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40220140505009
1. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 5, May (2014), pp. 89-99 © IAEME 89 FAULT ANALYSIS IN HYDRO POWER PLANTS USING MATLAB/SIMULINK P Sridhar1 , K Bhanu Prasad2 1 Professor, Department of EEE, Institute of Aeronautical Engineering, Hyderabad 2 Department of EEE, Institute of Aeronautical Engineering, Hyderabad ABSTRACT Scarcity of electrical power is the key problem in developing countries, needs are to be addressed. Due to the depletion of fossil fuel, their usage as a conventional source for production of electrical power is not adequate. Hydro power plant is a possible environment friendly solution in developing, hilly countries where rivers are available, for rural electrification. Hydro power plants are advantageous because of their low administrative and executive costs, possibility of using water for drinking and irrigation purposes, suitability for rural areas and low environmental pollutions. Hydro is a flexible source of electricity since plants can be ramped up and down very quickly to adapt to changing energy demands. Hydro turbines have a start-up time of the order of few minutes. Hydro power plant constructed at a remote area is capable of supplying electrical power to local consumers through an isolated transmission line. In the present study an attempt has been made to develop a Hydro power plant model and study the suitability of different controllers in a governor model for a fault occurrence in a transmission line by means of carrying out a MATLAB based simulation. With MATLAB/SIMULINK, the models of the proposed simulation system are all modularized and visualized, and can be reused easily [1]. Simulation results performed on the proposed control scheme have demonstrated the efficiency of proposed virtual model. Keywords: Hydro-Power Plant, Hydraulic Turbine, Governor, Excitation System, Line Fault, Controllers. 1. INTRODUCTION Excessive usage of fossil fuels has led to global climatic changes and warming. It is believed that attention must be drawn towards the application of renewable energy sources which possesses the potential to be the most suitable future fuel. With the increase in the demand for electrical INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING & TECHNOLOGY (IJEET) ISSN 0976 – 6545(Print) ISSN 0976 – 6553(Online) Volume 5, Issue 5, May (2014), pp. 89-99 © IAEME: www.iaeme.com/ijeet.asp Journal Impact Factor (2014): 6.8310 (Calculated by GISI) www.jifactor.com IJEET © I A E M E
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International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 5, May (2014), pp. 89-99 © IAEME 90 energy, hydro power plants have assumed importance [2]. Hydro power plants have been identified as a very appropriate alternative to conventional electricity generation for several developing countries around the world. However, these are affected by various technical and economic challenges. Hydropower is emerging as a major contributor to the world energy requirement [3]. It is inexhaustible and clean in nature and answers the problem of environmental pollution [4]. On the other hand it requires a large area and initial investment is very high. This paper describes the dynamic model of one of the main components of hydro power plants i.e. the hydro turbine governor. The detailed mathematical representation of the hydraulic turbine-penstock also presented in this paper. The dynamic performance of the hydraulic system is studied using time domain method. The introduced mathematical representation of a hydraulic system is including both turbine-penstock and the governing system. The primary source for the electrical power provided by utilities is the kinetic energy of water which is converted into mechanical energy by the prime movers. The electrical energy to be supplied to the end users is then transformed from mechanical energy by the synchronous generators. The speed governing system adjusts the generator speed based on the input signals of the deviations of both system frequency and interchanged power with respect to the reference settings. This is to ensure that the generator operates at or near nominal speed at all times. Simulation of the three-phase synchronous machine and hydro turbines is well documented in the literature and a digital computer solution can be performed using various methods. This paper discusses the use of SIMULINK software of MATLAB, in the dynamic modeling of the hydro plant components. The main advantage of SIMULINK over other programming software is that, instead of compilation of program code, the simulation model is built up systematically by means of basic function blocks. To be able to model the dynamics of the hydro power plant, dynamic behavior or differential equations of the synchronous machine as well as hydro turbine need to be considered. The Simulation of hydropower plant including its various components viz. Penstock and Turbine, PID Governor, PI Governor and Exciter etc., have been carried out in this work. The developed software demonstrates the dynamic behavior of the hydro power plants by changing load, speed, voltage etc. The type of exciter considered in this paper is a standard IEEE type1 exciter system. A fault is an electrical system is defined as a defect in the electrical circuit due to which current is diverted from the intended path. The nature of fault simply implies any abnormal condition which causes a reduction in the basic insulation strength between phase conductors or between phase conductors and earth. The most common and dangerous fault, that occurs in a power system is the short circuit or shunt fault. They occur as a result of breakdown of the insulation of the current carrying phase conductors relative to earth or in the insulation between phases. The short circuit fault can be classified as 1. Single Phase to ground (L-G). 