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Open access

G. Preduşcă and C. Fluieraru

Abstract

If the electrons and holes in excess are created in a semiconductor, either by means of light absorption, or using other methods, the thermic balance is disturbed, therefore these electrons and holes should be nullified after the source had been stopped. This process is named recombination. There are three main recombination types: radioactive, Auger and deep energy level recombination. All three are based on the doping concentration to a certain point. The life time is determined using the three recombination processes in semiconductor.

Open access

D. Puiu, B. Corbescu and C. Cepisca

Abstract

The power cables passing through penetration leads to growth of the thermal ageing mechanisms rate. The paper presents the results of the laboratory tests when the real environmental service conditions for penetration are simulated comparison with the result of the thermal computation of the power cables heating and of the temperature influence evaluation of temperature increase of the power cable components on the cable lifetime. For this particular case, a power cable with PVC insulation, we estimated a lifetime decrease about 20 years referring to lifetime (30÷40 years) for location in air.

Open access

L. Petrescu, E. Cazacu, V. Ioniţă and Maria-Cătălina Petrescu

Abstract

Electrical transformers are essential parts of power supply networks and it is important that their life-time to be preserved. The inrush current of this devices could determine malfunctioning of the transformers or even others component of the network. For this reason, determining the inrush current for single-phase transformers is an important issue in power quality analysis of electrical grids. In this paper we presented an experimental device (hardware set-up and software program) that can measure this in rush current features for small transformers (up to 10 kVA). Also, the device affords the users to measure inrush current knowing the geometry of the transformer, the dimensions and the magnetic characteristic of the core.

Open access

Herbert Danninger

Abstract

Traditionally, powder metallurgy has been based on two major industrial sectors – ferrous precision parts and hardmetals. Both of them relied heavily on the automotive industry, with focus on internal combustion engines. Today, there is an increasing trend towards alternative drivetrain systems, and powder metallurgy faces the challenge to find new applications to replace those lost with the decrease of classical internal combustion drives. In this presentation it is shown that the main strength of powder metallurgy lies in its enormous flexibility regarding materials, geometries, processing and properties. This enables PM to adapt itself to changing requirements in a changing industrial environment. Examples given are PM parts in alternative drivetrain systems, new alloying concepts and processing routes offering distinct advantages. With hardmetals, innovative microstructures as well as sophisticated coatings offer increased lifetime, applications ranging from metalworking to rockdrilling and concrete cutting. A particularly wide area is found in functional materials which range from components for high power switches to such for fuel cells. Soft and hard magnets are accessible by PM with particularly good properties, PM having in part exclusivity in that respect, such as for NdFeB superhard magnets as well as soft magnetic composites (SMCs). Metal injection moulding (MIM) is gaining further ground, e.g. in the medical area which is a fast-growing field, due to demographic effects. Finally, most additive manufacturing techniques are powder based, and here, the knowledge in powder handling and processing available in the PM community is essential for obtaining stable processes and reliable products. Conclusively it can be stated that PM is on the way to fully exploit its potential far beyond its traditional areas of applications.