Publications

@article{Akbari2009b,

title = {
An investigation on slot configuration in new generation of synchronous generators based on XLPE cables},

author = {Taherzadeh, M., Akbari, A., Ardebili, M.},

year  = {2009},

date = {2009-01-01},

journal = {ELECO 2009 - 6th International Conference on Electrical and Electronics Engineering },

number = {5355293},

pages = {I197-I201},

abstract = {Regarding the change of slot in high voltage synchronous generators, and the importance of slot leakage reactance in subtransient and transient short circuit currents and in the amount of synchronous reactance, this paper studies the effect of the changing of slot and conductor shape in high voltage synchronous on the amount of slot leakage reactance, using analytical formula and numerical analysis. Considering three different slot configurations for one sample high voltage synchronous generator, rated at 63kV and 25MVA, the slot leakage reactance is calculated by applying conventional formula for rectangular conductor cross-section, and using finite element method. Then, the results are compared to each other. Finally, the effect of the new slot configuration of high voltage generator on slot leakage reactance is shown. Therefore, from electromagnetic viewpoint, it has been tried to introduce a better slot configuration of high voltage synchronous generator in this paper. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2009b,

title = {New attempts in automated partial discharge identification using pulse sequence analysis},

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

year  = {2009},

date = {2009-01-01},

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

number = {5252382},

pages = {493-496},

abstract = {Measuring partial discharge and interpreting its patterns has become a common tool to recognize the type of insulation defects of high voltage equipments. Using statistical features of phase dependent patterns have the most use in PD analysis now. However, these patterns contain less information of PD pulses sequence which is in close relation with defect type. Therefore, nowadays more research studies are conducted in utilizing pulse sequence analysis (PSA) in PD classification. In this literature, a new automated PD classifier based on PSA is introduced and its application is investigated using experimental works on artificial PD defects},

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}

}

@article{akbari2008,

title = {Partial discharge localization in transformer windings using multi-conductor transmission line model},

author = {Ali Mazhab Jafari, Asghar Akbari},

year  = {2008},

date = {2008-01-01},

journal = {ELSEVIER, Electric Power Sys. Research},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2008b,

title = {Investigating Practical Experiments of Partial Discharge Localization in Transformers using Winding Modeling},

author = {Ali Mazhab Jafari, Asghar Akbari, Hasan Reza Mirzaei, Mohammad Kharezi, Mehdi Allahbakhshi},

year  = {2008},

date = {2008-01-01},

journal = {IEEE Trans. On Dielectric},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2008b,

title = {The characteristics of hardware and software modules for PD localization in power transformers using winding modeling },

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

year  = {2008},

date = {2008-01-01},

journal = {of IEEE International Symposium on Electrical Insulation},

number = {4570290},

pages = {108-111},

abstract = {
Partial Discharge localization in power transformers is an important task for test engineers. Although some theoretical methods have been proposed, there are no devices that directly guide them to a reasonable result. This paper deals with such a device and investigates the characteristics and requirements of its hardware and software modules in detail. The hardware module must be a VHF PD measuring system that enables us with single PD wave forms. The software module is based on winding modeling using transformer design data. At last the proposed hardware and software are verified experimentally},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2008b,

title = {Investigating practical experiments of partial discharge localization in transformers using winding modeling },

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

year  = {2008},

date = {2008-01-01},

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

number = {15 (4), 4591240,},

pages = {1174-1182},

abstract = {One of the well-known methods of partial discharge (PD) localization in transformers is based on winding modeling. Although the method is theoretically precise, the reliability of the method is not known in practice, because of the difficulties that arise in high frequency modeling of the winding. In this paper, to investigate the reliability of the PD localization method in practical cases, different types of PD including PD in air, PD in paper voids, PD in oil gaps and surface PD along insulator are produced. A 20 kV/0.4 kV research transformer with 6 accessible clamps along its winding and a specially prepared 63 kV winding with 30 accessible clamps are used as test objects. The generated PD pulses are injected to different clamps of the test objects and recorded at both ends of the windings by means of a wideband modern PD measuring system. A modified method based on using multi conductor transmission line model (MTLM) of transformer winding is used as PD localization method and to increase the reliability of the results, a method based on using calibration pulses is proposed. At last, the accuracy of PD localization results in the two test objects is investigated. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2008b,

title = {Partial discharge localization in transformer windings using multi-conductor transmission line model },

