector switching operations. In order to analyze local field values in the entire GIS geometry, the full-Maxwell approach needs to be involved for simulating the VFT generation process. According to power substation layout studies, 90

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Mitigation of Very Fast Transient Overvoltages in Gas Insulated UHV Substations

-angled GIS disconnectors are often used in GIS projects, since they offer most layout options and, at the same time, require the lowest number of GIS components. This implies that the test setups are asymmetric, thus the direct use of the full-Maxwell approach requires 3-D models, the application of which is considered to be highly demanding from a numerical point of view. The paper shows a comparison of the results obtained from full-Maxwell numerical simulations for a development test setup of 1100 kV GIS. The analyses are conducted for full 3-D geometry and for the corresponding 2-D-axisymmetric geometry. Example simulations of the VFT overvoltage (VFTO) waveforms are presented for both geometries, together with a comparison of the numerical effort needed for solving the associated field equations. The presented approach based on the 2-D-axisymmetric GIS model allows one to significantly reduce the numerical effort involved to support design work and development tests.