Ground Fault Protective Devices Research Articles

Solar Photovoltaic System Performance Improvement Using a New Fault Identification Technique

Identifying faults in the photovoltaic (PV) arrays is very much essential in improving the PV system’s safety and reliability. Solar PV arrays operate with non-linear characteristics, installed with maximum power point trackers (MPPT’s), and blocking diodes cause mismatch levels. Line-to-line and line-to-ground faults are identified, and the faulted circuits are isolated by means of over current protection devices (OCPD) and ground fault protection devices (GFPD). In order to improve the accuracy of fault detection, artificial intelligence (AI)-based techniques like Fuzzy inference, wavelet, support vector machine, and k-nearest neighbors are used. The drawback of AI-based techniques are (1) requirement of large dataset for effective fault identification and also show incompatibility if there is low irradiation and (2) require a larger number of voltage and current sensors. An experimental setup of 160 W, 4 × 4 solar PV array having PV modules (SPB) is subjected to different fault conditions (CS), and the faults are identified using the minimum number of sensors. The faults that are not detected by the conventional methods are detected using this proposed method, and the power gain due to the fault identification is around 152% which is 97 W in the PV array.

Examination of Rectifier AC Side Electric Circuit Ground Fault Detection Method in DC Electric Railway Substation

There are no ground fault protection devices in the AC circuit between the rectifier transformer and rectifier of DC electric railway substations. Therefore, the ground faults in the AC electric circuit are expected to be protected by overcurrent relays or DC ground fault overvoltage relays (64P) installed in the upper system. However, these protections are inadequate, so we examined methods to detect ground faults in the AC circuit between the rectifier transformer and rectifier. Thus, it was found that the ground fault current included a third harmonic current that was absent when there were no ground faults. Therefore, we created a prototype device to extract the third harmonic current, and confirmed that ground faults in the AC electric circuit between the rectifier transformer and rectifier could be detected by artificial ground fault tests.

Decentralized earth fault compensation in MV-grids - challenges and solutions

Decentralized earth fault compensation coils (EFCC) in resonantly grounded medium voltage networks are becoming increasingly popular. Their installation imposes several requirements on the earthing system in terms of equipment and personnel safety as well as the functionality of the ground-fault protection devices. Based on two practical examples of networks (urban and rural), the challenges and their possible solutions are presented and verified by on-site measurements. Due to the impressed current of the distributed EFCC, the earth potential rise (EPR), the touch voltage, the transmitted voltages to neighboring stations and to the low voltage installation (PEN conductors) have to be analyzed. The role of cable shields in relation to earthing and the influences on the distribution of the zero sequence currents discussed. In addition, this work investigates the currents flowing on the interconnecting cables between two different network areas under fault conditions with different distributions of compensation. The cable shields grounded at both ends are loaded by flowing zero sequence currents. This leads to additional heating of the cables. It is analyzed which zero-sequence currents are permanently permissible in order to avoid a maximum insulation temperature and to prevent additional aging of the cables

Design and Testing of a Frequency-Selective Grounding for $3\phi$ Power Transformers

Three-phase ( $3\phi$ ) power transformers can have their windings configured to create local neutral points, which can be connected to ground. The grounding of a $3\phi$ power transformer is intended to limit ground currents (including fault currents) and limit ground potentials. These objectives can be translated into the resistive grounding that is usually designed based on system ratings and transformer parameters. The resistive grounding, however, can impact the flow of the harmonic components present in the exciting currents of a $3\phi$ power transformer. As a result, undesired harmonic components are induced in primary and secondary voltages. This article presents the design and performance of a frequency-selective grounding that can achieve the objectives of grounding a $3\phi$ power transformer. The developed grounding is designed to provide a resistive path for low-frequency currents (faults), and to create a low impedance path for high-frequency currents (harmonics). The frequency-selective grounding is experimentally tested for a $3\phi$ power transformer with different primary and secondary winding configurations, different fault types, and source grounding. Test results show that the developed grounding can reduce the ground potential, harmonic distortion in primary and secondary voltages, and ground fault currents with a minimum interference with ground fault protective devices.

