Neutral Grounding Method Research Articles

Ground fault protection algorithm of active distribution network based on energy extremum direction

AbstractAfter large‐scale distributed power sources are connected to the distribution network, the fault current undergoes noticeable changes, affecting the accuracy of traditional single‐phase grounding fault algorithms. Therefore, the objective of this paper is to address the impact of distributed power integration on the grounding algorithms of distribution networks. The main contribution is: by establishing an electrical system structure and model for distribution network grounding faults that include distributed generation (DG), theoretically deriving and calculating the transient zero‐sequence current frequency changes at the moment of fault, analysing the directional characteristics of zero‐sequence currents under DG connection conditions, designing a local grounding fault judgment algorithm based on energy extremum direction, and providing a fault judgment and isolation process for grounding fault monitoring devices. The results show: through simulation and experimentation, the algorithm was tested, and the method can reliably judge grounding faults under various transition resistances, different numbers and capacities of connected distributed power sources, and different grounding switch‐on angles. The applicability of the algorithm covers both methods of neutral grounding through an arc suppression coil and ungrounded neutrals, adapting to scenarios with or without DG connections.

A novel high‐impedance neutral grounding method for medium‐ or large‐size hydroelectric generators

AbstractAs the capacity of medium or large hydroelectric generators increases, conventional grounding methods face challenges in effectively limiting single‐phase to earth fault current and neutral displacement voltage within acceptable range. Excessive fault current and neutral displacement voltage pose threats to the stability and safety of power generation and transmission systems. Inherent design deficiencies in conventional grounding methods lead to failures in meeting fault current and voltage requirements. To address this, this paper proposes a novel grounding method utilizing high impedance to restrict excessive fault current and neutral displacement voltage. The method minimizes both fault current and neutral displacement voltage by optimally selecting device parameters through minimal iterative trials. Additionally, a novel indicator is introduced to evaluate the effectiveness of grounding method by monitoring changes in neutral displacement voltage. The method is tested through theoretical calculation and field experiments, successfully implemented in large‐size hydroelectric generator.

A New Model for Correcting and Improving the Sequence Networks Method of Single-Phase Earth Fault to Accommodate All Resistance Grounding Systems

The method of sequence networks is still well-known and widely utilized for analyzing and computing unsymmetrical faults in power system networks today, particularly in solid grounding systems where it was initially introduced for short circuit analysis. When it comes to single-phase earth fault that is a dominant majority type of fault in power distribution grids, different neutral grounding methods with varied impedances result in distinct fault characteristics, to continue utilizing sequence networks could cause inaccurate calculations by the reason of neutral voltage during earth fault does not remain as close to zero as it’s pinned in solid grounding system. As neutral resistance increases gradually, the impact of line-to-ground capacitance becomes more pronounced and can no longer be ignored. In this case, applying sequence networks could lead to calculated results that are far from the actual situations in grids. This paper discovers and proves an obscurely hidden defect of the sequence network, while proposing a new and novel modeling to derive comprehensive equations of fault calculations for all types of resistant grounding systems, including solid grounding, low resistance grounding, high resistance grounding, and ungrounded systems.

A Hybrid Flexible Neutral Grounding Mode for Large Generators

Single-phase ground faults frequently occur at the generator stator windings. To realize reliable arc suppression, a dual-frequency active arc-suppression strategy has been widely considered. However, the existing method needs an inverter with large capacity, which is large in volume and high in cost, causing limited engineering application prospects. To reduce the capacity, a novel hybrid flexible neutral grounding method for large generators is proposed in this paper. It combines the dual-frequency active arc-suppression strategy with the arc-suppression coil-grounding mode. Thus, most of the fundamental components in the fault current are compensated by the arc-suppression coil, and the rest are compensated by the active arc-suppression device. The capacity of the inverter can be greatly reduced under the premise of reliably realizing arc suppression. To identify transient and permanent ground faults after arc suppression, the phase-angle relation between the third-harmonic voltage and current variation at the generator neutral point is used to form the fault-type identification criterion. The third-harmonic quantities can avoid the blind area at the neutral point caused by fundamental quantities. Simulation and experimental test results verify the effectiveness of the proposed method.

