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AC ripple on DC voltage:Experimental and theoretical investigation of the impact on accelerated ageing in electrical insulation

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High Voltage 2024年第4期9卷 902-910页

作者： Giovanni Gardan gian carlo Montanari Dipartimento di Ingegneria Industriale Universita degli Studi di PadovaPadovaItaly Center for Advanced Power Systems Florida State UniversityTallahasseeFloridaUSA

With the increasing penetration of DC systems into the high voltage and medium voltage power industry,DC voltage is becoming common for distribution/transmission and to supply different typologies of *** allowable extent of AC ripple superimposed to DC,and its effect on insulation ageing,is a long-term discussed *** most harmful phenomenon causing extrinsic ageing acceleration and insulation system premature failure is partial discharges(PD);thus,the risk of incepting PD due to AC ripple could become a primary issue for electrical asset equipment *** this work,the impact of AC sinusoidal ripple on insulation system life and reliability is dealt with,considering both intrinsic and extrinsic ageing but focusing on the latter,that is,the PD *** are performed to assess how the jump voltage(due to AC ripple)and the DC component impact on PD activity in terms of amplitude and repetition *** the first time,the correlation between the magnitude of jump voltage associated with ripple and PD inception is established,shedding a light on the allowable ripple extent which does not impact significantly on ageing and premature insulation *** approach can provide straightforward tools for design specification and ageing inference of insulation systems.

关键词： impact insulation electrical

A new approach to the design of surface subsystems of polymeric insulators for HV and MV apparatus under AC voltage

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High Voltage 2023年第4期8卷 651-658页

作者： gian carlo Montanari Debasish Nath Pasquale Cambareri Center for Advanced Power Systems Florida State UniversityTallahasseeFloridaUSA Dipartimento di Elettronica Informazione e BioingegneriaPolitecnico di MilanoMilanoItaly

The design of high voltage and medium voltage AC and DC standoff insulators,and,in general,of insulation systems where surface and interface properties are predominant factors,is based on specifications and standards that rely upon long-term experiences and lab *** insulating properties depend on electrical and thermal stresses,besides environmental factors,and the inception of extrinsic ageing phenomena,such as partial discharges,can be already a cause of reduced reliability and premature failure(for organic insulating materials).An innovative approach,based on field simulation,discharge modelling,and partial discharge inception measurements is presented by the authors,which can establish a solid basis to optimise insulation design for any type of supply voltage *** method,the three-leg approach,is applied here to a cable system under AC sinusoidal voltage,but it can work for any type of insulation system,such as bushings,switch gears,transformers,rotating machines,and power electronics boards.

关键词： insulation approach insulator

An innovative approach to partial discharge measurement and analysis in DC insulation systems during voltage transient and in steady state

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High Voltage 2021年第4期6卷 565-575页

作者： gian carlo Montanari Riddhi Ghosh Center for Advanced Power Systems Florida State UniversityTallahasseeFloridaUSA

Measuring partial discharges in DC insulation systems is an issue due to the lack of a reference relating the voltage waveform to the physics of discharge ***,DC is not always steady state,due to voltage and load transients that generate electric field profile variations inside an insulation system,which can affect partial discharge inception likelihood and *** discharge measurement technology must be able to separate discharge pulses from noise and identify the type of sources generating partial discharge,which is related to condition assessment and ***,measurement and analysis should be automatic and unsupervised,in order to get rid,partially or totally,of expert *** study addresses a new approach to partial discharge measurements in DC insulation systems,presenting algorithms for separation,recognition and identification,which are effective both in DC steady state and during voltage(and load)*** algorithms are automatic and do not require expert *** cases of algorithm application on test objects consisting of multilayer polymeric specimens with an internal cavity and defective cable models are presented and *** effectiveness is proved,at least at a laboratory level,with effective noise separation and identification of discharge typology.

