Vahid Abbasi, Ahmad Gholami,
Volume 6, Issue 1 (3-2010)
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. Javadi, M. Farzaneh, A. Peyda,
Volume 6, Issue 2 (6-2010)
Abstract
This paper deals with the measurement of AC corona inception voltage, Vincp, at
the tip of a rod electrode using a hemispherically-capped rod-plane electrode configuration
for various rod radii with a short air gap. Effects of atmospheric pressure and temperature
variation on Vincp are investigated experimentally. An empirical equation for the field form
factors of the hemispherically capped rod-plane electrodes is proposed with its range of
applicability. The obtained results are analyzed to derive a more accurate analytical
equation for the calculation of the electric field at corona inception voltage, Eincp, and the
average of electric field distribution, Emean
A. Tavakoli, A. Gholami,
Volume 7, Issue 3 (9-2011)
Abstract
Gas-insulated substations (GIS) have different specifications in proportion to air-insulated substations. Transformer failures related to lightning and switching are often reported in the gas insulated substation (GIS). This problem is the voltage magnifications due to reflections of switching and lightning surges at various junctions within the GIS. thereby overvoltages in GIS are more important than air-insulated substation. There are methods to suppress the stresses created by lightning and switching. However, these methods are suitable before installing the substation and during the substation design period. This paper presents feasible methods for mitigation of the overvoltage magnitude. The advantages of the proposed methods are their simplicity and low cost for implantation along with producing minimal changes in the installed GIS.
E. Akbari, M. Mirzaie, M. B. Asadpoor, A. Rahimnejad,
Volume 9, Issue 1 (3-2013)
Abstract
Insulator strings with several material and profiles are very common in overhead transmission lines. However, the electric field and voltage distribution of insulator string is uneven which may easily lead to corona, insulators’ surface deterioration and even flashover. So the calculation of the electric field and voltage distribution along them is a very important factor in the operation time. Besides, no remarkable endeavor regarding insulator material and profile and their impacts upon the electric field and voltage distribution has been made so far. In this paper several 230-kV insulator strings with different porcelain and glass units were simulated using 3-D FEM based software, and their electric fields and voltage distributions were calculated and compared together, to investigate the effect of insulator types on these quantities. Tower and conductors were included in all simulations and also the effect of corona ring on voltage and electric field distribution over insulator strings with different insulator types was investigated. Reported results show the dependency of voltage distribution to insulator material and profile.
M. Khodsuz, M. Mirzaie,
Volume 10, Issue 2 (6-2014)
Abstract
Metal oxide surge arresters (ZNO) are used widely in power system to protect equipments from over voltages. Non uniform potential distribution leads to the depressed service life and low safe reliability, so grading ring is applied on HV surge arrester order to uniform the electric field distribution. One of the problems of arresters is leakage current in power frequency that different parameters such as internal structure of varistors, heat sinks, grading ring can be influence on leakage current.
In this paper Maxwell and EMTP/ATP software has been applied to calculate the electric field, voltage distribution and leakage current in a high voltage surge arrester. First Maxwell is used to calculate the electric field and voltage distribution of a 230kV surge arrester with and without grading ring. Then equivalent circuit of surge arrester has been achieved by applying Maxwell software for 230kV surge arrester and extracting stray capacitances. The derived equivalent circuit has been simulated in EMTP/ATP software for evaluation of leakage current. Also in this work, the effect of grading ring dimensions and number of heat sinks on leakage current variation has been investigated. Results show grading ring dimension and heat sinks number impact on arrester leakage current.
K. Mokhtari, M. Mirzaie, M. Shahabi,
Volume 11, Issue 1 (3-2015)
Abstract
This paper aims to measure and analyze of the leakage current of 20 kV polymer and porcelain metal oxide surge arresters under humid ambient conditions by applying different voltages to the arresters terminal. The characteristics of the leakage currents at that stage have been investigated when changes in the ambient humidity were introduced in an artificial fog chamber. It is assumed that magnitude of the noise level during the tests is constant. The frequency and resistive component peak efficient analysis can then be done on the leakage current signal. The idea behind this is to get indicators for investigating of surge arrester behavior in humid conditions. Two important indicators were obtained to evaluate the behavior of the surge arrester in humid conditions
M Khodsuz, M Mirzaie,
Volume 11, Issue 4 (12-2015)
Abstract
This paper introduces the indicators for surge arrester condition assessment based on the leakage current analysis. Maximum amplitude of fundamental harmonic of the resistive leakage current, maximum amplitude of third harmonic of the resistive leakage current and maximum amplitude of fundamental harmonic of the capacitive leakage current were used as indicators for surge arrester condition monitoring. Also, the effects of operating voltage fluctuation, third harmonic of voltage, overvoltage and surge arrester aging on these indicators were studied. Then, obtained data are applied to the multi-layer support vector machine for recognizing of surge arrester conditions. Obtained results show that introduced indicators have the high ability for evaluation of surge arrester conditions.
