Using the Design of Experiments (DoE) Method to Elaborate an Electrical Ageing Model for the Insulation of Low Voltage Rotating Machines Fed by Inverters

A large amount of parameters related to both operating conditions and material design affects the electrical ageing of the low voltage rotating machine insulation. Accelerated ageing tests are usually undertaken in order to develop a theory to describe the electrical ageing process and to determine a lifetime model of these materials. However, to the best of our knowledge, there is no complete model allowing the prediction of an insulation lifetime from accelerated ageing tests, since there are many possible failure mechanisms and various synergetic effects between them. Another problem with accelerated ageing tests is that results of the tests tend to have a great deal of scatter. In the present work, we propose the use of the design of experiments (DoE) method, which is a useful statistical approach that would lead to a reliable and significant interpretation of the different ordering parameters of the insulation ageing process. Using the DoE method, the analysis of accelerated ageing test results allows identifying the factors that most influence the results, and those that do not, as well as details such as the existence of interactions and synergies between these factors. In the following, results from accelerated ageing tests on PEI varnishes, largely used in rotating machines insulation, are presented and analyzed with the DoE method

Lifetime Model of the Inverter-fed Motors Secondary Insulation by using a Design of Experiments

Numerous parameters (environmental conditions, material and equipments design) affect the ageing (and consequently the lifetime) of the Electrical Insulation System (EIS) of motors supplied by static converters. In order to find a modeling of the lifetime of such materials, accelerated tests have to be considered. The problem is that if we consider all the relevant parameters, these tests become costly and take a lot of time. Consequently the topic of this study is to use a statistical method called: the ‘Design of Experiments’ (DoE) to obtain the lifetime modeling by only a ‘reasonable’ number of experiments. Only electrical and thermal parameters will be modified in this study (vibrations and thermal cycling are not taken into account). In this work, the ageing of the secondary insulation of a motor fed by an inverter is supposed to be originated from partial discharges. In this kind of machine, if a partial discharge activity begin to grow, the first insulation link of the EIS to be affected by these discharges will be the secondary one (i.e.: the impregnation varnish). Consequently, this study is focused only on this secondary insulation. The results obtained by using the DoE method show that it is possible to classify the different ageing parameters and to find their effects on the insulation lifetime. The interactions between all the parameters will also be shown by this method. Finally, a mathematical model of the insulation lifetime taking into account all the parameters and their interactions will be presented and discussed

Evaluating User Experience in Multisensory Meditative Virtual Reality: A Pilot Study

Virtual Reality (VR) is known for its ability to immerse users in a parallel universe. Accordingly, VR offers great potential for mindfulness therapy, especially in a post pandemic world. However, the extent to which our senses should be recruited to yield an optimal feeling of presence in the Virtual Environment (VE) remains unclear. This study investigates lived and perceived effects of adding auditory and motor components to VR experiences, through narration and head movements respectively. Twelve participants experienced four nature-based VR videos in a within-subjects research design. The study employed a mixed method approach of psychometric and neurophysiological measures. Results support a significant relationship between positive affect and presence. While statistical support was not obtained for the remaining relationships, this study provides a feasibility assessment of utilizing NeuroIS methods in evaluating immersive user experiences, along with qualitative insights that extend our understanding towards optimized VE designs

Modélisation du vieillissement des isolants organiques sous contrainte électrique (application à la fiabilité des matériaux)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Electrical ageing of polymers: The role of micro-domains

International audienceRÉSUMÉ Les matériaux polymères sont des systèmes désordonnés présentant une évolution continue de leur structure, appelée « vieillissement physique ». La variation spatiale de leur morphologie aboutit à une distribution des différentes propriétés au sein de ces matériaux. Dans cet article, nous mettons en évidence la présence de microdomaines au sein des polymères par une technique expérimentale de mesure de la déformation induite par le champ électrique. Le rôle des microdomaines est ensuite pris en considération pour élaborer une approche phénoménologique sur le vieillissement électrique des isolants polymères. Les différents paramètres en jeu, telles l’évolution de la structure et la valeur du champ à une échelle locale, sont présentés d’une façon distribuée. Dans un premier temps le processus de vieillissement est décrit sur une échelle locale. Ensuite, une approche statistique pour présenter l’ensemble des contributions locales de la contrainte appliquée aboutissant à la rupture est exposée. ABSTRACT Polymer materials are disordered systems and their structure is continuously undergoing conformational changes called “the physical ageing”. Furthermore, polymers exhibit a spatially varying morphology and a distribution of their properties and characteristics. In this article, the existence of micro-domains into polymer materials is proved, using an optical strain measurement technique. Then after, the role of these microdomains is taken into consideration for a phenomenological description of their electrical ageing process. The different parameters affecting the ageing process, such as the local structure evolution and the local field value, are presented in a distributed way. In a first analysis the ageing process is described in a local scale. Afterwards, a statistical description of the totality of processes at play is necessary to present the global effect of the applied stress over the material structure which leads to the failure mechanism

