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A methodological contribution is presented in the framework of safety and security studies, where it is of paramount importance to be able to statistically characterize very rare and uncertain events. For this purpose, the paper illustrates a Bayesian methodology for the estimation of a stochastic process characterizing the maximum value of a succession of random variables (RV), representing the successive values of a disturbance in time. This stochastic process, already proposed and applied in power systems by the authors, is a powerful mathematical tool very adequate for describing a safety index (SI) for any engineering system, as discussed in the paper, also with some references to electrical applications. The paper is focused upon a Bayesian estimation (BE) technique, applied for the first time at the best of authorspsila knowledge, in which a new probability density function (pdf) -the so-called ldquoNegative Exponential Betardquo pdf - is adopted for converting prior information about rare events probabilities into accident rate information. Such BE is both efficient and easy to implement, as shown also by means of numerical simulations. In particular, the superiority of the BE with respect to the ldquoclassicalrdquo Maximum Likelihood (ML) estimation methods, traditionally adopted in power system applications, is illustrated in terms of ldquorelative efficiencypsila. The ML estimates are outperformed by the BE, especially when few experimental data are available, as typically occurs when dealing with rare events affecting safety.

In this paper a control strategy for an induction generator based stand-alone power system is examined. The tested system consists of a prime motor, an induction generator, a Voltage Source Inverter STATCOM and a variable load. The paper focus on dynamics performance and stability margin of the system under alternative control strategies. The regulation strategy is based on the control of dc and ac voltage profiles in order to contain the ac voltage droop on load. The control acts on prime mover torque and delay angle between inverter and induction generator voltages. The results of numerical simulation evidence the feasibility of control strategy.

In the paper an optimal procedure is proposed in order to face with power upgrading of transmission line of a double circuit line. The methodology is quite general, allowing to take properly into account all the technical constraints which have to be satisfied for a line acceptable behaviour. This procedure is based upon an optimal power flow which maximizes the power line capability, ensuring that the original line structure is not altered. The results of the optimal power flow could be of great interest being a powerful mean for the designers aligned with the recent tendency towards the exploitation of the existing structures, avoiding the construction of new transmission lines. In the last part of the paper relevant numerical applications are reported in order to demonstrate the feasibility of the proposed approach.