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58995925 a-report-on-eletrical-maintenance-in-hpcl


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58995925 a-report-on-eletrical-maintenance-in-hpcl

  1. 1. AbstractHPCL Vishakh refinery was established in 1957 and was subsequently mergedwith ESSO which was multinational oil company of USA, which was setup inMumbai and came with a new origin Hindustan Petroleum Corporation of IndiaLimited (HPCL) in 1998. Electrical maintenance is one of the most crucial aspectsin the refinery to ensure good productivity, reliability and safety against firehazards. The industry thus employs one of the most advanced forms ofmaintenance techniques, i.e., IR Thermography, Vibration Health Analysis, etc…This report of the project shows an overview of the employed maintenancetechniques. 1
  3. 3. ACKNOWLEDGEMENT We would like to thank Mr. S.K.Mishra, Sr. Manager-Training, foraccepting our request for industrial training at HPCL, Visakh Refinery. We express our deep sense of gratitude and respect to Mr. N.Rajarao,Chief Manager, and Maintenance Electrical.We heartily thank B.Jayanth Rao senior Manager, Planning Electrical for givingus enthusiastic support and guidance.We express our thanks to Mr. B.J.Benhar Babu, Manager Maintenance,Mr.Rama Chadra Rao Deputy Manager, Mr.nikki Agarwal Deputy manager,Mr. Pritam Majamder Engineer for guiding us with great attention, care andproviding vital support at HOCK, Visakh refinery. 3
  4. 4. About HPCLHPCL is a fortune 500 company, with annual turnover of Rs 1,16,428 crores and sales-/income from operations Rs 1,31,802 crores ( US $25,618M) during FY 2008-09, havingabout 20% marketing share in India and is strong market infrastructure. Correspondingfigures for FY 2007-08 are is to turnover of Rs 1,03,837 Crores and sales/ income fr4omoperations of Rs 1,12,098 Crores ( US $ 25,142M).HPCL operates two major refineriesproducing a wide variety of petroleum fuels and specialties, one in Mumbai (West coast)of 6.5 million metric tons per annum (MMTPA) capacity and the other inVishakhapatnam, (East coast) with a capacity of 7.5 MMTPA. HPCL holds an equitystate of 16.95% in Mangalore refinery and p0etro chemicals limited, in state-of-the-artrefinery at Mangalore with a capacity of 9 MMTPA. In addition, HPCL is constructing arefinery at Bhatinda, in state of Punjab. HPCL also owns and operates the largest luberefinery in the country producing lube based oils of international standards, with acapacity of 335 TMT. This lube refinery accounts for over 40% of India‘s total lube baseoil production. Presently HPCL produces over 300+ grades of lube, specialties andgreases.HOCK ‗s vast marketing network consists of 13 zonal offices in major cities and90 regional offices facilitated by a supply and distributio0n infrastructure compressingterminals, aviation service station, LPG bottling plants, and an inland relay depots andretail outlets, lube and LPG distributorships . HOCK, over the years has moved fromstrength to strength on all fronts the refining capacity sturdily increased from 5.5MMTPA in 1984/85 to 13 MMTPA presently. On the financial fronts, the turnover grewfrom RS 2687 Crores in 1984-85 to an impressive Rs. 1, 16,428 crores in FY 2008-09.HPCL has an ―Excellent‖ performance for fifteen consecutive years up to 2005-06, sincesigning of the first MOU with the ministry of petroleum and natural gas. HPCL won theprestigious MOU award for the year 2007-08 for excellent overall performance.Vishakh refinery:Rapid worldwide industrialization and scientific advancements has resulted incontinuously raising energy requirements in all sectors e.g. industries, transport etc.petroleum being one of the major source of energy there is a pressing need forincreasing the production of the crude oil as well as the desire fuel production.Concerted efforts are being made for maximizing the crude oil production from oil fields.As a result, quality of crude becomes heavier day by day. A simple distillation of crudeoil is not sufficient and economical top meet the demand of the petroleum products espdue to the increasingly heavy nature of crude oil producing using the modern advanced 4
  5. 5. method of crude production. Hence the refineries are required to adopt ―Bottom ofBarrel Processing Concept‖ for meeting the product demand.In the context, vishakh refinery was established in 1957 and was subsequently mergedwith ESSO which was multinational oil company of USA, which was setup in Mumbaiand came with a new origin Hindustan Petroleum Corporation of India Limited (HOCK)in 1978. Over the year the capacity of the refinery was increased to 1.5 MMTPA by de-bottlenecking units.The major refinery capacity augmentation was taken up in 14985 by commissioningseparate streams of 3.0 MMTPA crude distillation units ( CDU-2), fluidized catalyticcracking unit ( FCCU-2), crude oil receiving facilities at high seas ( Offshore tankerterminal ) and associated tankage and product dispatch facilities. Thus the installedcapacity has increased to 4.5 MMTPA. The facilities came up in 1985 were the state-of-the art control system for the better and efficient operation.An order to cater to the increased LPG consumption, the refinery works instrumental indeveloping first LPG import facilities on the eastern coast in 1987. As a step towardssurmounting the frequent power distribution and improve reliability of utilizes a CaptivePower Plant (CPP) of 14 MW capacity was widening its product range commissionedPropylene Recovery Unit (PRU) in 1992.In order to adhere to stringent environment norms the refinery had setup EffluentTreatment Plant (ETP) in 1993 and sulphur recovery unit (SRU) in 1994. With thesecond major expansion project VREP-2 completed in 1999 crude processing capacityincreased from 4.5 MMTPA to 7.5 MMTPA and secondary capacity increased from 1.5-1.6 MMTPA. To meet the stringent diesel fuel specification, Diesel Hydro DeSulphurisation unit (DHDS) was also commissioned in 1999 /2000. To meet additionalpower requirement of these new units, CPP capacity was augmented by 40 MW in1999, increasing total power generation capacity to 58 MW.It is a crude oil processing refinery having a capacity of 7.5 MMTPA. The processingunits include crude units, fluidized catalytic cracking units, propylene recovery units andtreating units like DHDS and SRU. The total load of the existing refinery is about 39MW. This load is being met by the HPCL with the help of four gas turbine generatorsand heat recovery steam generators. The combined power and steam output of steamgenerating units and the HRSG‘s at fight conditioned is about 54 MW and 174 TPH ofMP steam respectively. The HPCL‘s present power and steam requirements are met byfollowing in-house GTG‘s and HRSG‘s. 2x9MW FRAME-3, GTG 1 and 2 with HRSG‘sinstalled in 1990 2x20MW FRAME-5, GTG 3-6 with HRSG‘s installed in 1999. Apartfrom the captive generators, HPCL has two AP TRANSCO grid incomers at 132 KVlevel. 11KV supply is derived by two numbers 16/20MVA, 132/KV grid transformers. 5
