An increase in demand for electric power has forced utility transmission systems to continuously operate under stressed conditions, which are close to instability limits.

Operating power systems under such conditions along with inadequate reactive power reserves initiates a sequence of voltage instability points and can ultimately lead to a system voltage collapse. Significant research have been focused on time-synchronized measurements of power systems which can be used to frequently determine the state of a power system and can lead to a more robust protection, control and operation performance. This thesis discusses the applicability of two voltage stability synchrophasor-based indices from literature to analyze the stability of a power system. Various load flow scenarios were conducted on the BPA 10-Bus system and the IEEE 39- Bus System using PowerWorld Simulator. The two indices were analyzed and compared against each other along with other well-known methods. Results show that their performances are coherent to each other regarding to voltage stability of the system; the indices can also predict voltage collapse as well as provide insight on other locations within the system that can contribute to instability



1.1 Introduction

As a result of recent increases in demand for electric power, utility transmission systems have been forced to operate under stressful conditions, often close to instability limits. Efforts to construct new transmission lines or enlarge networks are limited due to economic and environmental constraints. According to U.S. Department of Energy, since 1982, the growth in peak demand for electricity has exceeded transmission growth by almost 25% every year. The deregulation of electricity market has resulted in increased bulk power across interconnected systems. In some utilities, the amount of transactions previously purchased in a year is now managed in one day.  Operating power systems under such conditions along with inadequate reactive power reserves initiates a sequence of voltage instability points and can ultimately lead to a system voltage collapse.

Special attention is being paid to determine methods for assessing voltage stability in real time and developing strategies to mitigate instability issues once they have been detected. Synchronized phasor measurement technology, which is already available at most substation location through protection relays for instance, is capable of directly measuring power system variables (voltage and current phasors) in real time, synchronized to within a millisecond. Together with the improvements on high-speed communication infrastructures, it is possible to build wide area measurement and protection systems to complement classic protection, applications and to prevent cascading system level outages. With this new direction on wide area measurement systems, come new approaches for wide area protection and control functions including generating indices for voltage collapse prevention. There are many studies on voltage stability indices including those based on phasor measurements. Some comparisons between these different indices can be found in later in this work as we proceed.

1.2 Seminar Objectives

The main objective of this seminar is to develop a novel algorithm for voltage stability assessment using synchrophasor data. The analysis will consider proximity to voltage collapse: “How close is the system to voltage instability?” and mechanism of voltage instability: “What are the voltage-weak areas?”

In consideration of these questions, this seminar will begin with a discussion on conventional and newer voltage stability methods presented in chapter 2, an analysis and comparison of two indices based on synchrophasor data using static analysis will be conducted and discussed. Various cases, such as increasing system load/generation and/or N-1 contingency will be created to demonstrate the application of indices in voltage stability analysis. Results will reveal their overall effectiveness in its application to the voltage stability problem. An application of these analyses is then briefly discussed in an investigation on the impact of wind generation on voltage stability considering the intermittent nature of wind generation and penetration level. The studied indices will be used in a case where a modeled wind farm is placed on a bus. Indices will be generated for various test cases. Lastly the novel algorithm for voltage stability measurement will be developed

1.3. Scopes of seminar

This seminar investigated several key aspects of voltage stability using simulated synchrophasor data. Two indices from VSI and VCPI were investigated in order to show how the synchrophasor data can be used to determine how far the entire system is from its voltage collapse point, as well as the weak points in a system. Steady state analysis was conducted using Power World Simulators, and the indices were generated in Matlab. The performances of the indices were tested in the 10 bus- 3-generator system, and a larger network consisting of 39 buses and 10 generators. Results show that their performances are coherent to each other with respect to voltage stability of the system.