A linearization method for commercial Hall-effect currenttransducers

The need for high-current transducers featuring wide-band and high-insulation levels is becoming a more and more impelling need in the electric power network, as the current distortion increases due to the proliferation of nonlinear, time-variant loads. The closed-loop Hall-effect current transducers show a good compromise between cost and metrological performance. On the other hand, they may introduce an unacceptable nonlinearity error when the dynamic range of the input current is a reduced portion of the dynamic range of the transducer and may show a large drift of their gain with temperature. The paper proposes a simple method for reduction of the nonlinearity error when the input signal is an unbiased sinewave and the automatic calibration of the gain. Experimental results are also reported, showing the method effectiveness     

Small mammals as biological indicators of radioactive contamination of the environment

An investigation was carried out in Sweden aimed at studying the contamination of small mammals (orders Rodentia and Insectivora) following the Chernobyl accident. The animals were captured in three differently contaminated areas in Sweden and, for control, in an area with negligible fallout. The results obtained show that the activity in the captured animals was correlated with surface deposition. The differences between the species investigated and the influence of feeding habits on the contamination levels are discussed.     

Harmonic power flow analysis for the measurement of the electricpower quality

The number and power of loads that pollute, from an electric point of view, the electric network are constantly increasing. Their connection to the electric network causes a significant distortion in the line current and, when their overall power is no longer negligible with respect to the network power, also some distortion in the line voltage, thus deteriorating the electric supply quality. The paper proposes a method, based on the evaluation of the harmonic powers, to identify whether the source producing harmonic distortion in the line currents and voltages of a three-phase system is a polluting load connected after the metering section or is the distortion of the line voltages. Some parameters are also defined in order to quantify the effects of the polluting load on the power quality. A Virtual Instrument is also described, realized to implement the proposed method and to verify it experimentally. The instrument accuracy is discussed     

A digital method for the identification of the source of distortionin electric power systems

The presence of distortion in voltages and currents in the electric power systems causes many inconveniences, ranging from an increment in the line loss to the irradiation of disturbances. The correct identification of the source of distortion is important for attaining an effective compensation of the nonactive components of power. This paper refers to a method, based on the evaluation of the sign of the harmonic active powers, originally designed for identification of the source of harmonic distortion in three-phase systems. An application of this method to the development of a new instrument is described. The instrument accuracy and the results of some experimental work are discussed     

Current decomposition in asymmetrical, unbalanced three-phasesystems under nonsinusoidal conditions

The most attractive theories found in the literature for the representation of the electrical systems under nonsinusoidal conditions can be divided to a great extent into those operating in the time domain and those operating in the frequency domain. When three-phase systems are concerned, the time-domain approach is mainly due to Akagi and Nabae under the name of “instantaneous power theory” or “p-q theory” and is based on the Park transformation. The frequency-domain approach is mainly due to Czarnecki. At a first reading, these two theories seem to be quite different. This paper shows how the application of some interesting properties of the Park transformation leads to a unified approach to the harmonic and sequence components and hence allows derivation of the frequency-domain current decomposition proposed by Czarnecki in a more straightforward way. Moreover, an extension of this decomposition to the case of asymmetrical supply voltages is considered     

A virtual environment for remote testing of complex systems

Complex systems, realized by integration of several components or subsystems, pose specific problems to simulation environments. It is, in fact, desirable to simulate the complex system altogether, and not component by component, since the operation of the single part depends on the surrounding system and an early verification can prevent damages and save time for modifications. The availability of detailed and validated models of the single parts is therefore critical. This task may be difficult to achieve. In fact, in industrial applications, where a system can be a mix of different devices produced by different manufacturers, the physical device may not be accessible to the modeler for proprietary or safety concerns. Starting from this point, the idea of creating a virtual environment able to test the real single component remotely, employing simulators with remote signal processing capability, has been considered. A methodology for remote model validation is presented. The effectiveness of the approach is experimentally verified locally and remotely. For the remote testing, in particular, the physical device under test is located at the Politecnico di Milano, Italy, and the Virtual Test Bed model is located at the University of South Carolina.     

Measuring equipment for the electric quantities at the terminals ofan inverter-fed induction motor

The electric quantities at the terminals of an inverter-fed induction motor are difficult to measure because of the large distortion on both the voltage and current signals. Special care must be taken in evaluating the rms values and power. A measuring device is proposed for the measurement of voltage and current rms values, their frequency, their frequency-domain components and the active power consumed by the motor. The measuring instrument is based on digital signal-processing techniques and is organized as a Virtual Instrument. The results of some experimental work done on a 3 kW induction motor supplied by a six-step inverter are reported     

A method and related digital instrument for the measurement of theelectric power quality

The ever increasing number and power of polluting loads (nonlinear, time-variant loads) connected to the electric power network causes a significant distortion in the line current and, as their overall power is no longer negligible with respect to the network power, also some distortion in the line voltage. This causes a deterioration of the electric power quality that may disturb the other connected loads. The availability of an instrument able to quantify the deterioration of the power quality due to the harmonic distortion, to assess whether or not this deterioration is caused by a polluting load connected after the metering section and to quantify the effects of such a load on the power quality therefore represents an important point for the correct operation of the electric power system. This paper proposes a measurement method, based on the evaluation of the harmonic powers, for the identification of the source producing pollution in a three-phase power system. Some parameters are also defined in order to quantify the electric power quality and the deteriorating effects of a polluting load. A digital instrument is also described, realized by means of virtual instrument techniques to implement the proposed method and to verify it experimentally. The measurement accuracy is discussed     

Clinical, ultrasonographic and tomographic features on the natural evolution of primary mesenteric fibromatosis: a case report

Primary mesenteric fibromatosis is a rare, histologically benign, pathology which is characterized by fibrous proliferation in the mesentery and made more serious by biological malignancy as it has a high inclination towards involving the visceral abdominal structures in its growth. While the cases reported in the literature describe the attempts to cure and reduce the tumor growth, this report describes the clinical, ultrasonographic and tomographic features during the natural growth rate of a case of inoperable primary mesenteric fibromatosis during a 20 month follow-up.