Concerning HV insulation in vacuum, there is still some uncertainty about the processes leading to breakdown, especially in the case of long time lags and large contact spacing. The present measurements show that mechanical shocks cause breakdown of the gap. Breakdown probability is highest for virgin contacts and decreases after heavy arcing. The role of nonmetallic inclusions and organic impurities is highlighted. In comparison with a demountable vacuum device industrial vacuum interrupters do not show any sensitivity to mechanical shocks. Besides breakdown probabilities and time lags, the temporal development of voltage and current during breakdown was measured. For a contact spacing of >14 mm and for breakdown sites located on the side face of the contacts, HV discharges were observed lasting for approximately 500 mu s. In this case, current is limited by a negative space charge layer in front of the anode. >
{"title":"Long-delayed breakdown in vacuum gaps under DC pulses","authors":"E. Dullni","doi":"10.1109/14.231525","DOIUrl":"https://doi.org/10.1109/14.231525","url":null,"abstract":"Concerning HV insulation in vacuum, there is still some uncertainty about the processes leading to breakdown, especially in the case of long time lags and large contact spacing. The present measurements show that mechanical shocks cause breakdown of the gap. Breakdown probability is highest for virgin contacts and decreases after heavy arcing. The role of nonmetallic inclusions and organic impurities is highlighted. In comparison with a demountable vacuum device industrial vacuum interrupters do not show any sensitivity to mechanical shocks. Besides breakdown probabilities and time lags, the temporal development of voltage and current during breakdown was measured. For a contact spacing of >14 mm and for breakdown sites located on the side face of the contacts, HV discharges were observed lasting for approximately 500 mu s. In this case, current is limited by a negative space charge layer in front of the anode. >","PeriodicalId":13105,"journal":{"name":"IEEE Transactions on Electrical Insulation","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1993-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90905964","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}
The polaron concept is used to describe trapping of charge in a dielectric medium. It is shown that trapping is associated with defects identified as being due to a local decrease of the electronic polarizability. The polarization energy around a charge is estimated, using a self-consistent calculation of the local field. In nonpolar dielectrics this energy is 5 eV per charge, in the limit of validity of the Clausius-Mosotti relation. In polar dielectrics it can be much higher. A flashover process is proposed as resulting from the destabilization of the space charge by a variety of perturbations (electrical, mechanical, thermal), followed by the mechanical relaxation of the lattice, initially polarized by the charge. >
{"title":"New approach to flashover in dielectrics based on a polarization energy relaxation mechanism","authors":"G. Blaise","doi":"10.1109/14.231522","DOIUrl":"https://doi.org/10.1109/14.231522","url":null,"abstract":"The polaron concept is used to describe trapping of charge in a dielectric medium. It is shown that trapping is associated with defects identified as being due to a local decrease of the electronic polarizability. The polarization energy around a charge is estimated, using a self-consistent calculation of the local field. In nonpolar dielectrics this energy is 5 eV per charge, in the limit of validity of the Clausius-Mosotti relation. In polar dielectrics it can be much higher. A flashover process is proposed as resulting from the destabilization of the space charge by a variety of perturbations (electrical, mechanical, thermal), followed by the mechanical relaxation of the lattice, initially polarized by the charge. >","PeriodicalId":13105,"journal":{"name":"IEEE Transactions on Electrical Insulation","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1993-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90513832","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}
Digital computer studies of long, contaminated insulator strings are performed using linear, lumped circuit models. The voltage distribution, currents, phase angle and wattage for each unit on the string are evaluated for practical combinations of uniform and nonuniform distribution of contamination. The variations in performance as a function of stray capacitance and shielding fields are discussed, taking into account a wide range of the pollution index, tower designs varying at different areas, and the environmental conditions of Saudi Arabia, the physics of the evaluation of the voltage distribution and phase angle variations along the insulator string as the surface is changed from clean, to dirty, to contaminated, to polluted are evaluated. The iteration technique is used to explore the effect of nonlinearities in resistance as a function of temperature variations and current limits. Changes in surface resistance due to liberated energy are considered. Studies are performed on a per-unit basis to simplify the adoption of the results to insulator strings used under various conditions. >
