Rivista e Edizione

Volume 73 (2022): Edizione 4 (August 2022)

Volume 73 (2022): Edizione 3 (June 2022)

Volume 73 (2022): Edizione 2 (April 2022)

Volume 73 (2022): Edizione 1 (February 2022)

Volume 72 (2021): Edizione 6 (December 2021)

Volume 72 (2021): Edizione 5 (September 2021)

Volume 72 (2021): Edizione 4 (August 2021)

Volume 72 (2021): Edizione 3 (June 2021)

Volume 72 (2021): Edizione 2 (April 2021)

Volume 72 (2021): Edizione 1 (February 2021)

Volume 71 (2020): Edizione 6 (December 2020)

Volume 71 (2020): Edizione 5 (September 2020)

Volume 71 (2020): Edizione 4 (August 2020)

Volume 71 (2020): Edizione 3 (June 2020)

Volume 71 (2020): Edizione 2 (April 2020)

Volume 71 (2020): Edizione 1 (February 2020)

Volume 70 (2019): Edizione 7 (December 2019)
Special Edizione

Volume 70 (2019): Edizione 6 (December 2019)

Volume 70 (2019): Edizione 5 (September 2019)

Volume 70 (2019): Edizione 4 (August 2019)

Volume 70 (2019): Edizione 3 (June 2019)

Volume 70 (2019): Edizione 2 (April 2019)

Volume 70 (2019): Edizione 1 (February 2019)

Volume 69 (2018): Edizione 6 (December 2018)

Volume 69 (2018): Edizione 5 (September 2018)

Volume 69 (2018): Edizione 4 (August 2018)

Volume 69 (2018): Edizione 3 (June 2018)

Volume 69 (2018): Edizione 2 (March 2018)

Volume 69 (2018): Edizione 1 (January 2018)

Volume 68 (2017): Edizione 7 (December 2017)

Volume 68 (2017): Edizione 6 (November 2017)

Volume 68 (2017): Edizione 5 (September 2017)

Volume 68 (2017): Edizione 4 (August 2017)

Volume 68 (2017): Edizione 3 (May 2017)

Volume 68 (2017): Edizione 2 (March 2017)

Volume 68 (2017): Edizione 1 (January 2017)

Volume 67 (2016): Edizione 6 (December 2016)

Volume 67 (2016): Edizione 5 (September 2016)

Volume 67 (2016): Edizione 4 (July 2016)

Volume 67 (2016): Edizione 3 (May 2016)

Volume 67 (2016): Edizione 2 (April 2016)

Volume 67 (2016): Edizione 1 (January 2016)

Volume 66 (2015): Edizione 6 (November 2015)

Volume 66 (2015): Edizione 5 (September 2015)

Volume 66 (2015): Edizione 4 (July 2015)

Volume 66 (2015): Edizione 3 (May 2015)

Volume 66 (2015): Edizione 2 (March 2015)

Volume 66 (2015): Edizione 1 (January 2015)

Volume 65 (2014): Edizione 6 (November 2014)

Volume 65 (2014): Edizione 5 (September 2014)

Volume 65 (2014): Edizione 4 (July 2014)

Volume 65 (2014): Edizione 3 (May 2014)

Volume 65 (2014): Edizione 2 (March 2014)

Volume 65 (2014): Edizione 1 (January 2014)

Volume 64 (2013): Edizione 6 (November 2013)

Volume 64 (2013): Edizione 5 (September 2013)

Volume 64 (2013): Edizione 4 (June 2013)

Volume 64 (2013): Edizione 3 (May 2013)

Volume 64 (2013): Edizione 2 (March 2013)

Volume 64 (2013): Edizione 1 (January 2013)

Volume 63 (2012): Edizione 6 (November 2012)

Volume 63 (2012): Edizione 5 (September 2012)

Volume 63 (2012): Edizione 4 (July 2012)

Volume 63 (2012): Edizione 3 (May 2012)

Volume 63 (2012): Edizione 2 (March 2012)

Volume 63 (2012): Edizione 1 (January 2012)

