Lightning overvoltages are one of the most dangerous factors affecting the power quality of a distribution grid. In medium voltage (MV) overhead distribution systems, lightning transients can be caused by either direct or indirect strikes. Indirect strikes are much more frequent than direct strikes and can cause flashovers, especially when the line insulation level is low. The most widely employed protection measures against lightning overvoltages are the use of the shield wires, and/or surge arresters, and increasing the line insulation level. In particular, many studies have shown a significant reduction in the induced voltage magnitudes, thanks to the use of the shield wires in both transmission and distribution systems. This paper deals with the possibility of adopting the shield wires to mitigate lightning induced overvoltages in MV networks, and proposes an analysis on the main parameters that influence their performances. This aim is pursued by means of a probabilistic and statistical analysis based on the response surface method (RSM), which permits to obtain the equation of the surface that best approximates a given model. The application and efficiency of the proposed RSM-based approach have been illustrated by applying it to a realistic situation of a rural distribution line.

Microgrids (MGs) may represent a solution in the near future to many problems in the energy and electric world scenarios; such as pollution, high reliability, efficiency and so on. In particular, MGs’ capability to work in an islanded configuration represents one of their most interesting features in terms of the improvement of the reliability of the system, the integration of renewable energy sources and the exploitation of the quick response and flexibility of power electronic devices in a stand-alone system. In order to study and validate innovative solutions and control strategies for islanded operation, there is a need to develop models for MG structures that can be reliable and sufficiently simple to be used for the purpose of the design and validation of innovative control systems. This paper proposes a simplified, first harmonic model for a generic structure of MG characterized by its use of only electronic power converter interfaced generation. The main advantages of the proposed method lie in the model’s simplicity and its reduced solving time, thanks to the limited number of necessary parameters to describe the system. Moreover, the developed formulation allows the avoidance of specific (and often licensed) software to simulate the system. The performances of the proposed model have been validated by means of a comparative analysis of the results obtained against a more accurate representation of the system performed in the power system CAD—electromagnetic transient and DC (PSCAD—EMTDC) environment, which allows for the representation of each component with a very high level of detail. Such comparison has been performed using the University of Genoa Savona Campus Smart Polygeneration Microgrid testbed facility, due to the availability of all the necessary numerical values.

The paper proposes a simple but effective model for no-inertia microgrids suitable to represent the instantaneous values of its meaningful electric variables, becoming a useful platform to test innovative control logics and energy management systems. The proposed model is validated against a more detailed microgrid representation implemented in the electromagnetic simulator PSCAD-EMTDC and then against experimental data collected on the University of Genoa test bed facility. Recorded data highlight a good tradeoff in matching the results of the proposed model, confirming its suitability to be used for the preliminary testing of new control logics for islanded microgrids.

Lightning-induced voltages are one of the main causes of shutdown in distribution lines. In this work, attention is focused on the effects of wideband modeling of electric grounding in the overvoltage calculation along insulator strings due to indirect lightning strikes. This study is done directly in the time-domain with the grounding being represented with an equivalent circuit accounting for its dynamics. Results show that the adoption of commonly adopted simplified grounding models, such as low-frequency resistance, may lead to an underestimation of the overvoltage. According to the results, differences in the order of 25% can be found in some studied cases.

This article proposes a method for the derivation of a formula that links the maximum lightning-induced-overvoltage occurring on an overhead distribution line with the variables that characterize the lightning return stroke, such as the peak current, front duration, and stroke location. The coefficients of such formulas are obtained thanks to a limited number of lightning field-to-line coupling simulations, thus guaranteeing a significant computational time saving with respect to already existing methods. The method is presented first with a preliminary analysis to get some insight into the functional relationship between each of such variables and the overvoltage. Then, the method is presented and validated against numerical calculations performed with a dedicated code, both in terms of punctual evaluations and overvoltage distribution.