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Unformatted text preview: May/June 2009 — Vol. 25, No. 3 21 F E A T U R E A R T I C L E The main causes of failure of SF6 circuit breakers, monitoring proce- dures, and methods of estimating re- maining life-time are reviewed. 0883-7554/07/$25/©2009IEEE Life Management of SF 6 Circuit Breakers based on Monitoring and Diagnosis Key words: Circuit breaker, diagnosis, life management, monitoring Introduction P ower utilities constantly try to cut costs, particularly those re- sulting from equipment failure. Circuit breakers are used to divide the power system into a number of dispersed load points, in order to deal with the limitations of the system and the energy demands of the customers. The reliability of circuit breakers is therefore an important factor in the maintenance of modern power supply systems. The cost of circuit breaker maintenance is increasing due to aging, system expansion, and increased reli- ability requirements. Effective monitoring techniques are neces- sary to provide condition assessment, and thus to identify prob- lems and likely failures sufficiently far in advance. In order to implement a monitoring system, it is necessary to develop a diagnostic system which can be conveniently installed and will accurately reflect the condition of each circuit breaker. In this context, it is important to appreciate the importance of circuit breaker age, operating environment, and risk manage- ment. Survey of Circuit Failures A circuit breaker system can be subdivided as follows: • Components at service voltage, i.e., main and arcing contacts, auxiliary resistors and capacitors, main insu- lation to earth (bushings, oil, and SF 6 ). • Control and auxiliary circuits, i.e., command coils, auxiliary switches and relays, heaters, thermostats, fuses, and lockout devices. • Other components, i.e., mechanical transmission com- ponents, actuator and damping devices, compressors, motors, pumps, pipe work and fittings, and energy stor- age elements. CIGRE  has provided excellent insights into the failure sta- tistics of circuit breaker components. The most common causes of failures are shown in Table 1. Most circuit breaker failures ob- served in the field can be attributed to mechanical problems and auxiliary control circuits. More specifically, 43 to 44% of the major failures are of a mechanical nature, 20 to 29% are related to auxiliary and control circuits, and 21 to 31% can be attributed to problems involving the current path interrupters. These statis- tics can be used as a guideline for the selection of components and parameters to be monitored. Xiang Zhang Institute of Electric Power Systems, Department of High Voltage Engineering, Schering Institute, Leibniz University, Hannover, Germany Jiaosuo Zhang Siemens High Voltage Circuit Breaker Co. Ltd., Hangzhou, P. R. China Ernst Gockenbach Institute of Electric Power Systems, Department of High Voltage Engineering, Schering Institute, Leib- niz University, Hannover, Germany Hossein Borsi Institute of Electric Power Systems, Department of...
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This note was uploaded on 06/08/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.
- Spring '11