Impact of distributed PV generation on relay coordination and power quality

Distributed generation (DG) has gained popularity among electricity end users who are determined to contribute to a cleaner environment by conforming to green and sustainable energy sources for various daily needs. The power system impact of such trends (e.g. roof-top solar-PV) need thorough investigation, such as impact on fault current levels on the distribution network. Varying fault current levels could adversely affect the operation of protection relays, which may lead to localized blackouts. Therefore, it is imperative to avoid localised blackouts due to mal-operation of protective relays under high penetration of DGs in distribution network. The focus of this research is to study the importance and implications of protective relays and over-current protection in the presence of distributed generation; where the impact of distributed generation on distribution network is identified. Relay coordination is observed to determine their operation characteristics to avoid mal-operation with the presence of DGs (e.g. solar-PV). This paper uses the UK generic distribution network model to simulate different scenarios in DIgSILENT Power Factory. The resulting power quality measures, such as voltage levels, short-circuit current levels and frequency are presented and discussed in the paper. The research highlights that small-scale DG penetration allows for existing protection infrastructure to continue operation and expensive upgrades for overall network are not required as fault levels remain the same

Analisa Dampak Penambahan Distributed Generation Terhadap Sistem Proteksi Penyulang Gondang Rejo 4

Abstract Protection system is a safety for electrical equipment, environment and system caused by technical problems, natural disruptions and operating errors. Distribution system have protective equipment that aims to maintain reliability. Protection coordination aims to secure the distribution system from distribances both inter phase interferences and ground phase interruptions. Protection coordination is a protection zone, which is the area that is protected by each protection equipment installed in the distribution system. This study analyzes protection system on 20 kV network due to the additional Disributed Generation (DG) by modeling it into ETAP ( Electrical Transient Analysis Program). Then enter data that has been obtained from PT PLN (persero) UP3 Surakarta and PLTSa Putri Cempo into software ETAP. Method is done by comparing the point before adding Distributed Generation (DG) and after adding Distributed Generation (DG). Simulation result show effect of Distributed Generation (DG) on the protection system on 20 kV network will not interfere with the coordination of protection in the feeder Gondang Rejo 4. Keyword : Short circuit current, Distributed Generation (DG), ETAP, Protection Syste

Impact of hybrid distributed generation allocation on short circuit currents

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonThe rapid development in renewable generation technologies and flexible distribution networks requires current infrastructure to be modified and developed to adapt high penetration levels of distributed generation. Existing distribution networks were not initially designed and anticipated to accommodate generators on large scale. Short circuit studies ensure the effectiveness of protection equipment settings and coordination is maintained in case of short circuit, despite any additional distributed generation is connected to the distribution network. This research aims to study and compare the different network fault situations for wind energy systems with induction generators, photovoltaic energy systems, and diesel generators connected to distribution networks. The simulation study will be conducted on the existing IEEE case study systems including 13 bus and 30 bus distribution test systems, using ETAP software. Short circuit analysis will be performed twice to include the ANSI/IEEE and the IEC methods for short circuit currents calculation. Simulated results showed that the wind energy systems have significant impact on the short circuit currents, whereas the photovoltaic energy systems are found to have inconsequential effect. The most moderate solution is found to be a distributed generation mix

Real-time modelling and simulation of distribution system protection with and without renewable distribution generation.

