Clamshell Inductive Current Coupler for Online Cable Condition Monitoring

Abstract

This document describes the adaptation of a clamshell inductive current coupler for online reflectometry testing (both frequency-domain reflectometry and spread spectrum time-domain reflectometry) to evaluate cable anomalies. The life span of safety-critical nuclear power plant cables is initially qualified for 40 years in accordance with IEEE 383 without additional testing. As plants extend their operating licenses to 60 and 80 years, justification for continued safe operation includes cable test and condition monitoring (CM) programs. Test programs traditionally involve manual interventions to disconnect the cables, perform one or several tests, then reconnect the systems, usually during refueling outages occurring only every two years. Offline testing poses an operational burden that can be minimized by online testing. This work investigates the adaptation of a clamshell inductive current coupler to inject a signal onto a cable conductor and listen for a reflected signal indicative of a damaged condition. The coupler provides >60 dB of protection, thereby allowing tests on cables up to 10 kV or more. Although the clamshell coupler is a known commercial product for cable performance testing, its use for energized cable CM constitutes a novel use case.