EPRI | Nuclear Sector Roadmaps August 2015

IN USE: RELAY AGING MANAGEMENT GUIDANCE

ISSUE STATEMENT

Relay failures have been one of the leading causes of scrams and emergency diesel generator (EDG) failures in recent years. Aging degradation is a contributor to these issues. The wide variations in relay types and designs, materials used within the relays, applications, service conditions, and pre-ventive maintenance (PM) options present challenges in determining the most effective PM and replacement strategy to ensure high reliability. More granular guidance is needed to help utilities effectively manage relay aging and ensure high reliability.

DRIVERS

ReliabilityReliability: Data for U.S. reactorsfor 2007 through 2011 revealed that relay problems caused:• 23 scrams, almost 5 per year• 2.5 million MWh of lost generation

Regulatory InterestThe Nuclear Regulatory Commission (NRC) identified con-cerns with certain electrical components (such as electrolytic capacitors and relays) being in service beyond vendor-recom-mended lifetimes without an additional evaluation being performed or the component being included in the licensee’s PM program.

RESULTS IMPLEMENTATION

Initial control relay project results documented in technical report 1022972, Control Relay Aging Management Guideline, were available for implementation in April 2011. These included a relay replacement strategy chart, industry best practices, and recommendations for implementation:

1. Verify that all critical components have been identified and appropriate PM tasks scheduled

2. Evaluate single point vulnerabilities and implement appropriate strategies to minimize their impact on safety and plant operations.

3. Designate an appropriate individual as the relay compo-nent engineer to ensure an effective PM program is in place, review operating experience, and perform moni-toring and trending functions

Technical Update 3002000541, Relay Series-Specific Guid-ance: Generic Service Life Anayses (GSLA) and Preventive Maintenance (PM) Templates was issued July 2013. This report focused on evaluation of the materials used in selected relays and how they are affected by various stressors. The Arrhenius Methodology was applied to determine reason-able service lives for each relay type based on thermal consid-erations. The results of these generic service life analyses (GSLA) were used along with vendor recommendations, qualification test results, operating experience data, and util-ity data to form the basis for relay series-specific PM tem-plates. This report also provides guidance on an effective aging management program which should address the items below:• EQ relays - maintain per EQ program• High cycling applications - replace per manufacturer’s

ratings• Condition based replacement - replace relays as concerns

are identified via performance issues, inspections, tests, or PMs

• Periodic subcomponent replacement - for those with lim-iting service lives, e.g., electrolytic capacitors

• Time based replacement should be done to address ther-mal aging issues, e.g., normally energized coil and/or high ambient temperature. Appendices included in this report provide example GSLA and PM Templates for 5 specific relay series.

• Time based replacements may also be used to address other specific concerns, e.g., environmental concerns (high dust, vibration, corrosive gas, etc.) or service duty stressors.

Proposed projects for the future focus on:• Heat rise and thermal aging testing to determine recom-

mended service lives for the relay series most commonly/widely used in critical applications

• Guidance on converting to digital relays, to include les-sons learned and best practices

• Guidance for compliance with NERC Standards• Coordinate efforts with the Procurement and Supply

Chain groups to develop guidance on receipt inspection and testing

Collectively, these projects should address industry needs for effective PM and replacement while addressing infant mor-tality, obsolescence, and digital upgrades.

Equipment Reliability August 2015

PROJECT PLAN

The industry has not been able to effectively leverage empiri-cal data to establish service life replacement intervals for components such as relays where the populations vary widely by manufacturer and model number.While operating experi-ence data is beneficial in identifying failure trends, it cannot be effectively used for reliability studies on such components due to the large variety of components, quantities used, applications, service conditions, and due to the lack of ser-vice life data on the healthy population. Utilities are encour-aged to collect such data on critical relays, or in single point vulnerability and high critical applications as a minimum. A review of this data in future years can provide a stronger basis for replacement strategies.

Temperature rise and thermal aging tests are being proposed to address service life recommendations for the most widely used relays in crtical applications. These results will be used along with vendor recommendations, qualification test results, operating experience data, and utility data to form the basis for relay model or series-specific preventive mainte-nance templates.

