Jeffery E. Dagle

Impacts of the distributed utility on transmission system stability

The distributed (or dispersed) utility concept is rapidly becoming a reality in some service areas. In this framework, modular generation and storage assets along with selected demand-side management programs are used in place of the more traditional infrastructure upgrades to ensure reliable service to a group of utility customers. From among the many technical challenges associated with the proliferation of distributed resources, this paper deals with the impacts of distributed architectures upon the bulk transmission system. Bulk transmission system transient and small-signal stability are addressed through the use of extensive case studies. Planning tools and methods are discussed, and some general conclusions related to stability issues are drawn.

Improving small signal stability through operating point adjustment

ModeMeter techniques for real-time small-signal stability monitoring continue to mature, and more and more phasor measurements are available in power systems. It has come to the stage to bring modal information into real-time power system operation. This paper proposes to establish a procedure for Modal Analysis for Grid Operations (MANGO). Complementary to PSS and other traditional modulation-based control, MANGO aims to provide suggestions such as redispatching generation for operators to mitigate low-frequency oscillations. Load would normally not be reduced except as a last resort. Different from modulation-based control, the MANGO procedure proactively maintains adequate damping at all times, rather than reacting to disturbances when they occur. The effect of operating points on small-signal stability is presented in this paper. Implementation with existing operating procedures is discussed. Several approaches for modal sensitivity estimation are investigated to associate modal damping and operating parameters. The effectiveness of the MANGO procedure is confirmed through simulation studies of several test systems.

Initial Results in Using a Self-Coherence Method for Detecting Sustained Oscillations

Summary form only given. This paper develops a self-coherence method for detecting sustained oscillations using phasor measurement unit (PMU) data. Sustained oscillations decrease system performance and introduce potential reliability issues. Timely detection of the oscillations at an early stage provides the opportunity for taking remedial reaction. Using high-speed time-synchronized PMU data, this paper details a self-coherence method for detecting sustained oscillation, even when the oscillation amplitude is lower than ambient noise. Simulation and field measurement data are used to evaluate the proposed methods performance. It is shown that the proposed method can detect sustained oscillations and estimate oscillation frequencies with a low signal-to-noise ratio. Comparison with a power spectral density method also shows that the proposed self-coherence method performs better.

MANGO – Modal Analysis for Grid Operation: A Method for Damping Improvement through Operating Point Adjustment

Small signal stability problems are one of the major threats to grid stability and reliability in the U.S. power grid. An undamped mode can cause large-amplitude oscillations and may result in system breakups and large-scale blackouts. There have been several incidents of system-wide oscillations. Of those incidents, the most notable is the August 10, 1996 western system breakup, a result of undamped system-wide oscillations. Significant efforts have been devoted to monitoring system oscillatory behaviors from measurements in the past 20 years. The deployment of phasor measurement units (PMU) provides high-precision, time-synchronized data needed for detecting oscillation modes. Measurement-based modal analysis, also known as ModeMeter, uses real-time phasor measurements to identify system oscillation modes and their damping. Low damping indicates potential system stability issues. Modal analysis has been demonstrated with phasor measurements to have the capability of estimating system modes from both oscillation signals and ambient data. With more and more phasor measurements available and ModeMeter techniques maturing, there is yet a need for methods to bring modal analysis from monitoring to actions. The methods should be able to associate low damping with grid operating conditions, so operators or automated operation schemes can respond when low damping is observed. The work presented in this report aims to develop such a method and establish a Modal Analysis for Grid Operation (MANGO) procedure to aid grid operation decision making to increase inter-area modal damping. The procedure can provide operation suggestions (such as increasing generation or decreasing load) for mitigating inter-area oscillations.

North American SynchroPhasor Initiative

In 2007, the U.S. Department of Energy (DOE) and the North American Electric Reliability Corporation (NERC), along with involved electric utility companies and other organizations, formed the North American SynchroPhasor Initiative (NASPI). This effort combines the previous Eastern Interconnection Phaser Project (EIPP) and various activities associated with wide area measurement system (WAMS) research, development, and deployment activities that have been underway in the North American electric power system for a number of years as the primary focal point for continued DOE and NERC support and facilitation. This paper provides an update on this activity, building on a paper presented at last years forum (Widergren et al., 2007).

