# مقالههای Ahmad Gholami

**توجه:**محتویات این صفحه به صورت خودکار پردازش شده و مقالههای نویسندگانی با تشابه اسمی، همگی در بخش یکسان نمایش داده میشوند.

##### ۱A New Method for Calculation of Corona Inception Voltage in Stranded Conductors of Overhead Transmission Lines

اطلاعات انتشار:
بیستمین کنفرانس بین المللی برق،
سال ۱۳۸۴

تعداد صفحات:
۷

In this paper a new method for onset voltages calculation of negative and positive corona are presented. This method is based on considering electric field and pressure in adjacent of the surface of conductors. This algorithm is simulated for different pressure and radius of conductors. The configuration of conductors are considered stranded as like as overhead high transmission lines. The calculated onset voltages which are obtained by this method agree with primary experimental measured values by researchers.<\div>

##### ۲Aging of Isolating Materials in Power Cables

اطلاعات انتشار:
هفدهمین کنفرانس بین المللی برق،
سال ۱۳۸۱

تعداد صفحات:
۸

There is more than 160 years that polymers are using in cable industry. Polyethylene of low and high density [ LDPE , HDPE ] and crosslinked polyethylene [ XLPE ] gradually succeeded paper and polyvinylchloride[ PVC]. This paper discusses some aspects of aging processes of polyethylene working conditions. Electrical and water treeing are considered, dependent upon morphology and induced characteristics of the insulating material. Subsequently presented interim tests on crosslinked polyethylene and ethylene propylene [ EP ] isolated cables aged under

identical conditions for 36 months at 30oC (±5oC) with and without application of voltage transients. Aging voltages were from 1 to 2.5 times of rated voltage. Failures during aging have occurred in EP isolated cable while none have occurred in XLPE isolated cable. Both type of cables

experienced a large drop in ac and impulse voltage breakdown strength early in the aging process. Voltage transients have slightly affected the ac and impulse voltage breakdown strength.<\div>

identical conditions for 36 months at 30oC (±5oC) with and without application of voltage transients. Aging voltages were from 1 to 2.5 times of rated voltage. Failures during aging have occurred in EP isolated cable while none have occurred in XLPE isolated cable. Both type of cables

experienced a large drop in ac and impulse voltage breakdown strength early in the aging process. Voltage transients have slightly affected the ac and impulse voltage breakdown strength.<\div>

##### ۳3–D FEM Calculation of Electric Field and Potential Distribution for HVInsulators Considering the Effects of Wind Force and Foggy Condition

اطلاعات انتشار:
بیست و سومین کنفرانس بین المللی برق،
سال ۱۳۸۷

تعداد صفحات:
۷

At present, porcelain and composite insulators are widely used in high voltage transmission line owing to their outstanding features. The electric field (E–field) strength along these insulators is great concern. Calculation of the electric field and potential distribution is extensively performed in the design and development of insulators for high voltage transmission applications. In conventional calculations of the E–field and potential distribution along the insulators, it is assumed that, there is no wind and foggy air condition. In this paper, three– dimensional (3–D) Finite Element Method (FEM) software–Maxwell is employed to calculate the effects of windy, dry and foggy air condition on the E–field and potential distribution over suspension porcelain string and composite insulator in 63kV transmission line. The calculation results show that the factors investigated have different levels of effects on the distribution of each insulator. The results can be served as a basic reference in the proper use of line insulators in practical condition.<\div>

##### ۴A Harmonic Balance Based Stability Domain Analysis of Period–1 Ferroresonance

اطلاعات انتشار:
بیست و پنجمین کنفرانس بین المللی برق،
سال ۱۳۸۹

تعداد صفحات:
۹

In an attempt to find regions at risk of ferroresonance, different time domain simulations and analytical approaches were investigated on a one phase laboratory transformer. A 2–D bifurcation diagram based on one–term harmonic balance method has been developed. It was shown increase of core losses during overvoltages, significantly affects the stability domain of period–1 ferroresonance. Time domain simulations show that a static core loss model as a function of the maximum flux of the transformer predicts the second bifurcation point with enough accuracy. This modeling approach was incorporated in harmonic balance analysis. Comparison has been made between analysis and measurements.<\div>

