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WRITE-UP

ON

AUTOMATIC TURBINE RUNUP SYSTEM

Project : RI HAND - STPP (2x500 MW)Package: Main Plant Turnkey PackageProduct : Steam TurbineNTPC drg. no.-1230-001-03HW-PVM-W-001

03 7.2.03 SH. NO. 19 ADDED. BSR Sd./- BSR Sd./- KBB Sd./-

02 3.9.2002References specificto Procontrol systemremoved.

BS RANA Sd. BS RANA Sd. KB BATRA Sd.

01 8.4.02Revised as per NTPCcomments dt. 21.3.02 BS RANA Sd. BS RANA Sd. KBB Sd.

00 11.02.02 First issue BS RANS Sd. BS RANA Sd. KB BATRA Sd.

Rev Date Remarks Prepared Checked Approved

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1.0 INTRODUCTION :

A successful start-up of the turbine normally requiresacquisition, analysis and collation of a wide varietyof information pertaining to various parameters likeoil pressure, vacuum, temperature, speed etc. Apartfrom this it is important to know the status of theauxiliary equipment. It is an arduous task for theoperator to handle and collate so many bits of information,swiftly and correctly. A microprocessor basedautomatic run-up system performs this task swiftly,accurately and at an appropriate time. The chances ofmal-operation due to human error in judgement of thesituations, get practically eliminated.

2.0 CONCEPT :

The Programmable Automatic Turbine Run-up System (ATRS)is based on the 'Functional Group Control' philosophy.The control area is divided into clearly defined functionalareas called 'Functional Groups'. Each function-al group is organised and hierarchically arranged inSub-Group Control (SGC), Sub-Loop Control (SLC) andDrive Interface Function.

2.1 SUB-GROUP CONTROL :

SGC executes commands to bring the equipment up-to aparticular defined status. The commands are executed ina predefined sequence in the form of steps. Desirednumber of criteria act as preconditions before the SGCcan take off or execute its defined sequence. Thefunctional group continues to function automaticallyall the time demanding enabling criteria based on theprocess requirements and from other Functional Groups, ifrequired. In case the desired criteria is not available,the system would automatically act in such a manner as toensure the safety of the main equipment.

The sequence is programmed in the processor. The processsignals are acquired through the input modules andare available on the bus.

For each step there is a waiting time and a monitoringtime which are defined below :

Waiting Time : It implies that the subsequent step willnot be executed unless the specified time elapses. Ifno waiting time is specified, the next step gets executedas soon as the enabling criteria are fulfilled.

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Monitoring Time : It is the time required for executingthe command of any step as well as the time requiredfor appearance of criteria for the next step. Underhealthy conditions it should happen within the specifiedtime, otherwise an alarm is initiated. Wheneverthere is uncertainty regarding the time required forcompleting a particular task, such as warming-up,pulling vacuum etc., the monitoring time is blocked.

ATRS can be switched on at any stage after completingcertain tasks manually, if so desired. In such cases,the SGC program quickly scans through the steps andstarts executing from the stage upto which the taskshave been completed manually. This is achieved byincorporating suitable overflow /bypass conditions inthe logic.

SGC issues commands either to the SLC or directly tothe drive through the Control Interface.

ATRS is organised in the following four Sub-Groups : Oil supply Evacuation Turbine HP Control Fluid

Each of these SGCs has its subordinate SLCs and driveinterface function. These SGCs in conjunction with theturbine governing system , Turbine Stress Controller andthe auto-synchronizer accomplish the function of start-upof the TG set.

Refer sh. no. 19 for A typical configuration of MAXDNA basedATRS .

2.1.1 Controls & Displays Available To Operator In A SGC :

Each subgroup control can be switched on and off fromOWS. The 'Startup' and 'Shutdown' program can also be startedmanually from there.

The control display as shown in Fig-1 with standardizedfunctions is provided in OWS for manualoperations and indications of the sub-group control.For display of the step and criteria, indication buttons areused. The number of display used for a particular SGC dependson the number of steps in program and the maximum number ofcriteria in any step.

Control button 3 (ref. Fig-1) is for clicking auto ormanual mode. In case of auto-mode, indication button 7 shallhave steady light, while in case of manual mode,indication button 6 shall have steady light. In manualmode, SGC will not execute the program. But the operationscan be performed at the control interface level to bring upthe various mechanical equipment to the desired status.

