Page 1 ABSTRACT The project is to protect three phase induction motor from single phasing, overvoltage and undervoltage.Forthreephaseinductionmotor,itisnecessarythatallphasesofsupply should present. While it is on load when any one of the fuse goes out, or missing, the motor will continue to run with two phases only, but it will start drawing huge current for the same load. This high current may run the motor unless switched offimmediately. A single phasing preventeravoidtypeofsinglephasingcondition,themotorwillnotrununlessallthree phases are present. In this context we need to design a preventer which prevents this type of faulty condition and protect costly motor under such conditions. Page 2 INDEX OF CONTENTS ABSTRACT ............................................................................................................................................ 1 CHAPTER 1 ........................................................................................................................................... 4 INTRODUCTION .................................................................................................................................. 4 1.Three phase motor operation ................................................................................................ 4 2.Single Phasing and Prevention ............................................................................................... 5 3.Effect of Single-Phasing on Three-Phase Motors .................................................................. 5 CHAPTER 2 ........................................................................................................................................... 7 METHODOLOGY ................................................................................................................................. 7 1.Circuit diagram for single phasing protection ....................................................................... 7 2.Over and under and over voltage protection .......................................................................... 9 3.Control circuit components ...................................................................................................... 9 3.1. Power Supply ......................................................................................................................... 10 3.2. Comparator (IC 741) and Relay Driver Circuit (ULN 2004) ..................................................... 10 3.3. PCB Relay ............................................................................................................................... 11 3.4.Contactor .......................................................................................................................... 13 CHAPTER 3 ......................................................................................................................................... 14 HARDWARE IMPLEMENTATION ................................................................................................... 14 1.Single phasing protection ....................................................................................................... 14 2.Over and under voltage protection ........................................................................................ 15 CHAPTER 4 ......................................................................................................................................... 17 CONCLUSION ..................................................................................................................................... 17 REFERENCES ..................................................................................................................................... 18 Page 3 LIST OF TABLES TABLE 1 .......................................................................................... ERROR! BOOKMARK NOT DEFINED. LIST OF FIGURES FIGURE 1 SINGLE PHASING CONDITION ....................................................................................... 6 FIGURE 2 CONTROL CIRCUIT DIAGRAM FOR SINGLE PHASING PREVENTER ................................... 7 FIGURE 3 CONTROL CIRCUIT DIAGRAM FOR OVER AND UNDER VOLTAGE PREVENTER ................ 9 FIGURE 4 OP-AMP IC ............................................................................FIGURE 5 ULN 2004 IC10 FIGURE 6 CIRCUIT SYMBOL FOR REALY..................................................................................... 11 FIGURE 7 PCB RELAY ............................................................................................................... 11 Page 4 CHAPTER 1INTRODUCTION Thethreephasemotorsareusedwidelyfortheindustrialanddomesticpurposes.They workproperlywhenthreephasesupplyisgiventothem.Butwhenatwophasesupplyis given to it, the working is not the same as with three phase supply. To avoid a condition like that either the supply should be cut-off for the good of the motor or some arrangements could be made to supply balanced three supplies to the motor. This project aims at the protection of thethreephaseinductionmotoragainstsuddenphaselossandoperationintwophasesby compensation of the lost phase to increase the continuity of motor operation. 