Master of Science in Electrical Engineering. University of KwaZulu-Natal. Durban, 2017.The conventional radial power distribution systems were initially not designed to accommodate distribution generation (DG). As DG penetration is being considered by many distribution utilities, there is a rising need to address many incompatibility issues that put a big emphasis on the need to review and implement suitable protection schemes. For a significant greenhouse gas reduction using photovoltaic systems, numerous generators ought to be embedded in the distribution system. For an effective penetration of PV systems on a large-scale into the current distribution network, considerable work to investigate the nature of incompatibility problems has been done and research is being carried out to develop successful integration strategies. The main objectives of the thesis are; to model and simulate a distribution system protection scheme, to study radial networks’ protection system challenges after embedding distributed generation sources, investigation on the impacts of high PV penetrations on protection systems of distribution networks and lastly make modification recommendations and essential review process of existing protection equipment settings. To accomplish the above-mentioned objectives, a radial distribution network is modelled, simulated and protection settings validated. The PV generation system is designed and added to specific distribution feeders and steady steady-state results obtained. The results show that addition of DGs cause the system to lose its radial power flow. There is an increase in fault contribution hence causing maloperation such as protection coordination mismatch. An overall protection scheme is then proposed based on the addition of DG’s and an efficient adaptive protection system for the distribution networks with a considerable penetration of dispersed generations implemented. The impact study is performed which is compared with the existing protection scheme and necessary modifications done. The entire analysis is simulated on a real-time digital simulator (RTDS) and results displayed in a MATLAB environment. For the islanded mode, relaying considerations are provided and implementation of anti-islanding techniques achieved

Fault location with DGs in radial distribution system using radial basis function neural network

Increasing penetration of Renewable Energy in energy market will contribute to increasing number of distributed generation (DG) existence in the grid, thus leading to conflict in fault location, detection and protection coordination in distribution system. This study is focuses on single-line-to-ground (LG) fault detection in a radial distribution system. The objective of this study is to estimate fault location in a radial distribution system in the presence of DGs by using Radial Basis Function Neural Network (RBFNN), with consideration to minimize monitor placement in system. Fault location has been estimated in term of faulty bus. Two types of radial distribution network with DGs have been tested in this study; 10 bus and 34 bus network. Fault analysis has been performed using Power World simulator and data generated has been applied for RBFNN development via MATLAB. RBFNN performance was then evaluated statistically, by SSE, R2 and RMSE. The proposed RBFNN has been able to accurately predict current magnitude at unmonitored buses by only few provided monitored buses readings. With accurate predicted results by the neural network, pattern of current magnitude during fault has been observed in order to identify faulty buses. It was shown in this study that faulty bus can be identified 100% using the proposed approach

MITIGATION OF MICROGRID INTERACTIONS ON PROTECTION SYSTEMS IN UTILITY NETWORKS

This thesis presents novel schemes and techniques to overcome the difficulties associated with the integration of distributed generation (DG) and microgrids in the context of existing short circuit characteristics and protection infrastructure adequacy. One such inadequacy is associated with the loss of coordination (LOC) in existing protection infrastructure, with disruption to an expected sequence between utility reclosers and fuses. This thesis aims to offer solutions to these issues, allowing for DG sources and microgrids to be integrated into utility distribution networks without significant effect on existing protection infrastructure. The integration of DG units into radial distribution networks can result in LOC between upstream reclosers and downstream fuses. To overcome this issue a novel reclosing scheme is proposed whereby a control unit, variable load bank and dedicated recloser are integrated at the point of common coupling (PCC) between the DG unit and the network. This scheme works by receiving a control signal from the distribution network head-end recloser via a communication channel to signal the detection of a fault. Post fault detection, in conjunction with the DG current exceeding pre-specified pick up levels, the control unit disconnects the DG unit from the network to a transfer impedance. This transfer allows the DG unit to continue to supply the transfer impedance at the pre-fault load sharing condition, without the requirement for a shut down. This causes the DG unit to maintain its pre-fault speed and frequency, resulting in a fast reconnection time once the system fault is cleared by the existing protection infrastructure. The scheme is also compared to another potential method, namely fault current limiters (FCLs). To address the possibility of communication failure in the novel reclosing scheme, a fault detection technique is proposed based on measurements of the rate of change of current output by DG sources. The rate of change of current (ROCOC) is measured over a specified time window to generate a fault detection signal when the ROCOC exceeds specified pickup values. A hybrid adaptive overcurrent and differential protection scheme is proposed to protect microgrids that operate in both grid and islanded modes. Differential relays are utilized for feeder backbones and buses while adaptive overcurrent relays are concurrently used for load points. The hybrid approach is to reduce both infrastructure upgrade requirements and setting computation complexity, whilst also addressing the potential lack of coordination when differing protection mechanisms are merged. The proposed scheme is validated through multiple time-domain simulations while the microgrid is in both grid and islanded modes of operation. A smart protection scheme is then proposed to predict and mitigate the short circuit contribution of a microgrid to a utility fault at a magnitude below the LOC limit. The scheme utilizes polynomial regression analysis (PRA) and particle swarm optimization (PSO) in conjunction with a directional element of a relay to allow for partial continual microgrid connection during utility faults. The directional element specifies the direction of short circuit current flow, only allowing the scheme’s operation when the microgrid current is flowing to the utility. The PRA and PSO utilize wind speed, irradiance and operating conditions of synchronous machine based (SM-based) generators to determine the short circuit contributions to utility faults from plants and units within the microgrid. The predictions are used to minimize generation source disconnection to reduce the microgrid short circuit contribution to below the LOC limit dictated by the utility network allowing for the original utility coordination to be maintained. Finally, a case study is offered to demonstrate the capacity of every approach to mitigate microgrid short circuit contributions while restoring pre-fault operating conditions shortly after fault clearance by utility protection infrastructure. In this thesis, all case studies have been conducted using realistic distribution network and microgrid designs and settings, ensuring the efficacy of the proposed approaches. Time-domain simulations are carried out on these test benchmark models within the EMTP-RV software environment for validation purposes

