Publications

@article{Mahdipour2020,

title = {Partial discharge localization on cross-bonded cable systems},

author = {M Mahdipour, A Akbari, P Werle, H Borsi},

year  = {2020},

date = {2020-01-02},

journal = {Electric Power Systems Research },

volume = {178},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ariannik2019,

title = {UHF Measurement in Power Transformers: An Algorithm to Optimize Accuracy of Arrival Time Detection and PD Localization},

author = {M Ariannik, MA Azirani, P Werle, A Akbari},

year  = {2019},

date = {2019-04-09},

journal = {IEEE Transactions on Power Delivery},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Jahangir2017c,

title = {UHF PD measurements on power transformers-advantages and limitations},

author = {H Jahangir, A Akbari, P Werle, J Szczechowski},

editor = {IEEE Transactions on Dielectrics and Electrical Insulation},

year  = {2017},

date = {2017-10-03},

journal = {IEEE Transactions on Dielectrics and Electrical Insulation},

volume = {24},

number = {6},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Jahangir2017b,

title = {Possibility of PD calibration on power transformers using UHF probes},

author = {H Jahangir, A Akbari, P Werle, J Szczechowski},

editor = {IEEE Transactions on Dielectrics and Electrical Insulation},

year  = {2017},

date = {2017-10-03},

journal = {IEEE Transactions on Dielectrics and Electrical Insulation},

volume = {24},

number = {5},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mahdipour2017,

title = {Impact of different bonding methods on high voltage cable shield induced voltage and current in normal and fault conditions},

author = {M Mahdipour, A Akbari, M Khalilzadeh, P Werle},

editor = { Iranian Conference on Electrical Engineering (ICEE)},

year  = {2017},

date = {2017-04-04},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Charge concept in partial discharge in power cables},

author = {M Mahdipour, A Akbari, P Werle},

year  = {2017},

date = {2017-03-06},

journal = {IEEE Transactions on Dielectrics and Electrical Insulation},

volume = {24},

number = {2},

pages = {817-825},

abstract = {Present paper discusses Partial Discharge (PD) occurrence and its relevant parameters in power cables. A spherical void in the insulation of a power cable is assumed as the origin of PD. To study PD in power cables, a model based on the three capacitor type is proposed, and the associated circuit elements for the spherical void and different layers of the cable are obtained with closed form solutions. In the procedure of deriving parameters of the model, a defect column is selected with a particular geometry which its boundaries are in the direction of the electric field. The results for PD magnitude and current pulse are acquired from the proposed model, along with Finite Element Method (FEM) simulations. Both methods show matching results but in contrast with the dipole model. FEM simulations are accomplished in 3D, on account of spherical geometry of the void. Other simulation results achieved from FEM and …},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Rezvani2016,

title = {Investigating field emission current in vacuum interrupters to estimate vacuum pressure level using PIC simulation},

author = {Mohammad Rezvani and Seyed Mohammad Taghi Bathaee and Asghar Akbari Azirani},

doi = {10.1002/etep.2198},

year  = {2016},

date = {2016-01-01},

abstract = {Condition monitoring of vacuum circuit breaker is one of the important factors to determine its life time. This is through a close monitoring of the internal pressure of vacuum interrupter for vacuum circuit breaker conditioning. The rise of internal pressure exceeding a certain threshold value causes loss of current switching capability and electric insulating properties. In recent decades, many methods of determining internal pressure have been investigated to evaluate the influences of different parameters. Although most of them are based on experimental tests, none of them was satisfying and reliable to provide enough information about residual vacuum pressure.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2016,

title = {Investigating field emission current in vacuum interrupters to estimate vacuum pressure level using PIC simulation},

