In 2009, the Consolidated Edison Company of New York saved approximately US$3 million using the circuit breaker maintenance ranking tool of the Electric Power Research Institute (EPRI). These costs are expected to continue annually as a result of the extended time intervals between major maintenance inspections of the utility's high-voltage circuit breakers. Additionally, expectations are for enhanced equipment reliability since the circuit breaker maintenance ranking (CBMR) tool directs attention toward equipment most likely in need of maintenance while minimizing unnecessary maintenance.

Three-Pronged Approach

Con Edison's circuit breaker replacement and maintenance program was developed to maintain equipment in a reliable, safe condition, capable of delivering the desired levels of operational availability and performance in a cost-effective manner. The program uses a three-pronged approach to determine the need for maintenance or replacement of a particular circuit breaker or class of circuit breakers:

• The first prong uses in-service monitoring and out-of-service diagnostic tools and tests to determine the condition of the circuit breaker.

• The second prong uses data collected during the teardown, overhaul or inspection of circuit breakers to predict the condition of other circuit breakers of the same type.

• The third prong uses EPRI's CBMR tool to assist in determining the condition of the circuit breaker.

A circuit breaker peer group — consisting of subject matter experts from engineering, maintenance and asset management — then directs the circuit breaker maintenance program and replacement program in accordance with predefined criteria. The first two prongs of the approach also provide information to refine the ranking calculations.

Maintaining Reliability on a Budget

Working with industry and utility experts, EPRI researchers have developed algorithms, combining standard operating and maintenance information with information about breaker application and design, to provide meaningful, risk-based inferences on a continuing basis about the equipment's expected condition and need for maintenance. The algorithms give measures of both a breaker's relative condition and the relative applicability of specific maintenance actions. The former can support a ranking scheme that categorizes a breaker population for general maintenance considerations and asset health and condition analysis. The latter can be used to trigger specific maintenance actions and reduce reliance on a time-based maintenance approach.

The algorithms have been incorporated into a decision-support tool that provides the benefits of a condition-based circuit breaker maintenance program without the attendant costs. Thirteen utilities are participating in the research project, and versions of the CBMR tool have been applied at several locations, in addition to Con Edison, with similar success.

The estimated cost savings Con Edison has realized from this process validated the utility's pursuit of the three-pronged approach. Using the data from the maintenance tool has helped the utility be more precise in the circuit breakers it selects for maintenance. As a result, the Con Edison team is able to focus limited resources on the appropriate equipment, improving the effectiveness and efficiency of the utility's circuit breaker replacement and maintenance program.

Historically, high-voltage circuit breaker maintenance has been based on service time and, to a lesser extent, operations count rather than a particular breaker's actual condition. This philosophy was adopted because of the limited amount of information that could be acquired about a circuit breaker's condition. Although such an approach served the industry well in the past, current concerns — including aging infrastructure, limited maintenance resources and increased demand for service reliability — have prompted maintenance and asset managers to investigate other approaches to circuit breaker maintenance priorities.

EPRI has provided CBMR and other decision-support tools to facilitate analytical resource allocation to help utilities reduce operating costs without adversely affecting service levels.

Circuit breakers are generally very reliable power-system components. Maintaining reliable high-voltage circuit breakers is complicated by the fact that many breakers may remain idle for extended periods of normal system conditions. Consequently, utilities have extensive preventive maintenance programs for circuit breakers. Through many years of experience, utilities have established programs for maintaining their breakers in good operating order.

However, by their sheer numbers, breakers represent a significant portion of a utility's power-delivery maintenance budget. In response to pressures to reduce maintenance expenses, utilities have shifted from the original manufacturer's maintenance recommendations — principally based on length of time in operation and number of operations — toward reliability-centered maintenance and a condition-based approach.

New Methodology

Ideally, any equipment maintenance decision would be made based on a thorough understanding of the component's deterioration processes and current state. Assessing a breaker's condition through direct observations or measurements is the best means of deciding when maintenance is appropriate. Such condition-based preventive maintenance ensures breakers are not over or under maintained and that their availability and reliability are optimized while maintenance costs are minimized.

However, determining a circuit breaker's condition is not necessarily a straightforward process. New inspection tasks, special expertise and expensive test equipment may be required and the breaker must often be removed from service. On-site condition assessments are costly and only provide a snapshot valid for the time of the assessment. On-line monitoring systems can be helpful for tracking some aspects of breaker condition, but retrofit systems have been difficult to justify economically for previously installed breakers.

For most breaker components, it is recognized that wear is not time dependent nor is the number of operations the only factor driving deterioration. Furthermore, service duty is not uniformly distributed over a breaker population. Some breakers will see more severe service duty than others because of their position in the power system. Many industry experts agree the application of time-directed maintenance programs to all breakers of a particular type is not the most effective use of maintenance resources. On the other hand, alternative approaches have not been well established.