Proceedings of the 14th International Middle East Power Systems Conference (MEPCON’10), Cairo University, Egypt, December 19-21, 2010, Paper ID 317. Comparative Study On Modelling Of Gas Turbines In Combined Cycle Power Plants H. E. M. A. Shalan El-Kureimat Power Station Ministry of Electricity Cairo, Egypt
[email protected] M. A. Moustafa Hassan Electrical Power Department Faculty of Engineering, Cairo University Giza, Egypt
[email protected] A. B. G. Bahgat Electrical Power Department Faculty of Engineering, Cairo University Giza, Egypt
[email protected] Abstract—Gas turbines are important for electric power generation specially the Combined Cycle Power Plants (CCPP). For this electric power generation, the dynamics of the gas turbines become increasingly more important. In order to study such dynamics, accurate models of gas turbines are needed. Recently, several gas turbine models have been proposed with different degree of complexity and success. The purpose of this work is concerned with understanding, modelling, and analysing the behaviour of the gas turbinebased plants to investigate the power system problems. This purpose is achieved by a complementary and comparative study of different dynamic models response that published in different literature for Combined Cycle Power Plants (CCPP). Among these models, there are three models were completely simulated using Matlab/Simulink. It is easy to conclude that the obtained results via these simulations in this study are highly matched with the results presented in the related scientific articles. The study illustrates the effectiveness and accuracy of frequency dependant model as well as the detailed model of gas turbines in CCPP. Index Terms: Combined Cycle Power Plant (CCPP), Gas Turbines Modeling, Modeling and simulation, Electric Power plants. HE gas turbine is a main part of the current power plant, which produces a great amount of energy for its size and weight. The gas turbine has established growing service in the past 40 years in the power industry both among utilities and merchant plants as well as the petrochemical industry, and utilities throughout the world. The last 20 years has seen a noticeable growth in Gas Turbine Technology. The growth is developed by the enhancement of materials technology, new coatings and new cooling schemes. This, with the conjunction of increase in compressor pressure ratio, has increased the gas turbine thermal efficiency from about 15 to over 45 percent, which is suitable for power plants. In the past, large coal and nuclear power plants dominated the electric power generation. However, natural gas-fired turbines now dominate the field of Power generation because of their black start capabilities, higher efficiencies, lower capital costs, shorter installation T I. 0B INTRODUCTION times, better emission characteristics, and abundance of natural gas supplies. The construction cost of gas turbine power plants is roughly half that of comparable conventional fossil fuel steam power plants, which were the primary power plants until the early 1980s. More than half of all power plants to be installed in the foreseeable future are forecast to be gas turbine or combined gas-steam turbine types. Current low prices for crude oil make fuels such as diesel, kerosene, and clean gaseous fuels such as natural gas the most desirable for gas turbines. However, these fuels will become much more expensive and will eventually run out. So, provisions must therefore be made to burn alternative fuels. Now, gas turbines are used in a wide range of applications. The two major application areas of gas turbine engines are: Aircraft propulsion. Electric power generation. For electric power generation, common uses include stationary power generation plants (electric utilities) and mobile power generation engines (ships and aircraft). The term ‘‘Combined Cycle Power Plant (CCPP)” describes the combination of gas turbine generator(s) (Brayton cycle) with turbine exhaust waste heat boiler(s) and steam turbine generator(s) (Rankine cycle) for the production of electric power. During the last decades there has been continuous development of combined cycle power plants due to their increased efficiency and their low emissions, as