Distribution networks are facing significant technical constraints that must be resolved at minimum cost: regulatory and customer pressures to improve reliability of supply, reduction of losses and the technical challenges related to the connection of an increasing amount of distributed generation. The use of new approaches is therefore being encouraged to develop cost-effective solutions often leading to the concept of Active Management. However, the lack of monitoring in present distribution networks is a barrier to the implementation of the corresponding automation functions. On the other hand a full monitoring of the distribution network is not economically realistic. Therefore, there is a need for intermediate solutions such as the one presented in this paper: EDF R&D has developed a distribution state estimator (DSE) based on voltage state variables. Such algorithm is expected to provide quasi-real time system supervision of voltages and power flows which are required as inputs of Distribution Management System (DMS) functions. Even if based on techniques applied to transmission networks, the requirements and performances of DSE are different and adapted to distribution needs. The paper discusses the limits of such approach and proposes thumbed rules for sensors placement as well as research perspectives to overcome these limits.

Under-frequency load shedding (UFLS) schemes are designed by specifying a given amount of load to shed at various frequency thresholds to prevent the collapse of the electrical power system in the event of a large generation-load imbalance. An UFLS step is constituted of a group of medium-voltage feeders that trip when a given frequency threshold is reached. This study focuses on the method to be used when allocating a given feeder to a given step. First, the authors introduce performance metrics to quantify the accuracy level with which the UFLS target is met. Second, they model: the allocation method currently used in France; a variant of that method; and a new method introduced in this study, based on an automated clustering technique. Third, based on real consumption patterns measured from a vast area in France, and using the introduced performance metrics, they compare the efficiency of the three described methods. This study is conducted for the current state of loading of the considered distribution network and for a hypothetical situation with an increased share of distribution-side photovoltaic generation. For the chosen performance metrics, they demonstrate that the first two methods provide similar results while the clustering-based method performs remarkably better.

Our work focuses on the European Network Code on Emergency and Restoration (NC-ER) which introduced an harmonization requirement of Under-frequency Load Shedding (UFLS) schemes. This new requirement implies that in the medium term, the UFLS scheme of all European countries will have to evolve. It stipulates an acceptable range for the main factors that define an UFLS scheme, namely: the number of load shedding steps, the percentage of load shed in each step, and the accuracy of the frequency measurement that is implemented in the protection relays. In this context, the contribution of this paper is twofold: first, we define a new performance criterion for UFLS schemes; and second, we apply this criterion to two opposite archetypal schemes, in order to highlight the pros and cons of both approaches.

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