Magazine et Edition

Volume 59 (2022): Edition 4 (August 2022)

Volume 59 (2022): Edition 3 (June 2022)

Volume 59 (2022): Edition s3 (June 2022)

Volume 59 (2022): Edition 2 (April 2022)

Volume 59 (2022): Edition 1 (February 2022)

Volume 58 (2021): Edition 6 (December 2021)

Volume 58 (2021): Edition 5 (October 2021)

Volume 58 (2021): Edition 4 (August 2021)

Volume 58 (2021): Edition 3 (June 2021)

Volume 58 (2021): Edition 2 (April 2021)

Volume 58 (2021): Edition 1 (February 2021)

Volume 57 (2020): Edition 6 (December 2020)

Volume 57 (2020): Edition 5 (October 2020)

Volume 57 (2020): Edition 4 (August 2020)

Volume 57 (2020): Edition 3 (June 2020)

Volume 57 (2020): Edition 1-2 (April 2020)

Volume 56 (2019): Edition 6 (December 2019)

Volume 56 (2019): Edition 5 (October 2019)

Volume 56 (2019): Edition 4 (August 2019)

Volume 56 (2019): Edition 3 (June 2019)

Volume 56 (2019): Edition 2 (April 2019)

Volume 56 (2019): Edition 1 (February 2019)

Volume 55 (2018): Edition 6 (December 2018)

Volume 55 (2018): Edition 5 (October 2018)

Volume 55 (2018): Edition 4 (August 2018)

Volume 55 (2018): Edition 3 (June 2018)

Volume 55 (2018): Edition 2 (April 2018)

Volume 55 (2018): Edition 1 (February 2018)

Volume 54 (2017): Edition 6 (December 2017)

Volume 54 (2017): Edition 5 (October 2017)

Volume 54 (2017): Edition 4 (August 2017)

Volume 54 (2017): Edition 3 (June 2017)

Volume 54 (2017): Edition 2 (April 2017)

Volume 54 (2017): Edition 1 (February 2017)

Volume 53 (2016): Edition 6 (December 2016)

Volume 53 (2016): Edition 5 (October 2016)

Volume 53 (2016): Edition 4 (August 2016)

Volume 53 (2016): Edition 3 (June 2016)

Volume 53 (2016): Edition 2 (April 2016)

Volume 53 (2016): Edition 1 (February 2016)

Volume 52 (2015): Edition 6 (December 2015)

Volume 52 (2015): Edition 5 (October 2015)

Volume 52 (2015): Edition 4 (August 2015)

Volume 52 (2015): Edition 3 (June 2015)

Volume 52 (2015): Edition 2 (April 2015)

Volume 52 (2015): Edition 1 (February 2015)

Volume 51 (2014): Edition 6 (December 2014)

Volume 51 (2014): Edition 5 (October 2014)

Volume 51 (2014): Edition 4 (August 2014)

Volume 51 (2014): Edition 3 (June 2014)

Volume 51 (2014): Edition 2 (April 2014)

Volume 51 (2014): Edition 1 (February 2014)

Volume 50 (2013): Edition 6 (December 2013)

Volume 50 (2013): Edition 5 (October 2013)

Volume 50 (2013): Edition 4 (August 2013)

Volume 50 (2013): Edition 3 (June 2013)

Volume 50 (2013): Edition 2 (April 2013)

Volume 50 (2013): Edition 1 (February 2013)

Volume 49 (2012): Edition 6-II (December 2012)

Volume 49 (2012): Edition 6-I (December 2012)

Volume 49 (2012): Edition 5 (October 2012)

Volume 49 (2012): Edition 4 (August 2012)

Volume 49 (2012): Edition 2 (April 2012)

Volume 49 (2012): Edition 1 (February 2012)

Volume 48 (2011): Edition 6 (December 2011)

Volume 48 (2011): Edition 5 (October 2011)

Volume 48 (2011): Edition 4 (August 2011)

Volume 48 (2011): Edition 3 (June 2011)

Volume 48 (2011): Edition 2 (April 2011)

Volume 48 (2011): Edition 1 (February 2011)

Volume 47 (2010): Edition 6 (December 2010)

Volume 47 (2010): Edition 5 (October 2010)

Volume 47 (2010): Edition 4 (August 2010)

Volume 47 (2010): Edition 3 (June 2010)

Volume 47 (2010): Edition 2 (April 2010)