{"title":"Analytical studies of HV insulators in Saudi Arabia-theoretical aspects","authors":"A. Farag, F. Zedan, T. Cheng","doi":"10.1109/14.236209","DOIUrl":"https://doi.org/10.1109/14.236209","url":null,"abstract":"Digital computer studies of long, contaminated insulator strings are performed using linear, lumped circuit models. The voltage distribution, currents, phase angle and wattage for each unit on the string are evaluated for practical combinations of uniform and nonuniform distribution of contamination. The variations in performance as a function of stray capacitance and shielding fields are discussed, taking into account a wide range of the pollution index, tower designs varying at different areas, and the environmental conditions of Saudi Arabia, the physics of the evaluation of the voltage distribution and phase angle variations along the insulator string as the surface is changed from clean, to dirty, to contaminated, to polluted are evaluated. The iteration technique is used to explore the effect of nonlinearities in resistance as a function of temperature variations and current limits. Changes in surface resistance due to liberated energy are considered. Studies are performed on a per-unit basis to simplify the adoption of the results to insulator strings used under various conditions. >","PeriodicalId":13105,"journal":{"name":"IEEE Transactions on Electrical Insulation","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1993-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74507676","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}
The boundary element method is used to calculate the electric field profiles at needle tips commonly used for electrical treeing tests. Field distributions are also obtained for polyethylene containing a space charge, at the needle tip, and are compared with the values previously obtained by the finite difference method. >
{"title":"Electric field calculations with the boundary element method","authors":"S. Bamji, A. Bulinski, K. M. Prasad","doi":"10.1109/14.236204","DOIUrl":"https://doi.org/10.1109/14.236204","url":null,"abstract":"The boundary element method is used to calculate the electric field profiles at needle tips commonly used for electrical treeing tests. Field distributions are also obtained for polyethylene containing a space charge, at the needle tip, and are compared with the values previously obtained by the finite difference method. >","PeriodicalId":13105,"journal":{"name":"IEEE Transactions on Electrical Insulation","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1993-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87753195","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}
Anode hotspot temperatures for vacuum gaps subjected to 50-Hz AC excitations are computed. The transient heat diffusion equation is solved using a finite difference method. The effects of nonlinear variation of thermal properties with temperature and phase change are studied using the ANSYS 4.4 finite element package. The peak temperatures are estimated by a seminumerical method. The results of a parametric study of the effects of electrode material, field intensification factor, and radius of the spot are presented. The results for stainless steel, copper, and aluminum anodes indicate that the temperature of hot spots can reach the melting point, so they are the main sources of microparticles. The asymmetry of the prebreakdown current waveform about its own peak, which is caused by thermal instability at the anode, is attributed to the nonlinear variation of thermal properties with temperature. The methods discussed can be used to estimate the size of microparticles originating from thermally unstable regions at the anode. >
{"title":"Anode hotspot temperature estimation in vacuum gaps under 50 Hz alternating excitations","authors":"T. Balachandra, G. Nagabhushana","doi":"10.1109/14.236208","DOIUrl":"https://doi.org/10.1109/14.236208","url":null,"abstract":"Anode hotspot temperatures for vacuum gaps subjected to 50-Hz AC excitations are computed. The transient heat diffusion equation is solved using a finite difference method. The effects of nonlinear variation of thermal properties with temperature and phase change are studied using the ANSYS 4.4 finite element package. The peak temperatures are estimated by a seminumerical method. The results of a parametric study of the effects of electrode material, field intensification factor, and radius of the spot are presented. The results for stainless steel, copper, and aluminum anodes indicate that the temperature of hot spots can reach the melting point, so they are the main sources of microparticles. The asymmetry of the prebreakdown current waveform about its own peak, which is caused by thermal instability at the anode, is attributed to the nonlinear variation of thermal properties with temperature. The methods discussed can be used to estimate the size of microparticles originating from thermally unstable regions at the anode. >","PeriodicalId":13105,"journal":{"name":"IEEE Transactions on Electrical Insulation","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1993-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83171133","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}
Water tree morphology as revealed by oxygen plasma etching of water trees in low-density polyethylene is reported. Water trees sectioned by freeze fracturing are found to be virtually invisible until treated by plasma etching. Etching attack is localized and produces either a pitted or a channeled structure, depending on the water tree growth conditions. The spatial distribution of the pits or channels is reminiscent of water tree void distribution. Secondary electron photomicrographs of trees grown under varied conditions are presented. >
