Mariusz Stepien

Tests of a vacuum gauge for an HTS hydrogenerator

The paper describes the methodology, test rig and results of vacuum gauge tests under rotational conditions. The gauge is dedicated to measurements of vacuum in the rotor of an HTS power generator. The tests were performed using a dedicated test rig where the data of the measurements were transmitted using a Bluetooth device.

HTS toroidal helical transformer

The paper describes novel HTS toroidal transformer with helical windings, operating at 50 Hz. The turns of outer winding are parallel to turns of inner one. This arrangement of windings results in the same length and shape of each turn. The latter ensures homogeneous distribution of flux density. The magnetic core, in turn, improves coupling between windings, giving at the same time homogeneous magnetic flux distribution in windings. Proposed shape of windings reduces perpendicular component of flux density in HTS wires. It allows for the best possible utilisation of the HTS wire. The transformer has the magnetic core cooled with LN2. The transformer has turn-to-turn ratio 1:1 as it is designed for modular system. Its windings are made of Bi2Sr2Co2Cu3Ox wire. Material of magnetic core has accepted power losses in LN2. The magnetic core is also kept in ambient temperature. Thorough analysis of proposed HTS transformer will be carried out using Finite Element Method (FEM) and measurements resulting in critical current, rated power density and rated efficiency. The circuit model of the transformer is also given.

Optimising the operation of servomechanical force systems used in the joining of thin-walled metal elements in the automotive industry

This article is concerned with controlling a servomechanical force system applied in the joining of thin-walled metal elements when manufacturing e.g. car bodies. The new, i.e. servomechanical electrode force control system is both an element and a parameter of a technology used for joining metal elements by means of resistance welding. The projection welding of 1.5 mm thick DX53 sheets was used to exemplify differences between the two i.e. pneumatic (classical) and servomechanical welding machine electrode force systems. An innovative solution applied in the servomechanical force system consists in using a hybrid algorithm in order to control the force and travel of welding machine electrodes during welding. The article presents the optimisation of the new, i.e. servomechanical electrode travel system being an alternative to the classical, i.e. pneumatic electrode force control system. As a result of the undertaken optimisation it was possible to increase the repeatability of a welding process and improve the quality of joints.

BLDC-control of forces in passive magnetic bearings in blood pump

Artificial heart needs blood pump which satisfies not only mechanical and electrical properties, but also very important biomedical properties, particularly frictionless, with compact design and efficiency. The only one solution to meet the requirements. It is blood pump integrated with BLDC motor with rotor suspended using passive magnetic bearings. Passive magnetic bearings are solution with all required features, they are frictionless, compact and lossless. The one disadvantage is instability of passive bearing system. A new solution for stabilization of magnetic bearings is proposed in this paper. It consists in application of proper control of BLDC drive to obtain forces that together with the forces generated by permanent magnets make overall system stable. Because the only one direction (one degree of freedom) in passive bearings is unstable, it can be stabilized using magnetic forces that come from the motor. An idea of passive bearings stabilized by BLDC drive is presented in the paper. There are also selected results of FEM modelling, magnetic field and force distribution.

Charging and discharging backup battery for artificial heart

The paper is devoted to the internal backup battery for an artificial heart. The main objectives are selection of the battery type, design of the DC-DC converter and performing required tests. The numerical model of the battery is used for analysis of the system. Results of measurements will be included.

Analysis of quench propagation using coupled electrical-thermal FEM model

The 2D and 3D FEM (Finite Element Method) dynamical model of quench is the aim of the paper. It is based on a coupled electrical-thermal model. The small grain of non-superconducting impurity existing inside of superconducting wire initiates quench in the model. Nonlinear, temperature dependent electrical and thermal parameters are assumed. The quench propagation is modelled with the sequential coupled electric thermal analysis resulting in its 3D dynamics. The dynamics is expressed by spatial distribution of current, Joule heat and temperature. The modelling is carried out for low temperature NbTi wire and high temperature BiSCCO-2223 tape under sinusoidal current excitation and self magnetic field. Obtained computational results can be taken as a tool for optimisation for superconducting wire structure and improvement of quench protection systems in superconducting applications.

Toroidal HTS transformer with cold magnetic core – analysis with FEM software

The aim of this paper is to present a thorough characterization of the toroidal HTS transformer by means of FEM analysis. The analysis was a 2D/3D harmonic electromagnetic and thermal analysis. The toroidal transformer operated in LN2 by being immersed together with the magnetic core in it, for which its power losses were acceptable. Two extreme variants of windings were analysed. The first one called parallel and the second called perpendicular. Three variants of the magnetic core were considered. In the first one the core was put outside of the windings, in the second the core was inside of the windings and in the third variant the core was outside as well as inside of the windings. The windings were made of HTS tape BiSCCO-2223/Ag while the magnetic core was made of the nanocrystalline material Finemet. The two windings, with a 1:1 turn-to-turn ratio, were uniformly distributed along the whole torus circumference. The output power, efficiency and power density are in the results of the analysis. The temperature distribution was also calculated. In summary, the performance of the transformer is better than those currently known.

Comparison of SMES and ScES based power conditioning systems

The selection of the less expensive power conditioning system (PCS) is the aim of the work where two types of PCS are taken into consideration. The first type of PCS is based on superconducting magnetic energy storage (SMES) while the second one is based on supercapacitor energy storage (ScES). The comparison is based on installed power as the criterion. An illustrative example is given in the work

Optimization of resistance welding by using electric servo actuator

The paper is focused on the control of resistance projection welding process applied in joining of thin-walled metal elements. The motion of electrode is generated by electric servo actuator that controls the force exerted on electrode or alternatively, just travel itself of electrode. The projection welding has been discussed for welding of 1.5 mm thick DX53 steel sheets where one sheet contains an embossed projection. Apart of electric servo actuator, another source of force has been described, i.e. pneumatic actuator (classical one), for the reason of comparison. The solution where the electric servo operates together with appropriate algorithm makes the new solution that is alternative for classical, pneumatic one. Optimized motion of electrode due to new proposed source of electrode force or/and travel, based on relevant algorithm yields improved quality of joints.

Analysis of thyristor switch in power conditioning system with SMES

Ensuring high level of power quality (PQ) is one of most important issues in supplying in industry loads. There exist some critical types of loads that should be protected from any voltage disturbance. If any voltage disturbance (like voltage sag or dip) occurs an alternative energy source is used to ensure constant voltage amplitude across protected load. In described power conditioning system (PCS), power electronic system is connected in parallel to group of protected loads. The PCS together with protected loads have to be disconnecting from the mains in the case of voltage sag or dip occurs. Disconnection is necessary, if any voltage disturbance occurs, to prevent from delivering energy to low impedance part of power system (the mains in such case) from energy storage that is contained in the PCS (in this situation high temperature superconducting magnetic energy storage (SMES)). In described system breaking the connection between the mains and the load takes place thanks to the thyristor switch (TS). Disconnection and reconnection modes of operation of the PCS are particularly described and analysed in the paper. To obtain relatively low turn off time of thyristor switch a new method of controlling the PCS has been proposed that can assist turning off process of the TS and decreasing turn off time. The resynchronisation of the load voltage and the mains voltage of the PCS is also presented in the paper. It is used to limit the amplitude of the mains current after reconnection process. Influences of resynchronisation and reconnection processes on load voltage are also analysed. To proof correctness of designed controller the simulation and experimental results have been presented and discussed in the paper