well as reduced natural gas prices. However, in a large-scale blackout occurred in Malaysia in August 1996, CCPP and gas turbine plants sequentially tripped out. The cause of this chain trip was thought to be a system frequency drop. Also, there were the blackout events in Italy, Denmark/southern Sweden and the USA/Canada, which resulted in major economic losses. Also strong crises in electric demand appeared in Egypt in summer of 2010, which made more focus on CCPP. Therefore, A mathematical model of a CCPP is needed, including relevant control and protective functions. In this study, a simple model for CCPP will be developed in the Simulink environment of MatLAB. This to help in obtaining accurate models, which are highly needed. In the last decades, several gas turbine models have been proposed with different degree of complexity and success. It should be known that the complete gas turbine model consists of the 970 The extended Rowen’s model [2] is enabled a more accurate modelling of a gas turbine operation installed as part of a CCGT. generator drive only. and hence assumed to be a part of a CCPP. Rowen extended the original model as in [2]. These characteristics are published in different literature. The model has been utilized to investigate the impacts of governor on system operation. These are listed below: 1.04 sec 0. and acceleration control. 2]. a) Rowen’s Model Assumptions: As illustrated in [1]. Several gas turbine modelling are based on different models. 3. Rowen’s model consists of a set of algebraic equations describing the steady-state characteristics of the gas turbine thermodynamics. CIGRE Model. The considered models are: 1. II. it is considered the starting point and backbone for development of most CCGT Figure (2): Rowen’s Model with IGV [2] b) Rowen’s Model Equations: There are four main function blocks in Rowen’s models as follows: 971 . Rowen’s Model. Rowen’s Model. IEEE Model. Rowen provided a model of a gas turbine that can be used for dynamic performance studies of a power system [1].325 kpa Table (1): Parameters of Rowen’s Model [1] Parameter ECR ETD Figure (1): Gas Turbine System Overview Some of them were discussed in details in [8]. 13]. Some models implement all of them together such as [1. and the control loops. simple time delays. In 1992. Allowable speed range is between 95 and 107 percent of rated speed. 2. Detailed Model.2 sec 950 oF TCD TR The current study focuses on the important three models. i. especially the exhaust temperature.turbine thermodynamics. Description Combustion reaction time delay Turbine and exhaust delay Compressor discharge time constant Turbine rated exhaust temperature Value 0. 2.e. models in recent years such as [4.e. Therefore. where the gas turbine had been equipped with modulating IGVs. The fuel system and control loops will be discussed later in another research results. 6. In 1983. Figure (2) shows the extended model with IGV (Rowen-II). 14.01 sec 0. W. Rowen-I model is based on the following assumptions: It is a heavy duty gas turbine. governor. This article is focusing on the comparative study for various gas turbines characteristics (thermodynamics) only. TA = 15 oC PA 101. 3. 10. Detailed Model. no Heat Recovery Steam Generator (HRSG). the fuel system. 4. GGOV1 Model. simple cycle. 15]. as illustrated in Figure (1). = ISO conditions apply. to include IGVs and their effect on the gas turbine dynamics. whereas the other models implement a separate block for the turbine dynamics such as [3. this study is considered a complementary study for different gas turbines models as well. Frequency Dependent (FD) Model. singleshaft. I. Furthermore. i.. 5. Rowen’s Model It is clear that a significant assumption modification had been adopted in Rowen-II model. Frequency Dependent (FD) Model. 