Wyniki 1-6 spośród 6 dla zapytania: authorDesc:"Stanislaw CZAPP"

Application of RCD and AFDD in low-voltage electrical installations for protection against fire DOI:10.15199/48.2019.11.04

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One of the sources of fire in buildings is a leakage current flowing through the resistive elements, e.g. conductive dust or a carbonized insulation of conductors. Such a current flow may warm up these elements to the temperature causing fire [1-3]. Due to leakage currents, a fire of wooden poles of an overhead line may arise [4]. In some cases, an explosion of explosive conductive materials may occur. When organic materials like wood or straw are heated by the current for a relatively long time, their gradual transition to the pyrophoric phase has to be taken into account. Because of the heating, the fire resistance of these materials significantly decreases - the minimum ignition temperature changes from 250 ºC to even 120 ºC [3, 5]. Fire may also be ignited by arc short-circuits or by a series arcing due to mechanical damage of a cable or a plug (e.g. cable crushing by a heavy object) [6, 7]. As protection against fire in low-voltage electrical installations, residual currents devices (RCDs) are used [8]. These devices disconnect supply in case of detection of earth current, which may initiate fire [3]. Such devices are also proposed to be a protective one in conjunction with fire alarm sensors [9]. However, some types of arc faults may not be detected by RCDs, especially series arcing, because no residual current flows in case of such a fault. For protection against such an accident, arc fault detection devices (AFDDs) are recommended to be used. In some countries, their application is obligatory [10, 11]. The further part of the paper presents the principles of RCDs and AFDDs application in low-voltage electrical installation, in order to prevent fire. Residual current devices in fire protection Leakage current flowing through the resistive elements may produce an amount of heat sufficient to initiate fire. This amount of heat is expressed by the following dependence: (1) Pth = Uo . I where: Pth - [...]

Metrological analysis of an computerized system of protection against electric shock in circuits with variable speed drives DOI:10.15199/48.2015.08.15

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Drive systems, that can be operated at variable speed, are equipped with power electronics converters. This causes distortion of the earth current, and consequently the need to take into account the use of proper protective devices in relation to earth current harmonics. This paper presents a system for protection against electric shock in circuits with power electronics converters and metrological analysis indicating the requirements for the present measurements for this purpose. The reasons for errors in rms current measurement have also been presented in this paper. Streszczenie. Układy napędowe o regulowanej prędkości kątowej zawierają przekształtniki energoelektroniczne, które są przyczyną odkształcenia prądu ziemnozwarciowego. Wyższe harmoniczne tego prądu utrudniają dobór zabezpieczeń przeciwporażeniowych i ocenę skuteczności ochrony przeciwporażeniowej. W artykule przedstawiono analizę metrologiczną systemu ochrony przeciwporażeniowej, który może być zastosowany w układach napędowych z przekształtnikami. Zwrócono uwagę na problem detekcji odkształconego prądu ziemnozwarciowego, w szczególności na przyczyny błędów pomiaru wartości skutecznej prądu. (Analiza metrologiczna komputerowego systemu ochrony przed porażeniem w układach napędowych o regulowanej prędkości kątowej). Keywords: electrical safety, non-sinusoidal currents, touch current, metrological analysis. Słowa kluczowe: bezpieczeństwo elektryczne, prądy niesinusoidalne, prąd dotykowy, analiza metrologiczna. Introduction Every electric circuit must be designed and performed in a way that gives effective protection against electric shock. In case of direct or indirect contact, when the risk of electrocution exist, the disconnection of supply should occur. In practice, shock hazard is analyzed almost exclusively for two typical current waveforms: sinusoidal AC (50/60 Hz) and smooth DC. Basic guidance of effect of these currents on a person is included in the document IEC/T[...]

System of protection against electric shock for circuits with power electronics converters DOI:10.15199/48.2015.11.35

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Effects of current on people are mainly considered for 50/60 Hz sinusoidal current and smooth direct current. However, modern low voltage circuits are very often equipped with power electronics converters - rectifiers, frequency converters, therefore non-sinusoidal earth currents (touch currents) occur. For non-sinusoidal currents safety criteria should be modified. This paper presents these modified criteria and a computer system of protection against electric shock which can be implemented in circuits with power electronics converters. The system is based on LabVIEW environment. Implementation of the safety system enables the disconnection of supply exclusively when real hazard of the ventricular fibrillation occurs. Streszczenie. Skutki rażenia człowieka są najczęściej analizowane dla prądu sinusoidalnego o częstotliwości 50/60 Hz lub nietętniącego prądu stałego. Jednakże w nowoczesnych instalacjach niskiego napięcia pojawia się coraz więcej przekształtników energoelektronicznych - prostowników, przekształtników częstotliwości, a w takich obwodach mogą płynąć odkształcone prądy ziemnozwarciowe (prądy rażeniowe). Przy prądach odkształconych kryteria bezpieczeństwa powinny być zmodyfikowane. W artykule przedstawiono zmodyfikowane kryteria bezpieczeństwa oraz komputerowy system ochrony przeciwporażeniowej, wykorzystujący środowisko LabVIEW, przeznaczony do obwodów z przekształtnikami. Zastosowanie tego systemu pozwala na wyłączenie zasilania, kiedy pojawia się zagrożenie migotaniem komór serca. (System ochrony przeciwporażeniowej do obwodów z przekształtnikami energoelektronicznymi). Keywords: electrical safety, non-sinusoidal currents, power electronics converters, touch current. Słowa kluczowe: bezpieczeństwo elektryczne, prądy niesinusoidalne, przekształtniki energoelektroniczne, prąd rażeniowy. Introduction Until recently shock hazard has been analyzed only for two typical current waveforms: sinusoidal AC (50/60 Hz) and smooth DC. Fig[...]