Volume 47 (2010): Edition 1 (February 2010)

Volume 46 (2009): Edition 6 (December 2009)

Volume 46 (2009): Edition 5 (October 2009)

Volume 46 (2009): Edition 4 (August 2009)

Volume 46 (2009): Edition 3 (June 2009)

Volume 46 (2009): Edition 2 (April 2009)

Volume 46 (2009): Edition 1 (February 2009)

Volume 45 (2008): Edition 6 (December 2008)

Volume 45 (2008): Edition 5 (October 2008)

Volume 45 (2008): Edition 4 (August 2008)

Volume 45 (2008): Edition 3 (June 2008)

Volume 45 (2008): Edition 2 (April 2008)

Volume 45 (2008): Edition 1 (February 2008)

Détails du magazine
Format
Magazine
eISSN
2255-8896
ISSN
0868-8257
Première publication
18 Mar 2008
Période de publication
6 fois par an
Langues
Anglais

Chercher

Volume 50 (2013): Edition 4 (August 2013)

Détails du magazine
Format
Magazine
eISSN
2255-8896
ISSN
0868-8257
Première publication
18 Mar 2008
Période de publication
6 fois par an
Langues
Anglais

Chercher

7 Articles
Accès libre

Physical and Technical Energy Problems: Testing of the Prototype for State Estimation of Large-Scale Power Systems / Lielo Energosistēmu Stāvokļa Novērtēšanas Prototipa Testēšana

Publié en ligne: 17 Sep 2013
Pages: 3 - 13

Résumé

Abstract

The paper describes the algorithm for distributed state estimation (SE) and is focused on its testing and validation. For this purpose, different events in the modeled power system of the 330-750 kV electrical ring Latvia - Lithuania - Belarus - Smolensk - Moscow - St. Petersburg - Estonia - Latvia were considered. The methods for testing the Inter-TSO SE prototype and dynamic network monitoring & modeling are based on comparison of the available SCADA data about real events with those of SE calculation. In total, four operational states were studied, including initial, accident and two post-accident operational states

Keywords

  • distributed and dynamic state estimation
  • SCADA
  • PMU
  • wide area monitoring
Accès libre

Design of Current Source Dc/Dc Converter for Interfacing a 5 Kw Pem Fuel Cell / Paaugstinošā Strāvas Avota Līdzsprieguma Pārveidotāja Izstrāde 5 Kw Ūdeņraža Degvielas Elementam

Publié en ligne: 17 Sep 2013
Pages: 14 - 21

Résumé

Abstract

In domestic applications the low DC output voltage of a hydrogen fuel cell used as the main power supply or a backup power source has to be matched to the level and frequency of the AC voltage of utility grid. The interfacing power converter system usually consists of a DC/DC converter and an inverter. In this work, a DC/DC step-up converter stage is designed for interfacing a 5kW proton exchange membrane (PEM) fuel cell. The losses of DC/DC conversion are estimated and, basing on the relevant analysis, the most appropriate configuration of converter modules is selected for a DC/DC converter stage of increased efficiency. The authors present the results of experimental analysis and simulation for the selected configuration of four double inductor step-up push-pull converter modules

Keywords

  • DC/DC converter
  • fuel-cell system
  • high-frequency power converters
  • double inductor step-up push-pull converter
Accès libre

Evaluation of Thermal Rating Methods Based on the Transmission Line Model / Termisko Jaudas Metožu Novērtējums, Balstoties Uz Esošo Elektropārvades Līnijas Modeli

Publié en ligne: 17 Sep 2013
Pages: 22 - 33

Résumé

Abstract

Electric power consumption has been growing continuously, especially in the last years. Therefore, implementation of new advanced technologies such as the overhead line thermal monitoring is topical for improvement of the existing transmission line network in order to increase its throughput capacity and reliability of power supply. In general, the real-time thermal monitoring systems are designed based on the existing methods using the limiting conditions for ampacity determination of high-voltage overhead lines. The paper considers commonly used methods for thermal rating estimation which include computation of the conductor temperature and of the conductor sag. Comparative analysis was performed for the measured and calculated steady-state conductor temperatures and line sagging, based on which the thermal rating methods were tested. The experimental measurements were conducted for three cases using special monitoring equipment. The study has been carried out based on the existing line model of the Latvian transmission grid

