![ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 02, June 2011
Or in non-dimensional form:
Where TW is the integration constant of the hydropower
Where the following notations were used: system and the variables have the following meaning:
Which represent the non-dimensional variations of the
parameters around the steady state values. It must be noted that this is a simplified method to compute
the hydraulic pressure loss, which can be used for run-of-the
B. The hydraulic feed system river hydropower plants, with small water head. If an exact
The hydraulic feed system has a complex geometrical value of the dynamic pressure is required, then the formulas
configuration, consisting of pipes or canals with different presented in [8], sub-chapter 8.4 “The calculation of hydro
shapes and cross-sections. Therefore, the feed system will energy potential” shall be used.
be considered as a pipe with a constant cross-section and Using the Laplace transform in relation (11), it results:
the length equal with real length of the studied system. In
order to consider this, it is necessary that the real system and
the equivalent system to contain the same water mass. Let Replacing (13) in (3) and (4) and doing some simple
consider m1, m2...mn the water masses in the pipe zones having
calculations, we obtain:
the lengths l1,l2,...,ln and cross-sections A1, A2,...,An of the real
feed system. The equivalent system will have the length
L=l1+l2+...+ln and cross-section A, conveniently chosen.
In this case, the mass conservation law in both systems will
lead to the equation:
Since the water can be considered incompressible, the flow
Qi through each pipe segment with cross-section A i is The mechanical power generated by the turbine can be
identical and equal with the flow Q through the equivalent calculated with the relation P= g.Q.H, which can be used to
pipe obtain the linearized relations for variations of these values
around the steady state values:
Where v is the water speed in the equivalent pipe, and vi is
the speed in each segment of the real pipe. Where ? is the turbine efficiency, and g, Q, and H were
From the mass conservation law it results: defined previously.
On the other hand, the mechanical power can be determined
using the relation P=Mù=2 M.N, which can be used to obtain
The dynamic pressure loss can be computed considering the the linearized relations for variations of these values around
inertia force of the water exerted on the cross-section of the the steady state values:
pipe:
Where = is the steady state power generated by
the turbine for a given steady state flow Q0 and a steady
Where L is the length of the penstock or the feed canal, A is
state head H0, and N0 is the steady state rotational speed.
the cross-section of the penstock, g? is the specific gravity
Using these relations, the block diagram of the hydraulic
of water (1000Kgf/m3), a is the water acceleration in the
turbine, for small variation operation around the steady state
equivalent pipe, and g=9.81 m/s 2 is the gravitational
point, can be determined and is presented in Figure 2, where
acceleration. The dynamic pressure loss can be expressed
the transfer functions for different modules are given by the
as:
following relation:
Using non-dimensional variations, from (9) it results:
56
© 2011 ACEEE
DOI: 01.IJCSI.02.02.1](https://image.slidesharecdn.com/1-120911235205-phpapp01/85/Development-and-Simulation-of-Mathematical-Modelling-of-Hydraulic-Turbine-2-320.jpg)
![ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 02, June 2011
REFERENCES [6] Asal H. P., R. Widmer, H. Weber, E. Welfonder, W. Sattinger.
Simulation of the restoration process after black Out in the Swiss
[1] P. Kundur. Power System Stability and Control. McGraw- grid. Bulletin SEV/VSE 83, 22, 1992, pp. 27-34.
Hill, 1994. [7] Weber, H., F. Prillwitz, M. Hladky, H. P. Asal. Reality oriented
[2] IEEE. Hydraulic turbine and turbine control models for system simulation models of power plants for restoration studies. Control
dynamic studies. IEEE Transactions on Power Systems, 7(1):167– Engineering practice, 9, 2001, pp. 805-811.
179, Feb 1992. [8] Weber, H., V. Fustik, F. Prillwitz, A. Iliev. Practically oriented
[3] Jiang, J. Design an optimal robust governor for hydraulic turbine simulation model for the Hydro Power Plant “Vrutok” in Macedonia.
generating units IEEE Transaction on EC 1, Vol.10, 1995, pp.188- 2nd Balkan Power Conference, 19.-21.06. 2002, Belgrade,
194. Yugoslavia
[4] IEEE Working Group. Hydraulic turbine and turbine control [9] C. Henderson, Yue Yang Power Station – The Implementation of
models for system dynamic studies. IEEE Transactions on Power the Distributed Control System, GEC Alsthom Technical Review,
Syst 1992; 7:167–79. Nr. 10, 1992.