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In case of auto-mode, control button 2 needs to be clickedfor starting the program in 'operation' i.e. 'Startup'direction while control button 1 needs to be clicked uponfor initiating the shutdown program. Steady light wouldappear in indication buttons 4 & 5 when the desired anddefined status of mechanical equipment is achieved.

Rapid flashing light in indication button 4 or 5 indicatesthat the program is running towards the desired statusand there is no fault.

Slow flashing light in indication button 4 or 5 indicatesthat the program is in the desired mode but a fault hasappeared somewhere.

Steady light in any of the indication button of step displayindicates the step number in which the program exists inany given moment. Steady light in step indications and slowflashing light in indication button 4 or 5 indicates that theprogram is stuck and there would also be steady light incriterion indication buttons indicating which criterion hasnot been fulfilled.

2.1.2 Method Of Representation & Other Features:

a. In the logic diagram, the control coordinator ofsubgroup control (SGC) is schematically represented asshown in Fig-2.1.

b. A typical step of subgroup control is represented asshown in Fig-2.2.

c. The steps for 'Startup' program are enumerated from1 to 50 while the steps for 'Shutdown' program areenumerated from 51 to 99.

d. The signals hooked with protection channel 'P' havethe highest priority and execute the logic even withoutseeking the availability of 'Release Criteria'.

2.2 SUB-LOOP CONTROL (SLC) :

A SLC, when switched on, actuates the equipment andbrings it to the desired status as demanded by theprocess and there is no sequence logic involved in it.In other words, SLC is like a watch-dog performing anassigned duty. All mechanical equipment which needs to

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be switched on/off based on process consideration ishooked-up in various SLCs. Standby equipment is alsointerlocked in SLCs.

SLC can be switched ON either manually or through SGCand issues commands to the drive through I/O modules.

SLC logic is also realised in the Processor.

2.2.1 Controls & Displays Available To Operator In A SLC:

The control display with standardized functions is providedin OWS for manual operation and indicationof the sub loop control. Fig-3 indicates the controldisplay for SLC.

2.3 DRIVE INTERFACE:

Each remote controlled drive has a drive interface blockwhich acts as a standard interface between the commandtransmitters and receivers in the plant and undertakesall necessary signal processing and monitoring.

The drive control interface receives manual commands from theOWS through input modules , active protection signals andenabling signals from the protectivelogic, as well as automatic controlcommands from the SGC/SLC. It interlocks theinput commands according to their priorityand validity and then passes actuation signals to theinterposing relays in the switchgear. The status check-backs received from the switchgear or actuators aremonitored, processed and transmitted to OWS, the protectivelogic and SGC .

2.3.1 The control displays with standardized functions areprovided on the OWS for manual control andcheck back of the drives. A typical control display isindicated in Fig-4.1.

2.3.2 For certain critical drives hardwired back up control tilesare provided on the control desk for operator interface.

2.3.3 In the logic diagram, the drive control interface isrepresented as shown in Fig-4.2.

3.0 OPERATING MODES :

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In addition to the normal automatic mode of operationof the sub-group, the following two modes are alsoavailable :

Step-by-step-mode: In this mode, all the criteriafor a particular step are simulated manually throughthe OWS and the command is issuedautomatically. This is helpful in case a criteria isactually fulfilled but the signal is not available tothe sub-group because of a faulty transmitter.

Operator guide mode : In this mode, the sub-group onlyreceives data from the plant and the control stations,but the output commands are blocked. The commands haveto be issued manually from OWS. This mode is usefulduring commissioning and for operatortraining.

These modes can be selected from OWS,whenever desired.

4.0 ATRS STRUCTURE & DESCRIPTION OF SYSTEM:

ATRS is organised in four subgroup controls. Thesegroups, in conjunction with the turbine governingsystem, Turbine Stress Evaluator/Controller (TSE/TSC)accomplish the various functions. The tasks assigned toeach subgroup control are described below for a typicalproject. Actual logics will however vary from projectto project.

4.1 Subgroup Control (SGC) Turbine :

SGC Turbine acts directly on the following systems : 1. Sub loop Control (SLC) Drains. 2. Warm up Controller. 3. Starting Device of turbine governing system. 4. Speed & Load Setpoint devices of turbine governing

system. 5. Auto-synchronizer.

SGC Turbine executes the following tasks, when switchedON. The operator manually switches on the SGC programat an appropriate time for running the turbine. Theprogram takes off only after all the 'Release Criteria'are fulfilled.

