Pub Date : 2018-06-01DOI: 10.1109/EIC.2018.8481094
Andrea L. Caprara, A. Cavallini, Luca Garagnani, J. Guo
Electrical distribution grids consist of many Medium Voltage (MV) devices, each one of them being a possible cause of fault. The demand for their increasing reliability and decreasing maintenance/replacement costs, together with the high number of installed apparatuses, is turning the focus of the condition assessment to smart solutions, integrable in networks, able to evaluate autonomously the condition of the electrical asset and, in case of anomalies, to request for man-operated support. In this paper, a novel approach to the continuous monitoring of PD phenomena in MV grids will be described. The devised solution addresses the requirements of the MV grids in that the system is non-invasive and low cost. PD data acquisition and processing systems are fully automatic, with the relevant assessment of the conditions of the MV piece of equipment. A comprehensive description of the proposed technological solution is reported, focusing mainly on the automatic acquisition and processing of PD data, automatic noise rejection and the recognition of increasing PD trend as a tool to trigger warning signals. To show the effectiveness of the proposed approach, case studies will be reported for various MV pieces of equipment, particularly on Switchgears and Ring Main Units.
{"title":"A Novel Approach for Continuous Monitoring of Partial Discharge Phenomena on Medium Voltage Equipments","authors":"Andrea L. Caprara, A. Cavallini, Luca Garagnani, J. Guo","doi":"10.1109/EIC.2018.8481094","DOIUrl":"https://doi.org/10.1109/EIC.2018.8481094","url":null,"abstract":"Electrical distribution grids consist of many Medium Voltage (MV) devices, each one of them being a possible cause of fault. The demand for their increasing reliability and decreasing maintenance/replacement costs, together with the high number of installed apparatuses, is turning the focus of the condition assessment to smart solutions, integrable in networks, able to evaluate autonomously the condition of the electrical asset and, in case of anomalies, to request for man-operated support. In this paper, a novel approach to the continuous monitoring of PD phenomena in MV grids will be described. The devised solution addresses the requirements of the MV grids in that the system is non-invasive and low cost. PD data acquisition and processing systems are fully automatic, with the relevant assessment of the conditions of the MV piece of equipment. A comprehensive description of the proposed technological solution is reported, focusing mainly on the automatic acquisition and processing of PD data, automatic noise rejection and the recognition of increasing PD trend as a tool to trigger warning signals. To show the effectiveness of the proposed approach, case studies will be reported for various MV pieces of equipment, particularly on Switchgears and Ring Main Units.","PeriodicalId":184139,"journal":{"name":"2018 IEEE Electrical Insulation Conference (EIC)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130129657","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-06-01DOI: 10.1109/EIC.2018.8481106
M. Kawada
Condition monitoring techniques for ground coils used in superconducting magnetic levitation (Maglev) systems are required. In this study, an on-board radio interferometer system with a vector-antenna was developed to locate partial discharge (PD) sources occurring in propulsion coils of superconducting Maglev systems and to know the propagation characteristics of electromagnetic (EM) waves emitted from PD sources. PD current generally develops into multiple directions, that is, the EM waves emitted from the PD current have also multidirectional components. The structures and the arrangement of propulsion coils and levitation-guidance coils might influence the propagation of EM waves. The vector-antenna composed of vertical and horizontal dipole-antennas was set to the center of the antenna-array of the on-board radio interferometer system. Three sets of mock-ups of the propulsion coil and the levitation-guidance coil were also developed in order to evaluate easily the on-board radio interferometer system. One of the propulsion coils has eight cylinder-shaped holes penetrating through the insulating material to the inner conductor for attaching a cap with a needle-electrode; one or some of the holes can be voluntarily chosen. PD current was generated in an air-gap between the tip of the needle-electrode and the surface of the inner conductor. Experimental results show that a PD source generated at a voluntary position of the propulsion coil could be located by using the on-board radio interferometer system; the vertical and horizontal components (electric fields) of the EM waves emitted from the PD source could be separately received by using the vector-antenna.
