M. Pozzi

Hosting Dispersed Generation on Italian MV networks: Towards smart grids

This paper describes the possible evolution of Italian distribution system in facing the growing penetration of Dispersed Generation (DG), in the perspective of smart grids. As for the Italian system, after discussing the Hosting Capacity of MV distribution networks, it is recognized that some challenges are to be faced due to the increasing amount of DG. Even though current technology provides satisfactory solutions to manage this new situation, loss-of-mains protection (LOM) is one of the most critical issues to be faced, at least for the Italian system. Only an intelligent use of Information and Communication Technology (ICT) will overcome the current limitations and make possible a larger DG penetration without hindering system security. Milano Wi-Power is a project undertaken by Politecnico di Milano dealing with the critical aspects of the communication systems applied to distribution networks. The specific goal is to test and validate, both through simulations and field trials, possible communication systems able to connect primary substations with DG units along the network.

Possibility of enhancing classical weighted least squares State Estimation with linear PMU measurements

The introduction of phasor measurement unit (PMU) technology is generally expected to significantly improve existing state estimation (SE) algorithms regarding accuracy, observability, convergence. Since PMUs measure current and voltage phasors, in case of complete observability of all the network with PMUs, the PMU based SE will be linear, and consequently the SE algorithm faster and more accurate. Indeed, the complete observability of the network just with PMUs is, for many transmission system operators (TSOs), quite far to be reached; therefore, it becomes necessary to find suitable strategies in order to use all data by PMUs, in the best way in the classical SE. This paper deals with the possibility of using PMUs information in the classical real time least squares SE, with particular attention to the Italian case. Simulations on the complete 380/220 kV Italian transmission system are reported, in order to show the obtained benefits.

ORPF procedures for voltage security in a market framework

The paper deals with the automatic procedures used for the definition of voltage profiles to be adopted in the operation of bulk power systems with the aim of optimizing both the economic and security issues. After reviewing the most important automatic algorithms for optimal reactive power flow (ORPF) existing in the technical literature, some new ORPF procedures are proposed. They are based on modern optimization techniques and on a new formulation of the objective function tailored for the operation of power systems in a deregulated framework. The final aim of the paper is to demonstrate the effectiveness of ORPF procedures for the critical evaluation of the working point of power systems obtained from the day-ahead market auction. Furthermore, the tests reported show that, even at the day-ahead stage of energy market, it is possible to define the optimal voltage set points for generating units to be adopted for hierarchical voltage control in real time operation.

Reactive power management in the Italian system: a proposal for an economic compensation

The deregulation of the electric systems requires the definition of market procedures for the effective management of reactive resources. However, the amount of payments for participating to the voltage regulation service is a task characterized by conflicting objectives, from both the technical and the economic viewpoints. The main subjects related with the reactive power management are: maintaining an adequate security level, defining correct economic signals, providing a simple and transparent structure, ensuring market equity, and avoiding additional charges on the final energy price. After a brief review of the hierarchical voltage regulation structure developed in the Italian power system, a practicable scheme, coherent with the above mentioned requirements, is proposed: the final aim is to assign a correct economic value to the reactive resources

Application of the load flow and random flow models for the analysis of power transmission networks

Abstract In this paper, the classical load flow model and the random flow model are considered for analyzing the performance of power transmission networks. The analysis concerns both the system performance and the importance of the different system elements; this latter is computed by power flow and random walk betweenness centrality measures. A network system from the literature is analyzed, representing a simple electrical power transmission network. The results obtained highlight the differences between the LF “global approach” to flow dispatch and the RF local approach of randomized node-to-node load transfer. Furthermore, computationally the LF model is less consuming than the RF model but problems of convergence may arise in the LF calculation.

Coordination of the hierarchical voltage control with the reactive power economic compensation

Voltage control and reactive power management are usually studied and applied mainly by the technical point of view. System operators and planners have developed complex control schemes, in order to achieve a secure and efficient operation. However, the deregulation of the electric systems requires the definition of market procedures ensuring an effective management of reactive resources on which the voltage regulation relies. If the economic issues related to the transmission network (and to the system control) have to be managed separately from the generation, the definition of payments for participating to the voltage regulation becomes a difficult task, bound by conflicting objectives, from both the technical and the economic viewpoints. Such objectives are: maintaining an adequate security level, defining correct economic signals for power plants equipment, providing a simple and transparent structure, ensuring market equity, and, last but not least, avoiding burdening on the final energy price. Whereas in a vertically integrated utility it should be sufficient to analyse the global behaviour of the system (transmission plus generation), within a competitive framework it is crucial to determine and meter the performance of each generator. After a brief review of the main procedures of reactive pricing available in literature, a simple scheme, aimed at enhancing the reactive resources management in the Italian market, is proposed, based on the economic quantification of the actual charges related to the voltage regulation.

Optimal Power Flow procedure for real-time security and economic re-dispatching in a market structure

This paper investigates the possibility of utilizing Optimal Active Power Flow (OAPF) and Optimal Reactive Power Flow (ORPF) algorithms for on-line safety and economic re-dispatching in an Ancillary Services Market (MSD) structure. It is described a procedure that the Italian Transmission System Operator (TERNA) has implemented recently for real-time operation. Starting from a real-time snapshot, the procedure ranks all the possible contingencies and re-dispatches the active (through OAPF) and reactive (through ORPF) power productions in order to prevent the effects of the most dangerous ones. The re-dispatching is achieved by minimizing the economic effort, according to the offer/bids on the MSD. The fulfilled constraints are: nodal balance, maximum flow limit for the transmission lines (under N and N-1 security conditions), nodal voltage limits, minimum and maximum power offered in the MSD, gradient limitations. Examples are provided about the application of the procedure to the Italian main transmission system (1700 buses).

A tool to investigate the PV and storage plants effective integration in the European interconnected transmission network

The assessment of RES integration in the transmission network operation is of great concern for TSOs. In the paper, “ad hoc” dynamic models of the European grid with RES and storage systems have been developed and validated through security enhancements analyses on battery storage applied to both real and forecasted scenarios of renewable penetration. In particular, a detailed network of the ENTSO-E system has been adopted for carrying out the dynamic analyses and achieving reliable results. Finally, comparisons have been made in terms of frequency deviations distribution for different ranges of PV generation variability and different levels of installed storage rated power. The study results suggest that the testing-suite is appropriate not only for the validation of the new models but also for the evaluation of control strategies to mitigate the influence of RES intermittent behavior in the transmission network.