1,720,963 research outputs found
Scheduling Automated Guided Vehicles: Challenges and Opportunities
No full textAutomated Guided Vehicles (AGVs) play a fundamental role in different logistic systems, being widely used for the automatic handling of materials, goods, and containers. The management of AGVs requires the solution of several optimization problems, such as task allocation/scheduling, routing, and path planning, which are often enriched by additional attributes, such as multi-load, battery constraints, and conflict avoidance. Many of these problems are faced in the real-world context of the Italian company E80 Group, one of the world leaders in the production of AGV systems. The literature is huge for all the aforementioned problems, and hence we focus only on the problem of scheduling AGVs, modeled as a Pickup and Delivery Problem (PDP). In particular, we propose a PDP formulation, discuss real-world and literature scheduling applications, and indicate challenges and research opportunities providing a guide for future researches
A review on the comparison of conventional and corona resistant nanofilled enamels
No full textThe low voltage rotating electrical machines, typically based on Type I random/wound windings, are normally controlled by power electronic drives. The power supply voltage waveforms are characterized by fast rise and fall time fronts and in case of resonance and reflection phenomena, overvoltage could appear at the connection terminals of the machine. These overvoltages can incept the partial discharges in the electrical insulation, leading to the total breakdown of the machine. The nanocomposite material used as enamel on the winding wires can lead to increase the performances of the insulating system. In recent years, new class of corona resistant materials based upon nano particles have been characterized. In this work, an overview of the research studies performed by the CMTEST laboratory staff of the University of Genova is presented to summarize the results obtained comparing the behavior of conventional and nano-filled enamels
Transient Earth Voltage Sensor Measurements as a Nonintrusive Tool for Partial Discharge Analysis in Switchgears
No full textEffects of a DC Offset on Lifetime and PD Activity during AC Aging Tests on Enameled Twisted Pairs
No full textEffect of Thermal Stress over the Partial Discharge Inception Voltage on Twisted Pairs
No full textPartial discharges are one of the main causes for what concerns the degradation of the electrical machines insulation system and their onset can bring the devices in question to their end of life precociously. In addition, although an electric machine does not show partial discharges when it is put into service, it is possible that this phenomenon develops over time due to the aging of the insulating material caused by the electrical stress to which it is subjected. However, depending on the application in which these machines are used, electrical aging may not be the only cause that leads to partial discharges. Some electrical machines with type I insulating system may in fact be used in more prohibitive applications that involve high temperatures, therefore in such cases a possible cause of the onset of partial discharges may be the thermal ageing. In this study, twisted pairs with thermal class W-240 °C composed of copper wires covered with a polyimide-based enamel were analyzed. Thermal ageing tests were carried out on several specimens at different temperatures in order to measure the trend of their Partial Discharge Inception Voltage (PDIV) over time. To prevent electrical ageing phenomena from modifying and influencing the results, the repeated PDIV measurements were made in a very short time. In the here considered case, the study demonstrated that at both test temperatures the specimens showed a rapid decrease in the PDIV values in the first 65 hours while subsequently there was a flatter trend. From the reported graphs it is clear how a higher temperature can lead to a more marked decrease of the PDIV values
Comparison of PD Patterns Obtained by Conventional Conducted Signals Measurement and TEV Sensor during Electrical Ageing Tests
No full textThe conventional Partial Discharges (PDs) measurement systems, IEC60270 compliant, normally use a quadripole as coupling device to convert the current pulses to output voltage signals when the system bandwidth is in the frequency range from 40 kHz to 1 MHz. This kind of measurement usually needs an off-line measure and an invasive procedure to connect the objects under test to the measurement system. Other measurement systems based on non-invasive sensors like High Frequency Current Transformer (HFCT) and Transient Earth Voltage (TEV) could be used if the provided results give comparable response. Focusing on TEV sensors, they can be coupled to measurement systems having a frequency bandwidth out of the range defined in IEC60270 standard. The comparison among TEV measurement system and those IEC60270 compliant can be based on the derived and statistical quantities computed starting from the PD pattern. PD Patterns have been collected during electrical ageing test applied to twisted pair located in an air insulated medium voltage switchgear (AIMVS)