  6. 6. The present contract demand with APTRANSCO in 13MVA at 0.9pf. HPCL is currentlyusing grid as hot standby and the grid incomers are not paralleled with the GTG‘s undernormal operating conditions.The refinery is located at latitude of 17‘41‖N and longitude of 83‘17‖ E on an area takenon a 99 years lease from Vishakhapatnam port trust. 6
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  8. 8. Table of contents: Introduction – About HPCL 1Chapter 1: Electrical Maintenance What is electrical maintenance? 4 Types of electrical maintenance 5  Breakdown maintenance 5 Preventive maintenance 6  Predictive maintenance 6 Methods used in predictive maintenance 7Infrared thermography 7 Motor current signature analysis 8 Equipment health analysis 9Tan delta test 11 Cable fault locating analysis 12 Surge generator 13 Digital time domain reflectometer 13 Indicator Digipoint 15 Cable route tracer 15 High potential test 17Chapter 2: captive power plant Introduction 19 Step-up sequence of CPP 19CPP facilities 20 Gas turbines 20 8
  9. 9. Theory of GTG 20 Generators 22 Generator details 23Functional description 24  Basic cycle 24  Gas turbine equipments 24  Air inlet equipment 25  Compressor section 25 Rotor assembly 26  Stator 26  Fuel system 28  Diesel system 29  Naphtha valve 29  Brushless generator- basics 29  Automatic voltage regulator 30  Heat recovery steam generator 31Chapter 3: power distribution in HPCL Substations 32 Switch gear 33 Bus 34 Power transformers 35 Sub 36 Motor control centre 36 Power control centre 36 Single line diagram of power distribution in HPCL Direct online starters in SS-50 37 Variable frequency drives 38 9
  10. 10. Variable frequency motor 39 Variable frequency controller 39 Dynamic breaking 40 Rectifier in VFD 40 Bibliography41 10
  11. 11. Chapter 1:What is electrical maintenance?Electrical maintenance is the upkeep and preservation of equipment and systems thatsupply electricity to a residential, industrial or commercial building. It may be performedby the owner or manager of the site or by an outside contractor. The work is commonlyperformed on a schedule based on the age of the building, the complexity ofthe electrical system or on an as-needed basis.The main areas of general electrical maintenance commonly include the power outletsand surge protectors, generators and lighting systems. These supply sources arechecked for structural integrity as well as internal stability.Preventive electrical maintenance is also generally part of a building‘s upkeep. This planordinarily includes the scheduled inspection of large systems and equipment by aprofessional electrician. The purpose of these periodic assessments is to fix smallproblems before they escalate into large ones. Preventive electrical maintenance isparticularly important at plants, hospitals and factories that heavily rely on thesesystems for daily operation.Electrical generators, switches and circuit breakers are regularly checked for solidconnections and intact wiring. If flaws are discovered, electricians normally repair thewiring. Depending on the condition of the wiring, the repairs are typically made bysplicing wires together. In some situations, the wires are encased in metal tubing calledconduit to protect them from wear. Keeping the wiring in good shape ensures aconsistent flow of power to heating, ventilation and air conditioning systems. 11
  12. 12. Flow chart showing electrical maintenanceTypes of electrical maintenance:Corrective maintenance:Breakdown maintenance can be defined as a maintenance task performed to identify,isolate, and rectify a fault so that the failed equipment, machine, or system can berestored to an operational condition within the tolerances or limits established for in-service operations.Corrective maintenance is the most commonly used maintenance approach but it iseasy to see its limitations. When equipment fails, it often leads to downtime inproduction, and sometimes damages other parts. In most cases, this is expensive. Also,if the equipment needs to be replaced, the cost of replacing it alone can be substantial 12
  13. 13. Planned Preventative Maintenance:(PPM) or more usual just simple Planned Maintenance (PM) or ScheduledMaintenance is any variety of scheduled maintenance to an object or item of equipment.Specifically, Planned Maintenance is a scheduled service visit carried out by acompetent and suitable agent, to ensure that an item of equipment is operating correctlyand to therefore avoid any unscheduled breakdown and downtime.Together with Condition Based Maintenance, Planned maintenancecomprises preventive maintenance, in which the maintenance event is preplanned, andall future maintenance is preprogrammed. Planned maintenance is created for everyitem separately according to manufacturers recommendation or legislation. Plan can bebased on equipment running hours, date based, or for vehicles distance travelled. Goodexample of PM program is car maintenance. After so many kilometers or miles oilshould be changed, parts renewed.Planned maintenance has some advantages over Condition Based Maintenance suchas: easier planning of maintenance and ordering spares, costs are distributed more evenly, No initial costs for instruments for supervision of equipment.Disadvantages are: less reliable than equipment with CBM More expensive due to more frequent parts change.Predictive maintenance (PdM):Predictive maintenance techniques help determine the condition of in-service equipmentin order to predict when maintenance should be performed. HPCL mostly uses this typeof maintenance. This approach offers cost savings over routine or time-based preventive maintenance, because tasks are performed only when warranted.The main value of Predicted Maintenance is to allow convenient scheduling ofcorrective maintenance, and to prevent unexpected equipment failures. The key is "theright information in the right time". By knowing which equipment that needsmaintenance, the liability. Other values are increased equipment life time, increasedplant safety, less accidents with negative impact on environment, an optimized spareparts handling, etc.The "predictive" component of predictive maintenance stems from the goal of predictingthe future trend of the equipments condition. This approach uses principles of statistical 13
