ABSTRACT In this thesis, relationship between two most important transient stability indices, critical clearing time and generator rotor angle is examined for one machine-infinite bus system and then extended to the multimachine case and is observed to be linear. By using the linear relationship between critical clearing time and generator rotor angle and utilizing the daily load curve, a new preventive method is proposed. The aim of this method is to make all critical clearing times longer than the relay and circuit breaker combination operation time. In the proposed method, desired critical clearing times are obtained by using on line system data and daily load curves. Then desired values are adjusted by generators output rescheduling and terminals voltage control Visual computer language is used for graphical and numerical solutions. Comprehension of one machine infinite bus system and multimachine system transient stability become easier.

abstract: Electric power system security assessment is one of the most important requirements for operational and resource planning of the bulk power system ensuring safe operation of the power system for all credible contingencies. This deterministic approach usually provides a conservative criterion and can result in expensive bulk system expansion plans or conservative operating limits. Furthermore, with increased penetration of converter-based renewable generation in the electric grid, the dynamics of the grid are changing. In addition, the variability and intermittency associated with the renewable energy sources introduce uncertainty in the electricity grid. Since security margins have direct economic impact on the utilities; more clarity is required regarding the basis on which security decisions are made. The main objective of this work is to provide an approach for risk-based security assessment (RBSA) to define dynamic reliability standards in future electricity grids. RBSA provides a measure of the security of the power system that combines both the likelihood and the consequence of an event. A novel approach to estimate the impact of transient stability is presented by modeling several important protection systems within the transient stability analysis. A robust operational metric to quantify the impact of transient instability event is proposed that incorporates the effort required to stabilize any transiently unstable event. The effect of converter-interfaced renewable energy injection on system reliability is investigated us-ing RBSA. A robust RBSA diagnostics tool is developed which provides an interactive user interface where the RBSA results and contingency ranking reports can be explored and compared based on specific user inputs without executing time domain simulations or risk calculations, hence providing a fast and robust approach for handling large time domain simulation and risk assessment data. The results show that RBSA can be used effectively in system planning to select security limits. Comparison of RBSA with deterministic methods show that RBSA not only provides less conservative results, it also illustrates the bases on which such security decisions are made. RBSA helps in identifying critical aspects of system reliability that is not possible using the deterministic reliability techniques. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2017

Indiana University-Purdue University Indianapolis (IUPUI) / The thesis extends the work done in [1] [2] by Rovnyak, et al. where the authors have described about transient event prediction and response based one shot control using decision trees trained and tested in a 176 bus model of WECC power system network. This thesis contains results from rigorous simulations performed to measure robustness of the existing one shot control subjected to missing PMU's data ranging from 0-10%. We can divide the thesis into two parts in which the first part includes understanding of the work done in [2] using another set of one-shot control combinations labelled as CC2 and the second part includes measuring their robustness while assuming missing PMU's data. Previous work from [2] involves use of decision trees for event detection based on different indices to classify a contingency as a 'Fault' or 'No fault' and another set of decision trees that decides either to actuate 'Control' or 'No control'. The actuation of control here means application of one-shot control combination to possibly bring the system to a new equilibrium point which would otherwise attain loss of synchronism. The work done in [2] also includes assessing performance of the one shot control without event detection. The thesis is organized as follows- Chapter 1 of the thesis highlights the effect of missing PMUs' data in a power system network and the need to address them appropriately. It also provides a general idea of transient stability and response of a transient fault in a power system. Chapter 2 forms the foundation of the thesis as it describes the work done in [1] [2] in detail. It describes the power system model used, contingencies set, and different indices used for decision trees. It also describes about the one shot control combination (CC1) deduced by Rovnyak, et.al. of which performance is later tested in this thesis assuming different missing data scenarios. In addition to CC1, the chapter also describes another set of control combination (CC2) whose performance is also tested assuming the same missing data scenarios. This chapter also explains about the control methodology used in [2]. Finally the performance metrics of the DTs are explained at the end of the chapter. These are the same performance metrics used in [2] to measure the robustness of the one shot control. Chapter 2 is thus more a literature review of previous work plus inclusion of few simulation results obtained from CC2 using exactly the same model and same control methodology. Chapter 3 describes different techniques of handling missing data from PMUs most of which have been used in and referred from different previous papers. Finally Chapter 4 presents the results and analysis of the simulation. The thesis is wrapped up explaining future enhancements and room for improvements.

Ever increasing demand for electricity, exploitation of large hydro and nuclear power at remote location has led to power evacuation by long EHV/UHV transmission systems. This thesis concentrates on transient analysis of EHV/UHV transmission systems for improved planning and protection. In this thesis, the uncontrolled and controlled switching methods to limit the switching surges during energization of 765kV and 1200k VUHV transmission lines are studied. The switching surge over voltages during the energization of series compensated line are compared with uncompensated line. A Generalized Electromagnetic Transients Program has been developed. The program incorporates specific models for studying the effectiveness of various means for control of switching surge over voltages during UHV transmission line energization and also simulation of various types of faults. Since power grids may adopt next higher UHV transmission level 1200kV, these studies are necessary for insulation coordination as well as transmission line protection relay settings. A new fault detection/location technique is presented for transmission line using synchronized fundamental voltage and current phasors obtained by PMUs at both ends of line. It is adaptive to fault resistance, source impedance variation, line loading and fault incidence angle. An improved Discrete Fourier Transform (DFT) algorithm to estimate and eliminate the decaying dc component in a fault current signal is proposed for computing the phasors. The settings for digital distance relays under different operating conditions are obtained. The relay should operate faster and be more sensitive to various faults under different conditions without loosing selectivity. An accurate faulted transmission line model which considers distributed shunt capacitance has been presented. The relay trip boundaries are obtained considering transmission line model under realistic fault conditions. For different loading conditions ideal relay characteristic has been developed. The obtained trip boundaries can be used for proper settings of practical relay. An adaptive relaying scheme is proposed for EHV/UHV transmission line using unsynchronized/synchronized fundamental voltage and current phasors at both ends of line. For fault location, the redundancy in equations is achieved by using two kinds of Clarke’s components which makes the calculations non-iterative and accurate. An operator for synchronization of the unsynchronized measurements is obtained by considering the distributed parameter line model. The distance to fault is calculated as per the synchronized measurements. Support Vector Machine(SVM) is used for high speed protection of UHV line. The proposed relaying scheme detects the fault and faulted phase effectively within few milli seconds. The current and voltage signals of all phases at the substation are fed to SVM directly at a sampling frequency of 1.0kHZi.e20 samples/cycle . It is possible to detect faulted phase with in 3msec, using the data window of 1/4th cycle. The performance of relaying scheme has been checked with a typical 765kV Indian transmission System which is simulated using the developed EMTP.