Kleiton de Morais Sousa

Fiber Bragg grating sensing applications in temperature monitoring of three-phase induction motors

This paper presents an analysis of simultaneous temperature and electrical parameters measurements in a three phase induction motor (TIM). The electrical parameters, namely voltage and current in the motor windings, were measured with Hall effect sensors and the temperature in the stator slots were monitored using fiber Bragg grating sensors (FBG). In the performed temperature analysis, two sets of sensors were used, containing four FBG in each fiber. Eight FBG sensors were uniformly distributed in the TIM stator. A special encapsulation of the sensor was elaborated to minimize mechanical disturbances in the fiber due to motor operation. Tests were performed with motor running at no load and with intentional voltage disturbances in the windings produced at every 15 minutes periods. It was observed that the temperature distribution is not uniform in the TIM stator either with or without a balanced voltage in the windings. A mean level increase of 0.5°C in temperature was registered in all of the sensors when there is a lack of balance in the voltage windings.

Induction Motors Vibration Monitoring Using a Biaxial Optical Fiber Accelerometer

In this paper, the implementation, characterization, calibration, and testing of a biaxial optical fiber accelerometer for vibration monitoring in three-phase induction motors is presented. The optical sensor uses fiber Bragg gratings to measure the displacement of an inertial mass relatively to a support base. The sensor characterization was measured through the impact hammer, allowing the determination of the natural frequencies in both sensitive directions, the values of 747.5 Hz and 757.5 Hz were estimated for the x-axis and the y-axis, respectively. For calibration, an electromagnetic exciter was used to introduce a controlled harmonic excitation at different frequencies, with this analysis, a high SNR was observed, on average over 30 dB for both sensitive directions, and a sensitivity of 100 pm × g-1 was obtained, up to one third of the natural frequency, in each direction. The tests were developed with the main aim of the analysis in induction motors based in vibration monitoring, the analysis can help to prevent wear in motors, increasing its efficiency, and lowering maintenance costs. The optical accelerometer measurements were compared with the ones from a capacitive sensor, during regular operation and with a broken rotor bar operating with 75% and 100% load. The performed tests with the optical sensor allowed to successfully analyze the frequency components, and its changes, for the regular and damage operation.

Dynamic Eccentricity Induced in Induction Motor Detected by Optical Fiber Bragg Grating Strain Sensors

Mechanical and electrical forces of a three-phase induction motor (TIM), in operation, can cause strain in the stator, which may lead to frustrating vibration problems. These problems may greatly reduce reliability and ultimately lead to increased maintenance cost. This paper shows the method to overcome this problem by carrying out the dynamic strain measurement analysis in a TIM running at no-load condition, using an optical fiber sensor. The dynamic strain induced by mechanical and electrical forces was measured by using fiber Bragg gratings (FBGs), installed inside the motor, in between two stator teeth. The electromagnetic immunity and reduced size of the FBGs render them suitable for this application. The frequency components of the strain in TIM were predicted using a model of the forces present in the air gap, considering static and dynamic rotor eccentricities. Two TIM motors, one of 2-poles and the other of 4-poles, and each equipped with two FBGs strain sensors, were used. The sensors were positioned between two stator teeth, separated by 120° from each other in the 2-pole motor and 90° in the 4-pole motor. The experimental analysis shows that the frequency components of the dynamic force spectrum presented by the two motors are the same as those predicted theoretically. Rotor eccentricity was achieved by attaching an unbalanced load to the rotor shaft. The amplitude of vibration at rotor rotational frequency increased when the unbalanced load on the rotor shaft increased. The measurement presented in this paper can be used to determine some TIM parameters, such as the effect of the motor power supply on its vibration signal. It can also be used as a potential maintenance tool for the continuous monitoring of the TIM with high sensitivity.

Vibration measurement of Induction Motor under dynamic eccentricity using optical fiber Bragg grating sensors

The vibration in Three-Phase Induction Motors (TIM) is due to mechanical and electrical forces existing during the motor operation. Vibration problems in induction motors can be extremely frustrating and may lead to greatly reduced reliability increasing the maintenance cost. The vibration was measured using fiber Bragg gratings (FBG) installed inside the motor between two stator teeth. The vibration frequencies in TIM are predicted using a model of the forces present in the air gap considering a static and dynamic rotor eccentricity. Two FBGs were positioned between two stator teeth, separated by 120° from each other. The analysis of the vibration spectrum at 60 Hz motor power supply presents the frequencies 60 Hz, 120 Hz, 180 Hz and 240 Hz. This combination of the mechanical and electrical frequencies continue to appear even when the motor electrical supply frequency is reduced by half. The measurement present in this paper can be used to determine some TIM parameters, like the effect of the motor power supply on its vibration signal and also be used like a potential maintenance tool for predictive purposes with high efficiency to continuously monitor the TIM.