Measures to Minimize Series Faults in Electrical Cords and Extension Cords

In electrical power systems, cords and extension cords are exposed to mechanical damage and other insulation stresses. Mechanical damage to stranded conductors can reduce locally their cross section or break them and cause anomalous local conditions of overheating or arcing. The ordinary protective devices cannot detect the series faults that persist, so the fault point remains energized and is subject to electric shock and fire hazards. Effective protection can be accomplished by implementing active and passive measures: installing arc-fault circuit interrupters or arc-fault detection devices, able to detect arcing faults, or wiring the circuits with a grounding protection conductor to involve the ground in every fault. In this way, residual current protective devices (residual current devices or ground fault protective devices) quickly protect the series faults not only with arc, but also without it. Ground-fault-forced cables facilitate by design the conversion of any kind of cable fault to a ground fault. They are particularly recommended for cords and extension cords, internal circuits to grounded equipment, uninterruptible power system continuity circuits, aircraft circuits, road tunnels, data centers, refrigerated containers parks, residences, and hospitals.

Development of the self-learning machine for creating models of microprocessor of single-phase earth fault protection devices in networks with isolated neutral voltage above 1000 V

The paper proposes the development of a self-learning machine for creating models of microprocessor-based single-phase ground fault protection devices in networks with an isolated neutral voltage higher than 1000 V. Development of a self-learning machine for creating models of microprocessor-based single-phase earth fault protection devices in networks with an isolated neutral voltage higher than 1000 V. allows to effectively implement mathematical models of automatic change of protection settings. Single-phase earth fault protection devices.

DC‐side fault detection for photovoltaic energy conversion system using fractional‐order dynamic‐error‐based fuzzy Petri net integrated with intelligent meters

Fault occurrence or voltage disturbance, such as mismatch operations or electrical faults caused by structural changes in photovoltaic (PV) panels, local/remote faults, or heavy load operation, can disturb a PV energy conversion system (PVECS) on both the DC and AC sides. On the AC side, any serious disturbance can be isolated using power fuses, overcurrent protection and ground-fault protection devices. Therefore, the authors propose the use of fractional-order dynamic-error-based fuzzy Petri net (FPN) to detect disturbance events in a microdistribution system. PV energy conversion depends on solar radiation and temperature, and a maximum power point tracking control is used to maintain stable output power and voltage to microdistribution loads. When the desired maximum power is estimated, a bisection approach algorithm is used to regulate the output voltage of the PVECS by adjusting the duty ratios of a buck–boost converter. The maximum power drops, which are compared with meter-reading power from intelligent meters, are used to detect faults on the DC side. Then, fractional-order dynamic errors between the desired and estimated powers and a FPN are employed to detect faults. For a small-scale PVECS, computer simulations are conducted to show the effectiveness of the proposed model.

On the Design and Capacity of a Grounding Configuration for Grid-Connected <roman>DGUs</roman>

Established standards and industrial codes, for interconnecting distributed generation units (DGUs), address voltage and frequency changes, levels and quality of injected power, islanding conditions, and protection. However, these standards and codes do not clearly address the grounding configurations for grid-connected DGUs. One of the challenges related to the grounding configuration for DGUs is the harmonics generated by power electronic converters employed in DGUs. These harmonics can raise the ground potentials and disrupt the function of ground fault protection. This paper develops and tests a frequency-selective grounding configuration for grid-connected DGUs. The developed grounding configuration offers limiting ground potentials and ground fault currents, while imposing negligible impacts on the function of ground fault protective devices. The frequency-selective grounding configuration is designed and tested for two wind energy conversion systems and a photovoltaic system. Test results show that the developed grounding configuration achieves its objectives with negligible impacts on the grounded DGU and its ground fault protection.