5. Open Inlet Guide Vanes (IGV) only. and a few related controls including the temperature control. as illustrated in Figure (4).2 0.6 0.92 0.3 0. The Parameters for Rowen’s turbine dynamics are presented in Table (1).7 0.9 0. To be able to analyse incidents with abnormal system frequency behaviour. the exhaust flow (WX) is inversely proportional to the ambient temperature (TA).4 0.5 WF (pu) 0. and full fuel flow rate (i. oF.9 1 PMG (pu) Many of gas turbine models are not suitable for determining the frequency dependency of the gas turbine. the relationship of the exhaust temperature to output power is shown in Figure (5). WF N Turbine rotor speed.95 1 P 0.94 55 60 65 70 TA ( o 75 F ) 80 85 600 o X 400 Figure (8): Turbine Exhaust Flow (WX) versus Ambient Temperature (TA) 0 0. pu. It should be noted that. Frequency Dependent (FD) Model Figure (4): Exhaust Temperature (TX) versus Fuel Flow (WF) 1000 800 F) T ( 600 400 200 0 0.75 0.4 0. Increasing of fuel flow lead to increase in the exhaust temperature. It is developed in order to clarify the effects that shaft speed and ambient temperature have on output power [6].96 0. d) Block F1\ to calculate the exhaust temperature like F1 but.7 X 0.8 ( p u ) 0. This is the main aim of FD model which is based on the physical principles.02 0 0.3 0. Where TR Turbine rated exhaust temperature. the output power depends mainly on the fuel flow. where it is increased (linearly as assumed) with increasing of the fuel flow. pu.9 0.1 0.6 M G Also.75 0.7 0.e. The governing equations for each block are described in [1.96 800 T ( F ) 0. c) Block F3 to calculate the flow of the exhaust gasses (WX).7 0.4 0.2 0. 14.85 Ligv (pu) 0.6 0. This model was simulated using MatLAB/Simulink environment [16].5 WF (pu) 0. Mass fuel flow.8 0. this relationship is depicted at fully open IGV position. o X Figure (5): Turbine Exhaust Temperature (TX) versus Power Output (PMG) 972 .85 Ligv (pu) 0.2 0 Figure (7): Exhaust Temperature versus Inlet Guide Vanes (IGV) Position 1. 18].95 1 Figure (6): Turbine Exhaust Flow versus Inlet Guide Vanes (IGVs) Position 600 T ( F a h r e n h e it ) 550 X 500 450 0. and the temperature of the exhaust gas will decrease accordingly.98 X 0. modified to include the impacts of changing air flow via IGV as well as ambient temperature.1 0.8 0. c) Results of Rowen’s Model and Discussion: The relationships between the various inputs-outputs variables of the gas turbine are presented in this subsection.9 1 200 III. and (7). This relationship between WX and TA is represented as in Figure (8).8 0. As shown in Figure (3).1 0. the IGV position data is obtained from [7]. Ligv = 1 pu & WF = 1).9 1 W (p u) Figure (3): Output Power (PMG) versus Fuel Flow (WF) 1000 1 0.5 0.6 0.98 W( p u ) 0. 10. b) Block F2 to calculate the output torque of the gas turbine (TRQD).8 0.3 0. 17. 1 0.4 0.2 0. It should be known that.94 0. 1 0. Furthermore. The effect of the IGV position on the exhaust gasses is shown in Figures (6). Increase of the IGV position will increase the exhaust gas flow.7 0.a) Block F1 to calculate the exhaust temperature (TX).8 0.9 0. where it is highly matched with the obtained results in [7]. the frequency dependence of the gas turbine model must be taken into account. the performance of the gas turbine is heavily affected by ambient conditions. For more details [19] could be referred. ambient pressure (PA). v) Maximum continuous power output block. The exhaust gas flow (WX) is practically equal to the air flow (WA) since the fuel flow (WF) is much smaller than the air flow. 11]. ii) Compressor Pressure Ratio (CPR) block.. The parameters of the gas turbine equations using FD model are illustrated in [6. Changes in frequency are equivalent to changes in shaft speed and would result in a change in airflow. In other words. the air becomes denser. 973 . The model is not intended for use for simulation of start-up. The FD model is illustrated using SIMULINK environment [16] in Figure (9). The contribution of this model (which based on physical principles) is to clarify that. an actual relationship between TA and PMX is depicted as shown in Figure (12) for practical 265 MW HDGT. and the ambient temperature. The related input variables are fuel flow (WF) and air flow (WA). The obtained results are very close to those given in [6]. The fuel flow and air flow are adjusted to provide a desired power output while maintaining the desired level of exhaust temperature for efficient heat transfer to the HRSG. The related output variables are mechanical power output (PMG) and the exhaust heat to the Heat Recovery Steam Generator (HRSG) as determined by the exhaust gas flow (WX) and exhaust temperature (TX). an important relation is reported between the ambient temperature (TA) and the maximum power output (PMX).a) Structure of FD Model: d) FD Model Equations: As shown in Figure (1). These changes will directly affect the maximum power output. The structure of the FD gas turbine model is given in [6. However. 