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International Journal of Engineering Trends and Technology (IJETT) – Volume 48 Number 4 June 2017Transformer Inrush Current Mitigation forSeries Voltage Sag CompensatorAnil Kumar Pathak1Dr. A. K. Jhala2 Pramod Kumar Rathore31M. Tech Department of Electrical & Electronics Engineering RKDF-CE, Bhopal (MP) IndiaAssociate Professor Department of Electrical & Electronics Engineering RKDF-CE, Bhopal (MP) India3Assistant Professor Department of Electrical & Electronics Engineering RKDF-CE, Bhopal (MP) India2Abstract- Manufacturing industries are located inindustrial park. Survey results suggest that 90% ofinterruption at industrial facilities is related voltagesag. An inrush mitigation technique is proposed andimplemented in a synchronous reference frame sagcompensator controller.Thevoltagesagcompensator is based on three phase voltage sourceinverter and a coupling transformer for serialconnection. In various companies voltage sag mayaffect many manufactures and may reduce theefficiency of the system which results sufficientlosses in the power system. It is the most costeffective solution against voltage sags. When voltagesag happen, the transformers, which are ofteninstalled in front of critical loads for electricalisolation, are exposed to the disfigured voltages anda DC offset will occur in its flux linkage. Atransformer inrush may occur at the start of sagcompensator. This over current may damage theinrush protection of the series connected inverterand the transformer output voltage is greatlyreduced due the magnetic saturation. When thecompensator restores the load voltage, the fluxlinkage will be driven to the level of magneticsaturation and severe inrush current occurs. Thecompensator is likely to be interrupted because of itsown over current protection. This paper proposes aninrush current mitigation technique together with astate-feedback controller for the Voltage sagcompensator.Keywords- SVPWM, Inrush current, Voltage sagcompensator.I. INTRODUCTIONTo strengthen the power network stability bymitigating the power quality issues. The study showshow much work is done in the field of power qualityand what can be done to increase reliability andstability.The main objective of the dissertation can begrouped as follows-ISSN: 2231-5381 Balancing the active and reactive power in powersystem. To maintain voltage profile across power systemby reducing the inrush current in the distributionsystem. Various methods and their effect on distributionsystem. To study the harmonic distortion due to variousmethods used for inrush current mitigation.Problem Formulation: The Electrical Power Systemis a very large network in which number of powerquality issues may occurs such as voltage sag/swell,harmonics, interruptions, transients, voltagefluctuation, noise, notching. In a power systemdifferent types of loads are connected across loadside as well as source side of system. In survey it isfound that most of the interruption at industrialfacilities is voltage sag related. Voltage sag is a mostinfamous problem as it goes on affecting a largenetwork.As the power network, consist of large numbers oftransformers which are affected by inrush currentdrawn due to sudden loading. Hence inrush currentacross the transformer also create the voltage sagwhich is not addressed in any voltage sagcompensator. A system to mitigate the inrush currentis required to minimize the voltage sag in thenetwork. Hence proposed mitigation techniquereduces the inrush current in distribution powersystem.Work Methodology:The dissertation will focus on the concept ofmitigation technique of power quality issues (inrushcurrent mitigation) and how they can be used tomaintain the power distribution system reliabilityand stability. Simulation of inrush mitigation technique withseries voltage sag compensator in MATLAB andits behavior when disturbances are applied on thesystem under critical load condition and also withdifferent control technique PWM & SVPWM. Study of different control techniques used formitigation.http://www.ijettjournal.orgPage 187