A Novel Transient Search Optimization for Optimal Directional Over Current Relay Coordination for Multi-technology Microgrid Protection

The directional overcurrent relays (DOCR) are a critical protection component in microgrids. Incorporating distributed generation into the microgrid can result in a breach of relay coordination within the distribution system. Variations in the magnitudes and directions of short-circuit currents can lead to erroneous tripping or failure to trip of DOCR in the system. As a consequence, the existing protection system may operate inaccurately. Hence, the failure of coordination between the primary and backup relays has a detrimental effect on the protection system. The current plug setting (CPS) and time dial setting (TDS) are key factors in determining the configuration of DOCR. Achieving proper coordination of these relays is a widely acknowledged challenging task due to the highly constrained nonlinear optimization problem it presents. Furthermore, the intricacy of this non-linearity increases as the network size grows. This paper introduces for the very first time a Transient Search optimization (TSO) based relay coordination for the protection of microgrids. Therefore, this research paper proposed a novel approach to optimize the coordination of DOCR in microgrids by employing the TSO algorithm with a modified objective function. The proposed objective function improves the relay coordination in the grid-connected and islanded mode of operation. The performance of the proposed method is assessed through testing on a multi-technology DG-connected 7-bus microgrid network. To demonstrate its effectiveness, it is compared to other popular metaheuristic optimization techniques. Moreover, the proposed algorithm successfully minimizes the total operating time while ensuring compliance with all constraints. The study validates that the proposed algorithm offers an efficient solution for the DOCR coordination problem, which holds significant benefits for microgrid protection

Вплив джерел розосередженої генерації на роботу комутаційно-захисного обладнання повітряних розподільних ліній 6-20кВ