2. Phase to Phase (L-L). 3. Two Phase to Ground (L-L-G). 4. Phase to Phase and Third Phase to Ground. 5. All Three Phases to Ground (L-L-L-G). 6. All Three Phases Short Circuited (L-L-L). The Line to ground fault occurs most commonly in overhead line practice. The balanced three phase fault is very rare in occurrence, accounting for only about 5% of the total, but is the severest of all types of faults and imposes the most severe duty on the circuit breakers and is used in
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International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 5, May (2014), pp. 89-99 © IAEME 91 the determination of circuit breaker rating. Faults sustained on the system and duration of the faults can be minimized by improving the system design. The type of fault simulated is L-L-L-G fault. 2. HYDRAULIC TURBINE MODELING Power system performance is acted by dynamic characteristics of hydraulic governor-turbines during and followed by any disturbance, such as occurrence of a fault, loss of a transmission line or a rapid change of load. Accurate modeling of hydraulic governor-turbines is essential to characterize and diagnose the system response during an emergency. Simple hydraulic systems governed by proportional-integral-derivative and proportional-integral controllers are modeled. This model examines their transient responses to disturbances through simulation in Matlab/Simulink The linear model of the hydraulic turbine is inadequate for studies involving large variations in power output and frequency. The block diagram shown in Fig.1 represents the dynamic characteristics of the turbine [5]. Fig.3 shows a block diagram of the hydraulic governor-turbine system connected to a power system network. The primary source for the electrical power provided by utilities is the kinetic energy of water which is converted into mechanical energy by the prime movers. The electrical energy to be supplied to the end users is then transformed from mechanical energy by the synchronous generators. The speed governing system adjusts the generator speed based on the input signals of the deviations of both system frequency and interchanged power with respect to the reference settings. This is to ensure that the generator operates at or near nominal speed at all times. Figure 1: Block Diagram of Non-Linear Turbine Model The mathematical equation representing dynamic behavior of the penstock-turbine is given as: [ ] − −= 2 10 2 1010 1 1 Xf Gate X Tdt dX p w --- (1)
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International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 5, May (2014), pp. 89-99 © IAEME 92 Mechanical power output is given by: [ ] WGateDQX Gate X AP nltmech ∆−− = ..10 2 10 --- (2) Where, ‘Tw’ is the water starting time constant ‘fp’ is the frictional loss coefficient ‘Pmech’ is the mechanical power ‘Qnl’ is the no-load water flow-rate. ‘At’ is the turbine gain constant ‘ωr’ is the rotor speed ‘D’ is the turbine damping constant. 3. SPEED GOVERNOR 3.1. PID Governor Model PID controllers are commonly used to regulate the time-domain behavior of many different types of dynamic plants. These controllers are extremely popular because they can usually provide good closed-loop response characteristics, can be tuned using relatively simple design rules, and are easy to construct using either analog or digital components. In modern hydroelectric power plants, the conventional PID control law is applied to control the hydraulic turbine speed, where the control signal ‘u’ is the sum of three elements of proportional, integral, and differential gain of hydraulic turbine speed deviation. The transfer function of a PID controller is given below: x sT sK s K Ku n di p ) 1 ( + ++−= --- (3) Where, ‘Kp’ proportional gain, ‘Ki’ integral gain, ‘Kd’ derivative gain, ‘Tn’ derivative filter time constant (in sec). Some of the electro-hydraulic governors are provided with three-term controllers with proportional-integral-derivative (PID) action. These governors provide higher response speeds by providing both transient gain decrement and transient gain increment. The proportional and integral gains can be adjusted to obtain desired temporary droop and reset-time. The derivative action is beneficial for isolated operation. Fig.2 shows the SIMULINK block diagram of the PID governor with head controller [6].
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International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 5, May (2014), pp. 89-99 © IAEME 93 Figure 2: Simulink model of PID Governor 3.2. PI Governor Model PI governor does not have a derivation action; hence it is equivalent to a hydraulic governor. Fig. 3 shows the PI governor SIMULINK model. Figure 3: Simulink model of PI Governor Similarly other governor models such as PD governor model and Fuzzy controlled governor model have been implemented. 4. EXCITATION SYSTEM An excitation system model is described [7] - Type DC excitation system, without the exciter's saturation, which utilize a direct current generator with a commutator as the source of excitation system power.