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

year  = {2008},

date = {2008-01-01},

journal = {Electric Power Systems Research },

number = {78 (6),},

pages = {1028-1037},

abstract = {Multi-conductor transmission line model (MTLM) of transformer winding has been used to find partial discharge (PD) location in transformers. To decrease computational complexity of the model, two methods for calculation of model parameters were studied and the most suitable method was chosen based on comparison between measured and calculated transfer functions of a 132 kV/20 kV transformer. To investigate the accuracy of MTLM in PD localization, PD pulses produced by a PD calibrator were injected into different points of a research 20 kV/0.4 kV transformer and measured at both ends of the winding. The sectional winding transfer functions computed by the model were used to refer measured PD signals to possible PD locations. Then by comparison of referred signals, PD location in the winding was estimated. © 2007 Elsevier B.V. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2008b,

title = {Partial discharge localization in transformer windings using multi-conductor transmission line model },

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

year  = {2008},

date = {2008-01-01},

journal = {Electric Power Systems Research },

number = {78 (6),},

pages = {1028-1037},

abstract = {Multi-conductor transmission line model (MTLM) of transformer winding has been used to find partial discharge (PD) location in transformers. To decrease computational complexity of the model, two methods for calculation of model parameters were studied and the most suitable method was chosen based on comparison between measured and calculated transfer functions of a 132 kV/20 kV transformer. To investigate the accuracy of MTLM in PD localization, PD pulses produced by a PD calibrator were injected into different points of a research 20 kV/0.4 kV transformer and measured at both ends of the winding. The sectional winding transfer functions computed by the model were used to refer measured PD signals to possible PD locations. Then by comparison of referred signals, PD location in the winding was estimated. © 2007 Elsevier B.V. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2008b,

title = {Partial discharge localization in transformer windings using multi-conductor transmission line model },

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

year  = {2008},

date = {2008-01-01},

journal = {Electric Power Systems Research },

number = {78 (6),},

pages = {1028-1037},

abstract = {Multi-conductor transmission line model (MTLM) of transformer winding has been used to find partial discharge (PD) location in transformers. To decrease computational complexity of the model, two methods for calculation of model parameters were studied and the most suitable method was chosen based on comparison between measured and calculated transfer functions of a 132 kV/20 kV transformer. To investigate the accuracy of MTLM in PD localization, PD pulses produced by a PD calibrator were injected into different points of a research 20 kV/0.4 kV transformer and measured at both ends of the winding. The sectional winding transfer functions computed by the model were used to refer measured PD signals to possible PD locations. Then by comparison of referred signals, PD location in the winding was estimated. © 2007 Elsevier B.V. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2008b,

title = {Partial discharge localization in transformer windings using multi-conductor transmission line model },

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

year  = {2008},

date = {2008-01-01},

journal = {Electric Power Systems Research },

number = {78 (6),},

pages = {1028-1037},

abstract = {Multi-conductor transmission line model (MTLM) of transformer winding has been used to find partial discharge (PD) location in transformers. To decrease computational complexity of the model, two methods for calculation of model parameters were studied and the most suitable method was chosen based on comparison between measured and calculated transfer functions of a 132 kV/20 kV transformer. To investigate the accuracy of MTLM in PD localization, PD pulses produced by a PD calibrator were injected into different points of a research 20 kV/0.4 kV transformer and measured at both ends of the winding. The sectional winding transfer functions computed by the model were used to refer measured PD signals to possible PD locations. Then by comparison of referred signals, PD location in the winding was estimated. © 2007 Elsevier B.V. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2008b,

title = {An algorithm for partial discharge localization in transformers using winding design data },

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

year  = {2008},

date = {2008-01-01},

journal = {Proceedings of 2008 International Conference on Condition Monitoring and Diagnosis, CMD 2008 },

number = {4580433},

pages = { 919-922
},

abstract = {
In this paper an algorithm for PD localization based on using multi-conductor transmission line model is introduced. In this algorithm sectional winding transfer functions are computed using the winding model. To calculate the parameters of the model including resistances, inductances and capacitances between different turns of the winding, it is necessary to have design data of the transformer. Since different designs are used for different transformers, it is necessary to investigate the needed design data for the algorithm for different types of winding structures. It is shown in this paper that the algorithm can be generalized for a wide range of transformer designs. The validity of the algorithm is verified by performing PD test on a 15.75kV/230kV, Δ/Y, 200 MVA, step-up power transformer. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2008b,

title = {Experimental investigation of PD diagnosis based on consecutive pulses data},

