inrush current in transformer

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					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

        Dr. David Jacobson,

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
electrical instability to the power grid. Thesedisturbances also causetrouble for the
power customers.This phenomenon known astransforrnerinrush current.

       Transformerinrush current is not a new phenomenon, is generallydealt with
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
consider residualmagneticflux of the transformer's
         the                                          iron corein decidingwhenthe
breakerclosingshouldoccur.This residualflux will depend the point on the sinewave
at which the transformerwas  previously disconnected,along with loading conditions,and

        Our project will seekto studythe phenomenon transformerinrush current.
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
o Automationof ControlledClosing(if time permits)
   2.1.              Modelingqnd Simulation

        A modelwill be developed    which will be usedto simulatetransformer      innrsh
current.In this model it will be necessary include or approximatethe effectsof
saturation, hysteresis, residualflu. It will alsobe necessary consider leakage
                         and                                       to           the
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
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

   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
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
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
real time system,  depending our implementation.
                             on                    This sectioncarriesa high amountof
risk to our timeline andwill only be attempted time permits.

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.

                               Table I - Project Specifications

                               Summarv of Snecifications
               Category                                        Specification
Transformer Model                               Model inrush in the averagecasewith l0%
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
                                                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
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
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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

                                   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.
      2, April200l
                              "TransformerModelingasApplied to Dffirential
[2] StanleyE. Zocholl, et al.
       Protection". Schweitzer             Laboratorieq October12, 2004
                                 Engineerine          Inc.
       <http://www.selinc.           prsl
                           com/techp 6025.pdf>
                     "TransformerControlledSwitchingtaking into accountthe core
[3] A. Mercieret al.
       ResidualFlw, a RealCaseStudy".CIGREAug. 28-Sept. 1988,3      paper13-02.

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