ControlledClosingto ReduceTransformer Inrush Current By GroupG03: DannyNorthcott- 6758344 ScottDyck - 6757531 Proposalsubmitted for 24.400Group DesignProject for the Departmentof Electrical and Computer Engineering in the Faculty of Engineering of the University of Manitoba Faculty and Industry Supenisors: Dr. Ani Gole,Ph.D.,P.Eng., Supervisor Departmental ManitobaHydro Ph.D.,P.Eng., Dr. David Jacobson, October15,2U)4 1. Introduction Whena transfonner connected a power grid, unpredictable undesired is to and transientconditionsarise.Thesetransientconditions,althoughlastinglessthan a second, can causeseveremechanicaldamage the transformerandthe switchgeff, ffi well as to electrical instability to the power grid. Thesedisturbances also causetrouble for the ean power customers.This phenomenon known astransforrnerinrush current. is Transformerinrush current is not a new phenomenon, is generallydealt with and by desensitizing protectiondevices, over sizingtransmission and components, attentive maintenance the affectedequipment. the past,closingresistors of In havebeenusedto mitigate the effectsof inrush currentby supplying a reducedvoltageduring the transient period.This methodworks wellobut is often economically unviable. Controlledswitchingis a relativelynew technique, which usesa preciselytimed closingof the circuit breakerto minimize the inrushcunent.The general technique to is consider residualmagneticflux of the transformer's the iron corein decidingwhenthe breakerclosingshouldoccur.This residualflux will depend the point on the sinewave on at which the transformerwas previously disconnected,along with loading conditions,and devicecharacteristics. Our project will seekto studythe phenomenon transformerinrush current. of First, we will developa computersimulationwhich accurately modelsthe response a of real transformerconnected different instantaneous at voltage andresidualflux conditions. We will thendesignandbuild a devicethat will allow energization a lab transformer of at any point on the incomingsinewave. This devicewill allow us to studyinrushcurrent andthe effectsof controlledclosing.If time pennits,we will usethis knowledge to designandbuild a systemwhich will effectivelyreduce inrushcurrentby monitoring residualflux, calculatingan optimumclosingangle,andautomatically closingthe primary switch. This would be a significant extensionto our project, and if not completed,every attemptwill be madeto supply adequate information for a future group seeking achieve to this goal. 2. Specifications The projectis organizedinto threemain parts. o Transformer Modeling and Simulation t DesignandImplementation ClosingCircuit of o Automationof ControlledClosing(if time permits) 2.1. Modelingqnd Simulation Transformer A modelwill be developed which will be usedto simulatetransformer innrsh current.In this model it will be necessary include or approximatethe effectsof to saturation, hysteresis, residualflu. It will alsobe necessary consider leakage and to the and inductance copper loss.The modelmustprovideaccess voltages, to currents, and flux instantaneously order to be of use,andwill be ableto predict the response a in of real transformerto within l0% of over currentsdrrringan average caseexcitation.Lab datawill be usedto matchthe parameters the simulatedtransfonnerto the lab of transformer.It would be desirableto developthis computermodel in an openended fashion,so that it canbe appliedto other transformers easily by adjustingparameters. The diffrculty level of this taskis moderate low, flnd so it carrieslittle or no risk to our to timeline. 2.2. of Designand Implementation ClosingCircuit A closingcircuit will be developed manuallycontrolthe connection the to of transformer the power supply.This devicewill accept userspecifiedclosingangle to a and connectthe transformerat the appropriate time. This meansthat the userwill be able to dial in the angleof any point on the incomingsinewave,andthe closingsignalwill be generated the correctinstant.The deviceshouldbe ableto closewithin half a secondof at userinput being receivedand shouldbe accurate within 5 degrees the input. There to of will be uncertaintyin closing the switch at the requiredtime, because the inherent of delaysin the control system,the ou@utdriver circuitry, &ildthe physical switching action.For this reason, will be necessary take account thesedelays.The diffrculty it to of of this taskwill be moderately high, andcarriessomesignificantrisk to our timeline.For this reason is considered the main designcomponent our project. it as of 2.3. Automotionof ControlledClosing(if timepermits) Hardwareinstrumentation be developed conjunctionwith the transformer will in model to measure recordthe flux in a transformerfrom externalmeasurements. and The transformerflux in real time. This controller must be able to calculatethe instantaneous devicewill be usedasa front endto the previouslydesigned closingcircuit. Therefore it is requiredto calculate optimumslosinganglefrom the meastredcone the flux. As a generalguideline,we will seekto reducethe worst caseexcitation inrush to I pu