  14. 14. process control to determine at what point in the future maintenance activities will beappropriate.Most PdM inspections are performed while equipment is in service, thereby minimizingdisruption of normal system operations. Adoption of PdM can result in substantial costsavings and higher system reliability.To evaluate equipment condition, predictive maintenance utilizes nondestructivetesting technologies such as infrared, acoustic (partial discharge and airborneultrasonic), corona detection in combination with measurement of process performance,measured by other devices, to trigger maintenance conditions. This is primarilyavailable in Collaborative Process Automation Systems (CPAS). Site measurementsare often supported by wireless sensor networks to reduce the wiring cost.Methods used in predictive maintenance at HPCL:Infrared thermography: The most popular and widely used application of infrared thermography is electricalswitchgear testing. No other commercial application has achieved the level of interestthan that of electrical infrared thermography. Daily, the electrical switchgear inthousands of buildings are checked by thermographers all over the country. ElectricalInfrared is now an integral part of any facility managers preventative/predictivemaintenance (P/PM) program.Infrared thermography is used to perform P/PM inspections on electrical equipmentbecause excess resistance on electrical apparatus indicates electrical faults such asloose connections, , it heats up. Thermography is used to see the excess heat(resistance) so that problems can be found and maintenance personnel can act tocorrect the problem before the component fails, causing damage to the component,safety hazards and/or production downtime. 14
  15. 15. Contacts seen by an Infrathermal cameraMotor current signature analysis:Traditional CSA (Current Signature Analysis) measurements can result in false alarmsand/or misdiagnosis of healthy machines due to the presence of current frequencycomponents in the stator current resulting from non-rotor related conditions such asmechanical load fluctuations, gearboxes, etc. more robust and less error pronetechnology.The operators of electrical drive systems are under continual pressure to reducemaintenance costs and prevent unscheduled outages that can result in lost productionand revenue. The application of condition based maintenance strategies rely onspecialized monitors to reliably provide a measure of the health of the drive system. 15
  16. 16. Fig: Motor current signature analysis Thus, unexpected failures and consequent downtime may be avoided and/or the timebetween planned shutdowns for planned maintenance may be increased. Maintenanceand operational costs are thus reduced. During the past twenty years, there has been a substantial amount of fundamental research into the creation of condition monitoring and diagnostic techniques for induction motor drives. Motor Diagnostic technologies have become even more prevalent through the 1990‘s and into he new century. The technologies include both Motor Circuit Analysis (MCA) and Motor Current Signature Analysis (MCSA) applied to both energized and de- energized electric motor systems. The applications appear to be almost endless. AC Motors and Alternators IDC Motors and Generators Single and Three phase systems Eddy-Current drives Variable Frequency Drives Incoming power qualityEquipment health Analysis:The emerging trend in the industry and major commercial complexes is PredictiveMaintenance. Predictive maintenance helps in improving up time of equipment or asystem thereby contributing to increased productivity and avoiding unplanned outages.Vibration monitoring & analysis is one the important and proven tools in analyzinghealth of the rotating machines as it can detect 80 to 90% of developing problems.Vibration values are definitely a good parameter to study the current condition ofrotating equipment. This value can be captured in varied ways. The interval betweenthese measurements can be optimized through Maintenance Partners for any type of 16
  17. 17. machinery. Because of this technique Maintenance Partners offers a powerful tool fordetecting damages in early stage. Fig: Vibration health analysisTan delta test:The tan delta test is a diagnostic procedure to assess the deterioration of the insulationof a medium- or high-voltage cable.Due to the well known water-tree effect the conductivity of the insulation increases, thisreflects in an increase of tan delta values.So, the interpretation of tan delta test results gives an idea about the aging process inthe cable-insulation and hence, allows an assessment of the operational reliability of thecable.The test engineer is able to distinguish between new, strongly aged and faulty cablesand appropriate maintenance and repair measures may be planned. 17
  18. 18. Fig: Tan delta test equipmentIf however the insulation deteriorates due to moisture the current will also show aresistive component, and the angle between voltage and current will decrease.By a highly accurate measurement of the phase lag between current and voltage thedissipation factor tan d can be determined.The dissipation factor tan d is defined as the ratio between active current and idealcapacitive current.That prevents the device under test from damages during the tan delta test andguarantees damage-free measurement.Cable fault locating analysis:The Process of cable fault location comprises of four distinct, but interrelated stages viz.1. Testing for detection of the nature of fault.2. Conditioning / burning of faults for location.3. Pre-location : Approximate location based on changed electrical relationship dueto fault.4. Pin Point location. 18
  19. 19. Surge Generator:Instrument has been primarily designed to produce high voltage surges for pre-locationof underground cable fault in combination with inbuilt Reflectometer. LCD Screen forReflectometer. Fig: surge generatorThe surges produced help in pinpointing the fault and tracing the route of the cablewhen used with acoustic DIGIPOINT, surge generator generates D.C. high voltage forpressure testing of the underground cables to find out faulty phase and the breakdownvoltage with leakage current.Digital time domain reflectometer:Reflectometer is a Laptop based Digital Time Domain Reflectometer for pre-location offaults in power Cables. Its state-of-art technology makes it easy to use and yet mostreliable for any fault condition. The interactive graphical user interface makes it easy, foreven a layman, to pre-locate the fault distance. Serial Port makes the device extremelyflexible.The device has three working modes namely IMPULSE MODE and PULSE ECHOMODE. Pulse echo mode is useful only for open and shot types of faults. The impulsemode when used with surge generator to pre-locate fault distance of almost all types of 19
  20. 20. faults including open, short and intermittent faults by way of ICM, Decay & ARMMethod.Fig: time domain reflectometerThe software provides a huge storage capacity so that you may use the Reflectometertest result for future reviews & analysis. The VOP (Velocity of Propagation) controlmakes it easy to precisely pre-locate the fault distance on cables with different velocityof propagation. The test waveforms can be printed as a hardcopy directly from thesoftware. The fault readings can be transferred over INTERNET for further assistance.The software is so programmed that it automatically saves all the test results, so thatyou never miss any important result. All the files are stored on the bases of date andtime of the reading taken.Indicator digipoint:The DIGIPOINT is an easy to use, dual channel Digital Acoustic Fault Locator. It is usedin conjunction with a Surge Generator to determine the exact position of faults in 20
