The importance of knowing available fault currents when specifying interrupting ratings for low voltage equipment

2002 ◽  
Author(s):  
J.J. Toth
Keyword(s):  
Low Voltage ◽  
Fault Currents

scholarly journals Testing Sensitivity of A-Type Residual Current Devices to Earth Fault Currents with Harmonics

Sensors ◽  
2020 ◽  
Vol 20 (7) ◽  
pp. 2044
Author(s):  
Stanislaw Czapp
Keyword(s):  
Power Systems ◽  
Electric Shock ◽  
Low Voltage ◽  
Wide Spectrum ◽  
Residual Current ◽  
Motor Speed ◽  
Earth Fault ◽  
Fault Currents ◽  
Wide Range ◽  
Sinusoidal Waveform

In many applications, modern current-using equipment utilizes power electronic converters to control the consumed power and to adjust the motor speed. Such equipment is used both in industrial and domestic installations. A characteristic feature of the converters is producing distorted earth fault currents, which contain a wide spectrum of harmonics, including high-order harmonics. Nowadays, protection against electric shock in low-voltage power systems is commonly performed with the use of residual current devices (RCDs). In the presence of harmonics, the RCDs may have a tripping current significantly different from that provided for the nominal sinusoidal waveform. Thus, in some cases, protection against electric shock may not be effective. The aim of this paper is to present the result of a wide-range laboratory test of the sensitivity of A-type RCDs in the presence of harmonics. This test has shown that the behavior of RCDs in the presence of harmonics can be varied, including the cases in which the RCD does not react to the distorted earth fault current, as well as cases in which the sensitivity of the RCD is increased. The properties of the main elements of RCDs, including the current sensor, for high-frequency current components are discussed as well.

scholarly journals A Systematic Method for the Design of Earthing System for Low-voltage Installations

2019 ◽  
Vol 8 (3S) ◽  
pp. 12-15
Keyword(s):  
Low Voltage ◽  
Low Cost ◽  
Computer Software ◽  
National Standards ◽  
Design Parameters ◽  
Electrical Systems ◽  
Fault Currents ◽  
Standards And Regulations ◽  
Earthing Systems ◽  
Industry Needs

Earthing system plays an essential role in electrical systems in terms of safety for people in the vicinity against the hazard of electric shocks as well as protection and proper operation of equipment during the incidence of electric faults by providing a low-impedance path that can dissipate fault currents to the conductive mass of earth. Engineers are faced with the design of adequate earthing systems that comply with national standards and regulations which apparently incorporate a variety of earthing methods and various formulae to obtain the design parameters such as the earthing resistance and conductor size. Manual calculation of such parameter makes the design quite laborious, tedious, and time-consuming but could conceivably be performed much quicker by a computer software. This paper presents a proposed step-by-step approach for the design of a reliable and effective earthing system for low-voltage installations. The main objective of this work is to develop a computer-aided and easy-to-use template which could be useful for industry practitioners in Malaysia who are responsible with earthing system design. A simple auto calculation software template was developed using Microsoft Excel spreadsheet. The template was tested by a consulting company in order to meet their industry needs. The developed template provides a technically acceptable computer simulation and yet a low-cost solution to the complex issue of effective design of earthing systems for low-voltage installations.

Low-voltage arcing-fault currents

1948 ◽  
Vol 67 (8) ◽  
pp. 769-771
Author(s):  
C. F. Wagner ◽  
L. L. Fountain
Keyword(s):  
Low Voltage ◽  
Fault Currents ◽  
Arcing Fault

scholarly journals FIRES ON THE HOUSEHOLD LOW-VOLTAGE DISTRIBUTION BOARD CAUSED BY THE ABSENCE OF POLE MOUNTED FUSES AND SURGE ARRESTERS

2013 ◽  
Vol 3 (4) ◽  
Author(s):  
Nedžad Hadžiefendić ◽  
Ivan Zarev ◽  
Nebojša Đenić ◽  
Marko Medić
Keyword(s):  
Low Voltage ◽  
Distribution Network ◽  
Fault Current ◽  
Fire Occurrence ◽  
Voltage Distribution ◽  
Protective Devices ◽  
Surge Arresters ◽  
Fault Currents ◽  
Electrical Distribution ◽  
Electrical Distribution Network

This paper deals with the issue of the fire occurrence which is caused by low-voltage electrical installations (household distribution board) due to the absence of protective devices (fuses and surge arresters) on the pillars of the electrical distribution network. The example of calculation of fault currents is given, for the fault current on the basis of which it is proved the necessity of installing of pole mounted fuse on the latest pillar of low-voltage electrical distribution network. In the paper there are examples of fire expertise for fires caused by non-installation of pole mounted fuses and surge arresters are presented. Key words:atmospheric discharges, over-voltages, fault current, fire, pole mounted fuse, surge arrester

scholarly journals Improving sensitivity of residual current transformers to high frequency earth fault currents

