A computer-based testing system to evaluate protective relays as a tool in power system protection education

Teaching power system relaying is a fundamental issue in a power system high-level course. However, for an effective instruction of this topic an experience with real equipments can be considered as fundamental. To achieve this purpose, in this paper a new approach for the practical learning of power system relaying is presented. This consists of a computer-based testing system of relay-operating characteristic. Different relay types and developed specific software are also an important piece of the laboratory practice. Using this system it is possible to understand the performance and limitations of different protective relay systems and to test a real relay disoperation. The benefit of using this system is not available through traditional lectures and textbooks

Investigating Performance and Reliability of Process Bus Networks for Digital Protective Relaying

To reduce the cost of complex and long copper wiring, as well as to achieve flexibility in signal communications, IEC 61850 part 9-2 proposes a process bus communication network between process level switchyard equipments, and bay level protection and control (P&C) Intelligent Electronic Devices (IEDs). After successful implementation of Ethernet networks for IEC 61850 standard part 8-1 (station bus) at several substations worldwide, major manufacturers are currently working on the development of interoperable products for the IEC 61850-9-2 based process bus. The major technical challenges for applying Ethernet networks at process level include: 1) the performance of time critical messages for protection applications; 2) impacts of process bus Ethernet networks on the reliability of substation protection systems. This work starts with the performance analysis in terms of time critical Sampled Value (SV) messages loss and/or delay over the IEC 61850-9-2 process bus networks of a typical substation. Unlike GOOSE, the SV message is not repeated several times, and therefore, there is no assurance that each SV message will be received from the process bus network at protection IEDs. Therefore, the detailed modeling of IEC 61850 based substation protection devices, communication protocols, and packet format is carried out using an industry-trusted simulation tool OPNET, to study and quantify number of SV loss and delay over the process bus. The impact of SV loss/delay on digital substation protection systems is evident, and recognized by several manufacturers. Therefore, a sample value estimation algorithm is developed in order to enhance the performance of digital substation protection functions by estimating the lost and delayed sampled values. The error of estimation is evaluated in detail considering several scenarios of power system relaying. The work is further carried out to investigate the possible impact of SV loss/delay on protection functions, and test the proposed SV estimation algorithm using the hardware setup. Therefore, a state-of-the-art process bus laboratory with the protection IEDs and merging unit playback simulator using industrial computers on the QNX hard-real-time platform, is developed for a typical IEC 61850-9-2 based process bus network. Moreover, the proposed SV estimation algorithm is implemented as a part of bus differential and transmission line distance protection IEDs, and it is tested using the developed experimental setup for various SV loss/delay scenarios and power system fault conditions. In addition to the performance analysis, this work also focuses on the reliability aspects of protection systems with process bus communication network. To study the impact of process bus communication on reliability indices of a substation protection function, the detailed reliability modeling and analysis is carried out for a typical substation layout. First of all, reliability analysis is done using Reliability Block Diagrams (RBD) considering various practical process bus architectures, as well as, time synchronization techniques. After obtaining important failure rates from the RBD, an extended Markov model is proposed to analyze the reliability indices of protection systems, such as, protection unavailability, abnormal unavailability, and loss of security. It is shown with the proposed Markov model that the implementation of sampled value estimation improves the reliability indices of a protection system