  21. 21. underground power cables. The instrument also indicates the cable by sensing andamplifying the electromagnetic signals produced at the time of surges. Fig: DigiphoneThe DIGIPOINT consists of two units – the Acoustic transducer or pick–up and theamplifier unit with head phones.The unique feature of DIGIPOINT provides a relative distance indicator with digitalcoincidence figure readout.This feature is very helpful for the operator in pinpointing the exact location of fault.Cable route tracer:The TII Advanced Cable Locator is a microprocessor-based system that incorporatesadvanced digital signal processing techniques to quickly and efficiently trace the pathof underground cables, both copper and fiber optic(with metallic trace wire).• Locates cable path• Measures cable or sonde depth with the push of a button.• Measures signal current in the cable.• Identifies cable using toning function.• Locates energized power cable with direct readout of cable depth.The cable locator provides accurate cable or sonde depth measurements,giving a digital readout in inches, feet and inches, or centimeters (user-selectable).Additionally, when used in conjunction with the EMS Marker Locating Accessory, thelocator can:• Pinpoint the exact location of buried EMS markers• Trace a cable path while simultaneously finding buried markers along the way. 21
  22. 22. Four modes of operation for accurate locates, even in congested areas:For cable path locating, the receiver uses one of four user selected locating modes –dual peak, dual null, differential or special peak (which increases the sensitivity of thereceiver for tracing over longer distances). The mode is selected depending on which ismost effective under the locating conditions.The receiver includes four volume settings, including a special ―expander‖ function thatmakes peaks and nulls more pronounced.The expander feature enhances the amplitude difference between two conductorscarrying the same signal, making the unit extremely accurate, even in congestedareas. A headphone jack is also included.The Advanced Cable Locator is easy to operate and requires very little training.Digital liquid crystal display (LCD) readout and push-button operation make the uniteasy to understand, for more precise locates. A ―memory‖ feature remembers operatorset-up from previous use.The system consists of two basic components:• Transmitter with built-in ohmmeter, which also senses and measures the presence offoreign voltage, and tests the continuity of the circuit.• One-piece hand-held receiver with bar graph that indicates received signal andproximity to the cable.The cable locator uses four active trace frequencies - 577 Hz, 8 kHz, 33 kHzand 200 kHz — which can be usedindividually or simultaneously to compensate for varying field conditions.High potential test:Hipot is an abbreviation for high potential. Traditionally, Hipot is a term given to a classof electrical safety testing instruments used to verify electrical insulation in finishedappliances, cables or other wired assemblies, printed circuit boards, electric motors,and transformers.Under normal conditions, the insulation in a product can break down, resulting inexcessive leakage current flow. This failure condition can cause shock or death toanyone that comes into contact with the faulty product. 22
  23. 23. Fig: Hipot test equipmentA Hipot test (also called a Dielectric Withstand test) verifies that the insulation of aproduct or component is sufficient to protect the operator from electrical shock. In atypical Hipot test, high voltage is applied between a products current-carryingconductors and its metallic shielding. The resulting current that flows through theinsulation, known as leakage current, is monitored by the hipot tester. The theorybehind the test is that if a deliberate over-application of test voltage does not cause theinsulation to break down, the product will be safe to use under normal operatingconditions—hence the name, Dielectric Withstand test. Environmental factors such ashumidity, dirt, vibration, shock and contaminants can close these small gaps and allowcurrent to flow. This condition can create a shock hazard if the defects are not correctedat the factory. No other test can uncover this type of defect as well as the DielectricWithstand test.Three types of Hipot tests are commonly used. These three tests differ in the amount ofvoltage applied and the amount (or nature) of acceptable current flow:Dielectric breakdown Test:: The test voltage is increased until the dielectric fails, or breaks down, allowing toomuch current to flow. The dielectric is often destroyed by this test so this test is used ona random sample basis. This test allows designers to estimate the breakdown voltage ofa products design.Dielectric Withstand Test: A standard test voltage is applied (below the established Breakdown Voltage) and theresulting leakage current is monitored. The leakage current must be below a preset limitor the test is considered to have failed. This test is non-destructive and is usually 23
  24. 24. required by safety agencies to be performed as a 100% production line test on allproducts before they leave the factory.Insulation Resistance Test This test is used to provide a quantifiable resistance value for all of a productsinsulation. The test voltage is applied in the same fashion as a standard Hipot test, butis specified to be Direct Current (DC). The voltage and measured current value areused to calculate the resistance of the insulation.Chapter 2Captive power plant:The power requirement of HPCL–VR was earlier being met from APSEB. Howeverfrequent interruption in power supply were observed which causes crude through putloss, damage to equipment, fire hazard and unscheduled shutdown. With the above inview APSEB permitted HPCL, to install CPP. The CPP commissioned in 1991 is bussedon cogeneration of power and steam, leading to more energy efficient use of fuels ascompared to a conventional power plant. The project step-up includes number of 9 MWCapacities (ISO) gas turbines generators (GTG‘s) along with two numbers heatrecovery steam generators (HRSG) of 2.94 T/HR at 15 at 256 Centigrade in unfiredcondition at GTG base load. For that in view of VR expansion process from 4.5 MMTPAto 7.5 MMTPA and to meet the power requirement of refinery another set to GTG‘s ofgenerating capacity to 25MW (ISO) each along with two number of HRSG of 60 T/HR at15 at 280 centigrade in unfire3d condition at GTG base load another auxiliaryequipment are installed on a part of VREP-H during 1999-2000 at a cost of RS.150crore approximately.Start-up sequence of CPP: Auxiliary lube oil pump starter. Auxiliary hydraulic pump starts. Jaw clutch of torque converter accessory gear box engages. Diesel engine starts and warms up for 120secs. When the timer T2 DW times out, and the DE speed is 1000rpm Ace. Solenoid picks up. Diesel engine speed goes to 2000rpm and HP shaft rotates. 24