关键词： insulation state separation

Discovery of an unknown conduction mechanism in insulating polymers

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High Voltage 2020年第4期5卷 403-408页

作者： gian carlo Montanari Paolo Seri Leonard A.Dissado Center for Advanced Power Systems Florida State University2000 Levy AvenueFL 32310USA DEI University of BolognaViale del Risorgimento2–40136BolognaItaly Department of Engineering University of LeicesterUniversity RoadLeicesterLE17RHUK

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 *** 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 *** 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 *** authors show that this motion is a consequence of molecular relaxation processes triggered by the electric field locally enhanced by the pulses *** accumulation at the electrodes increases interface field and thus contributes substantially towards premature failure in insulating dielectrics in DC fields.

关键词： conduction mechanism negligible

Ageing and reliability of electrical insulation: the risk of hybrid AC/DC grids

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High Voltage 2020年第5期5卷 620-627页

作者： gian carlo Montanari Peter Morshuis Paolo Seri Riddhi Ghosh CAPS Florida State UniversityTallahasseeUSA School of Electrical Engineering Xi'an Jiaotong UniversityXi'anPeople's Republic of China University of Bologna BolognaItaly

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 *** 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 *** 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 *** study aims at enhancing the attention on this topic,focusing on insulation ageing mechanisms and models of relevance for hybrid AC/DC assets and *** and life models for AC,DC and power electronics supply are discussed and compared to experimental data,focusing on partial discharge and space *** is shown how these two phenomena affect lifetime for different AC,DC and transient operating *** 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.

关键词： insulation electrical properly

Influence of thermal ageing on high-field polarisation characteristics and conductivity behaviour of submarine polymeric cables insulation

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High Voltage 2023年第1期8卷 138-148页

作者： Xize Dai Jian Hao gian carlo Montanari Zheng Jian Ruijin Liao Xinlong Zheng State Key Laboratory of Power Transmission Equipment&System Security and New Technology Chongqing UniversityChongqingChina Department of Energy Aalborg UniversityAalborgDenmark Center for Advanced Power Systems Florida State UniversityTallahasseeFloridaUSA Shinan Power Supply Branch Company of State Grid Chongqing Electric Power Company NananChina Zhoushan Power Supply Branch Company of State Grid Zhejiang Electric Power Company ZhoushanChina

Diagnosing insulation intrinsic ageing is essential for preventing insulation failure of submarine cables,and in case of failure,helping in any decision about maintenance *** this study,a novel aged cable diagnosis approach based on high-voltage frequency domain spectroscopy(HV-FDS)with broader frequency width is proposed to analyse the high-field polarisation characteristics and conductivity behaviour of 500 kV submarine polymeric cables insulation,aiming to support the evaluation of overall insulation *** measurement principle of HV-FDS and relaxation mechanism are stated,and then focus is on studying the extent of change of polarisation and conduction properties of submarine cables insulation as a function of ageing stress and ***,the high-field polarisation characteristics and conductivity behaviour are discussed in-depth based on the carrier transport and trap ***,the novel diagnostic indicator based on the high-field characteristics is extracted to quantify the thermal ageing state of submarine cables *** show that the high-field polarisation characteristics and conductivity behaviour seem to become sensitive diagnostic quantities if measured at reasonably high voltage,which are able to reveal mechanisms associated with thermo-oxidative ageing as that generated in the testing procedure considered in this *** is considerably higher than that experienced in typical dielectric spectroscopy approaches.

关键词： behaviour insulation characteristics

Pulse width modulation voltage source deadtime effect on partial discharge and lifetime of inverter‐fed motor insulation

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High Voltage 2022年第6期7卷 1185-1193页

作者： Shakeel Akram Peng Wang Pengfei Meng gian carlo Montanari Farhan Hameed Malik College of Electrical Engineering Sichuan UniversityChengduChina Center for Advanced Power Systems Florida State UniversityTallahasseeFloridaUSA Department of Electromechanical Engineering Abu Dhabi PolytechnicAbu DhabiUnited Arab Emirates