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International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 5, May (2014), pp. 89-99 © IAEME 94 This model, described by the block diagram of Fig.4, is used to represent field controlled dc commutator exciters with continuously acting voltage regulators. Figure 4: Exciter system model The exciter is represented by the following transfer function between the exciter voltage Vfd and the regulator’s output ef : eef fd sTKe V + = 1 --- (4) A signal derived from field voltage is normally used to provide excitation system stabilization, ef, via the rate feedback with gain, Ke, and time constant, Te. 5. HYDRO POWER PLANT MODELING The theoretical study of the behavior and stability of hydro power plants is complex and highly difficult due to the large number of variables, to the fact that hydro units cannot be standardized (each of them depending on the geographical situation of the area where it is placed) and to the non-linearity of the hydro power system. The entire simulation system for the analysis of three-phase to Ground fault on hydroelectric power plant has been developed in a MATLAB/Simulink based software environment. Subsystems have been utilized in the simplification of a system diagram and the creation of reusable systems. Further, a subsystem is a group of blocks that is represented by a subsystem block. The entire simulation system contains three subsystems: first, the speed governor and servomechanism, in which turbine speed, dead zone, valve saturation, and limitation are all considered; second: the hydrodynamics system (HS), which consists of tunnels, penstock, and surge tanks; and third, the turbine generator and network, which has a generator unit operating in isolation. In order to be able to analyze the stability of a hydro power plant, this should be theoretically divided into two subsystems: the hydro subsystem (from the reservoir to the turbine) and the electro- mechanical one (comprising the admission valves control system and speed governor. The general block diagram for a hydro power plant [8] is shown in Fig.5. The Simulation Model of Power Plant is shown in Fig.6. We have selected synchronous machine with active power 150 MW, Terminal voltage (Vrms) = 13.8 kV. Pmech = 150.32 MW. Field voltage Ef = 1.291 p u.
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International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 5, May (2014), pp. 89-99 © IAEME 95 Figure 5: Basic Block diagram of a Hydro Power Plant Figure 6: Simulation Model of Power Plant
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International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 5, May (2014), pp. 89-99 © IAEME 96 6. SIMULATION RESULTS The SIMULINK models for different types of governors have been simulated and their effectiveness against a LLLG fault has been studied. The model is considering of regulator servomotor, turbine and generator and servomotor type governor is regulated depending on the signal come from controller. Results are observed which show parameters such as generator terminal voltage, excitation voltage, stator current, rotors speed and rotor angular position. In this case, synchronous generator is connected to the load through a transmission line as shown in Fig.6. Initially the load is 15MW on the generator. At 10 seconds, disturbance is created by creating phase- phase fault for 0.2seconds. The values of the governor, exciter, synchronous generator and hydraulic turbine are same as given before. The simulation time for all models is 50 sec. The following observations can be made from the simulation results. PID Controller PI Controller Time Time Figure 7: Rotor Speed Deviation VS Time Time Time Figure 8: Stator Current Vs Time Time Time Figure 9: Mechanical Power Vs Time RotorSpeedDeviation RotorSpeedDeviation StatorCurrent StatorCurrent MechanicalPower MechanicalPower
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International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 5, May (2014), pp. 89-99 © IAEME 97 Time Time Figure 10: Speed Vs Time Time Time Figure 11: Field Voltage Vs Time Time Time Figure 12: Rotor Angle Deviation Vs Time Fig.7 shows the deviations in the rotor speed for individual controllers. For a PID controller the rotor speed deviates at the time of fault at t= 10 sec and reaches the magnitude of 0.35 (p.u) and takes t= 37 sec for entering stable state. For a PI controller the rotor speed deviates at the time of fault at t= 10 sec and reaches the magnitude of -0.35 (p.u) and takes t= 29 sec for entering stable state. Fig.8 depicts the stator current variations for PID and PI Controllers. For a PID controller the stator current increases dramatically as expected at the time of fault i.e. at t=10 sec and enters a transient region at t=20 sec when the fault is cleared and stabilizes at t= 38.2 sec. For a PI controller the stator current increases dramatically as expected at the time of fault i.e. at t=10 sec and enters a transient range at t=20 sec when the fault is cleared and stabilizes at t= 30 sec. Fig.9 explains the variations in the mechanical power. For a PID controller the mechanical power takes a dip at t=10 sec and keeps climbing up till t=50 sec. For a PI controller the Speed Speed FieldVoltage FieldVoltage RotorAngleDeviation RotorAngleDeviation
