Power transformers are considered capital investments in the infrastructure of every power system in the world. They are the heart of electric power distribution and transmission systems, and it is essential that they function properly. It is knowing that insulating fluid is highly used in a composite or impregnated dielectric system with reference to both dielectric strength and ease of contamination, many investigators have devoted great efforts to investigate fluidsbehaviours under operating conditions.The objective of this study is to examine the gassing tendency under electrical discharge of aged and unaged mineral oil, and analyze the parameters in degradation, with the aim to see the most significant parameters which can really presents the degradation severity.In this regard, various scenarios were considered. The study was carried on new and aged oil submitted electrical field. The 6802, 6181 and 924 tests are used in measure of parameters in degradation.In this work, the water contents, Interfacial tension, and gas pressure generated,are considered as a parametersignificant of degradation process.These parameters were used as inputsin approach model for prediction the transformer age (life), the result show that the water can be used for detection of early stage of degradation
In this paper, an improved PI (proportional integral) stator resistance estimation for a DTC
(direct torque controlled) induction motor is proposed. This estimation method is based on
an on-line stator resistance correction regarding the variations of the stator current
estimation error. In fact, the input variable of the PI estimator is the stator current estimation
error. The main idea is to tune accurately the stator resistance value relatively to the
evolution of the stator current estimation error gradient to avoid the drive instability and …
In the information science and technology such as computer science, telecommunications, processing of the signals or images transmission, the field effect components plays a major role. We are interested in this study in Schottky gate gallium arsenide field-effect transistors commonly called GaAs MESFET. In this paper, we mainly present the results of calculating the influence of gate length on input and output impedances of GaAs MESFET Transistors, this physical model is based on the analysis of two-dimensional Poisson equation in the active region under the gate. The theoretical results, based on analytical expressions that we have established, are discussed and compared with those of the simulation.
Direct torque control (DTC) is known to produce fast responses and robust control in AC adjustable-speed drives. However, in the steady-state operation, notable torque, flux, and current pulsations occur. In this paper, nonlinear DTC of induction motor drives is presented based on a space vector pulse-width modulation scheme combined with the input-output feedback linearization technique. The variation of stator and rotor resistance due to changes in temperature or frequency deteriorates the performance of the DTC controller by introducing errors in the estimated flux linkage and the electromagnetic torque. This approach will not be suitable for high power drives such as those used in tractions, as they require good torque control performance at a considerably lower frequency. Finally, extensive simulation results are presented to validate the proposed technique. The system is tested at different speeds and a very satisfactory performance is achieved.
In this paper a design of the fuzzy adaptive control(FAC) based on the lyapunov stability theory for improving the dynamic response of the double star induction machine (DSIM) is presented, the fuzzy adaptive control scheme gives fast dynamic response with no overshoot, it has an important feature of being highly robust, insensitive to plant parameters variations, the design procedure is established to control the speed of the machine,the simulation results show that the controller in enhancing the robustness of control systems with high accuracy.
This paper presents new method toward the design of hybrid control with sliding-mode (SMC) plus fuzzy logic control (FLC) for induction motors. As the variations of both control system parameters and operating conditions occur, the conventional control methods may not be satisfied further. Sliding mode control is robust with respect to both induction motor parameter variations and external disturbances. By embedding a fuzzy logic control into the sliding mode control, the chattering (torque-ripple) problem with varying parameters, which are the main disadvantage in sliding-mode control, can be suppressed, Simulation results of the proposed control theme present good dynamic and steady-state performances as compared to the classical SMC from aspects for torque-ripple minimization, the quick dynamic torque response and robustness to disturbance and variation of parameters.
This article presents the modeling of non-destructive testing systems containing magnetic materials using a fast numerical method. Its main aim consists of correcting the half analytical expression of the impedance variation, formulated by some authors, caused by the presence of a conducting plate below of an absolute ferrite core probe. The obtained results of this correction are found to be consistent and satisfactory comparatively to those of finite element method. It also deals with the study the method rapidity by comparing its simulation time to that of the finite element method. As result, the proposed method is found to be very fast and a very short simulation time is required to calculate the sensor impedance. Indeed, for the studied system the coupled circuit simulation time is lower than 1.09 s. This study is appreciable, since it permits to solve quickly the inverse problem by expressing the physical and geometrical features of the material or defect according to the measured parameters. More importantly, this method is applicable to any axi-symmetric systems and can be adapted for the simulation of three-dimensional configurations.
