Josemir Coelho Santos

Optical high voltage measurement using Pockels microsingle crystal

A new optical high voltage sensor using a Pockels microsingle crystal in a longitudinal modulation arrangement is presented. A prototype of the sensor is assembled and shows an advantage of directly measuring voltage levels up to 50 kV without any potential divider in a wide frequency bandwidth of direct current to 116 MHz. In conventional Pockels sensors, acoustic resonance driven by piezoelectric effect introduces oscillatory components to signals obtained from measurements of lightning impulse voltages. In the new sensor, the measured signal is free from the oscillatory components. An accuracy of 1.9% in good agreement with predicted values is obtained from the lightning impulse voltage measurement.

Optical High Voltage Measurement Technique Using Pockels Device

This paper describes a new optical high voltage measurement technique to realize optical voltage transformers (optical VTs) through which high voltages up to 400 kV can be directly measured. A prototype of an optical VT using Pockels device in a multi-segmented arrangement is designed based on the numerical calculation of the electric field distribution. The response characteristics of the developed prototype are examined for ac, dc, and lightning impulse voltages, and these experimental results showed good agreement with theoretical estimations. An oscillatory component appearing on the output signal of the sensor for the impulse voltage application is successfully eliminated using a fast Fourier transform (FFT) digital filter. It is also found that the sensor can respond to fast transients with a rising time of 40 ns, which defines the frequency response bandwidth of the system from dc to several MHz.

Development of distance sensors for diagnosing air-gap anomalies in synchronous generators

This paper presents the development of distance sensors to measure air-gap irregularities in synchronous generators for diagnosing static eccentricities. Capacitive and inductive sensors were developed to measure the thickness of the air-gap between the stator and the rotor poles. In order to obtain an absolute measurement of distance, an optical fiber chromatic confocal sensor system is used as a reference for the other sensors by means of a local calibration procedure. It can be concluded that capacitive and inductive sensors developed show satisfactory and promising results of air-gap measurement.

Dynamic response of optical fiber Bragg grating temperature sensors

This paper presents the results of thermal tests performed with commercial optical fiber Bragg grating (FBG) temperature sensors and raw FBGs fabricated by Photonics Division of IEAv. Test results show significant differences on dynamic response behavior among all sensors and gratings under fast variations of environmental temperature. This effect may suggest a limitation on the use of sensors based on this technique in applications requiring fast and precise response.

Modeling residual thermal stress-induced integrated optical waveguides on Bi 12 GeO 20 substrate for electrooptic modulation application

The residual thermal stress study of an optical waveguide based on isotropic material (bismuth germanate, BGO), the Pockels eletro-optic effect and the modal optical analyses were investigated for the optical modulation purpose. The analyses were performed by a full vector finite element based program. The optical propagation characteristics of the stress-induced waveguides and the main electro-optic parameters were evaluated considering different geometrical design.

Modeling of magnetostrictive optical modulator for application as a magnetic field sensor

The work presents a new proposition of an integrated optical device applicable as optical magnetometer. The studies of an optical waveguide formed by thermally induced static stress (ISS) and modulation achieved by magnetostriction of a TbCo2 thin film over Bismuth Germanate (BGO) are shown. The magnetooptical effect and the modal optical analyses were investigated for the optical modulation purpose. The analyses were performed by simulation software based on Finite Elements Method (FEM). The optical propagation characteristics of the magnetooptically disturbed guided mode in stress-induced waveguide were evaluated indicating the viability of proposed device application as magnetometer.

Capacitive and inductive sensors for diagnosing air-gap anomalies in synchronous generators

This paper presents the development of distance sensors to measure air-gap irregularities in synchronous generators. Among various causes, air-gap anomalies may arise due to shaft eccentricity, which will be dealt with in this work. A prototype machine was specially manufactured allowing the deformation of rotor and stator yokes, as well as the radial displacement of its shaft position. These features permit assessment of the performance of the sensors under study. The developed sensors are of the capacitive and inductive types, placed in the wedges of the stator slot openings, and symmetrically distributed along the air-gap surface.

Applicability of knowledge management practices at scientific research environment

The Knowledge Management (KM) is becoming a valuable strategic resource for the life of individuals and companies, and has been identified by scholars, researchers and scientists as relevant and required for the growth of organizations in various fields. This paper presents the results of a survey research with exploratory which seeks to identify what KM practices adopted by researchers in the research environment and to understand to what extent are contributing to scientific production. The results indicate that several KM practices are adopted in the research environment. However, it is observed that these are personal initiatives by researchers, without any coordination or management with specific purpose. This scenario shows that there must be a greater awareness of the importance of KM in the research environment. In this sense, an organizational culture should be noted that values knowledge not only as an essential device to researchers, but as a fundamental resource to research environments able to boost the production of scientific knowledge.

On-field instrument transformers calibration using optical current and voltage transformes

This paper presents the development of a system based on optical current transformers (OCTs) and optical voltage transformers (OVTs) for on-field calibration of conventional instrument transformers (ITs), avoiding necessities of removing the equipment for laboratory environment and interruption of supply for on-field calibration procedures. To accomplish these aims it was required the development of suitable OVTs and OCTs with accuracy classes equal to or better than 0.03%, suitable for calibration of conventional ITs intended to supply measuring instruments (accuracy classes equal to 0.3%). It was also necessary to develop the appropriate methodology to perform expedite on-field calibration of conventional ITs without interruption of service. As a further result of project, the on-field calibrations results may provide to sponsor utility recommendations for its maintenance procedures, aimed at replacing the identified off-class ITs or allow the use of algorithms for errors/losses compensation to be implemented on measuring instruments, in case of such resource be available.

Dynamic response of fiber Bragg gratings strain sensors

This paper presents the results of strain tests performed with fiber Bragg gratings written by interferometric or phasemask methods. The results show a significant difference on dynamic response these sensors when subject same conditions of temperature and mechanical stress. This effect may suggest a limitation on use of sensors based on this technique in applications requiring precise and fast responses.