Electric shock fault diagnosis of low-voltage residual current-operated protective device

As an important electrical safety protection device in low voltage distribution system, residual current protection device is to protect the insulation line leakage fault; the electric shock of the people plays an important role in fault. From the protection characteristics of residual current protective device to points, those can be divided into, residual current protection device for residual pulsating direct current and residual dc, according to the residual sinusoidal alternating current.

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

Sensors ◽

10.3390/s20072044 ◽

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.

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Research on the Key Factors of Mis-Operations and Correct Operations of the Residual Current Operated Protective Device

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.721.599 ◽

2014 ◽

Vol 721 ◽

pp. 599-602

Author(s):

Li Min Shao ◽

Meng Zhang ◽

Song Huai Du

Keyword(s):

Human Body ◽

Low Voltage ◽

Residual Current ◽

Protective Device ◽

Key Factors ◽

Safe Operation ◽

New Methods ◽

Electric Power Grid ◽

Basic Characteristics ◽

Sinusoidal Currents

Residual Current Operated Devices (RCDs) are the protective instruments of safe operation for power system. RCDs are important components for safety against indirect contacts in low voltage installations, and employed for protection against electric shock and earth faults. In order to develop a new rule of RCD tripping directly by the human body current while shocking, it is very important to detect and identify the contact current of the human body in the summation leakage current on the low-voltage electric power grid. The new methods can solve the above problems of RCD. So, the tripping characteristics of a series of products from different RCD manufacturers were tested and analyzed under sinusoidal currents. Thus, it obtained the basic characteristics of the RCD and found out the rules and problems. The results of this study will be theoretical significant, and also can guide to developing intelligent instruments and equipment of RCD for smart grid.

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Behavior of Residual Current Devices at Frequencies up to 50 kHz

Energies ◽

10.3390/en14061785 ◽

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.

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