A TECHNICAL REPORT ON STUDENTS INDUSTRIAL WORK EXPERIENCE SCHEME (SIWES)

Transcription

1 A TECHNICAL REPORT ON STUDENTS INDUSTRIAL WORK EXPERIENCE SCHEME (SIWES) UNDERTAKEN AT PACIFIC ELECTRIC ENERGY COMPANY LIMITED OMOTOSHO PHASE 1 POWER PLANT ORE, ONDO STATE, NIGERIA. PERIOD OF ATTACHMENT: 17 th JULY 2018 TO 28 th DECEMBER 2018 BY POPOOLA OPEOLUWA GRACE SUBMITTED TO THE DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING, FACULTY OF ENGINEERING, UNIVERSITY OF LAGOS, AKOKA, LAGOS STATE IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF BACHELOR IN SCIENCE (B.Sc.) DEGREE IN ELECTRICAL AND ELECTRONICS ENGINEERING

2 CERTIFICATION This is to certify that Miss POPOOLA OPEOLUWA GRACE with Matric No , of Electrical and Electronics Engineering Department, University of Lagos, compiled this report based on her Students Industrial Work Experience Scheme (SIWES) undertaken at Omotosho Electric Energy Power Generation Ltd, Omotosho, Ore, Ondo State. Name of Student/Trainee Signature and Date Name of Industry-based Supervisor Signature and Date Name of Institution-based Supervisor Signature and Date ii

3 DEDICATION This report is dedicated to my dear parents Engr. and Mrs. Popoola, my siblings and my dear friends for their inestimable and invaluable support in ensuring that I am educated and also to the entire staff of Omotosho Power Plant for making my stay at their power plant one to never forget and made it worthwhile. iii

4 ACKNOWLEDGEMENT Foremost gratitude to God Almighty for life, success, living and guidance; Sincere thanks to my parents, siblings and all family members for their invaluable support; Profound appreciation to all my lecturers for commendable tutelage; Heartfelt commendations to all staff of Omotosho Electric Energy Power Generation Ltd for their worthwhile training and rewarding supervision; Hearty regards to all my co-trainees, departmental mates and all friends for their compassionate companionship. iv

5 ABSTRACT This report gives an account of my Student Industrial Training Experience at Omotosho Electric Generation Plant which is under Pacific Energy Co. Ltd, which generates 335MW (total installed capacity) of electric power with the aid of eight 42.1MW gas turbines. It x-rays the operations of the gas turbines and other auxiliary equipment used around the plant to make generation smooth, general operation of the plant and specifically focuses on the maintenance works undertaken by the electrical, mechanical, instrumentation and control (I&C) and operations departments, highlight the skills and experience gained, enumerates the problems and challenges faced and dealt with and gives recommendations deemed appropriate for trainees, the company, the government, the university and the nation at large. v

6 Table of Content CERTIFICATION... ii DEDICATION... iii ACKNOWLEDGEMENT... iv ABSTRACT... v Table of Content... vi Table of Figures... ix List of Tables... x List of Abbreviations... xi CHAPTER ONE INTRODUCTION AIMS AND OBJECTIVES OF SIWES... 1 CHAPTER TWO OVERVIEW OF OMOTOSHO POWER PLANT HISTORY MISSION OMOTOSHO IN PICTURES ORGANOGRAM OF OMOTOSHO POWER PLANT ORGANIZATION CHART DEPARTMENTS AND THEIR FUNCTIONS... 4 CHAPTER THREE GAS TURBINE INTRODUCTION THERMODYNAMICS PRINCIPLES OF A GAS TURBINE TURBINE BASE AND SUPPORTS... 8 vi

7 3.2.1 TURBINE BASE TURBINE SUPPORTS INLET AND EXHAUST SECTION INLET SYSTEM EXHAUST SYSTEM COMPRESSOR SECTION COMPRESSOR ROTOR COMPRESSOR STATOR INLET CASING COMPRESSOR CASING DISCHARGE CASING COMBUSTION SECTION COMBUSTION CHAMBERS AND CROSSFIRE TUBES SPARK PLUG AND FLAME DETECTOR TURBINE SECTION LUBE OIL SYSTEM COOLING WATER SYSTEM LOAD GEAR GENERATOR SECTION ELECTRICAL EQUIPMENT NEUTRAL CUBICLE OUTGOING LINE CUBICLE CHAPTER FOUR ELECTRICAL MAINTENANCE DEPARTMENT ELECTRICAL vii

8 Roles of Electrical Department PICTURES FROM WORKING IN ELECTRICAL DEPARTMENT INSTRUMENTATION AND CONTROL (I&C) ROLES OF INSTRUMENTATION AND CONTROL DEPARTMENT CONTROL INSTRUMENTS PICTURES OF INSTRUMENTATION AND CONTROL INSTRUMENTS MECHANICAL MAINTENANCE DEPARTMENT INTRODUCTION ROLES OF MECHANICAL MAINTENANCE DEPARTMENT OPERATIONS DEPARTMENT ROLES OF OPERATIONS DEPARTMENT CONTROL PANELS HUMAN MACHINE INTERFACE (HMI) GAS TURBINE STARTUP AND SYNCHRONIZATION PROCEDURES CHAPTER FIVE SUMMARY OF WORK DONE CONCLUSION RECOMMENDATION APPENDIX viii