1.Three phase motor operation Themotorisconnectedtothethreephasesupplydirectly.A3phaseinductionmotor derives its name from the fact that the rotor current is induced by the magnetic field, instead of electrical connections. The operating principle of a 3 phase induction motor is based on the productionofe.m.f.TheACinductionmotorisarotatingelectricmachinedesignedto operatefromathree-phasesourceofalternatingvoltage.Thestatorisaclassicthree-phase stator with the winding displaced by 120. The rotor has skewed rotor conductors which are shortcircuitedbyendringforsquirrelcageinductionmotor.Therotormayalsohave windingwhichareconnectedtoslipringforslipringinductionmotor.Themotordraws twicethatoftheratedcurrentduringstartingforashort-timeandrunsbelowtherated current during normal operation. The starting current is limited by the starters like star-delta starter, rotor resistance starter. Page 5 2.Single Phasing and Prevention Inthreephaseinductionmotorsandloadwhenthereisanyfaultinasinglephasethe motorwilldrawmorecurrentinothertwophasesandwillsupplyreducedamountofload power.Itcanalsobedefineastheconditionwhereonephaseconductordevelopsonopen-circuitfaultorinthecaseofonepoleofthecircuitbreakernotmakingcontactwhile inductionmotorisrunningorthreephaseloadisconnected,conditionknownassingle phasingdevelops.Soastheefficiencyofthesystemisdecreaseditisnoteconomicalto operate the load in this condition. A device must sense and respond to the resultingincrease in current when the single-phasing condition occurs and do this in the proper length of time to savethemotorfromdamage.Sowedesignasystemcalledsinglephasingpreventerwhich will disconnect the load when there is fault in any of the phases. Similarly protection is also requirediflinevoltageisbeloworupperlimitofdesiredvoltage,toprotectmotorfrom damage over and under voltage protection also necessary. 3.Effect of Single-Phasing on Three-Phase Motors Theeffectofsingle-phasingonthree-phasemotorsvarieswithserviceconditionsand motorthermalcapacities.Whensingle-phased,themotortemperaturerisemaynotvary directly with the motor current. When single-phased, the motor temperature rise may increase atarategreaterthantheincreaseincurrent.Insomecases,protectivedeviceswhichsense onlycurrentmaynotprovidecompletesingle-phasingprotection.However,practical experiencehasdemonstratedthatmotorrunningoverloaddevicesproperlysizedand maintainedcangreatlyreducetheproblemsofsingle-phasingforthemajorityofmotor installations. In some instances, additional protective means may be necessary when a higher degreeofsingle-phasingprotectionisrequired.Generally,smallerhorsepowerratedmotors Page 6 havemorethermalcapacitythanlargerhorsepowerratedmotorsandaremorelikelytobe protected by conventional motor running overload devices. Figure 1 Single phasing condition Page 7 CHAPTER 2METHODOLOGY The hardware implementation includes many components which are discussed below. The circuit diagram is given below. 1.Circuit diagram for single phasing protection Figure 2 Control circuit diagram for single phasing preventer Page 8 The block diagram of Figure 2 explains the complete operation. The phase sensing circuit detectstheavailabilityofthethreephasesandgivesstatussignalstocomparator(Op-amp) and accordingly energizing signal to tripping coil or energizing coil of contactor connected in series with the main circuit. The relay driver IC ULN 2004 gives the output signal as per input status and operational modes to operate the relays and contactor. Three relays contacts (NC), corresponding to each phasecontrolcircuits,areconnectedinseriesofenergizingcoilofcontactor.Ifanyofthe threephasesgetopenthencorrespondingtothatphaseULN2004pinoutputwillgethigh andthepotentialdifferenceofrelaycontactiszero.Itmeansthatrelaywillgetde-energize anditwillopenthecircuitofenergizingcoilofcontactor.Itresultsindisconnectionof powersupplytothethreephasemotororload.Thecontrolcircuitrequirepropersupply source for the operation of control circuit. Page 9 2.Over and under and over voltage protection Figure 3 Control circuit diagram for Over and under voltage preventer 3.Control circuit components 230/12 V , 500mA potential transformer Power Supply 741Op-Amp Comparator ULN2004 relay driver IC Page 10 5V PCB relay Contactor 3.1. Power SupplyThe power which is required for the operation of the control circuit board is provided by the power supply unit. The rectifier board is required which provides constant +4.5 V for properoperationofcomparatorICs.A+4.5Vpowersupplyisprovidedfortherelay operation.This unit consists of the following,1. Transformer,2. Bridge Rectifier,3. Voltage Regulator 3.2. Comparator (IC 741) and Relay Driver Circuit (ULN 2004) Figure 4 Op-Amp ICFigure 5 ULN 2004 IC Comparatorgivesalogicoutputindicatingtherelativepotentialsonitstwoinputs.An op-amp amplifies the differential voltage between its two input and is designed always to be usedinclosed-loopapplications.Supplyvoltageisgivento+VandVisconnectedto ground.Theoutputofthiscomparatorwillbelogichigh(i.e.,supplyvoltage)ifthenon- Page 11 inverting terminal input is greater than the inverting terminal input of the comparator.If the inverting terminal input is greater than the non-inverting terminal input then the output of the comparator will be logic low (i.e., ground). Infaulty condition, output of comparator is highand therefore output of the relay driver IC (ULN2004) is low and normally close contact of pcb board relay is open, hence normally open type contactor coil is denergized results open the three phase supply of motor. 