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One of the main concerns when sizing protection systems in distribution networks with distributed generation connection is to ensure that islanding of these plants does not occur. For this, several protection techniques are used, among which is the use of an undervoltage relay. It happens that the voltage degradation caused by the occurrence of short circuits in feeders adjacent to the DG connection can sensitize this protection, causing undue actions. Thus, this work presents a methodology for custom parameterization of the undervoltage relay in order to reduce or avoid these actuations. The methodology checks for which situations the undue actuation occurs, evaluating the overcurrent protection actuation time and the voltage drop at the DG connection point. Starting from these data, a customized actuation curve for the undervoltage relay is established. This curve is based on steps in order to facilitate its application in undervoltage relays, where a maximum number of steps starting from two must be defined. For the scenarios tested through computer simulations, the methodology proved to be efficient, zeroing the number of undue actions for all scenarios except one. Uma das principais preocupações ao dimensionar sistemas de proteção em redes de distribuição com conexão de geração distribuída e garantir que não ocorra o ilhamento dessas usinas. Para isso, são empregadas diversas técnicas de proteção, onde, entre elas, está a utilização de relé de subtensão. Ocorre que a degradação da tensão ocasionada pela ocorrência de curtos-circuitos em alimentadores adjacentes ao de conexão da GD pode sensibilizar essa proteção, causando atuações indevidas. Dessa forma, esse trabalho apresenta uma metodologia para parametrização customizada do relé de subtensão de forma a reduzir ou evitar essas atuações. A metodologia verifica para quais situações ocorre a atuação indevida avaliando o tempo de atuação da proteção de sobrecorrente e a queda de tensão no ponto de conexão da GD. Partindo desses dados uma curva de atuação customizada para o relé de subtensão é estabelecida. Essa curva é baseada em degraus de forma a facilitar sua aplicação nos reles de subtensão, onde deve ser definido um número máximo de degraus partindo de dois. Para os cenários testados através de simulações computacionais a metodologia se mostrou eficiente zerando o número de atuações indevidas para todos os cenários a exceção de um.

Engineering laboratories are key elements in engineering learning and are essential for a concrete understanding of engineering topics and experiments. These key laboratories are no longer just hardware-dependent, they are a creative combination of programmable hardware and also user-defined driving software. In this work, an educational power system protective relaying laboratory platform was designed and implemented using a programmable logic controller (PLC) and human&ndash, machine interface (HMI) in order to introduce engineering students to the operating mechanisms experimentally. It engaged the students in selecting settings and upgrading the inverse definite minimum time (IDMT) protection relays for overcurrent, overvoltage, undervoltage, and differential current. With the platform and the help of the HMI, the students mastered (or came close to mastering) the field of protective relays, especially those explicitly implemented in the platform. The students were also able to see the real-time response that is equivalent to the relay operation time of the protective relays under the various possible settings, and the kinesthetic learning that was involved gave them a deeper understanding of what is involved in relays upgrading.

This paper proposes a dynamic model for the behavior of an AC undervoltage protection relay during voltage dips. The behavior is expressed by means of standardized voltage tolerance curves and highly depends on the point on-wave (phase angle) of the dip initiation. Using the model, it can be explained that AC undervoltage relays are much more sensitive to voltage dips of e.g. 50% Urated than to short interruptions (0% Urated), caused by the magnetic behavior. The model takes into account the electrical, magnetic and mechanical system equations. An experimental set-up with a programmable power source as dipgenerator is build to validate the model. Finally, a complete weaving machine is represented to analyze the influence towards voltage dip immunity by adding an undervoltage protection relay.