  25. 25. The lock up- solenoid 20DA-2 energies and the DE speed is held constant at 1800 rpm. At 18% of HP speed, cranking status is displayed on mark-IV up to 25% of HP speed is cranking. Purging timer T2TVSC starts when cranking is displaced and times out after 60 seconds. Diesel stop value opens and firing timer T2F starts and time allow for flame detection in 60 seconds (if within 60secs. No flame is established machine go back to cranking). The turbine warms up for 60seconds (T2W). At about 52% HP speed jaw clutch disengages and LP shaft starts rotating. After 5mins diesel engine stops. From 80% HP and LP shaft speed exceeds HP.CPP facilities:The major facilities implemented in CPP are as followsGas turbines:1&2These are complete package units with enclosure for whether protection, thermal andacoustic insulation. The individual unit houses gas turbine, load gears box and electricalgenerator. The operating speed of a gas turbine is 6000rpm and the trip speed is7150rpm.3, 4, 5&6The operating speed is 5100rpm. When the turbine starting system is actuated and theclutch is engaged, ambient air is drawn through the air inlet assembly, filtered aandcompressed in 17 stage axial flow compressor. Compressed air from the compressorflows into the annular space surrounding ten combustion chambers, from which it flowsinto the space between the outer combustion gasing. In the combustion liners andenters the combustion zone through the metering poles in each of the combustionliners.Theory of GTG:Gasses passing through an ideal a gas turbine undergothree thermodynamic processes. These are isentropic compression, isobaric (constant 25
  26. 26. pressure) combustion and isentropic expansion. Together these make up the Braytoncycle.In a practical gas turbine, gasses are first accelerated in either a centrifugal orradial compressor. These gasses are then slowed using a diverging nozzle known asa diffuser; these processes increase the pressure and temperature of the flow. In anideal system this is isentropic. However, in practice energy is lost to heat, due to frictionand turbulence. Gasses then pass from the diffuser to a combustion chamber, or similardevice, where heat is added. In an ideal system this occurs at constant pressure(isobaric heat addition). As there is no change in pressure the specific volume of thegasses increases. In practical situations this process is usually accompanied by a slightloss in pressure, due to friction. Finally, this larger volume of gasses is expanded andaccelerated by nozzle guide vanes before energy is extracted by a turbine. In an idealsystem these are gasses expanded isentropically and leave the turbine at their originalpressure. In practice this process is not isentropic as energy is once again lost to frictionand turbulence.If the device has been designed to power to a shaft as with an industrial generator ora turboprop, the exit pressure will be as close to the entry pressure as possible. Inpractice it is necessary that some pressure remains at the outlet in order to fully expelthe exhaust gasses. In the case of a jet engine only enough pressure and energy isextracted from the flow to drive the compressor and other components. The remaininghigh pressure gasses are accelerated to provide a jet that can, for example, be used topropel an aircraft. Fig: Brayton cycleAs with all cyclic heat engines, higher combustion temperatures can allow forgreater efficiencies. However, temperatures are limited by ability of the steel, nickel, 26
  27. 27. ceramic, or other materials that make up the engine to withstand high temperatures andstresses. To combat this many turbines feature complex blade cooling systems.As a general rule, the smaller the engine the higher the rotation rate of the shaft(s) mustbe to maintain tip speed. Blade tip speed determines the maximum pressure ratios thatcan be obtained by the turbine and the compressor. This in turn limits the maximumpower and efficiency that can be obtained by the engine. In order for tip speed to remainconstant, if the diameter of a rotor is reduced by half, the rotational speed must double.For example large Jet engines operate around 10,000 rpm, while micro turbines spin asfast as 500,000 rpm.Mechanically, gas turbines can be considerably less complex than internalcombustion piston engines. Simple turbines might have one moving part: theshaft/compressor/turbine/alternative-rotor assembly (see image above), not countingthe fuel system. However, the required precision manufacturing for components andtemperature resistant alloys necessary for high efficiency often makes the constructionof a simple turbine more complicated than piston engines.More sophisticated turbines (such as those found in modern jet engines) may havemultiple shafts (spools), hundreds of turbine blades, movable stator blades, and a vastsystem of complex piping, combustors and heat exchangers.Thrust bearings and journal bearings are a critical part of design. Traditionally, theyhave been hydrodynamic oil bearings, or oil-cooled ball bearings. These bearings arebeing surpassed by foil bearings, which have been successfully used in micro turbinesand auxiliary power units. Fig: Turbo shaft engineGenerators: 27
  28. 28. 1&2:Generators which converts mechanical energy is rated for 11.2MVA at 0.8,11kv,3-phase ,50hz , 4-pole machine which runs at a speed of 1500rpm . the generator iscoupled with the gas turbine through the load gear box which reduces gas turbine of6500rpmto 1500rpm. Dc excitation current is fed to generator rotor windingUsing brushless excitation system. Automatic voltage regulation keeps the outputvoltage constant. The generator is protected by appropriated relays against overcurrent, short-circuits and earth faults etc. the generator winding is cooled externallyusing forced air cooling system. the generator is enclosed within a metal using forcedair cooling systems . the generator is enclosed within a metal enclosure which isprotected by co2 extinguishing system against possible electrical fires.3, 4, 5&6:The generator is rated at 27.388mva at 0.8pf, 11kv, 3-phase, 50 Hz. The generator is2pole machine running at a synchronous speed of3000rpm. The turbine speed isreduced from 5100rpm to 3000rpm through a load gear box. The generators is providedwith open air ventilation system consisting of air filter unit by 2 axial flow fans located onthe rotor aft one at either end. The generator rotor is supported on 2 journal bearingslubricants by the turbine oil system Fig: cut-section of an alternatorGenerator – Details 1. Make - Bharat Heavy Electrical Limited 2. output rating - 11,250KVA 3. rated frequency -50hz 4. full load current -590A 5. P.F -0.8 6. rated speed -1500rpmThe generators are provided with a brushless excitation which eliminates the provisionof slip rings and brushes.Functional Description: 28