author = {
Rezvani, M., Bathaee, S.M.T., Akbari, A.},

year  = {2016},

date = {2016-01-01},

journal = {International Transactions on Electrical Energy Systems},

number = {26 (10)},

pages = {2193-2203},

abstract = {Condition monitoring of vacuum circuit breaker is one of the important factors to determine its life time. This is through a close monitoring of the internal pressure of vacuum interrupter for vacuum circuit breaker conditioning. The rise of internal pressure exceeding a certain threshold value causes loss of current switching capability and electric insulating properties. In recent decades, many methods of determining internal pressure have been investigated to evaluate the influences of different parameters. Although most of them are based on experimental tests, none of them was satisfying and reliable to provide enough information about residual vacuum pressure. Thus, the field emission current is modeled and simulated in this paper using plasma modeling by particle in cell method in order to determine the correlation between current and vacuum pressure. The simulation results demonstrate that a more precise value of internal vacuum pressure is given by applying magnetic field with impulse current simultaneously in order to determine residual vacuum pressure},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2015b,

title = {An improved computational approach for thermal modeling of power transformers},

author = {Allahbakhshi, M., Akbari, A.},

year  = {2015},

date = {2015-01-01},

journal = {International Transactions on Electrical Energy Systems},

number = {25(7)},

pages = {1319-1332},

abstract = {Summary Proposed IEEE/ANSI differential equation governing top oil temperature rise, and its improvements are widely used in top oil temperature prediction and parameter estimation for power transformer loss of life calculation and diagnostic systems. Approximately, all transformer thermal models employ backward Euler method to achieve related set of equations (or regressors) and use least square error estimator for parameter estimation. In this paper, we applied a new numerical integration methodology to solve the differential equation of thermal model. Related matrix format is calculated based on the numerical integration rectangle rule. Some comparison metrics are introduced to verify and compare the proposed computation methodology with conventional discretized backward Euler equation. The proposed method was tested on simulated top oil temperature using measured ambient temperature and load data in the field. Results showed a significant and meaningful improvement in top oil temperature prediction. Variations of calculated parameters, in the presence of noise, presented the superiority and advantages of the proposed computational methodology. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2015b,

title = {Calculation of short circuit electromagnetic forces in Dryformer using finite element method},

author = {Karimzadeh, F., Akbari, A., Ardebili, M., Azizian Fard, M.},

year  = {2015},

date = {2015-01-01},

journal = {International Transactions on Electrical Energy Systems},

number = {25(3)},

pages = {433-453},

abstract = {Dryformer is a new type of oil-free power transformers which its windings are made of high voltage cable. Calculation of electromagnetic forces acting upon windings under short circuit condition is an important stage in mechanical design of Dryformer. In this paper, 2D and 3D finite element models are utilized to analyze magnetic field and calculate short circuit forces upon Dryformer windings. The radial and axial forces upon high voltage and low voltage windings are investigated in 2D and 3D models, and the results are compared with each other. The results of this paper are very useful in mechanical design of Dryformer, where sufficient bracing must be provided to prevent winding being damaged. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2015b,

title = {Advancing new techniques for UHF PDdetection and localization in the power transformers in the factory tests},

author = {Mirzaei, H., Akbari, A., Gockenbach, E., Miralikhani, K.},

year  = {2015},

date = {2015-01-01},

journal = {
IEEE Transactions on Dielectrics and Electrical Insulation},

number = {22(1)},

pages = {448-455},

abstract = {Partial discharge (PD) detection in the ultra-high frequency (UHF) range is state of the art. One of the most critical points in this detection method is adopting proper and suitable antenna design. In this paper, a new design of UHF antennas is introduced which is suitable to be used on the transformers in the HV laboratories of the manufacturers. To ensure the applicability of the new antenna, experimental UHF PD measurements are carried out on a transformer tank model as well as on the real power transformers. Installing several UHF antennas on the transformer tank to perform defect localization is also an important issue. There are rigorous limitations and lack of the places to install the antennas. This problem is almost solved by using the mentioned new antenna design. The proper positioning of the antennas is the other critical point in the UHF method. Placing the antennas in improper positions will damage the localization accuracy. In this paper, an automatic algorithm is introduced to determine the best installation positions for the antennas to enhance the localization accuracy. The efficacy of this algorithm is investigated by using the results of experimental measurements on power transformers. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2015b,

