In recent years, it is seen that High Voltage Direct Current (HVDC) transmission line systems have come to the fore in the field of energy efficiency in the world. Therefore, it is predicted that analyzing the technological and economic advantages of HVDC transmission line systems will make an important contribution to energy efficiency policies. In this regard, this study aims to examine the technological and economic advantages of HVDC transmission systems through the historical development with applications in Turkey and in the world. In addition to this, it is expected that the evaluation of the effects of energy efficiency on the economy will bring a different perspective to the energy and economic literature. Therefore, it is thought that energy and economic policies for the spread of HVDC transmission line systems worldwide will be essential. The asymmetric distribution of natural energy sources in the world causes energy supply security problems in the countries such as Turkey in terms of high foreign dependence on energy. For this reason, it is necessary to meet the increasing energy demand and increase the existing capacity day by day. Besides, it is important to develop policies for efficient use of energy. HVDC technology is extremely important for a developing country like Turkey. Moreover, it is known that this energy transmission technology has become widespread in developed countries. Thereby, a technical comparison is done for investment costs of the transmission system in Germany. As a result, other than bringing economic benefits with the energy transmission of Turkey through HVDC, it has important potential for making energy transmission possible with her neighbors and European Union countries.

The tunneling properties of the model structure consisting of HTSC and normal metal are studied. The influence of the impurity concentration in Cu02 layers on the high energy features is investigated, taking into account tight binding band structure, d-wave gap symmetry, group velocity and tunneling directionality. The increasing of the impurity lifetime broadening factor changes the degree of tunneling conductance peaks asymmetry, leads to nonequal shifting of the quasiparticle peaks and their width. We consider that the underlying asymmetry of the conductance peaks is primarily due to the features of quasiparticle energy spectrum and the d-wave symmetry enhances the degree of the peaks asymmetry. The analysis of c-axis transport of quasiparticles and Cooper pairs of stacked intrinsic junctions in HTSC is done.