4.1.1 Steam & metal Temperature matching:

The matching of steam & metal temperatures is an extremelyimportant task before admitting the steam intothe turbine for the purpose of warming up the variouselements, speeding and subsequent loading. The ATRS

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accomplishes these tasks effectively and efficiently.Function generators are used to determine the desiredlevel of temperature based on the actual metal temperatureof the critical component (Ref. startup curves).

4.1.2 Warming-up:

ATRS acts on the warm-up controller to ensure a saferate warm-up of the ESV & CV of HP turbine as permittedby the TSE. In the warm-up stage, the operation of theturbine drains is equally important and all the drainsare hooked up in a sub-loop control (SLC). Depending onthe relative importance and significance of variousdrain valves, the criterion for opening/closing of eachindividual drain valve is defined and suitable logicbuilt in to ensure safe operation. After the warming upof ESV & CV of the HP turbine, the ATRS admits steaminto the turbine for rolling the turbine.

4.1.3 After ensuring adequate level of warming up and avail-ability of all important criterion, the ATRS takes theturbine from the barring speed to the first hold speedwhich is approx. 20% of the rated speed. During theprocess of raising the speed, the acceleration iscontrolled by the TSE/TSC so that the components do not getoverstressed. The ATRS ensure a definite hold forsoaking of turbine internal at this speed for a specifiedperiod if the HP metal temperature is less than250 degree C, otherwise the hold period is determined bythe time it takes for temperature margins of the TSE tobe within permissible limits.

4.1.4 After proper and adequate thermal soaking of the components,the ATRS raises the speed of the TG set to ratedspeed. For this period also, the acceleration is con-trolled by TSC except for the region where rotors crossthe critical speed zone. ATRS again ensures soaking asper process requirement and availability of margins.

4.1.5 After attaining a speed above 2950 rpm and when sufficienttemperature are available, the auto-synchronizertakes over and matches the turbine speed to a valuematching with the grid frequency. It simultaneouslyacts on the Automatic Voltage Regulator (AVR) formatching the grid and generator voltages. Auto-synchronizer-synchronizes the set at the right moment dependingon the frequency and phase angle. EHG immediatelyenables the set to take 10% load.

4.1.6 ATRS switches on the tracking device, which tracks thehydraulic controller to the output of theelectrohydraulic controller with a set margin.

4.1.7 It facilitates the shutdown of the set in a propersequence and switches on the SLC drains according tothe process requirement.

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4.2 Sub-Group Control (SGC) - Oil Supply:

SGC oil supply directly acts on the following system : a. Sub loop control (SLC) turning gear. b. SLC auxiliary oil pump 1. c. SLC auxiliary oil pump 2. d. SLC emergency oil pump. e. SLC jacking oil pump.

SGC oil supply performs the tasks as described in thesubsequent paragraphs and simultaneously prepares theoil system to meet the situational demands of the mainset by employing the technique of recycling.

4.2.1 Auxiliary oil pump no. 1 is switched on as first stepto provide the lubricating and control fluid at therequired ends.

4.2.2 The program switches on the oil temperature controller.The oil temperature controller provides an analogcontrol to maintain the oil temperature in the headersupplying oil to the bearings. The controller actuatesa three-way valve thereby controlling the quantity ofoil being cooled in the oil cooler and the quantity ofoil being taken directly from the tank to the header.

The program only switches on the temperature controllerand does not check back the actual oil temperature forthe reason that all operations on the lube oil systemcan be performed even if the oil temperature is not atthe desired level. However, the availability of oil atthe desired level of temperature is important for theactual rolling and therefore the oil temperature ischecked as the "Enabling Criteria" in the program forthe startup of the main turbine.

4.2.3 SGC lube oil supply system ensures the supply of motiveoil to the hydraulic turbine of turning gear as the SLCturning gear is switched "ON" by the SGC supply. TheSLC logic is such that it opens the gate valve supplyingoil to the turning gear whenever the turbine speedis less than 200 rpm. Therefore while starting theturbine from the standstill condition or during coastingdown, the oil supply to the turning gear is ensured.The oil supply to the turning gear is switched"Off" when turbine speed exceeds 250 rpm or SLC turninggear is switched "Off". Since the requirements for theturning of the turbine can arise at any point of timeduring operation, the operation of the turning gearvalve is hooked up in SLC mode.

4.2.4 The jacking oil pumps are also hooked up in SLC modeand SGC oil supply system switches on this SLC forjacking oil pump.

