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
This paper is focused on problems of power quality in systems with varying frequency, equipped with passive harmonics filter. Main differences between the ship system and land network have been pointed out. Influence of varying frequency on proper work of harmonic passive filters frequency change was presented. Simulation circuit and simulations results of theoretical research have been described. Especially influence of frequency on proper work of 5th and 7th harmonic filters was commented on.
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The paper presents the single phase uninterruptible power supply (UPS) system with galvanic separated DC-AC-DC-AC converters operating in parallel. The CAN physical layer based system of communication between converters has been developed and applied, which allow to utilize a decentralized master-slave control providing high availability factor of the whole UPS system. The control system of particular converters has been developed to ensure a high quality of the output voltage for both linear and nonlinear load.Read full article
In the context of renewable energy, this study treats the case of the conversion of photovoltaic and wind energy, which are parts of non pollutant energy, to electrical one in order to create a local archive. Annual data of delivered power are therefore given. In addition, the efficiency of each conversion system is calculated. Finally, the cost of solar and wind power plants are discussed and compared.
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Dynamic Voltage Restorer (DVR) is a custom power device that is used to compensate voltage sag. The DVR generally consists of voltage source inverter (VSI), injection transformers, passive filters and energy storage (battery). The efficiency of the DVR depends on the efficiency of the control technique involved in switching the inverters. The inverters are switched using Space Vector Pulse Width Modulation pulses (SVPWM) to maximize the usage of DC link voltage.Read full article
Driving rural development
Hydroelectric generation in China is not limited only to huge scale projects. In recent years, the country has become one of the most successful adopters of small hydroelectric facilities (plants up to 25 MW) as a means of achieving carbon emission free rural development.
The total installed capacity of small hydroelectric plants in China is estimated at approximately 50,000 MW and growing at about 6,000 MW annually.Read full article
This paper is presented by Chilectra, a subsidiary of the Endesa Group Spain and the biggest electric utility in Chile. It sets out a methodology for estimating and determining control parameters for the voltage quality to be delivered to its end customers.Read full article
Analyses to have a quantitative idea of the real behavior of Switching Power Supply (SPS) units from the point of view of waveform distortion and power absorption are developed. Results of several experimental tests performed by means of a test system built up at Laboratories of the Second University of Naples (Italy) are firstly reported.Read full article