525 research outputs found

    Continuous Monitoring of Neutral Grounding Resistors and Reactors

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    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

    Real time digital simulation and testing of generator protection elements.

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    Masters Degree, University of KwaZulu-Natal, Durban.Power system protection is designed to identify and isolate the system from any type of fault or abnormal condition which may endanger the equipment and operation of the system as a whole. Ground faults are the most common types of faults in generators and can damage the stator winding severely. Stator winding protection therefore becomes one of the crucial protection functions in generator protection. The grounding method used plays an imperative role in determining which protection functions are to be employed on the generator. This thesis reviews different types of stator winding faults that occur for a generator and how the generator is protected against these faults using different types of protection system. It also presents how the different types of generator grounding affect generator protection schemes, focusing on high and low impedance grounding. The development of real time digital simulators has greatly improved the simulation and testing of protection studies. In the past, mathematical models were not fully compatible for the representation of the complete synchronous generator stator. The Real Time Digital Simulator (RTDS) has developed a synchronous generator phase domain model which allows for simulation of generator stator internal faults. This thesis illustrates the suitability of the third harmonic voltage protection scheme against stator internal faults. An overview of abnormal conditions that occur on a generator was also reviewed, how they affect the generator and their protection systems. The thesis focused on reverse power, over-excitation, and differential and current unbalance protection. The loss of field excitation in synchronous generators also largely contributes to voltage instability. The large consumption of reactive power and rapid changes in the system components leads to severe damage of the generator and jeopardizes system stability. This thesis looks into loss of field excitation events and how their impacts can be reduced by using the R-X protection scheme. It also illustrates results based on closed loop testing conducted using hardware generator protection relay and the models developed on the RTDS. The simulation and testing of generator protection functions were proved to be theoretically and practically correct which could be used as a guideline for improvements in protection studies

    Efficacy of Smart PV Inverter as a Strategic Mitigator of Network Harmonic Resonance and a Suppressor of Temporary Overvoltage Phenomenon in Distribution Systems

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    The research work explores the design of Smart PV inverters in terms of modelling and investigates the efficacy of a Smart PV inverter as a strategic mitigator of network harmonic resonance phenomenon and a suppressor of Temporary Overvoltage (TOV) in distribution systems. The new application and the control strategy of Smart PV inverters can also be extended to SmartPark-Plug in Electric Vehicles as the grid becomes smarter. As the grid is becoming smarter, more challenges are encountered with the integration of PV plants in distribution systems. Smart PV inverters nowadays are equipped with specialized controllers for exchanging reactive power with the grid based on the available capacity of the inverter, after the real power generation. Although present investigators are researching on several applications of Smart PV inverters, none of the research-work in real time and in documentation have addressed the benefits of employing Smart PV inverters to mitigate network resonances. U.S based standard IEEE 519 for power quality describes the network resonance as a major contributor that has an impact on the harmonic levels. This dissertation proposes a new application for the first time in utilizing a Smart PV inverter to act as a virtual detuner in mitigating network resonance. As a part of the Smart PV inverter design, the LCL filter plays a vital role on network harmonic resonance and further has a direct impact on the stability of the controller and rest of the distribution system. Temporary Overvoltage (TOV) phenomenon is more pronounced especially during unbalanced faults like single line to ground faults (SLGF) in the presence of PV. Such an abnormal incident can damage the customer loads. IEEE 142-“Effective grounding” technique is employed to design the grounding scheme for synchronous based generators. The utilities have been trying to make a PV system comply with IEEE 142 standard as well. Several utilities are still employing the same grounding schemes even now. The attempt has resulted in diminishing the efficacy of protection schemes. Further, millions of dollars and power has been wasted by the utilities. As a result, the concept of effective grounding for PV system has become a challenge when utilities try to mitigate TOV. With an intention of economical aspects in distribution systems planning, this dissertation also proposes a new application and a novel control scheme for utilizing Smart PV/Smart Park inverters to mitigate TOV in distribution systems for the first time. In other words, this novel application can serve as an effective and supporting schema towards ineffective grounding systems. PSCAD/EMTDC has been used throughout the course of research. The idea of Smart inverters serving as a virtual detuner in mitigating network harmonic resonance and as a TOV suppressor in distribution systems has been devised based on the basic principle of VAR injection and absorption with a new control strategy respectively. This research would further serve as a pioneering approach for researchers and planning engineers working in distribution systems

    Review on power quality solution technology

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    This paper presents a comprehensive study of various possible solutions for power quality improvement in common applications and supply system. This includes improved power quality converters (IPQC), multi-pulse converters, active compensation, passive compensation and their hybrid configurations. Various configurations and topologies of custom power devices such as DSTATCOM (Distribution Static Compensator), DVR (Dynamic Voltage Restorer) and UPQC (Unified Power Quality Compensator) are also described in detail. Main applications of these devices are for reactive power compensation, harmonic elimination, voltage sag/swell mitigation, voltage regulation, load balancing, neutral current reduction etc. Many such cases of power quality problems have been taken up and suitable solutions have been identified for those cases. As an example, a model of DSTATCOM is developed and its performance is presented for a distribution system feeding nonlinear loads

    Digital generator protection

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    Imperial Users onl

    Hybrid Smart Transformer for Enhanced Power System Protection Against DC With Advanced Grid Support

