modelling and simulation of a gas turbine
TRANSCRIPT
Department of Science and Technology Institutionen för teknik och naturvetenskap Linköpings Universitet Linköpings Universitet SE-601 74 Norrköping, Sweden 601 74 Norrköping
ExamensarbeteLITH-ITN-ED-EX--05/009--SE
Modelling and simulation of a gasturbine
Henrik KlangAndreas Lindholm
2005-04-22
LITH-ITN-ED-EX--05/009--SE
Modelling and simulation of a gasturbine
Examensarbete utfört i Elektronikdesignvid Linköpings Tekniska Högskola, Campus
Norrköping
Henrik KlangAndreas Lindholm
Handledare Tomas StrömbergExaminator Måns Östring
Norrköping 2005-04-22
RapporttypReport category
Examensarbete B-uppsats C-uppsats D-uppsats
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Svenska/Swedish Engelska/English
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ISBN_____________________________________________________ISRN_________________________________________________________________Serietitel och serienummer ISSNTitle of series, numbering ___________________________________
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Institutionen för teknik och naturvetenskap
Department of Science and Technology
2005-04-22
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LITH-ITN-ED-EX--05/009--SE
http://www.ep.liu.se/exjobb/itn/2005/ed/009/
Modelling and simulation of a gas turbine
Henrik Klang, Andreas Lindholm
In this thesis, a gas turbine simulator for the Siemens GT10C was developed and implemented.
It concerns everything from the theory behind the simulator; both the hardware and software involved,to how the actual simulator was built using these tools. The theory concerns itself with basic automaticcontrol concepts, as well as basic turbine theory.
The simulator setup is being discussed concerning both technical and economic issues. A robusthardware solution is then selected, using the basic requirements, which the simulator then is builtaround.
The tools used are the Siemens SIMATIC automatic control system and the Siemens SIMIT real-timesimulator using a SIMBA Pro PCI card to interface with the PLC:s in the SIMATIC system. Matlab arealso used to a lesser extent to build the simulator behavior in SIMIT.
In the end, a fully featured simulator is presented that can be used for various purposes such as trainingoperators, trying out new concepts and testing the automatic control system used to control the turbine.
Further development that could be done, by other engineers, in the future, is also discussed.
Automatic control, fieldbus, gas turbine, modelling, S7, Siemens, SIMATIC, SIMBA, SIMIT, PLC,PROFIBUS, simulation
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© Henrik Klang, Andreas Lindholm
Preface i
Preface
This thesis is a result of about 20 weeks of analysis and implementation atSiemens Industrial Turbomachinery AB, Finspang, Sweden.
It is a compulsory part of the education for the authors to receive theirMaster of Science degree in Electronics Design Engineering from the Departmentof Technology and Natural Sciences (ITN) at Linkoping Institute of Technology.
The work was carried out in between June and November of 2004. The exam-iner at Linkoping Institute of Technology was Mans Ostring and the instructorat Siemens Industrial Turbomachinery AB, Thomas Stromberg.
The thesis was done in co-operation with another thesis worker, Daniel Wi-gren, which also is a student at Linkoping Institute of Technology studying toreceive a degree as a Master of Science in Applied Physics and Electrical Engi-neering.
Henrik Klang and Andreas Lindholm.
Stockholm and Finspang, February 2005.
ii
Thank you!
To everyone who deserves it.
Mandatory quotes from (in)famous persons iii
Mandatory quotes from (in)famous persons
“ ‘Students?’ barked the Archchancellor. ‘Yes, Master. You know?They’re the thinner ones with the pale faces? Because we’re a∗university∗? They come with the whole thing, like rats’ ” - TerryPratchett (author, Moving Pictures)
“Sometimes a scream is better than a thesis.” - Ralph Waldo Emer-son (US essayist & poet, Journals)
iv
Abstract
In this thesis, a gas turbine simulator for the Siemens GT10C was developedand implemented.
It concerns everything from the theory behind the simulator; both the hard-ware and software involved, to how the actual simulator was built using thesetools. The theory concerns itself with basic automatic control concepts, as wellas basic turbine theory.
The simulator setup is being discussed concerning both technical and eco-nomic issues. A robust hardware solution is then selected, using the basic re-quirements, which the simulator then is built around.
The tools used are the Siemens SIMATIC automatic control system and theSiemens SIMIT real-time simulator using a SIMBA Pro PCI card to interfacewith the PLC:s in the SIMATIC system. Matlab are also used to a lesser extentto build the simulator behavior in SIMIT.
In the end, a fully featured simulator is presented that can be used for variouspurposes such as training operators, trying out new concepts and testing theautomatic control system used to control the turbine.
Further development that could be done, by other engineers, in the future,is also discussed.
Keywords: Automatic control, fieldbus, gas turbine, modelling, S7, Siemens,SIMATIC, SIMBA, SIMIT, PLC, PROFIBUS, simulation.
CONTENTS v
Contents
Abstract iv
1 INTRODUCTION 11.1 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3 Questions at hand . . . . . . . . . . . . . . . . . . . . . . . . . . 11.4 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.5 History of the Finspang development site . . . . . . . . . . . . . 21.6 The structure of this thesis . . . . . . . . . . . . . . . . . . . . . 2
2 THEORY 42.1 Overview of fieldbus technology . . . . . . . . . . . . . . . . . . . 42.2 PROFIBUS R© . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.3 PROFIBUS-DP R© . . . . . . . . . . . . . . . . . . . . . . . . . . 62.4 MPI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.5 The Siemens SIMATIC totally integrated automation system . . 72.6 SIMATIC hardware . . . . . . . . . . . . . . . . . . . . . . . . . 72.7 Engineering and operator stations . . . . . . . . . . . . . . . . . 7
2.7.1 S7 PLC’s . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.7.2 DP-slaves explained . . . . . . . . . . . . . . . . . . . . . 9
2.8 SIMATIC software . . . . . . . . . . . . . . . . . . . . . . . . . . 92.8.1 SIMATIC manager . . . . . . . . . . . . . . . . . . . . . . 102.8.2 Hardware config . . . . . . . . . . . . . . . . . . . . . . . 112.8.3 SFC editor . . . . . . . . . . . . . . . . . . . . . . . . . . 112.8.4 CFC editor . . . . . . . . . . . . . . . . . . . . . . . . . . 122.8.5 NetPro . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122.8.6 Fail-safe versus non fail-safe . . . . . . . . . . . . . . . . . 122.8.7 WinCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.9 The Siemens SIMIT simulation system . . . . . . . . . . . . . . . 132.9.1 SIMBA Pro . . . . . . . . . . . . . . . . . . . . . . . . . . 132.9.2 Using SIMIT . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.10 The Siemens GT10C gas turbine . . . . . . . . . . . . . . . . . . 152.10.1 Compressor . . . . . . . . . . . . . . . . . . . . . . . . . . 162.10.2 Combustion chamber . . . . . . . . . . . . . . . . . . . . . 172.10.3 Power turbine . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.11 Turbine regulators . . . . . . . . . . . . . . . . . . . . . . . . . . 192.11.1 STC - starting control . . . . . . . . . . . . . . . . . . . . 192.11.2 NGGL - gas generator speed limiter . . . . . . . . . . . . 192.11.3 SC - speed controller . . . . . . . . . . . . . . . . . . . . . 202.11.4 T7L - exhaust average temperature limiter . . . . . . . . 202.11.5 T7Li - exhaust inner temperature limiter . . . . . . . . . 202.11.6 MPC - maximum servo position control . . . . . . . . . . 202.11.7 GAC - gas generator acceleration control . . . . . . . . . 202.11.8 GDC - gas generator deceleration control . . . . . . . . . 212.11.9 PAC - power turbine acceleration control . . . . . . . . . 212.11.10LLD - loss of load detection . . . . . . . . . . . . . . . . . 21
2.12 Automated start of turbine . . . . . . . . . . . . . . . . . . . . . 212.12.1 Unit sequence . . . . . . . . . . . . . . . . . . . . . . . . . 21
vi CONTENTS
2.12.2 Gas fuel sequence . . . . . . . . . . . . . . . . . . . . . . . 212.12.3 Turbine sequence . . . . . . . . . . . . . . . . . . . . . . . 232.12.4 A start of the turbine using the sequences . . . . . . . . . 23
2.13 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3 DECIDING THE SIMULATOR SETUP 253.1 Different solutions . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.1.1 Solution I - PLC—PLC . . . . . . . . . . . . . . . . . . . 263.1.2 Solution II - Simulator and control system in same PLC . 273.1.3 Solution III - PLC—PC/C/C++ (Java) . . . . . . . . . . 273.1.4 Solution IV - PLC—PC/Simulink . . . . . . . . . . . . . 283.1.5 Solution V - PLC–SIMIT (chosen) . . . . . . . . . . . . . 293.1.6 Conclussions . . . . . . . . . . . . . . . . . . . . . . . . . 29
4 IMPLEMENTING THE SIMULATOR AND THE MODEL 324.1 Setting up the simulator . . . . . . . . . . . . . . . . . . . . . . . 324.2 Closed and open loop control . . . . . . . . . . . . . . . . . . . . 324.3 Building HMI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334.4 The development cycle . . . . . . . . . . . . . . . . . . . . . . . . 344.5 A simulation diagram example (calculating heat flow) . . . . . . 35
4.5.1 Using performance data . . . . . . . . . . . . . . . . . . . 354.5.2 Heat flow versus speed, temperature and pressure . . . . . 384.5.3 The pilot flame . . . . . . . . . . . . . . . . . . . . . . . . 384.5.4 Necessary adjustments . . . . . . . . . . . . . . . . . . . . 384.5.5 A run with the model . . . . . . . . . . . . . . . . . . . . 38
5 RESULT 415.1 Conclusions and discussion . . . . . . . . . . . . . . . . . . . . . 415.2 Future development . . . . . . . . . . . . . . . . . . . . . . . . . 42
References 43
LIST OF FIGURES vii
List of Figures
2.1 Old fieldbus network. . . . . . . . . . . . . . . . . . . . . . . . . . 62.2 Modern fieldbus network. . . . . . . . . . . . . . . . . . . . . . . 62.3 Two Siemens SIMATIC S7 PLC boxes (back) connected to DP-
slaves (front). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.4 Basic configuration with a DP-rack in the hardware config editor 112.5 Two typical CFC-blocks, normal (left) vs. fail-safe (right). . . . . 122.6 SIMIT and SIMBA Pro interaction scheme (OS and ES comput-
ers connected to the S7 PLC are not included). . . . . . . . . . . 142.7 SIMBA Pro list of configured DP-slaves. . . . . . . . . . . . . . . 142.8 Example of a SIMIT diagram/modell. . . . . . . . . . . . . . . . 152.9 The GT10C gas turbine is a turbine with two rotors, the com-
pressor rotor and the power turbine rotor. This type is knownas a double shaft turbine. The three main parts of the turbine isenclosed in red. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.10 The compressor valves locations of the turbine. . . . . . . . . . . 173.11 Solution I, PLC to PLC communication (simplified schematic). . 273.12 Solution III & IV, PLC to PC (C/C++/SimuLink) communica-
tion (simplified schematic). . . . . . . . . . . . . . . . . . . . . . 293.13 Final hardware setup with the turbine PLC’s containing the con-
trol program and the PC containing the turbine simulation pro-gram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.14 The HMI of a turbine system (operator screen). . . . . . . . . . . 334.15 Grouping of diagram and operating screens in SIMIT. The dif-