[5] Nand Kishor, R.P. Saini, S.P. Singh A review on hydropower [10] Prillwitz F., A. Holst, H. W. Weber (2004), “Reality Oriented
plant models and control, Renewable and Sustainable Energy Simulation Models of the Hydropower Plants in Macedonia and
Reviews 11 (2007) 776–796 Serbia/Montenegro” In Proceedings of the Annual Scientific Session
TU Verna, Bulgaria.
59
© 2011 ACEEE
DOI: 01.IJCSI.02.02.1](https://image.slidesharecdn.com/1-120911235205-phpapp01/85/Development-and-Simulation-of-Mathematical-Modelling-of-Hydraulic-Turbine-5-320.jpg)
Development and Simulation of Mathematical Modelling of Hydraulic Turbine
- 1. ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 02, June 2011 Development and Simulation of Mathematical Modelling of Hydraulic Turbine 1 2 Gagan Singh and D.S. Chauhan 1 Uttarakhand Technical University, Dehradun, (U.K), India. hod_ee@dit.edu.in 2 Uttarakhand Technical University, Dehradun,(U.K),India. pdschauhan@gmail.com Abstract- Power system performance is affected by dynamic low water storage capacity in the reservoir; therefore the characteristics of hydraulic governor-turbines during and plant operation requires a permanent balance between the following any disturbance, such as occurrence of a fault, water flow through turbines and the river loss of a transmission line or a rapid change of load. Accurate modelling of hydraulic System is essential to characterize and diagnose the system response. In this article the mathematical modeling of hydraulic turbine is presented. The model is capable to implement the digital systems for monitoring and control replacing the conventional control systems for power, frequency and voltage. This paper presents the possibilities of modeling and simulation of the hydro power plants and performs an analysis of different control structures and algorithms. Figure 1: Functional block diagram of hydraulic governor-turbine Key words: mathematical modeling, simulation, hydraulic system interconnected with a power system network. turbine. flow in order to maximize the water level in the reservoir for a maximum efficiency of water use. Next, we will determine the I. INTRODUCTION mathematical model for each component of the hydropower system. Usually, a typical hydroelectric power plant consists of water tunnel, penstock, surge tank, hydraulic turbine, speed A. Mathematical modeling of Hydraulic turbine governor, generator and electric network. Hydrodynamics The representation of the hydraulic turbine and water and mechanoelectric dynamics are all involved in such a column in stability studies is usually based on the following nonlinear dynamic system. Generally, a hydroelectric assumptions:- generating unit has many different operating conditions and The hydraulic resistance is negligible. change in any operating condition results in small or large The penstock pipe is inelastic and the water is hydraulic transients. There are many instances of damage to incompressible. penstock or hydraulic turbine which are most probably The velocity of the water varies directly with the occurring due to large transients. Hydrodynamics is gate opening and with the square root of the net influenced by the performance of hydraulic turbine which head. depends on the characteristics of the water column feeding The turbine output power is proportional to the the turbine. These characteristics include water inertia, water product of head and volume flow. compressibility and pipe wall elasticity in the penstock. The hydraulic turbine can be considered as an element Different construction of hydropower systems and different without memory since the time constants of the turbine are operating principles of hydraulic turbines make difficult to less smaller than the time constants of the reservoir, penstock, develop mathematical models for dynamic regime, in order to and surge chamber, if exists, which are series connected design the automatic control systems. Also, there are major elements in the system. As parameters describing the mass differences in the structure of these models. Moreover, there transfer and energy transfer in the turbine we will consider are major differences due to the storage capacity of the the water flow through the turbine Q and the moment M reservoir and the water supply system from the reservoir to generated by the turbine and that is transmitted to the the turbine (with or without surge chamber).The dynamic electrical generator. These variables can be expressed as non- model of the plants with penstock and surge chamber is more linear functions of the turbine rotational speed N, the turbine complicated than the run-of-the-river plants, since the water gate position Z, and the net head H of the hydro system. feed system is a distributed parameters system. This paper Q = Q (H, N, Z) (1) will present several possibilities for the modeling of the M = M (H, N, Z) (2) hydraulic systems and the design of the control system. Through linearization of the equations (1) and (2) around II. MODELING OF THE HYDRAULIC SYSTEM the steady state values, we obtain: For run-of-the river types of hydropower plants have a 55 © 2011 ACEEE DOI: 01.IJCSI.02.02. 1