##### ۵Simulation of Ferroresonance in a Three Phase Three–Limbed Laboratory Transformer

اطلاعات انتشار:
بیست و پنجمین کنفرانس بین المللی برق،
سال ۱۳۸۹

تعداد صفحات:
۹

Ferroresonance behavior of a three–phase transformer with three limbed cores is different from those consisting of banks of single–phase transformers. This paper is concerned with simulation of period–1 ferroresonance of a three phase three limbed cores laboratory transformer. Static resistances as a function of maximum flux have been used to simulate nonlinear core losses of different limbs of the transformer in the presence of ferroresonance overvoltages. In an attempt to find lower limit of source voltage that ferroresonance exists, these resistances with single–valued saturation characteristics made a better prediction than conventional constant resistance core loss modeling. Comparisons have been made between different modeling approaches and experimental results. Proposed method can be used for period–1 ferroresonance stability analysis.<\div>

##### ۶Corona Ring Designation for 400 kV AC Transmission Line with Composite Insulators by FEM

اطلاعات انتشار:
بیست و ششمین کنفرانس بین المللی برق،
سال ۱۳۹۰

تعداد صفحات:
۱۰

this paper provides a three dimensional geometric model to simulate the electric field distribution along I–string and V–string composite insulators in 400kV AC transmission lines. Many factors affect the Efield distribution along composite insulators as well as the influence of tower, magnitude of voltage, corona ring, using bundled conductors, contamination, leakage current and environmental conditions. By optimization some of these factors, short and long term performance of composite insulators during their service life is assured. Here by using corona rings and changing its parameters such as caliber, mounting height, diameter and its shape, electric stress along composite insulators can be decreased and postpone the ageing phenomenon and decide to choose best configuration for I–String and V–String insulators. Effect of all parameters are simulated on electric field distribution by FEM in COMSOL Multiphysics software.<\div>

##### ۷An Improved Method for Probabilistic Evaluation of lightning–related failures of Overhead Transmission Lines with Considering Non–Vertical Strokes

اطلاعات انتشار:
نوزدهمین کنفرانس مهندسی برق ایران،
سال ۱۳۹۰

تعداد صفحات:
۶

lightning strokes cause non–predicted supply interruptions in power networks because of a failure of the insulation. This paper represents an improved procedure for the evaluation of flashover rates, overvoltages and risk of failure of insulation caused by both lightning vertical and non–vertical strokes on transmission lines using a Monte Carlo method. The main goal of this paper is increase the accuracy lightningrelated failures through an accurate modelling of network components such as footing impedance, transmission tower and the chain of insulators and also simulation lightning nonvertical strokes. Modelling network components, statistical parameters related to lightning and problem–solving algorithm is described. Parametric studies using this procedure can also be performed to determine the sensitivity of the flashover rate with respect to some parameters of the return stroke and the transmission line. Simulation results obtained using MATLAB and the ATP\EMTP show that considering the lightning nonvertical strokes Instead of vertical strokes leads to better evaluation for lightning–related failures of transmission line<\div>

##### ۸Analysis of Corona Effect on Lightning Performance of HV Overhead Transmission Line UsingATP\EMTP

اطلاعات انتشار:
بیستمین کنفرانس مهندسی برق ایران،
سال ۱۳۹۱

تعداد صفحات:
۴

This paper presents a model of lightning performance of a 400kV double circuit overhead transmission line using ATP\EMTP. Including the models of transmission line, towersurge response, footing impedance, impulse electric strength of line insulator and lightning stroke as well as corona, the paperintroduces a comprehensive lightning transients study. Based on this model, the paper discussed the influence of corona on two transient phenomena known as back flashover and shielding failure.<\div>

##### ۹Damping of Ferroresonance in Coupling Capacitor Voltage Transformers with Ferroresonance Suppressing Circuits

اطلاعات انتشار:
سومین کنفرانس تخصصی حفاظت و کنترل سیستم های قدرت،
سال ۱۳۸۷

تعداد صفحات:
۸

In order to restrain ferroresonance in coupling capacitor voltage transformers (CCVT), two kinds of ferroresonance suppression circuits (FSCs): theresonant types, and the fast–saturation reactor type, which are connected to secondary side of CCVTs, are proposed in this paper. Frequency domain analyses, forvoltage ratio magnitude, are carried out for CCVTs to obtain preferable FSC. Furthermore, using surge suppressors such as metal oxide varistors (MOV) toimprove the performance of the FSCs is investigated. Time domain simulations demonstrate that ferroresonance can be cleared in few cycles in presenceof FSCs. The Electromagnetic Transients Program (EMTP) is used for modeling and fine–tuning the FSCs.<\div>