Актуальність теми. До недавнього часу електроенергетичні системи характеризувалися централізованим виробництвом електричної енергії, мережами високої на середньої напруги для передачі електричної енергії та мережами низької напруги для її розподілу. Традиційно до розподільної мережі не було підключено жодних джерел розосередженої генерації, однак це змінюється починаючи з минулого десятиліття. В даний час до розподільної мережі підключені різні типи джерел малої генерації, більш відомих як розподілена генерація. Завдяки цілям скорочення CO2 багато дрібних джерел, інтегрованих у розподільну мережу, є відновлюваними джерелами енергії, наприклад, вітрогенератори, невеликі гідростанції та фотоелектричні панелі, також високоефективні не поновлювані джерела енергії, такі як газотурбінні установки. Підключення джерел розподіленої генерації не тільки змінює напрямок перетоків навантаження в розподільній мережі, але й може вплинути на струм короткого замикання. Більшість захисних приладів розподільної мережі налаштовані на спрацювання при виявленні струму короткого замикання або струму, який перевищує номінальний робочий струм мережі. Саме через те що джерела розосередженої генерації впливають на внесок мережі до струму короткого замикання, комутаційно-захисне обладнання мережі може працювати некоректно. В багатьох статтях ця проблема розглянута досить поверхово. Представлений огляд усіх можливих проблем захисту та їх класифікація. Мета та завдання дослідження. Основною метою роботи є розробка моделей та методів техніко-економічної оцінки впливу джерел розосередженої генерації на надійність повітряних розподільних мереж 6-20 кВ. Відповідно до мети поставлені наступні завдання: - аналіз світової практики оцінки надійності електропостачання; - аналіз сучасних технічних засобів розосередженої генерації як складової частини Smart Grid технології; - розробка моделей та методів техніко-економічної оцінки впливу джерел розосередженої генерації на надійність повітряних розподільних мереж 6-20 кВ. Об’єкт дослідження – підвищення надійності повітряних розподільних ліній в умовах розосередженої генерації. Предмет дослідження - методологія техніко-економічної оцінки впливу джерел розосередженої генерації на надійність повітряних розподільних мереж 6-20 кВ. Методи дослідження. Основу виконаних досліджень склали математичне моделювання, аналіз і синтез, порівняння та логічне узагальнення. Елементи наукової новизни одержаних результатів. 1. Розроблена математична модель для аналізу впливу джерел розосередженої генерації на роботу комутаційно-захисного обладнання. Практичне значення одержаних результатів. В електричних мережах, оснащених сучасним комутаційно-захисним обладнанням, узгоджене вирішення питань інтеграції джерел розосередженої генерації та оптимізації надійності може дати енергокомпаніям економічний виграш за рахунок можливості вивільнення дорогих комутаційних апаратів і їх використання в інших проектах.Actuality of theme. Until recently, power systems were characterized by centralized power generation, high to medium voltage grids for electricity transmission, and low voltage grids for its distribution. Traditionally, no distributed generation sources have been connected to the distribution network, but this has changed since the last decade. Currently, different types of small generation sources, better known as distributed generation, are connected to the distribution network. Thanks to CO2 reduction targets, many small sources integrated into the distribution network are renewable energy sources, such as wind turbines, small hydropower plants and photovoltaic panels, as well as highly efficient non-renewable energy sources such as gas turbine plants. Connecting distributed generation sources not only changes the direction of load flows in the distribution network, but can also affect the short-circuit current. Most switchgear protection devices are set to fire when a short circuit or current that exceeds the rated operating current of the network is detected. Due to the fact that the sources of distributed generation affect the contribution of the network to the short-circuit current, the switchgear and protection equipment of the network may not work properly. In many articles, this problem has been addressed rather superficially. An overview of all possible security issues and their classification is provided. The purpose and tasks of the study. The main purpose of the work is the development of models and methods of technical and economic assessment of the influence of sources of dispersed generation on the reliability of air distribution networks 6-20 kV. According to the purpose the following tasks are set: - analysis of the world practice of assessing the reliability of electricity supply; - analysis of modern dispersed generation equipment as an integral part of Smart Grid technology; - development of models and methods of technical and economic assessment of the influence of sources of dispersed generation on the reliability of air distribution networks 6-20 kV. Research objectives: analysis of information on the functioning of distribution electric networks; assessment of reliability of baseline reliability indicators, determination and consideration of influential factors, laws of distribution of random variables; selection and comparison of calculation models of reliability estimation of distribution electric networks with voltage of 6-10 kV on the basis of processing of received data of emergency statistics; sequence of implementation of the systematic approach to statistical analysis information and assessing the reliability of electricity supply. Object of research - to improve the reliability of air distribution lines under the conditions of dispersed generation. Subject of research - methodology for the feasibility study of the influence of dispersed generation sources on the reliability of 6-20 kV air distribution networks. Research methods. Mathematical modeling, analysis and synthesis, comparison and logical generalization were the basis of the performed researches. Elements of scientific novelty of the obtained results. 1. The mathematical model for the analysis of the influence of sources of dispersed generation on the work of switching-protective equipment is developed. The practical value of the results. n electric networks equipped with modern switchgear and protection equipment, a coordinated solution to the integration of distributed generation sources and optimization of reliability can give energy companies an economic advantage by being able to release expensive switchgear and use them in other projects

