Rubem G. Farias

Mandrel-Based Fiber-Optic Sensors for Acoustic Detection of Partial Discharges—a Proof of Concept

Acoustic emission monitoring is often used in the diagnosis of electrical and mechanical incipient faults in high-voltage apparatus. Partial discharges are a source of failure in power transformers, and the differentiation from other sources of acoustic emissions is of the utmost importance. This paper reports the development of a new sensor concept-mandrel-based fiber-optic sensor-for the detection of incipient faults in oil-filled power transformers, taking direct measurements inside a transformer. These sensors can be placed in the inner surface of the transformer tank wall, not affecting the insulation integrity of the structure, and improving fault detection and location. The applicability of these acoustic sensors in air, water, and oil is investigated and the paper presents the promising results obtained, which will enable the industrial development of practical solutions.

Fiber fabry-perot sensors for acoustic detection of partial discharges in transformers

Acoustic emission monitoring is often used in the diagnosis of electrical and mechanical incipient faults in high voltage apparatus. A great number of methods are available for condition monitoring and diagnosis of power transformer insulation, but only a few can take direct measurements inside a transformer. Partial discharges are a major source of insulation failure in power transformers and their detection can be achieved through the associated acoustic emissions. This paper reports the development of two sensing head configurations based on extrinsic and intrinsic fiber Fabry-Perot interferometers for the detection of incipient faults in oil-filled power transformers. These sensors can be placed inside the transformer tank without affecting the insulation integrity, improving fault detection and location. The performances of the sensing heads are characterized and compared with the situations where it operates in air, water and oil and promising results are obtained, which will allow the industrial development of practical solutions.

Particle Swarm Optimization Applied for Locating an Intruder by an Ultra-Wideband Radar Network

As it was shown by the authors in a previous work, the Finite-Difference Time-Domain (FDTD) method is adequate to solve numerically Maxwells Equations for simulating the propagation of Ultra-Wideband (UWB) pulses in complex environments. These pulses are important in practice in high-resolution radar and GPS systems and in high performance (wideband) wireless communication links, because they are immune to selective frequency fading related to complex environments, such as residences, offices, laboratories among others. In this case, it is necessary to use spread spectrum techniques for transmission, in order to avoid interferences to other wireless systems, such as cell phone networks, GPS, Bluetooth and IEEE802.11. It is worth to mention that by combining these techniques to UWB pulses; it is possible to obtain a signal with power spectrum density under noise threshold, what is a very interesting characteristic for this application. The proposed simulated environment is a building consisting of several rooms (laboratories) separated by masonry. Internal and external walls are characterized by specific widths and electrical parameters. Wood doors were included in the analysis domain. The analysis region is then limited by U-PML (Uniaxial Perfectly Matched Layers) technique and the system is excited by omni-directional antennas. In order to make the simulations more real, Additive White Gaussian Noise was considered. Aiming at verifying the robustness of the radar network, objects are included in the domain in a semi-random spatial distribution, increasing the contribution of the wave scattering phenomena. Omni-directional antennas were used to register transient electric field in specific points of the scenery, which are adequate for the propose of this work. From those transient responses, it is possible to determine the time intervals the electromagnetic signal requires to travel through the paths transceiver-intruder-transceiver and transceiver-intruder-receivers, forming, this way, a non-linear system of equations (involving circle and ellipses equations, respectively). In order to estimate the intruder position, the PSO method is used and a new methodology was conceived. The main idea is to apply PSO to determine the equidistant point to the circle and to the two ellipses generated by using the data extracted from received transient signals (those three curves usually does not have a single interception point for highly

Multistatic radar with ultra-wideband pulses: FDTD simulation

A simulation of a multistatic radar using the finite-difference time-domain method is performed to identify the presence of an intruder inside a residence. The radar operates with ultra-wideband pulses to obtain high resolution. One transmitter and three receivers, positioned outside the residence, are used to estimate the location of an intruder inside the residence without ambiguity.

Fibre laser sensor based on a phase-shifted chirped grating for acoustic sensing of partial discharges in power transformers

Partial discharges are a major source of insulation failure in electric power transformers. Their detection can be achieved through the associated acoustic emissions, and this work reports on the investigation of a fibre laser sensor based on a phase-shifted chirped fibre grating for acoustic emission detection in the power transformer environment. The performance of the sensing head is characterized and compared for different surrounding media: air, water and oil.

Acoustic Source Location of Partial Discharges in Transformers

Acoustic emission monitoring is often used in the diagnosis of electrical and mechanical incipient faults in high voltage apparatus. Partial discharges are a major source of insulation failure in power transformers and the differentiation from other sources of acoustic emissions is of the utmost importance. Also, it is important to give an indication of the PD source location in order to obtain a useful diagnosis. This paper reports the developments in partial discharges source location through the associated acoustic emissions using three different algorithms.

Application of particle swarm optimization to ultra-wideband multistatic radar used for protection of indoor environment

A numeric simulation of a multistatic radar using the finite-difference time-domain (FDTD) method and particle swarm optimization (PSO) is implemented in order to localize an intruder inside a laboratory complex. In order to obtain high resolution and to avoid interference with other radiosystems, the radar operates with ultra-wideband pulses and spectral spreading. The transmitted signal has a spectral peak at 1 GHz and the bandwidth of approximately 1 GHz. To estimate the location of the target, two transmitters and nine receivers are used. The transmitters operate in TDM mode in order to avoid interference between them.

Development of an Educational Environment for Simulating Multistatic UWB Radars for Locating an Intruder Inside Indoor Environment

This work describes a educational tool developed in Java language for simulating a multi-static radar. This radar is used to identify the presence of an intruder inside a residence. In order to obtain high resolution, the radar operates with ultra-wideband pulses (Gaussian monocycle), which have maximum spectral amplitude at 1 GHz and half power bandwidth of approximately 1 GHz. For the estimation of the intruders position, the optimization technique particle swarm optimization (PSO) is employed. The simulator allows that the users define the parameters to be used by the radar and obtain the estimation of the intruders position. Besides that, the software automatically generates animations of the wave propagation inside the residence, graphics of the signal at the receiving points and a final report with all the information related to the simulations.

Frequency-dependent FDTD method applied to optically-controlled coupled-dielectric-waveguide

The finite-difference time domain (FDTD) method for dispersive media is applied to the study of the electromagnetic wave propagation in optically-controlled coupled-dielectric-waveguides. The optical control is achieved by means of light incidence on semiconductor layers deposited onto the waveguides. The effects produced by the induced plasma in the semiconductor are analyzed through the dispersion characteristic of the waveguide structure.