##### ۱۰Corona Ring Optimization for Different Cases of Polymer Insulators Based on its Size and Distance

اطلاعات انتشار:
Journal of Artificial Intelligence in Electrical Engineering،
اول،شماره۲، ۲۰۱۲،
سال ۰

تعداد صفحات:
۷

This paper describes the impact of the distance and the size of the corona ring, on the magnitude and distribution of electrical potential across the polymer insulators. The procedure is based on finite element method numerical analysis and stochastic optimization algorithm of differential evolution (DE). The optimal selection of corona ring has a significant impact on the control of potential and, consequently, on dielectric strengths, both inside and outside the insulator. This method is used for optimized determining of the size and the distance of corona ring from polymer insulators in existing structures.

##### ۱۱AUTOMORPHISM GROUPS OF SOME NON–TRANSITIVE GRAPHS

نویسنده(ها):
Ahmad Gholami

اطلاعات انتشار:
Iranian Journal of Mathematical Sciences and Informatics،
دوم،شماره۱، May ۲۰۰۷،
سال ۰

تعداد صفحات:
۸

An Euclidean graph associated with a molecule is defined by a weighted graph with adjacency matrix M = [dij], where for ij, dij is the Euclidean distance between the nuclei i and j. In this matrix dii can be taken as zero if all the nuclei are equivalent. Otherwise, one may introduce different weights for distinct nuclei. Balaban introduced some monster graphs and then Randic computed complexity indices of them (1973, 2001). In this paper, with a simple method, we calculate the automorphism group of some weighted graphs.

##### ۱۲Halopriming and Hydropriming Treatments to Overcome Salt and Drought Stress at Germination Stage of Corn (Zea mays L.)

اطلاعات انتشار:
Desert،
نوزدهم،شماره۱، ۲۰۱۴،
سال ۰

تعداد صفحات:
۸

To study the effects of halopriming and hydropriming in overcoming salt and drought stress in corn (Zea mays L.), two experiments were separately conducted at Shahrood University of Technology. Seed treatments consisted of control (untreated seeds), soaking in distilled water for 32 h (hydropriming), and soaking in 50 mmol solution of CaCl2 for 16 h (halopriming). Germination and early seedling growth were studied using distilled water (control) and osmotic potentials of –0.4, –0.8, and –1.2 MPa from NaCl (salinity stress) and polyethylene glycol [PEG 6000 (drought stress)]. Results showed that in both salinity and drought experiments, germination percentage reduced significantly according to decreased osmotic potential. Hydroprimed and haloprimed seeds achieved the minimum reductions in germination percentage. The maximum reduction in germination percentage was recorded from untreated seeds (control). Minimum reduction percentages of root length (RPL root) and shoot length (RPL shoot) were attained from hydroprimed and haloprimed seeds due to NaCl and PEG conditions ( 0.4 MPa), and maximum RPL root and RPL shoot were attained from controlled seeds due to NaCl and PEG (–1.2 MPa) conditions. The reduction percentage of dry weight for root (RPD root) and shoot (RPD shoot) increased according to increased osmotic potential in both NaCl and PEG, but RPD for shoot was significantly affected compared with RPD for root. Interaction of seed priming treatment and osmotic potential for the germination index (GI) showed that under 0 and – 0.4 MPa, hydroprimed and haloprimed seeds had higher GI as compared with untreated seeds due to NaCl and PEG conditions. Interaction between the seed priming treatment and osmotic potential significantly affected the vigour index (VI) due to NaCl and PEG conditions, and halopriming significantly increased VI at high osmotic potentials. On average, the VI of haloprimed seeds was higher than that of untreated seeds at high osmotic potentials and was not significantly different from hydroprimed and untreated seeds at low osmotic potentials. It is concluded that under salinity stress, the osmotic effect is more important than the toxic effect in loss of seed germination. Moreover, hydropriming practically ensured rapid and uniform germination with few abnormal seedlings.

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