External network modeling-recent practical experience

Abstract

The pu'pose of this paper is to discuss recent practical experience in external network modeling at a number of utility control centers.This paper presents a set of short notes that discuss w e n t practical experiences on external network modeling. The introduction provides a framework for the rest of the short notes by discussing network representation, modeling issues, unobservable internal models versus unreduced external models, and data for the unobservable network The first short note discusses the solution methods consisting of power flow, one pass SE, and two pass S E The remaining short notes discuss recent practical experience on external network modeling at a number of utility control ceqters. The last short note describes techniques for developing REI equivalents. INIRODUCnONAs on-line security assessment becomes more prevalent in utility control centers, the need for understanding the problems of external network modeling increases. This paper presents eight short notes that describe various aspects of making external network modeling work in utility control centers. The first short note discusses specific methods of external network solution techniques. The remaining seven short notes relate practical experience in modeling and solving external networks for real-time security assessment. The contributors represent a variety of utility network sizes from small to large. Likewise, the utility control centers reported in this paper have varyihg amounts of real-time power system data ranging from only tie-line flows to large quantities of real-time inter-utility data exchange. The techniques used by the contributors span a wide range, including REI equivalents and specialized linear programming algorithms.It will be observed that there is a wide diversity in external network representation and solution techniques in this report. This diversity is caused by differences in power system characteristics, availability of external network data, availability of the external network modeling techniques and software during the development/implementation of the control centers, and experience of the developer/implementer. There does not appear to be a single, universal external network modeling approach that works uniformly well across the spectrum of power systems reported in this paper. The diversity of approaches is a reflection of this fact. WM 164-4 PWRSby the IEEE Power System Engineering Committee of the IEEE Power Engineering Society for presentation at the IEEE/PES 1993 Winter Meeting, Columbus, OH, January 31 -February 5, 1993. Manuscript submitted September 1, 1992; made available for printing November 30, 1992. A paper recommended and approvedIt should be understood that the issues of external network modeling occur only when network analysis functions, such as Contingency Analysis, Optimal Power Flow, and Dispatcher Training Simulator, are involved.Clearly, an external model is not needed for internal state estimation.Presentation and discussion of numerical test results are impractical UNREDUQZD MO...

Enhancement of network monitoring & security analysis using phasor measurement units

“…It is well documented that the external network model is valid as long as the external system state is equal to the base case solution [65], [76], [77]. This is certainly not the case due to the load variations taking place continuously in the entire system.…”

“…In the Ward equivalent [63], the external power system is represented with a fixed admittance matrix as well as an injection at the boundary buses. As explained in [64], and [65] the major problem with these traditional methods is their incapability in accurately modeling of external system behavior in case of change of operating condition. Many extensions of Wards and REI methods are available such as the one represented in [65], [66] whose objective is to deal with the linearity problem.…”

“…As explained in [64], and [65] the major problem with these traditional methods is their incapability in accurately modeling of external system behavior in case of change of operating condition. Many extensions of Wards and REI methods are available such as the one represented in [65], [66] whose objective is to deal with the linearity problem. The proposed method is to represent the external reactive power response to the shift in internal system.…”

“…The proposed method is to represent the external reactive power response to the shift in internal system. [65], [70], [71], [72] propose a method which represents the equivalent network with a reduced model of external system obtained from off-line studies. Next, the equivalent is updated in real-time to match the internal network solution at the boundaries.…”

“…The problem of external network modeling is well investigated by various researchers in the past several decades. The methods developed and presented in [65], [70], [73], and [79] address the issue of developing and maintaining external network equivalents based on real-time data available in the internal system. Measurements from the external system are assumed not to be readily available, at least not in large numbers.…”