Thermal and vibration dynamic analysis of an induction motor using optical fiber Bragg gratings

In this paper it is presented the results of temperature and vibration measurements in a Three-phase Induction Motor (TIM) running at no-load condition. Vibration and temperature analysis are the most successful techniques used for condition monitoring of induction motors. The vibration is measured using two FBGs installed inside of the motor between two subsequent stator teeth. The motor spectrum of vibration when power is at 60 Hz presents the frequencies 60 Hz, 120 Hz, 180 Hz, and 240 Hz as theoretically expected. For the temperature measurement two FBGs are encapsulated in an alumina tube fixed along the stator. The results show 0.9°C difference between the two FBG caused by the motor ventilation nearer of one FBG. These measurements can be used to determine TIM parameters and still be predictive maintenance tool.

Fiber Bragg Grating Temperature Sensors in a 6.5-MW Generator Exciter Bridge and the Development and Simulation of Its Thermal Model

This work reports the thermal modeling and characterization of a thyristor. The thyristor is used in a 6.5-MW generator excitation bridge. Temperature measurements are performed using fiber Bragg grating (FBG) sensors. These sensors have the benefits of being totally passive and immune to electromagnetic interference and also multiplexed in a single fiber. The thyristor thermal model consists of a second order equivalent electric circuit, and its power losses lead to an increase in temperature, while the losses are calculated on the basis of the excitation current in the generator. Six multiplexed FBGs are used to measure temperature and are embedded to avoid the effect of the strain sensitivity. The presented results show a relationship between field current and temperature oscillation and prove that this current can be used to determine the thermal model of a thyristor. The thermal model simulation presents an error of 1.5 °C, while the FBG used allows for the determination of the thermal behavior and the field current dependence. Since the temperature is a function of the field current, the corresponding simulation can be used to estimate the temperature in the thyristors.

A technique to package Fiber Bragg Grating Sensors for Strain and Temperature Measurements

This paper reports an effective method of packaging a fiber Bragg grating (FBG) for the simultaneous measurement of temperature and strain. The technique consists of embedding two fiber Bragg grating sensors inside a polymeric material with different geometrical characteristics. The mechanical and thermal characterizations of the optical transducer were performed. Then a matrix equation used measurements of the wavelength shifts from the two sensors and yielded information about the temperature and strain coefficients. The preliminary results demonstrate the feasibility of the encapsulation technique allowing measurements of temperature and strain in smart structures and harsh environments. The experimental procedure provides robustness to the sensor and the matrix equation approach has the potential to determine simultaneously the strain and temperature coefficients.

A power electronics and digital control experiment applied to teaching interdisciplinary in electrical engineering

This paper presents a interdisciplinary teaching experience applied to power electronics and digital control. The boost converter with a discrete-time PI controller implemented in a microcontroller is used in this experiment. It is presented a boost converter model and the controller design, beyond the description of instrumentation circuit used. Finally are presented experimental and simulated results. This experiment is applied to UTFPR electrical engineering students.

Broken Bar Fault Detection in Induction Motor by Using Optical Fiber Strain Sensors

In this paper, the dynamic strain measurement of a four-pole induction motor stator operating at 75% and 100% of the rated load is used to detect a broken rotor bar. Four fiber Bragg grating (FBG) strain sensors are installed inside the motor, between two stator teeth. Electromagnetic immunity and decreased size of the FBGs make them suitable for this application. When a broken bar is present, some characteristic frequencies in the stator strain spectrum appear. The values of these frequencies are proportional to the motor slip. Instrumentation allows the diagnosis of the broken bar in two different regions of the stator strain frequency spectrum: first, near the rotational frequency, and second, close to twice as much the supply frequency. Two different supply conditions are presented, feeding the motor from an electrical grid and by using a variable-frequency driver. The experimental results indicate that the broken rotor bar can be detected in all supply situations by using the two regions of the stator strain spectrum. By using the method presented in this paper, the broken rotor bar can be detected, even with a harmonic distortion in voltage. This is an advantage over the classic motor current signature analysis method.

Analysis of vibrations in electrical machines with an optical fiber accelerometer

The vibration in induction motors is due to mechanical and electrical forces existing during the motor operation. The vibration monitoring can help to prevent wear in motors, to increase its efficiency and lowering maintenance costs. Through knowledge and accurate diagnostic procedures, it is possible to detect the cause of the vibration. This paper presents the vibration measurement analysis in the induction motor running at no-load condition using a biaxial optical fiber accelerometer. The sensor is positioned on the induction motor, and the acquired data compared with the one from a capacitive sensor. Changing the power supply frequency from 10 to 60 Hz a higher SNR was observed for both directions on the optical sensor data. The characteristics of the optical sensor, immunity to electromagnetic interference and high sensitivity, 87.848 pm.g−1 and 92.351 pm.g−1 for two directions and independent directions, favors its use for monitoring vibrations in electrical machines. The results indicate a relation between deterioration and mechanical vibration and, thus, providing the motivation for additional study and a basis for future applications.