Information source: http://www.pserc.wisc.edu/ecow/get/publicatio/2005public/

ABSTRACT

    This paper describes how new functions for automated analysis of data collected in substations of an electric power system can be developed. The new functions are first defined and architecture of the integrated substation solution is proposed. Database and user interfacing needs are also presented. Once fully implemented, this solution will serve both local and remote operators allowing further benefits to be drawn from the concept of substation data integration and information exchange.

1 INTRODUCTION

    Development of substation automation systems was taking place for the last decade but the lack of enabling technologies and adequate standards were preventing such applications from becoming widespread. In the last few years the required technology became readily available and various standardization efforts were either completed or are close to a completion.

    The technology area of interest for substation automation is associated with communication interfacing that is specified in the new substation automation standard IEC 61850 [1]. This standard enables interoperability among different Intelligent Electronic Devices (IEDs) that perform various local substation functions. Once all the IEDs can communicate, which the new standard makes possible, one can then start developing new functions that will take advantage of this provision. As a results, a new concept, namely data integration and information exchange (DIIE) can be implemented allowing data from different IEDs to be integrated, information relevant to different users both locally in substations and at remote locations to be extracted, and eventually to be presented to various groups of users.

    One of the main requirements for such an implementation to take place is the compatibility of IEC 61850 with other IEC standards that define applications at the Energy Management System (EMS) and Distribution Management System (DMS). This compatibility is assured through the harmonization process that is currently taking place between IEC 61850, IEC 61970 [2] and IEC 61968 [3].

    This paper addresses the new trends in substation automation by first providing a specification of the new functions and related implementation architecture. Database and user interface requirements are discussed next. Conclusions and references are given at the end.

2 NEW AUTOMATED ANALYSIS FUNCTIONS

     In this section, new automated analysis functions are elaborated. Their goal is to enhance existing automation practices through a new concept of data integration and information exchange (DIIE).

    The Table I lists new automated analysis functions, together with their input/output data and brief description of each function. Most of the functionalities listed are performed locally in the substation, but it is important to note that some of the applications offer system-wide functionalities.

    Applications can be categorized per two main purposes:

    - status tracking.

    - automated analysis.

    The status tracking function provides additional level in the process of data integration that enables verification of data being collected in the substation. There are currently two functions aimed at status tracking: Two-stage State Estimation (TSSE) [4,5] and Substation Switching Sequence Verification (SSSV) [6]. Later one is primarily of local character, while the first one serves both the local and system-wide functions.

    Some of automated functions can be identified as device specific applications that provide automated analysis of data collected by specific IEDs in substation such as Digital Fault Recorder (DFR) [7], Digital Protection Relay (DPR), Power Quality Meter (PQM) [8], Remote Terminal Unit (RTU), Sequence of Events Recorder (SER), Programmable Logic Controllers (PLC), Circuit Breaker Monitors (CBM) [9], and Operator Meter (OPM). Other functions may be identified as substation-wide or even system-wide automated analysis applications. Examples are Fault Analysis including Fault location (FAFL) [10] and Two-stage State Estimation (partially executed as a local function as well) [4,5].

    Currently, four device-specific and two system-wide automated data analysis applications are already developed: Circuit Breaker Monitor Data Analysis (CBMA) [9], Digital Fault Recorder Data Analysis (DFRA) [7], Power Quality Monitor Data Analysis (PQMA) [8], Fault Analysis including Fault Location (FAFL) [10] and two Stage State Estimation [4,5].

     Input data are usually in the COMTRADE [11] file format, while the outputs are reports in an ASCII text file format containing the results of analysis. The developed applications are implemented using both a stand alone approach as well as an approach were they may be incorporated in an EMS solution.

3 NEW ARCHITECTURE

    Figure 1 shows an architecture supporting previously mentioned new automated analysis functions. The DIIE concept is introduced in order to enable implementation of new applications related to substation automation and EMS operation [13].

    All the data collected by substation IEDs has to be stored in a Substation Database. This process is called data integration and it serves the purpose of integration of the data coming from different IEDs, in some cases made by different vendors. Besides the data measured by IEDs, new substation database contains consistent, verified, pre-processed data and reports that are readily available for local and system-wide users or other applications that may be connected to the database.

    Information Exchange serves as a middle layer between the Substation Database and Applications and User interfaces, as shown in Figure 1. It enables the information that is extracted from the database to be sent to the specific applications at the system layer, which in turn serve various users through customized user interfaces.

    Main purpose of the Information Exchange part is to enable:

    - exchange of data, reports and application settings between applications and database;

    - exchange of data and reports between application and database on one side and the user on the other side.

    This DIIE approach enables full utilization of data since data coming from specific IEDs will serve multitude of functions, which was not the case in the past.

Figure 1 - Automated analysis functions

4 DATABASE REQUIREMENTS

    The general requirements for data integration and database implementation can be summarized as follows: capture all the available data from substation IEDs. Provide accurate measurement of all power system parameters of interest; manage and save the information; transfer IED data utilizing either automated file format filters for legacy devices or advanced communication protocols such as IEC 61850 for new IEDs; verify the data. There is a dedicated function called Verification of Substation Database (VSDB) [5,6], which performs collecting, processing and data consistency checking at the substation level. The status tracking function provides additional level in the process of data integration that enables verification of the data being collected in the substation and ensures the database consistency.

     Convert data into useful information. Pre-process the measured data to make them readily available for various applications and users. Preferred file format for all measurement data containing digital samples of monitored signals is COMTRADE. Therefore, file conversion functions enabling conversion of data from raw file formats to the COMTRADE are inseparable part of the substation architecture.

     Enable automated processing of measured and pre-processed data.

