The opening of the electricity market, liberalisation and privatisation of the generation, distribution and transmission have led to major changes in the field of electric power system operation as well as in the operations of individual companies. Traditional vertical structure of organisation of the generation of transmission and distribution has changed so that each of these companies acts independently on the market [1]. As a result of the structural changes and implementation of new technologies, especially renewable energy resources is reflected in the electric power systems (EPS), which operate under very changed conditions and closer to the thermal limits.
Consequently, EPS is also more vulnerable. Changes on the electricity market and the growing pressures of national regulators to reduce tariffs lead to the situation where the transmission system operators will be ever more forced to optimise the investment costs. Such operations lead to important business decisions, which will need to be introduced also in the process of network planning and investments into the transmission networks (TN). Deterministic methods of planning that are based on the classic N-1 criterion, which defines that an outage of one element in the network does not cause an overload of the system elements, voltage vioolations, interruption of power supply to consumers, system instability and cascading outages, provides information only on whether the security criterion is fulfilled or not, but it does not consider the probability of various operating states, probability of outage of individual element and its impact on the network [2], [3], [4], [5], [6].
Planning, based on a deterministic approach may also lead to over-dimensioning of transmission networks, which in turn leads to higher tariffs for consumers [1], [2]. To this end, a new methodology for probabilistic planning of TN is presented in this thesis. The said methodology takes into consideration the probability of occurrence of different operating states, the probability of outage of system elements and their impact on the EPS. The impact on the EPS is assessed on the basis of a new indicator (Impact on the Grid, IOG), which takes into consideration all breaches of voltage caused by the outage of an element, such as overloading, breaches of voltage, interruption in electricity supply of substations and generation downtimes. The new methodology, which based on a risk index demonstrates the reliability of the EPS, will help the transmission system operators (TSOs) in the decisions on investments into new elements of the EPS and help determining the priorities of individual investments, by way of which it will enable a lower investment costs in the still sufficient degree of reliability.
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