Volume 62 (2011): Edizione 6 (November 2011)

Volume 62 (2011): Edizione 5 (September 2011)

Volume 62 (2011): Edizione 4 (July 2011)

Volume 62 (2011): Edizione 3 (May 2011)

Volume 62 (2011): Edizione 2 (March 2011)

Volume 62 (2011): Edizione 1 (January 2011)

Volume 61 (2010): Edizione 6 (November 2010)

Volume 61 (2010): Edizione 5 (September 2010)

Volume 61 (2010): Edizione 4 (July 2010)

Volume 61 (2010): Edizione 3 (May 2010)

Volume 61 (2010): Edizione 2 (March 2010)

Volume 61 (2010): Edizione 1 (January 2010)

Dettagli della rivista
Formato
Rivista
eISSN
1339-309X
Pubblicato per la prima volta
07 Jun 2011
Periodo di pubblicazione
6 volte all'anno
Lingue
Inglese

Cerca

Volume 72 (2021): Edizione 1 (February 2021)

Dettagli della rivista
Formato
Rivista
eISSN
1339-309X
Pubblicato per la prima volta
07 Jun 2011
Periodo di pubblicazione
6 volte all'anno
Lingue
Inglese

Cerca

10 Articoli
Accesso libero

An improved method of model predictive current control for multilevel cascaded H-bridge inverters

Pubblicato online: 18 Mar 2021
Pagine: 1 - 11

Astratto

Abstract

Finite control set ModelPredictive control (FCS-MPC) with the principle of considering all voltage vectors to find the optimal voltage vector for multilevel inverter in a very small sampling cycle is hardly feasible because there is no modulation part, the implementation of optimizing common-mode voltage and switching number for the multilevel inverter should be performed in the cost function. To solve the above problem, this paper proposes an improved method of model predictive current control selecting 19 adjacent voltage vectors and using weighting coefficients for common-mode voltage elimination and switching optimization. By using a discrete-time model of the system to predict the future value of the current for the voltage vector in the previous sampling cycle and its 18 adjacent voltage vectors, the one that minimizes a cost function will be selected. Thus, in a multilevel inverter with any number of levels, the cost function is performed only 19 times in a sampling cycle. The computation on FPGA allows 19 calculations of the cost function to be performed in parallel, so the executing time is very small. The feasibility of the proposed algorithm is verified by simulation model on MATLAB-simulink software and the experimental 11-level cascaded H-bridge multilevel inverter model.

Parole chiave

  • predictive current control
  • cascaded hbridge (CHB)
  • multilevel inverter
  • the number of calculations
  • common-mode voltage (CMV)
Accesso libero

Comparison of the power balance in a Totem-Pole Bridgeless PFC topology with several inrush current limiting strategies

Pubblicato online: 18 Mar 2021
Pagine: 12 - 19

Astratto

Abstract

Limiting inrush currents is usually necessary when AC-DC conversion is used to supply DC loads such as battery chargers in particular, it must comply with IEC 61000-3-3. This document discusses the suitability of an active inrush current limiter that can be used to replace traditional thermistors and NTC relays. This strategy is based on the control of the phase shift of thyristor type power components. It has been implemented in a totem-pole bridgeless power factor corrector (PFC). Experimental results show that this solution differs from traditional solutions to ensure high energy efficiency (higher than 95%) while limiting inrush currents.

Parole chiave

  • totem-pole-bridgeless PFC topology
  • inrush current limitation
  • control of the phase shift of thyristor
Accesso libero

QUIC transmission protocol: Test-bed design, implementation and experimental evaluation

