Resumo em Inglês:

Abstract Partial discharges can occur in different types of electric equipment and cause progressive insulation deterioration, so there is interest in monitoring partial discharges for assessing the state of the isolation of an electric system and to predict failures. Techniques to detect partial discharges, such as detecting ultrasonic emission, have been proposed in the literature, but as various effects can co-occur during a discharge, identifying characteristics in sound and pressure waveforms and correlating then with discharge characteristics is difficult. Simulations can assist in these correlations by allowing the isolation of the different phenomena. In this work the drift diffusion model, including photoionization, is coupled with the linearized compressible Navier-Stokes equations to simulate ultrasonic waves produced by partial discharges. Previous works have used the incompressible Navier-Stokes equations, so they can simulate ionic wind produced by the Trichel pulses, but no sound. In the literature, simulations have focused either on streamers or Trichel pulses. In this work both discharges and produced sound waves are successfully simulated for the needle-plane geometry in air. The electric current and charge per pulse are compared with experimental results reported in the literature for the same discharge conditions. The simulations have demonstrated that the sound waves depart from the electrode tip for the Trichel pulses, and for the streamers two sound waves are produced, one from the electrode tip and the other from the whole discharge length. Differences in the wave front with respect to the relative position to the electrode tip were analyzed, showing that near the discharge spot the sound wave is not a spherical wavefront. The sound wave for one of the discharges in the Trichel pulse regime was compared with experimental results in the literature. Results are in good agreement with the experimental data found in the literature. Both current and sound waves were successfully predicted and correlated with the discharge, results that can be used to help in the detection of partial discharges.

Resumo em Inglês:

Abstract The theory of multiconductor transmission lines is based on the principle of superposition. According to this principle, any electric or magnetic field can be represented as the sum of individual electric or magnetic fields. This theory is used to analyze and design electrical systems involving multiple conductors. In this work, the procedures for analyzing electromagnetic transients in 3-conductor transmission lines are presented, which is the last step for generalization in the case of lines to “n” conductors. The paper presents elementary cases and a more general one to illustrate such an approach.

Resumo em Inglês:

Abstract This paper presents an equipment for monitoring synchronous generators condition through characteristics of the time derivative of the external magnetic field. The developed monitoring methodology allows the identification of established or incipient faults, by detecting changes in the magnetic signature of the synchronous generator. In this methodology, the measurement of signals outside the machine gives this equipment a non-invasive characteristic, allowing its monitoring without interfering or disturbing its operation. The developed system includes the specification of magnetic field sensors, signal measurement and processing equipment, as well as software for analysis and monitoring. The validation of the methodology used in this system was carried out through the analysis of experimental data, presenting efficient results in the detection of electrical and mechanical faults in synchronous generators of an experimental test bench and a hydroelectric power plant. As a result, the commercial specification of this equipment was obtained and two units were implemented in a hydroelectric power plant to monitor 305 MVA synchronous generators.

Resumo em Inglês:

Abstract This paper presents a methodology for the generation of a static reluctance network, with magnetomotive sources only in the rotor, applied in the analysis and design of surface mounted permanent magnet synchronous generators. In the analysis stage, this network can provide the magnetic flux in several points of the generator, enabling an estimate of the generator performance. In the design process, on the other hand, it provides the armature linkage flux and hence the induced EMF can be calculated. It is worth mentioning that the proposed methodology makes use of a good discretization level (high number of elements) on the teeth tips and in the air gap of the generator, in order to get better precision on the flux modeling of these regions. The main contribution of this paper is to present the development process of a static reluctance network applied to surface mounted permanent magnets synchronous generators with different dimensions. The proposed model has proved to be robust and flexible as it can be seen in the results. The reluctance network (RN) developed with the proposed methodology presented in this paper shows low variations of the magnetic flux values, when compared with finite element simulations.