title = {Dielectric recovery process in vacuum interrupters regarding to contact materials during post arc interval},

author = {Shemshadi, A., Salavati, A., Akbari, A., Taghi Bathaee, S.M.},

year  = {2015},

date = {2015-01-01},

journal = {IEEE Transactions on Dielectrics and Electrical Insulation },

number = {22(5)},

pages = {3059-3064},

abstract = {.This investigation presents new practical achievements concerning the velocity of dielectric recovery process inside a vacuum interrupter chamber. According to Andrews- Varey equations, a new model is developed using Matlab-Simulink software. This model is used for doing a new research on inter electrode plasma diffusion, which is the most important factor during insulation recovery interval. The developed model is performed so that it can predict the ionic sheath expansion velocity and post-arc current waveform caused by transient recovery voltage (TRV). One of the faced challenges is to obtain plasma parameters to be utilized based on the previous experimental results. Considering the initial conditions and the related software model Applied to nine different contact materials, and similar 100A quenching current, the achieved results are investigated in details. The main goal is to specify the influence of material (ion mass) and other parameters on the speed of inter-electrode plasma dispersion and voltage recovery process which will guide the designer towards selecting suitable contact material with regard to TRV waveform. Furthermore the effect of TRV value which is applied to the chamber is also investigated in details. In future works this model may be developed so that it can be applied to new metallic alloys made of doped various chemical elements. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2015,

title = {A method to capture and de-noise partial discharge pulses using discrete wavelet transform and ANFIS},

author = {Jahangir, H., Hajipour, E., Vakilian, M., (...), Blackburn, T., Phung, B.T},

year  = {2015},

date = {2015-01-01},

journal = {International Transactions on Electrical Energy Systems},

number = {25 (11)},

pages = {2696-2712},

abstract = {Due to the presence of excessive noise in the recorded partial discharge (PD) current signals, de-noising of these signals is a crucial task for performing any investigation on the subject. Meanwhile, to accelerate this de-noising process a single PD pulse can be extracted from the train of those recorded pulses, followed by its de-noising. In this paper a single PD pulse is extracted from the train of recorded PD pulses, using noisy recorded data cumulative energy. A de-noising technique based on adaptive neuro-fuzzy inference systems is proposed. To verify the validity of the proposed method, four different sources of PD signals are physically simulated. The proposed method is applied on laboratory recorded signals and is compared with a conventional method which is based on discrete wavelet transform (DWT) and linear adaptive filtering method. Furthermore, the proposed algorithm is used for extraction and de-noising of single PD activities of an on-site recorded data. This method introduces an efficient pulse distortion mitigation tool which requires no adjustment of any pre-set parameter - neither for different noise levels, nor for different kind of PD pulses. This is an important feature of the proposed technique},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2013,

title = {A Novel Method for Ultra-High- Frequency Partial Discharge Localization in Power Transformers Using the Particle Swarm Optimization Algorithm},

author = {H.R. Mirzaei, A.Akbari, E.Gockenbach,M. Zanjani, K. Miralikhani },

year  = {2013},

date = {2013-01-01},

journal = {IEEE Electrical Insulation Magazine},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2013b,

title = {A novel method for ultra-high-frequency partial discharge localization in power transformers using the particle swarm optimization algorithm},

author = {Mirzaei, H.R., Akbari, A., Gockenbach, E., Zanjani, M., Miralikhani, K.},