  29. 29. Definition of gas turbine: A gas turbine is machine or engine in which mechanical powerin the form of shaft is produced when a steam of air rushes on the blades r by bucketsof a wheel it turn round .Basic Cycle:A gas turbine operates by Continuously drawing in fresh air . Compressing thin air through a higher pressure Adding and burning fuel in the compressed air to increase its energy level. Directing the high pressure and temperature air to an expansion turbine converts the gas energy to mechanical energy of a rotating shaft. The resulting low pressure, low temperature gases are discharged to atmosphereGas Turbine EquipmentsAir inlet equipment:The air supply for the turbine flowsthrough a duct assembly prior toentering compressor the duct contains aair silencer and trash screen. The airsilencer consisting of a number ofacoustical panels from a section of ductassembly and attenuates the highfrequency sounds created bycompressor blades.Compressor section:The axial flow 15 stage compressor section consists of compressor rotor casing, and toexit guide vanes. In the compressor the air is confined to the space between the rotor 29
  30. 30. and the stator blades where it is compressed in stages by an alternate series of rottingblades which supply the force needed to compress the air in each stage and the statorblades guide the air so that it enters the following rotor stage at proper angle. Thecompressed air exists through the compressor discharge casing through thecombustion chamber. Air is also extracted from the compressor for the turbine coolingand for lube oil sealing at the bearings of the turbine.Rotor assembly:The compressor rotor is an assembly of 15 wheels two stub shafts assemblies, tie boltsand the compressor rotor blades and shafts are assembled by mating rabbets andsecured by 12 tie bolts arranged concentrically around the rotor axis. The forward stubshaft contains the journal and the thrust number for the number one runner and thethrust bearing assembly, sealing surfaces for the bearing oil deflectors and compressorflow pressure air deflectors. The aft stub shaft contains for no.2 journal and thrustbearing assembly, the sealing surfaces for the bearing oil deflectors compressor high-pressure air seal. The shaft wheel portion of the stub haft contains the first stagecompressor rotor blades. The compressor rotor assembly is dynamically balancedbefore it is assembled to the unbalanced turbine rotor assembly. This completeassembly is then dynamically balanced.Stator:The stator (compressor casing) enclosed the compressor portion of the rotor and isdivided into 4 sections; inlet casing, forward compressor, aft compressor and dischargecasing. The inner section, which directs the flow of outside air from the inlet equipment 30
  31. 31. to the compressor blades, contains no 1 bearing assembly and low pressure air seals.The forward section of the compressor casing is downstream of the inlet sectioncontains the stator for stages 0 through 3. the aft section downstream of the forwardsection contains the stator blades for stages 4 through 9.Combustion section:The combustion section consists of 10 combustion chambers, fuel nozzles, cross firetubes and transition pieces.The combustion chambers are arranged concentrically around the axial fuel compressorand are bolted to the compressor discharge section bulkhead. Air for combustion issupplied directly to the compressor to the combustion chambers. This arrangement iscalled a reverse flow system since the compressor discharge air flows forward aroundthe liners and then enters and flow back towards the turbine. Fuel is fed into thechambers of the turbine section. Figure showing combustion sectionTurbine section:In the turbine, high temperatures gases from the combustion section are convertedshaft horse power. This section comprises of the following components 31
  32. 32. 1. Turbine casing 2. First stage nozzle 3. Second stage nozzle 4. First stage turbine wheel(hp turbine) 5. Second stage turbine wheel(lp turbine) 6. Diaphragm assembly 7. Inter stage gas partsDiesel engine:The diesel engine starting motor (10hp,125v dc) starts the diesel engine duringstartup procedures. The diesel enginelube oil pressure should be sufficientenough for startup. Diesel engineminimum speed sensed by pressureswitch accelerating solenoid .Theaccelerating speed of the engine isnearly 2100rpm. The cooling for thisengine is provided by CWM line.Hydraulic torque converter:This is a single stage hydraulic device coupled to the starting diesel engine. It transmitsthe DE output torque to the turbine accessory gear; all moving parts of the torqueconverter are lubricated with the system lubricating oil. The torque converted housing isbolted directly to DE flywheel housing. Converter operating temperature will vary withsum temperature and converter speed ration.Fuel system:The turbine can use a variety of liquid and gaseous fuels, which may vary substantiallyin hydrocarbon composition, physical properties and levels of contamination. Highpressure fuel pumps how dividers have substantially improved the reliability of thesecritical fuels. Naphtha fuel to the GTG‘s is from the two fixed cum floating roof tanks 183A and 183 B each approximately. 2600KJL diesel system is from tanks 181, 182A eachof approx 300KL. The fuel is pumped from the tank by fuel forwarding pumps. A 32
  33. 33. pneumatic control bypass valve is provided in discharge of the pump for recirculation offuel back to maintain discharge pressure. The fuel travels to the pressure controllerwhere the pressure is controlled by pressure control valve (5.5-6 Kg/sqcm) with bypassvalve from where it goes to the filter skidDiesel System:From the 25 micron dual filter skid, diesel goes through the trip oil operated stop valueto reach main fuel pump. The servo controlled bypass value in the discharge line of themain fuel pump enters a 0.5 micron filter and then goes through the filter.The flow divided as six output ports each connected to a combustion chamber. The flowdivider which is driven by input pressure itself distributes diesel at equal pressure to allcombustion chambers through check values calibrated at 7kg/sqcm pop pressure.Naphtha Valve:The fuel from control valve travels two stages. Filtration consists of 25 microns and6micron dual filter skid. Accumulated pressurized with nitrogen are provided upstreamof a Naphtha control valve to take care of the pressure fluctuations in the system .Naphtha passes through the three way transfer valve and reached the PFD skid beforenaphtha change out takes place, diesel has to enter or pass through naphtha skid tochamber. the fuel after six micro naphtha filters enters naphtha PFD consists of a trip oiloperated stop valve a screw pump with discharge of which is controlled by a servooperated by pass valve.Brushless Generator-Basics:The permanent magnet generator (PMG) is coupled to shaft of the generator. The PMGhas a permanent magnet on its rotor. The stator has winding after star up of the turbine;the PMG is also rotating at the same speed as that of generator. The permanentmagnet causes a magnetic flux in the air gap between stator and rotor in the PMG. Thestator windings cut in this flux (on rotation) and thus an emf is reduced in the statorwindings. This is at 220v, 75 Hz. 33
