Paola Rinaldi

FMECA technique on photovoltaic module

The solar photovoltaic industry has seen rapid expansion in the past decade with an ever-increasing share of the electricity-generating capacity for the world. For the emerging photovoltaic (PV) industry the assessment of the quality and reliability of its products is becoming more and more important. To this aim and to ensure an optimal design and material choice, a failure modes, effects and criticality analysis methodology (FMECA) to classify the occurrence, the severity and the impact of all possible failure mechanisms on the PV system has been introduced. This helps to eliminate or reduce the impact of potential failure modes before the completion of the design and before failures occur in the field. By means of this analysis it can be noticed that a crucial aspect in PV systems is the cleaning status of the panel surface. In this paper this problem has been analyzed by means of an experimental activity. Finally a method for the assessment of the PV panel condition has been proposed.

The kneeling view: evaluation of the forces involved and side-to-side difference.

The kneeling view is a method to objectively measure posterior knee laxity. However, the actual amount of load applied and the reliability of this method in term of side to side difference are not known. We studies these issues in a group a 25 healthy volunteers who underwent measurements of posterior knee laxity in both knees. A standard digital scale was positioned under both kneeling supports to measure the actual amounts of posterior displacement forces applied. We measured the mass of the subject, the side-to-side difference of the weight applied into anterior aspect of the tibia, and the ratio weight of the subject/ amount of posterior displacement load applied. The average amount of forces applied was at least 75% of the body weight of each subject, with a side-to-side variability of 3.3% of the weight applied. The kneeling view can be considered, in terms of forces applied, a reliable and reproducible alternative method for the routine radiographic evaluation of the posterior knee laxity.

Implementation and Characterization of a System for the Evaluation of the Starting Instant of Lightning-Induced Transients

Voltage transients are one of the main causes of power quality (PQ) degradation. There is a search for investigation techniques that are capable of characterizing and classifying them depending on their origin. A distributed measurement system for PQ monitoring can be used in parallel with a lightning location system (LLS) to assess whether a lightning event is responsible for a voltage transient. This involves the accurate estimate of the transients starting instant. In this paper, a system for the measurement of the starting instant of voltage transients is described. It is hosted in each remote unit of a distributed system, which was built in our laboratory, for PQ monitoring. The results of the characterization tests are also reported and discussed. They lead us to conclude that our system for PQ monitoring can be used in parallel with an LLS to assess whether an impulsive voltage transient was induced by lightning.

Reliability Prediction Handbooks: Evaluation of the System Failure Rate

The evaluation of the failure rates for device, components and systems is often a very difficult task. In order to simplify the failure rate evaluation for established electronic and electromechanical devices, it is possible to use ad hoc handbooks. In fact, values for failure rates are given for many devices in the failure rate handbooks. In this chapter an historical overview on these handbooks is given. Many handbooks are available where the laws on dependency of the failure rate on different stresses are considered. In 5.1 a brief introduction about the first generation handbooks is given. In 5.2 the second generation handbooks are presented. A USA military handbooks is presented in the next 5.3, 5.4 and 5.5 are devoted to Farada and third generation handbook respectively. In 5.6 example of failure rate evaluation are discussed. Finally, the units for failure rate, the FIT, is introduced in 5.7.

Reliability Studies and Implementation of Remote Monitoring and Self-Diagnosis on a Smart System for Fast Transients Characterization in Power Networks

The paper presents the results of a study performed on a measurement system for voltage fast transients detection and characterization in medium voltage power networks. Such a system is thought for working in stand-alone mode for a preset number of months and far away. To this the system reliability study (performed by means of the Markov technique) have been carried out along with the implementation onto the system of a remote-monitoring & self-diagnostic procedures for assuring correct operating conditions by means of both preventive or corrective maintenance of the system. In the present paper the architecture of the self-diagnostic & remote-communication system along with the results of the system reliability study will be presented and discussed

Repairable Systems and Availability

In Chapter six the concepts of Availability will be explained and discussed. The Availability is a concept that refers to reparable systems. For such systems the time of operation is not continuous, since their operating life cycles are described by a sequence of up and down states. Therefore the system operates until it fails, then it will be repaired and so it returns to its original functioning state. It will fail again after some random time of operation, get repaired again, and this process of both failure and repair will reiterate; hence the state of the system alternates between a operating state and a repair state. In this case, the important variables to be determined are the times to failure and the times to repair. Availability is defined as “the aptitude of the element to perform its required function in given conditions up to a given point in time or during a given time interval assuming that any eventual external resource is assured.” The availability of a machine can also be defined as the percentage of time, in respect to total time, in which the machine is required to function.

A System for the Measurement of the Temperature Dependence Performances of Quartz Oscillators: a Study of the Analytical Model of the Failure Rate

This paper presents a method of investigation of the temperature dependence of the accuracy performances of quartz oscillators. Temperature effects may vary widely in significance depending on the environment. Quartz can be used as high stability oscillators, having oscillation frequencies ranging from few kHz to 20 MHz. A fundamental qualifying parameter is then represented by the frequency stability of the quartz crystal oscillator. For this reason, in this paper, an automatic system for the measurements of the quartz oscillation frequency as a function of changes in temperature, is presented. The system has been designed and realized in our laboratories. The results of the characterization tests and measurements are also reported and discussed.

A new technique for thermal resistance measurement in power electron devices

A simple technique is proposed for the thermal resistance measurement of electron devices. The new approach is based on the standard measurements which are normally carried out for the electrical characterization of power devices, without requiring special-purpose instrumentation and/or physics-based temperature-dependent electrical device models. Experimental results, which confirm the validity of the new method, are provided.

A system for the measurement of the starting instant of impulsive transients [power systems]

There is a search for investigation techniques capable of characterizing voltage transients, which are one of the main causes of power quality degradation, and classifying them depending on their origin. In a previous paper, the use of a distributed measurement system for power quality monitoring in parallel with a lightning location system was proposed to assess whether a lightning event is responsible for a voltage transient. An accurate estimate of the transients starting instant is required to tackle that task. In this paper, a system for the measurement of the starting instant of impulsive voltage transients is proposed and the procedures for its metrological characterization are described. The results of the characterization tests are also reported and discussed.

The Concept of “Statistical” Reliability

The reliability of an item or a system can be think, as a first approach, as the probability that the device or the system will adequately perform the specified function for a well-defined time interval in specified environmental conditions. Starting from this first definition it is well clear the importance of the probability and statistics science in both reliability definition and evaluation. This chapter is devoted to introduce some important probability and statistics concepts necessary for reliability evaluation. In particular, the statistical point of view is developed and discussed as a first approach to dependability feature of a system or device. A brief overview on probability and statistics concepts is given in the first pages of this chapter. In particular, in 2.2.1 the axioms of probability are given and the law of the large number is discussed in 2.2.2. Random variables are introduced in 2.3 and probability distributions are detailed in 2.4. Finally, the reliability function is derived. Furthermore, it is defined the concept of the failure rate model in section 2.7. In 2.8 the more used distribution laws are discussed.