A study of insulation failure in a high voltage current transformer
- Authors: Jimoh, A. A. , Mahlasela, V. S. , Nicolae, Dan-Valentin
- Date: 2005
- Subjects: Electric power transmission
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/22348 , uj:16190 , ISBN: 9075815085 , Citation: Jimoh, A.A., Mahlasela, V.S. & Nicolae, D.V. 2005. A study of insulation failure in a high voltage current transformer. EPE 2005 Conference, Dresden, Germany, 11-14 September 2005. DOI:10.1109/EPE.2005.219752
- Description: Abstract: The ageing and deterioration of insulation in high voltage (HV) plants have been a source of concerns to utilities. Breakdown of insulation leads to failures of HV equipment. The ageing and eventual failure of insulation in a high voltage curTent transformer (JHVCT) is the subject of investigation in this paper. A lumiiped parameter model ofHVCT is developed. This model is used to study the influlence of deteriorating and failed iinsulation on the state variables of the HVCT. Somie possible scenarios that could lead to a CT failure are investigated in this paper. For all the scelarios considered, steady alid transient equations relating the state variables of the mlodel have been developed and analyzed. The objectives of these analyses are to establish the behavioural claracteristics of the state variables, establish the interactions between these variables, and investigate the possible generations of harmonics under the various scenarios of deteriorating and outright failure of insulation in the CT. The paper concludes with a discussion of the results obtained
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Performance analysis of a three-phase induction motor with capacitance injection
- Authors: Jimoh, A. A. , Nicolae, Dan-Valentin
- Date: 2006
- Subjects: Three-phase machines , Induction motors , Reactive compensation , Power factor correction
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/22554 , uj:16209 , Citation: Jimoh, A.A. & Nicolae, D.V. 2006. Performance analysis of a three-phase induction motor with capacitance injection. OPTIM, 10th International Conference on Optimization of Electrical and Electronic Equipments, 17-20 May, 2006, Brasov, Romania.
- Description: Abstract: In this paper a static switched capacitor with an auxiliary three-phase stator winding, which is only magnetically coupled to the stator main winding, is explored for improving the starting and operating power factor of a three-phase induction motor. The scheme improves the power factor of the motor without compromising significantly on other performances. Important advantages of the scheme include preventing harmonics in the line current, and eliminating regeneration possibility as well as preventing high inrush currents at starting.
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Controlled capacitance injection into a three-phase induction motor through a single-phase auxiliary stator winding
- Authors: Jimoh, A. A. , Nicolae, Dan-Valentin
- Date: 2007
- Subjects: Fusion power plants , Electromagnetic induction , Reactor fuel reprocessing
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/18755 , uj:16039 , Citation: Jimoh, A.A. & Nicolae, D.V. 2007. Controlled capacitance injection into a three-phase induction motor through a single-phase auxiliary stator winding.IEEE International Electric Machines and Drives Conference, Antalya, Turkey, May 03-05, 2007:1183-1188. DOI:10.1109/IEMDC.2007.383598
- Description: Abstact: In this paper a controlled static switched capacitor three-phase auxiliary winding fed by a three-phase PWM with single-phase auxiliary winding, which is only magnetically inverter is proposed with some positive results. This solution coupled to the stator main winding, is explored for improving the is, however, complex and there are some doubts about the starting and operating power factor of a three-phase induction controller presented. Other solution presented in [7, 8] is motor. The scheme improves the power factor of the motor applicable only to a wound rotor machine, as the rotor is without compromising significantly on other performances. Important advantages of the scheme include preventing required to be connected to an external circuit. harmonics in the line current, and eliminating regeneration In this paper a single-phase stator auxiliary winding that is possibility as well as preventing high inrush currents at starting
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Controlled power flow capacitive divider for electric power tapping
- Authors: Jimoh, A. A. , Munda, J. , Britten, A. C. , Nicolae, Dan-Valentin
- Date: 2006
- Subjects: Electric power systems , Capacitance meters
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/15982 , uj:15724 , ISBN: 1-4244-0121-6 , Citation: Jimoh, A.A. et al. 2006. Controlled power flow capacitive divider for eletric power tapping. In: Proceedings of the 12th International Power Electronics and Motion Control Conference, 30 August-1st September, 2006, Portoroz. DOI: 10.1109/EPEPEMC.2006.4778611-1477
- Description: Abstract: Capacitive divider systems for tapping electric power from high voltage transmission lines are known to exhibit certain detrimental problems of stability, sub-resonance harmonic oscillations, and ferroresonance when coupled with non-linear loads. On the other hand, they can improve reactive power flow, power factor and contribute to improved harmonic filtration of the larger power system. This paper, therefore, proposes a controlled power flow conditioner as an essential integral component of a capacitive divider system to control power transfer between the high voltage transmission line, capacitive divider system, and the load. The ultimate objective of this conditioner is to mitigate or minimize the attendant problems associated with coupling the system to the load, and optimize the derivable benefits to the larger network.
