Residual Current Devices Research Articles

Research on detection and protection technology of DC residual current

Abstract To realize that the residual current device can accurately and quickly detect the fault when the fluctuating DC residual current occurs in the system and improve the system’s safety, a DC residual current detection and protection method based on VMD was proposed. Particle Swarm Optimization (PSO) was used to optimize the penalty factor and the number of decomposition layers of VMD. The minimum envelope entropy of the residual current signal is used as the fitness function to obtain the optimal combination. The criterion of fault occurrence is established based on the optimal modal component mutation characteristic of the residual current decomposed by VMD. Experiments show that this method can identify faults quickly and effectively when pulsating DC residual current is generated in the system.

Smart Building, Nuisance Electrical Failure, Remote Monitoring and Fault Recovery System

Smart Buildings are the fastest growing buildings compared to conventional buildings and are expected to grow at a rate of 8.3% for the next decay. The global commercial building automation market was valued at US$32.96 billion in 2020 and is expected to reach US76.49 billion by the year 2031. The implementation of technological advancement, demand for energy-efficient construction, low operational cost, and occupant comfortability have helped Smart Building to grow. However, Smart Buildings are still facing issues, from various sensor network diversity, clear definitions of Smart Buildings, and continuous smartness during full or partial electrical internal fault occurrence. This indicates the building is smart as long as a continuous power supply is present. Thus, this research study investigated Smart Building's drawbacks and designed a circuit to be a solution to one of the drawbacks to rectify the issues. The design provides full monitoring for real and nuisance failures and enables the performance of fault recovery procedures remotely. The circuit interfaces with the safety Residual Current Devices (RCD) and the wireless smart Wi-Fi-controlled socket outlets. Food industries, hotels, and restaurants could be the beneficiaries of this circuit. This is due to cold stores and fridges, which can lead to significant production loss/reduction when failure time increases.

Research on DC Electric Shock Protection Method Based on Sliding Curvature Accumulation Quantity

To address the limitations of current DC residual current protection methods, which primarily rely on the amplitude of DC residual current for fault detection and fail to safeguard against electric shocks at two points on the same side in DC Isolated Terra (IT) System systems, this paper introduces a novel protection method based on DC electric shock features. This paper first analyzes the sliding curvature accumulation and peak rise time features of DC basic residual current, load mutation current, and animal body electric shock current under multi-factor conditions. The analysis shows that sliding curvature accumulation in the range of 0.1 ≤ K ≤ 1 and a peak rise time of Δt ≥ 20 ms can effectively distinguish animal body electric shock. Then, based on this electric shock’s distinctive characteristics, an approach for identifying types of electric shock is developed. Finally, a DC residual current protective device (DC-RCD) is designed. The prototype test results demonstrate that the DC-RCD has an action time of ts < 70 ms. The proposed method accurately provides protection against electric shocks and effectively addresses the issue of inadequate protection when two fault points occur on the same side within an IT system. This approach holds significant reference value for the development of next-generation DC-RCDs.

Electric shock fault identification method based on DWT-AE-BPNN for residual current devices in power distribution systems

The protection dead-zone and threshold setting difficulties of the residual current devices (RCDs) in low-voltage distribution networks may lead to the misidentification of electric shock fault, resulting in severe life-threatening accidents. This paper proposes an electric shock fault identification method based on artificial intelligence for RCDs. Firstly, Mallat discrete wavelet transform (DWT) is applied to efficiently extract non-stationary electric shock feature signals from the total residual current with various noises, preventing weak non-stationary electric shock feature signals from being filtered out. Based on the average and maximum components of the signal mutation, an adaptive threshold can be determined to detect electric shock accurately, avoiding the false activation of RCDs caused by load fluctuations. Subsequently, an autoencoder (AE) is built to mine the non-linear features in which the signal of electric shock on living gradually rises and the signal of electric shock on non-living remains stable. Finally, a back propagation neural network (BPNN) is trained to classify the electric shock types from the non-linear features. The simulation and experiment have been conducted to obtain total residual current data under different conditions, and the electric shock fault real-time identification hardware platforms are developed. The accuracy of electric shock fault detection and classification can reach 100 %, which has advanced its practical applicability.