  34. 34. The variable dc current output of the AVR is brought to the stator winding of the mainexciter .This winding then induces a magnetic flux in the air gap of the exciter. The rotorwinding as it is rotating at the speed of the generator cuts flux and thus there is aninduced emf (ac) in the rotor. this rotor current is rectified by the diodes and theconsequents direct current(dc) is then fed through cables which run inside the hallowshaft the generator to the main field winding of the generators since the diodes aremounted on the rotor of the exciter of the regular maintence of carbon brushes etc. Fig: brushless generator connected to turbo shaftAutomatic Voltage Regulator:The AVR is intended for excitation and control of generators equipped with alternatorexciter employing rotating non control rectifier.Main parts of the regulator equipment are: 1. The closed loop control system including a separate gate control set and thyristor set each. Field discharge circuit. 2. An open loop control system for exchanging signal between regulator equipment and control room in power supply in power supply circuits. Generator voltage control. Un-delayed limiting control for the output current of the thyristor set. Limiting control for under excited range. Delay limiting control for the over excited range. Automatic field suppression during shutdown of the generator. 34
  35. 35. Delayed limiting control for stator over current. V/Hz limiterHeat recovery steam generators:A Heat Recovery Steam Generator (HRSG) is a steam boiler that uses hot exhaustgases from the gas turbines or reciprocating engines in a CHP plant to heat up waterand generate steam. This steam in turn drives a steam turbine and/or is used inindustrial processes that require heat.HRSGs used in the CHP industry are distinguished from conventional steam generatorsby the following main features: The HRSG is designed based upon the specific features of the gas turbine or reciprocating engine that it will be coupled to. Since the exhaust gas temperature is relatively low, heat transmission is accomplished mainly through convection. The exhaust gas velocity is limited by the need to keep head losses down. Thus, the transmission coefficient is low, which calls for a large heating surface area. Since the temperature difference between the hot gases and the fluid to be heated (steam or water) is low, and with the heat transmission coefficient being low as well, the evaporator and economizer are designed with plate fin heat exchangers. 35
  36. 36. Fig: Heat recovery steam generatorChapter-3Power distribution system in HPCL:The modern distribution system begins as the primary circuit leaves the sub-station andends as the secondary service enters the utilities. A variety of methods, materials, andequipment are used among the various utility companies, but the end result is similar.First, the energy leaves the sub-station in a primary circuit, usually with all three phases.Most areas provide three phase industrial service. There is no substitute for three-phaseservice to run heavy industrial equipment. A ground is normally provided, connected toconductive cases and other safety equipment, to keep current away from equipmentand people.Substations:A substation is a part of an electrical generation, transmission, and distribution system.Substations transform voltage from high to low, or the reverse, or perform any of several 36
  37. 37. other important functions. Electric power may flow through several substations betweengenerating plant and consumer, and its voltage may change in several steps.Fig: SubstationA substation that has a step-up transformer increases the voltage while decreasingthe current, while a step-down transformer decreases the voltage while increasing thecurrent for domestic and commercial distribution. The word substation comes from thedays before the distribution system became a grid. The first substations were connectedto only one power station, where the generators were housed, and were subsidiaries ofthat power station.Switch gear:The term switchgear, used in association with the electric power system, or grid, refersto the combination of electrical disconnects, fusesand/or circuit breakers used to isolateelectrical equipment. Switchgear is used both to de-energize equipment to allow work tobe done and to clear faults downstream. This type of equipment is important because itis directly linked to the reliability of the electricity supply. Fig: switch gearsThe very earliest central power stations used simple open knife switches, mounted oninsulating panels of marble or asbestos. Power levels and voltages rapidly escalated, 37
  38. 38. making open manually-operated switches too dangerous to use for anything other thanisolation of a de-energized circuit. Oil-filled equipment allowed arc energy to becontained and safely controlled. By the early 20th century, a switchgear line-up wouldbe a metal-enclosed structure with electrically-operated switching elements, using oilcircuit breakers. Today, oil-filled equipment has largely been replaced by air-blast,vacuum, or SF6 equipment, allowing large currents and power levels to be safelycontrolled by automatic equipment incorporating digital controls, protection, meteringand communications. The technology has been improved over time and can be usedwith voltages up to 1,100 kV.Bus bar system:In electrical power distribution, a bulbar is a strip of copper or aluminum thatconducts electricity within a switchboard, distribution board, substation or other electricalapparatus. Fig: Bus barsThe size of the bus bar determines the maximum amount of current that can be safelycarried. Bus bars can have a cross-sectional area of as little as 10 mm² but electricalsubstations may use metal tubes of 50 mm in diameter (1,963 mm²) or more as busbars, and an aluminum smelter will have very large bus bars used to carry tens ofthousands of amperes to the electrochemical cells that produce aluminum from moltensalts. 38
