Journal of Sustainable Energy

3

Authors: CÂRLAN M., CSUZI. I., COSTEA M.

This paper is presenting a method used to confirm the necessity of practicing maintenance works for two vehicles, tramways, whose operational statuses, defined by the levels of exploitation parameters, proved to be in precarious condition. Wear and tear has been the main cause leading to the occurrence of unnumbered moments when the vehicles were unavailable. Studies performed on data collected during a compelling enough period of time are highlighting, a tendency to increase the failure frequency with more than 10%. The wear and tear of the analyzed technical equipment is expressed by the status probabilities that are related to a later moment, and determined by using Markov chain theory, and entropic level - unit of measure for incertitude or chaos - phenomenons that are specific for system degradation - to be determined based on Shannon entropy concept[7],[11]. Based on these two sizes, the decision-maker may impose the optimal strategy regarding the maintenance works practice.[1]

5

Authors: BERINDE I., BRAD C.

Integration of wind power plant in medium voltage grid is comply with the same regulations as conventional plants. To realize in the point of common coupling grid, reactive power levels as close to zero is necessary to use reactive power compensators and ensuring the compensation. Static compensators STATCOM shunt satisfy this requirement very well, by absorption / injection of reactive power from / to grid based on the voltage amplitude the point of common coupling at grid. The article presents the behavior of wind power plant, which is connected to the compensator STATCOM, on medium voltage fault and the importance using it in the wind power plant

7

Authors: RUGINĂ V., BADEA A.

The paper presents the importance of evaluating energy efficient use that is explicitly stipulated in the strategic and legislative documents adopted at the national and international level, including the Directive 2012/27/EU and the Law 121/2014. Energy intensity frequently that is used in international evaluations and comparisons of energy efficient use is also used in Romania. The topic is approached both by specialists and politicians, newspapermen, representatives of the public opinion etc. This indicator has acquired axiomatic valences and its values are presented as unquestionable arguments for incontestable truths. Nevertheless, besides correct and well-balanced approaches one may come across distorted presentations and exaggerations resulting from superficially knowing the problem. The information and data presented in the paper can bring clarifications on this field. In the first place, energy intensity characterizes the economic efficiency of energy utilization and only to little extent the technical efficiency. Its value is directly linked to macroeconomic parameters, among which the parity between the national currency and the currencies in international circulation, the structure of the national economy etc. The paper presents different variants for the interpretation and calculation of the energy intensity indicator value, including the corresponding mathematical models. Based on the primary information obtained from reliable sources (National Institute of Statistics, EUROSTAT data base) values of this indicator are calculated in different variants that are considered and comparisons between the obtained results are made. Choosing the variant for defining and calculating energy intensity, respectively, depends on the purpose of the analysis to be carried out and needs to be explicitly presented together with the results obtained. The paper includes recommendations on how the calculation variants and the results obtained by carrying out these analyses according to their purpose (carrying out international comparisons, analyzing the evolution of internal situation in a certain period of time etc) should be used.