Keywords

  • power transmission line
  • atmospheric measurements
  • current measurements
  • comparative analysis
Accès libre

Effect of Microwave Pre-Processing of Pelletized Biomass on its Gasification and Combustion / Mikroviļnu Priekšapstrādes Ietekme Uz Granulētas Biomasas Gazifikācijas Un Degšanas Procesiem

Publié en ligne: 17 Sep 2013
Pages: 34 - 47

Résumé

Abstract

To effectively produce clean heat energy from biomass, microwave (mw) pre-processing of its different types - pelletized wood (spruce), herbaceous biomass (reed canary grass) and their mixture (50:50) - was carried out at the 2.45 GHz frequency with different durations of biomass exposure to high-frequency oscillations. To estimate the mw pre-processing effect on the structure, composition and fuel characteristics of biomass, its thermogravimetric (TG), infrared spectroscopy (FTIR) measurements and elemental analysis were made. The pre-processing is shown to enhance the release of moisture and low-calorific volatiles and the partial destruction of biomass constituents (hemicelluloses, cellulose), promoting variations in the elemental composition and heating values of biomass. The field-enhanced variations of biomass characteristics and their influence on its gasification and combustion were studied using an integrated system of a biomass gasifier and a combustor with swirl-enhanced stabilization of the flame reaction zone. The results show that the mw pre-processing of biomass pellets provides a faster weight loss at the gasification, and, therefore, faster ignition and combustion of the activated pellets along with increased output of heat energy at their burnout

Keywords

  • biomass pellets
  • pre-processing
  • gasification
  • combustion characteristics
  • heat energy production
Accès libre

Photocatalitic Properties of Tio2 and ZnO Nanopowders / Tio2 un Zno Nanopulveru Fotokatalitiskās Īpašības

Publié en ligne: 17 Sep 2013
Pages: 48 - 55

Résumé

Abstract

Photocatalytic activity of TiO2 and ZnO nanopowders is studied depending on the morphology, grain sizes and method of synthesizing. Photocatalysis of the prepared powders was evaluated by degradation of the methylene blue aqueous solution. Absorbance spectra (190-100 nm) were measured during exposure of the solution to UV light. The relationships between the photocatalytic activity and the particle size, crystal polymorph phases and grain morphology were analyzed. The photocatalytic activity of prepared TiO2 nanopowders has been found to depend of the anatase-to-rutile phase ratio. Comparison is given for the photocatalytic activity of ZnO nanopowders prepared by sol-gel and solar physical vapour deposition (SPVD) methods

Keywords

  • photocatalysis
  • photocatalytic activity
  • ZnO
  • TiO2
  • nanopowders
Accès libre

Structure, Composition and Magnetic Properties of Ferrofluid Nanoparticles after Separation / Feromagnētisko Šķidrumu Nanodaļiņu Struktūras, Sastāva un Magnētisko Īpašību Izmaiņas Pēc Separācijas

Publié en ligne: 17 Sep 2013
Pages: 56 - 61

Résumé

Abstract

The structure, composition and magnetic properties of iron oxide nanoparticles are studied as dependent on the synthesis technology and method of separation in ferrofluids. The goal of the present study is to improve the magnetic properties of wet-synthesized nanoparticles and achieve a narrow nanoparticle size distribution. The results of measurements show that by varying the conditions of the chemical coprecipitation method, different compositions and structures of the nanoparticles could be obtained. The separation of ferrite nanoparticles of a polydisperse colloid by centrifugation as well as by HGMS provides the possibility to obtain a nanoparticle set with narrow size distribution

Keywords

  • ferrofluids
  • iron oxide nanoparticle structure
  • magnetic properties
Accès libre

Determination of Two-Liquid Mixture Composition by Assessing Dielectric Parameters 1. Precise Measuring System / Divu Šķidrumu Maisījuma Sastāva Noteikšana, Izvērtējot to Dielektriskos Parametrus 1. Precīza Mērīšanas Sistēma