{"title":"Detection of Partial Discharges Occurring in Propulsion Coils of Superconducting Maglev Systems Using an On-Board Radio Interferometer System with a Vector-Antenna","authors":"M. Kawada","doi":"10.1109/EIC.2018.8481106","DOIUrl":"https://doi.org/10.1109/EIC.2018.8481106","url":null,"abstract":"Condition monitoring techniques for ground coils used in superconducting magnetic levitation (Maglev) systems are required. In this study, an on-board radio interferometer system with a vector-antenna was developed to locate partial discharge (PD) sources occurring in propulsion coils of superconducting Maglev systems and to know the propagation characteristics of electromagnetic (EM) waves emitted from PD sources. PD current generally develops into multiple directions, that is, the EM waves emitted from the PD current have also multidirectional components. The structures and the arrangement of propulsion coils and levitation-guidance coils might influence the propagation of EM waves. The vector-antenna composed of vertical and horizontal dipole-antennas was set to the center of the antenna-array of the on-board radio interferometer system. Three sets of mock-ups of the propulsion coil and the levitation-guidance coil were also developed in order to evaluate easily the on-board radio interferometer system. One of the propulsion coils has eight cylinder-shaped holes penetrating through the insulating material to the inner conductor for attaching a cap with a needle-electrode; one or some of the holes can be voluntarily chosen. PD current was generated in an air-gap between the tip of the needle-electrode and the surface of the inner conductor. Experimental results show that a PD source generated at a voluntary position of the propulsion coil could be located by using the on-board radio interferometer system; the vertical and horizontal components (electric fields) of the EM waves emitted from the PD source could be separately received by using the vector-antenna.","PeriodicalId":184139,"journal":{"name":"2018 IEEE Electrical Insulation Conference (EIC)","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132672392","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-06-01DOI: 10.1109/EIC.2018.8481057
Simeng Li, Qingquan Li, W. Si, Junyan Yao, Yalin Shi, T. Zhang
PD Mechanism is the theoretical basis for studying PD pulse characteristics and insulation diagnosis by PD. In this paper, a laboratory experiment for studying the PD pulses in oil-pressboard insulation by simulating a needle-plate model with positive DC voltage was performed; PD pulses were detected by a non-inductive resistor. The bipolar charge transport model and the hydrodynamic drift-diffusion model are used to simulate the streamer. Then the circuit model is built based on the streamer evolution to simulate the PD pulse, and PD mechanism is finally analyzed quantificationally. The main conclusions are: PD pulses in oil-pressboard insulation by simulating a needle-plate model at positive DC voltage are unimodal, their rising edge corresponds the process of oil gap breakdown (streamer propagation), and their falling edge corresponds the charge accumulation process at oil-pressboard interface (streamer interruption). The PD pulse essentially is the current pulse generated in coupling loop due to the defect, partly shorted by streamer, being charged.
{"title":"PD Mechanism Analysis in Oil-Pressboard Insulation with Needle-Plate Defect at Positive DC Voltage Based on Field-Circuit Joint Simulation","authors":"Simeng Li, Qingquan Li, W. Si, Junyan Yao, Yalin Shi, T. Zhang","doi":"10.1109/EIC.2018.8481057","DOIUrl":"https://doi.org/10.1109/EIC.2018.8481057","url":null,"abstract":"PD Mechanism is the theoretical basis for studying PD pulse characteristics and insulation diagnosis by PD. In this paper, a laboratory experiment for studying the PD pulses in oil-pressboard insulation by simulating a needle-plate model with positive DC voltage was performed; PD pulses were detected by a non-inductive resistor. The bipolar charge transport model and the hydrodynamic drift-diffusion model are used to simulate the streamer. Then the circuit model is built based on the streamer evolution to simulate the PD pulse, and PD mechanism is finally analyzed quantificationally. The main conclusions are: PD pulses in oil-pressboard insulation by simulating a needle-plate model at positive DC voltage are unimodal, their rising edge corresponds the process of oil gap breakdown (streamer propagation), and their falling edge corresponds the charge accumulation process at oil-pressboard interface (streamer interruption). The PD pulse essentially is the current pulse generated in coupling loop due to the defect, partly shorted by streamer, being charged.","PeriodicalId":184139,"journal":{"name":"2018 IEEE Electrical Insulation Conference (EIC)","volume":"38 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117281057","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-06-01DOI: 10.1109/EIC.2018.8481130
Simeng Li, Qingquan Li, W. Si, Junyan Yao, Yalin Shi, T. Zhang
The PD characteristics of oil-pressboard insulation with needle-plate defect at AC-DC combined voltage are unstable. In this paper, the time-variation trends of PD characteristics in pre-breakdown process at AC-DC combined voltage are studied via the tests in oil-pressboard insulation with needle-plate defect. The average PD repetition rate and average PD amplitude decrease with the PD developing, and the time-variation trends of them can be divided into fluctuation type and monotone type. The average PD amplitude has no obvious polarity effect, the average PD repetition rate has a polarity effect. In equivalent time-frequency spectrograms, most points move towards arch top with the developing of pre-breakdown processes, where PD equivalent time is 1300–1600 ns and PD equivalent frequency is 7.5-10 MHz. PD equivalent time-frequency spectrograms can be divided into half-arched type and whole-arched type at the end of pre-breakdown processes. The defect in pressboard caused by PD is a possible reason for the appearance of whole-arched time-frequency spectrogram.