Maximising Penetration of Distributed Generation in Existing Urban Distribution Network (UDN)

Electrical power generation is currently moving towards greater penetration of distribution generation (DG), using multiple small generators instead of fewer and larger units. This can potentially create improvements in efficiency, by allowing use of waste heat (cogeneration). However, it also generates new problems related to control and co-ordination of large numbers of DGs, usually connected across the urban distributed network (UDN). In particular, concerns about security of supply and reliability together with the integration of new energy resources, are presenting a number of new challenges to system operators. One of the major changes that are being observed is the connection of significant levels of generation to the UDN. To accommodate this new type of generation the existing UDN should be utilised and developed in an optimal manner. It is well known that present arrangements for planning, dispatching and protection of central power generators are not directly applicable to the new technology. This thesis presents a mathematical method that facilitates the large scale integration of CHP generation, as the most common type of DG, connected onto the UDN. A new methodology is developed to determine the optimal allocation and, size of CHP generation capacity with respect to the technical, environmental and economic constraints of the UDN. The method estimates the adverse impact of any particular constraints with respect to the size and location of DG/CHP plants connected into the UDN. Also, the method provides the basis for quantifying the contribution that DG/CHP units makes to the security of energy supply i.e to what extent the particular DG/CHP can reduce the operational performance demand for the UDN facilities and substitute for the network assets. The method is implemented and tested on a 34 busbars network that represents a section of an UDN. The impact of CHP generation on losses in the UDN is also analysed and incorporated into the optimal capacity allocation methodology. The installation of CHP generation is leading to a major change in the way UDNs are designed and operated. UDNs are now used as a media to connect geographically distributed energy generation to the electrical power system, thereby converting what were originally energy supply networks to be used both for distribution and harvesting of energy. A mathematical model in the form of a Multiple Regression Analysis is presented in order to determine the maximum capacity of CHP generation that may be connected in a given area, while taking account of connection costs as well as technical, environmental, economic and operational setting constraints. Results obtained from various analyses related to the network performance and management are used as data for multiple regression analysis. These analyses include: load flow, fault analysis, environmental and economic analysis. The increased applications of CHP generation presents a substantial challenge to the existing connection policies used to connect CHP plant into UDNs. The section of a typical Irish UDN is used as a case study, and with reference to the available network parameters, the cost and benefits of CHP generations are determined under a number of planning and operational strategies. It is shown that a substantial increase in the net benefits of CHP generation is gained if the appropriate connection method is applied from the start and equally that significant CHP generation connection costs are sustained if ad hoc methods are employed. Connection of CHP generation can profoundly alter the operation of a UDN. Where CHP generation capacity is comparable to or larger than local demand there are likely to be observable impacts on network power flows and voltage regulation. In fact, two major problems to be considered are the voltage levels and operation of protection during faults and disturbances. New connection of CHP generation must be evaluated to identify and quantify any adverse impact on the security and quality of local electricity supplies. There are a number of well-established methods to deal with adverse impacts caused by CHP generation connection into a UDN. While a range of options exist to mitigate adverse impacts, under current commercial arrangements the developer will largely bear the financial responsibility for their implementation. The economic implication can make potential schemes less attractive and in some instances have been an impediment to the development of CHP generation in urban areas. Development of a CHP generation system connection algorithm corresponding to the Least Cost Technically Acceptable (LCTA) method is absolutely vital in order to maximise the penetration of CHP generation into existing UDN with respect to different UDN/CHP system operational settings/constraints and minimal economic implication. In this thesis, results from a number of mitigation methods analysis are compared and used to create the connection process algorithm. This algorithm equally can be applied in the connection process of other distribution generation technologies into existing UDNs

