MICROCONTROLLER BASED POWER TRANSFORMER PROTECTION

UNIVERSITY OF NAIROBIFINAL YEAR PROJECTDEPARTMENT OF ELECTRICAL AND INFORMATION ENGINEERINGMICROCONTROLLER BASED POWER TRANSFORMER PROTECTIONSYSTEMPROJECT NO: 009ByOCHIENG’ ALLAN OMONDIREG. NO: F17/1365/2010SUPERVISOR: PROF. ELIJAH MWANGIEXAMINER: DR. G.N KAMUCHAA PROJECT REPORT SUBMITTED TO THE DEPARTMENT OF ELECTRICAL ANDINFORMATION ENGINEERING IN PARTIAL FULFILLMENT OF THEREQUIREMENTS OF THE DEGREE OF BACHELOR OF ELECTRICAL ANDELECTRONIC ENGINEERING OF THEUNIVERSITY OF NAIROBIAPRIL, 2015i

DECLARATION OF ORIGINALITY FORMName of StudentALLAN OMONDI OCHIENGRegistration Number F17/1365/2010CollegeARCHITECTURE AND EERINGELECTRICAL END INFORMATION ENGINEERINGCourse Name BACHELOR OF SCIENCE IN ELECTRICAL AND ELECTRONICENGINEERINGTitle of the work DESIGN OF A MICROCONTROLLER BASED POWER TRANSFORMERPROTECTIONDECLARATION1. I understand what Plagiarism is and I am aware of the University’s policy in this regard2. I declare that this final year project is my original work and has not been submitted elsewherefor examination, award of a degree or publication. Where other people’s work, or my own workhas been used, this has properly been acknowledged and referenced in accordance with theUniversity of Nairobi’s requirements.3. I have not sought or used the services of any professional agencies to produce this work4. I have not allowed, and shall not allow anyone to copy my work with the intention of passingit off as his/her own work5. I understand that any false claim in respect of this work shall result in disciplinary action, inaccordance with University Plagiarism Policy.SignatureDatei

AcknowledgementFirst and foremost, I thank the Almighty God for His guidance throughout my studies in theUniversity of Nairobi and the completion of this project.I am very grateful to my supervisor Professor Elijah Mwangi for his guidance throughout thisproject. The sessions that I had with professor inspired me to work harder every time we met.I also thank the Department of Electrical and Information Engineering and my lecturers forinstilling in me the knowledge that has brought me this far.Finally, I am grateful to all my classmates and friends who contributed to the success of mystudies in one way or another. I specifically thank Mr. Shaban Otaro, Mr Benard Osawa, andAwino Felix for being so great friends and brothers.ii

DedicationThis project is dedicated to my family for their support throughout my academic life. I amgrateful to my brothers Paul, Dan and Ken for always providing a listening ear whenever I was inneed. Lastly to my friend Joy for always being the supportive friend that God gave me.iii

ABSTRACTThe main intention of this project is to design a microcontroller based system that can be used inpower transformer protection. The system checks the operating parameters of the transformer i.e.current and reports the quantity that is flowing through the transformer. The system is designedsuch that it is able to detect currents above the normal operating level and isolate the powertransformer from the distribution line. This isolation process is to ensure that the transformer issafe from any excess current levels that can make it to overheat thus get damaged. It gives asolution to the need to reduce cost of maintenance and ensure that supply of electricity toconsumers is not interrupted for long periods taken while repairing or replacing destroyedtransformers.A current sensor ACS712x series has been used in this project as the interfacing instrumentbetween the power transformer and the PIC16F690 microcontroller. The PIC16F690 controls alloperations that the device does. A relay and a contactor have been used as the switching gears toisolate the transformer from the power system in case a fault occurs. A monochrome LCD hasbeen used to show system current readings and indicate cases of over-current fault. To warn anoperator of a fault occurrence, LEDs and a piezoelectric buzzer have been used. All theseperipheral devices depend on the microcontroller to make them operate or otherwise. Some ofthe tools used in this project include MPLAB - programming software used to write the programfor the microcontroller used in this project. Proteus- simulation software has also been used totest whether the design works appropriately before its implementation on hardware. Pickit3- hasbeen used to load program into the microcontroller using MPLAB.iv

ACRONYMS AND ABBREVIATIONSPICProgrammable Intelligent ControllerLCDLiquid crystal DisplayGNDGroundASCIIAmerican Standard Code for Information ExchangeLEDLight emitting diodeMOSMetal oxide semiconductorGSMGlobal System for MobilePCBPrinted circuit boardCTCurrent transformerRAMRandom access memoryROMRead only memoryACAlternating CurrentDCDirect CurrentADCAnalogue to Digital ConverterCPUCentral Processing UnitCMOSComplementary metal oxide semiconductorICIntegrated circuitACSAllegro current sensorMSBMost significant bitLSBLeast significant bitv

LIST OF TABLESTABLE 3.1TABLE 3.2TABLE 3.3TABLE 3.4Properties of PIC16F690 .16LCD pins description .17LCD Instructions [15].18HD44780 instruction set .19TABLE 4.1TABLE 4.2TABLE 4.3Microcontroller Pin Usage .22Bank selection bits .29Value of each bit in Volts and Amperes .37TABLE 5.1SIMULATED RESULTS .39vi

