Journal of Sustainable Energy

6

Authors: LINGVAY I., OPRINA G., CUCOȘ A., RADU E., VOINA A.

The By gravimetric measurements and coupled thermal analysis techniques (DTG+TG+DTA) the aging of different sorts of insulating oil was studied by thermal cycling between -400C and 850C. The experimental results showed that, during the thermal cycling of the investigated mineral oils, their composition changes due to the volatilization of the volatile fractions (mass losses between 3.9% and 5.8%), unlike the investigated vegetable oil that showed a mass increase of approx. 0.66%. It has also been found that the mineral oils can be ensure a safe operation, without significant changes up to a maximum of 1000C, as long as investigating vegetable oil can be used without degradation risk up to 2000C.

6

Authors: TOMA R., GAVRILAS M.

The paper presents a comparative study between the effects on voltage stability of the integration of a wind farm into the electricity grid with or without voltage dependent loads in the context of different locations of a synchronous compensator from the grid. The P-V curves are built by using the PowerFactory DigSilent 15.2.2 and a DPL script that implements a simplified form of the Continuation Power Flow method.

8

Authors: OPRINA G., CHIHAIA R.A., EL-LEATHEY L.A., NICOLAIE S., BĂBUȚANU C.A., VOINA A.

On a dynamic energy market characterized by the constant energy demand increase and economic as well as environmental constraints, the study and development of efficient conversion systems of wind’s energy has been approached by a considerable number of researchers. Given the modern economic and environmental challenges regarding the energy production and consumption, an advance in the research of innovative or improved wind energy conversion solutions has been registered. The objective of this paper is to provide a comprehensive, but not exhaustive overview of research achievements in counter-rotating wind turbine systems development, characterization and use. The review presents the first theoretical results that led to the counterrotating wind turbines development as well as the related methods used for investigating their performance. Valuable results have been found within various studies, which are carried out for different testing systems and conditions. Furthermore, there is still need of extensive studies, taking into account that the counter-rotating wind turbines have to prove their reliability in real operating conditions.