Synchrophasor Based Islanding & Open phase fault Protection in Distribution Systems

With the rapid growth of renewable energy resources, energy efficiency initiatives, electric vehicles, energy storage, etc., distribution systems are becoming more complex such that conventional protection, control, and measurement infrastructure – typically concentrated at the main substation, with little to no access to information along the feeder – cannot maintain the reliability of the system without some sort of additional protection, control and measurement functionalities. As an example, a dedicated communication channel for carrying the transfer trip signal from the substation to the Point of Common Coupling (PCC) to prevent islanding operation of alternative resources, has been a requirement for many utilities. In the transformation of the distribution system from a simple radial system to a bidirectional energy flow network, integration of many intelligent devices and applications will also be required. Thus, this situation calls for investment in communication infrastructure, and augmentation of protection, control, and measurement functionalities. The value of power system communication technologies such as synchrophasor measurement technology – which includes the Phasor Measurement Unit (measuring and providing voltage and current phasors in the real time via communication), communication infrastructure, and Phasor Data Concentrator (PDC) – is being recognized through large-scale deployments around the world. However, these implementations are predominantly limited to some monitoring-type applications and are being realized primarily in transmission systems and bulk power systems (≥100 kV), where performance requirements are much more stringent compared to distribution systems. So contrary to transmission systems, the current status of synchrophasor measurement technology can be utilized to its full extent in distribution systems, as shown in current research for anti-islanding and open-phase faults in the distribution feeder protection application, where the number of PMUs and performance required is somewhat lower than the bulk of power energy. Thus, the opportunity to invest in the implementation of synchronized measurement technology in distribution system is timely as it can be coordinated with other investments in feeder modernization, distributed generation (DG) integration, and infrastructure enhancements that are underway, including “smart grid” initiatives. In the first use case of this research, the behavior of the major DG types during islanding is studied through accurate transient modeling of utility type distribution systems using PSCAD-EMTDC and MATLAB. The study proposes augmentation of PMU-based solutions to the current passive islanding protection elements, such as voltage and frequency, and improving the non-detection zone of the passive elements by adapting their settings based on normal loading conditions at closest known instant prior to the fault or islanding occurrence. The solution proposes a system architecture that requires one PMU at each PCC bus and in the main substation. The communication aspect is based on the IEC 6850-90-5 report, where the PMU can subscribe directly to the data stream of the remote PMUs such that the need for PDCs in this application is eliminated, yielding better performance. In the second use case, an open-phase fault – a major concern for distribution utilities from safety of public and equipment perspective – has been studied. Clearing the open-phase fault without identifying the type of fault could result in an attempt by the recloser to reenergize the downed wire; conversely, an undetected open-phase fault could initiate ferro-resonance, thereby stressing equipment and increasing the risk to public safety, both urban and rural. This work discusses comprehensive analysis of symmetrical components of various types of open-phase faults in the distribution feeder with the presence of distributed generators (DGs) and proposes the use of phasor measurement data located at substation and PCC to identify the open-phase fault. The proposed algorithm relies on the rate of change of the various current and voltage sequence components. In the study conducted, the utility type feeder and substation are modeled in PSCAD-EMTDC, and different types of open-phase fault and shunt faults are studied to verify the dependability and security of proposed algorithm