Power system neutral point grounding

The method used for neutral point grounding is very important for power network operation. There are many ways of grounding, which are used in practice, and the decision on the method of neutral grounding depends on the situation in the network connected to the substation. When deciding on the method of neutral grounding it is necessary to thoroughly consider all the advantages and disadvantages of individual modes of neutral grounding, and then choose the best technical and economical solution. This paper analyzes the ways of neutral point grounding in medium voltage networks used in the current practice in Croatia which are isolated neutral point, low resistance earthing, partial compensation and resonant earthing. The use of shunt circuit-breaker is also described. Additionally, a survey of the relays used for the neutral point grounding system inside the substations was conducted and a brief analysis of the results is presented in the paper.

Flexible Grounding System for Single-Phase to Ground Faults in Distribution Networks: A Systematic Review of Developments

The neutral grounding method is one of the crucial technologies used to ensure the safe and stable operation of distribution networks. With the development of power electronics-based devices, the application of highly controllable inverters to grounding systems has become a new research direction. In this review paper, based on the summary and analysis for the research status, the flexible grounding system is systematically classified according to its control strategy and structure. And then, the following core technologies are summarized: faulted line selection, current component detection, high-resistance ground identification, ground parameter measurement, neutral point voltage control, and fault location. Subsequently, deficiencies of flexible grounding systems are summarized from the following four perspectives: reliability, accuracy, speed, and stability. Finally, some discussions and recommendations for future development and research direction are presented. Especially, the reliability-enhanced hybrid grounding system that combines active inverters and low resistance for high-resistance ground faults is recommended. This paper provides a systematic literature review of the crucial technologies for flexible grounding systems and can be used as a technical reference for future research.

Single-phase disconnection fault location of active distribution network based on negative-sequence differential impedance

Accidents such as overvoltage, personal injury and motor damage caused by singlephase disconnection faults occur frequently in active distribution networks. In response to this problem, firstly, the negative-sequence differential impedance is defined and a protection method based on negative-sequence differential impedance is proposed, the method uses the amplitude of negative-sequence differential impedance as an action quantity and uses its phase to construct an adaptive braking threshold. Secondly, in case of protection failure under overload, the zero-sequence voltage amplitude difference is proposed as an auxiliary criterion, and the influence of different types of distributed generators on the zero-sequence voltage difference on both sides of the fault fracture is analyzed. Finally, it is verified by simulation that the method can be positioned reliably and is not affected by the neutral point grounding method, transition resistance, load and distributed generators.

A Novel Method of Fault Line Selection in Low Current Grounding System using Multi-criteria Information Integrated

Single-phase grounding faults often occur in low-current grounding systems, and the selection of fault lines is an important factor affecting the reliability and safety of the distribution system. Aiming at the problem that the existing line selection criteria may cause misjudgment, this paper makes full use of the changes in the amount of fault information during the occurrence of a fault and proposes a multi-criteria line selection basis that integrates fault information. Since different neutral grounding methods will affect the change of the fault state quantity, the characteristic changes of the fault state quantity under different neutral grounding methods are fully discussed, and different fault quantities are selected as the basis for line selection. In addition, a membership function and a weight coefficient function are respectively set to indicate the possibility and credibility of a single criterion line selection result. The weighted summation of the membership functions corresponding to multiple criteria completes the information integration of multiple criteria, and the formed composite criterion reduces the proportion of misjudgments. The simulation experiment data proves that the proposed method can correctly, effectively, and reliably select faulty lines, greatly reduce the possibility of misjudgment and improve the efficiency and universality of line selection.