Pubblicato online: 18 Mar 2021
Pagine: 20 - 28

Astratto

Abstract

With the ever increasing demand for higher speed internet connectivity that can fulfil the application continuous need for higher bandwidth Google being the pioneer in many web-based services has launched a new UDP-based protocol named quick UDP internet connections (QUIC), which aims at providing faster data delivery without requiring upgrades or modifications to the network infrastructure. The goal of this paper is to provide an overview about QUIC protocol, propose the design and implementation of a test-bed, that is used experimentally to evaluate QUIC protocol under different network conditions and scenarios. In particular, the performance advantage of QUIC in terms of delay and throughput are examined taking into account different network conditions that resemble the real internet environment. Two scenarios are proposed, the first one investigates the protocol performance under a controlled network environment, while the second one tests the protocol in a real uncontrolled network. To achieve that, a test-bed is proposed and implemented that emulates the network impairments encountered in real-network such as packet loss, bit errors, and bandwidth limitation in a controlled manner. After that, QUIC is tested in real operational wired and wireless networks. In both scenarios, QUIC outperforms TCP in terms of delay, which strengthens QUIC position for being a potential alternative to TCP.

Parole chiave

  • Google
  • TCPIP
  • web services
  • broadband communication
  • performance evaluation
  • QUIC
  • wireless net-working
Accesso libero

On single pole instrument voltage transformer overheating

Pubblicato online: 18 Mar 2021
Pagine: 29 - 34

Astratto

Abstract

The paper deals with calculation of overheating of a voltage instrument transformer used in medium voltage substations. Calculation of the primary and secondary windings is compared with measured values. These values are evaluated according to IEC 618691:2007, IEC 61869-3:2011 and IEC 60085:2007. In evaluation we focused on the state 1.9 × nominal voltage and thermal limiting output state. The article also compares the results for various parameters of instrument transformers that are necessary for clarification of calculation.

Parole chiave

  • instrument transformer of voltage
  • overheating according to IEC 618693:2011
  • numerical model of over-heating
  • IEC 60085:2007
Accesso libero

Average temperature of oil-filled transformer windings with partial cooling ducts

Pubblicato online: 18 Mar 2021
Pagine: 35 - 39

Astratto

Abstract

An effective one-dimensional model is presented that describes the temperature profile of a winding of an oil-filled distribution transformer with an arbitrary number of partial cooling ducts. An analytical solution of the model is applied to a specific example — a low voltage winding of a 400 kVA distribution transformer with one or two partial cooling ducts. Starting from the exact solution, a simple and practical formula for the temperature rise of similar windings has been derived that is suitable for transformer designers.

Parole chiave

  • heat transfer
  • distribution transformers
  • temperature rise
  • partial cooling ducts
Accesso libero

Multiscale filter-based hyperspectral image classification with PCA and SVM

Pubblicato online: 18 Mar 2021
Pagine: 40 - 45

Astratto

Abstract

Hyperspectral imagery can offer images with high spectral resolution and provide a unique ability to distinguish the subtle spectral signatures of different land covers. In this paper, we develop a new algorithm for hyperspectral image classification by using principal component analysis (PCA) and support vector machines (SVM). We use PCA to reduce the dimensionality of an HSI data cube, and then perform spatial convolution with three different filters on the PCA output cube. We feed all three convolved output cubes to SVM to classify every pixel. Finally, we perform fusion on the three output maps to determine the final classification map. We conduct experiments on three widely used hyperspectral image data cubes (ie indian pines, pavia university, and salinas). Our method can improve the classification accuracy significantly when compared to several existing methods. Our novel method is relatively fast in term of CPU computational time as well.

Parole chiave

  • hyperspectral image classification
  • 2 D filter
  • 2 D convolution
  • support vector machines (SVM)
Accesso libero

Performance and security analysis of novel ZCCRW codes in lower earth orbit based MDM-OWC incorporating hybrid modulations

Pubblicato online: 18 Mar 2021
Pagine: 46 - 52

Astratto

Abstract

Explosive data rate requirements in the satellite communication for surveillance, military services, and broadcasting have put peer pressure on the optical wireless communication (OWC) systems. Secure data transmission against eavesdropper and performance enhancement at authentic user is major concern these days. In this work, performance and security analysis of spectral amplitude codes (SAC) in mode division multiplexed (MDM) OWC have been carried out and a novel zero cross correlation resultant weight (ZCCRW) code at 100 Gbps capacity has been presented. Random diagonal (RD), Enhanced double weight (EDW), Diagonal double weight (DDW) codes have been compared through simulations and also mathematical expressions are derived under the effects of eavesdropper. Hybrid modulations have been compared to check optimal modulation with combination of Laguerre-Gaussian (LG), and HermiteGaussian (HG) modes. Results have revealed that ZCCRW code with MD-DQPSK using LG modes provide best performance and least susceptibility to eavesdropper.