International Journal of Engineering Trends and Technology (IJETT) – Volume 48 Number 4 June 2017 Simulation and implementation of mitigationtechnique with series voltage sag compensator inabove simulation of test system. Analysis, performance and calculation of inrushmitigation technique with series voltage sagcompensator for different as well as online andoffline load conditions.II. PROPOSED METHODOLOGYWhen the grid is normal, the compensator isbypassed by the thyristors for high operatingefficiency. When voltage sags occur, the voltage sagcompensator injects the required compensationvoltage through the coupling transformer to protectsensitive loads from being interrupted by sags.However, certain detection time (typically within4ms) is required by the sag compensator controllerto identify the sag event. And the load transformer isexposed to the. Deformed voltage from the sagoccurrence to the moment when the compensatorrestores the load voltage. Also its short duration, thedeformed voltage causes magnetic flux linkagedeviation inside the load transformer, and magneticsaturation may easily occur when the compensatorrestores the load voltage, thus results in inrushcurrent. The inrush current could trigger the overcurrent protection of the compensator and lead tocompensation failure thus this paper proposes inrushmitigation technique by correcting the flux linkageoffsets of the load transformer. This technique canbe seamlessly integrated with the state feedbackcontroller of the compensator.compared with reference phase voltages. A carrierindex, I, is defined to designate the carrier regions inwhich the reference phase voltages lie during thesampling interval under consideration. When n isodd. The carrier index I for the top carrier is 1, and itincreases in steps of 1 towards the bottom carriers.The carrier index I for the lowest carrier is equal to(n-1). During a sampling interval, the carrier indices,, and (which can be from 1 to (n-1), for A, Band C phases, respectively, are determineddepending on the carrier region in which therespective phase voltage lies. The determination ofthe time durations,,, and.When n is odd, can be generalized as(1)(2)(3)When n is even, the triangular carrier & referencephase voltage, are as shown in this case, thereference phase voltage are centred on the middletriangular carrier. The determination of,, andcan be generalized as(4)(5)(6)Space vector is employed as it is an advancedtopology from the conventional PWM techniques.Space vector PWM technique is an advancement ofsinusoidal PWM as the pulses produced by digitalswitching of the fundamentalwaveform.Considering six switch operation we divide the VSIinto two parts as upper part and lower part. Theupper part contain the switches S1 S3 & S5 leavingthe lower part of the VSI with S2 S4 & S6.TABLE 1. SWITCHING STATESFig. 1. Simplified One Line Diagram of the Off-Line SeriesVoltage Sag Compensator Generalization of the Proposed SVPWMScheme for An n' Level PWM Inverter:The SVPWM, proposed for a three-level inverter,can be easily extended to any n-level PWMgeneration. In the SPWM scheme for an n levelinverter, the reference signals are compared with(n-1)level shifted carriers The triangular carriers and thereference signals, for an n-level PWM scheme, for nis odd, for n is even. The (n-1) triangular carriers areISSN: 2231-5381Switch1st Mode2nd Mode3rd mode4th Mode5th Mode6th Mode7th Mode8th 1S301010101Page 188

International Journal of Engineering Trends and Technology (IJETT) – Volume 48 Number 4 June 2017The signal generation of space vector is compared tothe triangular waveform to generate three PWMpulses to which NOT gates are given to get the otherthree pulses. The control signal of space vectorPWM is given blow fig. 2Fig. 3. Per phase equivalent circuit of the voltage sagcompensator series(7) (8)TWhereTFig. 2. Control signals of Space vector PWMTIII. SYSTEM CONFIGURATION OF THEPROPOSED COMPENSATORThe series compensator is consisted by a three phasevoltage source inverter. The leakage inductor ofcoupling transformerand capacitorisrecognized as the low-pass filter to suppress PWMripples of inverter output voltage . Fig. 3 showsthe equivalent circuit of series voltage sagcompensator and its dynamic equation can beexpressed as, is the inverter output voltage,is the filter inductor current,is the compensation voltage, andT (9) (10)IV. SIMULATION AND RESULTS ANALYSIS Simulation with proposed mitigation technique(PWM):Fig. 4. Simulation model with mitigation technique (PWM) a)Output waveforms:Source voltageISSN: 2231-5381http://www.ijettjournal.orgPage 189

International Journal of Engineering Trends and Technology (IJETT) – Volume 48 Number 4 June 2017Fig. 7. Load Current waveformFig. 5. Source voltage WaveformD)Magnetic Flux of Load Transformerb) Load VoltageFig. 8. Magnetic Flux WaveformFig. 6. Load Voltage WaveformFig. 5 shows the input source voltage waveformand Fig. 6 shows load voltage waveform which isget stabilized to normal value due to inrushmitigation technique.C) Output load current Offline mitigation technique (SVPWM) :Fig. 9 shows the simulation model with inrushcurrent with online mitigation technique with seriesvoltage sag compensator in which space vector pulsewidth modulation (SVPWM) technique is used.In offline mitigation technique at 0.3 sec loadconnected without compensator at 1 seccompensation on, from 1.5 to 2 sec load isdisconnected, at 2 sec and 2.3 sec load 2 and 3connected with compensation.Fig. 9. Simulation model With Migration Technique (SVPWM)ISSN: 2231-5381http://www.ijettjournal.orgPage 190