Modeling Features of a Single Phase-to-Earth Fault in a Medium Voltage Overhead Transmission Line

The modeling and calculation of a single phase-to-earth fault of 6 to 35 kV have specific features when compared with circuits with higher nominal voltages. In this paper, a mathematical analysis and modeling of a 3-phase overhead transmission line with distributed parameters consisting of several nominal T-shaped, 3-phase links with concentrated parameters replaced by 1 nominal T-shaped link were carried out. Further analysis showed that not accounting for the distributed nature of the line parameters did not cause significant errors in the assessment of the maximum overvoltage in the arc suppression in single phase-to-earth faults, and that sufficient accuracy insures the representation of the line by only 1 nominal T-shaped, 3-phase link. Such a modeling technique makes it impossible to identify the location of single-phase faults, which is the property of higher harmonic amplification of individual frequencies. Chain equivalent schemas with constant parameters are valid for a single frequency, thereby providing an opportunity to study the nature of the wave process by the discrete selection of parameters. Next in the mathematical representation, we consider the overhead transmission lines as lines with distributed parameters

Selective complex single-phase earth fault protection for distribution medium-voltage networks

This article deals with selective protection against single-phase earth faults at 6 – 10 kV electrical networks. Different kinds of earth faults, factors influencing the implementation of protection, various principles of protection implementation, are described. Requirements and structure of complex protection applicable to networks with any neutral grounding mode and providing separation of various kinds of earth faults are given in this text

Modeling and Protection Scheme for IEEE 34 Radial Distribution Feeder with and Without Distributed Generation

The existing power system was not designed with distribution generation (DG) in mind. As DG penetration is being considered by many distribution utilities, there is a rising need to address many incompatibility issues which puts a big emphasis on the need to review and implement suitable protection scheme. The usual practice for existing distribution feeders is the Overcurrent scheme which includes coordination between fuses and reclosers. But when DG is added to the distribution feeder, the configuration is no more radial as there is contribution of fault currents from the DG\u27s and if the existing protection scheme is applied then this could lead to various issues like fuse misoperation or nuisance tripping considering temporary and permanent fault conditions. This thesis presents a study on the modeling of existing IEEE 34 radial distribution feeder and scaling of the system from 24.9kV to 12.47kV keeping in mind the existing conditions and also proposes a protection scheme with and without the addition of DG\u27s to the feeder nodes. The protection scheme involves providing appropriate relaying with suitable fuse selection and Current transformer settings. Considerations for proper transformer grounding and capacitor bank fusing protection is also simulated and reviewed. When DG\u27s added, the results show increase in fault contribution and hence causing misoperations which needs to avoided. Relaying considerations are also provided when an islanded mode occurs. The entire analysis has been simulated by a combination of various tools like Aspen One liner, CYMDist and Wavewin with occasional simulations and calculations performed in MATLAB environment

Protection and Disturbance Mitigation of Next Generation Shipboard Power Systems

Today, thanks to modern advances mainly in the power electronics field, megawatt-level electric drives and magnetic levitation are being integrated into the marine power grids. These technologies operate based on Direct Current (DC) power which require Alternating Current (AC) to DC conversion within the current grid. Medium-voltage Direct Current (MVDC) and Flywheel Energy Storage Systems (FESS) are the next state-of-the-art technologies that researchers are leaning on to produce, convert, store, and distribute power with improved power quality, reliability, and flexibility. On the other hand, with the extensive integration of high-frequency power electronic converters, system stability analysis and the true system dynamic behaviors assessment following grid disturbances have become a serious concern for system control designs and protection. This dissertation first explores emerging shipboard power distribution topologies such as MVDC networks and FESS operation with charge and discharge dynamics. Furthermore, the important topic of how these systems perform in dynamic conditions with pulsed power load, faults, arc fault and system protection are studied. Secondly, a communication-based fault detection and isolation system controller that improves upon a directional AC overcurrent relay protection system is proposed offering additional protection discrimination between faults and pulsed-power Load (PPL) in MVDC systems. The controller is designed to segregate between system dynamic short-circuit fault and bus current disturbances due to a PPL. Finally, to validate the effectiveness of the proposed protection controller, different bus current disturbances are simulated within a time-domain electromagnetic transient simulation of a shipboard power system including a PPL system operating with different ramp rate profiles, pulse widths, peak powers, and fault locations. This overarching goal of this work is to address some of the critical issues facing the US Navy as warfighter mission requirements increase exponentially and move towards advanced and sophisticated pulsed power load devices such as high energy weapon systems, high energy sensor and radar systems. The analyses and proposed solutions in this dissertation support current shipbuilding industry priorities to improve shipboard power system reliability and de-risk the integration of new power system technologies for next generation naval vessels

