Benedito A. Luciano

An amorphous core transformer : design and experimental performance

Abstract The main aspects related to the design and experimental implementation of a 1 kVA, 220 V/110 V, 60 Hz amorphous metal core transformer (prototype) are presented. The core material is the amorphous alloy Fe 78 B 13 Si 9 . This as-cast core was annealed at 380 °C for 1 h in an argon atmosphere, under a DC magnetic field applied along the ribbon length to induce an uniaxial anisotropy. After having been annealed, samples of the core material were examined by differential scanning calorimetry (DSC) and by X-ray diffraction and no crystallization was observed. Experimental tests are presented to compare the amorphous core transformer performance with that of a commercial transformer with the same ratings values, but built with a steel core. In comparative terms, the amorphous core transformer presented lower active losses and lower excitation power than the commercial steel core transformer.

Applications of Thermoresistive Sensors Using the Electric Equivalence Principle

In this paper, a survey on the characteristics of thermoresistive sensors [positive temperature coefficient (PTC) and negative temperature coefficient (NTC)] and their applications to measurement structures that use the electric equivalence principle, in special radiometers and anemometers, is presented. The dynamic responses of the architectures and the influence of the operational amplifier offset voltage on the instrument performance are discussed. Alternative architectures employing pulsewidth modulation (PWM) and sigma-delta analog-to-digital (A/D) converters are also shown.

Fault-tolerant weld line detection for automatic inspection of storage tanks based on distance and visual information fusion

Quality control, cost reduction and above all, human and environmental safety are great reasons that stimulate the investments in technologies like automatic inspection. The automatic inspection of weld lines in storage tanks is of special interest, due to the fact that such tanks are currently used to store harmful products. For a reliable inspection it is necessary to accurate detect the weld line position. In this paper the development of a system to perform weld line detection in storage tanks is proposed. Two redundant systems, based on different physical principles, distance and visual information, are implemented and tested. Such systems make use of a fault-tolerant estimation process based on the α-β filter. Finally, the outputs of the two redundant systems are fused, aiming at to increase the confidence and performance of the system.

Nanocrystalline material in toroidal cores for current transformer: analytical study and computational simulations

Based on electrical and magnetic properties, such as saturation magnetization, initial permeability, and coercivity, in this work are presented some considerations about the possibilities of applications of nanocrystalline alloys in toroidal cores for current transformers. It is discussed how the magnetic characteristics of the core material affect the performance of the current transformer. From the magnetic characterization and the computational simulations, using the finite element method (FEM), it has been verified that, at the typical CT operation value of flux density, the nanocrystalline alloys properties reinforce the hypothesis that the use of these materials in measurement CT cores can reduce the ratio and phase errors and can also improve its accuracy class.

Execution Monitoring Applied to Data Estimation Processes

This paper presents how execution monitoring can be applied to detect sensor measurements faults and shows how to use this information to improve data estimation processes. Experimental results based on ultrasonic sensors measurement data are presented and the estimation process improvement could be verified.

ZnO Surge Arresters Diagnosis Using Microcontroller

Surge arresters are equipments used for the power electrical systems protection. They limit the voltage level during the occurrence of switching and atmospheric surges. A surge arrester failure can cause the equipments insulation breakdown or flashover, or even the surge arrester explosion. To avoid this problem, the maintenance of these equipments is made by means of regular monitoring. Measurement of the resistive leakage current and analysis of its harmonic components is one of the most used techniques to evaluate the degradation level of metal oxide surge arresters. In this paper is presented a new measurement technique for the resistive component of leakage current based on the orthogonal position between this component and the capacitive component. The technique is accomplished by means of inductive current sensors based on nanocrystalline alloys and a PIC microcontroller to provide the measurement of the first, third and fifth harmonic components of the resistive leakage current in the arrester.

Measuring the excitation current in transformers using hall effect sensors

This paper presents and discusses the use of Hall effect sensors to measure the excitation current in single-phase transformers. The Hall effect sensors have galvanic isolation of the order of a few kVrms and may have total measurement errors less than 0.7% of the nominal value. It is common in transformer tests, to use a varivolt to avoid inrush current, which can reach more than 20 times the rated operating current, and can interfere with or even damage electronic circuits for measurement. However with the use of these sensors, their characteristics make it possible to have a measuring device relatively robust, accurate and fast, thus eliminating the use of a varivolt, for testing the load current transformer single phase or three phase.

Current Transformer with Toroidal Nanocrystalline Alloy Core

An error compensation technique for measuring current transformers is described. It uses only passive components. An example is shown for current transformers installed in I50 kV switching devices. Initial ratio errors in the order of 4% and phase shifts around 20 min were reduced to 0.1% and 6 min after the compensation. The transformer with the compensation fulfils class 0.2 according to IEC standards.

A Robust ANN For Rotor Speed Indirect Measurement Of The Induction Machine

This paper presents a method for the modeling of the rotor speed indirect measurement in an induction machine. It uses an Artificial Neural Network (ANN) algorithm. The algorithm is developed considering the robustness of the induction machine. This method is investigated and realized via environmental MATLAB and C language. The induction machine model is developed and processed in MATLAB, analyzing the behavior of stator voltage and current, rotor flux and rotor speed. These values (stator voltage and current) are storages in a file and, after used with step input signals for the ANN algorithm developed in C language. The rotor speed is one of the three weights of an ANN. Keywords— Modeling of a System, Artificial Neural Networks, Rotor Speed, Induction Machine, Indirect Measurement, Parametric Uncertainty.

Induction Machine Speed Neural Estimator Implemented in Programmable Architecture

This work presents a state observer based on Artificial Neural Networks ( ANN’s) and a Programmable Architecture to estimate an Induction Machine ( IM ) speed . Indirect measurement system is the observer’s physical accomplishment formed by hardware components, voltage/current meters and digital circuit, by the software and the estimation algorithm. Speed obtained by simulation based on mathematical models and by estimation algorithm implementation in PSoC programmable circuit is compared to machine’s speed measured values by a tachometer.