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Novel heuristic and SVM based optimization algorithm for improving distribution feeder performance
- Authors: Jordaan, J. A. , Nicolae, Dan-Valentin , Jimoh, A. A.
- Date: 2012
- Subjects: Transmission , Electric transformer
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/17526 , uj:15895 , Citation: Jordaan, J.A., Nicolae, D.V. & Jimoh, A.A. 2012. Novel heuristic and SVM based optimization algorithm for improving distribution feeder performance. In: The 2012 International Joint Conference on Neural Networks. DOI;10.1109/IJCNN.2012.6252616-5. , DOI;10.1109/IJCNN.2012.6252616
- Description: Abstract: Secondary distribution networks generally perform as well as its LV feeders are performing. The main problem that a feeder is experiencing would be the load unbalancing due to the stochastic nature of its individual single-phase loads: larger losses in certain phases accompanied by bad voltage regulation and voltage unbalance. In order to address this problem, it may be economical to install apparatus to automatically balance or partially balance the loads progressing from the end of the feeder towards the front using smart devices based on a three-ways switch selector and an artificial intelligence algorithm to minimize the neutral current. The main idea behind this paper is therefore to keep the three phases progressively balanced along the whole length of the line. A Support Vector Machines (SVM) implementation and a heuristic method are presented as the numerical algorithms
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Torque ripple analysis of three-phase induction machines with non-uniform coil groups distribution
- Authors: Muteba, M. , Jimoh, A. A. , Nicolae, Dan-Valentin
- Date: 2013
- Subjects: Electronic motors , Electrostatic induction , Electric machinery induction
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/18069 , uj:15956 , ISBN: 978-1-4673-4974-1 , Citation: Muteba, M., Jimoh, A.A., & Nicolae, D.V. 2013. Torque ripple of three-phase induction machines with non-uniform coil groups distribution. IEEE International Electric Machines and Drives Conference (IEMDC2013), 12-15 May 2013, Chicago, USA. DOI: 10.1109/IEMDC.2013.6556313
- Description: Abstract Please refer to full text to view abstract
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Torque ripple reduction in five-phase induction machines using mixed winding configurations
- Authors: Muteba, M. , Jimoh, A. A. , Nicolae, Dan-Valentin
- Date: 2012
- Subjects: Torque ripple , Winding combinations , Induction machines
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/17823 , uj:15929 , ISBN:9781467301428 , Citation: Muteba, M.,Jimoh, A.A. & Nicolae, D.V. 2012. Torque ripple reduction in five-phase induction machines using mixed winding configurations. Electrical Machines(ICEM), 2012 xxth International conference:512-518.DOI:10.1109/ICEM!Mach.2012.6349918
- Description: Abstact: In this paper, the authors take a particular look at the effects of combination of different stator winding configurations in a 40 stator slots, 2-pole, and five-phase induction machine. They show, through computer simulation, that the combination of double and triple layer with 19/20 coil pitch reduced the torque ripple from 19.1%, for the conventional single layer full pitch, and from 10.6 %, for the conventional double layer with 19/20 coil pitch having the same rating, down to 8.7 % while maintaining the torque average. The same has to be said for the double combination which is the combination of double and triple layer combined with slot shift and coil side shift in one slot having 9/10 coil pitch. This double combination reduces tremendously the torque ripple from 28.8 %, for a conventional double layer 9/10 coil pitch, down to 10.2 % and still maintained the torque average. Some other winding combinations reduce both average and torque ripple
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DC current source to voltage source CT-based converter
- Authors: Nicolae, Dan-Valentin , Jimoh, A. A. , Van Rensburg, J. F. J.
- Date: 2007
- Subjects: Energy storage , Transformer substations
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/20504 , uj:16106 , Citation: Nicolae, D.V., Jimoh, A.A. & Van Rensburg, J.F.J. 2007. DC current source to voltage source CT-Based converter,International Aegean Conference on Electric Machines and Power Electronics & Electromotion Joint Conferences, Bodrum, Turkey, September 10-12, 2007:665-670. DOI10.1109/ACEMP.2007.4510587
- Description: Abstract: As generally known there is no energy transfer between a dc current and a current transformer. After a brief overview of other methods for tapping energy from the high voltage direct current transmission line, this paper presents the concept of a new dc to ac current source converter utilizing a current transformer. The advantage of this converter is that it is connected in series to the dc line and that at any moment in time the current flow is kept continuous. This paper presents the concept of the converter and simulation results.