9 Table of Figures Figure 1: Front View of Omotosho Power Plant... 3 Figure 2: Cross section of the eight (8) gas turbine generators... 3 Figure 3: Typical Open Cycle Gas Turbine... 7 Figure 4: Air filters above the Gas Turbine Generator unit Figure 5: Compressor section Figure 6: Combustion chamber Figure 7: Turbine Section Figure 8: Load Reduction Gear Figure 9: Stator of the Generator Figure 10:: Rotor of the Stator undergoing inspection Figure 11: Stator and Rotor of a Gas Turbine Generator Figure 12: Working on Auxiliary transformers in Switchyard Figure 14: Lighting arrestors Figure 13: Cleaning the Star point after a minor explosion Figure 16: Upper Isolator in 10.5KV Switchyard Figure 15: Star point of a Gas Turbine Generator Figure 17: Fuel shut-off valve Figure 19: Turbine wheel space thermocouple Figure 18: Condensate level guage Figure 20: Generator Auxiliary Control Panel Figure 21: Generator Control Panel Figure 22: H.M.I. showing the wheel space temperature at specific points Figure 23: H.M.I showing the startup where all parameters can be recorded ix

10 List of Tables Table 1: Maintenance Departments and their functions... 5 Table 2: Operation Departments and their functions... 5 Table 3: Administrative Department and their functions... 6 Table 4: List of Motors in Gas Turbine Generator Units x

11 List of Abbreviations AC CCWP CWP DC GT GTG HGPI HMI HSE I&C ISO ITF MCB MCC NBET NUC PID PBX SIWES Alternating Current Closed Circulating Water Pump Circulate Water Pump Direct Current Gas Turbine Gas Turbine Generator Hot Gas Part Inspection Human Machine Interface Health, Safety and Environment Instrumentation and Control International Organization for Standardization Industrial Training Fund Miniature Circuit Board Moto Control Center Nigerian Bulk Electricity Trading Plc. National Universities Commission Proportional Integral Derivative Private Branch Exchange Students Industrial Work Experience Scheme xi

12 CHAPTER ONE 1.1 INTRODUCTION The Students Industrial Work Experience Scheme (SIWES), as established by the Federal Government through the National Universities Commission (NUC) in 1973 under the National Development Plan decree 17, 1971 of the Industrial Training Fund (ITF), was designed to bridge the gap between the theoretical knowledge acquired by the undergraduate students in the universities and the real-life applications of this knowledge in industries. The Scheme therefore provides avenues for the acquisition of technical, industrial, commercial and managerial skills in order to generate a pool of trained indigenous manpower sufficient to meet the needs of the country. 1.2 AIMS AND OBJECTIVES OF SIWES The aims and objectives of SIWES are: To get students acquainted with the work environment, equipment involved in the work in their respective industry and also help students bridge the gap between theoretical knowledge and practical application. Enabling students appreciate the connection between their course of study and other related disciplines in the production of goods and services. Making set students appreciate the role of their professions as the creators of change and wealth and indispensable contributors to growing the economy and national development. Preparing students to contribute to the productivity of their employers and national development immediately after graduation. Provision of an enabling environment where students can development and enhance personal attributes such as critical thinking, creativity, initiative, resourcefulness, leadership, time management, presentation skills and interpersonal skills amongst others. Premised on the afore-mentioned aims and objectives, this technical report presents an account of my Industrial Training at Pacific Energy Co. Ltd, Omotosho, Ondo State from July to December

13 CHAPTER TWO 2.1 OVERVIEW OF OMOTOSHO POWER PLANT Omotosho Thermal Power Station engages in generating and distributing electricity from gas run turbines in Nigeria. The company is based in Omotosho, Okitipupa Local Government Area of Ondo State, Nigeria. 2.2 HISTORY The concept of the establishment of the plant started in 2002 when the government planned to increase the electricity power capacity of the nation to 10000MW to meet the ever increasing demands of the nation. Construction commenced on 28 th November, 2005 after finalization of design meetings and factory acceptance test in China. The contract for the supply, delivery, installation and commissioning of the power plant was awarded to China National Machinery & Equipment Import & Export Corporation. The plant consists of eight (8) frame 6B model PG6581B, simple cycle gas turbine generator units of 42MW (ISO Condition). The official commissioning of the plant was done on 27 th May, 2007 by President Olusegun Obasanjo. Pacific Energy took over the Omotosho Power Generating plant during the sale, acquisition and privatization of power plants in Nigeria. This 335MW capacity power plant has been rehabilitated with major turkey maintenance carried out on all of its gas turbines. It is daily operated and maintained by a team of Pacific Energy staff and boasts of generating 95% of its installed capacity evident by the recently concluded capacity test carried out by NBET. 2.3 MISSION Pacific Energy is primarily focused on acquiring and managing strategic businesses that create long term shareholder returns and socio-economic impact. 2

14 2.4 OMOTOSHO IN PICTURES Figure 1: Front View of Omotosho Power Plant Figure 2: Cross section of the eight (8) gas turbine generators 3

15 2.5 ORGANOGRAM OF OMOTOSHO POWER PLANT ORGANIZATION CHART CHIEF EXECUTIVE OFFICER OPERATIONS (AGM) MAINTENANCE (AGM) GENERAL DUTIES (AGM) LABORATORY DEPARTMENT MECHANICAL (AGM) CIVIL DEPARTMENT ELECTRICAL (PM) MEDICAL EFFICIENCY DEPARTMENT SAFETY DEPARTMENT OPERATION DEPARTMENT TURBINE AUXILIARY WORKSHOP ELECTRICAL DEPARTMENT INSTRUMENTATION AND CONTROL (I&C) PROCUREMENT STORE ACCOUNT HUMAN RESOURCES PERFORMANCE PLANNING LEGAL AUDIT 2.6 DEPARTMENTS AND THEIR FUNCTIONS The following presents the overview of the various departments in Omotosho Power Plant, their corresponding responsibilities for the efficient management and running of the power station. The departments can be broadly classified into three (3) departments as follows: Maintenance, Operations and Administrative Departments. 4

