Yilu Liu

Power system frequency monitoring network (FNET) implementation

Frequency dynamics is one of the most important measures of an electrical power system status. To better understand power system dynamics, an accurately measured wide-area frequency is needed. The concept of building an Internet-based real-time GPS-synchronized wide-area frequency monitoring network (FNET) was proposed in 2000 by Qiu et al., and this concept has been realized. The FNET system consists of frequency disturbance recorders and an information management system. The FNET has made the synchronized observations of the entire U.S. power network possible with very little cost for the first time. This paper summarizes the implementation of the FNET system and shows some preliminary observations and analyses of the data that have been collected from the FNET.

Wide-Area Frequency Monitoring Network (FNET) Architecture and Applications

Recent developments in smart grid technology have spawned interest in the use of phasor measurement units to help create a reliable power system transmission and distribution infrastructure. Wide-area monitoring systems (WAMSs) utilizing synchrophasor measurements can help with understanding, forecasting, or even controlling the status of power grid stability in real-time. A power system frequency monitoring network (FNET) was first proposed in 2001 and was established in 2004. As a pioneering WAMS, it serves the entire North American power grid through advanced situational awareness techniques, such as real-time event alerts, accurate event location estimation, animated event visualization, and post event analysis. Several papers published in the past several years discussed the FNET structure and its functionality. This paper presents some of the latest implementations of FNETs applications, which add significant capacities to this system for observing power system problems.

A method for determining customer and utility harmonic contributions at the point of common coupling

A new method is proposed in this paper to determine the harmonic contributions of a customer at the point of common coupling. The method can quantify customer and utility responsibilities for limit violations caused by either harmonic source changes or harmonic impedance changes. It can be implemented in current power quality monitors and digital revenue meters. The method makes it possible to develop fair and consistent billing schemes for harmonic distortion control.

An investigation on the validity of power-direction method for harmonic source determination

Power direction method has been used widely to identify the locations of harmonic sources in a power system. A number of utility-customer disputes over who is responsible for harmonic distortions have been settled with the help of the method. A closer examination of the method, however, reveals that it is unable to fulfill the task of harmonic source detection. Case studies can easily show that the method gives incorrect results. In this paper, problems associated with the method are investigated using case studies and mathematical analysis. The results show that the power direction method is theoretically incorrect and should not be used to determine harmonic source locations. Main cause of the problem is that the direction of active power flow is a function of the phase angle difference between the two sources. The direction of reactive power flow, on the other hand, has a better correlation with the source magnitudes.

Wavelet Networks in Power Transformers Diagnosis Using Dissolved Gas Analysis

Wavelet networks (WNs) are an efficient model of nonlinear signal processing developed in recent years. This paper presents a comparative study of WN efficiency for the detection of incipient faults of power transformers. After 700 groups of training and testing gases-in-oil samples are processed by fuzzy technology, we compare and analyze the network training process and simulation results of five WNs which include two types of WNs with two different activation functions and evolving WN. A lot of diagnostic examples show that the diagnostic accuracy and efficiency of the proposed five WN approaches prevail those of the conventional back-propagation neural-network method and are suitable for faults diagnosis of power transformers, especially with the evolving WN achieving superior performance.

Robust Energy Management of Microgrid With Uncertain Renewable Generation and Load

A scenario-based robust energy management method accounting for the worst-case amount of renewable generation (RG) and load is developed in this paper. The economic and robust model is formulated to maximize the total exchange cost while getting the minimum social benefits cost at the same time. Uncertainty of RG and load is described as an uncertain set produced by interval prediction. Then, the Taguchis orthogonal array (OA) testing method is used to provide possible testing scenarios. A simple, but practical, search strategy based on OA is designed for solving the optimization problem. By optimizing the worst-case scenario, the energy management solution of the proposed model is robust against most of the possible realizations of the modeled uncertain set by Monte Carlo verification. Numerical cases on the typical microgrid system show the effectiveness of the model and solution strategy. In addition, the influence of exchange electricity price and other parameters are also discussed in the cases.

Wide-area Frequency Based Event Location Estimation

This paper discusses the latest developments in wide-area frequency-based event location using FNET. FNET, meaning ldquoInternet based frequency monitoring networkrdquo, is a low cost and quickly deployable wide-area frequency measurement system with high dynamic accuracy. This project demonstrated the feasibility of using information from FNET to estimate the location of events in the electric grid. An on-line real time event detection tool using least squares methods was developed and tested on data from FNET. This paper outlines the methods used along with an examination of implementation feasibility.

Power system event location analysis using wide-area measurements

Power system frequency can tell volumes about the health and state of a power system. Moreover, the manner in which angle and frequency perturbations travel throughout the power grid has been closely studied in the past. Such perturbations are known to propagate throughout the grid as a function of time and space. Using measurements from a wide-area frequency monitoring network (FNET), one can observe the electromechanical wave signature of power system events in frequency data. In this paper, a brief synopsis of FNET is presented along with an analysis of several generator tripping events. The analysis is comprised of several event location methods and resulting observations. The eventual goal of this research is to formulate a robust event location algorithm that can be used online and in real-time to locate with sufficient accuracy the hypocenter of power system events irrespective of utility boundaries

Frequency Sensitivity and Electromechanical Propagation Simulation Study in Large Power Systems

A global view of power systems frequency behavior opens up a new window for analyzing systems dynamics. With the aid of global positioning system, measurements from different locations would have synchronous time; therefore a system-wide observation and analysis would be possible. As part of the US-wide power frequency monitoring network project this paper focus on simulation study results of power frequency dynamics of the Eastern U.S. system. The study assesses the frequency measurement accuracy needed to observe frequency dynamics from events such as remote generation drops. Electromechanical-wave propagation phenomena during system disturbances have been observed. The speeds of electromechanical-wave propagation in different areas of the U.S. systems were estimated and their characteristics were discussed.

Analysis of Power System Disturbances Based on Wide-Area Frequency Measurements

It is very important to understand system dynamics during disturbances in order to improve control measures to ensure power system security and reliability. Power system disturbances are examined in this paper based on wide-area frequency data from a nation-wide frequency monitoring network (FNET). Frequency characteristics of events in three major North America power grids are investigated. Typical frequency patterns of generation loss and load drop events are analyzed for Eastern Interconnection system, Western Electricity Coordinating Council system, and Electric Reliability Council of Texas system. The recovery patterns following disturbances are also studied to evaluate control performances of the interconnections.