{"title":"Partial Discharge Characteristics in Pre-Breakdown Processes of Oil-Pressboard Insulation with Needle-Plate Defect Under AC-DC Combined Voltage","authors":"Simeng Li, Qingquan Li, W. Si, Junyan Yao, Yalin Shi, T. Zhang","doi":"10.1109/EIC.2018.8481130","DOIUrl":"https://doi.org/10.1109/EIC.2018.8481130","url":null,"abstract":"The PD characteristics of oil-pressboard insulation with needle-plate defect at AC-DC combined voltage are unstable. In this paper, the time-variation trends of PD characteristics in pre-breakdown process at AC-DC combined voltage are studied via the tests in oil-pressboard insulation with needle-plate defect. The average PD repetition rate and average PD amplitude decrease with the PD developing, and the time-variation trends of them can be divided into fluctuation type and monotone type. The average PD amplitude has no obvious polarity effect, the average PD repetition rate has a polarity effect. In equivalent time-frequency spectrograms, most points move towards arch top with the developing of pre-breakdown processes, where PD equivalent time is 1300–1600 ns and PD equivalent frequency is 7.5-10 MHz. PD equivalent time-frequency spectrograms can be divided into half-arched type and whole-arched type at the end of pre-breakdown processes. The defect in pressboard caused by PD is a possible reason for the appearance of whole-arched time-frequency spectrogram.","PeriodicalId":184139,"journal":{"name":"2018 IEEE Electrical Insulation Conference (EIC)","volume":"22 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123495139","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-06-01DOI: 10.1109/EIC.2018.8481122
Joe V. Williams
One of the more challenging, and often misunderstood, design decisions in the manufacture of resin rich high voltage coils is selecting the proper ground wall build for the coil. How many layers of tape need to be applied to the coil for a given ground wall thickness? The selection of this proper build is critical to producing a coil that, after pressing, will have the proper ground wall density, and the proper ratio of glass, epoxy and mica, to assure maximum coil performance in the field as well as during the coil validation. This paper will explain how the proper gram density of a ground wall is determined, challenge some of the conventional wisdom, suggest target densities and acceptable ranges, and give examples for various resin rich mica tapes and design requirements. We will also explain how the volume of resin to mica and glass changes with these target densities.