Analysis of Fault Characteristics of Distribution Network with PST Loop Closing Device under Small Current Grounding System

With the rapid development of cities and the increasing complexity of distribution network systems, the cableization of transmission lines and the diversification of power users have brought new challenges to the supply reliability of distribution networks. Short-time outages caused by power outages and maintenance are one of the factors that affect the reliability of the power supply in the distribution network. The non-stop load transfer through a phase-shifting transformer (PST) operation can effectively improve the reliability of power supply to complex distribution systems. Considering the operation mode and structure form and fault type of the urban distribution network in China, comparing and analyzing the applicable scenarios of different neutral grounding methods, and based on the structure and zero sequence path characteristics of PST, an improved PST-based phase shifting and grounding transformer loop closing device with low power consumption is proposed. The fault characteristics of the PST-based loop closing device under the small current grounding system are also analyzed by the sequence component method, and, finally, the effectiveness of the phase-shifting and grounding transformer device is verified by simulation under PSCAD/EMTDC for fault routing and protection configuration of the urban distribution network in China.

Measurement Technology of Grounding Capacitance of Distribution Network Based on the Graded Adjustment of Grounding Transformer Winding

The traditional method of measuring grounding capacitance of distribution network is greatly affected by neutral grounding method, and the influence of harmonic elimination resistance and internal impedance of voltage transformer on measurement accuracy cannot be eliminated. Therefore, this paper proposes an accurate way to measure grounding capacitance of the distribution network which is not affected by the neutral point grounding method. It uses a special Y/ Δ-connected grounding transformer with taps connected to the distribution network to change the zero-sequence voltage of the distribution network by adjusting the grounding tap of the high-voltage side winding of the grounding transformer, and obtains the required zero-sequence through measurement voltage and zero sequence current to find the capacitance to ground of the system. The proposed measurement method is analyzed in PSCAD/EMTDC, which shows that the method has high measurement accuracy and is safe, simple and economical for the measurement of ground capacitance current.

Analysis of Single-phase Grounding Fault with Distributed Generation in Distribution Network

Different distributed generation (DG) types and neutral grounding methods affect single-phase ground fault current characteristics of distribution network. To analyse the single-phase ground fault current characteristics, this paper establishes a single-phase ground fault model with rotating and inverter-type DG accessed using symmetrical component method. By considering different grounding methods of distribution bus side and DG side, distribution characteristics and change laws of fault current as well as sequence currents on both sides of fault point when single-phase short circuits occur in different positions of system are discussed. To verify correctness of analysis, simulation experiments of models is carried out by Simulink. The results of this paper can provide reference for system relay protection configuration and neutral grounding method selection.

Визначення оптимального значення опору резистора заземлення нейтралі в мережах 20 кВ

At present, there is an objective need for a solution in the power system of Ukraine problems of improving the principles of construction of network topology by voltage classes and types of performance on based on scientifically sound technical solutions using modern methods and technologies. The article is devoted to the study of the optimal value of the resistance of the neutral grounding resistor in 20 kV networks. Distribution electric networks of Ukraine with a voltage of 6 (10) kV are included in the final link systems of providing consumers with electric energy. They are in direct interaction both with the consumer, and regional and main electric networks. Therefore, the state and the operation of 6 (10) kV electrical distribution networks has a significant impact on performance reliability, quality and efficiency of the integrated power system of Ukraine. Transition from voltage level 6 (10) kV on 20 kV is an actual and priority step to increase the efficiency of operation distribution network and a significant reduction in electricity losses. The paper presents the types of resistors and options for their installation in the neutral voltage network 20 kV. The relationship between the resistance of the neutral grounding resistor and the single-phase current is established short circuit, which directly affects the types of relay protections, as well as their number. Simulation of the 20 kV network operation mode was performed, based on the results of which the optimal one was chosen the value of the resistance of the neutral grounding resistor in the presented network, which is achieved sufficient sensitivity of relay protection devices at the lowest short-circuit current. This one was chosen for the study neutral grounding method, because resistive grounding has the following advantages: no arcs high-frequency overvoltages and multiple damages in the network; no need to disconnect the first single-phase earth fault; reducing the likelihood of impressions of staff and outsiders at single-phase short circuit; almost complete exclusion of the possibility of transition of single-phase circuit to ground in multiphase; simple implementation of sensitive and selective relay protection single-phase ground fault.

