ESTIMATION OF THE ELECTRODYNAMICAL FORCES NEAR FERROMAGNETIC COMPONENTS LOCATED INSIDE LOW VOLTAGE SWITCHING DEVICES

Inside power apparatus, electric conductors are often placed nearby ferromagnetic walls or inside ferromagnetic slots. It is important to know exactly the forces which appear in those situations, in order to ensure an adequate design of all machines, apparatus and power equipment. This paper presents a more generalized method to compute these forces, based on Maxwell’s tensors, and taking into consideration the asymmetry of the conductor placement inside a rectangular slot

Technical Solution for a Real-Time Air Quality Monitoring System

This article will present a simple technical solution for a low-power and real-time air quality monitoring system. The whole package of software and hardware technical solutions applied for recording, transmitting and analyzing data is briefly described. This original monitoring system integrates a single chip microcon-troller, several dedicated air pollution surveillance sensors (for PM10, PM2.5, SO2, NO2, CO, O3, VOC, CO2), a LoRaWAN communication module and an online platform. This system was tested and applied under real field conditions. Depending on the measured values, it provides alerts, or, it can lead to the re-placement of specific components in the exhaust equipment. This article will pre-sent some experimental results, validated also by official measurements of government operated air quality stations

Service Limits for Metal Oxide Varistors Having Cylindrical Symmetry as Function of the Ambient Temperature

This article presents an original experimental method applied to assess the stability limits of a given Metal Oxide Varistor (MOV), with cylindrical symmetry (cylinder or disk shape), as a direct relation between the ambient temperature and the service rated voltage, in the permanent operational regime. As the crossing current of a certain varistor is heavily influenced by its physical temperature, we must find an empirical relationship between these two parameters for a symmetrical configuration. Each ambient temperature can increase the temperature reference and any higher voltage will also produce an increased current, causing a uncontrolled runaway heating process, in an avalanche model. We tried to eliminate any references to technical dimensions or device values, focusing on material parameters. In the case of a symmetric MOV, we will consider the load coefficient, which is the ratio between the service DC voltage and the nominal DC opening voltage. By using experimental measurements and a simple mathematical model, we will establish the relation between the critical load coefficient and the ambient temperature in the case of symmetrical MOVs. This procedure could be applied to the design of more performant and safe surge arrester devices using existing MOVs, for all voltage levels and symmetrical configurations

Service Limits for Metal Oxide Varistors Having Cylindrical Symmetry as Function of the Ambient Temperature

This article presents an original experimental method applied to assess the stability limits of a given Metal Oxide Varistor (MOV), with cylindrical symmetry (cylinder or disk shape), as a direct relation between the ambient temperature and the service rated voltage, in the permanent operational regime. As the crossing current of a certain varistor is heavily influenced by its physical temperature, we must find an empirical relationship between these two parameters for a symmetrical configuration. Each ambient temperature can increase the temperature reference and any higher voltage will also produce an increased current, causing a uncontrolled runaway heating process, in an avalanche model. We tried to eliminate any references to technical dimensions or device values, focusing on material parameters. In the case of a symmetric MOV, we will consider the load coefficient, which is the ratio between the service DC voltage and the nominal DC opening voltage. By using experimental measurements and a simple mathematical model, we will establish the relation between the critical load coefficient and the ambient temperature in the case of symmetrical MOVs. This procedure could be applied to the design of more performant and safe surge arrester devices using existing MOVs, for all voltage levels and symmetrical configurations

Case Study about the Energy Absorption Capacity of Metal Oxide Varistors with Thermal Coupling

Metal oxide varistors are applied today inside modern surge arresters for overvoltage protection for all voltage levels. Their main issue is the thermal activation of their crossing current, which could lead to complete destruction by thermal runaway. This article presents a new technological solution developed in order to increase the thermal stability of metal oxide varistors. It consists in connecting in parallel two or more similar varistors (for dividing their current), having a thermal coupling between them (for equalizing their temperatures and forcing them to act together and simultaneously as much as possible). Starting from a finite element computer model performed for each situation (varistor standalone or parallel), up to real measurements, the thermal stability of the equipment was analyzed in permanent and impulse regime. Experiments were carried out in the same conditions. Experimental data obtain from two disk varistors corresponds very well to simulations, proving that parallel connection of varistors, combined with a thermal exchange between them is an efficient technical solution for thermal stability improvement, even if not apparently economically justified

