Читать книгу Smart Grid and Enabling Technologies - Frede Blaabjerg - Страница 18

The transmission system has the highest voltage rating and is used to transmit the energy from the bulk generation plant to the distribution networks through interconnecting substations. The transmission system may include overhead lines, underground and under water cables. This transmission system could be high voltage alternating current (HVAC) or high voltage direct current (HVDC). Traditionally, an HVAC system is mostly used, however, the HVDC is rapidly gaining popularity due to reduced losses and cost particularly over large distances. The electric power could also be transported and distributed via underground cables. Construction of an underground transmission system normally costs 4 to 10 times that of an equal distance overhead line [7]. The overall amount of power and distance that the power needs to be transported, overdetermine the essential design of the transmission and distribution systems. Hence, the greater the distance and the more power to be transferred, the higher the rated voltage is, and the higher the cost of the system will be as shown in Figure 1.2 [8]. This shows that distributed renewable energy generation allows for the reduction of the cost not only of the central power generation plants, but also of the transmission and distribution infrastructures. This is one of the drivers for the SG energy paradigm.