  39. 39. Transformers:HPCL uses a wide range of transformers which are very important in the powerdistribution system. A transformer is a device that transfers electrical energy fromone circuit to another through coupled conductors—the transformers coils. Avarying current in the first or primary winding creates a varying magnetic flux in thetransformers core and thus a varying magnetic field through the secondary winding.This varying magnetic field induces a varying electromotive force (EMF), or "voltage", inthe secondary winding. This effect is called mutual induction. HPCL is havingapproximately 79 transformers in the entire refinery with the ratings like 10MVA/11KVA,11/3.3KVA, 3.3/1.1KVA, 1.1KVA/415VA and etc. Fig: 10 MVA power transformer 39
  40. 40. Substation-50:Substation-50 is one of the most peculiar and important substation in the HPCL‘s powerdistribution system. In this substation there will be two incomers from the captive powerplant (CPP) which bears 11KV. The panels in this substation are of two kinds, they arePower Control Centre (PCC) and Motor Control Centre (MCC). The 111KV is firststepped down into 5 divisions, in this process the outgoing lines are fed to two types ofmotors like High Tension motors (HT) and Low Tension motors (LT). then the remaininglines will fed the 6 Motor Control Centre (MCC) (for motors) and 1 Light DistributionBoard (LDB) panels.Meter control centre (MCC): Duly wired with ACB/MCCB/SFU/DOL/STAR-DELTA/ATS Starters. Various designs provided like single/double front, fixed type, with Marshaling terminations. Cubicle type extensible on each side. Require Control voltage facilities with control. All starters are provided with type 2 co-ordination where required. Separate bus bar chamber for vertical droppers. Can be operating by remote on/off Fig: MCC panelPower control centre (PCC): Main LT Panel, PCC With single, Multiple incomer, bus couplers with proper interlocking, Required protection, fault indications, interlocking is provided. Various designs are offered in PCC like top, Middle, Bottom Horizontal bus chamber, panel with aluminum/copper bus bars, top/bottom/front/rear cable termination, combinations of APFC Part with PCC. 40
  41. 41. Required facilities like DG Incomer with AMF Functions, Cut-off of nonessential feeders at the event of failure of mains power. Panel with provision to connect bus duct at main incomer side. Fig: PCC panelDirect on-line starters in SS-50:A direct on line (DOL) or across the line starter starts electric motors by applying the fullline voltage to the motor terminals. This is the simplest type of motor starter. larger sizesuse an electromechanical contactor (relay) to switch the motor circuit. Solid-state directon line starters also exist. Fig: DOL starterA direct on line starter can be used if the high inrush current of the motor does notcause excessive voltage drop in the supply circuit. The maximum size of a motorallowed on a direct on line starter may be limited by the supply utility for this reason. Forexample, a utility may require rural customers to use reduced-voltage starters formotors larger than 10 kW. 41
  42. 42. DOL starter is sometimes used to start small water pumps, compressors, fans andconveyor belts. In the case of an asynchronous motor, such as the 3-phase squirrel-cage motor, the motor will draw a high starting current until it has run up to full speed.This starting current is commonly around six times the full load current, but may be ashigh as 6 to 7 times the full load current.Variable frequency drives:A variable-frequency drive (VFD) is a system for controlling the rotational speed ofan alternating current (AC) electric motor by controlling the frequency of the electricalpower supplied to the motor.[1][2][3] A variable frequency drive is a specific typeof adjustable-speed drive. Variable-frequency drives are also known as adjustable-frequency drives (AFD), variable-speed drives (VSD), AC drives, microdrives or inverterdrives. Since the voltage is varied along with frequency, these are sometimes alsocalled VVVF (variable voltage variable frequency) drives.Variable-frequency drives are widely used. In ventilation systems for large buildings,variable-frequency motors on fans save energy by allowing the volume of air moved tomatch the system demand. They are also used on pumps, elevator, conveyor andmachine tool drives.VFD motor:The motor used in a VFD system is usually a three-phase induction motor. Some typesof single motors can be used, but three-phase motors are usually preferred. Varioustypes of synchronous motors offer advantages in some situations, but induction motorsare suitable for most purposes and are generally the most economical choice. Motorsthat are designed for fixed-speed operation are often used. Certain enhancements tothe standard motor designs offer higher reliability and better VFD performance, such asMG-31 rated motors. 42
  43. 43. Variable frequency controller:The usual design first converts AC input power to DC intermediate power usinga rectifier or converter bridge. The rectifier is usually a three-phase, full-wave-diode bridge. The DC intermediate power is then converted to quasi-sinusoidal ACpower using an inverter switching circuit. VFD systemThe inverter circuit is probably the most important section of the VFD, changing DCenergy into three channels of AC energy that can be used by an AC motor. These unitsprovide improved power factor, less harmonic distortion, and low sensitivity to theincoming phase sequencing than older phase controlled converter VFDs. Sinceincoming power is converted to DC, many units will accept single-phase as well asthree-phase input power (acting as a phase converter as well as a speed controller);however the unit must be de-rated when using single phase input as only part of therectifier bridge is carrying the connected load.Dynamic breaking:Using the motor as a generator to absorb energy from the system is called dynamicbraking. Dynamic braking stops the system more quickly than coasting. Since dynamicbraking requires relative motion of the motors parts, it becomes less effective at lowspeed and cannot be used to hold a load at a stopped position. During normal brakingof an electric motor the electrical energy produced by the motor is dissipated as heat 43
  44. 44. inside of the rotor, which increases the likelihood of damage and eventual failure.Therefore, some systems transfer this energy to an outside bank of resistors. Coolingfans may be used to protect the resistors from damage. Modern systems have thermalmonitoring, so if the temperature of the bank becomes excessive, it will be switched off.Rectifier in VFD:A rectifier is an electrical device that converts alternating current (AC), whichperiodically reverses direction, to direct current (DC), which is in only one direction, aprocess known as rectification. Rectifiers have many uses including as componentsof power supplies and as detectors of radio signals. Rectifiers may be made of solidstate diodes, silicon-controlled rectifiers, vacuum tube diodes, mercury arc valves, andother components. Bibliography HPCL official website Network protection and automation guide Power systems – J.B.Gupta Electrical machines – P.S.Bhimbhra 44