Summary of EPRI Cable Research Results and On-going Work

Gary TomanSenior Project Engineer

EPRI-NRC Cable Coordination MeetingMarch 22, 2012

Topics

• Existing EPRI reports and data related to cable aging management and insights regarding their use and relevance

• On-going research on cable aging management topics• Some thoughts on potential future research

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Low-Voltage Cable (

Low-Voltage Cable (

Low-Voltage Cable (

Medium and Low-Voltage Cable Research Results

• 1022979 Cable Aging Management Training: Identification of Adverse Environments and Introduction to Visual/Tactile Assessment of Cable (computer based training)

• 1022968 Cable Aging Management Implementation Guidance (Resolutions of issues identified during i l t ti f bl i t )

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implementation of cable aging management programs)• 1022969 Electrical Cable Test Applicability Matrix for

Nuclear Plants

Medium Voltage Cable Used in Nuclear Plants

• Some early plants had XLPE insulation with only one having filled XLPE (highly failure prone in wet environments)

• Most early plants had black rubber insulated cables (a few butyl rubber, most black EPR)

• In ~1978 the transition to modern EPR occurred when

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In 1978, the transition to modern EPR occurred when silane treatment was added to the clay filler– Silane treatment causes the EPR to bind to the clay

more completely making a stronger compound with respect to wet aging

– The carbon was taken out of the insulation at approximately the same time so that the color (pink or brown) of the insulation was visible

Medium Voltage Cable Used in Nuclear Plants

• Those medium voltage cables that are shielded in nuclear plants have metal tape shields over a semi-conducting layer

• Safety-related medium voltage cables are mostly unshielded to allow accident operation with a single ground should a fault occur

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• Shielded cables are testable using tan δ or dielectric spectroscopy; non-shielded cables are not testable electrically

• Partial discharge testing is largely unsuccessful because of the high attenuation of the EPR and the tape shield and because black rubber appears to go to failure without partial discharge

Medium Voltage Cable System Research Results• 1020804 Aging Management Program Guidance for

Medium Voltage Cable Systems (publically available)• 1024894, 1022965, 1021069, and 1018777: Revisions 1

through 4 of Medium Voltage Cable Failure MechanismResearch for EPR cables– Correlation of breakdown voltage versus tan δ test result

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Correlation of breakdown voltage versus tan δ test result determined

– Failure path/mechanism identified for black rubber insulations

– Failure mechanism identified for modern “compact” cable design

– Modern (post 1978) cables continue to be free of wet aging failures (only manufacturing flaw related failures to date)

Medium Voltage Cable System Research Results

• 1019160 Failure Models and Data Analysis for Nuclear Plant Medium Voltage Cables for Consideration in Preventive Maintenance and Strategic Replacement– Identifies all medium voltage cable circuit failure

mechanisms for nuclear plant cable designs

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– An input to the Preventive Maintenance Basis Database– Statistically evaluates failure rates from data through

2009• 1019159 Common Medium Voltage Cable Specification for

Nuclear Power Plants

Current/On-Going Research

• MV Cable Failure Mechanism Research Continues (likely through 2013)

• LV Cable Wet Aging Pilot Study underway• Submergence Qualification for Modern (post-1978) Medium

Voltage Cable is underway (Kerite cable understudy; pink

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Okonite to be added in 2012)• End of Life Report on medium voltage cable being

prepared• Recommendations for Cable System Longevity in

Advanced Nuclear Plants nearing completion• Evaluation of an on-line continuous partial discharge

monitoring system is beginning

Thoughts on Potential Research

• Identification of normal radiation and thermal environments where cables are located in-containment

• Reduction of existing radiation and thermal data for practical use in cable aging management

• Determination of expected cost for cable system aging

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management through 80 or more years, including interactions with associated component replacement (e.g., new switchgear, control systems, motor control centers, etc. and replacement with fiber optic based instrumentation and control)

• …

Together…Shaping the Future of Electricity

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