PMU’s behavior with flicker-generating voltage fluctuations: an experimental analysis

Phasor measurement units (PMUs), which are the key components of a synchrophasor-based wide area monitoring system (WAMS), were historically conceived for transmission networks. The current trend to extend the benefits of the synchrophasor technology to distribution networks requires the PMU to also provide trustworthy information in the presence of signals that can occur in a typical distribution grid, including the presence of severe power quality (PQ) issues. In this framework, this paper experimentally investigates the performance of PMUs in the presence of one of the most important PQ phenomena, namely the presence of voltage fluctuations that generate the disturbance commonly known as flicker. The experimental tests are based on an ad-hoc high-accuracy measurement setup, where the devices under test are considered as “black boxes” to be characterized in the presence of the relevant signals. Two simple indices are introduced for the comparison among the different tested PMUs. The results of the investigation highlight possible critical situations in the interpretation of the measured values and provide a support for both the design of a new generation of PMUs and the possible development of an updated synchrophasor standard targeted to distribution systems

A Distributed PMU for Electrical Substations with Wireless Redundant Process Bus

6nononenoneCASTELLO P.; FERRARI P.; FLAMMINI A.; MUSCAS C.; PEGORARO P. A.; RINALDI S.Castello, P.; Ferrari, Paolo; Flammini, Alessandra; Muscas, C.; Pegoraro, P. A.; Rinaldi, Stefan

A Distributed PMU for Electrical Substations with Wireless Redundant Process Bus

Protection and measurement systems in electrical substations are required to have high availability. In an all-digital substation protection system, all the components (instrument transformers, processing units, merging units, intelligent electronic devices, communication network, and synchronization source) may affect the overall availability level. In this paper, a solution to enhance distributed PMU availability, during wired network failures, is presented. In the proposed scheme, the process bus has two parallel networks: 1) the classic wired Ethernet link and 2) a wireless link (implemented with industrial grade IEEE 802.11 devices), for sampled values packets, which carry measurement information. The time synchronization is carried out only through the wired Ethernet link, but the proposed solution is still able to compensate temporary failures of one of the communication links. Experimental tests have been performed to verify the performance of additional IEEE 802.11 link using different protocols and configurations. Communication parameters that can affect the PMU performance, like propagation latency, are characterized. It is shown that, if the measurement algorithm is opportunely designed, depending on the wireless link quality, it is possible to comply, with a single output, with M and P classes of the synchrophasor standard also during network restoration or, at least, to safeguard protection applications if higher latency occurs

A study of the applicability of software-defined networking in industrial networks