16 Table 1: Maintenance Departments and their functions S/N Department Roles 1 Electrical Maintenance Maintenance of the generator and its associated equipment, excitation equipment, Batteries and Inverters, Large and Small motors and for the provision of illumination in and around the plant. 2 Instrumentation and Control (I&C) Maintenance of all the instruments and control equipment of the plant e.g. Sensors, Control Valve and its accessories, Indicators and Recorders, Meters, Gauges etc. 3 Mechanical Maintenance Maintenance of lube oil systems, air-conditioning and ventilation systems, refrigerators; welding, and fabrication jobs as well as maintenance of automobiles (light and heavy vehicles, mobile plants) Table 2: Operation Departments and their functions S/N Department Roles 1 Performance management Alignment of the various departmental focuses/outputs to conform to the overall set objectives and targets of the plant. 2 Operation Monitoring and Control of the plant from the central control room. 3 Procurement Procurement of Services and materials (Spares and Consumables) for cost-effective maintenance, operation and upkeep of the plant. 5

17 4 Laboratory Preparation of water treatment, regeneration and dosing chemicals, transformer, lubricating and fuel oil analysis and quality control monitoring of water. 5 Health, Safety and Environment (HSE) Safety of the staff and equipment in the plant Table 3: Administrative Department and their functions S/N Department Roles 1 Finance and Accounts Financial appropriation of the station and for the payment of wages and salaries 2 Human Resources General administration, training, recruitment and other human resources services 3 Public affairs and Legal Fostering of cordial relationship among host communities, the public and the station and for legal matters. 4 Internal Audit Staff auditing 5 Clinic Routine clinical diagnosis and treatment of ailments, short-term admission of patients, health counselling etc. 6

18 CHAPTER THREE 3.1 GAS TURBINE INTRODUCTION The purpose of gas turbine power plants is to produce mechanical power from the expansion of hot gas in a turbine. Gas turbines are also used as jet engines in aircraft propulsion. The net power available on the shaft of the gas turbine is transformed into electrical power by the generator while the electrical started is an electrical engine which is only used when the plant is turned on. Figure 3: Typical Open Cycle Gas Turbine THERMODYNAMICS PRINCIPLES OF A GAS TURBINE A gas turbine is basically a constant flow internal combustion engine. The fuel is burned within the engine and serves to add heat to compress air which expands through the blades of a turbine. The simple gas turbine operates by drawing air into a compressor, compressing it and then discharging the air into a combustion chamber. In the combustion chamber, fuel is added and burned, heating the air further. The hot air is then expanded through a turbine. The efficiency of such a machine depends primarily upon the temperature to which the air can be raised, hence the constant endeavor to operate at maximum possible temperature. The output horsepower or power rating of the machine depends upon the weight of hot gas flowing through in 7

19 unit time. Thus a gas turbine output increases when using air of maximum density. Cold air produces a marked increase in gas turbine output. A gas turbine is not self-starting; it must be rotated, at 20% to 30% of its maximum speed before fuel is turned on. This is one to give sufficient air compression so that when fuel is injected, the gas turbine power will be able to drive the compressor and maintain the speed rise. Thus a starting motor is an essential auxiliary. A simple, open cycle, single shaft gas turbine. The meaning of open cycle is that the air used to drive the turbine is drawn from the atmosphere and returned to the atmosphere after use. 3.2 TURBINE BASE AND SUPPORTS TURBINE BASE The base that supports the gas turbine is a structural steel fabrication of welded steel beams and plate. Its prime function is to provide a support upon which to mount the gas turbine. Lifting trunnions and supports are provided, two on each side of the base in line with the two structural cross members of the base frame. In addition, the base supports the gas turbine inlet and exhaust plenums. The forward end of the base, under the accessory compartment, also functions as a lube oil storage tank. An oil drain channel is constructed along the web of the left longitudinal I-beam. The channel extends from the oil tank to the aft end of the base, providing a passage for the lune oil header. Finished pads on the bottom of the base facilitate its mounting on the site foundation TURBINE SUPPORTS The gas turbine is mounted to its base by vertical supports at three locations. The forward support is located at the lower half of the vertical flange of the forward compressor casing, and the aft two support-legs are located on either side of the turbine shell. The forward support is a flexible plate that rests on two machined pads attached to the forward cross frame beam of the turbine base. The support plate is bolted and doweled to these pads and to the forward flanges of the forward compressor casing. 8