Publié en ligne: 17 Sep 2013
Pages: 62 - 73

Résumé

Abstract

Concentration measurements are important in bioethanol industries, in the R&D areas, for chemical, medical and microbiological analyses and processing as well as for diagnostics, manufacturing, etc. The overview shows development of the structural design of a system for measuring the concentration of solutions and mixtures consisting of two dielectric liquids. The basic principles of the system's design are given along with relevant equations. The concentration of dielectric liquids is measured using devices with capacitive sensors (1-300 pF). The operational frequency of the developed measuring system is 100.000 kHz. Configuration of the system excludes some errors usually arising at measurements, and broadens its applicability. For testing, the system was calibrated for measuring the concentration of anhydrous ethanol + de-ionized water mixture. Experimental results have shown a stable resolution of ±0.005 pF at measuring the sensor capacitance and a reproducible resolution better than ±0.01% at measuring the ethanol volume concentration

Keywords

  • dielectric liquid
  • capacitive sensor
  • impedance measurement
  • dielectric constant
7 Articles
Accès libre

Physical and Technical Energy Problems: Testing of the Prototype for State Estimation of Large-Scale Power Systems / Lielo Energosistēmu Stāvokļa Novērtēšanas Prototipa Testēšana

Publié en ligne: 17 Sep 2013
Pages: 3 - 13

Résumé

Abstract

The paper describes the algorithm for distributed state estimation (SE) and is focused on its testing and validation. For this purpose, different events in the modeled power system of the 330-750 kV electrical ring Latvia - Lithuania - Belarus - Smolensk - Moscow - St. Petersburg - Estonia - Latvia were considered. The methods for testing the Inter-TSO SE prototype and dynamic network monitoring & modeling are based on comparison of the available SCADA data about real events with those of SE calculation. In total, four operational states were studied, including initial, accident and two post-accident operational states

Keywords

  • distributed and dynamic state estimation
  • SCADA
  • PMU
  • wide area monitoring
Accès libre

Design of Current Source Dc/Dc Converter for Interfacing a 5 Kw Pem Fuel Cell / Paaugstinošā Strāvas Avota Līdzsprieguma Pārveidotāja Izstrāde 5 Kw Ūdeņraža Degvielas Elementam

Publié en ligne: 17 Sep 2013
Pages: 14 - 21

Résumé

Abstract

In domestic applications the low DC output voltage of a hydrogen fuel cell used as the main power supply or a backup power source has to be matched to the level and frequency of the AC voltage of utility grid. The interfacing power converter system usually consists of a DC/DC converter and an inverter. In this work, a DC/DC step-up converter stage is designed for interfacing a 5kW proton exchange membrane (PEM) fuel cell. The losses of DC/DC conversion are estimated and, basing on the relevant analysis, the most appropriate configuration of converter modules is selected for a DC/DC converter stage of increased efficiency. The authors present the results of experimental analysis and simulation for the selected configuration of four double inductor step-up push-pull converter modules

Keywords

  • DC/DC converter
  • fuel-cell system
  • high-frequency power converters
  • double inductor step-up push-pull converter
Accès libre

Evaluation of Thermal Rating Methods Based on the Transmission Line Model / Termisko Jaudas Metožu Novērtējums, Balstoties Uz Esošo Elektropārvades Līnijas Modeli

Publié en ligne: 17 Sep 2013
Pages: 22 - 33

Résumé

Abstract

Electric power consumption has been growing continuously, especially in the last years. Therefore, implementation of new advanced technologies such as the overhead line thermal monitoring is topical for improvement of the existing transmission line network in order to increase its throughput capacity and reliability of power supply. In general, the real-time thermal monitoring systems are designed based on the existing methods using the limiting conditions for ampacity determination of high-voltage overhead lines. The paper considers commonly used methods for thermal rating estimation which include computation of the conductor temperature and of the conductor sag. Comparative analysis was performed for the measured and calculated steady-state conductor temperatures and line sagging, based on which the thermal rating methods were tested. The experimental measurements were conducted for three cases using special monitoring equipment. The study has been carried out based on the existing line model of the Latvian transmission grid

Keywords

  • power transmission line
  • atmospheric measurements
  • current measurements
  • comparative analysis
Accès libre

Effect of Microwave Pre-Processing of Pelletized Biomass on its Gasification and Combustion / Mikroviļnu Priekšapstrādes Ietekme Uz Granulētas Biomasas Gazifikācijas Un Degšanas Procesiem