ferent alphanumeric codes are an internal Siemens scheme fornaming different systems in the turbine. . . . . . . . . . . . . . . 34
4.16 Simple development process flowchart of the simulator model. . . 364.17 Data from performance tests used when developing the model. . 374.18 The relation between the curve taken from SCADA Pro (blue)
and the polygon curve done with Matlab (red). . . . . . . . . . . 374.19 The SIMIT model to calculate the heat flow value. . . . . . . . . 39
viii LIST OF TABLES
List of Tables
2.1 Comparison between PROFIBUS and older fieldbus standards . . 52.2 Speed versus pressure ratio in the compressor. . . . . . . . . . . . 172.3 Valve characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . 182.4 The unit sequence which starts up turbine. . . . . . . . . . . . . 222.5 Gas fuel sequence. . . . . . . . . . . . . . . . . . . . . . . . . . . 222.6 Turbine sequence. . . . . . . . . . . . . . . . . . . . . . . . . . . . 233.7 Quick recap of investment costs for each solution. Notes: 1A
more powerful PLC might be needed. 2If implemented. . . . . . . 30
ABBREVIATIONS ix
Abbreviations
AI Analogue InAPI Application Programming InterfaceAO Analogue OutCC Control CenterCFC Continuous Function ChartCP Communication PeripheralCPU Central Processing UnitDI Digital InDIP Dual-Inline PackageDO Digital OutDOS Disk Operating SystemDP Decentralized PeripheralES Engineering StationFAT Factory Acceptance TestGDC Gas generator Deceleration ControlGUI Graphical User InterfaceHMI Human Machine InterfaceI[/]O Input/OutputI2C Inter-Integrated CircuitIGV Inlet Guide VaneIPX Internetwork Packet ExchangeMAC Media Access ControlMPI Multipoint InterfaceNIC Network Interface CardOLE Object Linking and EmbeddingOPC OLE for Process ControlOS Operator StationOSI Open System Interconnection [Reference Model]PCI Peripheral Component InterconnectPCS Process Control SystemPID Proportional Integration DerivationPLC Programmable Logic ControllerPROFIBUS PROcess FIeld BUSPS[U] Power SUpplyPT Power TurbineRAM Random Access MemorySCADA Supervisory Control and Data AcquisitionSCL Structured Control LanguageSFC Sequential Function ChartTCP/IP Transmission Control Protocol/Internet ProtocolUR2 Universal Rack Type 2
1 INTRODUCTION 1
1 INTRODUCTION
1.1 Purpose
The primary purpose of this thesis is to develop a simulator and model fora specific gas turbine, the GT10C; which uses the Siemens SIMATIC system(“SIMATIC”, also referred to as “S7” where 7 is the latest version of SIMATIC).When this is done the model of the gas turbine will be implemented in the systemwhich has been devised.
Secondary purpose are to include more additions to the simulator, such assimulating the next coming stages in the turbine system; compressors, and otherloads. More wanted additions is to be able to simulate other turbine models inthe same family.
The first goal of the thesis is to analyze what kind of system that would beneeded to build and implement the simulator itself, both hard- and soft wise.When this is done, the actual simulator will be implemented in the developedsystem, and finally, at the end, tested against the actual turbine automationand control system located in multiple S7 PLC boxes.
This thesis is being carried out at Siemens Industrial Turbomachinery AB(“Siemens”) located in Finspang, Sweden which is a part of the Siemens group.
1.2 Background
Siemens Industrial Turbomachinery AB is about to adopt the S7 system, thusreplacing the currently used one developed by ABB.
The current project at hand (as of June 2004) is to install a GT10C gasturbine in Eischleben, Germany. This is the first project, in Finspang, to usethe S7 system from Siemens, thus the development of a simulator would behelpful in the entire development cycle of a turbine and its systems.
The simulator will be used for system testing, training new operators andsimulating new additions to the automatic control system, before the systemis tested in an actual turbine on site. This will help reduce, both developmentcost, and time to market, for new additions to the system. Moreover, it willshorten the time spent training operators for a specific turbine thus increasingtotal profit per installed turbine and project.
1.3 Questions at hand
A number of questions were formulated to use during the entire thesis process.Each one of these questions will be answered in this thesis report.
Primary,
• What kind of system should be used for the simulator?
• How should the communication work in between the simulator and thePLC. Is there any ready-made solutions to use?
• What system is feasible to use concerning cost, training, and implemen-tation time?
• In which way should the human machine interface of the simulator beimplemented and designed to be as easy as possible?
2
Secondary,
• How should other turbine models be implemented in the simulator andcan it be done in a reasonable time frame?
1.4 Limitations
The initial limitations will be to devise a simulator for only one turbine, theGT10C. Although extending the simulator for other turbine types such as theGTX100 would be favorable.
At first the model of the turbine shall be static, that is, no dynamic signalsshall be modeled. Static signals in this report refers to such ones that does notuse any feedback when calculating the output signals of the system.
If, and when, the static modeling is done, a half dynamic model should bedeveloped. In this report a half dynamic model is a model where analogue anddigital signals can be triggered by other signals, but not as a closed loop, suchas a PID (for further discussion of these concepts please refer to Section 4).
Furthermore, an external unit (load) of the turbine, shall be modeled if thereis any time.
1.5 History of the Finspang development site
The Finspang site has been developing and producing power generation equip-ment approximately 100 years. In 1913 Svenska Turbinfabriksaktiebolaget Ljung-strom (Swedish turbine factory Ljungstrom) was formed (known as STAL). Inthe 1950’s they merge with DeLaval and formes STAL-Laval.
In the middle of the 1980’s ASEA buys the entire company which laterbecomes ABB STAL AB.
In 1999 ABB Alstom Power Sweden AB is formed and in the same year thegas turbine GT10C is developed. This is the turbine that the simulator in thisthesis simulates.
Finally in 2003 Siemens buys the company and renames it Demag DeLavalIndustrial Turbomachinery AB which in October of 2004 became Siemens In-dustrial Turbomachinery AB.
1.6 The structure of this thesis
In the first chapter, THEORY, an explanation of automation control conceptsand turbine theory will be introduced. This is the perquisites to understandthe reasoning behind, both the model, and how the simulation system wasdeveloped. This chapter also explains the programs used and how they worktogether and individually.
In the chapter DECIDING THE SIMULATOR SETUP the entire sim-ulator hardware will be explained. Why and how the hardware and softwarewas chosen and how the system was put together. Both technical and economicissues are taken into consideration here.
In IMPLEMENTING THE SIMULATOR AND THE MODEL logicbehind the actual turbine model will be explained in detail. Also the HMI willbe shortly discussed and some other important aspects concerning the simulatorimplementation itself.
1.6 The structure of this thesis 3
Last, the chapter RESULT discusses the results, and what could have beendone differently. Also future improvement that would be possible is discussedhere.
4
2 THEORY
To be able to understand the next coming chapters some explanations of theterms and concepts, in this thesis, will be discussed below. A simple overviewof the programs used will also be presented to give the reader a more in depthview of the problems the authors faced and measures taken to solve these.
This chapter also explains, on a very low level, how a turbine works, andespecially the turbine which the simulator in this thesis is developed for.
2.1 Overview of fieldbus technology
Fieldbus[1][2] technology is a major step in the process control industry. Inolder systems, signals sent used to be unidirectional and traditionally 4−20mAanalogue.
Fieldbus technology on the other hand is a replacement for this type ofolder systems and extends the entire process control concept from the bottom-up approach to a more sophisticated top-down thinking. The modern fieldbus oftoday acts as an entire network; much like the Internet. It connects everythingfrom PLC’s, engineering and operator stations to low level field devices on thefactory floor such as actuators, sensors, transducers and drives.
The fieldbus networks makes use of modern communication standards suchas TCP/IP, IPX and Ethernet. These networks interconnect over large areaswhere the operator can be in Australia and the process which the operatorcontrols could be located somewhere in Europe (in theory, but not very likelyused in practise).
This in turn opens for entirely new possibilities such as remotely developingand upgrading systems, monitoring factory processes and supporting on site op-erators within the accessible process network. Optimizing processes and findingpossible bottle necks more rapidly are other benefits.
Down sides to the modern fieldbus networks could be speed and congestionproblems due to the large amount of traffic being sent on the same network(cable) and over other “unknown” networks such as Internet cables which theengineer does not have control over. Older[2] technologies relied on severalhundred of cables (Figure 2.1), one for each signal, up to the PLC’s and op-erator/engineering stations, while modern fieldbus networks interconnects theprocess objects with each other at central access points. The objects are oftenconnected in a serial fashion thus creating bottle necks along the way if muchtraffic and information exchange is needed between the process objects and theprocess control itself. Although this can be helped with new technologies suchas fiber cables sending information using light instead of electrical signals orinstalling a second cable so that the objects are connected in parallel; thoughthis would require another PLC box.
For an easy overlook of the difference between older network properties andmodern such as fieldbus, see Table 2.1.
Going more extensively into the positive properties of fieldbus technologysome are,
• Design and engineering - Building the networks around well definedand known standards and concepts both reduce design and planing time,as well as helps minimize the documentation needed.
2.2 PROFIBUS R© 5
older standards profibusSignals Analogue Digital (packet based)
Unidirectional BidirectionalCables One for each signal. Multiple signals can
share a cable.Networking Multiplexing of signals Signal information can be
needed at a central hub. easily relayed to multipleend points both localand global.
Diagnosis Basic diagnosis More extensive informationinformation. can be provided (“intelligent
slaves”).Commissioning More expensive due to Less cables, easier layout
complex networks and of the network.more cables.
Table 2.1: Comparison between PROFIBUS and older fieldbus standards
• Installation and commissioning - Since the fieldbus I/O’s can be morediverse with less cables required in the process, both cost and time is re-duced during commissioning and installation of the network and its sur-rounding process objects, PLC’s and higher monitoring tools.
