PRESENTED BY:
SAHAJA KARRE,
HIMASRI VEMULA

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REAL-TIME MONITORING AND ASSESSMENT OF CIRCUIT BREAKER OPERATIONS FOR DIAGNOSTICS AND CONTROL APPLICATIONS
Abstract:
Circuit breakers (CBs) are very important elements in the power system. They are used to switch other equipment in and out of service. Circuit breakers need to be reliable since their incorrect operation can cause major issues with power system protection and control. Today’s practice in monitoring circuit breaker operation and status in real time is reduced to the use of Remote Terminal Units (RTUs) of Supervisory Control and Data Acquisition (SCADA) system to assess CB status. More detailed information about the control circuit performance may be obtained by CB test equipment typically used for maintenance diagnostics.
This paper addresses two important issues:a) how improved CB monitoring may be implemented in real-time, and b) what would be the benefits of such an implementation. The results reported in this paper are coming from two research projects, conducted using funding from Center Point Energy and DOE-CERTS aimed at development of software for automated analysis of CB data and the other covering development of the CB data acquisition unit respectively. The paper is devoted to description of a prototype implementation of a real-time CB monitoring system. The system consists of a new CB monitoring data acquisition IED that is located at circuit breaker and captures detailed information about its operation in real-time. The CB files are transferred to the concentrator PC where the application software performs automated analysis and makes an assessment about the operational status of the breaker. The software is based on signal processing and expert system processing. Application example using actual field data is discussed The paper ends with some conclusions, acknowledgments and a list of references.
Introduction:
System wide real-time monitoring of circuit breaker operation and statuses currently is implemented using Remote Terminal Units (RTUs) of Supervisory Control and Data Acquisition (SCADA) system. Based on detected voltage levels on circuit breaker contacts, these units are providing information on final statuses of the circuit breakers such as “OPEN” or “CLOSE”. The transitions in time of control signals, such as Trip or Close Initiate, X and Y coil currents, Control and Yard DC voltages, Closing Coil and others, used by protection and maintenance engineers for evaluation of CB performance cannot be monitored using RTU and SCADA approach. A solution called Circuit Breaker Monitoring and Analysis (CBMA) developed at Texas A&M University, intends to solve described problems by integrating customized software and hardware solutions into a single, real-time monitoring and analysis system.
The system for real-time monitoring and analysis of circuit breaker operations described in this paper is an extension of widely used portable circuit breaker testing device concept. The traditional testing devices are temporally connected to the circuit breaker’s control circuit to record analog and digital signals. The operator opens and closes the circuit breaker each time the test is performed and data are recorded. The traditional analysis is done manually by overlaying traces from a “good” case recorded earlier and making a judgment of how different the new case is.
The new solution is based on a new CB monitoring data acquisition IED called Circuit Breaker Monitor (CBM), which would be permanently connected, to the substation CBs. CBM captures detailed information about each CB operation in real-time, regardless of whether the operation is initiated manually by the operator or automatically by the protection and control equipment and stores them in COMTRADE file format. As soon as the relevant CB control circuit signals are recorded and transmitted by wireless page link to the concentrator PC, analysis software automatically performs the analysis.
CBMA provides better understanding of the condition and operating performance of each individual breaker by monitoring and analyzing expanded set of analog and digital signals from circuit breaker control circuitry. The advanced signal processing algorithms and knowledge base of the expert system implemented in the analysis software, significantly improve the reliability and consistency of the analysis results. Thanks to the fast and low cost CBM devices, new monitoring and control system described in this paper, enables permanent, real time monitoring of status and performance of circuit breakers for the entire network.
In the first section of the paper, architecture of the whole system and basic processing algorithm are described. Second section explains the structure and basic functions of the hardware part of the system. Focus of the following section is on the organization of analysis software of the CBMA system. Basic building blocks, such as signal processing and expert system are elaborated and brief overview of knowledge base rules is given. At the end, an example of the stuck breaker case is illustrated with waveforms of relevant signals and expert system rules involved in problem detection process.
Architecture of CBMA system:
The CBMA system supports client/server architecture. The client part resides in substation. It consists of the CBM devices attached to the CBs and a software running on concentrator PC, both permanently installed in the substation, as shown in Figure 1.
CBMA system architecture
When breaker operates, recorded files are wirelessly transmitted to the concentrator PC. The client application automatically performs the analysis of recorded signals from the circuit breaker control circuit. For more efficient data manipulation, IEEE file naming convention is used for naming the recordings files. The signal-processing module of the analysis software extracts various parameters from recorded signal samples and expert system evaluate them against empirically obtained values and tolerances selected for specific type of circuit breaker.
The resulting report describes detected abnormalities and possible causes of the problem. If discovered problem presents serious threat to the reliability of future circuit breaker operation, programmable notification is sent to the server located in the central office. The notification is then processed and a warning is sent via email or pager to the maintenance and protection personal. Reporting is provided for both local and geographically dislocated users through implementation of local database and web server supporting information exchange through dynamic HTML pages.
Recorded files and reports can be downloaded to the server via Ethernet network relying on standard, fast and reliable TCP/IP protocol. In the central office or control center, the server part of CBMA consisting of the analysis module, a central database and master web server is running. The central database allows for easy archiving and retrieving of the records and analysis reports from all system substations. Master web application allows remote users to search for the records and/or analysis reports from anywhere on the corporate network (intranet).
Description of CBMA Hardware:
The system hardware in substation consists of circuit breaker monitors located on each breaker in the switchyard and a concentrator PC, used for gathering data, placed in the control room.
Circuit Breaker monitor IED:
The circuit breaker monitor IED (CBM) has three main tasks:
Perform data acquisition of signals from the Circuit Breaker control circuit and record sequences of tripping and closing
Convert captured signals into files according to COMTRADE file specifications Transmit files wirelessly to the concentrator device