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Overview of tapping methods from high voltage transmission lines
- Authors: Nicolae, Dan-Valentin , Jimoh, A. A. , Van Rensburg, J. F. J. , Case, M. J.
- Date: 2005
- Subjects: Tapping tools , High-voltage accelerators
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/22415 , uj:16200 , ISBN:9536037432 , Citation: Nicolae, D.V., Siti, M.W. & Jimoh, A.A. 2005. Overview of tapping methods from high voltage transmission lines. EDPE 2005 Conference, Dubrovnik, Croatia 26-29 September 2005.
- Description: Abstract: This paper takes an overview of various electric energy tapping methods from high voltage transmission lines.Some of these have been studied and implemented previously, some of them are in advance stage of implementation and other new methods have just been started and they are at the initial stage of modeling and simulation. this paper briefly covers the tapping methods for ac transmission lines including two new methods that are at the final stage of research. Dc transmission presents a more challenging situation, but this paper manages to present a few new methods for energy tapping.
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LV self balancing distribution network configuration for minimum losses
- Authors: Nicolae, Dan-Valentin , Siti, M. W. , Jimoh, A. A.
- Date: 2009
- Subjects: Distribution systems , Electric networks , Low voltage systems
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/21377 , uj:16144 , ISBN: 978-1-4244-2235-7 , Citation: Nicolae, D.V., Siti, M.W. & Jimoh, A.A. 2009. LV self balancing distribution network configuration for minimum losses. Proceedings of the IEEE PowerTech Conference, 26-02 July, 2009, Bucharest, Romania. DOI: 10.1109/PTC.2009.5282233
- Description: Abstract: please refe to full text to view abstract Please refer to full text to view abstract
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Multilevel high power converters for reversible power flow between utilities and power pool transmission corridor
- Authors: Nnachi, A. F. , Jimoh, A. A. , Nicolae, Dan-Valentin
- Date: 2007
- Subjects: Circuit breakers , Wind-powered generation , Power transmission
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/20003 , uj:16066 , ISBN 078038606x , Citation: Nnachi, A.F., Jimoh,A.A. & Nicolae, D.V. 2007. Multilevel high power converters for reversible power flow between utilities and power pool transmission corridor. IEEE AFRICON'07, Windhoek, Namibia, 26-28 September 2007:1-8. DOI:10.1109/AFRCON.2007.4401473
- Description: Abstract: Multilevel converters have emerged as the state of the art high power conversion for applications in reversible power flow. Electric power could be tapped from or injected to the grid regardless of the discrepancies in voltage levels, frequency, phase number and different modes of operation of the grid and the system. This paper presents an overview of different topologies of multilevel converters and modulation strategies with a verification of back-to-back neutral point converter for bidirectional power flow application
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Dynamic model and control of power converters for grid connected renewable energy systems
- Authors: Nnachi, A. F. , Nicolae, Dan-Valentin , Jimoh, A. A.
- Date: 2008
- Subjects: Electric current converters , Renewable energy sources
- Language: English
- Type: Conference procedings
- Identifier: http://hdl.handle.net/10210/20449 , uj:16099 , Citation: Nnachi, A.F., Nicolae, D.V. & Jimoh, A.A. 2008. Dynamic model and control of power converters for grid connected renewable energy systems. Proceedings of the Second IASTED Africa Conference Power and Energy Sysyems (Africa PES 2008), 8-10 September, 2008, Gaborone, Botswana.
- Description: Abstract: In order to investigate certain dynamic events of a grid connected renewable energy system (RES), a systematic model and control is developed. The RES with its converter is taken as a controlled dc current source and the grid side converter model is based on approximate power balance of the dc-link and the ac-side. Here an AC-side decoupled current controller in dq reference frame and simplified net dc-bus voltage controllers are implied. Among different dynamic events that is studied, the response of the system during three-phase to ground fault, step change in reference DC voltage, active and reactive power change are studied and presented.
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Synchronous reluctance machine with controlled capacitance injection
- Authors: Ogunjuyigbe, A. S. O. , Jimoh, A. A. , Nicolae, Dan-Valentin , Agee, J. T.
