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Przedmiotem artykułu jest zaprezentowanie technicznych rozwiązań rozdzielnic średniego napięcia służących do pierwotnego rozdziału energii elektrycznej na poziomie do 24 kV napięcia znamionowego. Przedstawiono historię technicznego rozwoju tego typu rozdzielnic, obowiązujące normy, zasadnicze wymagania konstrukcyjne. Głównym celem artykułu jest szczegółowe omówienie najważniejszych zagadnień konstrukcyjnych...
In order to correct the power factor and limit the flow of harmonics in the source, the effectiveness of active power filters associated to control law is no longer to be demonstrated. Almost all of these methods are designed for a perfect sinusoidal source and do not produce sinusoidal current when the voltages are disturbed. The work developed here concerns active filtering on a perturbed network,...
There are today many techniques for controlling active filters on single-phase networks in order to correct the power factor and limit the harmonics consumed at the source. Almost all of these methods are determined for a perfect sinusoidal source. The work developed here concerns the taking into account of a perturbed network, that is to say the presence of voltage harmonics at the connection point...
This paper describes the design of a DC grid as a utility grid of a business park. The center of the DC grid is a DC substation. The DC substation is supplied from the MV AC grid. With a transformer and an Active Front-End, the AC voltage of 10 kV is transformed into 750 VDC. At customer side, the 750 VDC is converted to the required DC voltage for his application.
The implementation of 15 kV Silicon Carbide (SiC) MOSFETs in a three-phase, three-level active power filter of 100 kVA for a 10 kVAC grid and their challenges is shown. Due to the high switching frequency of 16 kHz, respectively 32 kHz ripple frequency, it will perfectly suited for active filtering of harmonics in the medium voltage grid.
The paper examines the work of the microgenerator inverter during two-phase short circuits. It has been shown that the cause of the oscillation is incorrect synchronization of the inverter. It has been demonstrated that the reduction of the oscillations can be achieved by adapting the synchronization signal to the representation of unbalanced system voltages.
Supplying 25 kV, 50 Hz railway systems is a challenging task due to the load characteristics of those systems. Hence, several approaches are developed to improve their grid integration with the static frequency converter based substations. However, this supply system can be further refined by the application of a dc grid. Hence, this paper presents and discusses one possible approach to enhance the...
At microgrids, classical grid-regulating generators are replaced by converter-interfaced distributed generation (DG) or energy storage systems (ESSs). This causes a reduction of the total inertia of the system and hence the microgrid voltage and frequency become more susceptible under power variations. DC microgrids are specially affected by this phenomena as systems with rotating inertia can not...
The modular multilevel converter (MMC) provides a lot of features such as low harmonic voltage content, a high power quality or easy scalability. Due to its several advantages, it is a well-suited topology for high-voltage direct current (HVDC) applications. In a meshed DC grid, a current flow control is essential. In this paper, an MMC based HVDC current flow controller is described which allows...
This paper presents a protection scheme for a medium voltage dc (MVDC) link, that meshes three different MVAC distribution grids through ac/dc power converters. The proposed scheme includes active current limiters, hybrid circuit breakers and a communication layer for the coordination of these protection devices and power converters (logic selectivity). Active current limiters, installed just after...
Due to the increasing number of power-electronic components connected to the grid, medium-voltage dc (MVDC) grids are a promising alternative to established ac distribution grids. Within this work, the advantages and additional flexibility of substations for (urban) railways connected to future MVDC distribution grids are investigated. Possible topologies are presented and the efficiencies are compared.
This paper describes a converter that converts the DC traction supply voltage on a catenary or 3rd rail into a 3-phase AC voltage that can be used as a replacement for a connection to the public grid. The input requirements are based on the electrical constraints of traction supply systems, which have a wide variation in the voltage level. The output requirements are specified by the electrical constraints...
This paper presents a real-time co-simulation platform aimed to test control strategies for the management of the interaction between a smart grid and active prosumers. The main feature of the proposed framework relies on the multi-site approach that allows the decoupling between the network model and the system under test. This allows separate testing with the exchange of a limited amount of information...
Inverters connected to electrical grids are required to properly detect islanding conditions, namely, the condition of operating isolated from the main grid. To verify the effectiveness of grid-tied converters in dealing with unintentional islanding conditions, test procedures based on resonant parallel RLC loads are recommended by standards. In this paper, we show the feasibility of using power electronic...
The decentralization of control and management in electrical grid is an important evolution to integrate distributed generation into the power grids ensuring power reliability, quality and safety. Microgrids and Multi-Agent Systems are considered the key to apply this evolution. This paper presents a Multi-Agent System architecture (developed in JADE) for Microgrid operation. Furthermore, a rule-based...
The distribution networks have been subjected to increased demand for electricity and the inclusion of distributed generation (DG), which have affected the voltage regulation. In this work, it is proposed a smart distribution transformer, which encompasses an electronic on-load tap changer and a communication system. In addition to the automatic or remote voltage regulation, the system enables to...
Soon, virtual inertia for grid control must be covered by photovoltaic inverters. It is suggested to use DC link capacitors for this task. This requires 5 W, 50 J and a capacitor size of about 200 cm3 per installed kW, corresponding to the size of single phase DC link capacitors. It is shown that the additional power ripple (and thus current ripple) is in the order of 0.1% and the voltage ripple of...
The effect of several modular approaches to the design, on the efficiency and size of a Solid State transformer (SST) are investigated. The modular approaches are evaluated for the case of 400 kVA, 10 kV/0.4 kV solid state transformers, considering the daily loading profile of the distribution network. The SST is compared to an equally rated low-frequency transformer (LFT) in terms of efficiency,...
Distributed Renewable Energy generation can affect the power quality of local low voltage distribution grids. Large hydro, wind or solar power plants combined with too weak power distributed infrastructures will generate line voltage increase at the feeding point. A solution for automatic line voltage correction, based on a static AC/AC static converter and a transformer is presented here. Emphasis...
This paper presents a communication-assisted protection technique for dc microgrids. The technique, consist of a centralized fault detection, by use of the differential method; and a fault isolation strategy by coordinated operation of dc breakers and isolator switches. Hardware in the loop simulation is used to evaluate the proposed protection.
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