Circuit breakers are crucial components for power system operations. They play an important role in switching for the routine network operation and protection of other devices in power systems. To ensure circuit breakers are in healthy condition, periodical inspection and preventive maintenance are typically performed. The maintenance schedules and routines usually follow the recommendation of circuit breaker vendors, although the recommended schedules may be conservative.
New maintenance techniques and methodologies are emerging, while the circuit breakers keep improving in their designs and functions . As an example, some new circuit breakers have embedded monitoring instruments available to measure the coil current profiles and the operation timing . The recorded information can be used to monitor the condition of breakers during each operation. In this case, it may be more appropriate to replace the time-directed maintenance by condition-directed maintenance practice . When applied properly, both the size of the maintenance crew and maintenance cost may be reduced greatly with this approach. Since the number of circuit breakers in a power system is usually very big, a small maintenance cost saving per each circuit breaker can accumulate to a considerable benefit for the whole system. A more systematic solution is
Reliability Centered Maintenance (RCM), which can be used to select the most appropriate maintenance strategy.
During the maintenance or repair work, the maintenance crew will need to access information distributed across the utility and stored using different data formats. By equipping the crew with new information access methods to replace the old paper-based information exchange and logging method, the efficiency may be improved since less time will be spent on preparation, reporting and logging. An information access method that is capable of handling heterogeneous information sources will be helpful to achieve the above goal. Also, the new information access method should be secure and able to work on unreliable public networks.
The mobile agent software provides a flexible framework for mobile agent applications. An agent application program can travel through the internet/intranet to the computers where the mobile agent server or transporter is running. The mobile agent software also supports Distributed Events, Agent Collaboration and Service Bridge. Compared with client server systems, an agent can process the data locally and thus reduce the network traffic. Besides, the Java platform encapsulates the network layer from the agent, which makes the programming easier. The mobile agent software may fit very well in the circuit breaker maintenance scenario. In this paper, we considered how mobile agent software might be applied in circuit breaker maintenance and monitoring from the viewpoint of the maintenance crew.
CIRCUIT BREAKER MAINTENANCE TASKS
The maintenance of circuit breakers deserves special consideration because of their importance for routine switching and for protection of other equipment. Electric transmission system breakups and equipment destruction can occur if a circuit breaker fails to operate because of a lack of a preventive maintenance. The need for maintenance of circuit breaker is often not obvious as circuit breakers may remain idle, either open or closed, for long periods of time. Breakers that remain idle for six months or more should be made to open and close several time in succession to verify proper operation and remove any accumulation of dust or foreign material on, moving parts and contacts.
The circuit breakers mainly consist of the interrupter assembly (contacts, arc interrupters and arc chutes), operating mechanism, operation rod, control panel, sealing system, and breaking medium (SF6, oil, vacuum and air). To ensure the performance of a circuit breaker, all the components should be kept in good condition; therefore time-directed preventive maintenance has been widely adopted. The preventive maintenance tasks include periodic inspection, test, and replacement of worn or defective components and lubrication of the mechanical parts. The maintenance intervals are usually determined using experiences or following the recommended schedules provided by the vendor or standard.
The maintenance practices can be divided into three categories: corrective maintenance, preventive maintenance, and predictive maintenance.