A Study on the Operation Characteristics of Arc Fault Detection Device under Arc Generation

According to the National Fire Agency's statistics in South Korea, the number of fires caused by electrical factors is increasing every year. Residual current devices and molded case circuit breakers are used to prevent electrical fires, but it is difficult to prevent electrical fires caused by arc generation. To prevent electrical fires caused by arc generation, studies on arc fault detection devices (AFDDs) and product development for commercial purposes are being conducted. However, the performance of AFDDs under real-life conditions has not been sufficiently verified. In this study, we conducted experiments on three types of AFDDs to verify their performance when a series arc is generated. Moreover, we performed arc waveform measurement and analysis. For the series arc test, we used a series arc generator based on the KS C IEC 62606 standard. We conducted arc-breaking experiments of the AFDDs with resistive and inductive loads and performed waveform measurement and analysis of the arc voltage and current.

Assessing the efficiency of measures to enhance electric power quality in variable-frequency drive for scraper conveyors

The intensive implementation of variable-frequency drive machines and installations in underground mining processes necessitates addressing several issues, with a primary focus on ensuring the quality of electric power. Elevating the energy resource of mining machines and enhancing the energy efficiency of mining operations requires maintaining the rated indicators of electric power quality in mine power distribution systems. Achieving this involves assessing the level and composition of higher harmonic components in voltage and current within power circuits equipped with variable-frequency drives (VFD). Key objectives encompass the development of a simulation model based on the equivalent diagram of the power distribution system substitution with a scraper conveyor VFD to scrutinize the spectral composition of higher harmonic components in the power circuits of the mine power distribution system (MPDS). Additionally, the study involves analyzing the impact of harmonic filters (HFs), reactors, and sine filters on the quality of electric power in the VFD system of a scraper conveyor. Further analysis extends to the spectral composition of higher harmonic components in circuits related to insulation leakage and metering circuits of the residual-current device. Practical recommendations for improving electric power quality in the VFD system of a scraper conveyor are then developed based on the research findings. The established model of a variable-frequency drive system for scraper conveyors facilitates the assessment of the effectiveness of electric power quality improvement measures. The harmonic composition of voltage and current in the mine power distribution system is determined under maximum distortion conditions and in the presence of HFs, reactors, and sine filters. Research methods are chosen to unveil the spectral composition of voltage and current in symmetrical and single-phase modes of insulation leakage, as well as in metering circuits of residual-current devices (RCDs). It is noted that the harmonic composition of leakage voltage and current is primarily influenced by the parameters of the output voltage modulated by the autonomous frequency converter inverter. Considering the high level of harmonic components in voltage and current, adjustments to RCD settings, capacitive current compensator, and the protective shunting unit are recommended for electrical safety. The study emphasizes the importance of scientifically substantiating the rated indicators of higher harmonic components for leakage circuits and further exploring the physiological effects of higher current harmonics on the human body. The feasibility of installing a harmonic filter (HF) directly on the low-voltage supply section of a scraper conveyor should be technically justified. Interestingly, the presence of HFs, reactors, and sine filters does not significantly impact the harmonic composition or the magnitudes of coefficients of the harmonic components in the phase voltage of the system concerning ground and leakage currents through insulation. However, higher harmonic components induced in leakage current circuits may pose a potential hazard, leading to a violation of magnetic compatibility and posing risks in case of contact with live parts of electrical equipment.