Reducing Electrocutions in Industry: Application of a Class C Ground-Fault Current Interrupter in a Pulp and Paper Plant

Historically, Class A Ground-fault circuit interrupters (GFCIs) have been responsible for a substantial reduction in residential electrocutions. Yet they have not had much success in industrial applications because of the limitation on system voltage (maximum 240 V) and the 6-mA maximum allowed leakage current. As a result, industrial personnel protection has been lagging behind its residential counterpart. UL realized this gap and defined new GFCI classes to specifically address personnel protection in industrial applications. UL 943C defines the requirements of special-purpose GFCIs that can be used on systems up to 600 V and allows for a leakage current of 20 mA. This article describes the UL 943C requirements and the newly defined GFCI classes. The difference between equipment ground-fault protective devices (EGFPDs) and GFCIs is also addressed. Finally, the application of a Class C GFCI in a pulp and paper plant is described.

Unprotected Faults of Electrical and Extension Cords in AC and DC Systems

In electrical power systems, all the wiring exposed to mechanical damages and other insulation stresses, such as flexible cords, can be involved in overheating, arcing, and burning. Mechanical damages of the stranded bare conductors can locally degrade the effective sizing of the cross section and cause anomalous local conditions. The circuit protective devices (PDs) can be unfit to detect the faults of cords that remain so energized and available to electric shock and fire hazards. Some fire ignitions result from these types of special unprotected faults. To highlight the local incident energy in case of fault, this paper introduces the parameters steady and transient current densities that assist in analyzing these fault events. Efficient protection can be achieved by the integration of active and passive techniques: adopting arc-fault circuit interrupters or detection devices, recognizing arcing faults, and wiring circuits with a grounding protection conductor to involve the ground in every fault that, in ac systems, is rapidly protected by residual current PDs (or ground-fault PDs). At this aim, the use of special cables, namely, ground-fault-forced cables, is recommended, particularly for cords and extension cords also supplying Class II equipment. The dc system protection requires special care.

Arc-Fault Protection of Branch Circuits, Cords, and Connected Equipment

In electrical power systems, the fault frequently involves arcing and burning of wiring exposed to mechanical damage and other insulation stresses including wiring not fixed and connected by flexible cords and cables. IEC Standard 60364 ends the design of electric power systems at the outlets of branch circuits or at the fixed equipment. A complete design should include the connections of portable equipment and of extension cords (as requested by NFPA 70) that are exposed to arc faults and may cause fire and/or electric shock hazards. Since cords supplying Class II equipment are without a grounding protection conductor, the failure of the double insulation, caused by external damage, is unlikely to be easily detected as a ground fault. Protection must be provided to prevent the fault from extinguishing itself without being detected and remaining energized, thus presenting an electric shock hazard by direct contact with a live part, rendered accessible after local insulation failure. The authors highlight this worst case and suggest the protection achieved by wiring the circuits, particularly extension cords, with special power cables. Ground-fault forced cables (GFFCs) convert a line-to-line fault into a line-to-ground fault, that will be detected and protected by ordinary ground-fault protective devices. By adopting the GFFC type of cables internally to Class II equipment, the disconnecting protection could also be extended to equipment.

Trends and Practices in Grounding and Ground Fault Protection Using Static Devices

Grounded and ungrounded systems are in general use in both commercial and industrial distribution systems. Proponents of each type of system have established valid points to defend their position. This paper briefly identifies the types of systems in use in each category and lists some of the main advantages and disadvantages of each. With the advent of higher voltage levels in our low-voltage distribution systems and the trend towards solidly grounded systems, problems resulting from the lack of proper ground fault protective devices have caused some severe equipment burndowns. The need for adequate protection has been recognized by the 1971 National Electric Code. This recognition is being complemented by Underwriters' Laboratories with the introduction of appropriate standards. With the passing of the Occupational Safety and Health Act of 1970, more emphasis than ever before will be placed on adherence to the preceding code and standards. This paper will review the various methods of detecting ground faults using static devices and describe some of the equipment available for these applications.