3.3. PCB RelayThe output of relay driver IC ULN 2004 is given to the relay. The relay is given a +5 volts power supply from power supply circuit. A relay is an electrically operated switch. Currentflowingthroughthecoiloftherelaycreatesamagneticfieldwhichattractsa lever and changes the switch contacts. Figure 6 Circuit symbol for realy Figure 7 PCB Relay Page 12 Thecoilcurrentcanbeonoroffsorelayshavetwoswitchpositionsandhavedouble throw (changeover) switch contacts as shown in the diagram. The relay's switch connections are usually labeled COM, NC and NO. COM = Common, always connect to this, it is the moving part of the switch.NC = Normally Closed, COM is connected to this when the relay coil is off.NO=NormallyOpen,COMisconnecttoCOMandNOifyouwanttheswitched circuit to be on when the relay coil is on. Connect to COM and NO if you want the switched circuit to be ON when relay coil is ON. Connect to COM and NC if you want the switched circuit to be ON when the relay is OFF Advantages of RelaysRelays can switch AC and DC, transistors can only switch DC.Relays can switch higher voltages than standard transistors.Relays are often a better choice for switching large currents (> 5A).Relays can switch many contacts at once. Disadvantages of Relays Relays are bulkier than transistors for switching small currents.Relayscannotswitchrapidly(exceptreedrelays),transistorscanswitchmanytimes per second.Relays use more power due to the current flowing through their coil. Page 13 RelaysrequiremorecurrentthanmanyICscanprovide,soalowpowertransistor may be needed to switch the current for the relay's coil. 3.4. Contactor A contactor is an electrically controlled switch used for switching a power circuit, similar to a relayexceptwithhighercurrentratings.Acontactoriscontrolledbyacircuitwhichhasa much lower power level than the switched circuit. The contactor is actuated by the low power relaycircuit.Thecontactorconsistsofaelectromagneticcoilwhichattractsthemoving contacts by changing the contact positions. Contactor is of two types namely normally closed (NC) and normally open (NO). Page 14 CHAPTER 3 HARDWARE IMPLEMENTATION 1.Single phasing protectionInsinglephasingprotection,connectionshouldnotloose.Givethreephasepower supplythroughcontactorandcurrenttransformer.Makesurethatcontrolcircuitpower supply should not on before motor reach full load condition. As motor runs on full load, then switch on the control circuit supply.

Currenttransformersecondarycoilhasinduceda10voltageACfor2ampereline current. This voltage is fed into rectifier and get7voltage DC which is fed into inverting pin of op-amp 741. We take op-amp as comparator. Page 15 Now give external dc supply 4.5 voltage for reference on non inverting pin of op-amp. Alsogive4.5voltageto+VCCpinofop-ampand9thpinofULN2004relaydriver IC. Connect ground to-VCC of op-amp and pin-8 of ULN2004IC. Connect op-amp output pin to relay driver IC 1st pin. And connect output pin of relay driverICtoPCBenergizingpin.AnotherpinofPCBrelayto4.5voltage.Also replicate connection for another two phases.We take reference voltage less than rectified voltage because in healthy condition op-ampoutputislowandaccordingtorelaydriverICappropriateoutputpinofrelay driver IC is high, means 4.5voltage is available on both energizing terminal of PCB relay, and that will continue the contactor 240V AC supply by normally close contact. Hence motor continuously run in healthy condition. Butwhensinglephasingisoccur,atthatinstantvoltageiszeroonsecondaryof currenttransformer,thereforeop-ampoutputwillhighandaccordingtorelaydriver IC pcb relay contact will open and contactor open the contacts of motor power supply. And induction motor will protected from single phasing. 2.Over and under voltage protection Connectallconnectionasshownincircuitdiagramforoverandundervoltage condition.MakesureallconnectionshouldtightanddonotONcontrolcircuitsupply before motor run on rated voltage condition. Connectthreepotentialtransformer230/14VAConeachphase.Eachtransformer primary one terminal on line and another terminal on neutral. Secondary of each potential transformer is connect to rectifier to get dc voltage. Page 16 In over and under voltage protection there are two op-amp for each phase is used, one for over voltage condition check and another for under voltage condition check. We take 1.1 per unit voltage for over voltagecondition and 0.9 pu voltagefor under voltage condition. Means 253V phase to neutral for over voltage and 207V for under voltage condition. Therefore we have to take to reference voltages for over and under voltage condition. Wetake10VDCreferenceforovervoltageconditionand12.4VDCreferencefor over voltage condition. For healthy condition dc rectified voltage is in between 10 V to 12.4 V. If voltage will go below or above limit of reference voltage, op-amp will make output high and according to relay driver IC, PCB will make normally close contact to open and contactor coil will de energized and motor will stop. Page 17 CHAPTER 4 CONCLUSION Single phasing preventer continuously check continuity of three phase supply of the three phase induction motor and protect the motor against single phasing condition. Over voltage and under voltage control circuit continuously check line to neutral voltage, if over or under voltage condition found, control circuit trip the contactor and protect motor. Page 18 REFERENCES 1.B.A.Oza,N.C.Nair,R.P.Mehta,V.H.MakwanaPowerSystemProtectionAnd Switchgear Tmh Publication 2011. 2.RobertBoylestad,LouisNashelskyElectronicDevicesAndCircuitTheoryPrentice Hall.