2017 ◽  
Vol 66 (3) ◽  
pp. 485-494 ◽  
Author(s):  
Stanislaw Czapp ◽  
Krzysztof Dobrzynski ◽  
Jacek Klucznik ◽  
Zbigniew Lubosny ◽  
Robert Kowalak
Keyword(s):  
High Frequency ◽  
Low Voltage ◽  
Current Transformer ◽  
Residual Current ◽  
Fault Current ◽  
Earth Fault ◽  
Fault Currents ◽  
Proper Operation ◽  
Current Device ◽  
A Current

Abstract For protection against electric shock in low voltage systems residual current devices are commonly used. However, their proper operation can be interfered when high frequency earth fault current occurs. Serious hazard of electrocution exists then. In order to detect such a current, it is necessary to modify parameters of residual current devices, especially the operating point of their current transformer. The authors proposed the modification in the structure of residual current devices. This modification improves sensitivity of residual current devices when high frequency earth fault current occurs. The test of the modified residual current device proved that the authors’ proposition is appropriate.

scholarly journals Electrodynamic Contact Bounce Induced by Fault Current in Low-Voltage Relays

Energies ◽  
2019 ◽  
Vol 12 (20) ◽  
pp. 3926
Author(s):  
Andrzej Ksiazkiewicz ◽  
Grzegorz Dombek ◽  
Karol Nowak ◽  
Jerzy Janiszewski
Keyword(s):  
Low Voltage ◽  
Threshold Value ◽  
Fault Current ◽  
Contact Materials ◽  
Fault Currents ◽  
Current Threshold ◽  
Protection Devices ◽  
Electromagnetic Relays ◽  
Contact Welding ◽  
Selection Of

Due to fault currents occurring in electrical installations, high electromagnetic force values may be induced in current paths of low-voltage electromagnetic relays. This force may lead to an electromagnetic bounce that will further result in an electric arc ignition between contacts, and under some circumstances, it will result in contact welding. For the proper exploitation of relays, the threshold value of the maximum current, and thus the electrodynamic force, should be known. This force depends on several factors, including: contact materials, dimensions of relay current paths, relay electromagnetic coil, etc. This paper presents the results of calculations and an experiment on electromagnetic forces, which cover these factors. A static closing force, acting on the contacts, and the fault current were measured. As a result, values of the force and current threshold were obtained, which inform when an electrodynamic bounce may occur. The obtained result may be used in designing contact rivets and relay current paths together with the selection of adequate fault protection devices.

Processing of human melanoma cells for correlative TEM, LVSEM, and LM

1991 ◽  
Vol 49 ◽  
pp. 106-107
Author(s):  
Marek Malecki ◽  
J. Victor Small ◽  
James Pawley
Keyword(s):  
Electron Microscopy ◽  
Low Voltage ◽  
Fluorescent Microscopy ◽  
Blood Stream ◽  
Surface Topology ◽  
Integrin Receptors ◽  
Transmission Electron ◽  
Develop Technology ◽  
Voltage Scanning ◽  
Mechanisms Of Adhesion

The relative roles of adhesion and locomotion in malignancy have yet to be clearly established. In a tumor, subpopulations of cells may be recognized according to their capacity to invade neighbouring tissue,or to enter the blood stream and metastasize. The mechanisms of adhesion and locomotion are themselves tightly linked to the cytoskeletal apparatus and cell surface topology, including expression of integrin receptors. In our studies on melanomas with Fluorescent Microscopy (FM) and Cell Sorter(FACS), we noticed that cells in cultures derived from metastases had more numerous actin bundles, then cells from primary foci. Following this track, we attempted to develop technology allowing to compare ultrastructure of these cells using correlative Transmission Electron Microscopy(TEM) and Low Voltage Scanning Electron Microscopy(LVSEM).

High-pressure freezing of cells in suspension for low-voltage scanning electron microscopy (LVSEM)

1991 ◽  
Vol 49 ◽  
pp. 64-65
Author(s):  
Marek Malecki ◽  
James Pawley ◽  
Hans Ris
Keyword(s):  
Electron Microscopy ◽  
High Pressure ◽  
Low Voltage ◽  
Culture Media ◽  
Cell Structure ◽  
Freeze Substitution ◽  
Ice Crystal ◽  
High Pressure Freezing ◽  
Cell Culture Media ◽  
Voltage Scanning

The ultrastructure of cells suspended in physiological fluids or cell culture media can only be studied if the living processes are stopped while the cells remain in suspension. Attachment of living cells to carrier surfaces to facilitate further processing for electron microscopy produces a rapid reorganization of cell structure eradicating most traces of the structures present when the cells were in suspension. The structure of cells in suspension can be immobilized by either chemical fixation or, much faster, by rapid freezing (cryo-immobilization). The fixation speed is particularly important in studies of cell surface reorganization over time. High pressure freezing provides conditions where specimens up to 500μm thick can be frozen in milliseconds without ice crystal damage. This volume is sufficient for cells to remain in suspension until frozen. However, special procedures are needed to assure that the unattached cells are not lost during subsequent processing for LVSEM or HVEM using freeze-substitution or freeze drying. We recently developed such a procedure.

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