Sorin Dan Grigorescu

The influence of water trees on permittivity and loss factor of medium voltage cables polyethylene insulation

This paper presents an experimental study regarding the variation of permittivity and loss factor of power cables polyethylene insulation, due to the change of the frequency (f<inf>a</inf>) and the duration (τ) of the applied electrical field. The experiments were performed on XLPE flat disc samples from a medium voltage cable insulation. The samples were aged in an electric field of E = 4 kV/mm and f<inf>a</inf> = 3–5 kHz in the presence of a NaCl solution (0.1 mole/l) for a period τ = 24–96 hours. After ageing, water trees density and dimensions (lengths and diameters), the real and imaginary parts of the permittivity and loss factor were measured. The results show that the all quantities increase with f<inf>a</inf> and τ and the permittivity and loss factor increase with the decrease of the measurement frequency.

Aspects of metrological calibration of power quality analyzers

This paper presents some aspects of power analyzers utilization, related with your calibration by metrological laboratory. The full metrological characterization of power analyzers is a difficult technical process because the specifications in related standard are minimal. After a short presentation of parameters and measurement methods recommended by the important standards in the field of power quality, CEI EN 50160 and CEI EN 61000-4030, study of uncertainty propagation related to test calibration, this document describes the instruments configuration and evaluation of measurement errors and uncertainties for one parameter, voltage in sinusoidal and non-sinusoidal regime.

Health monitoring solution using dedicated ZigBee sensor network

Health monitoring systems using wireless networks has become a constant concern in various fields, not only of medical plan but also in other domains in which bio-signal data collection from field teams, such as: firefighters, rescue service or emergency medical services, is important, especially in areas lacking communications. Mobile wearable sensors allow now more flexibility in collecting and transmitting these data. This paper presents a health monitoring system designed to work using a ZigBee network, suitable to be used in various fields of applications.

About the Efficiency of Real Time Sequences FFT Computing

Fast Fourier transform (FFT) computing may improved using two ways: the first way consist in packing two separate real functions into the complex input array in such a way that their individual transforms can be separated from the result; the second method used to improve the FFT computation consists in packing the real input of length N array cleverly, without extra zeros, into a complex array having half of its length. In this paper an analysis of a combination of these two methods is performed and also a numerical simulation in order to detect the right conditions in which this method is applicable.

Data acquisition and image processing system for surface inspection

This paper presents the hardware and software structures of a proposed data acquisition and processing system, which is designated to perform an automated inspection of roads pavement condition. The system was designed to gather information from multiple sources - laser-based imaging systems for road profiling, cameras for environmental images, proximity sensors, all information being spatially correlated by means of odometry and geolocation. The system was tested while performing real road inspection, and some results are presented.

Integration of Dispersed Power Generation

Current paper deals with three main issues, regarding the operation of the electric power systems in the presence of distributed generation. The first issue regards the assessment of the main continuity of supply parameters, such as frequency of interruptions, duration of interruption, power not served and energy no served. This issues are the base guidelines for the network system operators’ decision of building new distributed generation capacities which might be able to mitigate the electric network loss of operation. The second issue addressed was the consume variability of the various low-voltage consumers. This particularity, in conjunction with the sheer number of consumers leads to the creation of serious unbalance for the daily curve. This means that if the network system operator cannot contain the load variability, it must buy energy from intraday energy market, with a price decisively higher than the one of the reserved capacity. This issue leads to a two-fold necessity: implementing a better know-how system in order to better contain the customers load fluctuation and the necessity of distributed generation implementation, in order to help load shedding. The third issue regards general technical aspects with respect to the electrical distribution systems operation in the presence of distributed generation.

Multiple sensor software and hardware architecture for field robots

Applications in Field Robotics often require synchronous acquiring various environment information using multiple sensors and devices, including digital cameras. For such applications, this paper proposes a software architecture that is designed to cope with large amount of mixed type data, acquired with various sample times, and gathered from multiple sensors and sensing devices. By allowing the integration of cameras having widely available communication interfaces, such as USB and Ethernet, the presented architecture is intended to allow a cost-effective and flexible robotic system configuration, providing consistent data and loss-less images to be further used in automated data processing. The paper presents the software design, which was implemented in LabVIEW environment, and an illustrative hardware configuration.

Lifetime estimation method of polyethylene power cables insulation subjected to electric field in the presence of water

Lifetime estimation of power cables insulations is a very important issue for development of a preventive maintenance policy of cables in order to avoid their premature breakdown and interruption of power supply to consumers. In this paper a lifetime estimation method of a low density polyethylene insulated cable is presented. For this purpose, accelerated tests on model cable samples immersed in a NaCl solution (having a concentration of 0.1 mole/l) and subjected to a sinusoidal voltage (U = 5 kV and variable frequencies between 1 and 5 kHz) for different ageing times τ (τ = 24...500 h) were performed. The water trees lengths were measured and the variation curves of maximum lengths 1wtm with the ageing time (1wtm (τ)) for three frequencies (1, 2 and 3 kHz) were drawn. Considering three end of life criteria (according to current standards), the lifetime lines were determined and the lifetime corresponding to an electric field of frequency 50 Hz was computed. Finally, it is shown that the tested polyethylene insulation is not recommended to be used for medium voltage underground cables.

Power quality and experimental determinations of the electrical arc furnaces

The three - phase electric arc furnaces represent one of the important generators of harmonic currents, reactive power and unbalanced conditions in the electrical power supply networks. This paper presents a study with experimental results concerning the parameters of quality of electrical energy at three-phase electric arc furnace.

Use of pedagogical agents to build multiple choice equations for an electric workshop based on LabVIEW

e-Learning, with its various aspects, represents a major trend in education. This paper presents a solution to extend the traditional multiple choice tests to effectively graphic design of calculus equations for an electric workshop. Equation built procedure was augmented using animated pedagogical agents to increase the effectiveness of learning and practical skills and improve the attractive aspect of the process. The implemented algorithms and software were tested on two groups of bachelor degree students from Electrical Engineering Faculty, proving useful results and ways to develop further works.