Information Parameters of Electrical Quantities of the Transient for Determining the Single-Phase Earth Fault Location in Сable Medium-Voltage Systems

Rapid fault determination of single-phase earth fault (SPEF) and SPEF location on the line are extremely important for the speedy elimination of damage and restoring normal operation of the power supply. Effective methods of SPEF determination on the cable lines under voltage do not still exist in medium voltage networks. The electrical values of the transition process that occurs during the breakdown of the insulation can be used for solving the problem of determining the place of single-phase including self-eliminating faults. The best method to study the electromagnetic transients at SPEF in medium-voltage networks and to identify the information parameters, which can be used for distant SPEF determination, is a combination of analytical methods on the basis of simplified models of the electrical networks and the method of computer simulation

Continuous Monitoring of Neutral Grounding Resistors and Reactors

Electrical power system components are designed three-phase balanced and symmetric with the internal connection of wye or delta. The common point of the wye-connected equipment, which is called neutral, is impedance grounded for many reasons such as fault ride through by controlling transient overvoltages, and limiting the ground overcurrents. Depending on the application, different neutral impedance grounding methods exist that employ resistors or reactors with/without neutral grounding transformers. These apparatuses are known as Neutral Grounding Devices (NGD). The most well-known sort of NGDsarethe Neutral Grounding Resistor (NGR) and Neutral Grounding Reactor (NGL) which are the main focus of this research work. As said, NGDs provide many benefits; however, they fail due to many reasons such as corrosion, lightning, and extended service life. Upon this failure, the advantages of impedance grounding are replaced by disadvantages of the ungrounded or solidly grounded traditional systems. Consequences of such a failure are the false sense of security, ungrounded system, transient overvoltages, overcurrents, line-to-ground voltage test non-safety, and so on. In order to prevent these issues, the intactness and integrity of the neutral-to-ground circuit shall be ensured. However, this cannot be done easily since the neutral-to-ground circuit is dead or de-energized during the steady-state condition. However, there has to be a continuous and online monitor, which without it there is no guarantee or indication that these apparatuses have failed. That is why the Canadian Electric Code (CEC) mandates monitoring of the neutral-to-ground circuit in industrial and commercial networks. Accordingly, this research work first reviews the existing monitoring methods to understand the fundamentals, and performance of these techniques. The performed literature survey results in a conceptual classification of the existing methods into three categories called passive, active, and passive-active. This part of the carried-out research highlights the advantages and disadvantages of the methods on one hand, and the evolution trend of the methods on the other. It also reveals that all of the existing methods suffer from one shared issue which is the hard-to-achieve continuous monitoring. In fact, they cannot provide continuous or uninterrupted operation in all system conditions, i.e., normal, faulted, and de-energized. It is this major shortcoming of the literature which motivates towards making a difference. Therefore, the mission is to resolve this issue relying on the existing measurement instruments and protection installations. As the results, three new or enhanced methods are achieved. The first technique is a cost-effective combination of two existing techniques resulted in a better performance. The performance of this proposed method is comprehensively studied using software analysis, and a fabricated prototype of the invented mechanism for full-range neutral voltage measurement. The resulted method provides reliable monitoring during both faulted and unfaulted conditions of the power system which is the most prominent advantage of the proposed technique since none of the existing methods, with the same measurements, provide the such a performance. The second proposed technique is an economical solution that employs the third harmonic of neutral and residual voltages for monitoring the NGR installed at the neutral of the unit-connected generators. The proposed technique is comprehensively studied including further hardware validations using an available industrial generator protective relay. The required measurement instruments and protection infrastructures are readily available which means that the proposed method could be implemented with no additional cost. In fact, the proposed method could be easily incorporated into the core of the existing digital protective relays. Lastly, the third technique employs an existing sub-harmonic injection based generator stator ground protection for monitoring the neutral-to-ground circuit of the same generator, which is equipped with either the neutral grounding resistor or neutral grounding reactor. This alternative is also a money-saving solution since it only demands a current sensor to measure the injected current. It is also easily retrofitted to installed digital protective relays. The other advantage of this proposed method is its functionality in de-energized condition of the power system besides its reliable performance in both faulted and unfaulted operation conditions. It is this one last accomplishment that brings the mission to completion