Protection concepts in distribution networks with decentralised energy resources

Die stetig steigende Anbindung von dezentralen Energieerzeugern (DER) an Mittel- (MS) und Niederspannungsnetze (NS) fordert eine Analyse der bestehenden Netzschutzkonzepte. Die Beeinflussung der Netzschutzkonzepte ist abhängig davon, wie die DER an das Mittelspannungsnetz angebunden sind. Die vorliegende Arbeit konzentriert sich auf die Analyse von Beeinflussungen durch kleine DER, die an das Mittelspannungsnetz über einen Umrichter angebunden sind. Das erste Problem, das in dieser Arbeit untersucht ist, ist die Beeinflussung der unterschiedlichen Schutzalgorithmen durch hohe Anteile von Harmonischen. Diese werden verursacht durch die steigende Zahl elektrischer Geräte, sowohl auf der Verbraucherseite als auch auf der Seite der Energieerzeuger. Die Beeinflussung, entsprechend der Norm IEC 61000-3–2, wurde an unterschiedlichen Typen von Netzschutzsystemen untersucht. Die getesteten Distanzschutzalgorithmen basierten auf konventionellen Methoden zu Berechnung der Impedanz wie: SinusAlgorithmen, Algorithmen basierend auf der Leitungs-Differentialgleichung erster oder zweiter Ordnung, Filteralgorithmen für Berechnung komplexer Zeiger, und Algorithmen, die auf künstliche Intelligenz basieren, wie harmonisch aktivierte neuronale Netze. Die unterschiedlichen Typen von Netzschutzprinzipien, die untersucht wurden sind: Überstrom, Distanz und Differenzial. Einige Untersuchungen wurden auch im Netzschutzlabor der Universität durchgeführt. Bei beiden Tests konnte nachgewiesen werden, dass die heutigen state-of-the-art Netzschutzsysteme durch Harmonische entsprechend IEC 61000-3–2, praktisch nicht beeinflusst werden. Der zweite Problemkreis der in dieser Arbeit diskutiert wird sind die Anforderungen, welche die Anbindung von DER an das Netz, an moderne Netzschutzsysteme stellen. Einige Beispiele illustrieren die Lage der Energieversorgung der Zukunft und zeigen Selektivitätsprobleme auf, sollten nur konventionelle Netzschutzsysteme benutzt werden. In dieser Arbeit wird ein neues Schutzkonzept für Mittelspannungsnetze mit hohem Anteil an DER vorgestellt und analysiert. Das Konzept beruht auf der neuen Norm für „Substation Automatisation System - IEC 61850“ und einem Netzschutz-Managementsystem. Die Methode der zusätzlichen Signal-Einspeisung wurde ebenfalls vorgestellt. Die Basis eines effizienten Netzschutz-Managementsystems ist das Wissen vom Verhalten des Systems in normalen Betrieb und unter Fehlerbedingungen. Die Computer- und Internettechnologie, die moderne Kommunikation, der interdisziplinäre Datenaustausch stellen ganz neue Anforderungen an die Wissensbasis energietechnischer Ingenieure. Mit dem Ziel neue Medien in der Ingenieurausbildung einzusetzen ist, im Rahmen dieser Arbeit ein E-learning Kurs entwickelt worden. Dabei ermöglicht das Internet neue Methoden zur Wissensvermittlung zu entwickeln. Die Unabhängigkeit von Zeit und Ort, die große Anzahl von Lehrmöglichkeiten und die Online-Diskussionen sind nur einige zu nennende Vorteile. In dieser Arbeit ist die Idee zur Realisierung sowie Ergebnisse des E-learning Kurses im Bereich digitaler Netzschutztechnik, als Erweiterung der konventionellen Lehrveranstaltung präsentiert worden. Dieser Kurs wird den Studenten der Universität in einem speziell gestalteten Multimedialabor angeboten. Es besteht via Internet die Möglichkeit den Kurses z.B. zu Hause zur Wiederholung und Prüfungsvorbereitung nochmals zu bearbeiten.    The continuously rising implementation of DER in the distribution network requests analyses of the present network protection concepts. Depending on the type of connection to the network, the influences of the DER on the network protection systems vary. This dissertation concentrates on the analyses of the influence of implementation of small DER, which are connected to the network via an inverter. The first problem discussed in this dissertation is the influence of high level of harmonics on the protection devices. The rising implementation of power electronic devices into the network, both on the side of the energy generation and energy consumption, leads to a high level of injected harmonics into the network. The influence of a high amount of harmonics, according to the Standard IEC 61000-3–2, on different types of algorithms implemented in different types of protection devices was investigated using a test network. The tested algorithms implemented in the distance protection devices were based on conventional methods such as steady state algorithms, algorithms using the differential equation of first or second order written for the protected line, algorithms based on the filter approach, and on the “new” methods using artificial intelligence i.e.: parametrical estimation and harmonic activated neuronal networks. The different types of protection devices that were investigated were based on the principle of over-current (definite-current and inverse time), distance and differential. Some of the tests were conducted in the protection technique laboratory at the university. From both tests (simulation and practical) it is concluded that the state-of-the-art protection devices are insensitive to harmonics according to the allowed level by the standard IEC 61000-3–2. The tendency of today’s protection technology engineers lies in searching for ways to shorten of the calculation time of the algorithms. The second problem discussed is the challenge set to the network protection systems in the distribution networks with implemented DER. A few examples illustrate the situation of the energy supply of the future illustrate the problems of lack of protection with the present protection concepts. In this sense, this work presents and analyses a protectionconcept in distribution networks with DER, using the substation automation system and the protection management system based on the new standard IEC 61850 for communication networks in substations. The method of using an additional signal injection as additional criteria for the presented network protection concept is also discussed. The basis for efficient protection system management is the knowledge of power system performance under fault and normal operation (service) conditions as well as the switchgear interfaces. This requires a proper knowledge of power system engineering. With a changeable power system infrastructure, the protection system management becomes a real challenge to the network protection experts. Computer- and internet technology, modern serial communications, sharing of data with other disciplines and a trend towards system engineering require a broader knowledge and close co-operation with others, beside the protection system engineers. With the goal of spreading the knowledge of network protection systems, in the frames of this work a special e-learning course was realised. The internet provides new possibilities for gaining and spreading knowledge. The time and place independence, the high amount of possibilities for knowledge sources and on line discussions are just a few of the possibilities. In this work, the idea, the realisation and the implementation of this new way of teaching and studying digital network protection alongside the conventional way are presented as well. An importance is also given to the feed back of the user of the e-learning course. This course is offered to the students at the university in a specially realised multimedia laboratory and used for gaining knowledge in the area of network protection technique. The possibility of using the course at home for re-capitulation of the taught material and for self-test is also possible, by simply logging on to the e-learning course. This course could also be used by engineers who want to refresh their knowledge in the form of a fast (self) training.   &nbsp