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

year  = {2008},

date = {2008-01-01},

journal = {Proceedings of 2008 International Conference on Condition Monitoring and Diagnosis, CMD 2008 },

number = {4580206,},

pages = {1262-1265},

abstract = {
Nowadays partial discharge (PD) measurement and analysis has known as a most effective tool in insulation monitoring of high voltage (HV) equipments. Almost all types of insulation defects is more or less accompanying with PD activities, while each has its own special patterns. To have a reliable estimation of defect type, patterns with high recognition potential should be used. Recently some studies have been made on patterns which are based on difference of excitation voltage magnitude at the instant of occurring PD pulses. The reports show good results, however, more investigations are needed to make the method applicable in practice and ensure the uniqueness of mentioned patterns for each defect type. For this purpose some tests on artificial PD defects as well as real PD activities in power transformers have been experienced and the test condition effects on patterns have been investigated. The results of these experiments are studied in this contribution},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2007b,

title = {
Document
Investigating suitable features for partial discharge localization in power transformer },

author = {Homaei, M., Mazhab Jafari, A., Akbari, A.},

year  = {2007},

date = {2007-01-01},

journal = {Proceedings of 2008 International Conference on Condition Monitoring and Diagnosis, CMD 2008 },

number = {4580434,},

pages = { 923-926},

abstract = {
It has been shown in the literature that Partial Discharge (PD) pulses can be localized in transformer windings successfully using sectional winding transfer functions. But it is necessary to have the transformer design data to use this method. So the method can not be employed in the cases that transformer design data are not available. Another method for estimating PD location in transformers is based on using extracted features from single PD pulse waveforms. This method does not need transformer design data. In this paper it is tried to find suitable features for PD localization. For this purpose, a specially prepared research transformer is employed and different type of PD are generated and applied to different points along the winding and are measured by means of a modern VHF PD measuring system. The features extracted from different transforms like KLT, DST, DCT and HADAMARD transforms are investigated and PD localization results are analyzed.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2006b,

title = {Assessment of drying quality for power transformer during manufacturing process using variation of transfer function},

author = {Akbari, A., Firoozi, H., Borsi, H., Kharezi, M.},

year  = {2006},

date = {2006-01-01},

journal = {Annual Report - Conference on Electrical Insulation and Dielectric Phenomena, CEIDP },

number = {4105382, },

pages = { 113-116
},

abstract = {The drying process is one of the most important tasks in transformers manufacturing stages. The drying quality in this stage is directly proportional to transformer lifetime. In this contribution, drying process at manufacturing site has been evaluated by use of Frequency Response Analysis (FRA). The measured transfer functions of power transformer during the stage of drying are analyzed. Using Artificial Neural Network (ANN), a method has been proposed to give an estimate for required time for drying process. Results show that the ANN could well forecast the required time for drying if the ANN is trained using the measured patterns. The estimation obtained from this method is valid for all the transformers which have the same design. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2006b,

title = {
Analyzing dynamic of moisture equilibrium in oil-paper insulation in power transformers for efficient drying},

author = {Akbari, A., Dehpahlevan, S., Borsi, H.},

year  = {2006},

date = {2006-01-01},

journal = {Annual Report - Conference on Electrical Insulation and Dielectric Phenomena, CEIDP },

number = {4105491, },

pages = { 545-548},

abstract = {Moisture equilibrium in oil-paper insulation is dependent on temperature and the condition of power transformer. There exist balance charts for the percent of moisture in oil or in paper insulation at different temperatures in steady state but the dynamic of immigrating water from oil in to paper insulation and vice versa is very complex so an appropriate mathematical model has to be used to analyze the phenomena. In the other hand the dynamic of water exchange between oil and cellulose in different conditions is very important for optimum drying of aged power transformers particularly when drying performed on-site. In this contribution the equilibrium of moisture in oil-paper insulation based on temperature and transformer parameters is analyzed and the application of this analysis is illustrated for an efficient on-line drying system for power transformers. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbarii2005,

title = {Effect of asymmetrical dimensions in Short circuit forces of power transformers },