Effect of soil moisture on current-carrying capacity of low-voltage power cables DOI:10.15199/48.2019.06.29

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Power cables are mainly installed in the ground, and parameters of the soil as well as additional cables equipment, e.g. a cable duct, significantly influence power cables current-carrying capacity [1-7]. This current-carrying capacity also depends on the position of buried power cables [8]. Moreover, sections of cables may be exposed to external sources of heat [9, 10], what should be taken into account during cables selection and it is very important in terms of reliability of supply [11]. Basic recommendations for calculation of power cables current-carrying capacity Iz are included in standards IEC 60287-1-1 [12] and IEC 60287-2-1 [13]. According to these standards, for AC power cables the capacity Iz can be calculated as follows: (1)   (1 ) (1 ) ( ) 0 5 ( ) 1 c 1 2 c 1 2 3 4 d 1 c 2 3 4 z R T n R T n R T T W , T n T T T I                           where: Iz - current-carrying capacity of a power cable, A,  - permissible temperature rise of the conductor above ambient temperature, K, Wd - dielectric losses per unit length per phase, W/m, T1 - thermal resistance per core between the conductor and sheath, (K.m)/W, T2 - thermal resistance between the sheath and armour, (K.m)/W, T3 - thermal resistance of external serving of the cable (e.g. PVC sheath), (K.m)/W, T4 - external thermal resistance of surrounding medium, e.g. soil, (K.m)/W, nc - number of conductors in a cable, -, R - AC current resistance of a conductor at its maximum operating temperature, /m, 1 - ratio of the total losses in metallic sheaths to the total conductor losses, -, 2 - ratio of the total losses in metallic armour to the total conductor losses, -. For popular low-voltage cab[...]

Harmonics produced by traction substations - computer modelling and experimental verification DOI:10.15199/48.2017.06.04

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Introduction The voltage and current waveforms in a power grid sometimes significantly diverge from a sinusoid. Current distortions most often result from a non-linearity of loads. Distortions in voltage waveforms result from a distorted current flowing through the supply network, from switching processes and resonance phenomena. An increased content of higher harmonics in the voltage is also affected by the fact that “distorting" (non-linear) loads are supplied with already distorted voltage. This also leads to an additional (secondary) distortion in their current waveforms and, in consequence in the voltages in the supply network. An increased content of harmonics is also affected by the asymmetry of the supply voltage. The distorted waveforms of voltages and currents can be described by means of the Fourier series: (1)        1 k k 0 cos sin 2 ( ) k f t a a kt b kt where: (2) T   2π , T - time period of the function f(t), (3)    t T t f t t t T a 0 0 2 ( ) cosh d k  , (4)    t T t f t t t T b 0 0 2 ( ) sinh d k  , t0 - any value of the time t. The greatest influence on power quality in a distribution network is displayed by high-power loads, such as arc furnaces or power electronics devices. The latter group includes, for example, traction rectifiers. A significant level of harmonics in the supply voltage may lead, for example, to damage to the capacitor banks used to compensate reactive power. Damage to capacitor banks has been reported in several 110 kV/15 kV substations which supply medium voltage networks in Poland’s Pomorskie Region (Voivodship). These reports, and the need to determine the level of voltage distortion on the buses of power substations which supply disturbing loads (here: traction substations[...]

Computer-aided analysis of resonance risk in power system with Static Var Compensators DOI:10.15199/48.2016.03.05

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Static Var Compensators operation in a power system may significantly improve voltage profiles in nodes and the reactive power balance, as well as ensure greater system stability in emergency conditions. However these devices may be a cause of a resonance in the system. The aim of this paper is to call attention to the need to include resonance phenomena in a compensator’s location evaluation process. The analysis performed in the paper indicates the factors which affect a circuit’s resonance conditions, including a change in network configuration and compensator’s structure. Streszczenie. Kompensatory SVC mogą znacząco poprawić poziom napięcia w węzłach systemu elektroenergetycznego, bilans mocy biernej, a także stabilność napięciową systemu w warunkach zakłóceniowych. Jednakże urządzenia te mogą przyczynić się do powstania rezonansu. Celem artykułu jest zwrócenie uwagi na potrzebę analizy zagrożenia rezonansem przy doborze kompensatorów SVC. Wskazano czynniki, które wpływają na powstanie rezonansu - należą do nich m.in. moc i struktura kompensatorów oraz zmiana konfiguracji sieci elektroenergetycznej. (Wspomagana komputerowo analiza zagrożenia rezonansem w systemie elektroenergetycznym z kompensatorami SVC) Keywords: reactive power, resonance, Static Var Compensators (SVC). Słowa kluczowe: moc bierna, rezonans, statyczne kompensatory mocy biernej SVC. Introduction One of the key issues in the operation of a power system is to maintain the parameters of supply voltage in the network’s nodes at the proper level. Elements which improve voltage stability in a network are reactive power sources, including shunt compensators. The most widespread types of compensators encountered in the power systems are mechanically switched capacitors and reactor banks. Many power systems also include more recent types of these devices, such as SVCs or STATCOMs. The construction of such installations is also being considered for [...]

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