Protection challenges in future converter-dominated power systems : investigation and quantification using a novel flexible modelling and hardware testing platform

Error on title page – year of award is 2023.The research work presented in this thesis addresses anticipated (and documented) protection challenges that will be introduced by the domination of power electronics interfaces in future power systems. A flexible and programmable voltage source converter (VSC) model with controllable fault response has been developed and this is tested using realistic network data (including transmission lines and the corresponding power flow/fault level data) from the GB transmission network, provided by National Grid ESO (the research project sponsor). The results of tests, where a range of variations to the converter controllers’ fault-responses have been implemented (e.g. to reflect different detection and initial converter response delays, output current ramp rates and magnitudes), are presented and analysed. The simulated voltage and current waveforms are injected into actual protection relays using secondary injection amplifiers. The responses of the relays are recorded and a number of issues are highlighted, particularly with respect to the response of distance protection. It is shown that, when the system is dominated by converter-interfaced sources (especially where the sources are modelled as being unable to provide “fast” and “high” fault currents, which is typically the case for actual converter systems), the responses of traditional distance protection systems (and other systems relying on measurement of current magnitude) could be delayed, lose discrimination, e.g. by tripping with a zone 2 delay for a zone 1 fault, or may be completely unable to detect faults at certain locations within the system. Based on the test results, potential solutions are then presented relating to changes to relay algorithms and/or the requirements for converters in terms of behaviour during faults. The outcomes of the work will be of interest to grid code developers (publications arising from this work have already been referred to by ENTSO-E guidance document for national implementation for network codes on grid connection [1]), transmission network operators, other researchers and protection/converter manufacturers. An overview of future work, relating to comprehensive studies (using injection and the developed system/converter models) of a range of faults/ infeeds/ converter mixes with a wide range of protection relays including distance and unit-type, and development of a standard commissioning testing method of protection relays under future power system scenarios that are dominated by converters, is included in the concluding section. This will assist in the investigation and resolution of issues associated with protection performance in future converter-dominated power systems.The research work presented in this thesis addresses anticipated (and documented) protection challenges that will be introduced by the domination of power electronics interfaces in future power systems. A flexible and programmable voltage source converter (VSC) model with controllable fault response has been developed and this is tested using realistic network data (including transmission lines and the corresponding power flow/fault level data) from the GB transmission network, provided by National Grid ESO (the research project sponsor). The results of tests, where a range of variations to the converter controllers’ fault-responses have been implemented (e.g. to reflect different detection and initial converter response delays, output current ramp rates and magnitudes), are presented and analysed. The simulated voltage and current waveforms are injected into actual protection relays using secondary injection amplifiers. The responses of the relays are recorded and a number of issues are highlighted, particularly with respect to the response of distance protection. It is shown that, when the system is dominated by converter-interfaced sources (especially where the sources are modelled as being unable to provide “fast” and “high” fault currents, which is typically the case for actual converter systems), the responses of traditional distance protection systems (and other systems relying on measurement of current magnitude) could be delayed, lose discrimination, e.g. by tripping with a zone 2 delay for a zone 1 fault, or may be completely unable to detect faults at certain locations within the system. Based on the test results, potential solutions are then presented relating to changes to relay algorithms and/or the requirements for converters in terms of behaviour during faults. The outcomes of the work will be of interest to grid code developers (publications arising from this work have already been referred to by ENTSO-E guidance document for national implementation for network codes on grid connection [1]), transmission network operators, other researchers and protection/converter manufacturers. An overview of future work, relating to comprehensive studies (using injection and the developed system/converter models) of a range of faults/ infeeds/ converter mixes with a wide range of protection relays including distance and unit-type, and development of a standard commissioning testing method of protection relays under future power system scenarios that are dominated by converters, is included in the concluding section. This will assist in the investigation and resolution of issues associated with protection performance in future converter-dominated power systems

Seeds of Solutions™: An economical & efficient approach towards power engineering education

Power demands are set to increase over the next twenty years; however, research shows that there may be a shortage of power engineers due to an appreciable percentage of the current power engineer workforce retiring, insufficient enrollment in power engineering programs and a lack of emphasis in power engineering at the university level. This thesis provides supporting research for future power demands, workforce and faculty shortages. Using temporary research in modern learning / teaching styles, student / teacher perceptions, educational trends and regional course offerings, this thesis describes a learning approach towards power engineering education. Designed specifically for universities with little to no power engineering course offerings and universities that wish to augment their existing approach, the approach incorporates an emphasis in fundamentals and engineering design making it economical and easy to implement. This thesis also includes three (3) video laboratory examples incorporating all elements of the approach