TABLE OF FIGURESFigure2.1 Generation, transmission and distribution of electrical power [2]. . 3Figure2.2 power system protection [3] . 4Figure2.3 unit protection [4] . 5Figure2.4 non-unit protection [4] . 5Figure2.5 circuit breaker [4] . 6Figure2.6 Station battery [1] . 6Figure2.7 Electro-magnetic induction [6] . 8Figure2.8 Photo of a power transformer [4] . 9Figure2.9 waveform of a magnetizing inrush current [4] . 10Figure2.10 over-excitation waveform (4) . 10Figure2.11 CT Saturation curve [7] . 11Figure2.12 Differential protection Scheme [7] . 12Figure2.13 Restricted Earth Fault Protection [5] . 12Figure2.14 Over current Phenomenon [9] . 13Figure2.15 Over current Protection Relay [9] . re4.9Figure4.10viimicrocontroller architecture [5]microcomputer memory organization [11]PIC16F690 Pin diagram [6]The structure of an LCD [15]LCD pin arrangement [5]Allegro Microsystems ACCS712 SeriesCurrent sensor functional block diagram [16].Relay circuit [17]1415151617192121microcontroller-LCD interface as done in the simulation software . 23microcontroller-LED connection . 24microcontroller-relay interface as done on the simulation software. 25microcontroller-sensor interface as done on the simulation software . 26flow chart of the program . 28the Status register . 29ADCON1 Register. 29The ANSEL register . 31ADCON1 Register. 31Left justification format. 33

Figure4.11 ADC output against input voltage [12] . ure5.6Figure5.7Figure5.8viiigraph of line current against current display . 40Relay closed Green blinks . 41LCD Display . 41Relay Open, Red LED blinking. 42Over current Fault. 42Normal transformer operation . 43current level approaching fault level . 44over current fault . 44

TABLE OF CONTENTSDECLARATION OF ORIGINALITY FORM . IACKNOWLEDGEMENT . IIDEDICATION . IIIABSTRACT . IVACRONYMS AND ABBREVIATIONS . VTABLE OF FIGURES . VIICHAPTER 1: INTRODUCTION . 11.1 BACKGROUND .11.2 PROBLEM STATEMENT .21.3 OBJECTIVES .21.4 SCOPE WORK .2CHAPTER 2: LITERATURE REVIEW . 32.1 ELECTRIC POWER SYSTEM .32.2 POWER SYSTEM PROTECTION .42.2.1Importance of power system protection .42.2.2 Types of protection systems .52.2.3Power Protection elements .62.2.4Functional requirement of a protection relay .72.3 TRANSFORMER PROTECTION .72.3.1Causes of fault in power transformer .9TRANSFORMER PROTECTION SCHEMES.9CHAPTER 3:REVIEW OF COMPONENTS USED .143.1 THE PIC16F690 MICROCONTROLLER .143.2 LIQUID CRYSTAL DISPLAY .163.3 CURRENT SENSOR .193.4 RELAY .213.5 CONTACTOR .21CHAPTER 4: DESIGN .224.1 HARDWARE DESIGN .224.1.1 Interfacing LCD to the microcontroller .22A)LEDS .23B)AUDIO ALERT .25C)RELAY/CONTACTOR CONTROL .254.1.3 Sensor interfacing to the microcontroller .264.1.4 The Oscillator .264.1.6 PCB design .274.2 SOFTWARE DESIGN .274.2.1 ADC Program .28ix

4.2.2 LCD DISPLAY.344.2.3 Relay and Fault Signals .37CHAPTER 5: RESULTS AND ANALYSIS .395.1 SIMULATED RESULTS .395.2 ANALYSIS .405.3 RESULTS AFTER IMPLEMENTATION .42CHAPTER 6: CONCLUSION AND RECOMMENDATINS .466.2 LIMITATIONS AND FUTURE RECOMMENDATIONS .47APENDIX A: CIRCUIT DESIGN .48APENDIX B: PIC16F690 ARCHITECTURE .49APENDIX C: ASSEMBLY LANGUAGE .51APENDIX D: BILL OF MATERIALS . 2REFERENCES. 3x

CHAPTER 1: INTRODUCTION1.1 BACKGROUNDIn the design of electrical power transmission and distribution system, there are various factorsthat need to be considered in the quest to satisfy the needs of electricity consumers. Electricalpower systems experience faults at various times due to various reasons. These faults must beforeseen and safety precautions applied to the power system. The power systems engineer mustinclude in his design, safety measures in order to avert any destructive occurrences that thesystem may undergo at any given time. Power system protection is very essential and necessaryfor a dependable electrical power supply. It ensures that the system is protected from itself andthat the consumer is also safe as he benefits from the electrical power supply. An electricalpower system consists of various components such as generators, switches, transmission cables,transformers, capacitor banks among other components. It cannot therefore operate without aneffective protective device to keep these components safe and the system stable. Faults in apower s

The transformer is a very important component in an electrical power system as distribution of electrical power to consumers is more efficiently effected. Every transformer is designed to comfortably supply a given load. Cases of overload or short circuits can lead to transformer being damaged. To