Nonisolated Three-Phase Current DC-Link Buck–Boost EV Charger With Virtual Output Midpoint Grounding and Ground Current Control

Non-isolated three-phase AC/DC converter concepts facilitate more compact and more efficient realizations of future EV chargers. However, without the galvanic isolation and/or high common-mode (CM) impedance provided by an isolation transformer, non-isolated chargers must employ other means to suppress CM leakage currents to ground sufficiently and to prevent nuisance tripping of mandatory residual current devices (RCDs). Typically, the required EMI filters reduce high-frequency (HF) CM leakage currents to uncritical values. However, low-frequency CM voltages, e.g., generated by third-harmonic injection, may drive significant LF CM currents through the parasitic capacitances of the DC output (including the battery pack) to protective earth (PE). Therefore, considering a non-isolated three-phase buck-boost current DC-link PFC rectifier system that consists of a buck-type current-source rectifier (CSR) stage and a three-level boost-type DC/DC-stage, this paper first proposes a virtual grounding control (VGC) of the DC output voltage midpoint. VGC employs the DC/DC-stage to compensate the LF (third-harmonic) CM voltage inherently generated by the CSR-stage, and thus controls the LF CM voltage between the DC output midpoint and PE to zero. This enables further a direct connection of the DC output midpoint to PE, where an additionally proposed ground current control (GCC) ensures near-zero LF CM leakage current. The proposed concepts are verified with a 10kW hardware demonstrator (power density of 6.4 kW/dm3 or 107.5 W/in3, full-load peak efficiency of 98.5%) considering TT (Terra-Terra) and TN (Terra-Neutral) grounding systems. With a direct connection of the DC output midpoint to PE, GCC limits the LF CM leakage current to < 6mA RMS, i.e., significantly below typical RCD trip levels, and, using the human-body impedance model according to UL 2202, achieves a test voltage of 110mV that is clearly below the most stringent limit (250 mV) of the standard.

The Time Response Analysis of a Hybrid Electronic Switch and Residual Current Devices System

The Time Response Analysis of a Hybrid Electronic Switch and Residual Current Devices System

Residual current detection method based on improved VMD-BPNN.

To further enhance the residual current detection capability of low-voltage distribution networks, an improved adaptive residual current detection method that combines variational modal decomposition (VMD) and BP neural network (BPNN) is proposed. Firstly, the method employs the envelope entropy as the adaptability function, optimizes the [k, ɑ] combination value of the VMD decomposition using the bacterial foraging-particle swarm algorithm (BFO-PSO), and utilizes the interrelation number R as the classification index with the Least Mean Square Algorithm (LMS) to classify, filter, and extract the effective signal from the decomposed signal. Then, the extracted signals are detected by BPNN, and the training data are utilized to predict the residual current signals. Simulation and experimental data demonstrate that the proposed algorithm exhibits strong robustness and high detection accuracy. With an ambient noise of 10dB, the signal-to-noise ratio is 16.3108dB, the RMSE is 0.4359, and the goodness-of-fit is 0.9627 after processing by the algorithm presented in this paper, which are superior to the Variational Modal Decomposition-Long Short-Term Memory (VMD-LSTM) and Normalized-Least Mean Square (N-LMS) detection methods. The results were also statistically analyzed in conjunction with the Kolmogorov-Smirnov test, which demonstrated significance at the experimental data level, indicating the high accuracy of the algorithms presented in this paper and providing a certain reference for new residual current protection devices for biological body electrocution.

Wymagania stawiane zabezpieczeniom różnicowoprądowym przeznaczonym do systemów ładowania pojazdów elektrycznych

The properties of residual current devices have been presented from the point of view of their ability to detect a specific shape of the residual current waveform. Moreover, the standard requirements relating to residual current protection used in electric vehicle charging installations have been pointed out. The operating characteristics of the IC-CPD and RDC-DD protections, which are intended for charging electric vehicles in mode 2 and mode 3, respectively, have been also discussed.

Impact of Harmonic Current on Residual Current Devices Performance in a Steel Making Plant

Impact of Harmonic Current on Residual Current Devices Performance in a Steel Making Plant

Foundation Earthing System – Its Application and Electrical Safety Considerations

Foundation earthing system greatly reduces the resistance to ground as compared to driven earthing rods. Low resistance to ground is desirable to protect lives – it ensures disconnection of power supply by Residual Current Device in the event of leakage current to ground. However, special attention must be given in the application of foundation earthing system to terrace houses and shop lots, where common ground slab steelwork is used throughout the entire row of houses or shop lots. This paper shows the field tests and findings of terrace houses with foundation earthing system, the requirements of the design and installation of foundation earthing system, and the importance of such installation to achieve low resistance to ground, to be able to operate the protective devices for supply disconnection during fault condition.

