Superconductivity and its Application in the Field of Electrical Machines

This paper provides a review on the most recent applications of superconductors in rotating electrical machines. The main types of superconductors for the present-day electrical applications are shown to highlight their main features. The main characteristics of superconducting synchronous machines, DC machines and induction machines for marine and vehicle propulsion, future electric aircraft, wind energy and industrial applications are discussed by presenting data of prototypes and demonstrators. The paper aims to raise awareness among researchers and engineers on the importance of superconductivity to enhance the performance of conventional electrical machines

Iron Losses and Parameters Investigation of Multi-Three-Phase Induction Motors in Normal and Open-Phase Fault Conditions

Among multi-phase solutions, multi-three-phase induction machines (IMs) are gaining an increasing interest in the industry due to their advantages to be configured as multiple three-phase units simultaneously on the same magnetic circuit. According to this scenario, the identification of the equivalent circuit parameters and conventional iron losses covers a key role in evaluating performance and efficiency, especially when the machine is operated in a wide torque-speed range. Therefore, the goal of this paper is to investigate the core losses and the saturation phenomena of multi-three-phase IMs operated in normal and open-three-phase fault conditions under different harmonic contents of the air-gap magnetomotive force. A procedure to identify the parameters of the equivalent circuit of the machine in faulty conditions is reported. Experimental results are presented on a 12-phase asymmetrical IM featuring a quadruple three-phase stator winding. Finally, a comparison between normal and faulty conditions in terms of efficiency and losses for several machine working points is reported

Experimental Assessment of Cryogenic Cooling Impact on Induction Motors

In this work, an experimental assessment of the influence of cryogenic cooling in a conventional induction motor is presented. The performance of a fractional kilowatt induction motor is evaluated when submerged in liquid nitrogen. Using the single-phase equivalent electric circuit, the influence of the temperature and skin-effect is analyzed in the variation of the machine's parameters, under ambient and cryogenic conditions. Also, the variation of the iron core and mechanical losses are evaluated. An analytical methodology is proposed to estimate the change of motor performance under cryogenic conditions. For the analyzed induction motor, measurements are performed to verify the predicted machine performance. The experimental tests in cryogenic conditions show the possibility of achieving higher efficiency levels with more than double the nominal torque. Also, due to the cryogenic environment, there was no thermal constraint in the operation of the induction motor

A Comparison of Cryogenic-Cooled and Superconducting Electrical Machines

This paper compares the steady-state operation of air-cooled, cryogenic-cooled and superconducting induction machines. The aim is to investigate the impact of a very low temperature and the influence of a superconducting rotor cage on the performances of standard designed, air-cooled machines. The research work includes a review of the state of the art of cryogenic-cooled and superconducting induction machines for various applications. The performances of the machines are assessed analytically by solving the single-phase equivalent circuit and considering the influence of the temperature, the skin-effect and the nonlinear behavior of superconductors. The analytical results are validated by experiments on a fractional kilowatt induction motor. The experimental activities include the characterization of the core losses at cryogenic temperature

Prevalence and clinical significance of isolated ambulatory hypertension in young subjects screened for stage 1 hypertension

Little is known about the clinical significance of isolated ambulatory hypertension, a condition characterized by low office but elevated ambulatory blood pressure. This study aimed to investigate the prevalence and the predictive value of isolated ambulatory hypertension diagnosed after 3 months of observation for the development of sustained hypertension within a cohort of 871 never-treated stage-1 hypertensive subjects. The study end point was progression to more severe hypertension and need of antihypertensive medication. In 244 subjects (28%), clinic blood pressure declined to <140/90 mm Hg after 3 months. Of these, 124 (14.2% of total) had low clinic and ambulatory blood pressures after 3 months (nonhypertensive subjects), whereas 120 subjects (13.8% of total) showed low clinic but elevated ambulatory blood pressure ( isolated ambulatory hypertension). During the 6 years of observation, the number of end points based on multiple clinic blood pressure readings progressively increased from the nonhypertensive subjects (19%) to the subjects with isolated ambulatory hypertension (35%) and to the subjects with high clinic and high ambulatory blood pressures (65%, P < 0.0001). In an adjusted proportional hazard model, isolated ambulatory hypertension status was associated with a 2.2 (P = 0.02) increase in the risk of reaching the end point in comparison with the nonhypertensive subjects. Final ambulatory systolic blood pressure was also higher in the former than the latter (P = 0.03). Our results indicate that among subjects screened for stage 1 hypertension, individuals with isolated ambulatory hypertension after 3 months of observation have increased risk of developing sustained hypertension in later life compared with subjects in whom both clinic and ambulatory blood pressures are normal

Association between coffee consumption and risk of hypertension

Impact factor 4.246 Q1 Punti 1

Glomerular hyperfiltration predicts the development of microalbuminuria in stage 1 hypertension: The HARVEST

Factors related to the development of microalbuminuria in hypertension are not well known. We did a prospective study to investigate whether glomerular hyperfiltration precedes the development of microalbuminuria in hypertension. We assessed 502 never-treated subjects screened for stage 1 hypertension without microalbuminuria at baseline and followed up for 7.8 years. Creatinine clearance was measured at entry. Urinary albumin and ambulatory blood pressure were measured at entry and during the follow-up until subjects developed sustained hypertension needing anti hypertensive treatment. Subjects with hyperfiltration (creatinine clearance > 150 ml/min/1.73 m(2), top quintile of the distribution) were younger and heavier than the rest of the group and had a greater follow-up increase in urinary albumin than subjects with normal filtration (P < 0.001). In multivariable linear regression, creatinine clearance adjusted for confounders was a strong independent predictor of final urinary albumin (P < 0.001). In multivariable Cox regression, patients with hyperfiltration had an adjusted hazard ratio for the development of microalbuminuria based on at least one positive measurement of 4.0 (95% confidence interval (CI), 2.1-7.4, P < 0.001) and an adjusted hazard ratio for the development of microalbuminuria based on two consecutive positive measurements of 4.4 (95% CI, 2.1-9.2, P < 0.001), as compared with patients with normal filtration. Age, female gender, and 24h systolic blood pressure were other significant predictors of microalbuminuria. In conclusion, stage 1 hypertensive subjects with glomerular hyperfiltration are at increased risk of developing microalbuminuria. Early intervention with medical therapy may be beneficial in these subjects even if their blood pressure falls below normal limits during follow-up