Electrical Aging of the Insulation of Low Voltage Machines: Model definition and test with the Design of Experiments

International audienceThe aim of this paper is to present a method for modeling the lifespan of insulation materials in a partial discharge regime. Based on the design of experiments, it has many advantages: it reduces the number of time-consuming experiments, increases the accuracy of the results and allows lifespan modeling under various stress conditions including coupling effects between the factors. Accelerated aging tests are carried out to determine the lifespan of these materials. The resulting model presents an original relationship between the logarithm of the insulation lifespan and that of electrically applied stress and an exponential form of the temperature. Results show that the most influential factors can be identified according to their effects on the insulation lifespan. Moreover, the lifespan model validity is tested either with additional points which have not been used for modeling or through statistical tests. Finally, it is shown that fractional plans are not suitable to reduce the number of experiments. This application of the experimental design is best used during the initial phase, before the final drive has been built and any on-line diagnostic

Prevalence of Lebanese stroke survivors: A comparative pilot study

Stroke is a leading cause of morbidity and mortality worldwide and its late burden has mainly been attributable to developing countries. Lebanon is one of these countries where epidemiological studies on stroke burden are scarce but necessary. Thus, the present study was conducted to assess the prevalence of stroke survivors among Lebanese inhabitants. A cross-sectional survey was carried out using randomly selected landline phone numbers on all governorates to retrieve data on stroke survivors and their sociodemographic characteristics. Results were then standardized over the Lebanese and the World Health Organization (WHO) world populations. A total of 6963 Lebanese inhabitants were included in the study; among these were 56 stroke survivors. This led to an adjusted stroke prevalence of 0.50% [95% confidence interval (CI) = 0.33–0.66%] and a world-standardized prevalence of 0.60% (95% CI = 0.42–0.78%). A significantly higher stroke prevalence was found among older age groups and more socioeconomically privileged areas. Overall, the study showed a relatively higher prevalence of stroke in this sample of Lebanese inhabitants when compared to other developing countries. However, larger community-based studies with a clinical assessment of stroke cases are needed to confirm our findings

Antibiotic dispensation by Lebanese pharmacists: A comparison of higher and lower socio-economic levels

Summary: Introduction: Indiscriminate use of antibiotics contributes to a global spread of antimicrobial resistance. Previous studies showed an excessive consumption of antibiotics purchased without medical prescription from community pharmacies, mainly in developing countries.There is a shortage of studies revealing the role of community pharmacists in the overuse of antibiotics. Our objective is to study the dispensing policy of non-medical prescription antibiotics in community pharmacies, assessing the possible influence of the socio-economic level of the area over this practice. Methods: A cross-sectional study was conducted between February and May 2011 among 100 pharmacists working in Beirut's pharmacies and its suburbs. Pharmacies were divided into 2 groups according to the socio-economic level of the population living in the pharmacy area. A self-administered questionnaire was filled by pharmacists. Results: Over-the-counter antibiotic availability existed in both higher and lower socio-economic areas: on the whole, 32% of antibiotics were dispensed without medical prescription, with higher frequency in lower socio-economic areas (p = 0.003). Dispensing injectable antibiotics without medical prescription was significantly higher in lower socio-economic areas (p = 0.021), as well as dispensing an association of 2 antibiotics without medical prescription (p = 0.001). Pharmacists working in lower socio-economic areas recommended more frequent antibiotics to children and the elderly (p < 0.001 and p = 0.004, respectively). Conclusion: Dispensing antibiotics without medical prescription in Beirut community pharmacies is a common practice, particularly in lower socioeconomic areas. This public health problem should be addressed at the social, educational, and legislative levels. Keywords: Dispensing antibiotics, Community pharmacist, Medical prescription, Socio-economic level, Lebano

Electrical Ageing Modeling of the Insulation of Low Voltage Rotating Machines Fed by Inverters with the Design of Experiments (DoE) Method

International audienceIn the context of more electric aircrafts, the reliability of the low voltage insulation systems in rotating machines is an important issue. But, modeling and understanding their electrical ageing is a complex phenomenon especially when they are fed by PWM inverter. They involve a large amount of parameters related to both operating conditions and material design, which act together. Accelerated ageing tests are usually run in order to describe the electrical ageing process and to determine the lifetime of these materials. Nevertheless, full ageing tests with all the various parameters for different samples become rapidly time consuming. Moreover, there is not any complete model for insulation lifetime prediction under accelerated ageing tests. In this paper work, we propose a method based on the design of experiments (DoE) method, which is a useful statistical approach that would lead to a reliable and significant interpretation of the different ordering parameters of the insulation ageing process. Moreover, this method will help to reduce the number of required experimental or numerical trials and will, take into account the possible failure mechanisms and the various synergetic effects between them. Using the (DoE) method, a preliminary model of the insulation “lifetime” is presented with respect to the most important parameters at play and interactions between them