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In case the turbine speed is below 510 rpm or falls belowthis value while coasting down, the JOP 1 gets switchedOn". In case JOP 1 does not develop the desired amountof pressure, the command for starting JOP 3 is issued witha time lag of 7 secs. As soon as the turbine crosses 540rpm, the JOP 1 gets switched off as per the logic of theSLC. However, JOP 3, if in service, will not get switchedoff as per SLC logic and operator would have to switch offthe JOP 2.

4.2.5 SGC lube oil supply also switches on the SLCs forauxiliary oil pumps 1 & 2, emergency oil pump (DC) soas to keep all the vital pumps ready for action, shouldan emergency arise or develop at any stage of theprocess.

4.2.6 If the turbine trips after attaining a speed of more than540 rpm, the program is designed in such a manner so as toperform the tasks stated in paragraph 4.2.3, 4.2.4 & 4.2.5.Similarly, if the turbine trips after the turbine attains3000 rpm, the whole program of oil supply is recycled toensure the turning of the turbine.

4.2.7 Shut down program of oil supply can only be started ifHP casing temperature, both top and bottom is below 100degree C, as otherwise an inadvertent switching off couldlead to the situation of no turning operation even whenthe turbine is hot.

All the vital pumps are switched off after the turbinecomes to standstill position.

4.3 Sub-Group Control (SGC) Evacuation :

SGC evacuation acts directly on the following vacuum pumpand its associated drives.

4.3.1 Although 'SLC Drains' is primarily hooked up with 'SGC- Turbine', 'SGC-Evacuation' also switches it on.

4.3.2 Before starting the evacuation process, the vacuumbreaker valve is first closed and the seal steam supplyvalve is also closed. Gland Steam Controller is put onmanual so that it is not able to open the seal steamsupply valve.

4.3.3 Both the vacuum pumps are then switched ON in hogging operation

4.3.4 The gland steam controller is put on 'auto' afterchecking that the turbine is on barring and the con-denser pressure is less than a preset value. The gland

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steam controller brings the pressure in the gland steamheader to normal, while evacuation is in progress.

4.3.5 The vacuum pumps continue the task of pulling thevacuum until absolute pressure in condenser hasreduced below 150 mbar and generator load is >5%.

After these criteria are achieved, the pre-selected mainvacuum pump continues running while the otherone is stopped and acts as a standby. Subsequently theSLC- vacuum pump is switched ON .

4.3.6 In case condenser pressure again rises above 120 mbar,both the vacuum pumps are switched ON under SLC logicsand vacuum pumps are again put into operation.

4.3.7 The shutdown program can be initiated by the operatorif the release conditions are present. Initially, SLCis switched Off and all the vacuum pumps are put outof operation. Then the vacuum breaker valve is openedto break the vacuum.

4.3.8 Speed dependent vacuum breaker

In order to protect the end stages of the LP turbinefrom impermissible ventilation energy during vacuumbreaking, the condenser pressure is limited as afunction of the steam turbine speed.

For this two separate characteristics, one for openand one for close are used. The vacuum breaker operatesautomatically as per these characteristics if fireprotection is operated.

SLC is provided for automatic opening and closing ofthe vacuum breaker manually. By manually activating theSLC, the automatic opening & closing is started. Thisstarting is only released when a steam turbine trip isactuated. The open/close of the vacuum breaker will beperformed as per setpoint characteristics.

Vacuum breaker can also be manually opened and closedfrom the control room. If the vacuum breaker is openedmanually. It is closed automatically when the speeddependent maximum permissible condenser is reached.

4.4 Sub-Group Control- HP Control Fluid

SGC HP control fluid acts on the following system: 1. Subloop Control HPCF pumps

2. Subloop control HPCF heating

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3. HPCF pumps4. HPCF re-circulation pumps5. HPCF temperature control valve

4.4.1 Both the CF pumps get switched ON through the SLC. Incase the running pump does not develop the requiredpressure , the standby pump gets switched ON.

4.4.2 After getting the required CF pressure , SLC heating isput ON and CF circulation pump which feeds theregeneration circuit is also put ON. Temperature controlvalve is put in Auto mode to regulate the temperature.

4.4.3 CF temperature in the tank is maintained between 55 to57 C by switching ON/OFF the CF heater through the SLC.Additional safeguard is provided to switch OFF theheater in case the CF temperature in the heater exceeds65 C.

4.4.4 In the shutdown program, all the oil pumps are switchedOFF and an SLC CF pump is also put OFF. SLC heating iskept on to maintain the temperature required for thenext start-up and can be manually switched off, if required.