EPRI established a Nuclear Utility Relay Users Group in November 2012 to address topics related to component and system engineering issues. Information sharing will include lessons learned, best practices, regulatory issues, INPO updates, obsolescence issues, vendor quality, and digital upgrades. Going forward, an annual meeting will be held supplemented with periodic webcasts and conference calls to keep members abreast of issues and to identify appropriate agenda topics for the upcoming meeting.

Based on input at the August 2013 Relay Users Group meet-ing, the following projects are recommended as future EPRI projects:

Short term• Perform heat rise and thermal aging testing to determine

recommended service lives for the relay series most com-monly/widely used in critical applications. This informa-tion will be used to provide relay series specific informa-tion similar to that issued in Technical Update 3002000541, Relay Series-Specific Guidance: Generic Ser-vice Life Anayses (GSLA) and Preventive Maintenance (PM) Templates.

• Utilities have identified lessons learned on obsolescence issues and converting to digital relays; however, the sig-nificance of this collective experience may not be fully appreciated or leveraged. Utilities see value in this data being more vigorously collected and evaluated to identify significant issues and trends as well as best practices.

• Coordinate efforts with the Procurement and Supply Chain groups to develop guidance on receipt inspection and testing, and maintenance of relays while in storage as applicable.

Intermediate term• Guidance on compliance requirements for NERC Stan-

dards is needed to help utilities ensure effective programs are in place to address activities such as blocking relay functions, testing, and reporting. Unique system configu-rations and asset ownership boundaries can introduce unrecognized challenges in fully satisfying these new standards.

• The industry has not been able to benefit from empirical data such as population by manufacturer and model num-ber, and service life achieved by healthy relays. Utilities are encouraged to collect such data over the upcoming year or so to support an evaluation. This data can be extremely valuable in corroborating the analytical results being developed in the projects currently underway. As noted earlier, using failure data only and absent of popula-tion data can provide inappropriate insights and drive the wrong behavior.

The 2014 Relay Users Group meeting will tentatively be held in August.

RISKS

• The limited knowledge of specific failure causes, associ-ated service conditions, and population and service life data for healthy relays creates a significant challenge in establishing reliability-based replacement intervals for relays. The wide variation in manufacturers, model num-bers, quantities in use, applications and service conditions exacerbate this situation.

• Using failure-based operating experience in determining acceptable service lives will likely drive replacements more often than needed, resulting in higher costs, greater use of resources, and a greater likelihood of infant failure and human error. Until better empirical data is obtained, the model or series specific guidance discussed above remains the best option.

• The generic service life analyses project and relay thermal aging tests will only address the relay series most widely used in critical applications. Utilities should consider data mining or a sampling program to establish a better basis for service life of other relay types used in critical applications.

EPRI | Nuclear Sector Roadmaps August 2015

RECORD OF REVISION

This record of revision will provide a high level summary of the major changes in the document and identify the Road-map Owner.

revision description of change

0 Original Issue: December 2012 Roadmap Owner: Ken Caraway

1 Revision Issued: August 2013 Roadmap Owner: Ken Caraway

Changes: Revised Results Implementation to issuance of Technical Update 3002000541, and Project Plan to address proposed temperature rise and thermal aging tests. Flow chart updated - 2013 revised to reflect issuance of report and project underway. Proposed Test-Based Service Life Analysis project added.

2 Revision Issued: December 2013 Roadmap Owner: Ken Caraway

Changes: Revised proposed projects for the future and relative priorities in the Project Plan based on utility needs and priorities as discussed at the August 2013 Nuclear Utility Relay Users Group meeting. Flow chart revised to reflect these changes.

2 Revision Issued: August 2014 Roadmap Owner: David Knapp

3 Revision Issues: December 2014 Roadmap Owner: David Knapp

Changes: Removed projects older than 2013, added Working Groups for PM Templates and Relay Failures from Relay Users Group for 2014/2015, moved projects not addressed yet to 2016.

4 Revision Issued: August 2015 Roadmap Owner: David Knapp

Changes: Removed projects older than 2014, added vendor support for PM Templates and Relay Failures Working Groups for 2016, added Relay Specialist Guide for 2016, added Alternative Relay Technology research project for 2017–2018, moved projects not to be addressed yet to 2017/2018.

Equipment Reliability August 2015