year  = {2013},

date = {2013-01-01},

journal = {
IEEE Electrical Insulation Magazine},

number = {29(2)},

pages = {26-39},

abstract = {Nowadays, the localization of partial discharge (PD) in power transformers by measurement of ultra-high-frequency (UHF) electromagnetic (EM) waves from a PD source is receiving more attention. This method is based on comparing the differences in the arrival times, to antennas in the transformer, of EM waves emitted from the PD source. From the measured UHF signal, and factoring in the influence of the transformer active part on the EM wave propagation, the correct determination of an EM wave arrival time in the localization algorithm is a critical task that influences the accuracy of the UHF PD localization method. Nearly all weak points in the dielectric system of power transformers generate PD. These discharges gradually degrade the insulation, leading to transformer failure. It is possible to detect these defects in the early stages of PD generation by measuring and analyzing the PD data. Suitable maintenance and repair strategies can then be implemented. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2013b,

title = {A novel approach for reduction of electric field stress in vacuum interrupter chamber using advanced soft computing algorithms },

author = {Shemshadi, A., Akbari, A., Taghi Bathaee, S.},

year  = {2013},

date = {2013-01-01},

journal = {IEEE Transactions on Dielectrics and Electrical Insulation},

number = {20(5)},

pages = {1951-1958},

abstract = {This investigation presents a new algorithm for optimized internal shape design of high voltage equipments like a vacuum interrupter (VI) chamber, regarding to electric field intensity distribution pattern. At first a commercial vacuum chamber is modeled using Solid-Works and Comsol-Multiphysics softwares. The model design parameters are changed randomly to generate a new structure which is analyzed using finite element (FE) method to obtain 8 regions with maximum electric field intensity. This loop continues some times to arrange a data bank from input parameters vector and coupled output matrix for 8 internal electric field intensity components. The next stage is to train a suitable general regression neural network (GRNN) for every electric field output, separately, to form an objective functions with 8 objective components. Regarding the constrains and inequality conditions specified, a multiobjective genetic algorithm (GA) is arranged to run. A set of non-dominated points, called Pareto Front, are specified by this optimization algorithm which are edited and clustered in five sets using k-mean statistical function. In every set the point with smallest distance from the center point of that set is elite for final modeling and validation check. So the final optimized point is specified after F.E. modeling. This algorithm is studied in the case that the main shield is considered float. In continue we analyze the electric field reduction percentage achieved, which causes lower electric field stress on the insulators especially on the contact surfaces region. With respect to Fowler-Nordheim (FN) equation lower electric field causes lower field emission currents especially at the insulation recovery interval which increases the endurable transient recovery voltage (TRV) level of the chamber. Furthermore and in the future works the maximum size reduction of a vacuum interrupter chamber, or other equipment, can be performed with small change in the introduced algorithm.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2012,

title = {Influence of the airflow speed along transmission lines on the DC corona discharge loss, using finite element approach},

author = {A. Shemshadi, K. Niayesh, and A. Akbari},

year  = {2012},

date = {2012-01-01},

journal = {PHYSICS OF PLASMAS 19, },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2012b,

title = {Influence of the airflow speed along transmission lines on the DC corona discharge loss, using finite element approach},

author = {Shemshadi, A., Niayesh, K., Akbari, A.},

year  = {2012},

date = {2012-01-01},

journal = {PHYSICS OF PLASMAS 19,},

number = {19(7)},

pages = {073506},

abstract = {Corona discharge is of great interest from the physical point of view and due to its numerous practical applications in industry and especially one of the most important sources of loss in the high voltage transmission lines. This paper provides guidelines for the amount of electric loss caused by corona phenomenon occurred around a DC high voltage wire placed between two flat plates and influence of wind speed rate on the amount of corona loss using COMSOL Multiphysics. So electric potential distribution patterns and charge density diffusion around the wire are studied in this article. © 2012 American Institute of Physics},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{akbari2012b,

title = {An experimental effort to understand how behaves winding high frequency response in power transformers},