11]. Ao. Any parameter affecting the mass flow of the air (WA) entering the gas turbine will have an impact on the performance of the gas turbine. The details for each block are given in [6]. as shown in Figure (10). iv) Output power block. shutdown or detailed dynamics associated with the performance of the gas turbine combustion systems. which are similar to Rowen’s model assumptions. Air flow may be regulated by Inlet Guide Vanes (IGV) and is also a function of ambient air temperature (TA). the model could be divided into five separate blocks: i) Air flow block. The model was completely simulated using Matlab/Simulink environment [16]. a combustion system and a turbine. For more clarification and comparison. the gas turbine is operating more efficiently due to a reduction in ambient temperature. 19]. the gas turbine consists of an axial compressor. iii) Exhaust temperature block. It is clear from the obtained results that. The shaft power required to drive the compressor is constant. the maximum power output of a gas turbine (PMX) depends on shaft speed (and hence the system frequency). As shown in Figure (11). When the ambient temperature decreases.) are obtained directly from the test data of actual machines [17]. WF solely determines PMG and the only significant dynamics effects between their changes are time lags. e) Results and Discussion of FD Model: Figure (9): FD Model Structure Using SIMULINK b) FD Model Assumptions: As illustrated in [6. It is clear that. These results highly match the illustrated results in [6]. this model is based on the following assumptions: It is expected that the model is valid for variations in shaft speed between 95 to 105 percent and for unit loading above half load. the various parameters of the model (e. etc.g. resulting in an increase in the Compressor Discharge Pressure (CDP). This subsection shows the thermodynamic equations representing the dynamic behaviour of the gas turbine that modelled before. This change then translates firstly into a change in the pressure ratio across the compressor and secondly into a change in fuel level (in order to maintain the given firing temperature). This point is different with respect to Rowen model. and A2. A1. and shaft speed (N). 96 0.01 1 N (pu) (b) 14 TA = 15 o C ( p u ) 0. 0.99 0.e. 15] for the Detailed model. is based mainly on the modelling proposed in [3. the Detailed Model is valid for a single-shaft combined cycle plant.98 A 0. 974 .04 1.92 1. Therefore. Other similar models are presented in different literature.01 1.05 Using a simplified steam turbine model.99 0.7 12 1.95 1. The gas turbine equations. 13] by including a supervisory control of the combustion temperature.05 (c) 1. It should be noted that.96 0.98 0.. b) Detailed Model Assumptions: (b) Figure (12): Actual Relationship between TA and PMX of 265 MW HDGT [18] (a) A Summer Day (b) A Winter Day c) Equations of Detailed Model: Algebraic equations that describe the CCPP model can be classified according to [12. The main aim for this model is to study the dynamic behaviour of the CCPP in the presence of a frequency drop.95 0. Detailed Model This model.03 1.02 1 P ( p u ) 0.5 0.98 0.97 0. 13.01 1 N (pu) 0.03 1. as well as to the heat exchange in the recovery boiler [3.98 0. assuming that the power generation depends exclusively on the heat recovery from the gas turbine.95 0. Some assumptions for the Detailed model are adopted.99 0. 18]. Vournas [15] extends the results of Kakimoto and Baba [12.03 1. 13] (IEEE model).02 1.96 0. WF << WA and therefore WF + WA ≈ WA). The turbine. however. which.99 1 N (pu) 1.04 1.96 0. The Detailed Model is represented using SIMULINK environment [16] in Figure (13).02 1.95 Figure (10): Effects of Speed Changes on different turbine parameters (a) Air Flow (b) Compressor Pressure Ratio (c) Maximum Continuous Power IV. The steam turbine equation. This model extends the gas turbine modelling by adding a simplified steam turbine model.97 0.9 C P R ( b a r ) P M X 13. 