Rapid growth of Latvian economy resulted in rapid growth of electricity demand in cities and rural regions. Consumers’ reliability requirements are increasing, but improvement of reliability is directly related to electricity supply reservation possibilities in case of one or more network components failure. This article describes conditions for independent operation of decentralized renewable power supply sources, evaluates its exploitation possibilities and feasibility for local consumers’ reservation.Read full article
Interharmonics are voltages or currents with a frequency that is a non-integral multiple of the fundamental supply frequency, while each harmonic frequency is an integral multiple of the supply frequency. Interharmonics, always present in the power system, have recently become of more importance since the widespread use of power electronic systems results in an increase of their magnitude.Read full article
The Israel Electric corp. deployed a nationwide Power Quality Monitoring System (PQMS). The PQMS monitors the quality of supply of all of its high voltage costumers, as well as a sample of its medium voltage customers. The PQMS monitors both the voltages and the currents. The PQMS has been operational since October 2005. The paper presents preliminary measurement results obtained from the PQMS.
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If we continue business-as-usual, climate change — according to both the worst prognoses and the more optimistic ones — will confront humanity with serious consequences and a high price tag. However, the cost to society of mitigating climate change by reducing greenhouse gas emissions is also high. So inevitably, the question arises: what we should do? Pay today for mitigating climate change or pay later to deal with its consequences?Read full article
Nowadays, in many countries the increase of generating capacity takes place in small units of so-called distributed generation (DG), and among them in hybrid power (generating) systems (HPS). They use primary energy conventional sources as well as renewable energy sources (RES), and in many cases produce electricity and heat (CHP). It is very often that definition of distributed generation is connected with definition of renewable energy sources.Read full article
In this paper, the authors study a variable speed wind generation system based on Doubly Fed Induction Generator (DFIG) in case of large balanced voltage dip and analyzed a remedial solution that allows for the turbine to stay connected and helps grid recovery through reactive power injection, by supplying the grid with reactive power during faults. Simulation results show the effectiveness of the solution in different operating points of the four working regions of the power-speed turbine characteristic.
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Rapidly increasing share of distributed generation (DG) in distribution networks introduced the need for active distribution network operation. As current distribution networks were not designed to integrate the power generation, the DG introduced many technical challenges in sense of power quality, network planning, protection schemes, voltage stability…. This paper presents the advantages of active approach in distribution network operation.Read full article
Reactive power is a very important quantity in electric power systems since it affects the efficiency of these systems. Also, capacitive loads can produce over-voltages in electric transformers by Ferranti effect, which produces bad power quality, so it is necessary to measure the reactive power correctly. In this paper reactive phenomena in three-phase power systems with unbalanced voltages are expressed and measured in the light of the IEEE Std 1459-2000.Read full article
In many applications of power quality monitoring, distributed measurement systems are required to provide an evaluation of the harmonic status of the system. Anyway, in distribution systems, only a few network nodes can, with acceptable costs, be equipped with measurement devices. As a consequence, lack of information has to be covered by means of suitable Harmonic State Estimation (HSE) techniques.Read full article
The paper proposes a simplified power circuit topology for the auxiliary power supplies (APS) with output powers up to 50 kW to be used in 3.0 kV DC commuter trains. Focus is on the implementation of 6.5 kV IGBTs to improve power density, system integrity as well as the reliability of the APS. For instance, a topology proposal, an analysis and a comparison with other types is presented. Some problems of converter control and protection as well as hardware design considerations are discussed.Read full article