{"title":"Resin Rich High Voltage Coil Design Gram Density Optimization","authors":"Joe V. Williams","doi":"10.1109/EIC.2018.8481122","DOIUrl":"https://doi.org/10.1109/EIC.2018.8481122","url":null,"abstract":"One of the more challenging, and often misunderstood, design decisions in the manufacture of resin rich high voltage coils is selecting the proper ground wall build for the coil. How many layers of tape need to be applied to the coil for a given ground wall thickness? The selection of this proper build is critical to producing a coil that, after pressing, will have the proper ground wall density, and the proper ratio of glass, epoxy and mica, to assure maximum coil performance in the field as well as during the coil validation. This paper will explain how the proper gram density of a ground wall is determined, challenge some of the conventional wisdom, suggest target densities and acceptable ranges, and give examples for various resin rich mica tapes and design requirements. We will also explain how the volume of resin to mica and glass changes with these target densities.","PeriodicalId":184139,"journal":{"name":"2018 IEEE Electrical Insulation Conference (EIC)","volume":"30 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124951173","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-06-01DOI: 10.1109/EIC.2018.8481040
C. Staubach, T. Hildinger
In this paper different kinds of electrical driven failure modes in the end-winding region, are discussed and classified. Failure types related to the stress grading system are analyzed via numerical simulation models and root causes are given for the different defects based on the calculation results. Typical pictures of various findings are presented and explained. In a last step possible diagnostic measurements to identify issues related to the stress grading are discussed and some PD-pattern are presented exemplarily. The aim of this work is to give the basis to correlate findings in the end-winding and especially the highly stressed stress grading area with their most likely cause of defect.
{"title":"Failure Mode Assessment of the Generator Stress Grading System","authors":"C. Staubach, T. Hildinger","doi":"10.1109/EIC.2018.8481040","DOIUrl":"https://doi.org/10.1109/EIC.2018.8481040","url":null,"abstract":"In this paper different kinds of electrical driven failure modes in the end-winding region, are discussed and classified. Failure types related to the stress grading system are analyzed via numerical simulation models and root causes are given for the different defects based on the calculation results. Typical pictures of various findings are presented and explained. In a last step possible diagnostic measurements to identify issues related to the stress grading are discussed and some PD-pattern are presented exemplarily. The aim of this work is to give the basis to correlate findings in the end-winding and especially the highly stressed stress grading area with their most likely cause of defect.","PeriodicalId":184139,"journal":{"name":"2018 IEEE Electrical Insulation Conference (EIC)","volume":"152 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116392149","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-06-01DOI: 10.1109/EIC.2018.8481090
A. Jahromi, Mohsen Hosseinkhanloo, Laurent Lamare
Under load tap changers (ULTC) have the most share of defects in transformers causing enormous expenses to utilities. ULTCs have been a weak part of any transformer as they deteriorate over time due to mechanical problems or contact wear from repeated operations. Erosion of the contacts over time is expected due to the nature of their function. Coking of the contacts causes overheating, which can cause thermal runaway. Diagnostics of ULTC is a key for any utility. The goal of diagnostics is to provide equipment owners with a ranking that prioritizes maintenance activities. This goes beyond the simple good/bad distinction, to provide some grading to permit different management options. Historically, DGAs in ULTCs have been considered rather insignificant due to the large amount of gases normally generated by the arcs. This has however been reconsidered the recent years and the opinion today is that quite a lot of information is gained by DGAs of ULTC oils. Dissolved gas analysis (DGA) has been proven to provide relevant information about transformer and tap changer health or faults. On the other hand, winding DC resistance measurement can be a complementary method for identification of defective connections triggered by DGA detected fault. In this paper, the DGA analysis is employed to analyze the gases generated in the transformer tank by a possible fault at selector switch tap. Diagnostics performed using both DGA and DC winding resistance tests for a 30MVA 63/20kV three-phase transformer with an in-tank ULTC. The results showed that combination of DGA and DC winding resistance is a simple and effective diagnostic technique to detect coking and carbonized contacts of the ULTC tap selector contacts. Trending of transformer tank DGA data and DC winding resistance proved to be reliable to trigger internal inspection, overhaul and repair of ULTC tap selector.