20 The aft supports are leg-type supports, located one on each side of the turbine shell. Both vertical support legs rest on machined pads on the base and attach snugly to the turbine exhaust-frame-mounted support pads. The legs provide centerline support to supply casing alignment. On the inner surface of each support leg a water jacket is provided, through which cooling water is circulated to minimize thermal expansion and to assist in maintaining alignment between the turbine and the generator. The leg-type supports maintain the axial and vertical position of the turbine, while a gib-key coupled with the support legs maintains its lateral position. 3.3 INLET AND EXHAUST SECTION The flow inlet and exhaust is designed for ensuring the following functions: To supply the gas turbine with filtered air flow To provide anti-icing To distribute the bleed heating air flow in homogenous spray To reduce the compressor air inlet acoustical level To protect the air inlet duct against high pressure drop INLET SYSTEM The air inlet duct must provide clean and unrestricted airflow to the engine. Clean and undisturbed inlet airflow extends engine life by preventing erosion, corrosion, and foreign object damage (FOD). Consideration of atmospheric conditions such as dust, salt, industrial pollution, foreign objects (birds, nuts and bolts), and temperature (icing conditions) must be made when designing the inlet system. Fairings should be installed between the engine air inlet housing and the inlet duct to ensure minimum airflow losses to the engine at all airflow conditions. The inlet duct assembly is usually designed and produced as a separate system rather than as part of the design and production of the engine. 9

21 Figure 4: Air filters above the Gas Turbine Generator unit EXHAUST SYSTEM After the gas has passed through the turbine, it is discharged through the exhaust. Though most of the gaseous energy is converted to mechanical energy by the turbine, a significant amount of power remains in the exhaust gas. This gas energy is accelerated through the convergent duct shape of the exhaust to make it more useful as jet thrust - the principle of equal and opposite reaction means that the force of the exhausted air drives the airplane forward. 3.4 COMPRESSOR SECTION The axial flow compressor section consists of the compressor rotor and the compressor casing. Within the compressor casing are the variable inlet guide vanes, the various stages of rotor an stator blades, and the exit guide vanes. In the compressor, air is confined to the space between the rotor Figure 5: Compressor section 10

22 and stator where it is compressed in stages by a series of alternate rotating (rotor) and stationary (stator) airfoil-shaped blades. The rotor blades supply the force needed to compress the air in each stage and the stator blades guide the air so that it enters the following rotor stage at the proper angle. The compressed air exists through the compressor discharge casing to the combustion chambers. Air is extracted from the compressor for turbine cooling for pulsation control during startup COMPRESSOR ROTOR The compressor rotor is an assembly of 15 wheels, 2 stub shafts and wheels assemblies through bolts, and the rotor blades. Each wheel and the wheel portion of each stub shaft has slots broached around its periphery. The rotor blades are inserted into these slots and they are held in axial position by staking at each end of the slot. The wheels and stub shafts are assembled to each other with mating rabbets for concentricity control and are held together with tie bolts. The forward stub shaft is machined to provide the active and inactive thrust faces and the journal for the no.1 bearing, as well as the sealing surfaces for the no.1 bearing oil seals and the compressor low pressure air seal. The stage 17 wheel carries the rotor blades and also provides the sealing surface for the highpressure air seal and the compressor to turbine marriage flange COMPRESSOR STATOR The stator (casing) area of the compressor section is composed of three major sections: Inlet casing. Compressor casing. Compressor discharge casing. These sections, in conjunction with the turbine shell and exhaust frame form the primary structure of the gas turbine. They support the rotor at the bearing points and constitute the outer wall of the gas path annulus. The casing bore is maintained to close tolerances with respect to the rotor blade tips for maximum efficiency. 11

23 INLET CASING The inlet casing is located at the forward end of the gas turbine, in the inlet plenum. Its prime function is to uniformly direct air to the compressor. The inlet casing also supports the n 1 bearing assembly. The n 1 bearing lower half is cast integral with the inner bell mouth. The upper half bearing housing is a separate casting, flanged and bolted to the lower half. The inner bell mouth is positioned to the outer bell mouth by seven airfoil-shaped radial struts and seven axial tie bars. Both the struts and tie bars are cast into the bell mouth walls. Variable Inlet Guide Vane: Variable inlet guide vanes are located at the aft end of the inlet casing. The position of these vanes has an effect on the quantity of compressor air flow. Movement of the inlet guide vanes is actuated by a hydraulic cylinder connected to the inlet guide vane control ring that turns the individual pinion gears mounted on the end of each vane. The gears, the ring and the vanes are shown next page COMPRESSOR CASING The forward compressor casing contains the first- through tenth- compressor stages. It also transfers the structural loads from the adjoining casing to the forward support which is bolted and doweled to this compressor casing s forward flange. Extraction ports in the casing permit removal of fiftheleventh- and thirteenth-stage compressor air. Air from fifth and eleventh-stages is used for cooling and sealing functions and is also used for starting and shutdown pulsation control. Air from thirteenthstage is used for the cooling of the second-stage nozzle DISCHARGE CASING The compressor discharge casing is the final portion of the compressor section. It is the longest single casting. It is situated at the midpoint between the forward and aft supports and is, in effect, the keystone of the gas turbine structure. The function of the compressor discharge casing is to contain the final seven compressor stages, to form both the inner and outer walls of the compressor diffuser, provide inner support for the first-stage nozzle and join the compressor and turbine stators, and support the outer combustion cans. The compressor discharge casing consists of two cylinders, one being a continuation of the compressor casings and the other being an inner cylinder that surrounds the compressor rotor. The two 12

