With an impetuous growth of DC links and future grids that will be often hybrid,providing AC and DC supply to nearby or the same customer,an important element is often neglected,that is,electrical insulation.There are...With an impetuous growth of DC links and future grids that will be often hybrid,providing AC and DC supply to nearby or the same customer,an important element is often neglected,that is,electrical insulation.There are no doubts that overhead lines will step back compared to insulated cables,for known reasons of environmental impact,right of way and reliability,especially in an urban or harsh environment.On the other hand,while AC insulation systems have been investigated and used for decades,there is no analogue experience for DC polymeric insulation,nor for insulation systems subjected to power electronics supply.This study aims at enhancing the attention on this topic,focusing on insulation ageing mechanisms and models of relevance for hybrid AC/DC assets and grids.Ageing and life models for AC,DC and power electronics supply are discussed and compared to experimental data,focusing on partial discharge and space charge.It is shown how these two phenomena affect lifetime for different AC,DC and transient operating conditions.The main drivers for insulation design and material selection are discussed,showing that insulation reliability can be achieved only if operating stresses,ageing mechanisms and life models are known and accounted for properly by insulation designers.展开更多
Quality control,commissioning and diagnostic tests on insulation systems of electrical apparatus are necessary to reduce the failure risk under operation,eliminate infant mortality failures and reduce the impact of ag...Quality control,commissioning and diagnostic tests on insulation systems of electrical apparatus are necessary to reduce the failure risk under operation,eliminate infant mortality failures and reduce the impact of ageing on insulation system reliability.This study tries to establish a path which,based on the statistical-phenomenological modelling of the hazard rate,or bathtub curve,drives in the choice of test overvoltage and procedures.The choice of the test voltage and its waveform should be made carefully to improve reliability(reduce failure hazard)in any section of the bathtub curve.This may require,however,different choices depending on the section which corresponds to the planned test.For example,large overvoltages could be acceptable to remove the infant mortality to ensure the highest reliability of newly commissioned apparatus,but they can incept highly energetic,and,thus,fast degradation mechanisms on apparatus operating on the field for a period of time,that can worsen,rather than improving,the insulation system reliability.Resorting to partial discharge measurement during any overvoltage test seems to be the optimal solution to find the most appropriate overvoltage for any type of testing need,leveraging the Latin concept that‘in medio stat virtus’.展开更多
Polymer dielectrics are widely used in electrical and electronic apparatus and devices because of their capability to insulate conductors,withstand high fields and suffer negligible conductive losses.Their near-to-zer...Polymer dielectrics are widely used in electrical and electronic apparatus and devices because of their capability to insulate conductors,withstand high fields and suffer negligible conductive losses.Their near-to-zero conductivity has been explained in terms of long-accepted theories of electronic and ionic transport that lead to the accumulation of local net charge regions at high electric fields.Here the authors describe a previously unknown conduction mechanism consisting of small bipolar ultra-fast charge pulses crossing the polymer with the mobility,as large as,4 to 5 orders of magnitude greater than that of the previously known.The authors show that this motion is a consequence of molecular relaxation processes triggered by the electric field locally enhanced by the pulses themselves.Pulse accumulation at the electrodes increases interface field and thus contributes substantially towards premature failure in insulating dielectrics in DC fields.展开更多
文摘With an impetuous growth of DC links and future grids that will be often hybrid,providing AC and DC supply to nearby or the same customer,an important element is often neglected,that is,electrical insulation.There are no doubts that overhead lines will step back compared to insulated cables,for known reasons of environmental impact,right of way and reliability,especially in an urban or harsh environment.On the other hand,while AC insulation systems have been investigated and used for decades,there is no analogue experience for DC polymeric insulation,nor for insulation systems subjected to power electronics supply.This study aims at enhancing the attention on this topic,focusing on insulation ageing mechanisms and models of relevance for hybrid AC/DC assets and grids.Ageing and life models for AC,DC and power electronics supply are discussed and compared to experimental data,focusing on partial discharge and space charge.It is shown how these two phenomena affect lifetime for different AC,DC and transient operating conditions.The main drivers for insulation design and material selection are discussed,showing that insulation reliability can be achieved only if operating stresses,ageing mechanisms and life models are known and accounted for properly by insulation designers.
文摘Quality control,commissioning and diagnostic tests on insulation systems of electrical apparatus are necessary to reduce the failure risk under operation,eliminate infant mortality failures and reduce the impact of ageing on insulation system reliability.This study tries to establish a path which,based on the statistical-phenomenological modelling of the hazard rate,or bathtub curve,drives in the choice of test overvoltage and procedures.The choice of the test voltage and its waveform should be made carefully to improve reliability(reduce failure hazard)in any section of the bathtub curve.This may require,however,different choices depending on the section which corresponds to the planned test.For example,large overvoltages could be acceptable to remove the infant mortality to ensure the highest reliability of newly commissioned apparatus,but they can incept highly energetic,and,thus,fast degradation mechanisms on apparatus operating on the field for a period of time,that can worsen,rather than improving,the insulation system reliability.Resorting to partial discharge measurement during any overvoltage test seems to be the optimal solution to find the most appropriate overvoltage for any type of testing need,leveraging the Latin concept that‘in medio stat virtus’.
文摘Polymer dielectrics are widely used in electrical and electronic apparatus and devices because of their capability to insulate conductors,withstand high fields and suffer negligible conductive losses.Their near-to-zero conductivity has been explained in terms of long-accepted theories of electronic and ionic transport that lead to the accumulation of local net charge regions at high electric fields.Here the authors describe a previously unknown conduction mechanism consisting of small bipolar ultra-fast charge pulses crossing the polymer with the mobility,as large as,4 to 5 orders of magnitude greater than that of the previously known.The authors show that this motion is a consequence of molecular relaxation processes triggered by the electric field locally enhanced by the pulses themselves.Pulse accumulation at the electrodes increases interface field and thus contributes substantially towards premature failure in insulating dielectrics in DC fields.