• Easier operation and maintenance - The data being transferred onthe network can be more diverse than traditional analogue process net-works since the standards is built around packet sending services similarto TCP/IP. This means that, not only digital and analogue signal infor-mation can be sent, but also extensive diagnostic information from eachprocess object located in the system process. The information can also beeasily sent to several endpoints in the factory network as well as larger net-works such as the Internet. This makes it easier co-operating and findingthe actual errors or solutions to the problems at hand.
There are several fieldbus standards such as PROFIBUS, INTERBUS, MPIand Industrial Ethernet. Some are proprietary while others are open. Commonfor all is that they are used by industrial applications and are certified to workunder the very different environment of a plant versus an office. The differenceare mostly in how the software protocol is implemented, as well as physicalproperties of the cables and signal levels.
2.2 PROFIBUS R©PROFIBUS[3] specifies everything from the medias electrical properties (thecable) to the protocol specifications over the cables.
PROFIBUS is a simple two-wire buss (much like Phillips I2C), built to berobust in rugged environments, using a minimal and easy to implement protocol,with a minimal overhead. Thus reducing down time and need for maintenance.
PROFIBUS is an open standard1 and was developed as a research project, in-volving several major corporations and research institutes, between 1987−1990.
1IEC 61158-1 through IEC 61158-6
6
PLC
Location A
Location B Location C
Figure 2.1: Old fieldbus network.
PLC
Location A
Fieldbus Cable
I/O device I/O device
Location B Location C
Figure 2.2: Modern fieldbus network.
PROFIBUS is the leader of fieldbus communication with over 20 per cent of theworld market. Approximately 500.000 plants and factories use PROFIBUS,with over 5 million nodes2 installed.
2.3 PROFIBUS-DP R©
PROFIBUS-DP[3] is a extension of the PROFIBUS standard which is designedfor fast data exchange at field level. The distribution is cyclic. It works muchlike “token ring”, where a token is “passed” between the different stations and“taken” by a particular station if information is to be sent by it. There arethree different DP-protocols. The one used in the SIMATIC system is DP-V1which supports features such as fail-safe (more about fail-safe in Section 2.8.5).
Each object connected to the PROFIBUS-DP network has a unique id inbetween 1-127 where 0 is reserved for so called broadcast operations (sendinginformation to several nodes at once).
2A node is a PROFIBUS station with a unique PROFIBUS address such as PLC’s, sensorsand actuators.
2.4 MPI 7
2.4 MPI
MPI[4], Multipoint Interface, is a closed Siemens standard. It is used as aprogramming interface for S7 PLC’s (see Section 2.7 for information on S7PLC’s), but can also be used as a interface to operator panels simultaneously.Each MPI interface, or node, is identified by an address.
2.5 The Siemens SIMATIC totally integrated automationsystem
The Siemens SIMATIC concept (“SIMATIC”) is a product line of both hard-ware and software products for plant control applications.
The SIMATIC system itself is independent of the medium used to transportinformation, but it supports both MPI (proprietary of Siemens) and PROFIBUSstandards, as well as Industrial Ethernet. The various communication interfacescan be used at the same time, combining them, depending on the configurationand system needed.
A core product of the SIMATIC system is PCS7 which is a software suite(Process Control System 7) that is needed to build the programs used in theprocess plant control. Each control system is then loaded onto a S7 PLC box.The S7 PLC is set in run mode and then starts to interchange information withthe surrounding objects through the various interfaces available (a more detaileddescription is provided in the next coming sub chapters).
It can be discussed if the software or hardware should be explained firstin this thesis, since they are so closely related. The reader should be advised,however, that there is no clear distinction between the hardware and software.
2.6 SIMATIC hardware
The SIMATIC hardware suite consists of a line of hardware modules used tobuild the entire plant control system, from top to bottom.
At the core is the S7 PLC boxes which are used to control the plant process.Around these S7 PLC boxes the network is built, both using Ethernet, PROFI-BUS and MPI interfaces, depending on what, and where to connect peripheralequipment such as operating stations and engineering stations DP-slaves andeven other PLC’s.
Another integral part of the systems are, as already mentioned above, DP-slaves. The DP-slaves controls the process objects of the plant, and communi-cates to the S7 PLC’s via a network.
2.7 Engineering and operator stations
A operator station is a computer were the turbine is controlled and monitored.There usually exist more than one of these so the engineer can see severalprocesses simultaneously.
At the engineering stations the service personnel can make change to thecontrol program and test these news changes. There usually exists only one ofthese.
8
2.7.1 S7 PLC’s
The S7 PLC’s differ in function, speed and memory capacity. The configura-tion needed is dependent upon the application. Processes such as conveyor beltsystems with few stations could settle with a simpler S7 PLC’s, while more com-plex systems such as turbines and paper machines could need several powerfulS7 PLC’s working together as a cluster or separate, dividing the handling ofDP-slaves and the calculations needed to run the plant process.
The most basic S7 PLC hardware configuration consists of the following:
• Rack (“UR2”) - Where the hardware components are mounted.
• PS - Supplies power and provides battery backup if the system shouldhappen to lose power.
• CPU - The central unit which runs the PLC program stored on a memorycard.
• CP - The communication processor module used to interface with Ether-net.
The PS, CPU and communication process modules are placed in a UR2 rack.The UR2 rack is both a mechanical and electrical “backplane”. The rack letsthe different components communicate with each other as well as provides a me-chanically stable platform for use in harsh industrial environments. Dependingon the type of the rack it can mount multiple “PLC cells”, where each groupconsists of a power supply, CPU and communication processor.
The PS supplies power to the rack through the backplane. The PS alsoconsists of two batteries (rechargeable), which are used if the regular powerfrom the grid is lost, thus creating redundancy. The S7 PLC program itselfis stored on a flash memory card, which holds the information, even during apower loss. Although, the configuration data which holds information of whatkind of components that is mounted on the rack, is stored in a volatile RAMthus making PS redundancy important via the batteries.
Another source of redundancy can be created by adding a extra PS to therack. For these purposes, and depending on the saftey needed, there are differenttypes of PS such as redundant and non-redundant. Obviously, creating a non-redundant solution is a solution with low initial costs, but could be proven afatal decision afterwards, due to production loss caused by downtime of thePLC-system.
The CP modules is in many ways like a normal network interface card(“NIC”) found in any modern PC, thus having connections for ethernet wiring.Since Industrial Ethernet (a subset of Ethernet) is very much like normal Eth-ernet the wiring can be connected to switches and hubs like any other computernetwork. The engineer can then program the PLC through the CP cards in-terfaces as well as through the MPI interface as mentioned earlier. Also, theethernet interfaces are often connected to the ES and OS stations where the op-erator can control the plant through the S7 PLC. There are CP modules whichholds fiber optic connectors thus handling fiber optic nets if the S7 PLC needsto process time critical data and process objects.
At the heart of the plant control is the CPU module(s). It consists of a CPU,and a memory module. The memory module size needed depends on the size of
2.8 SIMATIC software 9
the plant control program it needs to store. Also, depending on the model typeof the CPU module it can be exchanged for larger modules (varying between1-16MB).
The CPU module also holds a DP interface and a combined DP/MPI in-terface. The MPI can be used to programme the CPU modules flash card viaan expansion card in a PC. Usually, though, the memory card is programmedthrough the CP modules Ethernet connection (that is via a network).
It is through the DP interface that the DP-slaves are connected. That is, theDP interface handles the process objects communication (see next sub chapterfor a more throughout description). As with the other kinds hardware modulesdetailed above there are different types of CPU’s available, varying in speed andcapabilities such as redundancy and fail-safe (see Section 2.8.5 for an explanationof fail-safe).
2.7.2 DP-slaves explained
A DP-slave is a hardware process object which handles the communicationin between the S7 PLC and the sensor, actuator, drive or any other type ofmeasurement point located in the plant or process hierarchy. Each DP-slavehas a unique PROFIBUS node id, between 1-127, as mentioned before. The iditself can usually be set by DIP-switches directly on the device. The name itselfis derived from the fact that the objects use the PROFIBUS-DP R© protocol tocommunicate with one or more master (S7 PLC box(es)).
Each PLC box are also considered to be a node in the system and is therforeassigned a node number. By default a S7 PLC usually assigned node id 2 (id 0is reserved for broadcast packets).
The DP-slaves are connected via a PROFIBUS interface (cable) to a S7PLC. Each slave can hold a variable number of I/O’s and types such as a 16analog signals input or 4 input digital signals output matrix.
The slaves can be connected in serial to the same S7 PLC using the samecable and interface. As with the S7 CPU there are fail-safe, redundant andfiber-optic versions of most DP modules.
Industrial processes, such as a turbine may involve more than twenty DP-slaves in the plant network containing hundreds of signals, while even morecomplex plant processes such as a paper machine may contain thousands ofsignals and an even larger amount of slaves.
2.8 SIMATIC software
With the hardware explained briefly, one should note that the software of theSIMATIC suite is just as important and, sometimes, overly complex. TheSIMATIC software suite consists of a plethora of components. While someare a integral part in this thesis, other, are not, thus these are excluded. Onlythe most important programs which the authors has used, are explained below,to make the thesis as easy as possible to grasp.
SIMATIC software has been developed and used since the DOS days (late80:s), before Windows. Since each new revision of the system, it has been up-dated, upgraded and reworked. Although, not from the bottom and up, rather,the other way around. This has created a non-modern suite of componentswhich are not very easy to use. SIMATIC and the components are, to say the
10
Figure 2.3: Two Siemens SIMATIC S7 PLC boxes (back) connected to DP-slaves (front).
least, software built on old concepts which the developers have tried to fusionwith new ones such as drag and drop and GUI. Therfore, SIMATIC is relativelyhard to work with initially, creating a steep learning curve for beginners.
A summary of the programs explained are included in the list,
• SIMATIC manager - All-in-one control center for the SIMATIC suiteof programs.
• WinCC - OS and ES station development and usage.
• Hardware config - Configuration of the hardware setup, used in thefactory process, at all levels.
• Continuous function chart editor - Drag and drop editor where func-tion blocks are interconnected to create the PLC functions (i.e. PID reg-ulators, logic blocks et.c.).
• Sequential function chart editor - Program used to build sequencesusing function blocks (very much like flow charts).
• PG\PC interface - Sets the interface used when programming the CPUmodule.
• NetPro - Program to set up communication between PLC’s and OS.
2.8.1 SIMATIC manager
SIMATIC manager is the control center in SIMATIC used to organize, set upand develop the software projects from a central point. Each and one of theother programs in the SIMATIC suite is started from the manager itself.
