This paper discusses the power systems stability margin improvement by means of preventive control based on generation re-dispatch using a neural sensitivity model. This model uses multilayer perceptron networks with memory structure in the input layer. The training of this model is made with temporal data samples from time domain simulations, incorporating information about the dynamic behavior of the system, unlike the methods proposed in the literature in which the pre-fault system data are used instead. The sensitivity is used as a guideline in selecting the most effective set of generators in the reallocation of the amount of active power capable of increasing system security. The effectiveness of the proposed methodology has been demonstrated through the application to a large system.

Nowadays, the analysis of the lightning performance of high-voltage (HV) underground sections has become increasingly important, thanks to their increasing usage with overhead transmission lines. In this way, the objective of this paper is to investigate the sensitivity of the overvoltages, at the terminal of underground cables (UCs), due to the incidence of negative lightning flashes at the shield wire or the tower top. It is done by means of different representations of the grounding behavior, different points of lightning incidence, different values of soil resistivity, and considering or not the variation of the soil electrical parameters with frequency. It is observed that a reliable investigation on lightning overvoltages is important and it must consider a suitable representation of the grounding behavior. An improper modeling can lead to nonrepresentative results. In this way, it is highlighted how the frequency dependence of the soil parameters influences the results in many different situations. For long distances from the UCs and low soil resistivity regions, all the grounding models produce similar results. On the other hand, for regions with high soil resistivities, the use of a proper model for the tower grounding is important, since the discrepancies between the results produced considering or not the dependence of the soil parameters with frequency become substantial. The inclusion of the grounding behavior with frequency allows to obtain reliable simulations of the transient behavior of the insulated cables, which constitute the underground section under study.

This study proposes the expressions for return impedances and admittances for the transient modelling of subsea cables buried below the seabed. Unlike buried cables or overhead lines where only one of the external media shows losses, for a subsea cable buried in the seabed both media are lossy. The expressions are derived from quasi‐transverse electromagnetic (quasi‐TEM) approximation of a full‐wave modelling. A comparison of a full‐wave‐based results and the ones using a quasi‐TEM approximation indicates wideband validity of the proposed expressions. Two test cases are considered: a single‐core armoured cable and a three‐core (i.e. pipe‐type) configuration. An evaluation of the characteristic admittance and the propagation function in the frequency domain is carried out to assess the impact of the change in the external media when compared with a cable floating in the sea. A transient model for the subsea cable is derived in frequency domain and time‐responses are obtained using the numerical Laplace transform. The results indicated some differences in the transient waveform obtained when compared with the responses for a cable floating in the sea.

This paper proposes to represent the frequency dependence of soil parameters via a rational approximation in the frequency domain. Two types of causal soil models were considered, namely, Smith–Longmire and Alipio–Visacro (AV). Results indicated that for both soil models, the analyzed parameters maintain a fixed ratio between the poles and residues, and for the AV soil model, there is a unique set of poles, representing a “universal” set of relaxation frequencies. Thus, without resorting to an additional fitting process, one can find a suitable rational approximation of a frequency-dependent soil for an arbitrary conductivity, which is very useful for its inclusion in computational codes in time or frequency domains.