1,354,603 research outputs found
Valutazione delle riserve idriche nei bacini dei Rii Piscinas e Naracauli (Sardegna meridionale)
No full textI bacini idrografici dei rii Piscinas e Naracauli sono ubicati nella parte sud-occidentale della Sardegna, in un'area che sino a pochi anni addietro fu sede di un intenso sfruttamento minerario
Power quality monitoring in modern electric distribution systems
No full textIn electric power systems, there may be disturbances in the supply voltage and the load current drawn by a user. These disturbances happen when the frequency and amplitude are not equal to their corresponding nominal values, when there are non-sinusoidal waveforms, and when there is the presence of negative and zero-sequence components in three-phase systems. Power quality (PQ) is a generic expression used to characterize the disturbances. This paper offers an overview of the methods and instruments currently used in PQ measurements and some research activity to improve the
On the selection of the "best" test waveform for calibrating electrical instruments under nonsinusoidal conditions
No full textThe paper deals with a test method, based on the generation of signals with known and pre-assigned harmonic content, for calibrating measurement devices to be used under nonsinusoidal conditions. The attention is concentrated on selecting the most suitable waveforms for the characterization of measurement instruments, by considering both the amplitude and the relative phase of the different harmonics. The aim is to identify the situations that cause, more than others do, uncertainty problems while measuring different quantities. This investigation is theoretically performed by means of a number of numerical simulations, in which pre-defined values for each uncertainty source have been added to the voltage and current acquisition channels
A PMU for the Measurement of Synchronized Harmonic Phasors in Three-Phase Distribution Networks
No full textOwing to the extension of electric distribution networks, monitoring and control issues rely on large-scale distributed measurement systems, which are able to carry out simultaneous measurements of electrical quantities in several points of the monitored systems. In this paper, the implementation of digital procedures that are suitable for the evaluation of the synchronized harmonic phasors in a flexible phasor measurement unit (PMU) based on PXI modular hardware is presented. The results of the experimental tests are shown to characterize the measurement system to evaluate the behavior of the designed instrument under real operating conditions on three-phase electric distribution networks
A space vector based approach for synchrophasor measurement
No full textThis paper proposes a simple technique to estimate the positive sequence synchrophasor and the frequency of three-phase voltages or currents in power systems. The approach is based on the space vector transformation using a reference frame which rotates at the rated angular frequency ω0 of the power system. All the frequency components are shifted by ω0, so that the positive sequence phasor appear as a very low frequency term. The frequency shift also decreases the ratio between the frequency of the positive sequence phasor and those of the disturbances, so that they can be rejected by using a simple IIR filter thus requiring low computational effort. Then, the magnitude and phase of the phasor as well as its frequency can be easily estimated through an ordinary least square optimization. A proper tuning of the parameters allows the approach to comply with P-class or M-class requirements of the standard IEEE C37.118.1
A distributed system for the synchronized acquisition of fast voltage transients
No full textVoltage transients are the main causes of complaints for medium-voltage customers, and hence interest is focused on investigation techniques able to help in classifying and localizing such events in accordance with their origin. In this light of fact, a distributed measurement system for performing synchronized acquisition of fast voltage transients is presented in this paper. The system, designed to fulfill specific constraints about the reliability of the provided information, has been used in a one-year long measurement campaign performed in a medium voltage network. The main obtained results are presented
GPS-Based System for the Measurement of Synchronized Harmonic Phasors
No full textA measurement system, based on high-performance Global Positioning System (GPS) receivers and general-purpose acquisition (DAQ) boards, for the evaluation of the synchronized harmonic phasors in the nodes of an electric distribution network, is presented. To meet the requirements of different fields of application, two measurement procedures have been implemented: One is based on a fixed observation window, whereas, in the other one, the observation interval is a function of the actual power system frequency. Experimental tests are presented to characterize the measurement system: The results show that the proposed procedures allow the accuracy that is usually required in power quality monitoring of distribution systems to be reached
Generalized Likelihood Ratio Test for Voltage Dip Detection
No full textAn alternative detection algorithm, based on the generalized likelihood ratio test (GLRT), is proposed for the detection of voltage dips in power systems. The proposed method is compared to the classical approaches based on the voltage root mean square. It is shown that the GLRT may provide competitive performance in terms of capability of correctly detecting the dip starting instant. A DSP-based experimental setup for the implementation of the method is also presented
Performance comparison of advanced techniques for voltage dip detection
No full textSeveral different approaches for the detection of voltage dips in electic power systems have been proposed in the literature to overcome the limits of the procedure proposed by the International Standard, based on the voltage root mean square. In this paper the most promising of these approaches are compared, by computer simulations, in terms of both statistical performance and response time, which is a critical issue for the development of real-time compensation systems
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