Thermal Analysis of Power Rectifiers in Steady-State Conditions

Power rectifiers from electrical traction systems, but not only, can be irreversibly damaged if the temperature of the semiconductor junction reaches high values to determine thermal runaway and melting. The paper proposes a mathematical model to calculate the junction and the case temperature in power diodes used in bridge rectifiers, which supplies an inductive-resistive load. The new thermal model may be used to investigate the thermal behavior of the power diodes in steady-state regime for various values of the tightening torque, direct current through the diode, airflow speed and load parameters (resistance and inductance). The obtained computed values were compared with 3D thermal simulation results and experimental tests. The calculated values are aligned with the simulation results and experimental data.publishedVersio

THE INFLUENCE OF BUSBARS CONNECTION ON FUSELINK TEMPERATURE AT FAST FUSES

The paper, based on three-dimensional thermal modelling and simulation finite element method software package, presents a comparison between the thermal behaviour of a fast fuse without busbar terminals and the one with these busbars mounted on it. The maximum fuselink temperature is lower in the second case when the thermal model had taken into consideration the busbar connections, actually, the real situation. Also, a thermal analysis for different type of load variations has been done in both cases of the fast fuse geometry with and without busbar terminals

Cervical related disability – interactions of pain features, psychological states and clinical presentation

Background: Cervical pain related to different spine pathologies is a major cause of disability. The relationship between clinical patterns, pain, psychological states was demonstrated. Disability in patients with cervical pain remains still high. Material and methods: A total of 42 patients (14 males, 28 females) with cervical pain were assed using visual analogue scale (VAS), hospital anxiety and depression scale (HADS), patient health questionare-9 (PHQ-9), neck disability index (NDI) and other clinical data. Results: Acute pain was present in 24 % of patients while gradual in 76%. Among clinical patterns the most common form was referred pain (52%) followed by axial neck pain (33%) and radiculopathy in (14%). NDI correlated with pain intensity (VAS) and the psycho-emotional state (for HADS and PHQ-9, p < 0.001). A higher depression score was found in patient with referred pain and radiculopathy (mean 8.0 points ±4 points according to PHQ9 score). Also, NDI was higher in patients with comorbidities, current joint pain and systemic disorders, referred pain, with acute onset, and no previous trauma. Conclusions: The results from the current study highlighted an association between NDI and pain intensity and psychological state, predominantly in the group with referred pain, and radiculopathy. Acute cervical pain, with no previous trauma, with systemic disorders and other joint pain interfered with a higher risk for developing disabilities. Further research looking at multiple factors such as clinical presentation features of cervical pain and clinical outcomes will additionally guide the development of adequate management strategies for cervical pain

Clinical features and outcome in patients with Guillain-Barré syndrome

Background: Guillain-Barré syndrome (GBS) is a heterogeneous group of autoimmune polyradiculopathies, in which disease biomarkers, and outcome predictors are under continuous research. Material and methods: Thirty-three patients with GBS (12 females/21 males) aged between 24 and 73 years were assessed, using clinical data, Modified ERASMUS GBS Outcome (MEGOS) score and electromyography (EMG). Results: The average age of onset was 52.1 ± 12 years. The mean time period before hospitalization was 15 days. Clinical symptoms at onset were areflexia (24%), paresthesia (25%), weakness in the legs (36%) and arms (22%). 15 patients (45.4%) had cranial nerves involvement, while 11 (33%) developed respiratory failure of which five (15%) required mechanical ventilation. EMG revealed myelinopathy in majority of the patients – 19 (70%), axonopathy – 6 (22%), and axonomyelinopathy – 2 (8%). 27 (81%) patients received plasmapheresis, 2 (6.06%) – plasmapheresis with immunoglobulins, and 6 (18%) received no plasmapheresis due to contraindications. Treatment outcomes were as follows: 29 (88%) patients saw improvement, 2 (6.06%) had stable disease. There were 2 (6.06%) deaths in the cohort. Mean MEGOS was 4.0 ± 2 (male 5.0 ± 2; female 4.0 ± 2). Patients with myelinopathy and axonomyelinopathy had a higher MEGOS. Hospitalization delay and higher MEGOS score correlated with more severe disease evolution. Conclusions: Patients with delayed hospitalization, predominantly men, who had myelinopathy and mixed forms of GBS have a less favorable prognosis of the disease. Increased attention to the onset of symptoms consistent with GBS is needed in order to ensure a prompt diagnosis and hospitalization, as well as specialized treatment

Thermal Analysis of Power Semiconductor Device in Steady-State Conditions

Electronic devices can be damaged in an undesirable manner if the junction temperature achieves high values in order to cause thermal runaway and melting. This paper describes the mathematical model to calculate the power losses in power semiconductor devices used in bidirectional rectifier which supplies a resistive-inductive load. The obtained thermal model can be used to analyse the thermal behaviour of power semiconductors in steady-state conditions, at different values of the firing angle, direct current, air speed in the case of forced cooling, and different types of load. Also, the junction and case temperature of a power thyristor have been computed. In order to validate the proposed mathematical model, some experimental tests have been performed. The theoretical values are in good concordance with the experimental data and simulated results

