Insulation systems in high-voltage electric machines play a pivotal role in the reliable operation and longevity of the equipment.Mica-based insulation materials have proven to possess and maintain excellent dielectri...Insulation systems in high-voltage electric machines play a pivotal role in the reliable operation and longevity of the equipment.Mica-based insulation materials have proven to possess and maintain excellent dielectric properties in the long run and prevent premature insulation degradation.Numerous qualifications tests,such as voltage endurance,are outlined in IEC and IEEE standards.The authors,however,take a different parametric approach,opting for reliability assessment of insulation systems using derived three-parameter Weibull models.Therefore,instead of simple pass–fail criteria,empirical data is employed to determine failure rate probabilities quantitatively and objectively.Experimental data,including breakdown,dissipation factor,and partial discharge mea-surements,are used to construct the Weibull distribution model to predict fault and failure rates and calculate hazard functions.The rigorous examinations interpreted through the analytical model help assess insulation system resilience and particularly the impact of electrical field stress and mica content.Variation of electrical stress from 66.75 to 71.20 V/mil demonstrated how the mean time to failure of the system changed from 146.4 to 85.1 at 3 Un,hence identifying opportunities for design improvement and uncovering performance boundaries.Ultimately,the developed framework enhances comprehension of insulation system failure probabilities,guiding design decisions and ensuring a secure and reliable operation of electrical machines across applications.展开更多
Hybrid AC-DC networks are transforming high-voltage transmission and medium-voltage distribution grids by embracing the advantages of both AC and DC systems,which facilitates the inclusion of renewable energy sources ...Hybrid AC-DC networks are transforming high-voltage transmission and medium-voltage distribution grids by embracing the advantages of both AC and DC systems,which facilitates the inclusion of renewable energy sources and distributed generation.As modular multilevel converters(MMCs)are vastly employed in such hybrid networks,determining their maximal fault current in worst-case scenario is a critical design factor for planning and implementation of a reliable protection scheme.This study develops a novel mathematical framework that applies a Lagrangian energy method to calculate the maximal fault magnitude.This method allows to account for converter's internal energy and compute its impact on the amplitude of the fault current.It is shown when the converter is interfacing weak AC sources with high internal impedance such as wind farms or solar farms,dumping the internal energy of the converter into the fault is the salient contributing factor of the fault magnitude.Furthermore,to distinguish and classify the output overcurrent as either ignorable transients or destructive faults,a perceptron with sigmoid threshold is employed.The model is verified using a simulated medium-voltage hybrid AC-DC distribution network.展开更多
文摘Insulation systems in high-voltage electric machines play a pivotal role in the reliable operation and longevity of the equipment.Mica-based insulation materials have proven to possess and maintain excellent dielectric properties in the long run and prevent premature insulation degradation.Numerous qualifications tests,such as voltage endurance,are outlined in IEC and IEEE standards.The authors,however,take a different parametric approach,opting for reliability assessment of insulation systems using derived three-parameter Weibull models.Therefore,instead of simple pass–fail criteria,empirical data is employed to determine failure rate probabilities quantitatively and objectively.Experimental data,including breakdown,dissipation factor,and partial discharge mea-surements,are used to construct the Weibull distribution model to predict fault and failure rates and calculate hazard functions.The rigorous examinations interpreted through the analytical model help assess insulation system resilience and particularly the impact of electrical field stress and mica content.Variation of electrical stress from 66.75 to 71.20 V/mil demonstrated how the mean time to failure of the system changed from 146.4 to 85.1 at 3 Un,hence identifying opportunities for design improvement and uncovering performance boundaries.Ultimately,the developed framework enhances comprehension of insulation system failure probabilities,guiding design decisions and ensuring a secure and reliable operation of electrical machines across applications.
文摘Hybrid AC-DC networks are transforming high-voltage transmission and medium-voltage distribution grids by embracing the advantages of both AC and DC systems,which facilitates the inclusion of renewable energy sources and distributed generation.As modular multilevel converters(MMCs)are vastly employed in such hybrid networks,determining their maximal fault current in worst-case scenario is a critical design factor for planning and implementation of a reliable protection scheme.This study develops a novel mathematical framework that applies a Lagrangian energy method to calculate the maximal fault magnitude.This method allows to account for converter's internal energy and compute its impact on the amplitude of the fault current.It is shown when the converter is interfacing weak AC sources with high internal impedance such as wind farms or solar farms,dumping the internal energy of the converter into the fault is the salient contributing factor of the fault magnitude.Furthermore,to distinguish and classify the output overcurrent as either ignorable transients or destructive faults,a perceptron with sigmoid threshold is employed.The model is verified using a simulated medium-voltage hybrid AC-DC distribution network.