- Date: 2008
- Subjects: Capacitators , Switched capacitator circuits
- Language: English
- Type: Conference procedings
- Identifier: http://ujcontent.uj.ac.za8080/10210/382760 , http://hdl.handle.net/10210/18737 , uj:16038 , Citation: Ogunjuyigbe, A.S.O. et al. 2008. Synchronous reluctance machine with controlled capacitance injection. OPTIM'08, 22-24 May, Brasov, Romania. DOI: 10.1109/OPTIM.2008.4602384
- Description: Abstract This paper describes a detailed analysis, verified by practical experimental results, of a synchronous reluctance machine with two similar stator windings and capacitance injection using a static switch. The steady state equivalent circuit is developed and used to investigate leading capacitance injection into the machine via a balanced three phase auxiliary winding that is only magnetically coupled to the main winding. The scheme was found to improve the torque and power factor performance of the machine as well as reduce harmonics in the line current. Two switching topologies were utilized for the static control in this arrangement, and both were found to present good and comparable results. Experimental results corroborate the simulations.
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Analysis of synchronous reluctance machine with magnetically coupled three-phase windings and reactive power compensation
- Authors: Ogunjuyigbe, A. S. O. , Jimoh, A. A. , Nicolae, Dan-Valentin , Obe, E. S.
- Date: 2010
- Subjects: Synchronous machinery
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/18578 , uj:16017 , ISSN :17518660 , Citation: Ogunjuyigbe, A.S.O. et al. 2010. Analysis of syhnchronous reluctance machine with magnetically coupled three phase windings and reactive power compensation. IET Electric Power Applications, 4(4):291-303. , DOI:10.1049/iet-epa.2009.0134
- Description: Abstract: Synchronous reluctance machine with simple salient rotor is known to have poor power factor because of its poor reactance ratio. This study presents the use of an auxiliary winding attached to a balanced capacitor to improve the effective reactance ratio as well as the performance characteristics of synchronous reluctance machine. A unique feature of this configuration is that although the machine runs at synchronous speed, the effective reactance ratio of the machine can be improved by appropriate sizing of the capacitor attached to the auxiliary winding, with the constraint of the ampere turn rating of the auxiliary winding. The operational characteristics of a simple salient rotor synchronous reluctance machine equipped with this configuration were investigated and shown to have a desirable performance. How the effective reactance ratio, power factor and airgap flux distribution depend on the size of capacitor attached to the auxiliary winding is determined using a simplified mathematical model of the system. Analytical results and experimental measurements are in good agreement, and demonstrate the effectiveness and benefits of the configuration
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Test results on synchronous reluctance machine with auxilliary winding for leading reactive power injection
- Authors: Ogunjuyigbe, A. S. O. , Jimoh, A. A. , Nicolae, Dan-Valentin
- Date: 2008
- Subjects: Synchronous machinery , Performance standards , Capacitance injection
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/16468 , uj:15776 , Citation: Ogunjuyigbe, A.S.O., Jimoh, A.A. & Nicolae, D.V. 2008. Test results on synchronous reluctance machine with auxilliary winding for leading reactive power injection. Proceedings of the second IASTED Africa Conference Power and Energy Systems (AfricaPES 2008)September 8-10, 2008, Gaborone, Botswana
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Improving synchronous reluctance machine performance by direct capacitance injection through an auxiliary winding
- Authors: Ogunjuyigbe, A. S. O. , Jimoh, A. A. , Nicolae, Dan-Valentin
- Date: 2007
- Subjects: Synchronous generators , Capacitors , Power-factor meters
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/20415 , uj:16094 , Citation: Ogunjuyigbe, A.S.O., Jimoh, A.A. & Nicolae, D.V. 2007. Improving synchronous reluctance machine performance by direct capacitance injection through an auxiliary winding. ICEMS’07 International Conference on Electrical Machines and Systems 2007, October 8-11, Seoul Olympic Parktel, Seoul, Korea:1055-1060
- Description: Abstract: Synchronous reluctance machine with a conventional rotor structure and a 3-phase auxiliary winding attached to a balanced capacitance for power factor improvement will find application in high speed , high power drives. This paper presents an understanding of its operation using the electromagnetic as well as the electric circuit concepts. Analytical and simulation results of this machine configuration show that the torque as well as the power factor performance is better compared to conventional reluctance machine.
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Synchronous reluctance machine with magnetically-coupled, double three-phase windings
- Authors: Ogunjuyigbe, A. S. O. , Obe, E. S. , Nicolae, Dan-Valentin , Jimoh, A. A.
