Successfully reported this slideshow.
Upcoming SlideShare
×

# Eee598 Project New

781 views

Published on

This is a transient stability analysis of a sample four machine system, done using pslf for the course, \'Power System Stability\'.

• Full Name
Comment goes here.

Are you sure you want to Yes No
• Be the first to comment

• Be the first to like this

### Eee598 Project New

1. 1. STABILITY ANALYSIS OF A SAMPLE FOURMACHINE SYSTEM USING CLASSICAL MODEL WITH THE HELP OF PSLF A PROJECT REPORT Submitted by Members of Group 5 Fei Gao Supriya Chathadi Changxu Chen Habibou Maiga Submitted to Dr. Vijay Vittal In partial fulfillment for completion of the course EEE598: POWER SYSTEM STABILITY at ARIZONA STATE UNIVERSITY, TEMPE
2. 2. EEE598-Group 5 Table of Contents1. Introduction ............................................................................................................................. 32. Input Data Files ....................................................................................................................... 4 2.1 Power Flow Case File ............................................................................................................4 2.2 Transient Stability File ...........................................................................................................43. Transient Simulation Description and Results ........................................................................... 4 3.1 Relative Rotor Angles Plots .................................................................................................10 3.2 Absolute Rotor Angle Plots ................................................. Error! Bookmark not defined.4. Shortcomings of Classical Model ............................................................................................. 125. Inference................................................................................................................................ 126. References ............................................................................................................................. 13Appendix 1 ................................................................................................................................... iAppendix 2 ................................................................................................................................. iiiAppendix 3 .................................................................................................................................. v APPENDICES APPENDIX 1 PSLF Power Flow Mismatch APPENDIX 2 PSLF Dynamic Data File APPENDIX 3 One Line DiagramArizona State University 2
3. 3. EEE598-Group 51. IntroductionThis report documents the results of the transient stability study performed for the project usingthe PSLF software. The project assigned is to: a. Prepare a dynamic data file for the given four machine, six bus system (shown in Appendix 3) with the classical model from the detailed machine model which is given. b. Simulate a 3-phase short circuit at bus 5 and determine the critical clearing time. c. Plot the relative and absolute angles for all the machines and determine the stability of the system; conclude which among the two is better to measure the loss in synchronism.A brief overview of the procedure is presented below in the form of a flowchart in Figure 1.Detailed explanation and results follow. Import „.raw‟ file Solve Power Flow Prepare the dynamic data file, „.dat‟ for four generators with classical model Read and Initiate the „.dat‟ file Run pre-fault, faulted & post-fault simulations with reference bus specified (relative rotor angle plot) and find critical clearing time (by trial and error) Run pre-fault, faulted & post-fault simulations with reference bus zeroed (absolute rotor angle plot) and find critical clearing time (by trial and error) Figure 1Arizona State University 3
4. 4. EEE598-Group 52. Input Data Files2.1 Power Flow Case FileThe raw file from [1] is imported into the PSLF software using the “Import PTI” option. Thiscreates the PSLF case file for the sample four machine system. The “solv” command is used tosolve the power flow. As the mismaches are almost negligible (Appendix 1 shows the results),we conclude that the power flow converges.2.2 Transient Stability FileThe dynamic data given in [2] is for a detailed machine model. A simplified PSLF dynamicdata file which models all the four machines with the classical model was created and is shown in appendix 2. Only the sub transient reactance ( xd ), and inertia constant (H) of the generatorsare used. (The syntax for the classical generator model in the dynamic file was written frompage 809 of [3]). The “rdyd” command in PSLF is used to read the file and “init” is used toinitiate it.3. Transient Simulation Description and ResultsA stable power system is one in which the synchronous machines, when perturbed, will eitherreturn to their original state if there is no net change of power or will acquire a new stateasymptotically without losing synchronism. One convenient quantity is the machine rotor anglemeasured with respect to a synchronously rotating reference. If the difference in angle betweenany two machines increases indefinitely or if the oscillatory transient is not suficiently damped,the system is unstable [4].A 3-phase short circuit is simulated at bus # 5 by trying different number of cycles for theapplication of fault, in order to determine the critical clearing time. The critical clearing time isdefined as the time at which the system is at the edge of instability.The PSLF plot feature is used to represent the results in the form of relative and absolute rotorangle plots, which are used to analyze the stability of the system.The “run” command is used to perform the simulation, where several dynamic parameters needto be specified for different conditions.PSLF requires the simulation to be broken into three parts:  Pre fault simulation: This step allows the system to reach steady state before any disturbance is applied. This procedure is often called the flat run. To let the system runArizona State University 4
5. 5. EEE598-Group 5 in steady state for 1 second, the simulation is run by setting the “next pause time” as 1s. Figure 2 shows the modifications to be done in the dynamic parameter dialog. Figure 2Arizona State University 5