Parole chiave

  • OWC
  • IsOWC
  • MDM
  • ZCCRW
  • OCDMA
  • ZCC
  • LG
  • HG
Accesso libero

A single-layer metallo-dielectric superstructure for enhancing the performances of EBG cavity antenna

Pubblicato online: 18 Mar 2021
Pagine: 53 - 60

Astratto

Abstract

A novel single-layer metallo-dielectric superstructure is proposed in this paper. It is constructed by two asymmetric unit- cells optimally arranged on the same layer to construct a partially reflective surface to be placed over a multilayer microstrip slot antenna named feed antenna for enhancing its performances. The radiation is expected to be maximum at the center of the formed layer. Thus, to maintain a high-gain performance, the unit-cells placed at the center are designed to provide a quasi-optimal reflection phase with high reflectivity at the frequency band of interest. A prototype of the proposed antenna operating at 10 GHz with overall size of 2.133λ0 ×2.133λ0 ×0.56λ0 is successfully designed and fabricated. The calculated and measured antenna gain results indicate that the proposed antenna exhibits a wider radiation bandwidth performance of about 41.15% and 36.15%, respectively.

Parole chiave

  • wideband and high gain performances
  • wide radiation bandwidth
  • single layer partially reflective surface (PRS)
  • electromagnetic-band-gap cavity antenna (ECA)
  • equivalent circuit
Accesso libero

Preparation and gas-sensing properties of very thin sputtered NiO films

Pubblicato online: 18 Mar 2021
Pagine: 61 - 65

Astratto

Abstract

We present results on very thin NiO films which are able to detect 3 ppm of acetone, toluene and n-butyl acetate in synthetic air and to operate at 300°C. NiO films with 25 and 50 nm thicknesses were prepared by dc reactive magnetron sputtering on alumina substrates previously coated by Pt layers as heater and as interdigitated electrodes. Annealed NiO films are indexed to the (fcc) crystalline structure of NiO and their calculated grain sizes are in the range from 22 to 27 nm. Surface morphology of the examined samples was influenced by a rough and compact granular structure of alumina substrate. Nanoporous NiO film is formed by an agglomeration of small grains with different shapes while they are created on every alumina grain.

Parole chiave

  • NiO films
  • reactive magnetron sputtering
  • alumina substrate
  • gas sensors
  • acetone
  • toluene
  • n-butyl acetate
Accesso libero

New model of explanation for phase angle pattern of online partial discharge measurement in winding insulation of turbine generator

Pubblicato online: 18 Mar 2021
Pagine: 66 - 77

Astratto

Abstract

On-line partial discharge (PD) measurement in electrical insulation of the turbine generator (TG) is an essential approach to control the quality of insulation and to avoid any undesired shutdowns of TG. Although in the last few decades the number of research in PD on-line monitoring methods in the stator winding of TG has increased significantly, it is still not clear yet why PD only appears at certain phase angles of the AC cycle in the phase resolved partial discharge (PRPD) pattern. Moreover, there is not yet any clarification on how the winding configuration of stator may affect PD phase angle pattern. For this reason, this work examines detailed study of the impact of the winding diagram on PD occurrence in the stator winding of real turbine generator class TVF-60-2 (60 MW, 10.5 KV). In addition, a computer simulation of various sizes of ellipsoidal cavities from 0.1 to 2.5 mm between conductor bar and stator core were carried out by using Laplaces equation in Finite Element Analysis (FEA) software ComSol to investigate the relation between the cavity size and coefficient of electric field. As a result of that, the phase angle of PD occurrence in the stator winding will highly depend on the configuration of bars connection, and the computer simulation has helped identifying the PD inception voltage and applied voltage of various ellipsoidal defects size. These two results have helped proposing an initial new theoretical model of explanation the relationship between voltage distributions and phase angle of PD occurrence to determine the degradation level of insulation caused by ellipsoidal defects in the insulation bars of the stator winding which can be used for stator windings of TG rated 6 kV and higher. This model is the initial step to develop a further comprehensive model of explanation for PRPD patterns which will consider all other types of defects as well as the space charge effects from the previous PD.