24 cylinders are concentrically positioned by ten radial struts. These struts extend from the inner cylinder outward to a vertical bulkhead. The bulkhead has ten circular openings permitting air flow to enter the combustion system. This bulkhead also provides support to the ten combustion chamber assemblies. A diffuser is formed by the tapered annulus between the outer cylinder and inner cylinder of the discharge casing. The diffuser converts some of the compressor exit velocity into added pressure. 3.5 COMBUSTION SECTION The combustion system is the reverse flow type which includes 10 combustion chambers having the following components: Liners. flow sleeves. Transition pieces. Crossfire tubes. Flame detectors, crossfire tubes, fuel nozzles and spark plugs igniters are also part of the total system. Hot gases, generated from burning fuel in the combustion chambers, are used to drive the turbine. In the reverse flow system high pressure air from the compressor discharge is directed around the transition pieces and into the annular spaces that surround each of the 10 combustion chamber liners. Compressor discharge air which surrounds the liner, flows radially inward through small holes in the liner wall and impinges against rings that are brazed to the liner wall. This air then flows right toward the liner discharge end and forms a film of air that shields the liner wall from the hot combustion gases. Fuel is supplied to each combustion chamber through a nozzle. Combustion chambers are numbered counterclockwise when viewed looking down stream and starting from the top of the machine. The ten combustion chambers are interconnected by means of crossfire tubes. These tubes enable flame from the fired chambers containing spark plugs to propagate to the unfired chambers. The Gas turbine generators used in Omotosho Power Station are made up of 10 combustion chambers. 13

25 3.5.1 COMBUSTION CHAMBERS AND CROSSFIRE TUBES Discharge air from the axial flow compressor enters the combustion chamber from the cavity at the center of the unit. The air flows up-stream along the outside of the combustion liner toward the liner cap. A part of this air enters the combustion chamber reaction zone through the fuel nozzle swirl tip and through metering holes in both the cap and liner. The hot combustion gases from the reaction zone pass through a thermal soaking zone and then into a dilution zone where additional air is mixed with the combustion gases. Metering holes in the dilution zone allow the correct amount of air to enter and cool the gases to the Figure 6: Combustion chamber desired temperature. Along the length of the combustion liner and in the liner cap are openings whose function is to provide a film of air for cooling the walls of the liner and cap. The 10 combustion chamber casings are identical with the exception of those fitted with spark plugs or flame detectors SPARK PLUG AND FLAME DETECTOR Spark plug: Combustion is initiated by means of the discharge from two high-voltage, retractable electrode spark plugs installed in adjacent combustion chambers (No.1 and 10). These spring-injected and pressure-retractable plugs receive their energy from ignition transformers. At the time of firing, a spark at one or both of these plugs ignites the combustion gases in the chambers. The gases in the remaining chambers are ignited by crossfire through the tubes that interconnect the reaction zones of the remaining chambers. As rotor speed increases, chamber pressure causes the spark plugs to retract and the electrodes are removed from the combustion zone. Flame Detector: During the starting sequence, it is essential that an indication of the presence or absence of flame be transmitted to the control system. For this reason, a primary flame monitoring 14

26 system is used consisting of four sensors which are installed on four adjacent combustion chambers (No 2 and 3, 7 and 8) and an electronic amplifier which is mounted in the turbine control panel. 3.6 TURBINE SECTION The three-stage turbine section is the area in which energy in the form of high energy, pressured gas produced by the compressor and combustion sections is converted to mechanical energy. Each turbine stage is comprised of a nozzle and the corresponding wheel with its buckets. Turbine section components include the turbine rotor (wheels, buckets), turbine shell, (nozzles, shrouds), exhaust frame and exhaust diffuser. The turbine converts the gaseous energy of the air/burned fuel mixture out of the combustor into mechanical energy to drive the compressor, driven accessories, and, through a reduction gear, the propeller. The turbine converts gaseous energy into mechanical energy by expanding the hot, high-pressure gases to a lower temperature and pressure. Each stage of the turbine consists of a row of stationary vanes followed by a row of rotating blades. This is the reverse of the Figure 7: Turbine Section order in the compressor. In the compressor, energy is added to the gas by the rotor blades, then converted to static pressure by the stator vanes. In the turbine, the stator vanes increase gas velocity, and then the rotor blades extract energy. The vanes and blades are airfoils that provide for a smooth flow of the gases. As the airstream enters the turbine section from the combustion section, it is accelerated through the first stage stator vanes. The stator vanes (also called nozzles) form convergent ducts that convert the gaseous heat and pressure energy into higher velocity gas flow. In addition to accelerating the gas, the vanes "turn" the flow to direct it into the rotor blades at the optimum angle. As the mass of the high velocity gas flows across the turbine blades, the gaseous energy is converted to mechanical energy. Velocity, temperature, and pressure of the gas are sacrificed in order to rotate the turbine 15

27 to generate shaft power. The efficiency of the turbine is determined by how well it extracts mechanical energy from the hot, high-velocity gasses. Since air flows from a high-pressure zone to a low pressure zone, this task is accomplished fairly easily. The use of properly positioned airfoils allows a smooth flow and expansion of gases through the blades and vanes of the turbine. All the air must flow across the airfoils to achieve maximum efficiency in the turbine. In order to ensure this, seals are used at the base of the vanes to minimize gas flow around the vanes instead of through the intended gas path. In addition, the first three stages of the turbine blades have tip shrouds to minimize gas flow around the blade tips. 3.7 LUBE OIL SYSTEM The lube oil system is designed to lubricate the shaft line including the load gear box and the atomizing compressor gear box, to provide oil for the trip oil system and to provide oil for the hydraulic system. The lubricating oil system is a close loop where oil flows is built up from the oil tank by two Alternative Current motor driven main pumps (one in normal operation and one in standby), a Direct Current motor driven emergency pump for emergency shutdown. The conditions for lubricating oil are: Oil tank warming up to allow cold start of the unit with acceptable oil viscosity Oil flow cooling down to evacuate heat from the bearings Oil flow filtering Oil header pressure regulating at constant pressure Oil mist elimination The lubricating oil temperature during gas turbine operation is between 49 o C 3.8 COOLING WATER SYSTEM The cooling water system is designed for insuring cooling down of the following: The atomizing air system The lubricating oil The flame detectors 16