     Make the information available for local/substation and system-wide use.

    Figure 2 displays one implementation approach for data integration in the substation. Measurements data are collected from various IEDs which monitor lines, buses, breakers and disconnect switches installed in the substation.

    Three main functions of substation application are:

     Data acquisition. Preferred protocol used for data acquisition and communication is IEC 61850.

     Data display. Event reports, logged files or waveforms of the signals recorded in COMTRADE files are displayed in one unique GUI, which enables comparison of data from various sources.

     Database loader. It automatically loads pre-verified and converted data into the database.

    Figure 2 Concept of data integration at substation level

5 USER INTERFACE

    User interface in can be divided into two categories:

    - substation application user interface, this interface reports to the user data acquisition status and displays raw measurement data;

    - web application user interface, this interface provides remote access to the data stored in the databases.

    List of functions supported by the web application user interface is given in Table II. Interface supports several modes of database searches. Based on user inputs and retrieved data, contents of the pages dynamically changes. Figure 3 displays one example of dynamically created web page [9].

6 IMPLEMENTATION SCENARIO

    Figure 3 Dynamically created web page

5 USER INTERFACE

    At present, development efforts are underway to implement functions discussed in Table I for a specific layout of the substation system. The one-line diagram of the selected substation layout is shown in Figure 4.

    Figure 4 One-line substation diagram

7 CONCLUSIONS

    Based on the discussion given in the paper, several major conclusions can be outlined:

    - Substation automation standards and technology enable easy integration of substation data, which offers many new benefits not available before.

    - In order to explore the new benefits, one has to define new functions that will enhance the capability to analyze system disturbances and monitoring operation of substation equipment.

    - The new functions will take advantage of the data integration and information exchange concept that assumes the multiple uses of data from any given IEDs by various groups of utility staff.

    - All new functions need to be automated so that the analysis is performed in a timely manner and without operator’s intervention.

    - Design of appropriate database and user interface is a critical part of the implementation since this determines how well the different utility staff can get access to the data and information.

ACKNOWLEDGMENT

    The work reported in this paper was supported by a variety of funding sources including DOE-CERTS, Power Engineering Research Center (PSerc), Texas Higher Education Coordinating Board (THECB), CenterPoint Energy and TXU. Many former graduate students contributed to the developments reported in this papers: S. Jakovljevic, C. Nail, Z. Ren, Z. Galijasevic, Y. Liao, X, Xu. The work is continuing with participation of several current graduate students: N. Ved, Y. Wu and X. Luo.

REFERENCES

     1. IEC Std. 61850, “Communication Networks and Systems in Substations”, work in progress, International Electrotechnical Commission, Online.. Available: www.iec.ch.

     2. IEC 61970-301, “ Common Interface Model (CIM),” International Electrotechnical Commission, 2002.

     3. IEC Std. 61968 (Draft), “System Interfaces for Distribution Management,” International Electrotechnical Commission, Online.. Available: www.iec.ch.

     4. S. Zhong, A.Abur, “Implementation of two stage Estimation for Topology Error Identification,” IEEE PES General Meeting, Toronto, Canada, July 2003.

     5. S. Jakovljevic, M. Kezunovic, “Advanced Substation Data Collecting and Processing for State Estimation Enhancement,” IEEE PES Summer Meeting, Chicago, July 2002.

     6. S. Jakovljevic, M Kezunovic, “Software for Enhanced Monitoring in Integrated Substations,” Power Tech 2003, Bologna, Italy, June 2003.

     7. M Kezunovic, T. Popovic, D.R. Sevcik, A. Chitambar, “Requirements for Automated Fault and Disturbance Data Analsysis,” CIGRE Colloquium, SC B5 – Protection, Sydney, Australia, September 2003

     8. M. Kezunovic, Y. Liao, X. Xu, A. Abur, “Power Quality Assessment Using Advanced Modeling, Simulation and Data Processing Tools,” Int’l. Power Quality Conference 2002, Singapore, October 2002

     9. M. Kezunovic, G. Latisko, Z. Ren, D. Sevcik, J. Lucey, E. Koch, W. Cook, “Automated Analysis of Circuit Breaker Operation,” 17th International Conference on Electricity Distribution – CIRED 2003, Barcelona, Spain, May 2003.

     10. M. Kezunovic, S. Luo, D. R. Sevcik, “A Novel Method for Transmission Network Fault Location Using Genetic Algorithms and Sparse Field Recordings,” IEEE PES Summer Meeting, Chicago, July 2002

     11. EC Std. 60255-24, “Common format for transient data exchange (COMTRADE) for power systems”, First Edition 2001-05, International Electrotechnical Commission, 2001.

     12. M Kezunovic, “Data Integration and Information Exchanged for Enhanced Control and Protection of Power Systems,” Hawaii International Conference on Systems Science, Waikoloa Village, HI, January 2003.

    M. Kezunovic, and A. Abur, “Data Integration and Information Exchange: Impact on Future Substation and EMS Applications and Related Implementation Requirements”, EPRI Technical Report, Project #055434, 2004

BIOGRAPHIES

    Mladen Kezunovic (S'77, M'80, SM'85, F'99) has been with Texas A&M University since 1987 where he is the Eugene E. Webb Professor and Director of Electric Power and Power Electronics Institute. His main research interests are digital simulators as well as application of intelligent methods to control, protection and monitoring. Dr. Kezunovic is a registered professional engineer in Texas, and a Fellow of the IEEE.

    Goran Latisko received both his BSc. and MSc. Degrees in El. Engr. from University of Novi Sad, Yugoslavia in 1998 and 2003 respectively. He is currently a research associate at Department of Electrical Engineering at Texas A&M University researching application of information technologies to substation automation and data integration.