Parole chiave

  • cavity
  • PD inception voltage
  • partial discharge
  • PD phase angle
  • stator winding
10 Articoli
Accesso libero

An improved method of model predictive current control for multilevel cascaded H-bridge inverters

Pubblicato online: 18 Mar 2021
Pagine: 1 - 11

Astratto

Abstract

Finite control set ModelPredictive control (FCS-MPC) with the principle of considering all voltage vectors to find the optimal voltage vector for multilevel inverter in a very small sampling cycle is hardly feasible because there is no modulation part, the implementation of optimizing common-mode voltage and switching number for the multilevel inverter should be performed in the cost function. To solve the above problem, this paper proposes an improved method of model predictive current control selecting 19 adjacent voltage vectors and using weighting coefficients for common-mode voltage elimination and switching optimization. By using a discrete-time model of the system to predict the future value of the current for the voltage vector in the previous sampling cycle and its 18 adjacent voltage vectors, the one that minimizes a cost function will be selected. Thus, in a multilevel inverter with any number of levels, the cost function is performed only 19 times in a sampling cycle. The computation on FPGA allows 19 calculations of the cost function to be performed in parallel, so the executing time is very small. The feasibility of the proposed algorithm is verified by simulation model on MATLAB-simulink software and the experimental 11-level cascaded H-bridge multilevel inverter model.

Parole chiave

  • predictive current control
  • cascaded hbridge (CHB)
  • multilevel inverter
  • the number of calculations
  • common-mode voltage (CMV)
Accesso libero

Comparison of the power balance in a Totem-Pole Bridgeless PFC topology with several inrush current limiting strategies

Pubblicato online: 18 Mar 2021
Pagine: 12 - 19

Astratto

Abstract

Limiting inrush currents is usually necessary when AC-DC conversion is used to supply DC loads such as battery chargers in particular, it must comply with IEC 61000-3-3. This document discusses the suitability of an active inrush current limiter that can be used to replace traditional thermistors and NTC relays. This strategy is based on the control of the phase shift of thyristor type power components. It has been implemented in a totem-pole bridgeless power factor corrector (PFC). Experimental results show that this solution differs from traditional solutions to ensure high energy efficiency (higher than 95%) while limiting inrush currents.

Parole chiave

  • totem-pole-bridgeless PFC topology
  • inrush current limitation
  • control of the phase shift of thyristor
Accesso libero

QUIC transmission protocol: Test-bed design, implementation and experimental evaluation

Pubblicato online: 18 Mar 2021
Pagine: 20 - 28

Astratto

Abstract

With the ever increasing demand for higher speed internet connectivity that can fulfil the application continuous need for higher bandwidth Google being the pioneer in many web-based services has launched a new UDP-based protocol named quick UDP internet connections (QUIC), which aims at providing faster data delivery without requiring upgrades or modifications to the network infrastructure. The goal of this paper is to provide an overview about QUIC protocol, propose the design and implementation of a test-bed, that is used experimentally to evaluate QUIC protocol under different network conditions and scenarios. In particular, the performance advantage of QUIC in terms of delay and throughput are examined taking into account different network conditions that resemble the real internet environment. Two scenarios are proposed, the first one investigates the protocol performance under a controlled network environment, while the second one tests the protocol in a real uncontrolled network. To achieve that, a test-bed is proposed and implemented that emulates the network impairments encountered in real-network such as packet loss, bit errors, and bandwidth limitation in a controlled manner. After that, QUIC is tested in real operational wired and wireless networks. In both scenarios, QUIC outperforms TCP in terms of delay, which strengthens QUIC position for being a potential alternative to TCP.