28 3.9 LOAD GEAR The load gear is located between the gas turbine and the generator, and its function is to transmit the torque of the turbine shaft to the generator shaft through speed reduction. The load gear is a one-step reduction gear. The gear teeth are inviolate double helical teeth. The pinion assembly is connected with the output shaft of the turbine through a rigid coupling, and the low speed gear is directly connected to the generator rotor. The gear shafts are laid out in the longitudinal vertical plane, and the drive shaft (pinion shaft) is above. The casing is divided into three parts: upper, middle and lower. They are bolted on the horizontal joints to be an integral. The whole gear box is installed on a specially designed base plate. The main technical capability data is: Nominal load: Nominal speed of the low speed gear: Nominal speed of the pinion: Center-to-center: Total axial length: Efficiency: 54000kW 3000rpm 5163rpm 660mm 2320mm 99% (under nominal load) Figure 8: Load Reduction Gear 17

29 3.10 GENERATOR SECTION The gas turbo-generator is manufactured in accordance with the technology introduced from the BRITISH BRUSH ELECTRICAL MACHINES LIMITED. It is a three phase synchronous generator which uses the enclosed water-to-air cooling mode. It is horizontal and driven with a gear case. The air cooler is placed on the top of the generator and is directly connected to the stator frame. The rotor windings adopt the advanced internal direct cooling for the conductors. The excitation of the generator is brushless excitation. The excitation system consists of a three-phase AC exciter which is coaxial with the generator and a single-phase AC permanent magnet auxiliary exciter. The excitation current by the main exciter is inputted to the excitation windings of the generator. The generator is equipped with an automatic voltage regulator. The generator specifications are given below: Nominal capacity: 38MW Nominal voltage: 10500V Nominal current: A Frequency: 50Hz Power factor: 0.8 Efficiency: 97.8% Short circuit ratio: 0.46 Sub-Transient reactance: Connection: Y Protective type: Enclosed Rotation direction: Clockwise viewed from prime mover towards generator Generator critical speed: 1333r/min (first step), 3780r/min (second step) The temperature of the cooling air should not be more than 40 0 C. 18

30 Figure 10:: Rotor of the Stator undergoing inspection Figure 9: Stator of the Generator Figure 11: Stator and Rotor of a Gas Turbine Generator 19

31 3.11 ELECTRICAL EQUIPMENT NEUTRAL CUBICLE A neutral cubicle (neutral cab) is provided for the lead from the neutral of the generator. In the cubicle, there are six current transformers and a neutral arrestor. Each phase has two current transformers, and each current transformer has two secondary compartments which are provided for protection and measurement respectively. In the lower section of the cubicle there are connection terminals for the secondary outgoing line connection OUTGOING LINE CUBICLE An outgoing line cubicle (outgoing line cab) is provided for the leads from the generator outlet. In the cubicle there are a three-phase arrestor, three protective capacitors and a discharge counter. Besides, there are connection copper bars for outgoing cables. 20

32 CHAPTER FOUR ACTIVITIES CARRIED OUT IN DEPARTMENTS This chapter gives a detailed description of the responsibilities of the technical departments in the company. 4.1 ELECTRICAL MAINTENANCE DEPARTMENT The Electrical maintenance department was first department I visited upon resumption at Omotosho Power Plant. This department is comprised of both Electrical and Instrumentation and Control (I&C) Sections ELECTRICAL Electrical department is the department in power generation companies equipped with the responsibility of maintenance of all electrical parts of the gas turbine units, installation and maintenance of switchgears in the station environment, servicing and repair of electrical devices used in the company, daily routine maintenance of equipment around the plant, servicing of breakers, transformers, isolators, contactors, and electrical equipment in general. The maintenance carried out by this department is either preventive, predictive or corrective in nature Roles of Electrical Department The department carries out maintenance on electrical devices and equipment in offices around the plant such as air conditioning units, switches, breakers, lighting equipment and so on. Routine maintenance is carried out on a daily, monthly, quarterly or yearly basis on equipment in the switch yard, control room and other electrical equipment in other departments like electric pump motor in the laboratory department. In this type of maintenance, the equipment is checked if it is in good working conditions and also the environment is made sure to be well ventilated and clean of dirt. Preventive maintenance is carried out on equipment in order to avoid a future of possible breakdown of the equipment. 21

33 PICTURES FROM WORKING IN ELECTRICAL DEPARTMENT Figure 12: Working on Auxiliary transformers in Switchyard Figure 13: Lighting arrestors Figure 14: Cleaning the Star point after a minor explosion 22

34 Figure 16: Star point of a Gas Turbine Generator Figure 15: Upper Isolator in 10.5KV Switchyard INSTRUMENTATION AND CONTROL (I&C) Instrumentation is the branch of engineering that deals with the measurement and control of parameters such as vibration, temperature, pressure, gas flow rate, etc. it is a collection of instruments and their application for the sole purpose of observation, measuring and control. When a variable is being measured using an instrument related to it, the output signal is sent to a control system (Mark VI) or other computerized controllers, where it is being interpreted into readable values from the Human Machine Interface (HMI) and is then used as comparison for set points to trigger alarms when exceeded or used to control devices in the power station i.e. solenoids, actuators, switches and so on in other to achieve accurate processes. This department deals with the maintenance of these instrumentation and control systems that have been designed to provide advanced monitoring and diagnostics to prevent damage to the unit and to enable it to operate at its peak performance. 23