- 2. ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 02, June 2011 Or in non-dimensional form: Where TW is the integration constant of the hydropower Where the following notations were used: system and the variables have the following meaning: Which represent the non-dimensional variations of the parameters around the steady state values. It must be noted that this is a simplified method to compute the hydraulic pressure loss, which can be used for run-of-the B. The hydraulic feed system river hydropower plants, with small water head. If an exact The hydraulic feed system has a complex geometrical value of the dynamic pressure is required, then the formulas configuration, consisting of pipes or canals with different presented in [8], sub-chapter 8.4 “The calculation of hydro shapes and cross-sections. Therefore, the feed system will energy potential” shall be used. be considered as a pipe with a constant cross-section and Using the Laplace transform in relation (11), it results: the length equal with real length of the studied system. In order to consider this, it is necessary that the real system and the equivalent system to contain the same water mass. Let Replacing (13) in (3) and (4) and doing some simple consider m1, m2...mn the water masses in the pipe zones having calculations, we obtain: the lengths l1,l2,...,ln and cross-sections A1, A2,...,An of the real feed system. The equivalent system will have the length L=l1+l2+...+ln and cross-section A, conveniently chosen. In this case, the mass conservation law in both systems will lead to the equation: Since the water can be considered incompressible, the flow Qi through each pipe segment with cross-section A i is The mechanical power generated by the turbine can be identical and equal with the flow Q through the equivalent calculated with the relation P= g.Q.H, which can be used to pipe obtain the linearized relations for variations of these values around the steady state values: Where v is the water speed in the equivalent pipe, and vi is the speed in each segment of the real pipe. Where ? is the turbine efficiency, and g, Q, and H were From the mass conservation law it results: defined previously. On the other hand, the mechanical power can be determined using the relation P=Mù=2 M.N, which can be used to obtain The dynamic pressure loss can be computed considering the the linearized relations for variations of these values around inertia force of the water exerted on the cross-section of the the steady state values: pipe: Where = is the steady state power generated by the turbine for a given steady state flow Q0 and a steady Where L is the length of the penstock or the feed canal, A is state head H0, and N0 is the steady state rotational speed. the cross-section of the penstock, g? is the specific gravity Using these relations, the block diagram of the hydraulic of water (1000Kgf/m3), a is the water acceleration in the turbine, for small variation operation around the steady state equivalent pipe, and g=9.81 m/s 2 is the gravitational point, can be determined and is presented in Figure 2, where acceleration. The dynamic pressure loss can be expressed the transfer functions for different modules are given by the as: following relation: Using non-dimensional variations, from (9) it results: 56 © 2011 ACEEE DOI: 01.IJCSI.02.02.1
- 3. ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 02, June 2011 For an ideal turbine, without losses, the coefficients a ij TABLE I. VARIATIONS OF THE TIME CONSTANT OF THE HYDRO SYSTEM resulted from the partial derivatives in equations (12 - 16) have the following values: a11=0.5; a12=a13=1; a21=1.5; a23=1. In this case, the transfer functions in the block diagram are given by the following relation: the reservoir, for a constant water flow, Q=725m3/s. III. SIMULATION RESULTS Example. Let consider a hydroelectric power system with the following parameters: -Water flow (turbines): QN=725 m3/s; -Water level in the reservoir: HN=30 m; -The equivalent cross-section of the penstock A=60m2; -Nominal power of the turbine PN=178MW; -Turbine efficiency =0.94; -Nominal rotational speed of the turbine= N=71.43 rot/min; -The length of the penstock l= li=20m; Fig. 2. The block diagram of the hydraulic turbine. It shall be determined the variation of the time constant TW Figure 3. Variation of the integral time constant TW: a) by the for the hydro power system. flow Q, b) by the water level H For the nominal regime, using relation (12), where li=20m, It can be seen from the table or from the graphs that the the time constant of the system is: time constant changes more than 50% for the entire operational range of the water flow through the turbine or if the water level in the reservoir varies. These variations