North American SynchroPhasor Initiative - An Update of Progress

In 2007, the U.S. Department of Energy (DOE) and the North American Electric Reliability Corporation (NERC), along with involved electric utility companies and other organizations, formed the North American SynchroPhasor Initiative (NASPI). The goal of NASPI is to improve power system reliability through wide-area measurement, monitoring and control. This will be achieved by facilitating a robust, widely available and secure synchronized data measurement infrastructure for the interconnected North American electric power system. It also includes associated analysis and monitoring tools for better planning and operation, and improved reliability. With funding from the American Recovery and Reinvestment Act of 2009, several smart grid investment grant and demonstration projects have recently been selected for award that will significantly advance synchrophasor technology. This paper provides an update on NASPI with current status and work underway.

SynchroPhasor measurements: System architecture and performance evaluation in supporting wide-area applications

The infrastructure of phasor measurements have evolved over the last 15 years from isolated measurement units to networked measurement systems with footprints beyond individual utility companies. This phasor measurement network, to a great extent, is a bottom-up self-evolving process except some local systems built by design. Given the number of phasor measurement units (PMUs) in the system is small (currently about 70 in each of the western and eastern interconnections in North America), the current phasor network architecture satisfies todaypsilas operational requirements. However, the architecture will become a bottleneck when large number of PMUs are installed (e.g. Gt1000~10000). The need for phasor architecture design has yet to be addressed. This paper reviews the current phasor networks and investigates future architectures, as related to the efforts undertaken by the North American SynchroPhasor Initiative (NASPI). Then it continues to present staged system tests to evaluate the performance of phasor networks, which is a common practice in the Western Electricity Coordinating Council (WECC) system. This is followed by field measurement evaluation and the implication of phasor quality issues on phasor applications.

Successes and Challenges for Synchrophasor Technology: An Update from the North American SynchroPhasor Initiative

The North American SynchroPhasor Initiative is a collaboration between the electric industry, NERC and U.S. DOE to advance the use of synchrophasor technology for improved grid reliability. Over the past year NASPI members have completed drafting or updating several key technical interoperability standards and guidelines, helped recipients of federal ARRA awards to plan and implement Smart Grid Investment Grants, written a guideline to phasor technology, developed new guidance for phasor measurement unit location, and advanced the design and built key elements of new phasor data systems, including Phasor Gateways, Phasor Data Concentrators and a Phasor Signal Registry. NASPI holds three well-attended conferences each year to share information and work on new issues and challenges.

Autonomous Demand Response for Primary Frequency Regulation

The research documented within this report examines the use of autonomous demand response to provide primary frequency response in an interconnected power grid. The work builds on previous studies in several key areas: it uses a large realistic model (i.e., the interconnection of the western United States and Canada); it establishes a set of metrics that can be used to assess the effectiveness of autonomous demand response; and it independently adjusts various parameters associated with using autonomous demand response to assess effectiveness and to examine possible threats or vulnerabilities associated with the technology.

Deriving optimal operational rules for mitigating inter-area oscillations

This paper introduces a new method for mitigating inter-area oscillations of a large scale interconnected power system by means of generation re-dispatch. The optimal mitigation procedures are derived by searching for the shortest distance from current operating condition to a targeted operating condition with the desired damping ratio of the oscillation mode. A sensitivity-based method is used to select the most effective generators for generation re-dispatch and decision tree is trained to approximate the security boundary in a space characterized by the selected generators. The optimal operational rules can be found by solving an optimization problem where the boundary constraints are provided by the decision tree rules. This method is tested on a Western Electricity Coordinating Council (WECC) 179-bus simplified model and simulation results have demonstrated the validity of the decision-tree-based method and shown promising application in real time operation.