35 ROLES OF INSTRUMENTATION AND CONTROL DEPARTMENT Instrumentation and Control (I&C) department is regarded as the brain of the power station, and is saddled with the responsibility of maintaining, servicing, monitoring, calibrating and installing all the instruments used in the operation and control of the power plant. Some of the roles of engineers in the instrumentation and control department are: Maintenance of Mark VI Maintenance of computer systems in the plant Maintenance of control devices like solenoids, actuators, switches, etc. Maintenance of controllers Maintenance of thermocouples and so on CONTROL INSTRUMENTS The following presents a brief description of some of the control instruments used in Omotosho Power Plant. CONTROL VALVES: Control valves are valves used to control conditions such as flow, pressure, temperature and liquid level by fully or partially opening or closing in response to signals received from controllers that compare a set point to a process variable whose value is provided by sensors that monitor changes in such conditions. The opening or closing of valves is done by means of electrical, hydraulic or pneumatic systems. Accessories which are normally attached to the control valves include positioners, lock up valves and controllers, as briefly discussed below: VALVE ACTUATOR: This is a device that operates a valve and moves the flow-control element to the desired position- opened, closed, or throttling. The actuator must overcome valve unbalance and frictional forces, and provide enough loading to shut off the control element against the seat. The actuator is typically powered by pressurized air POSITIONER: Valve positioner is a device that precisely positions the valve plug or stem. Valve positioners are used on many valves to overcome frictional forces inherent to the valve and actuator assembly. The positioner's primary function is to accurately move the valve to the desired 24

36 position in response to a signal from a controller. The positioner command signal can be pneumatic, analogue or digital. LOCK UP VALVE: This device is responsible for the safe operation of the actuator. It provides constant air pressure to the diaphragm of the valve depending on the output of the positioner. At shut-off, it maintains the actuator at closed position and at any other position or fully opened, it keeps the valve at that position without any variation. SWITCHES There are several kinds of switches used in control engineering and they are classified based on the quantity or signal which turns them (automatically) on or off at preset values or points of such quantity or signal. Hence, examples of such switches are: Pressure (and Differential Pressure) Switches, Temperature Switches, Level Switches, Ethernet switches and Limit Switches. PRESSURE SWITCHES: A pressure switch is a form of switch that makes electrical contact when a certain set pressure has been reached on its input. This is used to provide ON/OFF switching from a pneumatic or hydraulic source. The switch is either designed to make contact either on pressure rise or pressure fall. DIFFERENTIAL PRESSURE SWITCHES: A differential pressure switch is an instrument that converts differential pressure change between two systems to an electrical function. When the pressure in one or two systems increases or decreases to a set differential point relative to the other, the electrical state of the differential pressure switch changes, ON to OFF and/or OFF to ON to operate an electrical circuit or issuing an alarm in the central control room. LIMIT SWITCHES: A limit switch is a mechanical device which can be used to determine the physical position of equipment. For example, an extension on a valve shaft mechanically trips a limit switch as it moves from open to shut or shut to open. The limit switch gives ON/OFF output that corresponds to valve position. Normally, limit switches are used to provide full open or full shut indications. Many limit switches are the push-button variety. When the valve extension comes in contact with the limit switch, the switch depresses to complete, or turn on, the electrical circuit. LEVEL SWITCHES: General side mounted liquid level switches are designed for horizontal mounting in a tanks or vessel through flanged pipe connections. It is specially designed with an external test plunger mechanism. The device operates on a pivoted float with attached magnet follows the liquid level to initiate an electrical signal when it reaches a specific position. 25

37 Switching action is obtained by means of a magnetic follower system. These two basic component assemblies are in different compartments separated by a pressure-tight chamber. CONTROLLERS A controller is a device that generates an output signal based on the input signal it receives. The input signal is actually an error signal, which is the difference between the measured variable and the desired value, or set point. This input error signal represents the amount of deviation between where the process system is actually operating and where the process system is desired to be operating. The controller provides an output signal to the final control element, which adjusts the process system to reduce this deviation. The characteristic of this output signal is dependent on the type, or mode, of the controller. Four modes of control commonly used for most applications are: Proportional (P), Proportional plus reset (PI), Proportional plus rate (PD), Proportional plus reset plus rate (PID). Each mode of control has characteristic advantages and limitations. PID CONTROLLER: A Proportional-Integral-Derivative Controller (PID Controller) is a generic loop control loop feedback mechanism (controller) widely used in industrial control systems. A PID controller calculates an error value as the difference between a measured process variable and a desired set point. The controller attempts to minimize the error by adjusting the process control inputs. The PID parameters used in the calculation must be tuned according to the nature of the system. The PID controller calculation (algorithm) involves the separate parameters; the proportional, the integral and derivative values. The proportional value determines the reaction to the current error, the integral value determines the reaction based on the sum of the recent errors and the derivative value determines the reaction based on the rate at which the error has been changing. The weighted sum of these three actions is used to adjust the process via control elements such as the position of a control valve. The response of the controller can be described in terms of the responsiveness of the controller to an error, the degree to which the controller overshoots the set point and the degree of system oscillation. ELECTRO-PNEUMATIC CONVERTERS (TRANSDUCERS): These converters are precision electronic pressure controllers designed for continuous process control application. Electro-pneumatic transducer is a device that receives a current (ma) DC input signal and transmits a proportional pneumatic output pressure. A typical application is in electronic control 26

