Fabio Fiamingo

Models of Wind-Turbine Main Shaft Bearings for the Development of Specific Lightning Protection Systems

One of the main cause of damages for wind turbine power plants is certainly constituted by lightning. Direct and indirect events can indeed produce damages and malfunctions of electrical and mechanical components. Concerning mechanical components, blades and bearings are the most involved parts. In particular, lightning-damages produced at bearings positioned at the mechanical interface between rotating parts of the wind turbine, can result in high costs, considering the difficulties involved in the replacement of such components. The paper presents a numerical and an analytical model of wind turbine main shaft bearings aimed at calculate their electrical impedance along with their experimental validation. These models provide useful criteria for the design of wind turbines lightning protection systems (LPS). In this respect, the paper presents also the development of a specific LPS for the protection of wind turbine bearings and the relevant effectiveness analysis obtained by means of experimental tests.

Models of Wind-Turbine Main-Shaft Bearings for the Development of Specific Lightning Protection Systems

One of the main causes of damages for wind-turbine power plants is lightning. Direct and indirect events, indeed, can produce damages and malfunctions of electrical and mechanical components. Concerning mechanical components, blades and bearings are the most involved parts. In particular, lightning damages to main-shaft bearings can result in high costs of maintenance, due to the inherent burden in the replacement of these components. The paper focuses on the modeling of wind-turbine main-shaft bearings. Two models are presented and experimentally validated: one numerical and one analytical, both conceived in a way to make the calculation of the bearing electrical impedance possible. The paper shows how these models are helpful for the design of wind-turbines lightning protection systems (LPSs). In this respect, it illustrates the criteria for the design of such an LPS and assesses the validity of design solutions by means of experimental tests.

Factors influencing the selection and installation of surge protective devices for low voltage systems

The present paper aims to illustrate the influence of the main factors which affect the selection and installation of an SPD for the protection of electrical and electronic systems against overcurrent and overvoltage due to direct lightning flash to a structure. The two most typical SPDs are considered, namely switching and limiting type. Simple rules are established for the selection of effective SPD with regard to the discharge current, its protection level and location.

Surge protective devices for low voltage systems: practical approach for the protection distance evaluation

The evaluation of the protection distance of an SPD is a main step for assessment of effective reduction of the failure probability of an electrical and electronic system within a structure. The evaluation of this distance is performed taking into account the traveling and induction phenomena in the circuit formed by SPD and apparatus to be protected. By means of computer simulation the conditions for which the phenomena could cause hazardous situation for the internal systems are investigated. As a result, simple relations and diagrams are given in order to help in the estimation of the proper SPD protection distance.

Risk assessment of photovoltaic installations, due to lightning, according to IEC 62305 - 2nd Edition

Photovoltaic power generating system (PVPGS) can be affected by direct and nearby flashes. In case of direct lightning, physical damage and failure of some apparatus can happen. Also the nearby lightning, by electromagnetic pulse (LEMP), can cause damages. An insufficient protection from lightning damages can increase the time of the return of investment (ROI) of the PV power generating system. The risk assessment is performed by taking into account the 2nd edition of IEC 62305-2, and the results are compared with those obtained by using the 1st edition.

On critical distance between an spd and protected appliance with respect to their voltage coordination

The paper deals with the assessment of the critical length between SPD and the equipment to be protected with the aim of proper coordination of the SPD protection level and the impulse withstand voltage of the equipment. Main concern has been paid to influence of different steepness of the front of lightning current and the SPD earthing conditions. In order to assess the relation between considered distance and voltage increase on the terminals of the device to be protected the P-Spice simulation has been applied.

Sensitivity Analysis of the Circuit Model of a Medical Equipment for the Evaluation of Leakage Currents

In an operating theatre the most hazardous events related to the circulation of low leakage currents (currents of the order of decades of microamperes that are not functional) through the human body during a surgical procedure (micro-shock), should be identified. The electrical circuit model of a surgical layout could be an important tool for the micro-shock risk analysis. The international standards on safety of Electrical Medical Equipment (EME) require the measurement of leakage currents in order to evaluate their compliance with limit values. Modeling of leakage current measurements set-up of each EME involved in a surgical procedure is a fundamental step to obtain the circuit model of a surgical layout. The case of a commercial defibrillator is taken as example to show how the circuit model is built. The model parameters assigned and the currents simulated are characteristic input and output data of the single test performed. In the present work, an evaluation of the model output of a commercial defibrillator due to the uncertainty in the estimation of model input is presented in order to verify the robustness of the circuit model. This evaluation has been performed by the adaptive Monte Carlo method. The results are encouraging for the application of the circuit in a modeling of a surgical intervention.

Safety System With Harmless First Fault: Complete and IT-M System

In electrical power systems, such as data centers and hospitals, where service continuity is essential, the electrical operation needs a skilled organization and a team available at all times (24/7) to have a fast emergency response. The hospital management considers doctors, surgeons, administrators, medical devices rightly at the forefront, but electrical and technological systems and the team of technicians wrongly as ancillaries. This paper emphasizes the importance of the business continuity management for service continuity and highlights how medical IT-systems have not to carry out power outage for fault due to overcurrents and overvoltages. When a fault occurs, the protection system could include a countdown time so that emergency response team must solve the problem before the system collapses.

Modeling Medical Electrical Equipment for Estimation of Leakage Currents during a Surgical Procedure

During a surgical procedure leakage currents can flow through the heart of the patient. The values of such currents can be estimated by an electrical circuit model. More specifically, three medical electrical equipment in an operating theatre, in contact with the patient and fed by an isolated power supply, are considered and are simulated. Two of them are always involved in a surgical procedure: an operating table and a patient monitor, the third one is a defibrillator which can be put into operation during emergencies. The comparison between the leakage currents simulated by the circuit and the ones measured are presented. The agreement is quite satisfactory. An estimation of the model sensitivity due to the uncertainty in the knowledge of the model parameters has been performed too, by using the Monte Carlo method. The proposed model is applied to study critical scenarios in which leakage currents flowing into the patient’s chest in normal, single and double fault conditions could be dangerous and could introduce a risk of microshock not tolerable.

Smart building and lightning risk assessment: an approach to the protection of building automation systems high exposed to overvoltage failure

The paper deals with development of the probabilistic approach to the assessment of risk due to lightning flashes striking smart buildings. Overvoltages resulting from flashes direct or near the building and the incoming lines are considered as well as the effect of direct coupling of the lightning electromagnetic field (LEMP) on equipment and devices of building automation systems. Special attention is devoted to the probability of systems failure and on the way to evaluate the influence of different protection measures in reducing such probability. The most critical points of the system and the optimal selection, installation and coordination of protection means are discussed in order to reduce the risk to a tolerable level.