Since building a control system often needs a team of people collaboratingSIMATIC manager makes use of multi-project concepts which enables engineersto simultaneously develop the models and control systems, also known as con-current engineering.
2.8 SIMATIC software 11
The manager shows projects currently open, a summary of the hardwareconfigured for the projects, and the different components included in the controlprogram.
The manager also shows connected DP nodes (masters and slaves) for aneasy overview of the connected devices, making diagnosis and detection of errormore manageable.
Since most plant applications include more than one PLC controlling theprocess, more than one PLC program, at a time, can be loaded in the manager.
2.8.2 Hardware config
The hardware config editor is reached from the SIMATIC manager. This iswhere the engineer sets up the entire hardware network, concerning everythingfrom what kind of PLC to use to the type of media interconnections between thenodes and where the OS and ES stations should be connected in the automaticcontrol system network.
Figure 2.4: Basic configuration with a DP-rack in the hardware config editor
In Figure 2.4 a hardware setup can be seen as defined by the hardwareconfiguration editor. The window to the left in Figure 2.4 represents the com-ponents which the engineer have physically mounted on the UR2 rack. Sincethere are different kinds of S7 CPU’s, CP’s and PS’s the correct version mustbe configured. Each number in the window corresponds to the slot on the rack.As seen, the CPU and the PS is mounted in two slots each.
To the right, on the “PROFIBUS cable”, a DP-slave is mounted. In thiscase a IM153-2 slave, which holds 16 analog out signals (cannot be seen in thefigure). This example illustrates a minimal system with very few signals but isnevertheless a good example of how a plant network could be built using thehardware config interface.
2.8.3 SFC editor
In the sequential function editor the engineer builds the sequences in which theturbine should be started. In other words, in which order the CFC charts shouldbe executed in order to start up the turbine in a controlled way.
The editor also includes transition steps which has to be fulfilled before thesequence continues. The sequences, which is mentioned more in detail in thesub chapters of chapter 2.11, is built in the SFC editor.
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2.8.4 CFC editor
The continuous function chart editor is where the engineer builds the actualcontrol program. Components such as PID-regulators, OR-blocks and timerfunctions can be dragged-and-dropped into the editor. The components canthen be configured and connected to their respective I/O ports.
There are two kinds of fundamental “low-level” blocks in the editor; fail-safeand normal blocks. The fail-safe blocks have a distinct yellow color while theothers are grey as seen in Figure 2.5.
The blocks seen in Figure 2.5 has the function of being out and input blocksout and into the PLC itself. The blocks are thus the “boundaries” of the PLCprogram.
Figure 2.5: Two typical CFC-blocks, normal (left) vs. fail-safe (right).
2.8.5 NetPro
This program is used to set up the communication in between the PLC’s and theoperator station(s). In addition to hardware config where the communication isinitially set up, this program modifies the necessary “blocks” to ensure that thecommunication in between the PLC and OS works correctly concerning messageand alarms sent between the process, PLC’s and OS.
2.8.6 Fail-safe versus non fail-safe
A fail-safe block differs from the non fail-safe ones in a few important aspects.First of all fail-safe blocks needs special CPU’s known as H-series modules. Ifthis is not the case the control program cannot be loaded, at all, into the CPU’smemory module. Typically, fail-safe-able modules are more expensive than theirnon fail-safe counterparts, this is why the engineer should consider the pro’s andcon’s of using fail-safe versus a more low-cost setup.
A fail-safe block switches to an alternate value and sets the output of theblock (that is, a value going into the process to a DP-slave) if a fail-safe modeshould happen to be enabled. The fail-safe mode can be set for a number ofreasons, such as the DP-slave failing electrically or if the cable is failing to deliverthe signals to the CPU’s DP-interface (i.e. no acknowledgement is received fromthe DP-slave of the packets safe delivery).
Fail-safe is mainly used in plant processes with sensitive components whichcould be damaged if the signals are lost. For example mechanical systems suchas gas turbines. Fail-safe are also used in explosively classified environmentssuch as oil and gas platforms.
2.9 The Siemens SIMIT simulation system 13
2.8.7 WinCC
WinCC, or Windows Control Center, is the program where the operator picturesare built in. The connections to the signals from the CFC-editor is connectedto GUI components in WinCC such as buttons, diagrams, pictures and sliders.
WinCC can be run on multiple PC’s known as operator stations (“OS”)which makes it easier to have an overview of the gas turbine process and tocontrol it through the GUI.
2.9 The Siemens SIMIT simulation system
The Siemens SIMIT simulation system is a program suite used for plant sim-ulation and modelling. It has an easy to use interface, in many ways similarto Mathworks Simulink (included in Mathworks Matlab). SIMIT is a real timesimulation system, that is; simulation of the models and analysis of the data isdone in real time (although the data generated can be saved), while programssuch as Simulink can simulate the entire model instantly and let the engineeranalyze the model and its results at once.
Clearly, this has its pro’s and con’s. It’s harder to know and estimate how thesimulation is expected to develop and expand as time increases since SIMIT andSIMATIC has to interact and calculate values such as PID-controller settingsdynamically as the process evolves.
SIMIT has been designed for less complex models in mind, as the user wouldnotice rather quickly. Still, more advanced programs are possible, as seen bythis thesis.
2.9.1 SIMBA Pro
The SIMIT suite can be extended with a SIMBA Pro PCI card (“SIMBA”). Thecard itself is fitted into a PCI slot in a PC and accessed via a special softwarewhich SIMIT uses to relay its information flow through to the PCI card itself(through the use of a hardware driver). The schematic view of SIMIT combinedwith the SIMBA Pro PCI card is seen in Figure 2.6.
SIMBA Pro has two connectors. Each can be connected to a PROFIBUSnetwork, which means the card can handle two networks at the same time.
SIMBA Pro does not need SIMIT to function as it is a self-reliant system.SIMIT should be seen as an add on containing more advanced graphical GUIand better analysis tools. SIMBA Pro holds several tools and components tobe able to simulate simpler processes.
The values of the I/O ports of the DP-slave can also be set individually ifneeded. Since SIMBA Pro is built for S7 communication through PROFIBUSthe DP-slave configuration can be easily imported into SIMBA Pro from theSIMATIC hardware config program. A list of a imported DP-slave configurationcan be seen in Figure 2.7.
SIMBA Pro also handles fail-safe DP-slaves by adding extra signals for thefail-safe to be turned on or off for each signal in the hardware config configuredin the fail-safe mode.
14
SIMBA Pro
Software
SIMBA Pro
PCI card
Driver
SIMIT
SW
In
terfa
ce
PROFIBUS-DP S7 PLC
x86 Simulator PC with Windows 2000
Figure 2.6: SIMIT and SIMBA Pro interaction scheme (OS and ES computersconnected to the S7 PLC are not included).
Figure 2.7: SIMBA Pro list of configured DP-slaves.
2.9.2 Using SIMIT
Although the GUI has not been designed with ease of use in mind, managingSIMIT is fairly simple. SIMIT consists of basic component types such as tanks,PID-regulators and digital logic which simply is dragged, dropped and connectedtogether to achieve the needed function (as in for example Simulink). Thecomponents can then be connected to signals coming from the S7 PLC, throughthe SIMBA Pro card, via input and output elements known as peripheral blocks.
The signal list in SIMIT can be imported from the PLC program in theSIMATIC system, thus not needing to enter the signals by hand. Since therecan be hundreds of signals this is a very convenient feature.
2.10 The Siemens GT10C gas turbine 15
Each signal has a hardware address and an alias assigned to it (this is doneduring the development cycle of the PLC program in SIMATIC). The alias is aname used when connecting I/O ports in SIMIT to simplify the process sinceonly a hardware address would be confusing and rather cumbersome.
A very simple example is shown in Figure 2.8 where two input signals, IN-PUT SIGNAL 1 and INPUT SIGNAL 2, is added together. The result issent through a sin block, and finally output to the OUTPUT SIGNAL port.More complex concepts such as feedback (PID-regulators) are also available tothe engineer.
Figure 2.8: Example of a SIMIT diagram/modell.
SIMIT differentiates between what it calls operator screens and diagramscreens. This is very much like the concept of SIMATIC. The logic and functionsof the simulation is built in the diagram view, using, as explained, componentsof various types. The components are then connected to the operator screenswhich displays and presents the values the diagram screen produces during thesimulation. The DISPLAY component seen in Figure 2.8 is such a component.
The DISPLAY component is simply dragged to a operator screen andthe output is then displayed at this screen during the simulation. Interactiveswitches and buttons can also be added to the operator screens to control andinfluence the diagrams, yet, analogous to SIMATIC.
Custom components can be made in SIMIT thus reducing the need to con-nect large clusters of blocks to achieve the desired functionality. The program-ming language is proprietary to SIMIT but very similar to object oriented syn-tax.
2.10 The Siemens GT10C gas turbine
The theory explained here is in no way meant to be a comprehensive descriptionof how an actual turbine works down to the very core, rather, it should be seenas an overview.
Some concepts, tables and formulas in the following sub chapters are takenfrom internal Siemens documents, thus there are no reference to these in thetext.
A gas turbine core engine can be decomposed into three different parts;compressor, combustion chamber and power turbine. This can be seen in Figure2.9.
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Figure 2.9: The GT10C gas turbine is a turbine with two rotors, the compressorrotor and the power turbine rotor. This type is known as a double shaft turbine.The three main parts of the turbine is enclosed in red.
2.10.1 Compressor
The function of the compressor is to compress the surrounding air. When theair is compressed the temperature and pressure increase. To avoid surge3 inthe compressor, two bleed valves, are used as well as an inlet guide vane (IGV).These elements can be seen in Figure 2.10(BV1 and BV2).
The IGV controls the amount of air that flows into the compressor. The bleedvalves are used to level out the pressure in the compressor to avoid fluctuation inthe pressure, which is an unwanted effect. BV1 is just an ordinary on/off valveand BV2 is a control4 valve. BV2 is connected to the air inlet through piping,this to be able to control the temperature in the combustion chamber. At ahigher flame temperature the emissions are lower. The CO and NOx valuesdecrease and the turbine is in that way more environment friendly.
BV1 is used only during the start of the compressor and closes when thespeed Nnorm of the compressor reaches 6800rpm. BV1 is fully closed between6950rpm and when stopping the turbine it remains closed until 400rpm.
Nnorm = N ·√
288t2 + 273
(2.1)
The relation Eq. 2.1 between the valves position and speed is later used inthe SIMIT modell to verify a stable operation mode of the compressor. That is,if the simulated values is out of range, the turbine control system would trip5
since the model is not working as expected.To ensure stable operations and required engine performance, the compressor
guide vanes must be controlled according to Table 2.2. P3 is the compressordischarge pressure (MPa) is calculated as an average of three different pressuretransmitters.