author = {Firoozi, H., Akbari, A., Ghiasi, M.I.},

year  = {2012},

date = {2012-01-01},

journal = {International Review of Electrical Engineering},

number = {7(2)},

pages = {3916-3925},

abstract = {Frequency Response Analysis (FRA) is a powerful technique for condition monitoring and fault diagnosing of power transformers. The challenge in this regards is the analysis of the transformer transfer functions due to different faults. In other words, the correlation between different faults and transfer functions is not fully yet known. The main idea in this study is that the transformer physical and insulating structure during manufacturing stages are changed. Therefore, investigations on the variations of winding transfer function in these stages can be very helpful. In this contribution the transformer winding is simulated in different manufacturing stages. All simulations performed for a 63/20kV, 30MVA power transformer based on available design information. Some measurements are also performed to verify the simulation results. The obtained results are useful to understand high frequency characteristics of winding and also can be used to interpret the changes in the transfer function due to different common faults},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2012b,

title = {Investigating partial discharge UHF electromagnetic waves propagation in transformers using FDTD technique and 3D simulation},

author = {Zanjani, M., Akbari, A., Shirdel, H.R.N., Gockenbach, E., Borsi, H.},

year  = {2012},

date = {2012-01-01},

journal = {Proceedings of 2012 IEEE International Conference on Condition Monitoring and Diagnosis, CMD },

number = {2012 6416187},

pages = {497-500},

abstract = {On-line partial discharge (PD) measurement in power transformers has become increasingly popular in recent years. Measuring PD signals at ultra high frequency (UHF) range have many advantages. So, numerical methods have been implemented to model the propagation of electromagnetic (EM) wave in power transformers. Utilizing conventional softwares, such as CST to simulate EM wave propagation in power transformers need tremendous amount of time and memory. So such packages are difficult to be used in these fields of study. In this paper we will verify the program written in C++ environment to simulate UHF wave propagation using the results obtained from CST package in small scale. Using the proposed FDTD code, it is possible to simulate EM wave propagation inside large power transformer. This task cannot be accomplished by CST software in a simple PC. To ensure the validity of the proposed codes, results of simulating EM wave propagation in small volumes such as distribution transformer is compared with CST software package results. After validation, these codes are used to model larger transformers. Finally, the characteristics of PD source are investigated using simulated PD signals detected at different sensor locations},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2012b,

title = {Investigating the partial discharge electromagnetic wave propagation in power transformers considering active part characteristics },

author = {Mirzaei, H.R., Akbari, A., Zanjani, M., Gockenbach, E., Borsi, H.},

year  = {2012},

date = {2012-01-01},

journal = {IEEE International Conference on Condition Monitoring and Diagnosis, CMD },

number = {2012 6416173},

pages = { 442-445},

abstract = {UHF partial discharge localization in power transformers is getting more interests. One of the great advantages is the immunity of the measurements from external noises due to transformer tank electromagnetic shielding. The time delay of arriving signals to two or more UHF antennas installed in different locations at transformer tank is the key parameter for accurate localization algorithms. Due to presence of active part and transformer tank, unfortunately sometimes there is not a direct path for PD electromagnetic waves to propagate from defect site to antennas positions. Through the propagation path, these waves would be reflected and attenuated striking different materials inside transformer. Some materials like core did not allow the wave to propagate through them. Some parts like windings and dielectric boards impose attenuations to wave energy. Such attenuations in some cases might be so high that energy of the parallel long paths may be stronger than the shortest path and this would result in inaccurate localization. Propagating the wave along such paths are mainly caused by reflecting the waves by transformer tank and other components. In this paper using the CST software, the effects of these issues on PD UHF wave propagation in transformers are studied. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2012b,

title = {Investigating suitable positions in power transformers for installing UHF antennas for partial discharge localization },

author = {Mirzaei, H.R., Akbari, A., Zanjani, M., (...), Gockenbach, E., Borsi, H.},

year  = {2012},

date = {2012-01-01},

journal = {IEEE International Conference on Condition Monitoring and Diagnosis, CMD},

