Distribution system plays a significant role in the overall electrical power system due to its impact on electricity costs, reliability as well as security of supplied energy. Optimal development planning of modern distribution system is mainly required to satisfy continuous change in customer demands and generations in a cost-effective manner, utilizing the available smart solutions. All these aspects need to be addressed in modern distribution planning methodology that can be applied today in real-life. Review has shown that there are no distributions planning models that adequately model security of supply of radially operated networks. Moreover, the optimal development planning models still do not consider multiple operating regimes, which has become a necessity due to connection of low carbon technologies. Numerous techniques published on this subject tend to ignore the regulations and planning standards that must be complied during system development, resulting in methodology that is not in-tuned with business practices. Furthermore, a comprehensive model that integrates all major components of today’s real-life distribution planning is still lacking, even though many of them have been addressed individually. In this thesis, integrated planning methodology for development of distribution system is proposed, incorporating utility practices in the UK. The overall methodology built on two independent stages, investment stage and operation stage. The operation stage is further cast into two sub-stages, quality of supply planning and minimization of operation costs planning. The overall planning methodology incorporates the novel probabilistic decision tree concept for distribution system planning to consider probable network uncertainties. The first model which is the investment stage determines the new construction and reinforcement of circuits and switchgear, along with circuit decommissioning. Multiple operating regimes due to fluctuation in generation and load profiles are considered, in addition to explicit modelling of N-1 security constraint according to P2/6 planning standards. The quality of supply planning determines the allocation of switchgear and its automation to maximise the reliability benefits from the regulatory incentive regime. Finally, the operation model determines the optimal network configuration that minimises the total operation costs of distribution system. The final outputs are list of cables and switchgear for construction, reinforcement, and decommission, benefits harvested due to quality of supply investments on switchgear, optimal network running arrangement, etc. These studies have proven to be important in formulating effective strategies for development of distribution system, in compliance to the planning standards and resulted in higher network operation capabilities.

In reregulated and restructured electricity markets the production and retail of electricity is conducted on competitive markets, the transmission and distribution on the other hand can be considered as natural monopolies. The financial regulation of Distribution System Operators (DSOs) has in many countries, partly as a consequence of the restructuring in ownership, gone through a major switch in regulatory policy. From applying regulatory regimes were the DSOs were allowed to charge their customers according to their actual cost plus some profit, i.e. cost-based regulation, to regulatory models in which the DSOs performance are valued in order to set the allowable revenue, i.e. Performance-Based Regulation (PBR). In regulatory regimes that value performance, the direct link between cost and income is weakened or sometimes removed. This give the regulated DSOs strong cost cutting incentives and there is consequently a risk of system reliability deterioration due to postponed maintenance and investments in order to save costs. To balance this risk the PBR-framework is normally complemented with some kind of quality regulation (QR). How both the PBR and QR frameworks are constructed determines the incentive that the DSO will act on and will therefore influence the system reliability development. This thesis links the areas of distribution system reliability and performancebased regulation. First, the key incentive features within PBR, that includes the quality of supply, are identified using qualitative measures that involve analyses of applied regulatory regimes, and general regulatory policies. This results in a qualitative comparison of applied PBR models. Further, the qualitative results are quantified and analysed further using time sequential Monte Carlo simulations (MCS). The MCS enables detailed analysis of regulatory features, parameter settings and financial risk assessments. In addition, the applied PBRframeworks can be quantitatively compared. Finally, some focus have been put on the Swedish regulation and the tool developed for DSO regulation, the Network Performance Assessment Model (NPAM), what obstacles there might be and what consequences it might bring when in affect. / QC 20101221