{"title":"Water tree morphology","authors":"J. King, M. Grundmeyer, D. Stepp, D. Hugo","doi":"10.1109/14.236205","DOIUrl":"https://doi.org/10.1109/14.236205","url":null,"abstract":"Water tree morphology as revealed by oxygen plasma etching of water trees in low-density polyethylene is reported. Water trees sectioned by freeze fracturing are found to be virtually invisible until treated by plasma etching. Etching attack is localized and produces either a pitted or a channeled structure, depending on the water tree growth conditions. The spatial distribution of the pits or channels is reminiscent of water tree void distribution. Secondary electron photomicrographs of trees grown under varied conditions are presented. >","PeriodicalId":13105,"journal":{"name":"IEEE Transactions on Electrical Insulation","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1993-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84187730","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}
Specimens of an aromatic polyamide (Aramid) paper, which were subjected to various degrees of moisture adsorption as well as water immersion, were investigated in order to estimate how much the adsorbed moisture and the stored water affect the dielectric and thermoanalytical behavior. In the humid specimens the dielectric properties did not change much and there were no endothermic and exothermic peaks. In the soaked specimens the dielectric properties changed remarkably and there were endothermic and exothermic peaks due to free water recognized at approximately 0 degrees C. It is concluded that the dielectric properties of Aramid paper are rather stable to moisture adsorption because its polyamide linkage bonds tightly with the adsorbed water which is in the shape of nonfreezing bound water, but when the total water content increases over the saturated moisture value of 6.8%wt, increases in the dielectric properties take place due to the free water in the fiber structure. In the bound water region, Aramid paper has higher DC resistivity values compared with other synthetic papers such as polyester paper. >
{"title":"Dielectric and thermoanalytic behavior of moisture and water in aromatic polyamide paper","authors":"S. Yasufuku, M. Todoki","doi":"10.1109/14.236218","DOIUrl":"https://doi.org/10.1109/14.236218","url":null,"abstract":"Specimens of an aromatic polyamide (Aramid) paper, which were subjected to various degrees of moisture adsorption as well as water immersion, were investigated in order to estimate how much the adsorbed moisture and the stored water affect the dielectric and thermoanalytical behavior. In the humid specimens the dielectric properties did not change much and there were no endothermic and exothermic peaks. In the soaked specimens the dielectric properties changed remarkably and there were endothermic and exothermic peaks due to free water recognized at approximately 0 degrees C. It is concluded that the dielectric properties of Aramid paper are rather stable to moisture adsorption because its polyamide linkage bonds tightly with the adsorbed water which is in the shape of nonfreezing bound water, but when the total water content increases over the saturated moisture value of 6.8%wt, increases in the dielectric properties take place due to the free water in the fiber structure. In the bound water region, Aramid paper has higher DC resistivity values compared with other synthetic papers such as polyester paper. >","PeriodicalId":13105,"journal":{"name":"IEEE Transactions on Electrical Insulation","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1993-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83192509","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}
The discusser raises questions regarding the above-titled paper by R. Bartnikas and J.P. Novak (ibid., vol.27, p.3-14, 1992) as to how the authors would relate their term 'spark' to 'streamer' and 'Townsend discharges'. The discusser also questions the authors' claim that at voltages slightly above the discharge inception point, pseudoglow discharges appear, which, with further increase of the voltage, transform into glow discharges and these in turn, with an even further voltage increase, transform into spark discharges, and cites experimental work that counters this claim. The authors agree with the discusser on the need for clarification and standardization of terminology. They contest the discusser's point regarding pseudoglow discharges and provide further discussion in support of their claim. >
{"title":"On the spark to pseudoglow and glow transition mechanism and discharge detectability (Discussion, wi","authors":"M. Danikas, R. Bartnikas, J. Novak","doi":"10.1109/14.236202","DOIUrl":"https://doi.org/10.1109/14.236202","url":null,"abstract":"The discusser raises questions regarding the above-titled paper by R. Bartnikas and J.P. Novak (ibid., vol.27, p.3-14, 1992) as to how the authors would relate their term 'spark' to 'streamer' and 'Townsend discharges'. The discusser also questions the authors' claim that at voltages slightly above the discharge inception point, pseudoglow discharges appear, which, with further increase of the voltage, transform into glow discharges and these in turn, with an even further voltage increase, transform into spark discharges, and cites experimental work that counters this claim. The authors agree with the discusser on the need for clarification and standardization of terminology. They contest the discusser's point regarding pseudoglow discharges and provide further discussion in support of their claim. >","PeriodicalId":13105,"journal":{"name":"IEEE Transactions on Electrical Insulation","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1993-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77339974","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}