Protection Scheme based on Artificial Neural Network for Fault Detection and Classification in Low Voltage PV-Based DC Microgrid

With the expansion of the DC distribution market, protection, and operational concerns for Direct Current (DC) Microgrids have increased. Different systems have been investigated for detecting, finding, and isolating defects utilising a variety of protective mechanisms. It might be difficult to locate high-resistance faults and shorted DC faults on low-voltage DC (LVDC) microgrids. Therefore, in this study, a Field Transform Technique like Short-Time Fourier Transform (STFT) is proposed for detecting the Fault Current (FC). This method detects the faults Pole-ground (PG), pole-pole (PP), and Arc fault are the major fault types in the DC network with PG fault as the most common and less severe. One of the difficulties the DC system faces in the incidence of a malfunction is the protection of essential converters. During this fault, the diodes, being the most vulnerable component of the system, may encounter a substantial surge in current, which can potentially cause damage if the current surpasses double their specified capacity for withstanding. After the Fault detection (FD), a Taguchi-based ANN is presented to classify the detected faults. This method effectively classifies PV-based faults. Then, to safeguard the FC, the Improved Self-Adaptive Solid State Circuit Breaker (I-SSCB) is introduced. It safeguards the FC in the low-voltage PV-based DC microgrid (DCMG) and restricts FC in the DCMG. The suggested approach is evaluated using the Matlab software and the proposed method produces 400A current and 100 KW power during the PV temperature of 25°C. The output current of the ANN is then 1A for a duration of 0.3 to 0.4 seconds. The fault voltage and FC produced in this proposed work are 1900V and 1950A. Therefore, the proposed work's current and voltage values are 21 KV and 0.35 I. Therefore, the proposed method produces more power and limits the FC in the LV-DCMG. In future studies, the improved or modified neural network or machine learning (ML)-based techniques can be utilized which may improve the protection scheme of the work

Transient Control of Synchronous Machine Active and Reactive Power in Micro-Grid Power Systems

There are two main topics associated with this dissertation. The first is to investigate phase–to–neutral fault current magnitude occurring in generators with multiple zero–sequence current sources. The second is to design, model, and tune a linear control system for oper- ating a micro–grid in the event of a separation from the electric power system. In the former case, detailed generator, AC8B excitation system, and four–wire electric power system models are constructed. Where available, manufacturers data is used to validate the generator and exciter models. A gain–delay with frequency droop control is used to model an internal combustion engine and governor. The four wire system is connected through a transformer impedance to an infinite bus. Phase–to–neutral faults are imposed on the system, and fault magnitudes analyzed against three–phase faults to gauge their severity. In the latter case, a balanced three–phase system is assumed. The model structure from the former case – but using data for a different generator – is incorporated with a model for an energy storage device and a net load model to form a micro–grid. The primary control model for the energy storage device has a high level of detail, as does the energy storage device plant model in describing the LC filter and transformer. A gain–delay battery and inverter model is used at the front end. The net load model is intended to be the difference between renewable energy sources and load within a micro–grid system that has separated from the grid. Given the variability of iiboth renewable generation and load, frequency and voltage stability are not guaranteed. This work is an attempt to model components of a proposed micro–grid system at the University of Wisconsin Milwaukee, and design, model, and tune a linear control system for operation in the event of a separation from the electric power system. The control module is responsible for management of frequency and active power, and voltage and reactive power. The scope of this work is to ❼ develop a mathematical model for a salient pole, 2 damper winding synchronous generator with d axis saturation suitable for transient analysis, ❼ develop a mathematical model for a voltage regulator and excitation system using the IEEE AC8B voltage regulator and excitation system template, ❼ develop mathematical models for an energy storage primary control system, LC filter and transformer suitable for transient analysis, ❼ combine the generator and energy storage models in a micro–grid context, ❼ develop mathematical models for electric system components in the stationary abc frame and rotating dq reference frame, ❼ develop a secondary control network for dispatch of micro–grid assets, ❼ establish micro–grid limits of stable operation for step changes in load and power commands based on simulations of model data assuming net load on the micro–grid, and ❼ use generator and electric system models to assess the generator current magnitude during phase–to–ground faults