3When a surge occurs the compressor stalls, that is, stops to work.4A control valve lets the PLC control the exact position of the valve, that is, how much it
should open.5A trip of a turbine is when the control program shuts the turbine down because of errors
(signals outside the safety limits set up by the control program).
2.10 The Siemens GT10C gas turbine 17
Figure 2.10: The compressor valves locations of the turbine.
P1 is the compressor inlet pressure (MPa). The surge protection is activatedwhen the speed exceeds 6000rpm.
Nnorm(rpm) P3/P1≤ 6000 1.06500 2.57500 4.88700 7.69800 13.8
≥ 10500 14.2
Table 2.2: Speed versus pressure ratio in the compressor.
To detect compressor surges, the compressor operating line is supervised. Ifthe compressor pressure ratio is lower than in Table 2.2, a surge is likely to haveoccurred and a trip will be initiated.
When the compressed air has passed through the compressor it reaches thecombustion chamber.
2.10.2 Combustion chamber
In the combustion chamber the compressed air and the ignited fuel help increasethe pressure even more. The combustion chamber contains a ring with fuelburners which are constructed in such a way that the flame is rotating. This isto maintain a flame that keeps the same shape, if not a pulsation effect couldoccur, when the flame flickers. This in turn result in high vibrations, high axialdisplacement and damage to the turbine.
The amount of fuel inserted into the combustion chamber is controlled bytwo gas fuel control valves. The primary gas fuel control valve is used in thestart sequence and split range controlled with the main gas fuel control valve.
The primary gas fuel valve is at nominal speed closed to a minimum of “stay-alive” percentage opening, this to avoid flame extinction if the gas generator
18
low load high loadmain heatflow primary heatflow primary heatflow
pos. (%) (MJ/s) pos. (%) (MJ/s) pos. (%) (MJ/s)0 -2 0 -2 0 -28 0 20.5 0 20.5 015 4.9 25 2.7 25 1.4820 10.5 30 5.46 30 3.8625 17.6 35 9 35 7.9830 25.7 40 13.78 40 12.4740 43.9 50 20.8 50 20.845 53.2 55 25.3 55 25.350 62 60 30.18 60 30.1855 70.2 65 32.98 65 32.9860 77.2 70 36.19 70 36.1965 82.8 75 38.89 75 38.8970 87 80 40.98 80 40.9875 92.1 90 42.98 90 42.9880 97.2 100 45.2 100 45.2
Table 2.3: Valve characteristics.
deceleration control (GDC) goes active. The GDC is activated if the load6 onthe turbine is lost due to an malfunction.
When the high pressurized warm air expands through the compressor thekinetic energy is transformed to mechanical energy by the turbine blades andincrease the speed of the compressor, thus if the air and heat flow through theturbine is not controlled the compressor would accelerate rapidly. The heatflow value can be derived from the fuel gas valves characteristics when a certainpercentage opening generates a certain heat flow. The characteristics of the gasfuel valves can be seen in Table 2.3. The valve characteristics is used in thecontrol program of the turbine (that is, in the SIMATIC system) and also inthe SIMIT model to obtain the heat flow value. The heat flow now expands andcontinues through the power turbine.
2.10.3 Power turbine
Because the exhaust pressure is lower than the pressure in the combustion cham-ber the warm air now expands further through the turbine blades. The energyof the heat flow is once again transformed from kinetic energy to mechanicalenergy thus the speed of the power turbine increase in correlation to the heatflow value.
The power turbine has an inertia which has to be conquered in order for thepower turbine to start accelerating. As the power turbine is now turning theonly thing missing is the actual load which can be a generator or a mechan-ical drive. Usually the mechanical drive application is a compressor used forcompressing gas in pipelines, but there is also mechanical drives, as mentioned
6The load is the equipment which the turbine drives, such as a water jet in a boat (thisis not entirely accurate since it does not drive the water jet directly, rather it uses somethingcalled a mechanical drive in between).
2.11 Turbine regulators 19
before, connected to water jet propulsion systems like the Stena Carisma ferryover Oresund.
2.11 Turbine regulators
The regulators role is to ensure that the turbine never reach a damageableoperation mode.
In normal operation the following regulators are used,
1. STC
2. NGGL
3. SC
4. T7L
The other controllers are used to monitor that this happens in a controlledway. What the different regulators monitor can be found under the respectiveregulator heading in the text bellow.
These regulators are,
1. STC - starting control
2. NGGL - gas generator speed limiter
3. SC - speed controller
4. T7L- exhaust average temperature limiter
5. T7Li - exhaust inner temperature limiter
6. MPC - maximum servo position control
7. GAC - gas generator acceleration control
8. GDC - gas generator deceleration control
9. PAC - power turbine acceleration control
10. LLD - loss of load detection
2.11.1 STC - starting control
In order to accelerate the gas generator at a limited rate, the starting controlproduces a set point for the desired heat flow as a function of time. It therebyprevents too rapid acceleration and thermal stress of the turbine. The set pointsis ramped from ignition level with a certain speed. The STC function controlsthe gas fuel servos until the NGGL function takes over.
2.11.2 NGGL - gas generator speed limiter
The NGGL controls the gas generator speed from 5600rpm and up to a certainspeed where the speed controller takes over. It also controls that the gas gen-erator does not exceed maximum allowed speed. When the gas generator speedis more than 5600rpm the set point is ramped with a max setting of 40rpm/s.The set point has no manual mode and the operator is not able to change it.
20
2.11.3 SC - speed controller
The speed controller takes over at minimum speed of the power turbine at3250rpm. The set point to the controller is set by the operator in automaticmode or received from the compressor performance controllers. This controlleris normally in operation until full load is achieved when T7L (or NGGL) takesover. The feedback to the speed controller is the power turbine speed. The SCcontroller also makes sure that the power turbine maintains the correct speed.This to ensure that the correct flow and pressure in the pipelines are maintained.
2.11.4 T7L - exhaust average temperature limiter
T7L controller monitors the exhaust temperature so that the temperature doesnot get to high and damages the turbine.
As the load increase the exhaust temperature increase. The T7L controllerlimits the exhaust temperature which is the normal maximum load limiter. Theset point is a function of ambient temperature, ambient humidity, compressordelivery pressure, exhaust gas pressure and compressor inlet pressure. If the op-erator selects peak load the set point is automatically adjusted to a higher value.The feedback to the T7L controller is the turbine exhaust average temperature.
In an ideal world it should be sufficient with these controllers but in thereal world it is also necessary to make sure that other operating modes which isdamageable in the long run never occurs. This is why there are six additionalcontrollers.
2.11.5 T7Li - exhaust inner temperature limiter
The T7Li controller monitors the inner temperature so that the temperaturedoes not get to high and damage the turbine.
T7Li limits the inner exhaust temperature. This protects the turbine fromhigh exhaust temperature if the combustion chamber bypasses malfunctions.
2.11.6 MPC - maximum servo position control
MPC limits the maximum fuel input. The operator sets the set point in MJ/s.Normally the set point corresponds to more than 100 per cent load. MPC is asmentioned earlier not used at normal operation but the operator can manuallylimit the maximum amount of fuel fed to the combustion chamber. It is alsoused as backup control upon feedback error. The error freezes the actual desiredheat flow signal and it becomes the set point for the MPC controller.
2.11.7 GAC - gas generator acceleration control
GAC shall prevent the turbine from surging and from transient over tempera-tures in the gas generator during loading. The set point is a function of nor-malized gas generator speed. The operator is not able to change the set point.To avoid overheating and compressor surge, there is an upper limit of the fuelflow, set by the actual normalized compressor speed.
To prevent damage on the engine in mechanical drive applications there isa loading limitation on compressor discharge pressure increase, as a function of
2.12 Automated start of turbine 21
power turbine speed variation. The register is valid for all matching options;the points in between are linear interpolated.
2.11.8 GDC - gas generator deceleration control
To avoid flame out, there is a lower limit of the fuel flow, set by the actualnormalized compressor speed. This is also valid for power generation. It isalso necessary to increase the GDC level for mechanical drive applications. Itis increased with required fuel flow to match the base load at minimum speed,after that the minimum speed has been reached.
2.11.9 PAC - power turbine acceleration control
In order to accelerate the power turbine at a limited rate, the power turbineacceleration control limits the set point for the desired heat flow as a functionof power turbine acceleration. It thereby prevents too rapid acceleration andthermal stress of the power turbine. The set point is fixed during start upand put aside during operation. The feedback to the PAC limiter is the powerturbine speed.
2.11.10 LLD - loss of load detection
The function of the loss of load detection is to sense the power turbine speedvalue, and calculate the rate of change over one sample. If it exceeds a certainlevel the fuel level is set to GDC level at maximum speed and BV2 is openedto brake the gas generator speed/load.
2.12 Automated start of turbine
Because of the complexity of the turbine different start up sequences is used toensure that all systems are started and set to their operation levels. There arethree different sequences which a mechanical drive turbine has to go throughbefore it is up and running.
2.12.1 Unit sequence
The unit sequence is a start/ stop sequence with 26 steps. The main purposeof this sequence is to start up different systems: such as lube oil, ventilationetc. Table 2.4 shows the steps included in the sequence. Some of the steps areenclosed in a function group which in turn uses a lot of signals. As an examplethe lube oil function group has to start two of three pumps, the function groupalso monitor that the lube oil has the correct temp, pressure and level.
2.12.2 Gas fuel sequence
The gas fuel sequence is used for leakage test of the two gas shut off valves. Italso controls that each one of the gas fuel control valves is working properly withdifferent set points which the valve has to reach in a certain time. The sequencealso sets the start position for the gas fuel valves. The gas fuel sequence includesnine steps. Table 2.5 shows the complete gas fuel sequence.
22
Unit Sequence Type off(step) descriptionStart Start of unit sequenceStep 1 Start preparation FGStep 2 Cooling water onStep 3 Lube oil FG onStep 4 Ventilation FG onStep 5 Reset trip systemStep 6 Prepare compressorStep 7 Jump to step 9 if trip system resetStep 8 Reset trip systemStep 9 Compressor piping pressurizedStep 10 Start turbine sequence, continue at turbine in serviceStep 11 SpareStep 12 SpareStep 13 Unit in service until ordered offStep 14 Start preparation FG offStep 15 SpareStep 16 Stop gas turbineStep 17 Stop compressorStep 18 Deactivate turbine and compressor sequenceStep 19 Unit standbyStep 20 Compressor unpreparedStep 21 Deactivate ventilationStep 22 Deactivate lube oilStep 23 Deactivate water coolingStep 24 Spare
End End of unit sequence
Table 2.4: The unit sequence which starts up turbine.