17. a) Structure of the Detailed Model: (a) Detailed model which giving the available thermal power to the gas turbine and the steam turbine is modelled by algebraic equations.. such as: ii. The Combustor. 12.e. The details of the turbines equations are discussed and illustrated in [12.01 1 N (pu) 0. the mixture of air and gas is approximately equal to airflow (i. are slightly different.03 1.5 TA = 35 o C 0.02 1.97 0. P2 ≈ P3).02 1 W( p u ) 0. Using FD Model 0.05 1.94 0.04 1.97 0.05 1. Neglecting the pressure loss in the combustor (i. as was introduced in [15].04 1.94 0. 15.1 1 1.6 0.96 0. 15] into two main areas as below: i.(a) 1. These equations are relating the adiabatic compression and expansion.8 13 12.96 0. The compressor.98 M X Figure (11): Effects of Ambient Temperature on Maximum Continuous Power Output.02 1.92 1. 13.98 0. In the gas turbine. 1 0. P GT f e (pu ) 975 . pp. Rowen. Song. P.8 0.8 0. However. and the obtained result is highly matched with the results presented in [11]. Kunitomi. J. F. 6. and S. P. Columbus.. Pourbeik. and S. “Model development and simulation of transient behavior of heavy duty gas turbines. the gas turbine produces approximately two-thirds of the total power output of a typical combined-cycle power plant. 9. It is well known that. since these three models consider the IGV. T. L. W. W. July/August 1992.8 [5] PCC PGT 0. there are three models were completely simulated using MatLAB/Simulink. Turbomachinery International. Hajagos and G.Massucco. the exhaust temperature.2 0 0. Denegri. 123. VII. “Simplified Mathematical Representations of Single Shaft Gas Turbines in Mechanical Drive Service”. discussed. V. 28–Feb. Jan. T.5 0. B. A. 2.6 0. Vol. Winter Meeting. Berube. [1] References [2] . Rowen. 1. “Management and Dynamic Performances of Combined Cycle Power Plants During Parallel and Islanding Operation”.” IEEE Trans. 1994. 2001. Bagnasco. t .. Ahner. Okamoto. “Utility Experience with Gas Turbine Testing and Modeling”. M. Soc. Power. Y. Jan. 1. pp. de Mello and D. The study illustrates the usefulness and accuracy of frequency dependant model as well as the detailed model of gas turbines in CCPP. June 1998. “Simplified mathematical representations of heavy-duty gas turbines”. However. “Dynamic models for combined cycle plants in power system studies. Vol. 2001. Ro.6 0. 1698–1708. and the output power.7 0. S. 1983. Among these models. whereas the other one-third produced by the steam turbine. Ihara. H. Tada. 26-32. T. different gas turbine models are presented.” ASME J. Vol. H. Kurita. the main important models consider IGV which gives nearer representation to practical. To that extent. J. 865–869. ASME J. A. S. 2001. Figure (14) shows the effect of the increase of fuel flow on various output variables such as the firing temperature (turbine inlet temperature). OH.4 0. B. “Modeling frequency dependency of gas turbine output. Main Comparative points for the GT Models The main comparative points for the different GTs models that discussed in this study are summarized and listed in [19] as well as in Table (2). IEEE Transactions on Energy Conversion.2 PST 0 0 10 20 30 40 50 60 70 80 90 100 Time (sec) [7] Figure (15): Relationship between the GT and ST Outputs W. It is easy to conclude that the obtained results via these simulations in this study are highly matched with the results presented in the related scientific articles. Columbus. pp.It should be noted that the temperatures in the IEEE model are worked out in Kelvin. No.” presented at the IEEE Power Eng.I. Eng. R. Eng. I. The compared models are of different level of accuracy. Kim. t [3] PGT te tf 0. OH. they are suitable for different types of studies and have been utilized for different purposes.6 0. and W. Price. VI. 105.1.4 [6] 0. 