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 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 Behavior of Residual Current Devices at Frequencies up to 50 kHz

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1785
Author(s):  
Stanislaw Czapp ◽  
Hanan Tariq
Keyword(s):  
Electric Shock ◽  
High Frequency ◽  
Pulse Width Modulation ◽  
Low Voltage ◽  
Residual Current ◽  
Indirect Contact ◽  
Additional Protection ◽  
Operating Current ◽  
Low Voltage Circuits ◽  
Frequency Components

The use of residual current devices (RCDs) is obligatory in many types of low-voltage circuits. They are devices that ensure protection against electric shock in the case of indirect contact and may ensure additional protection in the case of direct contact. For the latter purpose of protection, only RCDs of a rated residual operating current not exceeding 30 mA are suitable. Unfortunately, modem current-using equipment supplied via electronic converters with a pulse width modulation produces earth fault currents composed of high-frequency components. Frequency of these components may have even several dozen kHz. Such components negatively influence the RCDs’ tripping level and, hence, protection against electric shock may be ineffective. This paper presents the results of the RCDs’ tripping test for frequencies up to 50 kHz. The results of the test have shown that many RCDs offered on the market are not able to trip for such frequencies. Such behavior was also noted for F-type and B-type RCDs which are recommended for the circuits of high-frequency components. Results of the test have been related to the requirements of the standards concerning RCDs operation. The conclusion is that these requirements are not sufficient nowadays and should be modified. Proposals for their modification are presented.

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 Diagnosis and Protection of Alternators Against Mass Faults

2020 ◽  
Vol 89 (1-4) ◽  
pp. 14-20
Author(s):  
Kouidri Mohammed Ali ◽  
Nouar Allal ◽  
Djilali Mahi
Keyword(s):  
Common Type ◽  
Fault Current ◽  
Circuit Breakers ◽  
Industrial Systems ◽  
Generator Protection ◽  
Earth Fault ◽  
High Impedance ◽  
Ground Fault ◽  
Fault Currents ◽  
Protection Systems

Generator protection system is one of the complicated industrial systems incorporating many group elements; measurement transformer, relays, circuit breakers and wiring connectors. Generally, protection systems are described using four characteristics; dependability, Sensitivity, rapidity and selectivity. The stator earth fault is a relatively common type of fault. The generators normally have grounded high impedance, that is to say, a ground via a neutral point resistor. This resistance is normally dimensioned to give a ground fault current of the order of 5 to 15 A in the event of permanent earth fault in high voltage terminals of the alternator. Relatively low ground fault currents cause. The new protection technique, it is called an intermittent defect, this type of defect usually has the following characteristics, A very short earth current pulse of high intensity (up to several hundred amps), lasting less than 1 ms. It occurs / disappears automatically over half a period, possibly over several periods, depending on the state of the power grid and the characteristics of the fault. Over longer periods (from several seconds to several minutes), it can evolve into a permanent fault.

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.

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