This paper analyses the impact of square wave pulse voltage deadtime on the partial discharge(PD)and the lifetime of turn-to-turn insulation.A bipolar repetitive pulse voltage with a deadtime of 0–10μs is produced using double half-bridge solid-state switches having push–pull technology controlled by a field-programmable gate *** mechanism of the discharge process at rising and falling edges of the pulse voltage before and after deadtime is analysed in *** discharge amplitude and PD probability at the rising/falling edges of the voltage waveform increase as the deadtime increases from 0 to 10μs due to the remanent *** number of PD and their intensity is higher at the first rising/falling edges of pulse voltage as compared to the second rising/falling edges for all deadtimes 0–10μ*** the deadtime increases beyond 2μs,the number of PDs increases and concentrates at a specific phase angle of rising/falling *** localise discharges degrade the insulation material and reduce its *** study helps to identify the inverter-fed motor insulation faults due to *** can provide guidelines to motor insulation designers to determine the limit value of deadtime to compensate PD and ensure the safer operation of such motors.

关键词： dead insulation inverter

Testing cable system reliability after commissioning and during operation life:in medio stat virtus?

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High Voltage 2021年第1期6卷 34-41页

作者： gian carlo Montanari Paolo Seri Riddhi Ghosh Stefano Franchi Bononi Marco Albertini Center for Advanced Power Systems Florida State University2000 Levy Avenue FLUSA DEI University of BolognaViale del RisorgimentoBolognaItaly Prysmian S.p.A. Via ChieseMilanItaly

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 *** 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 *** choice of the test voltage and its waveform should be made carefully to improve reliability(reduce failure hazard)in any section of the bathtub *** may require,however,different choices depending on the section which corresponds to the planned *** 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 *** 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’.

关键词： apparatus insulation operation

Pancreatic fat and β-cell function in overweight/obese children with nonalcoholic fatty liver disease

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World Journal of Gastroenterology 2015年第15期21卷 4688-4695页

作者： Lucia Pacifico Michele Di Martino Caterina Anania gian Marco Andreoli Mario Bezzi carlo Catalano Claudio Chiesa Department of Pediatrics and Child Neuropsychiatry Sapienza University of Rome Department of Radiological Sciences Sapienza University of Rome Institute of Translational Pharmacology National Research Council

AIM: To analyze the associations of pancreatic fat with other fat depots and β-cell function in pediatric nonalcoholic fatty liver disease(NAFLD).METHODS: We examined 158 overweight/obese children and adolescents, 80 with NAFLD [hepatic fat fraction(HFF) ≥ 5%] and 78 without fatty liver. Visceral adipose tissue(VAT), pancreatic fat fraction(PFF) and HFF were determined by magnetic resonance imaging. Estimates of insulin sensitivity were calculated using the homeostasis model assessment of insulin resistance(HOMA-IR), defined by fasting insulin and fasting glucose and whole-body insulin sensitivity index(WBISI), based on mean values of insulin and glucose obtained from oral glucose tolerance test and the corresponding fasting values. Patients were considered to have prediabetes if they had either:(1) impaired fasting glucose, defined as a fasting glucose level ≥ 100 mg/d L to < 126 mg/d L;(2) impaired glucose tolerance, defined as a 2 h glucose concentration between ≥ 140 mg/d L and < 200 mg/d L; or(3) hemoglobin A1 c value of ≥ 5.7% to < 6.5%.RESULTS: PFF was significantly higher in NAFLD patients compared with subjects without liver involvement. PFF was significantly associated with HFF and VAT, as well as fasting insulin, C peptide, HOMA-IR, and WBISI. The association between PFF and HFF was no longer significant after adjusting for age, gender, Tanner stage, body mass index(BMI)-SD score, and VAT. In multiple regression analysis withWBISI or HOMA-IR as the dependent variables, against the covariates age, gender, Tanner stage, BMI-SD score, VAT, PFF, and HFF, the only variable significantly associated with WBISI(standardized coefficient B,-0.398; P = 0.001) as well as HOMA-IR(0.353; P = 0.003) was HFF. Children with prediabetes had higher PFF and HFF than those without. PFF and HFF were significantly associated with prediabetes after adjustment for clinical variables. When all fat depots where included in the same model, only HFF remained significantly associated

关键词： Nonalcoholic fatty liver disease Pancreaticfat Visceral fat Beta-cell function Children