{"title":"Under Load Tap Changer Diagnostics Based on Transformer DGA and DC Resistance Tests","authors":"A. Jahromi, Mohsen Hosseinkhanloo, Laurent Lamare","doi":"10.1109/EIC.2018.8481090","DOIUrl":"https://doi.org/10.1109/EIC.2018.8481090","url":null,"abstract":"Under load tap changers (ULTC) have the most share of defects in transformers causing enormous expenses to utilities. ULTCs have been a weak part of any transformer as they deteriorate over time due to mechanical problems or contact wear from repeated operations. Erosion of the contacts over time is expected due to the nature of their function. Coking of the contacts causes overheating, which can cause thermal runaway. Diagnostics of ULTC is a key for any utility. The goal of diagnostics is to provide equipment owners with a ranking that prioritizes maintenance activities. This goes beyond the simple good/bad distinction, to provide some grading to permit different management options. Historically, DGAs in ULTCs have been considered rather insignificant due to the large amount of gases normally generated by the arcs. This has however been reconsidered the recent years and the opinion today is that quite a lot of information is gained by DGAs of ULTC oils. Dissolved gas analysis (DGA) has been proven to provide relevant information about transformer and tap changer health or faults. On the other hand, winding DC resistance measurement can be a complementary method for identification of defective connections triggered by DGA detected fault. In this paper, the DGA analysis is employed to analyze the gases generated in the transformer tank by a possible fault at selector switch tap. Diagnostics performed using both DGA and DC winding resistance tests for a 30MVA 63/20kV three-phase transformer with an in-tank ULTC. The results showed that combination of DGA and DC winding resistance is a simple and effective diagnostic technique to detect coking and carbonized contacts of the ULTC tap selector contacts. Trending of transformer tank DGA data and DC winding resistance proved to be reliable to trigger internal inspection, overhaul and repair of ULTC tap selector.","PeriodicalId":184139,"journal":{"name":"2018 IEEE Electrical Insulation Conference (EIC)","volume":"85 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115617707","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-06-01DOI: 10.1109/EIC.2018.8480887
A. Céspedes, D. García, B. García
Power transformers comprise one of the most important assets in the power systems. Damage in a power transformer can lead to a collapse in the electrical transmission network, disturbing a big number of users. The cellulosic insulation plays a key role in the life of power transformer. Several studies have demonstrated that high levels of moisture in the cellulosic insulation increase its rate of ageing limiting the power transformer's life expectancy. In this work, the experimental validation of a sensor aimed at determining the moisture content of cellulosic insulation is presented. The working principle of the sensor is based in the use of the Frequency Dielectric Spectroscopy method (FDS) to relate the main dielectric characteristics of the sensor and those of the transformer solid insulation. The validation presented in this work considers different temperatures and moisture contents under equilibrium and non-equilibrium conditions. Additionally, the experimental dielectric curves of the sensor are compared with simulation data obtained by means of a finite-element model that reproduces the applied experimental conditions, to validate the modeling process.
{"title":"Experimental validation of a moisture sensor for cellulosic insulation of power transformers","authors":"A. Céspedes, D. García, B. García","doi":"10.1109/EIC.2018.8480887","DOIUrl":"https://doi.org/10.1109/EIC.2018.8480887","url":null,"abstract":"Power transformers comprise one of the most important assets in the power systems. Damage in a power transformer can lead to a collapse in the electrical transmission network, disturbing a big number of users. The cellulosic insulation plays a key role in the life of power transformer. Several studies have demonstrated that high levels of moisture in the cellulosic insulation increase its rate of ageing limiting the power transformer's life expectancy. In this work, the experimental validation of a sensor aimed at determining the moisture content of cellulosic insulation is presented. The working principle of the sensor is based in the use of the Frequency Dielectric Spectroscopy method (FDS) to relate the main dielectric characteristics of the sensor and those of the transformer solid insulation. The validation presented in this work considers different temperatures and moisture contents under equilibrium and non-equilibrium conditions. Additionally, the experimental dielectric curves of the sensor are compared with simulation data obtained by means of a finite-element model that reproduces the applied experimental conditions, to validate the modeling process.","PeriodicalId":184139,"journal":{"name":"2018 IEEE Electrical Insulation Conference (EIC)","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115172171","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-06-01DOI: 10.1109/EIC.2018.8481110
T. Umemoto, Yasutomo Otake, M. Yoshimura, Takashi Nada, Ryoji Miyatake
SiC-based nonlinear resistive material has been used for end-turn stress grading (SG) of turbogenerators over decades. In order to reduce power dissipations and avoid thermal breakdown of the SG material, high-voltage class generators adopt multiple-layer SG system, at which two SG materials with different nonlinear resistivity are used. With increasing capacity and efficiency of the apparatus, electrical, and especially thermal stresses at the system may become problematic, hence higher reliable SG system is required. For suppressing the local heating effectively, an optimization method of the multiple-layer system was investigated, where a new combination of the two SG materials was proposed and length of the SG layer in the longitudinal direction along a coil was optimized by using analytical approximations of the power dissipation. The optimized SG system showed 20% lower power dissipation and also 15% higher flashover voltage than those of the conventional one. Consequently, the effectiveness of the optimization method proposed was successfully confirmed.