173 p.Las redes industriales interconectan sensores y actuadores para llevar a cabo funciones de monitorización, control y protección en diferentes entornos, tales como sistemas de transporte o sistemas de automatización industrial. Estos sistemas ciberfísicos generalmente están soportados por múltiples redes de datos, ya sean cableadas o inalámbricas, a las cuales demandan nuevas prestaciones, de forma que el control y gestión de tales redes deben estar acoplados a las condiciones del propio sistema industrial. De este modo, aparecen requisitos relacionados con la flexibilidad, mantenibilidad y adaptabilidad, al mismo tiempo que las restricciones de calidad de servicio no se vean afectadas. Sin embargo, las estrategias de control de red tradicionales generalmente no se adaptan eficientemente a entornos cada vez más dinámicos y heterogéneos.Tras definir un conjunto de requerimientos de red y analizar las limitaciones de las soluciones actuales, se deduce que un control provisto independientemente de los propios dispositivos de red añadiría flexibilidad a dichas redes. Por consiguiente, la presente tesis explora la aplicabilidad de las redes definidas por software (Software-Defined Networking, SDN) en sistemas de automatización industrial. Para llevar a cabo este enfoque, se ha tomado como caso de estudio las redes de automatización basadas en el estándar IEC 61850, el cual es ampliamente usado en el diseño de las redes de comunicaciones en sistemas de distribución de energía, tales como las subestaciones eléctricas. El estándar IEC 61850 define diferentes servicios y protocolos con altos requisitos en terminos de latencia y disponibilidad de la red, los cuales han de ser satisfechos mediante técnicas de ingeniería de tráfico. Como resultado, aprovechando la flexibilidad y programabilidad ofrecidas por las redes definidas por software, en esta tesis se propone una arquitectura de control basada en el protocolo OpenFlow que, incluyendo tecnologías de gestión y monitorización de red, permite establecer políticas de tráfico acorde a su prioridad y al estado de la red.Además, las subestaciones eléctricas son un ejemplo representativo de infraestructura crítica, que son aquellas en las que un fallo puede resultar en graves pérdidas económicas, daños físicos y materiales. De esta forma, tales sistemas deben ser extremadamente seguros y robustos, por lo que es conveniente la implementación de topologías redundantes que ofrezcan un tiempo de reacción ante fallos mínimo. Con tal objetivo, el estándar IEC 62439-3 define los protocolos Parallel Redundancy Protocol (PRP) y High-availability Seamless Redundancy (HSR), los cuales garantizan un tiempo de recuperación nulo en caso de fallo mediante la redundancia activa de datos en redes Ethernet. Sin embargo, la gestión de redes basadas en PRP y HSR es estática e inflexible, lo que, añadido a la reducción de ancho de banda debida la duplicación de datos, hace difícil un control eficiente de los recursos disponibles. En dicho sentido, esta tesis propone control de la redundancia basado en el paradigma SDN para un aprovechamiento eficiente de topologías malladas, al mismo tiempo que se garantiza la disponibilidad de las aplicaciones de control y monitorización. En particular, se discute cómo el protocolo OpenFlow permite a un controlador externo configurar múltiples caminos redundantes entre dispositivos con varias interfaces de red, así como en entornos inalámbricos. De esta forma, los servicios críticos pueden protegerse en situaciones de interferencia y movilidad.La evaluación de la idoneidad de las soluciones propuestas ha sido llevada a cabo, principalmente, mediante la emulación de diferentes topologías y tipos de tráfico. Igualmente, se ha estudiado analítica y experimentalmente cómo afecta a la latencia el poder reducir el número de saltos en las comunicaciones con respecto al uso de un árbol de expansión, así como balancear la carga en una red de nivel 2. Además, se ha realizado un análisis de la mejora de la eficiencia en el uso de los recursos de red y la robustez alcanzada con la combinación de los protocolos PRP y HSR con un control llevado a cabo mediante OpenFlow. Estos resultados muestran que el modelo SDN podría mejorar significativamente las prestaciones de una red industrial de misión crítica

DFT-based Synchrophasor Estimation Algorithms and their Integration in Advanced Phasor Measurement Units for the Real-time Monitoring of Active Distribution Networks

The increasing penetration of Distributed Energy Resources (DERs) at the low and medium-voltage levels is determining major changes in the operational procedures of distribution networks (DNs) that are evolving from passive to active power grids. Such evolution is causing non-negligible problems to DN operators (DNOs) and calls for advanced monitoring infrastructures composed by distributed sensing devices capable of monitoring voltage and current variations in real-time. In this respect, Phasor Measurement Units (PMUs) definitely represent one of the most promising technologies. Their higher accuracy and reporting rates compared to standard monitoring devices, together with the possibility of reporting time-tagged measurements of voltage and current phasors, enable the possibility to obtain frequent and accurate snapshots of the status of the monitored grid. Nevertheless, the applicability of such technology to DNs has not been demonstrated yet since PMUs where originally conceived for transmission network applications. Within this context, this thesis first discusses and derives the requirements for PMUs expected to operate at power distribution level. This study is carried out by analyzing typical operating conditions of Active Distribution Networks (ADNs). Then, based on these considerations, an advanced synchrophasor estimation algorithm capable of matching the accuracy requirements of ADNs is formulated. The algorithm, called iterative-interpolated DFT (i-IpDFT) improves the performances of the Interpolated-DFT (IpDFT) method by iteratively compensating the effects of the spectral interference produced by the negative image of the spectrum and at the same time allows to reduce the window length up to two periods of a signal at the nominal frequency of the power system. In order to demonstrate the low computational complexity of such an approach, the developed algorithm has been subsequently optimized to be deployed into a dedicated FPGA-based PMU prototype. The influence of the PMU hardware components and particularly the effects of the stability and reliability of the adopted UTC-time synchronization technology have been verified. The PMU prototype has been metrologically characterized with respect to the previously defined operating conditions of ADNs using a dedicated PMU calibrator developed in collaboration with the Swiss Federal Institute of Metrology (METAS). The experimental validation has verified the PMU compliance with the class-P requirements defined in the IEEE Std. C37.118 and with most of the accuracy requirements defined for class-M PMUs with the exception of out of band interference tests