Gas fuel sequence Type off(step) descriptionStart Start of gas fuel sequenceStep 1 Primary fuel gas control valve checkStep 2 Main fuel gas control valve checkStep 3 Start position of fuel valves checkStep 4 Ventialtion position checkStep 5 Isolation valve leak testStep 6 Open shut off valve ignition burner 6Step 7 Start position checkStep 8 Main ignitionStep 9 Gas in operationStep 10 Close isolation valve
End End of gas fuel sequence
Table 2.5: Gas fuel sequence.
2.12 Automated start of turbine 23
2.12.3 Turbine sequence
This sequence initiates the purging of the turbine. The turbine needs to doa purging before start to ensure that there is no gas trapped inside it. Thesequence is also used for accelerating the turbine with help of the start motorafter ignition. After 5400rpm the start motor is disengaged and the turbine isnow accelerating by itself, by controlling the gas fuel valves. This sequence alsomonitor when the ignition starts and ignites the fuel gas by looking at pilot flameand main flame indicators. The turbine sequence includes nine steps. Table 2.6displays a complete list of all the steps included in the turbine sequence.
Turbine sequence Type off(step) descriptionStart Start purge FG, fuel prep FG, stop coolingStep 1 Start pilot ignitionStep 2 Start startmotor, main ignition, stop purgeStep 3 Acclerate with startmotor, start emergency lube oil,
stop pilot ignitionStep 4 Acclerate without start motor, stop start motorStep 5 Turbine in serviceStep 6 Stop gas turbine, flame out, stop fuel
stop emergency lube oil, start coolingStep 7 Reset turbine sequenceEnd End of turbine sequence
Table 2.6: Turbine sequence.
2.12.4 A start of the turbine using the sequences
In the start of the gas turbine the unit sequence is activated first, the sequenceexecutes each step when the transition criteria are fulfilled. When the sequenceenter step 10, ventilation and lube oil systems are activated and running, thecompressor is ready for start. The trip system is also reset and operative. Nowthe turbine sequence starts at step 1. This step also starts the gas fuel sequencewhich runs through the valve check and leakage test. At the same time thecompressor turbine has purged the turbine for 75 seconds at 2300rpm and alsoincreased the speed to 2600rpm which is the speed of ignition. Pilot ignitionis initiated and the compressor turbine accelerates with help of the start motoruntil 5400rpm where the start motor is disengaged, in the mean time the mainignition also has been activated. The turbine exhaust temperature increasesrapidly to 400 degrees centigrade. The gas fuel sequence has now reached step 9and will maintain this step until a stop is initiated. Now the turbine acceleratesby itself only using the gas fuel valves, the turbine sequence now reaches step5 and the turbine is in service. When the heat flow value is over 17.77MJ/sthe power turbine starts rotating and accelerates controlled by the turbinesten controllers to a speed of 3250rpm. The unit is now in service and the unitsequence has reached step 13. It is now up to the operator to set the appropriatespeed of the power turbine or use the set point set from the compressor PLC.
24
2.13 Summary
A short summary, and quick facts list follows. It is not meant to be comprehen-sive; rather it should be used as a reminder on what the chapter is about.
Since the THEORY part is very important to get a firm grasp of the de-tails explained and discussed the reader should feel that he or she is somewhatfamiliar with the words and concepts in this summary before proceeding.
• PROFIBUS is the medium used to send information from and to DP-slavesin the plant.
• PROFIBUS connects through the DP interface of a S7 CPU module.
• S7 and PROFIBUS is a distributed system built on modern network tech-nologies.
• A S7 rack (UR2) typically consists of PS, CPU and CP modules.
• The CPU module holds two DP and one MPI interface (shared with oneof the DP interfaces).
• The CP module communicates via Ethernet (fiber optics or electrical sig-nals).
• The CP module handles communication with OS and ES stations.
• There are two fundamental types of building blocks in the CFC-editor,fail-safe and non fail-safe.
• DP slaves controls the process objects (such as motors and sensors) andsends the information through the DP interface (cables) to the S7 PLC.
• Each signal in the PCS7 system have a unique address’ depending on theDP-slave address.
• Each unique address has a signal name alias to make it easier looking upand working with signals rather then using the address’.
• The engineer can program the CPU from both the MPI and Ethernetinterface depending on the situation.
• The SIMBA Pro card holds two PROFIBUS interfaces which can be di-rectly connected to the S7 CPU’s DP interfaces.
• The SIMIT simulation system is a real time system and the GUI is verysimilar to Mathworks Simulink.
• SIMIT uses SIMBA Pro and the PCI-card through a software interface tocommunicate to a S7 PLC.
3 DECIDING THE SIMULATOR SETUP 25
3 DECIDING THE SIMULATOR SETUP
The following chapter describes how the simulator was developed. This includesinitial analysis of what system and solution to use and how to build the simulatoritself both soft- and hardware wise.
3.1 Different solutions
The first steps of the initial analysis was to devise what kind of solution to usefor the simulator. A number of conditions had to be met,
• The investment costs had to be reasonable.
• The simulator hardware had to be fast enough to be able to simulate agas turbine.
• PROFIBUS communication between the simulator and the turbine PLCboxes should be simulated if possible.
• It should be easy to modify and develop in future engineering projects.
This thesis revolves around the GT10C gas turbine, but since there is a needto extend it to other models, one of perquisites would be to make the simulatoreasy to modify and re-engineer when needed. Each delivered turbine comeswith “options”, that is, specific parts which the customer decides. This makeseach turbine unique thus the simulator should be able to be modified to handleall these different “options” as they are ordered by the customer. Therfore itshould be easy to understand and change the simulation system itself, althoughthe basic knowledge of automatic control and the SIMATIC system should beknown.
If the PROFIBUS communication between the PLC and the simulator shouldbe tested, the simulator cannot be in the same PLC as the control program. Asit is now a test can be done using the program in the PLC to try out differentparts of the control system. But since this is only local, the communication inthe cables will not be tested, thus, propagation time, delay and other factorswill be left out of the test making the results inconclusive compared to a realtest of the control program against a turbine.
If the PROFIBUS communication could be included, somehow, all the im-portant PROFIBUS factors mentioned above could be taken into account tocheck if the control program is feasible and also making the simulator moreaccurate.
Making sure that the hardware used for the simulator is fast enough tohandle all the signals is also an important factor. Although, it is very difficultto conclude if the simulator setup finally chosen will be able to handle the loaddone by the control program, therfore, one have to do an estimation if it ispossible.
Another important feature of the simulator is to be able to use the originalOS pictures which the engineers at site uses to control an actual turbine with.That is, it is not just enough to simulate the signals the control program excepts.It’s also important to be able to use these operating pictures to “control” thesimulator as one does with a turbine. Thus, if both the turbine and the simulator
26
is seen as two black boxes the engineers should be able to “switch” these andthe person operating the turbine should notice no difference at all.
Initially there were discussions between four different solutions (as the su-pervisor of this thesis suggested). These were devised before the actual thesiswork begun, thus it was not known if they were possible to implement or not;which is the first thing this thesis will discuss.
The fifth solution was developed at a later stage after tips by SIMATICconsultants at Siemens.
3.1.1 Solution I - PLC—PLC
The first solution involved two PLC’s connected to each other via the properinterfaces. The first S7 PLC is the turbine PLC where the control automationprogram is located. The second one holds the actual simulator of the turbine.Therfore, the simulator would be built in the same environment as the turbinecontrol program by using SIMATIC tools.
A few questions involving this idea could be asked,
• Can there be two masters on the same buss (cable)?
• Cost of having the simulator in another PLC
• Can the S7 PLC handle a simulation program in respect to memory avail-able and the speed of the internal CPU of the PLC itself?
The cost of another PLC is a major disadvantage. Since the PLC’s are de-signed to work in rugged industrial conditions they are more expensive. A PLCcosts somewhere around 100KSEK and would thus result in large expenses.One could argue, however, that the PLC being used to develop the simulatorsoftware latter could be used in a turbine project where it is actually needed,that is; reused. Thus, just pushing back the investment cost to an earlier datethan needed for an actual turbine project (which would lie forward in time).
If the simulator is to be sold to a third party (as a product) the expense ofthe entire setup cost would be to large if a dedicated PLC is to be used for thesimulation.
After some more research into this solution the authors of this thesis came tothe conclusion that it is not feasible. This is mainly due to one single reason; onehave to change the control program itself. Adding and removing features fromthe control program would be dangerous and could cause unnecessary confusion.Obviously, simulating the turbine without changing the control program is theonly solution accepted (that is, if there is no other possible ones, but since thereare this condition can be set).
To bypass this, a possible fix could be to somehow connect the S7 PLC’sto a PC and program a software which would act as a “switch” and changethe packets being sent and reroute them to the simulator and the other wayaround. This is certainly possible but would take extensive time to implement,surpassing well over 20 weeks, which is the time frame that the simulator shouldbe developed within.
Thus this solution was discarded at an early stage. See Figure 3.11 for anschematic of this solution.
3.1 Different solutions 27
S7 DP
CP
PS
U
� � � �Cable
Turbine Control System
S7 DP
CP
PS
U
Simulator
Figure 3.11: Solution I, PLC to PLC communication (simplified schematic).
3.1.2 Solution II - Simulator and control system in same PLC
• Would both the control program and turbine program fit?
• Is the PLC fast enough to handle both programs at once?
• Would the solution mirror an actual turbine in real life since no commu-nication on physical mediums is used.
Certainly, from an economic perspective this solution would be the best; touse the same PLC for both the turbine control system and the simulator itselfwould result in no direct investment costs for extra PLC’s.
In reality, though, this is not the case. The control program and the simu-lator program would require extra memory. And because the PLC used for thecontrol program itself has a limit on how large memory cards it can handle onehave to invest in a PLC that can handle larger memory. This way this solutionwould actually result in the need to invest in more expensive PLC’s.
Also, the PLC can not be reused in a latter turbine project because it canhandle more memory than needed (the customer would not accept investing ina better PLC than needed, creating a more expensive turbine).
Finally, this solution excludes any PROFIBUS communication. This makesthe simulation less real life like and non accurate.
3.1.3 Solution III - PLC—PC/C/C++ (Java)
The questions that should be discussed concerning this solution is,
• What kind of PC would be needed, how fast?
• Is there a possibility (in reasonable time) to make a gateway betweenSimulink and the simulator?
• How should the PROFIBUS network, connected to the simulator PLC, beinterfaced to the PC?