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    The traditional grid is rapidly transforming into smart substations and grid assets incorporating advanced control equipment with enhanced functionalities and rapid self-healing features. The most important and strategic equipment in the substation is the transformer and is expected to perform a variety of functions beyond mere voltage conversion and isolation. While the concept of smart solid-state transformers (SSTs) is being widely recognized, their respective lifetime and reliability raise concerns, thus hampering the complete replacement of traditional transformers with SSTs. Under this scenario, introducing smart features in conventional transformers utilizing simple, cost-effective, and easy to install modules is a highly desired and logical solution. This dissertation is focused on the design and evaluation of a power electronics-based module integrated between the neutral of power transformers and substation ground. The proposed module transforms conventional transformers into hybrid smart transformers (HST). The HST enhances power system protection against DC flow in grid that could result from solar storms, high-elevation nuclear explosions, monopolar or ground return mode (GRM) operation of high-voltage direct current (HVDC) transmission and non-ideal switching in inverter-based resources (IBRs). The module also introduces a variety of advanced grid-support features in conventional transformers. These include voltage regulation, voltage and impedance balancing, harmonics isolation, power flow control and voltage ride through (VRT) capability for distributed energy resources (DERs) or grid connected IBRs. The dissertation also proposes and evaluates a hybrid bypass switch for HST module and associated transformer protection during high-voltage events at the module output, such as, ground faults, inrush currents, lightning and switching transients. The proposed strategy is evaluated on a scaled hardware prototype utilizing controller hardware-in-the-loop (C-HIL) and power hardware-in-the-loop (P-HIL) techniques. The dissertation also provides guidelines for field implementation and deployment of the proposed HST scheme. The device is proposed as an all-inclusive solution to multiple grid problems as it performs a variety of functions that are currently being performed through separate devices increasing efficiency and justifying its installation

    A Hardware-in-the-Loop Platform for DC Protection

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    With the proliferation of power electronics, dc-based power distribution systems can be realized; however, dc electrical protection remains a significant barrier to mass implementation dc power distribution. Controller Hardware-in-the-loop (CHiL) simulation enables moving up technology readiness levels (TRL) quickly. This work presents an end-to-end solution for dc protection CHiL for early design exploration and verification for dc protection, allowing for the rapid development of dc protection schemes for both Line-to-Line (LL) and Line-to-Ground (LG) faults. The approach combines using Latency Based Linear Multistep Compound (LB-LMC), a real-time simulation method for power electronic, and National Instruments (NI) FPGA hardware to enable dc protection design with CHiL. A case study is performed for a 1.5 MW Voltage Source Rectifier (VSR) under LL and LG faults in an ungrounded system. The deficiency in real-time simulation resolution of Commercial-off-the-Shelf (COTS) for dc fault transients is shown, and addressed by using LB-LMC RT solver inside NI FPGA hardware to achieve 50 ns resolution of dc fault transients

    Development of the Impedance-based Arc-Flash Determination Device (IADD)

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    This thesis entitled, \u27Development of the Impedance based Arc-Fault Determination Device (IADD)\u27 details the development of a testing device that, when attached to an electrical node on the power system and through observations on voltage, current and phase shift with a step load change, determines the effective Thevenin or Norton impedance at the point of test. This thesis includes discussion of the theory and design process that enables the determination of an equivalent circuit, software development using National Instruments\u27 LabView software development package and suggestions for future development. The purpose of this thesis is to produce a device that can accurately and correctly predict the expected bolted fault current at the test location of interest. The importance of accurately measuring phase shift to determine X/R ratio and bolted fault current by the IADD method is examined. Several other factors that effect system impedance, performance of the IADD, and the resultant NFPA arc flash hazard level are explored. The IADD has applications in both industrial/commercial applications and power distribution systems for determining system impedance. These applications are discussed. Several laboratory and field test cases are examined and conclusions are drawn on the performance of the IADD versus other methods of determining fault duty

    Effect of Series Active Voltage Conditioners on Modernized Grid

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    Modernized “Smart” grids incorporate renewable energy sources on a widespread scale. Foreseen expansion in integrating more renewables is driven by global CO₂ emission concerns and depletion of fossil fuels. Active elements/devices are added to smart grids to enhance power availability and quality with the aid of advances in power electronics and communication systems. Active Voltage Conditioner (AVC) represents state-of-the-art in the field of voltage regulation and conditioning, however; integrating it into modernized grids has not been the subject of detailed study yet. This thesis details the AVC-Grid interaction mechanism and associated performance parameters. ABB PCS100 AVC computer model based on MATLAB/PLECS platform is used as a basis for the proposed mathematical model. Accordingly, operational V-I characteristics is derived and impact of equivalent grid stiffness is analyzed. In this thesis, the modeling of AVC has been introduced as seen by the grid in light of MATLAB/PLECS simulations. The conditioning ratio to describe the “depth” of load conditioning had been introduced. Modeling of AVC operational characteristics has been developed and dependency on conditioning ratio and equivalent grid stiffness had been investigated. Also, the analysis of grid behavior due to AVC operation during overvoltages and undervoltages has been carried out as well as discussing the envisaged impact on tied WTG/PV systems. The thesis represents an initial attempt to model the AVC and discusses its envisaged impact on smart grids
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