Non-Pilot Protection of the Inverter-Dominated AC Microgrid

The main objective of this research is to develop reliable non-pilot protection and control strategies for the inverter-dominated microgrid. First, an improved Proportional-Derivative (PD) droop control strategy is proposed for enhanced disturbance response of the inverter-dominated AC microgrid. The proposed strategy significantly improves microgrid dynamic response and stability without requiring communication between distributed energy resources. Moreover, the impacts of large startup currents of induction motors on the stability and power quality of the inverter-dominated microgrid are investigates and recommendations for minimizing the associated adverse effects are made. Subsequently, a fast, selective, and reliable protection strategy for the inverter-dominated microgrid is introduced. The proposed protection strategy utilizes phase- and sequence-domain protective elements for reliable detection of symmetrical and asymmetrical faults without the need for communication signals or adaptive relays settings. The protection strategy is robust against the grid-connection mode of the microgrid and enables fuse protection of laterals. It can also be implemented on the existing commercially available relays. The acceptable performance of the proposed protection and control strategies is verified through numerous fault studies conducted on a realistic study system in the PSCAD/EMTDC software environment. Additionally, the proposed protection strategy is implemented in a SEL-351 relay and evaluated using the SEL-AMS industrial relay testing platform

Overcoming asymmetrical communication delays in line current differential protection circuits

Communications asymmetry leads to current differential protection relay misoperation by causing relays at either end of a power line to sample load current waveforms at different moments in time. The increased use of current differential protection and developments in communication technologies in power systems has led to the increase likelihood of relay misoperation due to communication delay asymmetry. The main cause of communication delay asymmetry is split-path-communications, whereby transmit and receive directions of a communications channel take separate paths with different delays. Split-path-communications are the result of faults in one direction of a communications channel, causing that direction only to switch from main to alternate paths. This project studies AusNet Services’ communications network and those similar to it, to find the typical sources of communication delays. Delays are measured between a variety E1 interfaces in the AusNet Services network, and the results used to calculate the per unit delays through given types of cross-connections. These are used in conjunction with a current differential relay response calculator, to create a model that displays a relay’s response to a communications channel with specified attributes. The chance of split-path-communications can be avoided by using communications equipment with bidirectional switching capabilities. The Avara DB4 family of branching E1 cards have this capability; however, this project reveals that a fault in the DB4 firmware code means that they may still cause protection relays to misoperate due to asymmetry. The DB4 firmware was updated, and further testing proved that it now prevented relay misoperation

Monitoring and Protection of Power Distribution Networks with IEC 61850-9-2 Standard

In the modern power grid, communication plays a vital role in making the system more reliable and secure. The communications network transfers data between different units to a control center or to Intelligent Electric Devices (IEDs) in order to accurately control or protect the modern power system. The paper discussed possible ways to monitor the measured values for protecting the power system according to IEC 61850-9-2 (sample value). The sequence of the process consists of streaming the sample value packet, decoding it, and phasor extraction and filtering, which are discussed here. To validate the research, Sundom Smart Grid was used as a pilot to measure the values converted to digital form (IEC 61850-9-2) and to stream it to the system through a highly secure communications network. To decode the SV packet, two scenarios are presented in the case study, based on processing useful features of the IEC 61850-9-2 standard-based raw data streamed from the SSG, including μPMU in a range of embedded instruments and a real-time simulator. The main result of this paper is an algorithm for analyzing SV packets and determining whether the network is operating normally.©2020 IET. This paper is a postprint of a paper submitted to and accepted for publication in 15th International Conference on Developments in Power System Protection (DPSP 2020) and is subject to Institution of Engineering and Technology Copyright. The copy of record is available at the IET Digital Library.fi=vertaisarvioitu|en=peerReviewed

Distributed photovoltaic systems: Utility interface issues and their present status

Major technical issues involving the integration of distributed photovoltaics (PV) into electric utility systems are defined and their impacts are described quantitatively. An extensive literature search, interviews, and analysis yielded information about the work in progress and highlighted problem areas in which additional work and research are needed. The findings from the literature search were used to determine whether satisfactory solutions to the problems exist or whether satisfactory approaches to a solution are underway. It was discovered that very few standards, specifications, or guidelines currently exist that will aid industry in integrating PV into the utility system. Specific areas of concern identified are: (1) protection, (2) stability, (3) system unbalance, (4) voltage regulation and reactive power requirements, (5) harmonics, (6) utility operations, (7) safety, (8) metering, and (9) distribution system planning and design