Showing 6 results for Abbasi
Vahid Abbasi, Ahmad Gholami,
Volume 6, Issue 1 (March 2010)
Abstract
Abstract: The application of electric field theory to widely different aspects of electrical
insulation has led to more understanding the phenomena. Electric fields may be considered
as the main reason for insulation failure. The purpose of this paper is to modify importance
of analyzing electric field in insulation design. The SF6 circuit breaker is chosen as case
study that encounters critical situations during its application. The other phenomena affects
insulation is the presence of polar species in a non-polar molecular material locally
modifies the polarization energy, thus creating local states (traps) on neighboring
molecules. Results of calculations carried out for arrays of spatially connected dipoles
indicating that local states of a considerable density may be created, modifying the densityof-
states function, and therefore influencing the effective mobility of charge carriers. The
main result of polarization during application in circuit breaker is loss of life. In this paper
the reduction of negative effects of electric field and polarization by choosing a suitable
insulation structure in a 33 kV SF6 circuit breaker according to calculation in critical areas
is investigated that can also be studied in other types of circuit breakers.
H. Abbasi, A. Gholami, A. Abbasi, ,
Volume 7, Issue 1 (March 2011)
Abstract
This paper consist of two sections: control and stabilizing approach for chaotic behaviour of converter is introduced in first section of this paper for the removal of harmonic caused by the chaotic behaviour in current converter. For this work, a Time- Delayed Feedback Controller (TDFC) control method for stability chaotic behaviour of buck converter for switching courses in current control mode is presented. This behaviour is demonstrated by presenting a piecewise linear discrete map for this converter and then combining the feedback equation to obtain the overall equation of the converter. A simple time-delay feedback control method is applied to stabilize the Unstable Periodic Orbits (UPOs). In second section is studied the effect of a parallel metal oxide surge arrester on the ferroresonance oscillations of the transformer. It is expected that the arresters generally cause ferroresonance drop out. Simulation has been done on a three phase power transformer with one open phase. Effect of varying input voltage has been studied. The simulation results reveal that connecting the arrester to the transformer poles, exhibits a great mitigating effect on ferroresonant over voltages. Phase plane along with bifurcation diagrams are also presented. Significant effect on the onset of chaos, the range of parameter values that may lead to chaos and magnitude of ferroresonant voltages has been obtained, shown and tabulated.
M. J. Abbasi, H. Yaghobi,
Volume 12, Issue 4 (December 2016)
Abstract
The doubly fed induction generator (DFIG) is one of the most popular technologies used in wind power systems. With the growing use of DFIGs and increasing power system dependence on them in recent years, protecting of these generators against internal faults is more considered. Loss of excitation (LOE) event is among the most frequent failures in electric generators. However, LOE detection studies heretofore were usually confined to synchronous generators. Common LOE detection methods are based on impedance trajectory which makes the system slow and also prone to interpret a stable power swing (SPS) as a LOE fault. This paper suggests a new method to detect the LOE based on the measured variables from the DFIG terminal. In this combined method for LOE detection, the rate of change of both the terminal voltage and the output reactive power are utilized and for SPS detection, the fast Fourier transform (FFT) analysis of the output instantaneous active power has been used. The performance of the proposed method was evaluated using Matlab/Simulink interface for various power capacities and operating conditions. The results proved the method's quickness, simplicity and security.
V. Abbasi, L. Hassanvand, A. Gholami,
Volume 13, Issue 3 (September 2017)
Abstract
Specific and sensitive operation of circuit breakers makes an individual position for them in power networks. Circuit breakers are at the central gravity of variations and execution operations. Therefore, an optimum operation is the main reason to investigate about new gases to be used in MV and HV circuit breakers instead of SF6. The arc process has enormous complexity because of hydrodynamic and electromagnetic combination equations, and that is the exact reason why most of the previous simulations were processed in two-dimension analysis. But, in this paper a three-dimension simulation with sufficient results has been fully discussed. Different evaluations on the other gases have taken under study in order to find a suitable substitute instead of SF6 gas, which can also bring an optimum operation for the breakers and can be even friendly with the environment. The simulations have been carried out based on the finite element method (FEM) and magneto-hydrodynamic equations. A three-dimension model under the transient state has been chosen in the simulations to find a feasible substitute for SF6 gas. The main factors of the analysis are threefold as follows: arc temperature on the different regions, the cooling ability and arc resistance. CO2, CF3I and N2 are nominated to substitute the SF6 gas and their effects on cooling ability, nozzle evaporation, contacts erosion and arc resistance will be discussed.
V. Abbasi,
Volume 14, Issue 3 (September 2018)
Abstract
Cable termination faults are problematic in electrical networks almost always. Technology has solved problems somewhat, but there are many annual reports about damaged cable terminations. For analyzing the problems, faults in two regional electricity companies are studied. At first step, damaged cable terminations are analyzed statistically and grouped according to their problems. Then, some of the damaged cable terminations are checked to classify vulnerable areas. The investigation is completed by simulation, analysis and study of equivalent circuit. Conclusions underline important points which can be helpful for reducing the damages.
V. Abbasi, S. Hemmati, M. Moradi,
Volume 15, Issue 1 (March 2019)
Abstract
Stress grading (SG) layer in cable terminations limits the critical electric field and properties of SG materials are important issues which have to be considered during manufacturing and selecting procedure. In this paper, two different types of (SG) materials are analyzed by both theory and test. According to the applied theory, important parameters as: electrical resistivity, breakdown voltage and thermal conductivity are determined by experiments. Experimental steps are defined in the paper with which theory and experiments are matched together to complete the investigation. The paper discusses electro-thermal breakdown theory and quality of two different SG layers based on the test results. The theory and experimental procedure can be used for prediction of breakdown voltage in cable terminations. The employed method is useful for qualifying the cable terminations by users who want to buy and install heat shrink cable terminations.
