Innovative Differential Protection Scheme for Microgrids Based on RC Current Sensor

The modern power system and future ones include several intelligent devices. It also integrates renewable energy sources, energy storage, energy microgrid control system, hybrid networks, and smart grids with the wide application of information technology and communication. The most crucial goal in the smart grid application is improving safety reliability within the network. Recent studies have recommended the development of smart grid technology that enhances the reliability of electric power systems increases efficiency and improves the detection of faults for protection; this will reduce the duration of interruption of the number of customers affected by the outages. Moreover, smart grid technology decreases the power loss of energy usage and improves the efficiency of the system. And protection is one of the most important challenges facing smart grid deployment. In this chapter, protection for smart grids using differential relays is presented. The differential scheme is a very reliable method of ensuring the safety of protected areas. This chapter discusses the differential relay parameters with various fault conditions. Therefore, the protection scheme affirms the rapid separation of the fault zone to reduce damage to the equipment. The simulation results show that the method is effective and reliable

Time domain analysis of switching transient fields in high voltage substations

Switching operations of circuit breakers and disconnect switches generate transient currents propagating along the substation busbars. At the moment of switching, the busbars temporarily acts as antennae radiating transient electromagnetic fields within the substations. The radiated fields may interfere and disrupt normal operations of electronic equipment used within the substation for measurement, control and communication purposes. Hence there is the need to fully characterise the substation electromagnetic environment as early as the design stage of substation planning and operation to ensure safe operations of the electronic equipment. This paper deals with the computation of transient electromagnetic fields due to switching within a high voltage air-insulated substation (AIS) using the finite difference time domain (FDTD) metho

Определение насыщения трансформатора тока на основе использования искусственной нейронной сети

When current transformer is saturated, mainly due to the presence of an exponentially decaying DC component in the fault current, its secondary current has a distinctive distorted waveform which significantly differs from its primary (true) waveform. It leads to an underestimation of the secondary current value calculated by the relay protection compared to its true value. Thus, in its turn, results in trip time delay or even in a relay protection devices operation failure, since its settings and algorithms are calculated and designed on the assumption that the secondary current waveform is sinusoidal and proportional to the primary. And since, when using classical electromagnetic current transformer, it is impossible to exclude the possibility of its saturation, the detection of such abnormal condition is an urgent technical problem. The article proposes to use an artificial neural network for this purpose, which, together with the traditional method of saturation detection based on adjacent secondary current samples comparison, allows implementing a fast and reliable current transformer saturation detector. The article details the stages of the practical implementation of such an artificial neural network. The MATLAB-Simulink environment was used for assess the proposed saturation detector operation. The experiments that had been performed confirmed that proposed method provides fast and accurate saturation detection within the wide range of the power system and current transformer parameters change.При насыщении трансформатора тока, преимущественно вследствие наличия экспоненциально затухающей апериодической составляющей в токе повреждения, его вторичный ток имеет характерную непериодическую искаженную форму, существенно отличающуюся от его первичной (истинной) формы, что ведет к занижению вычисляемого релейной защитой значения вторичного тока по сравнению с его истинным значением. Указанное приводит к затягиванию   времени   срабатывания или вовсе к отказу  функционирования  устройств релейной защиты, так как уставки и алгоритмы релейной защиты рассчитаны и построены соответственно из предположения о том, что форма сигнала вторичного тока является синусоидальной и пропорциональной первичному. А поскольку в общем случае при использовании классических электромагнитных трансформаторов тока исключить возможность их насыщения невозможно, то выявление указанного режима функционирования является актуальной технической задачей. В статье предлагается использовать искусственную нейронную сеть, которая совместно с традиционным способом определения насыщения на основе сравнения значений соседних выборок вторичного тока позволяет реализовать быстрый и надежный детектор насыщения трансформатора тока. Детально рассмотрены этапы практической реализации такой искусственной нейронной сети. В среде имитационного моделирования MATLAB-Simulink методом вычислительного эксперимента выполнена проверка функционирования предложенного детектора, которая подтвердила, что он позволяет быстро и безошибочно определять насыщение в широком диапазоне изменения параметров энергосистемы и самого трансформатора тока.

Protection of multi-inverter based microgrid using phase angle trajectory

This thesis presents a simple, yet a clever way of using the current phase angle to develop low bandwidth communication-assisted line protection strategies for medium and low voltage AC microgrids, particularly those with multi-inverter interfaced distributed generators. It is now a trend in both AC transmission and distribution segments of power network that inverters interface renewable energy to the system. Unlike synchronous generators the fault feeding, and control characteristic of these generators are different and mostly influenced by the topology, switching, control deployed in the power electronics interface. The limited and controlled fault current challenges the existing conventional protection schemes. Offering higher power supply reliability and system resilience than conventional radial distribution systems, multi-inverter based microgrids, particularly those with loop and mesh typologies, are characterised by bidirectional power flow. This further constrains traditional protections such that communication-less protection schemes become ineffective for such systems. So unit protection types, such as differential protection, become more technically suitable for such microgrids despite the necessity for a communication system. In this thesis, two current direction based protection schemes for medium voltage islanded microgrids have been developed. The change in current flow direction in a line is detected using the cosine of the positive sequence current phase angle. Expressing the change and no-change of the flow directions as binary states, a low bandwidth communication based protection scheme is proposed comparing the binary states from local and remote ends of the line. To further enhance the scope and reliability of this scheme, a second protection scheme is proposed in Chapter 7 whereby the cosine function is combined with the rate of change of the slope of the phase angle (ROCOSP). This combination allows the detection and isolation of a fault even with the failure of the communication channel between relays protecting a faulted line. Furthermore, these scheme can work together and share the communication infrastructure as primary and backup protections. The performance of these schemes was assessed through simulations of microgrid models developed in Matlab/Simulink.Open Acces

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

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

Medical Grade High Frequncy Power Distribution Units

The focus of this thesis is to design, model, build, and test a series resonance converter that uses a high frequency isolation transformer, offering significant reduction in size and cost, for powering a Computed Tomography (CT) scanner. The design increases the power quality for the load by isolating the grid side disturbances, and providing regulated desired voltage. The proposed architecture also allows for an optimized point of integration with an UPS, a regulated DC bus to improve waveform fidelity of x-ray generator, and active monitoring and control of the power architecture. Conventional CT systems use a 60Hz transformer, which not only occupies large footprints but also uses large amounts of copper and iron with increasing cost trajectory. In comparison to the traditional Power Distribution Units (PDU), the medical grade high frequency PDU presented in this thesis provides higher power quality and performance at a lower cost. The new CT systems possess unprecedented performance capability in terms of rotational speed and x-ray voltage modulation ( Ultra-Fast kV ) fidelity. In order to achieve such capabilities, a tightly regulated high power DC bus (700VDC, 150kW) is required. The system implemented in this thesis satisfies these new requirements. Design requirements, proposed architecture and controls, modeling, implementation and test results of the proposed system, including thermal analysis and electromagnetic compatibility, are presented in details in this thesis

Digital generator protection

Imperial Users onl