The effect of earth fault current harmonics on tripping of residual current devices

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.

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A Methodology to Prevent Failure in Single Pole Reclosing Operations

International Journal of Emerging Electric Power Systems ◽

10.1515/ijeeps-2017-0054 ◽

2017 ◽

Vol 18 (6) ◽

Author(s):

Pablo Mourente Miguel

Keyword(s):

Transmission Line ◽

Single Phase ◽

Circuit Breaker ◽

Electric Arc ◽

Residual Current ◽

Fault Current ◽

Operating Mechanism ◽

Operating Cycle ◽

Earth Fault ◽

The Operating Mechanism

AbstractAfter a phase to earth fault in a transmission line, opening of the circuit breaker poles at line extremities interrupts the fault current in the faulted phase. However, due to coupling between phases there is still a residual current through the electric arc, which is then denominated secondary arc. Interruption of the secondary arc defines if single pole reclosing operation will succeed. Nowadays, studies evaluate the likelihood of secondary arc interruption to define application of single phase reclosing. By several reasons, the secondary arc interruption may not occur leading the single pole reclosing operation to a failure. In this case, the circuit breaker pole has to open again and that depletes the energy stored in the operating mechanism. As the rated operating cycle of a fast reclosing circuit breaker is O – 0,3 s – CO – 15 s CO, a failure in the first reclosing shot makes necessary an interval longer than 15 s to perform a second reclosing shot. The methodology presented herein establishes a verification beforehand if a single pole reclosing will be successful. With the secondary arc still active, the single pole reclosing is blocked and the system proceeds to a three pole reclosing. Blocking of the first reclosing shot keeps the energy stored in the operating mechanism and the three pole reclosing shot may proceed with an interval of 300 ms.

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Factors affecting the earth fault current in large-scale rural medium voltage cable network

22nd International Conference and Exhibition on Electricity Distribution (CIRED 2013) ◽

10.1049/cp.2013.1064 ◽

2013 ◽

Author(s):

J. Jaakkola ◽

K. Kauhaniemi

Keyword(s):

Large Scale ◽

Fault Current ◽

Factors Affecting ◽

Medium Voltage ◽

Cable Network ◽

Earth Fault ◽

The Earth

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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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