number = {2012 6416223},

pages = {625-628},

abstract = {One of the critical points in the UHF partial discharge (PD) localization in power transformers is the installation position of the UHF antennas inside the transformer or on its tank. In the UHF localization method which is based on comparing the differences of the arrival times of the partial discharge electromagnetic waves, ideally at least four antennas must be used to have an effective localization. Mechanical limitations such as the existence of iron tank and high electric field intensity inside transformer must be considered in installing UHF antenna. Beside these problems, the effect of antennas positions on localization accuracy must be taken into account. The positions of the antennas have a direct relation with arrival time differences for potential PD positions inside transformer. In this paper a method to identify best places for antennas installation is proposed to obtain more accurate defect localization.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2011b,

title = {A method for discriminating original pulses in online partial discharge measurement },

author = {
Allahbakhshi, M., Akbari, A.},

year  = {2011},

date = {2011-01-01},

journal = {Measurement: Journal of the International Measurement Confederation},

number = {44 (1)},

pages = { 148-158},

abstract = {Partial discharge (PD) measurement is a promising method for condition assessment of insulation systems in high voltage equipments. Conventional PD measuring systems have some difficulties in the measurements especially in online conditions and noisy environments. There is a growing tendency to use new measuring systems for separation of PD pulses from different sources and rejection of external noises. In this investigation a new ultra wideband PD measuring system and relevant methodology are discussed. The proposed system uses an efficient detection method for extracting PD pulses embedded in noisy signal, meanwhile, a wavelet multiresolution analysis is applied to reduce background and communication noise level. In this paper some new and modified features for pulse classification procedure have been proposed. The proposed system, methodology and features have been implemented on a hydrogenerator and also a power transformer. Finally performance of the system is discussed},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2011b,

title = {Novel fusion approaches for the dissolved gas analysis of insulating oil },

author = {Allahbakhshi, M., Akbari, A. },

year  = {2011},

date = {2011-01-01},

journal = {Iranian Journal of Science and Technology, Transaction B: Engineering},

number = {35 (E1)},

pages = { 13-24
},

abstract = {Dissolved Gas Analysis (DGA) is the most reliable technique to identify the incipient faults in power transformers. There are several DGA techniques in use such as Doernenburg, Rogers, IEC, etc. On the other side there is an increasing tendency to combine data from multiple sources and models to achieve more reliable results than individuals. This investigation proposes two fusion approaches consisting of fusion architectures and respective combination methods to combine DGA techniques and the gas ratios utilized in these techniques. The proposed approaches in this article apply a modified flexible neuro-fuzzy and a gating network as combination methods. Various gas concentration data were used for training and validating the models. Results showed that the proposed approaches have more advantages compared to the conventional DGA techniques. Finally, the importance degree of each gas-ratio to detect each fault was investigated},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2011,

title = {A method for discriminating original pulses in online partial discharge measurement},

author = {Mehdi Allahbakhshi, Asghar Akbari},

year  = {2011},

date = {2011-01-01},

journal = {ELSEVIER, Measurement},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2011b,

title = {Application of Interactive Multiple Models in Thermal Modeling of Power Transformers},

author = {Asghar Akbari, Mehdi Allahbakhshi, Reza Golpari},

year  = {2011},

date = {2011-01-01},

journal = {European Transactions on Electrical Power},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2011b,

title = {Novel Fusion Approaches for the Dissolved Gas Analysis of  Insulating Oil},

author = {Mehdi Allahbakhshi and Asghar Akbari},

year  = {2011},

date = {2011-01-01},

journal = {Iranian Journal of Science and Technology (Shiraz Uni.)},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2011b,

title = {Application of interactive multiple models in thermal modeling of power transformers},

