Basis and method for electrical power grid development planning

Planning the development of an electrical power grid is a sophisticated multilevel process, which involves putting into practice different relevant methods of analysis, models, software packages, standards etc. The inputs and criteria for different planning levels may also vary. Planning of the transmission grid greatly depends on decision making on a higher level of hierarchy, influencing electrical power supplies of large areas. Development of a medium voltage (MV) grid, on the other hand is affected by locally generated inputs, such as local load shift. The business as usual approach is to separately derive development plans for transmission and distribution systems. This article examines one of the possible methods for creation of a combined long term (with a 15 year perspective) transmission and distribution systems' contact level (35-110 kV in current case) electrical power grid development plan, centered around grid optimization through primary distribution substations and their feeding lines location. The method proposed aims to minimize joint costs of transmission and distribution system operators (TSO-s and DSO-s) for electrical power grid development on a given planning horizon. It is shown that a co-operative approach can result in lower costs of electrical power grid development for the society as a whole. The results are applicable to practical usage.