New Technical Parameters and Operational Improvements of the Metal Oxide Varistors Manufacturing Process

At the beginning, this article details the manufacturing procedures for varistor materials. Starting from the initial composition of two large series of varistors (those with two additive oxides and those with five additive oxides), there is a major overview of the main stages of the technological process and the equipment used for the production, emphasizing the technological changes that were made. The article continues with the study of the influence of the sintering pressure and the sintering temperature on the electrical properties of the varistor materials made before. There were two experimental series of 7 varistors, one series based on 2 additive oxides and one based on 5 additive oxides. Each varistor of these series was sintered at another temperature, the fundamental purpose being to determine an optimal sintering temperature for each chemical composition. A second activity consisted of manufacturing two more series of varistors with the same chemical composition (2 oxides and 5 additive oxides), which were sintered at two different pressures, for having a set of conclusions on the influence of sintering pressure on the electric performances. All conclusions are underlying a new process for manufacturing metal oxide based varistors

Photogrammetry as a Digital Tool for Joining Heritage Documentation in Architectural Education and Professional Practice

Given the accelerated technological advance in all fields, vast knowledge of digital tools becomes mandatory for future interior designers and architects. Thus, experimenting with as many such methods and technologies must become a priority for the teaching process. Noticing a high demand for digitalization during the COVID-19 pandemic, the Polytechnic University of Timisoara has decided to encourage the implementation of digital teaching throughout disciplines, preparing students for their future careers. Photogrammetry as a study method, among others, has the potential to outrank traditional documentation techniques currently applied in architectural education and practice. The presented research was divided into two main phases: an educational, experimental workshop and a project restoration application. After learning, testing, and refining the close-range photogrammetry workflow, the authors and students took the best practices and applied them to an ongoing facade restoration project in Timisoara, scanning original and restored plaster ornaments and finally 3D printing one of the models. The article aims to show that, unlike traditional teaching methods, using photogrammetry as a documentation process creates a coherent link between theoretical education and restoration practice. Consequently, the exercise brings students closer to the applicable side of their careers through a contemporary digital technique

Analysis of the Wind System Operation in the Optimal Energetic Area at Variable Wind Speed over Time

Due to high mechanical inertia and rapid variations in wind speed over time, at variable wind speeds, the problem of operation in the optimal energetic area becomes complex and in due time it is not always solvable. No work has been found that analyzes the energy-optimal operation of a wind system operating at variable wind speeds over time and that considers the variation of the wind speed over time. In this paper, we take into account the evolution of wind speed over time and its measurement with a low-power turbine, which operates with no load at the mechanical angular velocity ωMAX. The optimal velocity is calculated. The energy that is captured by the wind turbine significantly depends on the mechanical angular velocity. In order to perform a function in the maximum power point (MPP) power point area, the load on the electric generator is changed, and the optimum mechanical velocity is estimated, ωOPTIM, knowing that the ratio ωOPTIM/ωMAX does not depend on the time variation of the wind speed

Green Interactive Installations as Conceptual Experiments towards a New Meaning of Smart Design

Nature-based design process with its embedded concept of form that follows function can be materialized as products capable of incorporating aesthetics and functionality similar to the characteristics of its natural role models. The paper addresses the topic of green installations created through a design process that simulates nature’s smart developmental mechanisms. The aim is to create an interactive installation capable of receiving and interpreting external factors that would determine the ensemble’s behavior and influence its future development and evolution. The main challenge lies in the fact that the smart feature is often achieved by intensive use of technology, which often overshadows inventive ways in which the behavioral and aesthetic properties of the material can be reinterpreted. The interactive green installation “Modgrew” investigates the possibilities of obtaining smart features through the experimental testing of two main types of configurations. The results underline the fact that, by applying the principles of biomimetic design, technologies from different fields can be combined towards obtaining a smart product. The conclusions highlight the need for future studies cover subjects such as the efficiency of automation, the possible reconfiguration of modules, behavioral optimization over time, the identification of minimal tech alternatives and the reduction of maintenance necessities