Trends in Locally Balanced Energy Systems without the Use of Fossil Fuels: A Review

In recent years, the idea of the operation of energy systems (power systems, heating systems) has changed significantly. This paper is an overview of locally balanced energy systems without the use of fossil fuels. The paper justifies the concept of local energy balancing in a new energy system that does not use fossil fuels (coal, natural gas, and crude oil), based on European Union guidelines and formal documents as well as the literature on the subject. In this context, the issue of local energy self-sufficiency, utilizing renewable energy sources, as well as the concept of local smart grids based on innovative market mechanisms are raised. Attention is also paid to technical issues with regard to locally balanced energy systems, in particular photovoltaic sources and energy storage. Challenges related to the use of electrical protection in networks with many sources of energy are described. In such networks, the power flow is not in one direction only. Moreover, the selection of protections is problematic due to the distribution of short-circuit currents. Additionally, earth fault currents in such networks may be distorted, and this negatively affects the operation of residual current devices. The basic nomenclature describing locally balanced systems has been sorted out as well. Finally, possible future research paths in the field of creating locally balanced systems without the use of fossil fuels are presented.

A New-Designed Biological Electric Shock Identification Method in Low-Voltage Distribution Network

In general, residual current devices (RCDs) have problems such as protection dead-zone and difficulty in threshold setting. A new method for identification of biological electric shock (BES) in low-voltage distribution network based on threshold method is proposed. Firstly, the total residual current of the circuit is denoised by Kalman filter, and then two threshold methods are investigated to determine the electric shock (ES) event and type respectively. Specifically, the first threshold consists of the maximum and average value of the current changes in the previous period, which is an adaptive value of dynamic change. If the current sampling value exceeds the threshold for 10 times in total within 5ms, an ES is considered to have occurred. Then considering that the amplitude of the waveform of the first three periods after BES has the characteristics of gradual changes, the sampling values of the three periods are recorded. The second threshold is a fixed threshold which is obtained by weighting the phase point changes corresponding to the second-period and the third-period waveforms, and then the specific ES types are distinguished. The proposed method is implemented on hardware devices and analyzed in various common ES situations. The results show that for the three cycles of waveforms collected after the occurrence of grounding or ES, the accuracy of this method is 97.84% and the recognition time is 2.07ms. In addition, based on the analysis of the actual BES data, a simple digital model is proposed to simulate the actual biological response, and it can be of great help in the subsequent study of such problems.

A Study on the Development of ETEC-IGR Test Devices for the Reliability Evaluation of RCD and ETEC-DPS

In this study, ETEC-IGR was developed in order to test the residual current protective device (RCD) and electric fire prevention system (ETEC-DPS) used in low-pressure electrical facilities. Furthermore, the reliability of the developed product was verified with Minitab PGM. The ETEC-IGR was designed to supply single-phase two-wire power and was equipped with an insulation transformer to protect against surge voltages and ground defects during testing. The results revealed that the load current (IL) may linearly flow from 0 A to 50 A, and the leakage current (IG) and the leakage current of the resistance component (IGR) may vary from 0.0 mA to 30 mA. Furthermore, the standby power was 98.43 W when the developed ETEC-IGR and the ETEC-DPS were connected. Moreover, the standby power was analyzed as 97.59 W when only the developed ETEC-IGR was connected. In addition, the standby power of the ETEC-DPS was interpreted as 0.84 W, and it was judged that the characteristics of the developed product were excellent. In addition, the heat dissipation environment, noise level, winding resistance, insulation resistance, voltage fluctuation rate, and AC/DC withstand voltage test of the developed test device met the relevant regulations. The normal distribution analysis of the developed ETEC-IGR revealed that the standard deviation was 0.3209, AD was 0.520, and P was 0.171. Thus, the data were interpreted as appropriate. In addition, the measured data were found to be more than 95% reliable, and the error was also less than 1 W. Furthermore, the reliability was verified with the 95% confidence interval in the box plot and histogram analysis.