M. Rasoulpoor, M. Mirzaie, S. M. Mirimani,
Volume 12, Issue 1 (3-2016)
Abstract
This paper investigates the effect of metallic sheaths on losses and temperature of medium voltage power cables. Two grounding methods of sheaths, including both ends bonding and single point bonding that causes different situations on cable ampacity, are considered. Electrical losses of cables that are main sources of heat are calculated in both conductor and metallic sheath of the cables. Sheathed and unsheathed medium voltage single conductor cables in flat and trefoil formations with different distances are considered, while calculated losses are compared in different constructions. Calculations of resistive losses are performed based on finite element method (FEM) and IEC standard formulations. The results of two methods are compared and analyzed. Moreover, the effects of eddy currents and circulating currents of sheath on total resistive losses are evaluated. Finally, thermal analysis based on FEM is executed to achieve maximum temperature of cable in different constructions. Simulation results show the importance of metallic sheaths and grounding system effects in power cable ampacity analysis.
V. Abbasi, L. Hassanvand, A. Gholami,
Volume 13, Issue 3 (9-2017)
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 (9-2018)
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.
M. Khodsuz, S. Seyyedbarzegar,
Volume 15, Issue 1 (3-2019)
Abstract
The essential role of surge arresters is equipment protection against over-voltages to increase system reliability. Different monitoring techniques have been used to diagnose surge arrester condition. Leakage current analysis methods by the extraction resistive and capacitive components of leakage current are a conventional method for surge arrester monitoring. Insufficient appropriate thresholds are most important restriction of these kinds of methods. In this paper, the impact of pollution, ultraviolet aging and varistors fault on harmonic spectrum of leakage current have been evaluated experimentally. Real tests and examinations have been done on different metal oxide surge arresters to investigate effects of mentioned factors on leakage current harmonics. To show results performance, bees-adaptive network based fuzzy inference system has been applied.
V. Abbasi, S. Hemmati, M. Moradi,
Volume 15, Issue 1 (3-2019)
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.
S. Hajiaghasi, Z. Rafiee, A. Salemnia, T. Soleymani Aghdam,
Volume 15, Issue 3 (9-2019)
Abstract
Since the insulators of transmission lines are exposed to different environmental conditions, it is important task to study insulators performance under different conditions. In this paper, silicone rubber insulators performance under different environmental conditions including rainy, icy, salt and cement are proposed and exactly is studied. Electric fields (E-fields) and voltage distributions along the insulator under various conditions have been evaluated. Moreover, the corona rings effects on insulator performance under these conditions have been presented. A 230 kV silicone rubber insulator is selected, modeled and simulated with finite element method (FEM) using the COMSOL software. The simulation is repeated for different environmental conditions and efficiency of corona ring for each scenario is evaluated. The results indicate that environmental conditions have a significant effect on the insulator performance and the corona ring somewhat alleviate the adverse effect of environmental conditions on the insulator performance.
P. Intra, P. Wanusbodeepaisarn, T. Siri-Achawawath,
Volume 15, Issue 3 (9-2019)
Abstract
The object of the present work was to design, construct and evaluate a cylindrical tri-axial charger for charging of submicron aerosol particles by unipolar ions. The corona discharge characteristics, the intrinsic and extrinsic particle charging efficiencies, and the losses of aerosol particles were experimentally evaluated for particle diameters in the range between 50 nm and 500 nm under different operating conditions. The conditions included the corona voltages of about 7.0 to 8.0 kV, the mesh screen voltages of about 100 to 300 V and the aerosol flow rate was set at 1.5 L/min. It was found that the ion current increased from 2.90´10-10 to 3.66´10-8 A and 2.40´10-10 to 1.36´10-7 A and the number concentration of ions increased from 7.50´109 to 5.92´1011 ions/m3 and 6.21´109 to 2.19´1012 ions/m3 when the corona voltage increased from 5.5 to 8.0 kV at the mesh screen voltage between 100 and 300 V, respectively. The intrinsic charging efficiency of particles introduced a constant value of about 99% for particle diameter in the range between 50 nm and 200 nm and decreased with particle diameter in the range between about 300 nm and 500 nm at a given corona voltage. The best extrinsic charging efficiency of the studied charger occurred between 1.32% and 38% for particle diameter in the range from 50 nm to 500 nm at corona and ion trap voltages of about 7.0 kV and 300 V respectively. The highest electrostatic loss of particles was observed at 50 nm particles and it was about 89.08, 90.73 and 91.91% at a mesh screen voltage of about 300 V for corona voltages of about 7.0, 7.5 and 8.0 kV, respectively. Finally, the highest diffusion losses were at about 28.88, 23.03 and 11.15% for singly charged, neutralized and non-charged particles of 500, 500 and 50 nm, respectively.