The third alternative, using a PLC to communicate with the simulator ona normal PC would require minimal investment. An ordinary PC have to bebought, nothing over the top; today’s PC’s are high performance work toolscertainly surpassing even the processor power of a SIMATIC PLC. Thus creatinga simulator program that could respond in adequate time to the PLC softwarewould be a non-trivial problem.
28
Obviously, the problems with this solution does not depend on the PC speed,rather it depends on if it is feasible to build a simulator program in a program-ming language such as C++ from scratch.
Certainly, from the authors perspective, designing a basic program whichincludes the elements needed, would be possible. PID regulators, different kindsof flows, action and reaction elements and so on are so basic that they wouldbe easily implemented in a object oriented language such as C++ or even Java.Although, this would take time, designing a software is, with all the unknownfactors involved in this project is hazardous. When a certain point is reacheda not so easy obstacle could show itself (that is an obstacle that could take tolong time to breach), since the exact function of the simulation program is hardto conceive in just a few months, this has to be a evolutionary process, and thetime at hand would not be sufficient.
The work needed of examining the basic requirements, programming thesimulator, and then needing to implement the elements and connecting these inthe simulator could prove to take to long. When at the same time the authorshad to learn the inner workings of a turbine and other issues revolving aroundthis.
Although, since some other solutions which the authors were working onsimultaneously were not going too well, the decision was to see if a simple sim-ulation framework could be programmed. The choice fell on the programminglanguage Java due to its short development cycle for prototyping simple pro-grams and its object oriented style (which is ideal for a simulation programwhere objects in, for example, a industrial process in involved).
A pre-study began, programming a basic interface for a simulation engine.At the same time a interface had to be done which communicated via a PCI-card to the PLC itself. For this reason, a CP5614A2 card was bought fromSiemens. This card can simulate a PROFIBUS slave unit and thus be used bythe program to implement a process object.
After a few weeks of examining the API included with the card, the con-clusion was that the task of actually implementing the slave simulation wouldbe impossible because the PCI-card only handled one PROFIBUS slave at atime, and the simulation program would need at least hundred and more towork. Another PCI-card could probably have been bought which could handlemore slaves simultaneously but since that would have taken even more time,and because another solution which seemed to work was being done at the sametime (Solution V – SIMIT), the idea was discarded.
3.1.4 Solution IV - PLC—PC/Simulink
The difference between the C++ solution and the Simulink would be to useSimulink as a simulation framework instead of C++/Java. The problem withbuilding a interface to the PLC would still be here, i.e. one have to use a PCI-card as in the C++/Java-solution. Moreover, one have to learn the SimuLinkC++ interface and adapt it to the PCI-cards API-interface.
This solution was actually dropped at an early stage since it would be tocumbersome to learn both the Simulink API and a PCI CP-card API.
3.1 Different solutions 29
S7 DP
CP
PS
U
� � � �
PC
+S
imu
Lin
k o
r C
/ C +
+
Cable
Turbine Control System
Figure 3.12: Solution III & IV, PLC to PC (C/C++/SimuLink) communication(simplified schematic).
3.1.5 Solution V - PLC–SIMIT (chosen)
The last, and final solution, which was latter used, is SIMIT. By tips froma SIMATIC consultant about the SIMBA Pro card (described in the theorysection) this solution was investigated. The SIMIT solution is a suite with thepurpose of testing the entire factory floor process (or a turbine as in this case,more can be read in the THEORY section).
Since the interface between the PC program (that is; SIMIT), and theSIMATIC PLC’s (Simba Pro PCI Card) is already done the time could befully focused on understanding the turbine and implementing a working simu-lator. This solution, however, is far from free. The Simba Pro card itself costs30KSEK and one license of SIMIT is 50KSEK. And that is just the “basic”suite. If more objects such as flows and pipes are needed in the model the pricegoes up.7
On the other hand, since the problem was lack of time, this solution comescheap in the long run. Using SIMIT, the objectives set up could be met in time,or at least, it is more likely they could be met in time than using any othersolution.
The downside to this solution is the price of just one license. This hinderssimultaneous development by more than one engineer, since investing in multiplelicenses would become to expensive.
A schematic of the PLC–SIMIT solution can be seen in Figure 3.13. Thetwo PLC’s seen are where the turbines control program reside. The SIMIT PCis the one simulating the turbine itself.
3.1.6 Conclussions
The final choice is far from obvious. As mentioned in the THEORY chapter,SIMIT lacks in some areas. The preferred solution would have been using eithera more powerful simulation program such as Simulink or writing a fully new
7It should be noted, to the confused reader, that, even though this thesis was done atSiemens, and Siemens themselves are the creators of SIMATIC, internal economic politics(which says that each department should uphold its own costs) states that the software haveto be payed in full to other departments and companies in the Siemens sphere. I.e. eventhough this thesis was done at a Siemens company they still have to pay for Siemens software.
30
program in C/C++/Java. But considering cost versus time the decision wasnevertheless easy to make.
As time progressed it would show that SIMIT was not able to handle thedemands needed. It lacked fail-safe slave support. This is why solution III(PLC–C/C++) was more carefully examined than most of the other solutionsas a desperate attempt to solve the fail-safe issues.
This shows the problem when using commercial programs: it is hard toinfluence the developers to add the support needed for a particular project,even though they are based within the same company.
The fail-safe problem was solved, if not fully, in an acceptable way, whichmade it possible to continue with the project.
As seen in Figure 3.13 the final solution contain two PLC’s, one for themain program which takes care of most of the systems, while the turbine governprogram PLC contains the regulator of the turbine (i.e. the PID-controllers).This makes the above decisions of the chosen simulator setup not totaly accuratesince it is done for a setup with just one PLC for the entire turbine controlprogram; this is no different from using two or even three PLC’s; the reasoningis still the same.
Solution I II III IV V
Extra PC Yes Yes YesAdditionalcommercialsoftware Yes YesExtra PLC Yes Maybe1
Extra PLCmemory YesInterface card Possibly Yes Yes YesTestsRedundancy? Partly No Yes2 Yes2 YesChg. in PLCprogram? Maybe YesCan it be donein 20 weeks Uncertain Probably Uncertain Uncertain ProbablyTotal cost(KSEK) ∼ 100 ∼ 120 ∼ 15 ∼ 50 ∼ 80
Table 3.7: Quick recap of investment costs for each solution. Notes: 1A morepowerful PLC might be needed. 2If implemented.
3.1 Different solutions 31
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Figure 3.13: Final hardware setup with the turbine PLC’s containing the controlprogram and the PC containing the turbine simulation program.
32
4 IMPLEMENTING THE SIMULATOR ANDTHE MODEL
In order to create a reasonable model to test the gas turbine control system, alarge amount of data was processed. The model that was finally developed inthis thesis is a bit rough; but with a 20 weeks limited development time, fastdecisions and easy solutions, where demanded.
The best way is to use thermodynamics and calculate pressures, tempera-tures et cetera through equations and complex mathematical expressions anddependencies; but that approach would require an entire department workingfor a few months, thus this option was dropped rather quickly. Thus, anotherplan had to be devised to achieve the goal of a reasonably good model.
4.1 Setting up the simulator
Setting up the simulator system with SIMIT, PC’s and PLC’s was seen like aneasy task from the beginning. Though this proved to be more of a challengethan expected.
Although Simba PRO does support fail-safe DP-slave support in the latestversions, SIMIT does not. This causes the final simulator to be somewhat crip-pled, but it works with a few tricks and simple solutions. Full fail-safe supportis not expected until Mars or April of 2005. Until then the simulator cannotbe seen as fully reliable but the overall functionality can be tested without toomuch problems.
4.2 Closed and open loop control
Open loop control is when the signal from the PLC’s drives the output of ananalogue signal or a digital signal. The signal can be used for, in the analoguecase positioning of a valve, or in the other case as an open order to an on/offvalve. When the system does not require any input for these actions it is calledopen loop control.
Closed loop control requires an input signal as an answer from the process.This is necessary in delicate situations when it is necessary to closely monitorcertain positions for valves et cetera. The analogue value is sent to the processjust like in the open loop case, but now an input signal is monitored in the PLCand compared to the output value. In other words the ordered valve position ischecked against the actual valve position. When these are the same everythingis fine. When they differ the regulators of PI or PID type is regulating theoutput signal so that the correct response is achieved from the process.
If it is a digital signal the input signal to the PLC is achieved through apositioning switch. These switches are located at fully open and fully closedposition of the valves. In some cases the digital response from the process alsoincludes breakers and other electrical equipment.
The model consists of both open loop and closed loop signals. Open loopsignals are straight forward to implement in SIMIT. Closed loop signals onthe other hand takes development time because they are more sensitive to theprocess feedback. Thus, the closed loop signals needs more simulation andanalysis when simulating against the control program to ensure that the signalsbehave correctly.
4.3 Building HMI 33
4.3 Building HMI
The human machine interface consists of,
• Diagram screens.
• Operator screens.
First off, one need to consider that the simulator should be easy to maintainand improve. Thus the HMI needs to be easy to overlook and understand.
For this purpose a common graphical user interface for all the systems wasdesigned to make maintainable and improvement tasks easier, as well as usingit.
Each picture contain a version number, the system name and the authorsof the system. This makes co-operation between more than one engineer easiersince version handling is a major subtask that could take much of the develop-ment time if not done correctly. And since SIMIT does not contain any easyconcurrent engineering system this is a must. In Figure 4.14 the user interfaceof an operator screen can be seen. For a diagram screen see Figure 4.19.
Figure 4.14: The HMI of a turbine system (operator screen).
Another aspect of a well designed user interface is that each signal groupshould be well defined and easy to overlook in a quick way for an engineer. Thisactually proved to be a problem; how the signals should be grouped. This wasdecided on an individual basis for each system. For example, should alarm signaltoggling be implemented in the same system as it is grouped or in a operatorscreen where all alarm signals are located. Here, the decision fell on the firstproposal, since each gas turbine system is well defined by Siemens engineersand going outside the system grouping would prove non intuitive. This is if an
34
engineer which is familiar with the gas turbine system classification scheme atSiemens would work with the simulator.
Each signal group is defined the same way both in the operator as well asthe diagram screens to get a more intuitive connection between the two. Thegoal was to make the entire diagram scheme visible on the screen at the sametime; although this proved to be an impossible task. Thus, the diagram wasdivided into pages (a feature which SIMIT support).
In Figure 4.15 a list of how diagram and operator screens are grouped, inSIMIT, can be seen.
Figure 4.15: Grouping of diagram and operating screens in SIMIT. The differentalphanumeric codes are an internal Siemens scheme for naming different systemsin the turbine.