- Date: 2009
- Subjects: Electromagnetism , Electric transformers
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/22421 , uj:16198 , Citation: Ogunjuyigbe, A.S.O, et al. 2009. Synchronous reluctance machine with magnetically-coupled, double three-phase windings. Proceedings of the Electromotion Joint Symposium, 1-3 September 2009, Lille, France.
- Description: Abstract: Please refer to full text to view abstract Please refer to full text to view abstract
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Performance analysis of capacitance compensated dual stator winding synchronous reluctance machine
- Authors: Ogunjuyigbe, A. S. O. , Jimoh, A. A. , Nicolae, Dan-Valentin , Obe, E. S.
- Date: 2010
- Subjects: Capacitance meters , Synchronous machinery , Torque
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/18633 , uj:16024 , ISSN:1827-6660 , Citation: Ogunjuyigbe, A.S.O. et al. 2010. Performance analysis of capacitance compensated dual stator winding synchronous reluctance machine. International Review of Electrical Engineering,5(2), April 2010:437-446
- Description: Abstract: Synchronous reluctance machine with simple salient rotor are known to have poor power factor because they have a low effective reactance ratio. This paper used a 3 phase auxiliary winding and balanced capacitance compensation to ifluence the effective reactance ratio of a synchronous reluctance machine with simple salient rotor structure, such that its power factor and torque/ampere performance is improved. A mathematical model and dq equivalent circuit suitable for dynamic and steady state analysis was developed and used to study the synchronous operation of this machine.Analytical as well as experimental results for a 4-pole, 36 slots simple salient rotor reluctance machine showed that the effective reactance ration increased with the capacitance size, and the machine operated at a maximum power factor of 0.969 without altering the geometry of the rotor. the torque per ampere of the machine also improved with the size of capacitor attached to the auxilary winding.
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On-line remote and automatic switching of consumers' connection for optimal performance of a distribution feeder
- Authors: Popoola, O. , Jimoh, A. A. , Nicolae, Dan-Valentin
- Date: 2007
- Subjects: Phase transformations , Voltage-frequency converters
- Language: English
- Identifier: http://hdl.handle.net/10210/20144 , uj:16073 , ISBN:078038606x , Citation: Popoola, O., Jimoh, A.A. & Nicolae, D. 2007. On-line remote and automatic switching of consumers' connection for optimal performance of a distribution feeder, IEEE AFRICON’07, Windhoek, Namibia, 26-28 September, 2007:1-6. DOI:10.1109/AFRCON.2007.4401536
- Description: Abstract: Load balancing on phases is performed using a conventional trial and error approach. With this approach, service interruption is unavoidable; hence rearrangement of consumers load distribution points on phases cannot be performed frequently. Also phase voltage and current imbalances might improve using this approach but the change does last for too long. To get the secondary distribution to operate at its optimal performance, a technique in the form of remote and automated technology is needed. This paper contributes such a technology at the low voltage side of the distribution network. The proposed static transfer switching technology is based on the open-transition switch that enables transfer or arrangement of consumer loads in a three-phase system within milliseconds and supervisory control system for effective co-ordination, computational and control of other intelligent units
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On-line automatic switching of consumers' connections for improved performance os a distribution feeder
- Authors: Popoola, O. , Jimoh, A. A. , Nicolae, Dan-Valentin
- Date: 2009
- Subjects: Electric power distribution , Electric networks
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/21132 , uj:16116 , ISBN: 978-1-4244-3811-2 , Citation: Popoola, O., Jimoh, A.A. & Nicolae, D.V. 2009. On-line automatic switching of consumers' connections for improved performance os a distribution feeder. Proceedings of the IEEE Power Systems Conference & Exposition, 15-18 March, 2009, Seattle, USA. DOI: 10.1109/PSCE.2009.4840160
- Description: Abstract: Resolving imbalances on phases is performed using conventional trial and error approach which involves service interruption. Phase current and voltage may improve however the resultant effect does not last for too long. To improve the performance of the secondary distribution system there is a need for an on-line and automating technology. The aim of this paper is to pioneer a method and technology for resolving imbalances in a secondary distribution system as a result of the uneven distribution of single phase load across a three phase power system. The technology developed involves monitoring, acquisition/display of collected data and self changing switching actions electronically for rearrangement or transfer of consumer loads. The proposed switching technology is based on opentransition switch that enables transfer or rearrangement of consumer loads in a three-phase system within milliseconds with supervisory control system. Validation of the proposed technology was carried out using these methodologies: Matlab (Simulink), Virtual Instrumentation-Lab VIEW and Hardware implementation.
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