6. 6. EEE598-Group 5  Fault simulation: A fault is applied at bus #5. This step is used to determine the critical clearing time by trial and error method. In this step, the “faulted bus” is first set to 5 and the “bus fault status” is changed to 1; which means there is a three phase fault on bus # 5. The “next pause time” is changed to (1+n/60), where n is the number of cycles for which the fault is applied. A number of simulations were performed by varying „n‟ between 4 and 5 cycles and the corresponding rotor angle plots are observed to determine the critical clearing time for a 3-phase short circuit at bus # 5. The changes made in the dynamic parameters are shown in Figure 3. Figure 3Arizona State University 6
7. 7. EEE598-Group 5  Post fault simulation: This step is used to examine the stability of the system after the fault is cleared. The “bus fault status” is set to „0‟ to clear the fault. The “next pause time” is set to 5 seconds to run the simulation for the rest of the time after fault- clearing. For classical model, the simulation is generally run for 5-6 seconds only as the stability of the system is determined in the first swing. The assumption that the mechanical power is constant does not hold for time periods beyond 5-6 seconds. This is one of the disadvantages of using classical model (discussed in detail in Chapter 4). Figure 4Arizona State University 7
8. 8. EEE598-Group 5After completing the simulation, the “plot” feature is used to view the plots of all the four rotorangles.480 628 3960PSLF makes use of relative plots with reference to the bus at the far end from the fault bydefault. In this case, bus # 3 is automatically chosen as the reference because it is the locatedboth physically and electrically farthest from bus # 5 (faulted bus); shown clearly in Appendix3. Figure 5Arizona State University 8
9. 9. EEE598-Group 5Section 3.1 shows the relative rotor angle plot obtained when the three phase fault at bus# 5 iscleared after 4.3 cycles and 4.4 cycles.The angle plots for 4.3 cycles show that the machines are operating in synchronism (anglesreturn back). But in case of 4.4 cycles, the angles grow infinitely even after fault is cleared(unstable system).Thus, it is found that the system just losses synchronism when the fault is applied for 4.4cycles. This means that when the fault is applied for 4.3 cycles, the system is at the edge ofinstability; which is the critical clearing time for this system.It is not possible to plot the absolute rotor angles with the help of PSLF as it is basicallyrelative software. Also abArizona State University 9
10. 10. EEE598-Group 53.1 Relative Rotor Angles Plots4.3 cycles clearing time:Arizona State University 10
11. 11. EEE598-Group 54.4 cycles clearing time:Arizona State University 11
12. 12. EEE598-Group 54. Shortcomings of Classical ModelThe assumptions made for classical model [4] are as follows:1) Transient stability is decided in the first swing.2) Constant generator main field-winding flux linkage.3) Neglecting the damping powers.4) Constant mechanical power.5) Representing loads by constant passive impedance.But today, large system interconnections with the greater system inertias and relatively weakerties result in longer periods of oscillations during transients. Generator control systems,particularly modern excitation systems, are extremely fast. Also, the assumption that themechanical power is constant does not hold for greater time periods.In short, the classical model is inadequate for system representation beyond the first swing.Since the first swing is largely an inertial response to a given accelerating torque, the classicalmodel does provide useful information as to system response during this brief period.5. InferenceBased on the simulation results presented in the previous sections, the following observationscan be made: The critical clearing time for the given system for a 3 phase fault at bus #5 is 4.3 cycles. The relative rotor angle plots give a better measure of the loss of synchronism than the absolute rotor angles because of the following reasons: o Most of the power flow softwares use this option by default. o Synchronism is a measure of how close the machines operate with one another; which means the performance of a machine is measured with respect to another one. This is the concept behind relative angle plot. o This is the reason why relative angles are used in industrial standards as well.Arizona State University 12
13. 13. EEE598-Group 56. References [1] Power flow raw file, “2area.raw”, EEE598, Fall 2011. [2] Detailed Dynamic data file, “dyn.dat”, EEE598, Fall 2011. [3] PSLF User Manual [4] “Power System Control and Stability” by P.M. Anderson and A.A. FouadArizona State University 13
14. 14. EEE598-Group 5 Appendix 1 PSLF Power Flow MismatchArizona State University i
15. 15. Appendix 1 EEE598-Group 5It -P-error- --Bus-- ----Name---- --Kv-- area -Q-error- --Bus-- ----Name---- --Kv-- area -delta-A- --Bus-- ----Name---- --Kv-- area -delta-V- --Bus-- ----Name---- --Kv-- area0 0.0029 6 B L 230.00 2 -0.0004 6 B L 230.00 2 0.0233 2 BD AR1 230.00 1 0.000015 6 B L 230.00 2 1 -0.0000 5 B L 230.00 1 -0.0000 6 B L 230.00 2 0.0000 5 B L 230.00 1 0.000000 6 B L 230.00 2Stopped after 2 iterationsEstimated solution error 0.0002 MW, 0.0005 MVARat buses 5 B L 230.00 6 B L 230.00Actual mismatch is = -0.0001 MW -0.0004 MVAR at bus 5 [B L ] 230.00Arizona State University ii
16. 16. EEE598-Group 5 Appendix 2 PSLF Dynamic Data FileArizona State University iii
17. 17. Appendix 2 EEE598-Group 5# area 1 [AREA 1 ]#modelsgencls 1 "BD AR1" 230.00 "1" : #9 mva=900.00 6.5000 0.0000 0.0000 0.3000 0.0000 0.0000gencls 2 "BD AR1" 230.00 "1" : #9 mva=900.00 6.5000 0.0000 0.0000 0.3000 0.0000 0.0000## area 2 [AREA 2 ]#modelsgencls 3 "BD AR2" 230.00 "1" : #9 mva=900.00 6.5000 0.0000 0.0000 0.3000 0.0000 0.0000gencls 4 "BD AR2" 230.00 "1" : #9 mva=900.00 6.5000 0.0000 0.0000 0.3000 0.0000 0.0000Arizona State University iv
18. 18. EEE598-Group 5 Appendix 3 One Line DiagramArizona State University v
19. 19. Appendix 3 EEE598-Group 5 GEN1 BUS# 1 GEN 2 ZL_12= 0.0025 + j0.025 BUS# 2 Zt_15= 0.0035 + j0.035 ZL_25=0.001 + j0.01 BUS# 5 Loads ZL_56=0.022 + j0.22 BUS# 6 Zt_53= 0.0285 + j0.255 GEN4 Loads ZL_64=0.004 + j0.01 BUS# 4 ZL_43=0. 0025 + j0.025 GEN3BUS# 3Arizona State University vi