4.4 The development cycle
A major problem was that the turbine control program was developed simul-taneously as the simulator program. This created confusion and often resultedin major changes in the simulator program on a daily basis. At the end of thedevelopment cycle the program had to be verified against the turbine controlprogram and had to be evaluated against several important criteria. If not ful-filled the development cycle had to be restarted, and as stated, often with a newturbine control program with major differences from the old.
A few criteria has to be met for the simulator. These are,
• Real time response.
• Behavior.
• Interface communication.
4.5 A simulation diagram example (calculating heat flow) 35
Real time response connects to the closed-loop problem as explained before.If the real time response is not correct in SIMIT the turbine will behave in a nonstandard way, often causing the turbine control program to fail. This, of course,connects to the behavior of the turbine. Although, the behavior, includes all ofthe modeled signals which affect the simulation of the turbine.
Finally, interface communication have to be checked and verified since eachsignal has to reach the destination it is meant to.
A conclusion could thus be that all these properties are closely connected toeach other and, obviously, have to be fulfilled for the simulator to work correctly.
The development cycle can be seen in Figure 4.16.
4.5 A simulation diagram example (calculating heat flow)
It would be impossible, in this thesis, to describe how all the diagram andoperator screens was developed. Thus, an example as seen in Figure 4.19 willbe discussed more precise here to let the reader get a grasp of the developmentprocess.
4.5.1 Using performance data
By using saved data from performance tests, from the Siemens test rig facility forcore engines, a relation between heat flow values and turbine speed was found.In turn the turbine speed also relates to temperature, pressure and flow. All ofthese signals are included in the performance tests, why it is possible to createa reasonable model of the gas turbine. These values are presented graphicallyas trends of signals in the program SCADA Pro, this program is a trend andmonitoring program which is not a part of the SIMATIC suite. By adding allof the signals to SCADA Pro (see Figure 4.17), reviewing them and talking tothe staff engineers at Siemens and by reading internal documents of the enginebehavior one were able to get an understanding of how the turbine works.
Every line on the picture in Figure 4.17 is a signal, the test run of the turbineis 2.5h, and by setting the resolution in seconds in SCADA Pro to appropriatelevel these signals could be exported as a text file. The data for each line consistsof a register of time and value. The time is stretched over 2.5 hours (which isthe turbine running from start to stop) and the program samples every 2s whichleads to an enormous amount of data which had to be fitted in a polygon block,in SIMIT, which only had 20 entries. A polygon block is a register where acertain input value relates to a certain output value. One could say that this isa transfer function.
Instead of time as one of the parameters another relation had to be used.The decision was made to use the speed as this corresponds to the heat flowvalue as mentioned above. A Matlab program that only uses the most significantpoints on the line was used. This can be seen in Figure 4.18.
Because of the way the polygon block works it was sufficient with 20 en-tries. Between two points a line is interpolated so the curve with the 20 entriescorresponds with a reasonably small error compared to the real curve.
This entire operation was preformed on more than 140 signals. When alldata was processed and all polygons created the next thing to do was to buildthe actual model in SIMIT.
36
Start
Develop model
from
specifications
(Updated)
control program
Implement model
in SIMIT
Test model
against turbine PLC
Sim . diagram
screens
Sim . operator
screens
Interface
communication
Behaviour
Real time
response
Fills the
demands?
Updated
control
program?
End
Yes
Yes
No
Data from test
rig facility
Analyze data in
SCADA Pro
Process data in
MATLAB
Analyze system
description
documents
No
Figure 4.16: Simple development process flowchart of the simulator model.
4.5 A simulation diagram example (calculating heat flow) 37
Figure 4.17: Data from performance tests used when developing the model.
Figure 4.18: The relation between the curve taken from SCADA Pro (blue) andthe polygon curve done with Matlab (red).
38
4.5.2 Heat flow versus speed, temperature and pressure
Because of that it is not possible to obtain the heat flow value directly from theSIMATIC system another method was used. The heat flow value relates to howmuch the gas fuel valves are open which are controlled by the SIMATIC system.This gave the heat flow value indirectly through the ordered valve position.
Now when the heat flow value is calculated it is possible to set up the rela-tions between heat flow to speed and all other entities like temperature, pressureand flow.
4.5.3 The pilot flame
The pilot burner is fed with ignite gas through burner six which can be selfattained from the fuel system. This burner is used for starting the turbine aswell as later when running the turbine. In the beginning only burner 6 is usedto obtain a pilot flame through the ignition gas and a start plug, which ignitesthe gas. The pilot flame is later used to ignite the other fuel burners. Thereis a closed loop control on the pilot flame. There is no response from a flameindication transmitter, the ignition gas is stopped and the startup sequenceis stopped. When the pilot flame has ignited the other burners a main flameindication transmitter is triggered and the fuel system is now up and running.
Burner 6 is in the combustion chamber of the turbine. The other 17 burnersare at this stage not used. When the the pilot flame is indicated as on by thecontrol system it opens the fuel flow to the other burners.
4.5.4 Necessary adjustments
Until this moment the model is built under the influence that a heat flow isestablished. This of course cannot be if the pilot and the main flame have notbeen ignited. Therfore, it was also necessary to build program functions thateasily can switch from different operating mode with flame or without flame.
When the sequences are running, the program estimates process values inorder to continue with the next step, this happens both before and after ignition.Some signals as pressure and temperature level are switched in at some steps toensure that the sequence continues. In SIMATIC this is called transition steps,where certain signals have to be fulfilled before the sequence continues with thenext step. By running the sequences and looking at the transitions (as seen inTable 2.4 one becomes aware of all the necessary requirements which had to beincluded in the model). Other necessary requirements which had to be takeninto account is that a temperature has a delay when cooling off, in resemblance,as the plate on the stove is turned off. This resulted in several first order timedelay blocks (PT1, Figure 4.19), the function of these block is that the rampup/down the value to the given set point in certain time, like a step response.At some locations it was also necessary to have different ramp speed at differentheat flow values to achieve a working model.
4.5.5 A run with the model
When all sequences are run through, like mentioned in Section 4.5.3, the unit isin service. Now it is up to the operator to set the speed of the power turbine, ifa max load was set by the operator. By using the model one can simulate that
4.5 A simulation diagram example (calculating heat flow) 39
Figure 4.19: The SIMIT model to calculate the heat flow value.
40
the heat flow value increases as well as the speed of the power turbine. And asthe speed increase the pressures, flows and temperatures also increase.
By using this simulator it is very easy to see how the regulators behave atstart up and switching in between. When reaching the maximum load anotherphenomenon has to be taken in account. When the regulators works closelytogether the exhaust temperature gets very high at max load. Then the T7Llimiter (Section 2.11.4) in operation, makes sure that the temperature is notincreasing to dangerous levels while NGGL (Section 2.11.2) tries to reach theset point set by the operator.
Here, the model was too fast in the beginning and the system was unstable.By adding a first order time delay the model was stabilized.
5 RESULT 41
5 RESULT
5.1 Conclusions and discussion
First of all, all action points and questions at hand was not fulfilled. The authorshad to leave out the implementation of other turbine models; one proved to bemore than enough to be able to handle within the decided time frame. Thiscould be something for future engineers to work on (see the next section).
To summarize things the positive advantage of the solution developed is,
• The PLC’s are not overloaded since SIMIT is a program running on astand-alone PC.
• The communication and load by the PROFIBUS cables are simulated ina proper way.
• An easy overlook of the simulator can be seen since it is divided intosystems and signal groups. These system and signal groups also followsthe Siemens system of grouping thus making it easier for other engineersto easily understand the simulator screens.
• The final simulator can be used as a factory acceptance test tool.
• It is more advanced than the current model used.
There are, however, a few negative points,
• The employees have to learn a new tool for simulation.
• SIMIT can not simulate signals of higher resolution than 10ms which couldlead to problems when powering up and down the turbine.
Finally, a test against the control program using the model in SIMIT wasperformed. Obviously, at first several problems was encountered, thus the modelhad to be adjusted. After some more development a successful start of theturbine was performed using the simulator.
The involved personnel, on the department where this thesis was developed,was satisfied with the developed model since it simulates a turbine more accuratethan the current.
Finally, a presentation of the model was done for the Siemens personnel fromthe research and development departments to verify that the model worked ina satisfactory way and to show the SIMIT software which has never been usedat this Siemens facility. This resulted in a discussion on how the model couldbe used with for example customer training.
The HMI was also seen as simple which would not require to much “knowhow” about control systems which would make it simpler for sales personnel todemonstrate it to potential customers.
As of February 2005 Siemens has decided to improve the simulator by de-veloping it on other turbine models. This has resulted in the employment ofanother thesis worker which are to examine if this is possible.
Siemens has understood the importance of having such an environment asthis to simulate different test cases and system behavior. Also the customershave started to demand, more and more, that the systems being sold should
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be stable and bug free. With this simulator setup the chances of this are muchhigher. This, in turn, will lead to lower costs when installing the turbines onsite.
5.2 Future development
The model which has been created works satisfactory as a turbine but someadjustments must be made to ensure that the model truly behaves like a realturbine.
Another improvement which should be done is that the model built is justfor the core engine with a simple add-on of load; a compressor. If Siemens wishto simulate the behavior of a real compressor there are additional things thathave to be taken under consideration such as suction pressure, temperature andpolytrophic efficiency of the compressor. This is not included in the scope ofthe model presented in this thesis.
The model also have some problems in the start before reaching 3250rpmof the power turbine. The entire system is not entirely stable, this is probablybecause the temperatures and acceleration of the power turbine is too rapid, inother words the LLD (loss of load detection, Section 2.11.10) limit is reachedwhich makes the regulators switch to GDC i.e. the turbine is decelerated, seeSection 2.11.8. Here it would be necessary to recall the data from a real sitewith a compressor mounted to further develop the model to act more accurate.
Another problem could be that the actual regulators are set with a too highgain which in turn gives an unstable behavior. Nevertheless this is not in thescope of this thesis since the goal was to get a “rough”, initial model, of aturbine.
To further improve and tweak the model could thus be investigated as anentire thesis itself.
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References
[1] Abb in australia, September 2004. URL http://www.au.abb.com/global/auabb/auabb500.nsf!OpenDatabase\char’38db% =/global/auabb/auabb504.nsf\char’38v=DB6\char’38e=us\char’38c=5C2BD9E042EE7A41% C1256D86001BEF70.
[2] Fieldbus technology, October 2004. URL http://murray.newcastle.edu.au/users/students/1999/c9518176/fieldbuste% ch.html.
[3] Profibus - profibus & profinet., June 2004. URL http://www.profibus.com/profibus.html.
[4] Siemens AG. S7-400 and m7-400 programmable controllers- hardware and installation., September 2004. URL http://www.siemens.co.jp/simatic/japan/as/plc/data/400/424ish\_e.pdf.