current. This is our generalguideline,which will force variousconstraints the designof our on real time system, depending our implementation. on This sectioncarriesa high amountof risk to our timeline andwill only be attempted time permits. if It is evidentthat this is a large,ambitiousproject for a two persongroup,and so meeting the minimum requirements shouldsuffrcewith the provision of upgradeabilityto the designat a later date.The hardwareand softwareshouldprovide an easymechanism for othersin the future to upgradethe devicewithout completelyre-designingit. A summary of the specifications given in the tablebelow. are Table I - Project Specifications Summarv of Snecifications Category Specification Transformer Model Model inrush in the averagecasewith l0% accuracy. of DesignandImplementation Closing Accept a user supplied closing angle. Circuit Connect the transformer within half a secondof receiving command. Connect the transformer according to user input with no greater that 5 degreeserror. Automation of Controlled Closing Calculatetransfonnerflux in real time. (If time permits) Calculate optimumclosinganglebased the on residualflux. Worst caseexcitationinrushof 1 pu. Milestones, Division of Labour 3. Tasks, and The organization of the project will consist of modules and tasks, where each module is composed of many tasks, and generally consists of some deliverable or a milestone at the end. The project modules are given below, and are shown in more detail on the following Gantt chart. . Transformer Modeling and Simulation o Design and Implementation of Closing Circuit o Automation of Controlled Closing (if time permits) 3.1. Transformer Modeling and Simulation The transformer modeling and simulation will consist mainly of modeling a saturable inductor, hysteretic inductor, and then the transformer model rcalization and evaluation. This module will be spearheaded Scott, and will use considerableinput by from Dr. Gole. 3.2. Design and Implementation of Closing Circuit The closing circuit design can be broken into three main functional units. These componentswill consist of a user interface to accept inputs, a calculation and control circuit, and a switching device to connect the power supply to the transformer. Scott will head up the design of the control circuit, while the VO design will be the responsibility of Danny. Danny will also take responsibility of the module as a whole. 3.3. Automation of Controlled Clasing (if time permits) This module will be sharedbetween Scott and Danny, as it will be a bonus if we even attempt it. Danny will be responsible for designing and testing the flux measuring circuit, while Scott will design the algorithm to calculate the optimum closing time. There will also be a requirement to provide communication between this device and a PC, for analysis of flux and other measureddata. This task will also be Scott's. Table 2 - Division of Project Modules Division of Work Module Assignment Transformer Modeling and Simulation Scoff Design and Implementation of Closing Circuit Danny o User Interface . Danny o Control Circuit . Scott o Switching Device/]vletering o Danny Automationof ControlledClosing Danny and Scott (if time permits) o Flux MeasuringCircuit o Danny . Closingtime optimization o Scott o PC Interfacing o Scott Proiect Gantt Chart The Gantt chart, which outlines the organization of the project, is given on the following page. rf) 9 : O :(Y o :N = ru[ e e E t8f, tFs Ot : (\| s-t o z 5l (\l !ti 'l F-l l.l . P p8 .!J 6 -8 F P = & c) CD cL cL cl .! a E E E g o o o c L t r , E E . O E !1.I e (J . r r 9 a 5 E € 8 E E C E E S o B d FF g ; EssE F E o EEEIE s, C) g o dn EfiEEfi o Es E G z .r c o o ! €frFFE e-R o-= gP o oq 6F .o5 9E o.o 4. BudgetandRequiredResources An approximate of consumable list itemsis given below. Most of theseitemsare Components the availablein the deparfinentand will be suppliedby the departrnent. for thyristor switchingdevicewhich the department doesnot havewill be suppliedby ManitobaHydro. Proiect Budset Item Department Costs MB Hvdro Cost PassiveCircuit Components $7s Microcontroller $25 Dials, Switches Indicators and $25 PCB ProtoWping Materials $s0 ThvristorSwitchingDevice $s0 $100 lsolation Components $s0 Subtotal $27s.00 $100.00 TOTAL $375.00 items,variousresources be requiredfor the In additionto theseconsumable will completionof this project. o Consultationwith technicalstaff. . Use of PIC Development Programmer. . Useof lab tansformer andmeteringequipment. o Useof Matlab,PSpice, andPSCADon lab computers. 5. References "Elimination of Transformer Inrush Currents  JohnH. BrunkeandKlaus J. Frdhlich. by ControlledSwitching". IEEE Transactions PowerDelivery VOL. 16,No. on 2, April200l "TransformerModelingasApplied to Dffirential  StanleyE. Zocholl, et al. Protection". Schweitzer Laboratorieq October12, 2004 Engineerine Inc. <http://www.selinc. prsl com/techp 6025.pdf> "TransformerControlledSwitchingtaking into accountthe core  A. Mercieret al. ResidualFlw, a RealCaseStudy".CIGREAug. 28-Sept. 1988,3 paper13-02.
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