Robert Sekula

Manufacturing of voltage transformer enhanced by 3-D computer simulation tools

The paper presents application of newly developed three-dimensional (3-D) computer tool used for simulation of the automated pressure gelation process. The tool that is based on commercial CFD software-Fluent-enables the simulation of filling and curing stages and gives useful information helping to understand the phenomena occurring inside the mold. To simulate the complex rheology of the material, Macoskos model for viscosity and Kamals model for curing kinetics were used and successfully applied in the software. First simulations were applied for arbitrary set parameters and formulated recommendations were later applied to approve the existing process. The simulation was performed for voltage transformer used in medium voltage applications and resulted in the optimization of the process parameters what allowed reduction of manufacturing time of the transformer considerably. Additionally the results of experimental verification of the simulation were presented in the paper showing very good agreement between simulation results and measured data.

An Investigation into the Influence of Filler Silanization Conditions on Mechanical and Thermal Parameters of Epoxy Resin-Fly Ash Composites

The insulation material of electronic devices should offers high thermal conductivity whilst retaining suitable mechanical properties. Epoxy resin is an example of a material that is commonly used by industry for electronic insulation, despite the fact that neither the thermal conductivity nor the mechanical properties are particularly satisfying. These properties can be enhanced by incorporating filler, with silica flour representing the most popular filler. An economically appealing solution is to replace silica flour with fly ash as filler material, however it must be remembered that compatibility of fly ash and epoxy resin is not ideal. In order to improve the coupling between these two materials, fly ash particles covered with [3-(2-Aminoethylamino)propyl]trimethoxysilane were obtained with six different conditions of the silanization process, where the amount of silane, the temperature and the time of the reaction were changed. The presence of the silane layer was confirmed via Fourier Transform Infrared Spectroscopy, Thermogravimetric Analysis and Scanning Electron Microscopy. The mechanical properties, including tensile strength, Young Modulus and fracture toughness, as well as the thermal conductivity of the final samples were investigated. In the case of composites with silanized fillers, all of the mechanical properties were improved, and an enhancement of thermal conductivity was observed for several composites. Moreover, the differences in coupling between the silanized fly ash and the untreated fly ash, and the epoxy matrix were precisely recorded by means of SEM. The presented studies confirm that an effective silanization process can significantly improve the properties of composites, while also verifying the usefulness of waste material. The results highlight that fly ash may be utilized to create a more economically affordable insulation material.

Review of biomass as a source of energy for Poland

To the present day, biomass has not been considered as an energy source for Poland, and over 95% of energy is generated through fossil fuel combustion. However, it is necessary to search for new energy sources because of high prices of traditional energy carriers and massive environmental pollution caused by these fuels. Biomass seems to be one of the best renewable energy sources. Basic components of biomass in Poland and estimations of energetic resources of biomass are presented.

Industrial Application Of A New CFD Simulation Approach.

This paper presents first industrial application of a new CFD, full 3-D simulation approach. The numerical approach was developed as user friendly, engineering Web-based tool that enables engineers to start fully 3D reactive molding simulations remotely. The tool that is based on commercial CFD software Fluent enables the simulation of filling and curing stages and gives useful information helping to understand the phenomena occurring inside the mold. The elaborated method starts with CAD geometry preparation according to the set of specific rules. Secondly the geometry is uploaded via the Website. In the next step the Web application analyzes the geometry and detects its structure automatically. This initial information allows creating a specific Website where, in consequence, engineer (responsible for the final process and product design) is able to enter process parameters (e.g. velocities, temperatures, material properties etc.) and start calculations. The meshing and solving stages are performed in fully automated way. Afterwards the Web application creates the report with simulation results. This report is available via Website. Based on these information the engineer makes decision to accept the design and process parameters or to restart the simulation for further optimization.

Modeling and Prediction of Thermal Cycle Induced Failure in Epoxy-Silica Composites

Epoxy resins filled with dielectric mineral particles are frequently used as insulating materials in power industry applications. Due to their excellent dielectric properties and relatively good thermal performance (resistance, ageing and conductivity) their usability is common and extensive. However, the mechanical performance of the resins is influenced by several factors such as resistance to crack propagation, especially in low temperature applications. This phenomenon is normally linked with appearance of two phase systems where particle filled epoxy material interacts with metallic inserts having significantly different thermal expansion coefficients. This kind of epoxy-metal interface can produce relatively high stresses in the product structure during thermal cycle loading. The paper deals with mechanical problems of power industry products and introduces the methodology for numerical modeling of failure in silica filled epoxy systems subjected to severe temperature gradients. Various aspects of material behavior modeling are covered in this article, including polymerization process, viscoelastic stress relaxation as well as stochastic cracking.

Two-Step Procedure of Fly Ash Modification as an Alternative Method for Creation of Functional Composite

An appropriate filler is a key component required to achieve an useful composite with expected properties. Not only sophisticated types of filler, like graphene are popular, but also more common ones, like silica flour or fly ash because of their low costs. Besides production costs, adequate size and possibility of functionalization of particles surface to create stable bonds with a matrix are essential in filler selection. To create an useful filler for epoxy resin based composites with use of a waste material, namely fly ash, two-step procedure was proposed. In the first part, raw material was sieved and five different ranges of the filler size were obtained. After mechanical tests with fracture toughness, tensile strength and Young Modulus, as well thermal conductivity, the best size of the fly ash was chosen for further modification. During the second step, filler was modified with coupling agent [3-(2-aminoethylamino)propyl]trimethoxysilane in order to enhance the coupling between particular components of composite. Presence of the silane layer was confirmed with infrared spectroscopy and scanning electron microscopy measurements, whilst prepared epoxy composite filled with silanized fly ash was examined similarly as previous composites. Obtained results have proved the significant influence of size of a filler and bonding to the matrix on mechanical and thermal properties of fly ash-epoxy resin composite. Proposed simple method of fly ash modification is an environmentally friendly way for utilization of the fly ash. Moreover, it creates an alternative material applicable in electrical devices as functional composite.

eRAMZES - Novel Approach For Simulation Of Reactive Molding Process.

This paper describes a unique multiphysics simulation tool allowing one to analyze and optimize reactive molding process used for the production of electrical insulation (in the form of epoxy resin embedding) in many power products. The presented methodology differs from the standard approach, since it excludes the requirement for high end-user’s knowledge and experience in the area of CFD (Computational Fluid Dynamics) and mechanical simulations. The role of the tool user is limited only to the definition of CAD geometry and process parameters via user-friendly Website. The remaining operations involved in numerical computations, including CAD geometry analysis and discretization, solving and postprocessing, are executed automatically and the simulation results are published online. In this way the presented tool gives engineers an opportunity to verify the product/mold design and manufacturing process prior to the production launching or to improve the existing solutions without time-consuming and expensive experimental trials. In addition, the time needed to perform simulation (especially to prepare numerical mesh) is significantly shortened.

Sequential fluid dynamics and structural mechanics simulations of a reactive moulding process

A wide range of medium and high voltage electrical equipment, including switch gears, voltage and current transformers, sensors and bushings is produced by reactive moulding technology, in particular by means of automated pressure gelation method. Application of appropriate materials, process parameters (mould temperature, filling time, filling velocity, initial temperature of internal parts, gelation time), as well as design and geometric parameters of the product are key factors for better quality components. In this paper, a new approach for modelling both moulding stages, namely filling and curing is presented. The simulation tool is based on a commercial CFD package. To simulate the reactive nature of the system with exothermic effect, viscosity and reaction kinetics models were successfully implemented. Novel simulation procedures for stress and shrinkage calculations, as well as simulation results with their experimental verification are also presented in the paper.