will Next there is a study of the variation of the time constant create huge problems during the design of the control system due to the variation of the water flow through the turbine for for the turbine, and robust control algorithms are a constant water level in the reservoir, H=30m, as well as the recommended. variation due to the variable water level in the reservoir for a In figure 4 the block diagram of the turbine’s power con- constant flow Q=725 m3/s. In table I, column 3 and figure 3 a) trol system, is presented using a secondary feedback from are presented the values and the graphical variation of the the rotational speed of the turbine. It can be seen from this time constant TW for the variation of the water flow between figure that a dead-zone element was inserted in series with 500 m3/s and 110 m3/s, for a constant water level in the the rotational speed sensor in order to eliminate the feedback reservoir, H=30m. In table 1. column 4 and figure 3 b) are for ±0.5% variation of the rotational speed around the syn- presented the values and the graphical variation of the time chronous value. This oscillation has no significant influence constant TW for the variation of the water level in on the performance of the system but would have lead to 57 © 2011 ACEEE DOI: 01.IJCSI.02.02.1
- 4. ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 02, June 2011 permanent perturbation of the command sent to the turbine In figure 6 the variations of the turbine power (graph a) and gate. rotational speed (graph b) for the control system a feedback from the turbine power but no feedback from the rotational speed are presented. Figure 4. Block Diagram of the control system for hydraulic turbines The constants of the transfer functions had been computed for a nominal regime T W =0.8s. The optimal parameters for a PI controller are: KR=10, TI=0.02s. The results of the turbine simulation for different operational regimes are presented in figure 5, for a control system using feedbacks from the turbine power and rotational speed, with a dead- zone on the rotational speed channel for ±0.5% variation of the rotational speed around the synchronous value (a) Power variation with 10% around nominal value, b) Rotational speed variation for power control). Figure 6 Control structure with only power feedback a) Power variation with 10% around nominal value b) Rotational speed variation for power control IV. CONCLUSIONS The detailed mathematical modeling of hydraulic turbine is vital to capture essential system dynamic behavior .The possibility of implementation of digital systems for monitoring and control for power, frequency and voltage in the cascade hydro power plant was discussed. The simplified mathematical models, capable to accurately describe dynamic and stationary behavior of the hydro units a developed and simulated. These aspects are compared with experimental results. Finally, a practical example was used to illustrate the design of controller and to study the system stability. ACKNOWLEDGEMENT The authors would like to thank Professor S.P. Singh (I.I.T Roorkee, India) for his continuous support and valuable suggestions. Figure 5 Control structure with feedbacks from turbine power and rotational speed: 58 © 2011 ACEEE DOI: 01.IJCSI.02.02.1
- 5. ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 02, June 2011 REFERENCES [6] Asal H. P., R. Widmer, H. Weber, E. Welfonder, W. Sattinger. Simulation of the restoration process after black Out in the Swiss [1] P. Kundur. Power System Stability and Control. McGraw- grid. Bulletin SEV/VSE 83, 22, 1992, pp. 27-34. Hill, 1994. [7] Weber, H., F. Prillwitz, M. Hladky, H. P. Asal. Reality oriented [2] IEEE. Hydraulic turbine and turbine control models for system simulation models of power plants for restoration studies. Control dynamic studies. IEEE Transactions on Power Systems, 7(1):167– Engineering practice, 9, 2001, pp. 805-811. 179, Feb 1992. [8] Weber, H., V. Fustik, F. Prillwitz, A. Iliev. Practically oriented [3] Jiang, J. Design an optimal robust governor for hydraulic turbine simulation model for the Hydro Power Plant “Vrutok” in Macedonia. generating units IEEE Transaction on EC 1, Vol.10, 1995, pp.188- 2nd Balkan Power Conference, 19.-21.06. 2002, Belgrade, 194. Yugoslavia [4] IEEE Working Group. Hydraulic turbine and turbine control [9] C. Henderson, Yue Yang Power Station – The Implementation of models for system dynamic studies. IEEE Transactions on Power the Distributed Control System, GEC Alsthom Technical Review, Syst 1992; 7:167–79. Nr. 10, 1992. [5] Nand Kishor, R.P. Saini, S.P. Singh A review on hydropower [10] Prillwitz F., A. Holst, H. W. Weber (2004), “Reality Oriented plant models and control, Renewable and Sustainable Energy Simulation Models of the Hydropower Plants in Macedonia and Reviews 11 (2007) 776–796 Serbia/Montenegro” In Proceedings of the Annual Scientific Session TU Verna, Bulgaria. 59 © 2011 ACEEE DOI: 01.IJCSI.02.02.1