28 – Feb. This point is indicated in Figure (15). Vol. vol. 2. K. whereas expressed in Fahrenheit in Rowen. Delfino. Also Gas Turbine responds quickly with any change in the combined power.4 0. presented at the Power Engineering Society Winter Meeting. Conclusions Figure (13): Turbine Thermodynamics in Detailed Model d) Results and Discussion of Detailed Model: The Detailed model was simulated using MatLAB/Simulink environment [16]. Kim. Power Syst. and normalized in per unit values in the Detailed model.3 The main objective of this proposed study is to present an overview of existing gas turbine models and to compare between them..9 1 [4] WF (pu) Figure (14): Effect of Fuel Flow on GT Temperatures and Output Power 1 Mechanical Power (pu) 0. and compared. Aug. W. vol. 589–594. Gas Turbines and Power. pp. 13. Julia Ritchie.” in Proc.moee. "New Thermal Turbine Governor Modeling for the WECC" Modeling & Validation Work Group. Version 7. official internet site. Gillian Lalor. August 2003. and Mark J. Model V94. Vol. May 2003. 3.3A (SGT5-4000F). (Temp. D. IEEE Trans. Dynamic system Simulation for Matlab. Version 7. and WX & simple time delays Exist All in pu values except temperatures in oF IEEE 1994 [3] Single-shaft SCGT. June 2007. Abdelwahab. CPR. Siemens Gas Turbines Manuals. John Mantzaris. Smith. but can be a part of a CCGT Separated FD 2001 [6] Single-shaft SCGT. PM. 71-78.02.egH). M. “Frequency Control on an Island Power System with Increasing Proportions of Combined Cycle Gas Turbines. Power Generation Group. but simple linear transfer functions representation Not exist CIGRE 2003 [9] Detailed 2007 [15] Setup Configuration CCPP Single-shaft CCGT GT Representation & Control Loops Together Simple block of second order transfer function Not exist Separated GT Representation Detailed thermodyna mic treatment Detailed thermodynami c treatment IGV Modeling Exist All in pu values except temperatures in K Exist All in pu values. Kosterev. E. 18. of Thermodynamics. and Kazuhiro Baba. and cannot be a part of a CCGT Together Two main algebraic equations to Calculate TX and TRQD & simple time delays Not exist All in pu values except temperatures in oF Rowen-II 1992 [2] Single-shaft SCGT. L. Naoto Kakimoto. "WIN-TS". M. D. MATLAB. and S. O’Malley. Table (2): Main Comparative Points For The Considered GT Models [19] Model Point of Comparison Publishing Year Main Article Rowen-I 1983 [1] Single-shaft SCGT. “Performance of Gas Turbine-Based Plants During Frequency Drops”. pp. No. IEEE Powertech Conf. Ihara.[8] [9] [10] [11] [12] [13] [14] CIGRE Task Force C4. L. 2003. End of 2010. Damian Flynn. on Power Syst. K.” IEEE Trans. but can be a part of a CCGT Separated Five main algebraic equations to calculate WA. It can be used for representing gas turbines Together No thermodynami c treatment. "Dynamic Behavior of a Combined Cycle Power Plant in the Presence of a Frequency Drop". W. Int. and G. Cairo University. Ministry of Electricity and Energy of Egypt. Pereira.. TRQD. but can be a part of a CCGT Together Three main algebraic equations to Calculate TX. 2008. 20. Jun. M. The Language of Technical Computing. Italy. pp. 2002... 2). and PMX &only one simple time constant Exist All in pu values except temperatures in K. 10 (No.0. W. Vol. August 2005.1 (R2008a). Siemens AG. 2003. and CDP in bar Exist Exist Not exist Exist GGOV1 2002 [8] Valid for all thermal PP except nuclear plant. H. 3.25. on Power Syst. " Modeling and Control of Gas Turbine in Combined Cycle Power Plant". Y. 11. Tada. updated June 2010. available at (Hwww. Vol. Modeling of Gas Turbines and Steam Turbines in Combined Cycle Power Plants. Davies. Undrill. A. Windows Turbine-Generator Analysis Systems. but finally expressed in pu values) Not exist Not exist Exist Exist Parameters Units pu values pu values CDP Parameter Acceleration Control Loop TIT Parameter WX Parameter Not exist Exist Not exist Not exist Not exist Exist Not exist Exist Not exist Not exist Exist Exist Not exist Exist Not exist Not exist Not exist Exist Not exist Not exist 976 . 724–729.324 (R2008a). IEEE Trans. O’Malley. TX. No. J. 2003. 2. J. No. calculated first in K & oC. Lalor and M. “The Impact of Combined-Cycle Gas Turbine [15] [16] [17] [18] [19] Short-Term Dynamics on Frequency Control”. Richardson.. G. Electrical Engineering in Japan. 3.6. Kurita. Oct.gov. 18. Kunitomi. SIMULINK. Vol. Power Syst. and Costas Vournas. Giza. Vol.Sc Thesis. Kazuhiro Baba and Naoto Kakimoto. 143. Egypt. Price. “Modelling and Stability of a Single-Shaft Combined Cycle Power Plant”. “Modeling combined-cycle power plant for simulation of frequency excursions. No. S. Patterson. Bologna.