"Approbation of the developed method for determining network insulation parameters on an operating excavator"

"One of the factors that determine the safety of electrical installations in ungrounded AC systems is the insulation resistance to earth. Early recognition and fault clearance, accompanied by a change in the active and reactive components of the insulation conductivity in ungrounded AC systems, will ensure work safety in electrical installations. Due to the fact the scale of cases of electrical injuries continues to remain significant, despite the tightening of the requirements of regulatory and technical documentation and the creation of newer effective methods and protection equipment against electric shock, therefore, increasing the level of electrical safety in the operation of mining machines and complexes is an urgent task. The article depicts the results of the approbation of the developed method for determining network insulation parameters on an operating excavator. The developed method is based on measuring phase voltages and angles of their vectors before and after connecting an additional capacitance to the phase of the electrical network and to the earth. According to the developed method, numerical data of the insulation condition in an electrical network with a voltage up to 1000 V and the single-phase earth fault current were calculated. During the approbation of the developed method, the lack of the existing protective residual current device was identified. Keywords: network insulation, admittance, susceptance, neutral shift, zero-sequence voltage. "

Mathematical Modeling of Time Response Analysis of Residual Current Devices with Electronic Switches

Today, relay contact and electronic residual current relays are used in order to protect human life against electrical shocks and machinery and equipment from malfunctions caused by excessive current. These residual current relays step in at 30 mA level and cut the current from the system. With the developed electronic switch and residual current device hybrid system, the human body residual current value and current cut-off response time were calculated using Monte Carlo Simulation frequency / intensity distributions. In the field of application, data sets were created in this study, which can be realized using physical and ambient data related to the human body resistance value. In this study, the reaction time of the system developed according to the amount of electric current, temperature of the human body, skin and moisture properties, shoes worn, decking, material type characteristics was modeled mathematically by using Monte Carlo simulation.

Characteristic leakage current of household devices and their impact on the tripping behaviour of residual current devices

• Modern power electronics (e.g. PV inverters) can have significant leakage currents. • Leakage current depends on the frequency-dependent input impedance of devices. • Tripping behaviour of RCDs (A, B, F) of five manufacturers is studied. • Leakage current significantly impacts the tripping behaviour of RCDs of type A. • Constant supraharmonic components did not affect the tripping behaviour of any RCD. Power electronic devices can produce distorted leakage currents that might cause malfunctions in protection devices, which can lead to dangerous situations. This article analyses the leakage current of presently common power electronic household devices, electric vehicles (EVs), photovoltaic inverters (PVs) and battery storage under different network conditions and studies their impact on the tripping behaviour of residual current devices (RCDs). The article focuses on RCDs of type A as they are the most used RCDs in Central Europe, but the tripping behaviour of RCDs of types F and B is also studied. In order to get reliable results, RCDs of five different manufactures are tested. The results confirm that the leakage current has an important effect on the tripping behaviour of the RCDs. The measuring results presented in the article indicate the need for further research and possible changes or extensions of existing standards.

Residual current devices in installations with PV energy sources

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Influence of the Design of a Residual Current Device on Its Break Time

Residual current devices (RCDs) are devices that can provide very good protection measures against electric shock. Yet, under certain circumstances, they can cause unnecessary and unexpected switching off of power in the protected circuits. The main component that determines the properties of an RCD is the summation current transformer. In recently produced RCDs, whose operation is independent from the installation voltage, the summation transformer, apart from detection of the residual current, has yet another task: it must also provide an appropriate energy value to the electromagnetic release in order to carry out mechanical disconnection of the contacts. In this type of RCD, the core of the summation transformer should be made of magnetic material with very high permeability and appropriate geometric dimensions. Manufacturers of RCDs, in order to reduce production costs and to promote miniaturization of the devices, use cores for summation transformers made of amorphous or nanocrystalline materials quite often. In such RCD designs, the impedance-matching circuit is used in the secondary circuit of the summation transformer to ensure proper sensitivity to the residual current. The paper describes the impact of using additional impedance-matching elements in the secondary circuit on the RCD break time. The paper presents the results of tests and measurements of the RCD break times of various internal structures.