Resumo em Inglês:

Abstract Optical plasmonic nanoantennas have proven useful in nanoplasmonic applications, paving the way for more efficient wireless optical communications. In this work, we propose a parametric study of a plasmonic horn nanoantenna in flat H sectorial format and beveled horn, both designed to radiate in the three wavelengths of optical communications: [850 nm (352.9 THz), 1310 nm (229 THz) and 1550 nm (193.5 THz)]. The modeling of the chosen nanoantennas was performed in COMSOL Multiphysics version 6.0. The simulation results prove that the geometries presented satisfactory results of reflection coefficient and gain. In addition, to complement the parametric study, the conductive metal (in gold, silver and aluminum) was varied for each nanoantenna. Through the study, it was noticed that the nanostructures simulated in silver and aluminum are potential for applications in optical nanolinks and energy harvesting.

Resumo em Inglês:

Abstract Solid rotor induction motors (SRIMs) are asynchronous motors suited for high speed applications. This work presents an experimental case study where standard loss segregation procedures for induction motors are performed with a two-phase smooth solid rotor induction motor in order to verify their applicability. Even though the machine is supposed to operate at high frequency, the tests are performed at reduced frequency and voltage in order to avoid the effects of time harmonics. An adjustment in the separation of losses is proposed to contemplate the effects of the high no-load slip, and the behavior of the stray losses under high per-unit slip is analyzed in a load test. The test results are finally extrapolated for the rated condition.

Resumo em Inglês:

Abstract This paper presents the implementation of a 3-bit microstrip fractal-based phase shifter operating in the 430 MHz to 470 MHz frequency range. The fractal structure is used to confine different delay line lengths in the same area due to the space-filling properties of the used Hilbert fractal curve. The proposed design has three bits corresponding to 45, 90, and 180 degrees phase changes selected according to the switching circuit based on a Double Pole Double Throw (DPDT) switch implemented with PIN diodes. Comparisons between simulated and measured results are shown according to the chosen degree of use of PIN diodes.

Resumo em Inglês:

Abstract The presented model for wideband circularly polarized microstrip antenna is an improved version of the previous models which is widely applicable to satellite, microwave relay and radar. The designed circularly polarized antenna having overall volume of 20× 20 × 1.6 mm3 actively works at the impedance bandwidth of 9000 MHz (4.0–12.9 GHz) having 105%(with 8900 MHz taken as center frequency). The 3-dB axial ratio bandwidth is obtained as 5500 MHz (5.4–10.9 GHz) depicting 67.5% (with 8150 MHz taken as the center frequency). Measured results of impedance bandwidth, axial ratio, gain and VSWR agrees to the simulation results.

Resumo em Inglês:

Abstract A hemispherical dielectric lens antenna is proposed to provide beam-steering for communication networks operating in X-band. Two different printed antennas are simultaneously used to guarantee high performance and diversity of applications, one a wideband linear polarized antenna, and the other a narrowband circular polarized antenna. To ensure this, the design relies on adding printed angled feeders correctly positioned in relation to the center of a homogeneous dielectric lens. A prototype was simulated, fabricated and tested. The measured results show that the antenna is capable of operating from 8.0 GHz to 12 GHz (gain of 14.2 dBi) or 9.5 GHz to 10 GHz (gain of 17.52 dBi).

Resumo em Inglês:

Abstract In this paper, a compact, single port, multimode reconfigurable UWB-NB antenna with a novel feeding network is presented. The proposed antenna consists of a pentagonal-shaped monopole radiator, a beveled-shaped partial defected ground plane with a rectangular slot, and a reconfigurable bypass feeding network. The antenna realizes a wideband frequency range from 2.4 to 18 GHz and four narrow band frequency ranges, 5.3 to 6.8 GHz, 6.0 to 7.6 GHz, 7.2 to 8.8 GHz and 8.4 to 11.4 GHz. The antenna provides an omnidirectional radiation pattern with gain from 2.2 to 6.2 dBi maximum at 12 GHz and voltage standing wave ratio (VSWR) ranges from 1 to 2. The fabricated antenna has an overall dimension of 18×21×1.6 mm3. Sensing and tuning ranges of the fabricated antenna shows good agreement with the simulation results. The proposed antenna has an advantage of simple design, low profile, single port excitation and omnidirectional radiation pattern making it suitable for applications such as handheld mobile cognitive radio systems.