Improved Gubkin- and Jefimenko-type electret motors, where the electrets are not shielded and are not required to have mechanical strength, were designed and produced. Their rotors were constructed using Teflon FEP film electrets and metal disks. An intermediate type electret motor was produced to complete the family of electret motors. An experimental torque close to the theoretical value for each type of motor is obtained. In a Jefimenko-type motor the maximum value of the experimental torque is 38 mu N-m when the applied DC voltage is 2000 V. Each type of motor has been run synchronously with a square wave voltage. The Jefimenko-type motor had the highest rotation rate. The upper limit was 1260 rpm when the peak voltage of the square wave was 1400 V. None of the motors dealt with in this study can be started, nor can their rotational direction be changed by applied voltage only. However, it is suggested that an electret motor consisting of a stator and a rotor having different number of poles could be controlled by applied voltage only. >
{"title":"Improvement of conventional electret motors","authors":"Y. Tada","doi":"10.1109/14.236207","DOIUrl":"https://doi.org/10.1109/14.236207","url":null,"abstract":"Improved Gubkin- and Jefimenko-type electret motors, where the electrets are not shielded and are not required to have mechanical strength, were designed and produced. Their rotors were constructed using Teflon FEP film electrets and metal disks. An intermediate type electret motor was produced to complete the family of electret motors. An experimental torque close to the theoretical value for each type of motor is obtained. In a Jefimenko-type motor the maximum value of the experimental torque is 38 mu N-m when the applied DC voltage is 2000 V. Each type of motor has been run synchronously with a square wave voltage. The Jefimenko-type motor had the highest rotation rate. The upper limit was 1260 rpm when the peak voltage of the square wave was 1400 V. None of the motors dealt with in this study can be started, nor can their rotational direction be changed by applied voltage only. However, it is suggested that an electret motor consisting of a stator and a rotor having different number of poles could be controlled by applied voltage only. >","PeriodicalId":13105,"journal":{"name":"IEEE Transactions on Electrical Insulation","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1993-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80315683","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}
Poly(p-phenylene sulfide) polymers, both highly linear and crosslinked, were investigated to determine how their structural differences affect their dielectric and thermoanalytical behavior over a temperature range from room temperature to 300 degrees C. The T/sub g/ of the crosslinked type was 3 degrees C higher than that of the linear type according to the differential scanning calorimetry (DSC) measurement, suggesting a slight lag in micro-Brownian motion in the amorphous phase. Permittivity and dielectric dissipation factors as well as global thermally stimulated current (TSC) spectra were similar below T/sub g/. The linear type showed larger permittivity and dielectric dissipation factor values above T/sub g/, due to interfacial polarization. The linear type showed a strong rho peak at approximately 160 degrees C in the global TSC spectra, suggesting the release of injected space charges trapped at the crystal/amorphous interfaces, while the crosslinked type showed a weak rho peak at approximately 190 degrees C in the spectra, suggesting a decrease of the interface effect due to crosslinking. >
{"title":"Dielectric and thermoanalytical behavior of poly(p-phenylene sulfide) polymers","authors":"S. Yasufuku, M. Todoki","doi":"10.1109/14.236215","DOIUrl":"https://doi.org/10.1109/14.236215","url":null,"abstract":"Poly(p-phenylene sulfide) polymers, both highly linear and crosslinked, were investigated to determine how their structural differences affect their dielectric and thermoanalytical behavior over a temperature range from room temperature to 300 degrees C. The T/sub g/ of the crosslinked type was 3 degrees C higher than that of the linear type according to the differential scanning calorimetry (DSC) measurement, suggesting a slight lag in micro-Brownian motion in the amorphous phase. Permittivity and dielectric dissipation factors as well as global thermally stimulated current (TSC) spectra were similar below T/sub g/. The linear type showed larger permittivity and dielectric dissipation factor values above T/sub g/, due to interfacial polarization. The linear type showed a strong rho peak at approximately 160 degrees C in the global TSC spectra, suggesting the release of injected space charges trapped at the crystal/amorphous interfaces, while the crosslinked type showed a weak rho peak at approximately 190 degrees C in the spectra, suggesting a decrease of the interface effect due to crosslinking. >","PeriodicalId":13105,"journal":{"name":"IEEE Transactions on Electrical Insulation","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1993-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80460292","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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