Overvoltage Analysis during Earth Fault for Different Treatment of Neutral Point in Distribution Network

Abstract The paper consists of three parts. In the introduction and the first part of this paper are given basic theoretical considerations on possible ways for treatment of the neutral point in distribution grids with special reference to the method of neutral grounding of distribution transformers through a low ohmic resistor and a compensation coil. The second part gives the use analysis of a low ohmic resistor and a compensation coil as the future choice of neutral point grounding on the particular distribution grid powered by a substation TS 35/10 kV. In the third part of the paper, the results were obtained using an adequate dynamic distribution model, using the EMTP-ATP software package. Also, in this part, calculations are made for neutral grounding through a low ohmic resistor, a compensation coil, as well as in the case of isolated grids, and a comparison of the obtained values of the overvoltage coefficients.

Electrical Safety Analysis in the Presence of Resonant Grounding Neutral

The resonant grounding is one of the possible methods of the system neutral grounding for the medium voltage distribution. IEEE standards do define this grounding configuration, but important advantages and drawbacks of the resonant grounding might not be fully known, due to its rather uncommon application in North America. On the other hand, resonant grounding in Europe is imposed by the increased requirements for power quality, especially for medium-voltage (MV) industrial users, imposed to electric utilities by regulatory authorities, with the purpose to protect the interests of users and consumers. Level of the continuity of the service, magnitude and phase of ground-fault currents, magnitude of touch voltages, all depend on how the neutral is connected to ground. In this paper, the authors will discuss electrical safety features of the resonant ground, and analyze issues when a substation, originally operated with different methods of system neutral grounding, is reconfigured with a resonant ground. In particular, a conservative approach for preserving safety during high-voltage (HV)-MV substations’ reconfiguration is herein proposed; the cases of the substation reconfiguration from resonant grounding to isolated-from-ground and vice versa shall be analyzed. Finally, the analysis of the impact of the use of Petersen coil on the global grounding systems will be provided.

Перенапряжения от однофазных замыканий в сетях номинального напряжения 110 кВ

Overvoltages induced by single-phase ground faults in 110 kV networks operating in different neutral grounding modes are investigated. Owing to low values of resistance and high values of inductive and capacitive reactances, the transients in power lines and transformers that occur in 110 kV networks differ essentially from similar processes in 6 to 35 kV networks. This difference results in that the transient overvoltage free components have higher amplitudes, and that they have lower attenuation coefficients. It has been established that 110 kV networks cannot operate with the isolated neutral, because the overvoltage in this case may exceed seven times the nominal phase voltage, which would greatly complicate the transformer winding phase insulation. The use of a neutral grounded through resistance or inductive reactance with a value equal to the zero-sequence impedance of the considered circuit significantly reduces the level of ground fault currents and especially overvoltage. Neutral grounding through resistance leads to more efficient results, because the overvoltages and ground fault current have in this case fairly low values. Neutral grounding through inductive reactance results in somewhat higher overvoltage and ground fault current values. If the neutral is grounded through a nonlinear inductance, the overvoltages have still lower values, but the ground fault current approaches the value of the short-circuit current as in the case of the solidly grounded neutral. Comparison of the relevant results relating to various grounding methods of 110 kV networks has shown that the best results are obtained in case of using the neutral grounded through resistance with the value equal to the zero-sequence impedance of the considered network circuit. In this case, the overvoltage levels in the phases do not exceed 1.78 of the phase voltage value, and the ground fault current is much less than the short-circuit current in case of using the solidly grounded neutral. However, in choosing the neutral grounding method, it should be constantly borne in mind what particular task has to be solved: to limit the short-circuit current or to limit overvoltages. In the second case, the use of the neutral grounded through a fast-saturating reactor is a more acceptable choice.