38 loops where the final control element, generally a control valve is pneumatically operated. Other instruments include: Transmitters, Dampers, Indicators and Recorders PICTURES OF INSTRUMENTATION AND CONTROL INSTRUMENTS Figure 17: Fuel shut-off valve Figure 19: Condensate level guage Figure 18: Turbine wheel space thermocouple 27

39 4.2 MECHANICAL MAINTENANCE DEPARTMENT INTRODUCTION The mechanical department are responsible for the maintenance of all mechanical parts of the unit, lube oil systems, air-conditioning and ventilation systems, refrigerators, welding, and fabrication jobs as well as maintenance of automobiles (light and heavy vehicles, mobile plants) ROLES OF MECHANICAL MAINTENANCE DEPARTMENT Mechanical department is one of the maintenance departments in Omotosho Power Plant. The following highlights the maintenance carried out by this department which are on daily, weekly, monthly and annual basis. The roles of this department involve: Maintenance of the generators and their allied components Maintenance of large motors e.g. CCWP, CWP etc. Maintenance of small motors Maintenance of all the automobiles Maintenance of the ventilating system (air-conditioners etc.) Maintenance of all the furniture in the plant Maintenance of all the mechanical parts in the unit Maintenance of lube oil tank Servicing of generators which included replacement of oil and fuel filters Welding of cracked inner body of exhaust system 4.3 OPERATIONS DEPARTMENT The operations department is the department that deals with the monitoring and control of the plant from the central control room and the unit control room 28

40 4.3.1 ROLES OF OPERATIONS DEPARTMENT The Operations Department is equipped with the following responsibilities: Overall operation of the Gas-Turbine-Generator (G.T.G) System, which is the most essential system in the power plant. Operation of all the auxiliary systems and equipment connected to the G.T.G for the generation of electricity. These systems include: the accessory drive system, the fuel system, the cooling water system, lube oil system, fire protection system, hydraulic supply system, compressor washing system, oil mist eliminator system, pumps, motors etc. Monitoring of plant parameters for the purpose of control. The main parameters monitored include: Pressure, Temperature, Level, Flow, Voltage, Current, Power, Speed and Position among others. This is done via the various instruments such as meters, gauges, indicators, recorders etc. Periodic logging of appropriate data (log sheets) for the purposes of control, analysis and performance evaluation. Onward transmission of generated power to the transmission switchyard. Control of the interconnected/synchronized/grid frequency, voltage and power stability, under the supervision of the National Control Centre, Oshogbo CONTROL PANELS The operation of Omotosho Power Plant, being automated, is done through the control panels. A number of devices, instruments and facilities are provided on the panels for information and use by the operators. Lamps: To indicate circuit conditions. Red (circuit on), Green (Circuit off) and Amber (faulty/abnormal condition) Push Buttons: To initiate or stop control actions Indicators, Meters and Gauges: To indicate values of controlled parameters (e.g. pressure, temperature, voltage, current, power etc.) at every instant of time. 29

41 Mimic Panels: To provide information on the flow of action/process flow and indicate the relative location and linkages of the plant's equipment. Annunciator Board: To provide audible and visual indication of abnormal plant/equipment conditions ANNUNCIATOR BOARD CIRCUIT BREAKER DANGEROUS GAS DETECTORS Figure 20: Generator Auxiliary Control Panel CURRENT, VOLTAGE INDICATORS LAMP INDICATORS FREQUENCY, SYNCHRONIZER AND VOLTAGE METERS DIGITAL MULTIMETER Figure 21: Generator Control Panel 30

42 HUMAN MACHINE INTERFACE (HMI) This is an environment or interface where the brain of the unit sends data for record and monitoring purposes. Figure 23: H.M.I showing the startup where all parameters can be recorded Figure 22: H.M.I. showing the wheel space temperature at specific points 31

43 4.3.4 GAS TURBINE STARTUP AND SYNCHRONIZATION PROCEDURES To start up a gas turbine generator, the following procedures have to be followed duly: 1. Take shift leader order to start GT and conduct inspection prior to startup. 2. Check and confirm the following; GT MCC voltage, MARK VI control cabinet and communication of switchboard, abnormal alarms on generator protection panel and reset, gas detecting device and fire protection device, turning gear, oil tank level, cooling water pressure, valves in gas station in correct position. 3. Start BLACK START diesel generator, 3KV voltage should be normal. 4. Manaully start and stop DC oil pump 88QE. 5. Enter control. Enter start up. Click on mode select. Select Auto light is on click on Master reset. STARTCHECK shows READY TO START. The 88CR[starting motor], hydraulic oil pump, lube oil pump, start automatically. STARTING show in the satus. 6. When speed reach a self-sustained speed at 60% the 88CR stop working and shaft continue to power itself. 7. When the speed reach 83% the inlet guide vane open to 57% to allow in flow of air. 8. At 95% the hydraulic pump, and lube oil pump stop working and turbine cooling motor 88TKs start immediately. 9. At full speed no load the exhaust temperature is been checked, bearing temperature, reeturn oil situation and the machine is ready to be synchronise. 10. Synchronization process is actuated, load is been increase from 5MW, 10MW,20MW to Select base load. 32