Parole chiave

  • Google
  • TCPIP
  • web services
  • broadband communication
  • performance evaluation
  • QUIC
  • wireless net-working
Accesso libero

On single pole instrument voltage transformer overheating

Pubblicato online: 18 Mar 2021
Pagine: 29 - 34

Astratto

Abstract

The paper deals with calculation of overheating of a voltage instrument transformer used in medium voltage substations. Calculation of the primary and secondary windings is compared with measured values. These values are evaluated according to IEC 618691:2007, IEC 61869-3:2011 and IEC 60085:2007. In evaluation we focused on the state 1.9 × nominal voltage and thermal limiting output state. The article also compares the results for various parameters of instrument transformers that are necessary for clarification of calculation.

Parole chiave

  • instrument transformer of voltage
  • overheating according to IEC 618693:2011
  • numerical model of over-heating
  • IEC 60085:2007
Accesso libero

Average temperature of oil-filled transformer windings with partial cooling ducts

Pubblicato online: 18 Mar 2021
Pagine: 35 - 39

Astratto

Abstract

An effective one-dimensional model is presented that describes the temperature profile of a winding of an oil-filled distribution transformer with an arbitrary number of partial cooling ducts. An analytical solution of the model is applied to a specific example — a low voltage winding of a 400 kVA distribution transformer with one or two partial cooling ducts. Starting from the exact solution, a simple and practical formula for the temperature rise of similar windings has been derived that is suitable for transformer designers.

Parole chiave

  • heat transfer
  • distribution transformers
  • temperature rise
  • partial cooling ducts
Accesso libero

Multiscale filter-based hyperspectral image classification with PCA and SVM

Pubblicato online: 18 Mar 2021
Pagine: 40 - 45

Astratto

Abstract

Hyperspectral imagery can offer images with high spectral resolution and provide a unique ability to distinguish the subtle spectral signatures of different land covers. In this paper, we develop a new algorithm for hyperspectral image classification by using principal component analysis (PCA) and support vector machines (SVM). We use PCA to reduce the dimensionality of an HSI data cube, and then perform spatial convolution with three different filters on the PCA output cube. We feed all three convolved output cubes to SVM to classify every pixel. Finally, we perform fusion on the three output maps to determine the final classification map. We conduct experiments on three widely used hyperspectral image data cubes (ie indian pines, pavia university, and salinas). Our method can improve the classification accuracy significantly when compared to several existing methods. Our novel method is relatively fast in term of CPU computational time as well.

Parole chiave

  • hyperspectral image classification
  • 2 D filter
  • 2 D convolution
  • support vector machines (SVM)
Accesso libero

Performance and security analysis of novel ZCCRW codes in lower earth orbit based MDM-OWC incorporating hybrid modulations

Pubblicato online: 18 Mar 2021
Pagine: 46 - 52

Astratto

Abstract

Explosive data rate requirements in the satellite communication for surveillance, military services, and broadcasting have put peer pressure on the optical wireless communication (OWC) systems. Secure data transmission against eavesdropper and performance enhancement at authentic user is major concern these days. In this work, performance and security analysis of spectral amplitude codes (SAC) in mode division multiplexed (MDM) OWC have been carried out and a novel zero cross correlation resultant weight (ZCCRW) code at 100 Gbps capacity has been presented. Random diagonal (RD), Enhanced double weight (EDW), Diagonal double weight (DDW) codes have been compared through simulations and also mathematical expressions are derived under the effects of eavesdropper. Hybrid modulations have been compared to check optimal modulation with combination of Laguerre-Gaussian (LG), and HermiteGaussian (HG) modes. Results have revealed that ZCCRW code with MD-DQPSK using LG modes provide best performance and least susceptibility to eavesdropper.