{"title":"Optimization of Multiple-Layer End-Turn Stress Grading System for High Voltage Turbogenerators","authors":"T. Umemoto, Yasutomo Otake, M. Yoshimura, Takashi Nada, Ryoji Miyatake","doi":"10.1109/EIC.2018.8481110","DOIUrl":"https://doi.org/10.1109/EIC.2018.8481110","url":null,"abstract":"SiC-based nonlinear resistive material has been used for end-turn stress grading (SG) of turbogenerators over decades. In order to reduce power dissipations and avoid thermal breakdown of the SG material, high-voltage class generators adopt multiple-layer SG system, at which two SG materials with different nonlinear resistivity are used. With increasing capacity and efficiency of the apparatus, electrical, and especially thermal stresses at the system may become problematic, hence higher reliable SG system is required. For suppressing the local heating effectively, an optimization method of the multiple-layer system was investigated, where a new combination of the two SG materials was proposed and length of the SG layer in the longitudinal direction along a coil was optimized by using analytical approximations of the power dissipation. The optimized SG system showed 20% lower power dissipation and also 15% higher flashover voltage than those of the conventional one. Consequently, the effectiveness of the optimization method proposed was successfully confirmed.","PeriodicalId":184139,"journal":{"name":"2018 IEEE Electrical Insulation Conference (EIC)","volume":"32 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125397720","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-06-01DOI: 10.1109/EIC.2018.8481129
Alireza Naeini, E. Cherney, S. Jayaram
Evaluating the performance of the stress grading system by simulating the electric field and potential distributions in the overhang region shows that high conductive stress grading tape (SGT) reduces the maximum electric field at this region. For simulation studies, an accurate conductivity that takes into account the effects of vacuum pressure impregnation (VPI) process, temperature, and tape builds is measured. As the electric field on the SGT is enhanced under operating conditions, the conductivity of the SGT has been measured in a high electrical field condition under pulse conditions to minimize the effects of temperature rise on the SGT. The conductivity of a one half-lap layer and a double half-lap layer of SGT at different temperatures is measured. The results show that for both designs, the higher the tape conductivity the lower the maximum electric field in the SGT region. For evaluating the simulation model, the temperature profile along the stress grading system is measured and simulated under high frequency sinusoidal voltage.
{"title":"Effect of Stress Grading Tape Conductivity on the Electric Field Distribution in Stress Grading System of an Inverter-Fed Rotating Machine","authors":"Alireza Naeini, E. Cherney, S. Jayaram","doi":"10.1109/EIC.2018.8481129","DOIUrl":"https://doi.org/10.1109/EIC.2018.8481129","url":null,"abstract":"Evaluating the performance of the stress grading system by simulating the electric field and potential distributions in the overhang region shows that high conductive stress grading tape (SGT) reduces the maximum electric field at this region. For simulation studies, an accurate conductivity that takes into account the effects of vacuum pressure impregnation (VPI) process, temperature, and tape builds is measured. As the electric field on the SGT is enhanced under operating conditions, the conductivity of the SGT has been measured in a high electrical field condition under pulse conditions to minimize the effects of temperature rise on the SGT. The conductivity of a one half-lap layer and a double half-lap layer of SGT at different temperatures is measured. The results show that for both designs, the higher the tape conductivity the lower the maximum electric field in the SGT region. For evaluating the simulation model, the temperature profile along the stress grading system is measured and simulated under high frequency sinusoidal voltage.","PeriodicalId":184139,"journal":{"name":"2018 IEEE Electrical Insulation Conference (EIC)","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125469209","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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