Modelling and analysis of delta-connected distribution transformers with symmetrical neutral-grounding structure for microgrid networks

The conventional grounding methods for the delta-connected secondary windings, such as corner grounding and mid-tap grounding, result in unbalanced phase-to-ground voltages. To overcome this issue, the neutral-grounding method can be employed, but when it operates under unbalanced load conditions, the neutral current flowing through the grounding winding may cause overheating and failures. We then propose a symmetrical method for the grounding of three-phase transformer windings, based on neutral grounding of the delta-connected configuration that can help to distribute the neutral currents. In addition, the proposed method provides a multi-voltage solution relevant for microgrid networks, reduces the costs, and makes it more convenient for planning and design. We formulate the mathematical model of a three-phase neutral-grounded transformer bank with three grounding windings based on the nodal admittance matrices and the coupling-free equivalent circuits. A function block of the equivalent circuit of the model is implemented in MATLAB/Simulink and is verified by field testing. The proposed method can provide a reference for engineers for the design and operation of microgrid networks.

Ground-Fault Characteristic Analysis of Grid-Connected Photovoltaic Stations with Neutral Grounding Resistance

A centralized grid-connected photovoltaic (PV) station is a widely adopted method of neutral grounding using resistance, which can potentially make pre-existing protection systems invalid and threaten the safety of power grids. Therefore, studying the fault characteristics of grid-connected PV systems and their impact on power-grid protection is of great importance. Based on an analysis of the grid structure of a grid-connected PV system and of the low-voltage ride-through control characteristics of a photovoltaic power supply, this paper proposes a short-circuit calculation model and a fault-calculation method for this kind of system. With respect to the change of system parameters, particularly the resistance connected to the neutral point, and the possible impact on protective actions, this paper achieves the general rule of short-circuit current characteristics through a simulation, which provides a reference for devising protection configurations.

A Novel Neutral Electromagnetic Hybrid Flexible Grounding Method in Distribution Networks

This paper proposes a flexible neutral grounding method based on electromagnetic hybrid Petersen coil (EHPC), which consists of a magnetically controlled reactor and an active power compensator (APC). Under normal conditions, the system's neutral point grounds through a reactor of high reactance. When a single line-to-earth fault occurs, the EHPC can be controlled flexibly to suppress the recovery voltage of faulty phase and to reduce the ground-fault current to almost zero. This paper expounds the two operating modes and corresponding characteristics, the measuring method of insulation parameters of the system (mainly including capacitance to earth and leakage resistance), and the full compensation principle for arc suppression based on the equivalent negative impedance of EHPC. This paper also proposes a compound control method of neutral-to-earth impedance based on neutral-point displacement voltage and a compensating method for the harmonic component of the ground-fault current. Compared to traditional grounding methods, this method can be fast and reliably make the residual current approach almost zero without arc reignition while greatly reducing the output capacity of APC and, thus, decreasing the cost of this device. Simulations and experiments verify the correctness of this measuring method and feasibility of this flexible grounding control strategy.

Investigation of Earth Fault Characteristics Under Different Neutral Grounding Methods

Medium voltage (MV) distribution systems use different methods for grounding the neutral point. Influences of these grounding methods on the single line to ground (SLG) fault characteristics are discussed in this paper. Jordanian MV network is used as a case study. The network has both underground cables and overhead lines. Simulation models are implemented in both MATLAB®/SIMULINK® and DigSilent/Power Factory®softwares. The models allow detailed investigation of the different fault factors and grounding methods. Results are obtained to evaluate the impact of each grounding method on the SLG fault features. Isolated neutral, solid grounding, resistance grounding and Petersen coil (Arc suppression coil) grounding are compared for different fault locations, fault incidence angles, and fault resistances. Current and voltage waveforms, as well as symmetrical components are used to describe the fault case.

The Choice of 10 kV Neutral Point Operation Mode in Fushun Grid

This paper discusses that the capacitive current is a must of producing arc grounding overvoltage, and the method and necessary to restrain arc grounding over voltage. It also explains the concept of capacitive current and arc suppression coil, and the test method and significance of measuring capacitive current. Based on the comprehensive field test and evaluation of 29 substations, it provides the correct selection of neutral point operation mode and gives a development direction to 10 kV power network neutral point grounding method of Fushun grid.