Parole chiave

  • OWC
  • IsOWC
  • MDM
  • ZCCRW
  • OCDMA
  • ZCC
  • LG
  • HG
Accesso libero

A single-layer metallo-dielectric superstructure for enhancing the performances of EBG cavity antenna

Pubblicato online: 18 Mar 2021
Pagine: 53 - 60

Astratto

Abstract

A novel single-layer metallo-dielectric superstructure is proposed in this paper. It is constructed by two asymmetric unit- cells optimally arranged on the same layer to construct a partially reflective surface to be placed over a multilayer microstrip slot antenna named feed antenna for enhancing its performances. The radiation is expected to be maximum at the center of the formed layer. Thus, to maintain a high-gain performance, the unit-cells placed at the center are designed to provide a quasi-optimal reflection phase with high reflectivity at the frequency band of interest. A prototype of the proposed antenna operating at 10 GHz with overall size of 2.133λ0 ×2.133λ0 ×0.56λ0 is successfully designed and fabricated. The calculated and measured antenna gain results indicate that the proposed antenna exhibits a wider radiation bandwidth performance of about 41.15% and 36.15%, respectively.

Parole chiave

  • wideband and high gain performances
  • wide radiation bandwidth
  • single layer partially reflective surface (PRS)
  • electromagnetic-band-gap cavity antenna (ECA)
  • equivalent circuit
Accesso libero

Preparation and gas-sensing properties of very thin sputtered NiO films

Pubblicato online: 18 Mar 2021
Pagine: 61 - 65

Astratto

Abstract

We present results on very thin NiO films which are able to detect 3 ppm of acetone, toluene and n-butyl acetate in synthetic air and to operate at 300°C. NiO films with 25 and 50 nm thicknesses were prepared by dc reactive magnetron sputtering on alumina substrates previously coated by Pt layers as heater and as interdigitated electrodes. Annealed NiO films are indexed to the (fcc) crystalline structure of NiO and their calculated grain sizes are in the range from 22 to 27 nm. Surface morphology of the examined samples was influenced by a rough and compact granular structure of alumina substrate. Nanoporous NiO film is formed by an agglomeration of small grains with different shapes while they are created on every alumina grain.

Parole chiave

  • NiO films
  • reactive magnetron sputtering
  • alumina substrate
  • gas sensors
  • acetone
  • toluene
  • n-butyl acetate
Accesso libero

New model of explanation for phase angle pattern of online partial discharge measurement in winding insulation of turbine generator

Pubblicato online: 18 Mar 2021
Pagine: 66 - 77

Astratto

Abstract

On-line partial discharge (PD) measurement in electrical insulation of the turbine generator (TG) is an essential approach to control the quality of insulation and to avoid any undesired shutdowns of TG. Although in the last few decades the number of research in PD on-line monitoring methods in the stator winding of TG has increased significantly, it is still not clear yet why PD only appears at certain phase angles of the AC cycle in the phase resolved partial discharge (PRPD) pattern. Moreover, there is not yet any clarification on how the winding configuration of stator may affect PD phase angle pattern. For this reason, this work examines detailed study of the impact of the winding diagram on PD occurrence in the stator winding of real turbine generator class TVF-60-2 (60 MW, 10.5 KV). In addition, a computer simulation of various sizes of ellipsoidal cavities from 0.1 to 2.5 mm between conductor bar and stator core were carried out by using Laplaces equation in Finite Element Analysis (FEA) software ComSol to investigate the relation between the cavity size and coefficient of electric field. As a result of that, the phase angle of PD occurrence in the stator winding will highly depend on the configuration of bars connection, and the computer simulation has helped identifying the PD inception voltage and applied voltage of various ellipsoidal defects size. These two results have helped proposing an initial new theoretical model of explanation the relationship between voltage distributions and phase angle of PD occurrence to determine the degradation level of insulation caused by ellipsoidal defects in the insulation bars of the stator winding which can be used for stator windings of TG rated 6 kV and higher. This model is the initial step to develop a further comprehensive model of explanation for PRPD patterns which will consider all other types of defects as well as the space charge effects from the previous PD.

Parole chiave

  • cavity
  • PD inception voltage
  • partial discharge
  • PD phase angle
  • stator winding

Pianifica la tua conferenza remota con Sciendo