author = {
Akbari, A., Allahbakhshi, M., Golpari, R.},

year  = {2011},

date = {2011-01-01},

journal = {
European Transactions on Electrical Power},

number = {21(7)},

pages = {2053-2061},

abstract = {
Power transformers are one of the most expensive equipments in power systems. The efficiency and optimal utilization of these equipments are very important issues. Some factors, like temperature, moisture and oxidation can affect the solid and liquid insulations and reduce the useful life of power transformer. Temperature of a power transformer depends on the ambient temperature, present and past loading and cooling classes. Proper thermal model is essential to predict temperature in different conditions of cooling system. Such model leads to analyze useful life and improve loading and utilization of a power transformer. In this contribution a thermal model for power transformers based on the new technique of Interactive Multiple Modeling (IMM) is suggested to predict the top-oil temperature. Practical validation is carried out with measured load and temperature data of a power transformer. Consequently the prediction error for the conventional thermal model and the new suggested model based on IMM technique are compared},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2011b,

title = {Calculating Dryformer leakage reactance using analytical and finite element methods},

author = {Karimzadeh, F., Akbari, A., Ardebili, M.},

year  = {2011},

date = {2011-01-01},

journal = {International Conference on Power Engineering, Energy and Electrical Drives},

number = {6036476},

abstract = {Dryformer is an oil-free power transformer that its windings are made of high voltage cross-linked polyethylene (XLPE) cables. Leakage reactance calculation is a key step in transformer design process. Special structure of Dryformer makes conventional analytical methods useless for leakage reactance calculation in this type of transformer. In this paper, an analytical method is proposed for calculating leakage reactance of Dryformer based on its winding structure. The validity of proposed model is verified by means of 3D and 2D finite element models.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2010c,

title = {Synchronous distributed partial discharge measurement system },

author = {Azizian Fard, M., Akbari, A., Shojaee, R., Rasuli, M.A.},

year  = {2010},

date = {2010-01-01},

journal = {
International Review of Electrical Engineering },

number = {5(5)},

pages = {2478-2483},

abstract = {Partial discharge measurement is a major diagnostics method of insulation systems in high voltage equipments, which makes it convenient to assess the insulation status and its prospective condition. Here the design of a distributed modular conventional system with the capability of synchronous operation is presented. The system relays on an FPGA in each module for preprocessing and controlling purposes, where the PD signals acquired by each module are preprocessed for the extraction of common PD features in order to avoid superfluous data. The extracted potential features are temporary stored in external memories and finally delivered to host computer via serial channel for further statistical and mathematical analysis. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2010c,

title = {Suggesting an agent based design methodology for condition monitoring of high voltage apparatus},

author = {Shojaee, R., Akbari, A., Fard, M.A., Allahbakhshi, M.},

year  = {2010},

date = {2010-01-01},

journal = {Proceedings of the 2010 IEEE International Conference on Solid Dielectrics, ICSD 2010 },

number = {5568194
},

abstract = {Condition monitoring of high voltage equipments has always been a central part of condition based maintenance programs which is highly preferred by generation, transmission and distribution companies. Through their development there has been a great deal of changes in condition monitoring systems aimed at providing systems of high reliability, modularity and adaptivity as well. Multi agent systems with the aforementioned features can be appropriate means of implementing distributed, modular and intelligent monitoring systems. In this paper designing of a high voltage monitoring system based on multi agent system will be considered in which tasks are distributed among different levels where the tasks and purposes of each level are defined according to the whole goals of the system. It finally results in an intelligent multi agent system combined of different levels. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2010c,

title = {
Partial discharge defects classification using neuro-fuzzy inference system},

author = {Fard, M.A., Akbari, A., Shojaee, R., Mirzaei, H.R., Naderi, P.},

year  = {2010},

date = {2010-01-01},

journal = {Proceedings of the 2010 IEEE International Conference on Solid Dielectrics, ICSD 2010 },

