The Direct Condition Assessment of Operating Low-Voltage Insulated Cables

Abstract

Electric utilities and heavy industry are experiencing increased insulated cable failures in low-voltage networks and medium-voltage circuit applications with catastrophic results. Cables that have been operating more than 50-years in direct buried, conduit, and metal raceway schemes fail for a variety of reasons. Time and heat are the chief contributors to insulation failure. Cables are difficult and dangerous to test because most test techniques require that the cable be taken out of service, disconnected, and often evaluated with destructive test signals. Older cables that should be tested may be skipped as the disconnection and movement of the cable in preparation for invasive testing can cause insulation mechanical failure. A nondestructive, non -invasive test technology that is applied to operating cables in a variety of applications is reviewed. The direct-reading insulation condition assessment technology induces non-destructive signals in the operating conductor. The technology evaluates the condition of cable insulation, insulators that suspend or support non-insulated conductors, and is useful in locating separations of concentric neutrals in jacketed and non-jacketed cables. The technology is also helpful in identifying cable phasing. Unique attributes of the technology allow for the test of entire circuits or segments of circuits without altering the operating system. Field test scenarios and test results are presented along with a technology overview.