986 IEEE TRANSACTIONS ON POWER SYSTEMS, VOL. 18, NO. 3, AUGUST 2003 User-Friendly, Open-System Software for Teaching Protective Relaying Application and Design Concepts Mladen Kezunovic, Fellow, IEEE Abstract—This paper describes modeling and simulation software developed specifically for teaching protective relaying application and design concepts. The emphasis was on imple- menting user-friendly and open-system solution that will allow an easy use and straight-forward future expansion. This is achieved by introducing new libraries of signal sources and relay elements developed for the SIMULINK environment of MATLAB. Com- bined with the power block set (PBS) toolbox of MATLAB, the mentioned libraries allow for a variety of studies aimed at better understanding protective relay design approaches, and related applications. Index Terms—Electromagnetic transient program, faults, protective relaying, relaying schemes, time-domain simulation, transients. I. INTRODUCTION P ROTECTIVE relaying is a complex electrical engineering field requiring knowledge from a number of diverse engineering disciplines such as electromagnetics, circuits, power systems, computers, communications, signal processing, controls, intelligent systems, etc. Teaching protective relaying application and design concepts involves a multidisciplinary approach where the physics of the fundamentals together with diverse mathematical formulations need to be merged in a common framework. One convenient and yet powerful way is to use modeling and simulation as the common framework [1]. To be efficient, such a framework needs to be user-friendly and amenable to future expansions as the continued needs to incorporate new developments grow. This paper describes a de- velopment of the software aimed at meeting such requirements. Recently published IEEE survey paper discussing different approaches to modeling protective relays and related power system events indicates a variety of possible software tools that may be used for this purpose [2]. Well-known software packages can be used to simulate power system faults in both the time-domain (electromagnetic transients) [3]–[5] and phasor (unbalanced steady state) [6]–[8] modes. Some of the packages have the provision for incorporating protective relay models developed by the user [9], [10] while the others have the generic relays models already included [6]–[8]. In all of the mentioned cases, it is difficult to add the modeling and sim- ulation features to teach specific protective relaying concepts that go beyond the level of detail originally provided by the Manuscript received November 19, 2001; revised April 28, 2002. This work was supported in part by the National Science Foundation under Grant ECS-96- 19294 and in part by EPRI under Contract WO 8618-02. M. Kezunovic is with the Department of Electrical Engineering, Texas A&M University, College Station, TX 77843-3128 (e-mail: kezunov@ee.tamu.edu). Digital Object Identifier 10.1109/TPWRS.2003.814849 software. Additions of new relay models and implementations of specific fault scenarios as well as the flexibility of changing the way the models of relays and power system interact is constrained by the specific user and programming interface rules embedded in the existing software. To facilitate the mentioned user tasks, a specialized teaching software environment is developed using a commercial software that was built to allow for flexibility in providing user inter- faces and implementing custom models. The MATLAB soft- ware package with SIMULINK support and Power Block Set toolbox [11]–[14] is utilized to develop customized model li- braries for teaching protective relaying concepts. This paper provides details of this development and indicates how the user- friendly interface and open-system goals are achieved. The paper starts with discussion of the reasons for using MATLAB and associated tools. Developments of new libraries are described next. The use of the overall solution in teaching the relaying concepts is also presented. Conclusions are given at the end. II. MODELING PROTECTIVE RELAYS IN MATLAB MATLAB has been selected as the programming shell for the new protective relay modeling software. Particular factors that support the selection of MATLAB are [11]–[14] a) MATLAB is a de-facto standard that already dominates the university environment and is more and more recognized in industry including the power engineering field. b) A flexible software structure of MATLAB comprising li- braries, models, and programs enables one to integrate different model components in one package conveniently. c) MATLAB and its time domain solver SIMULINK create a friendly and open system. New models and libraries may be just added to the package without deep knowledge nor modification of the existing parts. This is very useful if the user is also involved in continued development of the software. d) Fast-development with MATLAB using powerful calcula- tion and visualization means of the package enables one to expand the software quickly and efficiently without de- veloping any extra programming tools. e) A wide selection of TOOLBOXes, comprehensive collec- tions of predefined functions for solving application-spe- cific problems, is already available with MATLAB and is likely to grow even faster in the future. f) Power system blockset, one of the latest extensions of MATLAB, is enabling modeling the basic components of power systems. It provides computations similar to 0885-8950/03$17.00 © 2003 IEEE