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

year  = {2005},

date = {2005-01-01},

journal = {Proceedings of the Eighth International Conference on Electrical Machines and Systems 3},

number = {1575055, },

pages = { 1746-1749},

abstract = {Calculation of the Short circuit forces is very important in power transformer design. The main goal of this paper is calculation of these forces along the LV&HV windings in power transformer by using Finite Element Method (FEM). After that we will try to describe how forces are changing by increasing of asymmetrical dimensions and misalignment of LV&HV electrical centers. Ultimately by using these approach briefly aforementioned will help us in designing procedure},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2004b,

title = {A novel database format for partial discharge monitoring and evaluation, based on the information of single PD pulses},

author = {Akbari, A., Akbari, A., Borsi, H., Gockenbach, E., Werle, P.},

year  = {2004},

date = {2004-01-01},

journal = {Proceedings of the 2004 IEEE International Conference on Solid Dielectrics ICSD 2004},

number = {2},

pages = {. 672-675},

abstract = {Numerous wide-band partial discharge detection and measurements have shown excellent results in order to diagnose and to evaluate high voltage apparatus. The shape of single PD pulses can be gathered with this method of measurement in time domain, if the signal is sampled and digitized with sufficient sampling frequency and resolution. There is a lot of information in these single PD pulses which can be used for evaluation diagnosis and monitoring of high voltage devices. As new monitoring systems based on wide-band partial discharge measurements are under development by many researchers and specialists a common format for date processing particularly for database systems is necessary. In this contribution a novel format for a database system for PD monitoring and evaluation systems is suggested. It is shown, that saving special features of single PD pulses not only causes a reduction of the huge amount of data to a limited value but also, that the real useful information of PD pulses can be reconstructed easily. A PD monitoring system operating based on this database format is introduced, as well as the advantages of this format for data reduction. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2004b,

title = {Experiences with a Non-invasive Capacitive Sensor for On-line Partial Discharge Detection in Power Transformers},

author = {Akbari, A., Borsi, H., Gockenbach, E., Hadighi, M.},

year  = {2004},

date = {2004-01-01},

journal = {ETG-Fachberichte (Energietechnische Gesellschaft im VDE) },

number = {97},

pages = {301-304},

abstract = {Most power transformers are equipped with special capacitive connections in the lower part of the bushing (bushing tap). By means of these connections partial discharge could be detected and measured in high frequency ranges but the poor earthing of these connections in PD measuring device may suffer the voltage distribution along the bushing. Additionally some of the old transformers haven't this facility and because of the ageing, online PD measurements are also necessary for these devices. This contribution suggests an appropriate method to equip the transformers with a non-invasive capacitive PD sensor. This sensor particularly is suitable for on-line PD measurement and can be adapted to existing transformers. The optimisation method for this type of sensor is suggested and the experiments in the laboratory and also on-site are reported. The effect of various parameters on the performance of the sensor is described and the optimisation method for this type of sensor is suggested as well. The use of this sensor allows the partial discharge detection and localisation within a transformer and contributes therefore to a better monitoring and diagnostic of power transformers. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2002,

title = {Transfer Function based Partial Discharge Localisation in power Transformers},

author = {Akbari, Borsi, Werle},

year  = {2002},

date = {2002-01-01},

journal = {IEEE Electrical Insulation Magazine  },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akbari2002b,

title = {Transfer function-based partial discharge localization in power transformers: A feasibility study},

author = {Akbari, A., Werle, P., Borsi, H., Gockenbach, E.},

year  = {2002},

date = {2002-01-01},

journal = {IEEE Electrical Insulation Magazine },

number = {18 (5),},

pages = { 22-32},

abstract = {A study of transfer function-based partial discharge (PD) localization in power transformers was presented. Two techniques for electric PD measurements namely, narrow band and wide band were discussed. The use of sectional winding transfer functions (SWTF) for online PD evaluation in power transformers which has several advantages was also discussed. The advantages are: localization of PD sources, discrimination between PDs inside or outside of the transformer, and evaluation of actual PD amplitudes along the winding. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}