RMIT University, School of Engineering
Advanced Power Systems
Experiment 2 - Transient Stability
? Objectives
? Familiarisation with the DIgSILENT Power Factory software package and dynamic simulation functionalities.
? Applying the theory of equal area criterion to determine the critical clearing angle and the rotor swings of a generator when a fault forces the electrical power transfer to zero. Hence, determine the stability/ instability of the system when the fault is cleared.
? To determine the critical clearing angle and the rotor swings after a fault, which disrupts electrical power transfer partially. Hence, determine the stability/ instability of the system when the fault is cleared.
? Equipment and Software
DIgSILENT Power Factory Ver. 2019 which is available on all computers in the computer lab as well as RMIT myDesktop.
? Prerequisites
1. Should complete DIgSILENT Power Factory Learning Tutorial available in Canvas and Experiment 1
2. Revise Lecture materials and the DIgSILENT PF Dynamic Simulation Functionalities Guide available in Canvas
? DIgSILENT Power Factory Software Package
DIgSILENT Power Factory is the leading high-end power system analysis tool for applications in generation, transmission, distribution and industrial systems. It is integrating all required functions, easy to use, fully Windows compatible and combines reliable and flexible system modelling capabilities with state-of-the-art algorithms and a unique database concept. Besides the stand-alone functionality, the Power Factory engine integrates smoothly into any GIS, DMS or EMS supporting open system standards. The DIgSILENT offers following functionalities.
? Balanced and unbalanced power flow;Fault analysis;
? Harmonics, Frequency scans;
? RMS Stability;
? EMT simulations for three, two and single phase AC systems and DC systems;
? Protection simulation and co-ordination;
? Distribution, transmission and generation reliability;
? Small signal analysis (eigenvalues); Static and dynamic voltage stability;
? Active and reactive power dispatch; State estimation;
? Open tie optimization, optimal capacitor placement, cable sizing;
? Built-in automation interface (DPL),
? ODBC driver, interfaces for GIS and SCADA integration; PSS/E compatibility
? Experimental Procedure:
1) For this experiment, the single line diagram of the system to be studied is given in Figure.1 and the generator, transformer and line data are provided in the table below.
Figure 1: Single-line diagram of the system for the study
Generator Components X pu
Generator voltage pu 1.01 Transformer 0.13
Turbine Power PG MW 760 Line-1 0.55
Inertia Constant H seconds 4.4 Line-2 0.1
Transient Reactance X’ pu 0.26 Line-3 0.4
Frequency Hz 50 Fault clearing time T1 ms see (3)
Assume that the slack generator bus is an “infinite bus”. The per-unit values of reactances are on a 1000 MVA, 500 kV/20 kV base and the inertia constant is also on a base of 1000 MVA. The generator is a 2-pole, 50 Hz machine. Assume that all the components have negligible resistances.
2) Now construct the circuit shown in Figure 1 using DIgSILENT Power Factory based on the data available in the table. Assume the nominal voltage of 500 kV for transmission lines and 20 kV for the generator terminal and the transformer is accordingly 500kV/20kV. The base MVA of the system is 1000 MVA.
Hints:
? Use the “External Grid” Element in DIgSILENT PF to build the network model and “DIgSILENT Learning Tutorial will Guide to Construct this Model”
? Use “Dynamic Simulation Functionalities Guide” for conducting the dynamic simulations with DIgSILENT PF.
3) Create a 50 ms three-phase short-circuit fault at bus-3 and plot rotor angle and synchronous generator terminal voltage.
4) Increase the fault duration until synchronous generator goes out-of-step and then determine the critical clearing time and angle.
5) In order to compare the simulation results with simplified calculations; use the provided system data to perform the following tasks for your report:
a) When the generator delivers the specified power to the system with the specified terminal voltage, calculate the initial conditions of the generator, i.e. the magnitude of the ideal voltage behind the transient reactance and the rotor angle.
b) While the generator is operating at the specified conditions, a short-circuit occurs on Bus-3 at time t = 0. The fault causes power imbalance in the generator and the rotor angle begins to swing from the initial rotor angle. At the instant the rotor angle swings through 30o from the initial position, the fault is cleared by tripping Line-2 and Line-3.
(i) Calculate the maximum power transfer possible from the generator to the infinite bus under
(1) the pre-fault condition; (2) during the fault and (3) post- fault clearance.
(ii) What is the critical clearing angle for this fault? Compare this with your answer in part 4.
(iii) Will the generator operate stably after this fault? If so, what is the maximum rotor swing?
How to submit your Lab-Report?
The experiment should be performed either in a group of two or individually and the Lab report should be prepared accordingly. The lab report is due One Week after the scheduled Lab Session and should be submitted through Canvas. The experiment and report should include the following:
(i) Screen shot of the DIgSILENT Power Factory single-line diagram with the results for the simulated case including graphs and discussion for tasks 2 to 4 along with the calculations, results and discussions related to task 5. (MS Word or PDF)
(ii) Your DIgSILENT Power Factory *.pfd file should also be submitted with the report.