number = {5568128},

abstract = {Partial discharge measurement is among the most important diagnostics methods of insulation systems in high voltage equipments, which makes it convenient to assess the insulation status and its prospective condition. Partial discharge activities may stem from various defects, and correspondingly behave differently. Since the origins of the PD activities are of major concern in insulation diagnostics, a large number of recognition methodologies have been proposed and used for this purpose. Among them, Phase Resolve Partial Discharge (PRPD) analysis has gained more attractions. However, sometimes the complexity of the patterns is of much more sophistication where utilization of intelligent based or expert system is inevitable. In this paper an Adaptive Neuro-Fuzzy Inference System (ANFIS) based classification method has been considered, where statistical features are extracted from the measured PRPD data first, then Fuzzy IF-THEN classification rules which are obtained from experts are employed in training procedures of the ANFIS model, and finally the classification of the PD defects is done automatically by the trained system, which makes it ready to be interpreted for decision making purposes.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2010c,

title = {An experimental review on application of wavelet transform on partial discharge evaluation of power transformers },

author = {
Mirzaei, H.R., Akbari, A., Allahbakhshi, M., Kharezi, M.},

year  = {2010},

date = {2010-01-01},

journal = {Proceedings of the 2010 IEEE International Conference on Solid Dielectrics, ICSD 2010 },

number = {5568076
},

abstract = {Partial Discharge (PD) measurement and analysis is now a popular method in condition monitoring and dielectric diagnosis of power transformers. Discrete Wavelet Transform (DWT) is a powerful and well known method to analyze PD data in both time and frequency domains. In this contribution, the application of this transform on de-noising of recorded PD signals, defect classification and separating PD pulses of simultaneous defects is investigated and reviewed experimentally. For this purpose, an unconventional ultra wide band acquisition system is used to detect and record PD pulses data in time domain. Experimental works including those made during on-site PD measurement on a power transformer and PD commissioning test of a dry type transformer as well as experiments on artificially made PD defects are investigated. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2010,

title = {Design of Sugeno-Type Fuzzy Logic Controller for Torque Distribution in a Parallel Hybrid Vehicle},

author = {A.Shemshadi, S.M. Bathaei, A. Akbari, S. Jalali

},

year  = {2010},

date = {2010-01-01},

journal = {International Review of Electrical Engineering (IREE)},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2010c,

title = {Localization of turn-to-turn fault in transformers using artificial neural networks and winding transfer function},

author = {Faridi, M., Kharezi, M., Rahimpour, E., Mirzaei, H.R., Akbari, A.},

year  = {2010},

date = {2010-01-01},

journal = {Proceedings of the 2010 IEEE International Conference on Solid Dielectrics, ICSD 2010 },

number = {5568131},

abstract = {
To automate the procedure of localizing turn-to-turn faults in transformers windings, a method is proposed by employing of Artificial Neural Networks (ANN). For this purpose, a specially made distribution transformer winding is used as a test object to approve the capability of proposed method. This winding is appropriately designed to perform short circuit faults between any two desired adjacent turns. Then the frequency response of winding in both healthy and faulty conditions is measured using the Low Voltage Impulse (LVI) test. Extracted features from frequency responses are used to train and test the proposed ANN. The results show that this method is able to determine the location of turn-to-turn fault in winding.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2009b,

title = {A new approach for separating internal and external PD pulses in the ultra-wide-band measuring system},

author = {Allahbakhshi, M., Akbari, A., Mirzaei, H.R.},

year  = {2009},

date = {2009-01-01},

journal = {the IEEE International Conference on Properties and Applications of Dielectric Materials},

number = {5252388},

pages = {469-472},

abstract = {
in this paper an ultra-wide-band partial discharge measuring system is introduced. These systems are approximately new. Advantages of this system such as effective noise reduction, feature extraction based on pulse waveform are discussed. A new feature for separating different types of pulses is proposed. This feature is dominant frequency of the pulse waveform. A practical partial discharge measurement using the mentioned system was done on a hydro-generator in three cases. Applying the new feature showed the effective separating performance. Keywords: Generators; Partial Discharge; online monitoring; Ultra-wide-band measurement. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}