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International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 5, May (2014), pp. 89-99 © IAEME 98 mechanical power starts climbing at t=10 sec and keeps climbing up till t=24 sec and dips till t= 28.5 sec before its starts climbing till t=50 sec. Fig.10 shows the speed of the alternator variations, a PID controller, the speed of the alternator rises at t= 10 sec to reach a peak value of 1.54 pu and stabilizes at t= 36.5 sec. For a PI controller the speed of the alternator dips at t= 10 sec to reach a peak value of 0.652 and stabilizes at t= 28.5 sec. Fig.11 exhibits the field voltage variations. For a PID controller the field voltage rises drastically at t= 10 sec and stabilizes at t= 37.5 sec. For a PI controller the field voltage rises drastically at t= 10 sec and stabilizes at t= 30 sec. Fig.12 reveals the rotor angle deviations. For a PID controller the rotor angle deviation increases from t =10 sec till it stabilizes at t =32 sec. For a PI controller the rotor angle deviation decreases from t =10 sec till it stabilizes at t =24 sec. CONCLUSION SIMULINK is a powerful software package for the study of dynamic and nonlinear systems. Using SIMULINK, the simulation model can be built up systematically starting from simple sub- models. The hydro power plant model developed. Several tests and operating conditions can be applied on the model. In this paper a three phase fault to ground case was shown, many other faults or operating conditions as over load conditions can be applied and examined by this model. The significance of controllers in Hydro power plant control system is to implement the system operator knowledge to higher degree. A PI based turbine governor was proposed. It maintains the frequency constant in spite of changing user load at any operating point. According to the simulation results PI controller has proven to be the most suited controller for governing mechanism. The values of Proportional gain and Integral gain play an important role in determining the stabilizing time hence their optimization is absolutely necessary. The Simulation results prove that PI based turbine governor has good performances. Moreover, good transient and steady state responses for different operating points of the processes can be achieved. 9. ACKNOWLEDGEMENTS The authors would like to acknowledge gratefully the constant encouragement and continuous support by the Management, Principal and staff members of Electrical & Electronics Engineering Department of Institute of Aeronautical Engineering, Hyderabad. REFERENCES [1] Hongqing Fang, Long Chen, Nkosinathi Dlakavu, and Zuyi Shen, “Basic Modeling and Simulation Tool for Analysis of Hydraulic Transients in Hydroelectric Power Plants”, IEEE Transactions on Energy Conversion, VOL. 23, NO. 3, SEPTEMBER 2008. [2] Issam Salhi, Mohammed Chennani, Saïd Doubabi Nabil Ezziani (2008):Modeling and Regulation of a Micro Hydroelectric Power Plant, proceedings of the IEEE International Symposium on Industrial Electronics, 2008,pp 1639-1644. [3] Mousa Sattouf Int. Journal of Engineering Research and Applications ISSN: 2248-9622, Vol. 4, Issue 1(Version 2), January 2014, pp.295-301.
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International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 5, May (2014), pp. 89-99 © IAEME 99 [4] Ghanashyam Ranjitkar, Jinxing Huang and Tony Tung (2006): Application of Micro- hydropower Technology for Remote Regions, IEEE EIC Climate Change Technology, 2006 pp 1-10. [5] P.P. Sharma, S. Chatterji and Balwinder Singh, “MATLAB BASED SIMULATION OF COMPONENTS OF SMALL HYDRO-POWER PLANTS”, VSRD International Journal of Electrical, Electronics & Communication Engineering, Vol. III Issue VIII August 2013. [6] IEEE Working Group on Prime Mover and Energy Supply Models for System Dynamic Performance Studies, "Hydraulic Turbine and Turbine Control Models for Dynamic Studies," IEEE® Transactions on Power Systems, Vol. 7, No. 1, February, 1992, pp. 167-179. [7] "Recommended Practice for Excitation System Models for Power System Stability Studies,"IEEE® Standard 421.5-1992, August, 1992. [8] H.Weber, F.Prillwitz, “Simulation of hydro power plants in Macedonia and Yugoslavia”, 2003 IEEE Bologna Power tech, June 23-26 2003, Bologna. [9] Ankush Gupta, Ameesh Kumar Sharma and Umesh Sharma, “Future Potential of Small Hydro Power Project in India”, International Journal of Electrical Engineering & Technology (IJEET), Volume 4, Issue 2, 2013, pp. 427 - 442, ISSN Print: 0976-6545, ISSN Online: 0976-6553. [10] Bilal Abdullah Nasir, “Design of High Efficiency Pelton Turbine for Micro-Hydropower Plant”, International Journal of Electrical Engineering & Technology (IJEET), Volume 4, Issue 1, 2013, pp. 171 - 183, ISSN Print : 0976-6545, ISSN Online: 0976-6553. [11] Shambhu Ratan Awasthi, Vishnu Prasad and Saroj Rangnekar, “Demand Based Optimal Performance of a Hydroelectric Power Plant”, International Journal of Advanced Research in Engineering & Technology (IJARET), Volume 4, Issue 7, 2013, pp. 109 - 119, ISSN Print: 0976-6480, ISSN Online: 0976-6499.
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