Corona resistant insulating systems characterization for low voltage rotating machine
No full textThe type I insulating system for low voltage electric machines is characterized by organic enamel as primary insulation material and impregnating resin as secondary insulating materials. It is known that these machines are supplied by a PWM inverter and if there is a relative long distance between the machine and the power electronics, the resonance and the reflection phenomena could cause overvoltage in the power supply voltage. This overvoltage could incept partial discharge (PD) activity in the insulating systems. This kind of insulating system can't resist under PD activity and the machines quickly reach total breakdown conditions.In an insulating system composed by enamel and resin, it takes great importance the chemical compatibility between them and the adopted impregnation techniques. In this study, two kind of impregnating resin applied on twisted pairs with a conventional enamel, have been analyzed to compare the different behavior. Ageing tests have been performed until the specimen total breakdown, and the PD activity has been monitored. Analyzing the derived quantities of the PD activity, a predictive lifetime model has been obtained
DC component effect on Electrical Ageing tests
No full textThe Partial Discharge phenomenon represents one of the major causes of the deterioration and ageing of the insulating systems of electric machines and, consequently, leads to a considerable shortening of their lifetime. Although the theory and practice focus more on partial discharges caused by a sinusoidal power supply, this study aims to analyze the possible consequences due to the presence of a DC component. This objective in fact has been taken into consideration due to the numerous and continuously increasing use of power electronics in the electrical systems: this can introduce a DC offset into the power supplies. A circuit capable of combining a high voltage AC supply with a high voltage DC one has been therefore designed and realized. Several specimens based on twisted pair wires have been subjected to the resulting voltage. During the degradation process the Partial Discharges activity has been monitored. The obtained results suggest that, in the here considered case, the presence of a DC component does not significantly affect the specimen lifetime and the activity of Partial Discharges
Online Predictive Maintenance Monitoring Adopting Convolutional Neural Networks
No full textThermal, electrical and mechanical stresses age the electrical insulation systems of high voltage (HV) apparatuses until the breakdown. The monitoring of the partial discharges (PDs) effectively assesses the insulation condition. PDs are both the symptoms and the causes of insulation aging and—in the long term—can lead to a breakdown, with a burdensome economic loss. This paper proposes the convolutional neural networks (CNNs) to investigate and analyze the aging process of enameled wires, thus predicting the life status of the insulation systems. The CNNs training does not require any kind of assumption of how the factors (e.g., voltage, frequency and temperature) contribute to the life model. The experiments confirm that the proposal obtains better estimations of the life status of twisted pair specimens concerning existing solutions, which are based on strong hypotheses about the life model dependency on the factors
Preliminary Investigations of the Electrical Tree Growth at Frequencies of 50 Hz and 2.2 kHz by means of Partial Discharge Analysis
No full textDuring fault situations within high voltage direct current (HVDC) links, transient overvoltages with frequency components of several kHz, can occur and incept electrical trees inside the cable insulation. Since the relationship between applied voltage and frequency and the growth of the electrical trees is not completely understood, a deeper investigation is necessary. In particular, starting from cross-linked polyethylene (XLPE) samples obtained from a commercial HVDC cable, electrical treeing tests have been performed by applying a voltage level with two different frequencies: 50 Hz and 2.2 kHz. During the tests, the partial discharge (PD) activity has been monitored. The obtained results show that the time to breakdown obtained from the samples subjected to the 50 Hz power supply is shorter than those obtained with 2.2 kHz. Analyzing the PD activity and the sample by means of digital microscope, different tree shapes were visible, which influence the degradation time of the performed test. The obtained results of this preliminary study suggest that increasing the frequency does not necessarily lead to a reduction of the time to breakdown but influences the shape and the growth of the electrical trees
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