Temperature Distribution of HBC Fuses with Asymmetric Electric Current Ratios Through Fuselinks

In many industrial applications high breaking capacity (HBC) fuses are used to protect electrical installations against overcurrents, especially in the power distribution network. At high rated current, HBC fuses have more parallel fuselinks mounted inside. The technological and mounting processes of the fuselinks inside the fuse results in an asymmetrical current distribution through the parallel fuselinks. In this article a model of a high breaking capacity fuse using two parallel fuselinks is proposed. The influence of electric current, cross-section of the notches, distance between notches and current imbalance through fuselinks on the maximum temperature rise of both fuselinks, has been investigated. Also, a 3D thermal model for the same HBC fuse has been developed. The temperature spread into the fuse and its elements has been obtained. In order to prove the validity of the mathematical and 3D model different tests have been considered. The experimental, simulation and computed results give similar values and it results that this model can also be used for fuses with many parallel fuselinks and it permits the design of new fuse elements with optimal thermal distribution

Numerical Analysis of Thermal Behaviour of DC Fuse

One of the very well-known protections for electrical apparatus against overloads or short circuits is the fuse. It can be used to protect both AC or DC electrical installations and it has also proven its effectiveness in the protection of different loads. This paper describes a three-dimensional model of a DC fuse with two different types of fuselink notches: circular and rhombic. The obtained 3D thermal model can be used to investigate the thermal behaviour of DC fuses in both steady-state and transient conditions at different values of overloads or short circuits. With the aim to validate the proposed 3D thermal model, a series of experimental tests have been achieved. The thermal simulated values are in good concordance with the experimental results (a relative error less than &plusmn;6% has been obtained between experimental and simulation data)

Uporaba regeneratorja za magnetno hlajenje

In this article, the mechanism and functioning of a refrigeration system based on the magnetic system and the magnetocaloric effect are examined. Magnetic refrigeration plants operate based on a state-of-the-art technology that does not contain any toxic refrigerant that is harmful to the environment and the ozone layer. The magnetocaloric effect is created by a rare earth metal called gadolinium. We have studied the benefits of using this type of mechanism for both domestic and industrial needs. High efficiency, net energy consumption lower than the classic, silent systems, and a lack of typical refrigerant characterize this type of installation. The following layout describes the initial prototype for AMR in magnetocaloric refrigeration.V tem članku je proučen mehanizem in delovanje hladilnega sistema, ki temelji na magnetnem sistemu in magnetokaloričnem učinku. Magnetne hladilne naprave delujejo po najsodobnejši tehnologiji, ki ne vsebujejo nobenega strupenega hladilnega sredstva, ki je škodljivo za okolje in ozonski plašč. Magnetokalorični učinek ustvarja redka zemeljska kovina, imenovana goldonij. Proučevali smo prednosti uporabe tovrstnih mehanizmov tako za domače kot industrijske potrebe. Za to vrsto namestitve je značilna visoka učinkovitost in nizka poraba energije. Predstavljen članek opisuje začetni prototip za AMR v smislu magnetokaloričnega hlajenja

Analiza in učinkovitost gadolinijske magnetokalorične plošče

In this article, the influence of a controlled magnetic field on gadolinium plates was modelled and simulated to be used in magnetic refrigeration installations. This is a state-of-the-art technology that does not use refrigerants and does not work based on vapour compression, which is based on the operation of the magnetocaloric properties of the material usedin the case below, this material, in the form of a flat plate, has certain magnetocaloric properties and under the influence of magnetic induction can be used successfully in such innovative installations. The advantages of using gadolinium in the form of a flat plate in a magnetic regenerator and thermal energy dissipation on its surface under the controlled magnetic field\u27s influence were studied.V tem članku je bil izdelan model in simuliran vpliv nadzorovanega magnetnega polja na gadolinijeve plošče za uporabo v magnetnih hladilnih napravah. To je najsodobnejša tehnologija, ki ne uporablja hladilnih sredstev in ne deluje na osnovi kompresije hlapov. Tehnologija temelji na delovanju magnetokaloričnih lastnosti uporabljenega materialav spodnjem primeru ima ta material v obliki ravne plošče določene magnetokalorične lastnosti in se pod vplivom magnetne indukcije lahko uspešno uporablja v inovativnih instalacijah. Proučene so bile prednosti uporabe gadolinija v obliki ravne plošče v magnetnem regeneratorju in odvajanja toplotne energije na njegovi površini pod vplivom nadzorovanega magnetnega polja