Publié en ligne: 17 Sep 2013
Pages: 34 - 47

Résumé

Abstract

To effectively produce clean heat energy from biomass, microwave (mw) pre-processing of its different types - pelletized wood (spruce), herbaceous biomass (reed canary grass) and their mixture (50:50) - was carried out at the 2.45 GHz frequency with different durations of biomass exposure to high-frequency oscillations. To estimate the mw pre-processing effect on the structure, composition and fuel characteristics of biomass, its thermogravimetric (TG), infrared spectroscopy (FTIR) measurements and elemental analysis were made. The pre-processing is shown to enhance the release of moisture and low-calorific volatiles and the partial destruction of biomass constituents (hemicelluloses, cellulose), promoting variations in the elemental composition and heating values of biomass. The field-enhanced variations of biomass characteristics and their influence on its gasification and combustion were studied using an integrated system of a biomass gasifier and a combustor with swirl-enhanced stabilization of the flame reaction zone. The results show that the mw pre-processing of biomass pellets provides a faster weight loss at the gasification, and, therefore, faster ignition and combustion of the activated pellets along with increased output of heat energy at their burnout

Keywords

  • biomass pellets
  • pre-processing
  • gasification
  • combustion characteristics
  • heat energy production
Accès libre

Photocatalitic Properties of Tio2 and ZnO Nanopowders / Tio2 un Zno Nanopulveru Fotokatalitiskās Īpašības

Publié en ligne: 17 Sep 2013
Pages: 48 - 55

Résumé

Abstract

Photocatalytic activity of TiO2 and ZnO nanopowders is studied depending on the morphology, grain sizes and method of synthesizing. Photocatalysis of the prepared powders was evaluated by degradation of the methylene blue aqueous solution. Absorbance spectra (190-100 nm) were measured during exposure of the solution to UV light. The relationships between the photocatalytic activity and the particle size, crystal polymorph phases and grain morphology were analyzed. The photocatalytic activity of prepared TiO2 nanopowders has been found to depend of the anatase-to-rutile phase ratio. Comparison is given for the photocatalytic activity of ZnO nanopowders prepared by sol-gel and solar physical vapour deposition (SPVD) methods

Keywords

  • photocatalysis
  • photocatalytic activity
  • ZnO
  • TiO2
  • nanopowders
Accès libre

Structure, Composition and Magnetic Properties of Ferrofluid Nanoparticles after Separation / Feromagnētisko Šķidrumu Nanodaļiņu Struktūras, Sastāva un Magnētisko Īpašību Izmaiņas Pēc Separācijas

Publié en ligne: 17 Sep 2013
Pages: 56 - 61

Résumé

Abstract

The structure, composition and magnetic properties of iron oxide nanoparticles are studied as dependent on the synthesis technology and method of separation in ferrofluids. The goal of the present study is to improve the magnetic properties of wet-synthesized nanoparticles and achieve a narrow nanoparticle size distribution. The results of measurements show that by varying the conditions of the chemical coprecipitation method, different compositions and structures of the nanoparticles could be obtained. The separation of ferrite nanoparticles of a polydisperse colloid by centrifugation as well as by HGMS provides the possibility to obtain a nanoparticle set with narrow size distribution

Keywords

  • ferrofluids
  • iron oxide nanoparticle structure
  • magnetic properties
Accès libre

Determination of Two-Liquid Mixture Composition by Assessing Dielectric Parameters 1. Precise Measuring System / Divu Šķidrumu Maisījuma Sastāva Noteikšana, Izvērtējot to Dielektriskos Parametrus 1. Precīza Mērīšanas Sistēma

Publié en ligne: 17 Sep 2013
Pages: 62 - 73

Résumé

Abstract

Concentration measurements are important in bioethanol industries, in the R&D areas, for chemical, medical and microbiological analyses and processing as well as for diagnostics, manufacturing, etc. The overview shows development of the structural design of a system for measuring the concentration of solutions and mixtures consisting of two dielectric liquids. The basic principles of the system's design are given along with relevant equations. The concentration of dielectric liquids is measured using devices with capacitive sensors (1-300 pF). The operational frequency of the developed measuring system is 100.000 kHz. Configuration of the system excludes some errors usually arising at measurements, and broadens its applicability. For testing, the system was calibrated for measuring the concentration of anhydrous ethanol + de-ionized water mixture. Experimental results have shown a stable resolution of ±0.005 pF at measuring the sensor capacitance and a reproducible resolution better than ±0.01% at measuring the ethanol volume concentration

Keywords

  • dielectric liquid
  • capacitive sensor
  • impedance measurement
  • dielectric constant

Planifiez votre conférence à distance avec Sciendo