The integrity of the electric power cables is vital to the safety of an entire electrical system. To ensure the health of the cables, a technique is needed for both detecting/locating defects, and predicting hard defects before they occur. The theory and limitations of the classical wiring diagnostic techniques time domain reflectometry (TDR) and frequency domain reflectometry (FDR) are discussed. This study then introduces joint time-frequency domain reflectometry (JTFDR) as a unique solution for the cable diagnostics and prognostics. By employing an interrogating incident signal and advanced post-processing of the reflected signals, JTFDR is shown to be capable of overcoming those limitations. JTFDR is experimentally proven to be successful for detecting and locating both hard and incipient defects. The prognostic capabilities of JTFDR are also demonstrated via accelerated ageing tests of an electric power cable. By utilising the incident/reflected signal information in the time and frequency domains simultaneously, JTFDR is proven to be a more effective diagnostic technique than the classical TDR and FDR. JTFDR can also be used to monitor incipient defects and better predict hard defects before they occur.

Application of joint time-frequency domain reflectometry for electric power cable diagnostics

Lifetime predictions for semi-crystalline cable insulation materials: I. Mechanical properties and oxygen consumption measurements on EPR materials

Utilities are experiencing premature failures of power cables. In order to prevent electrical outages and to save on repair expenses, a nondestructive and nonintrusive condition assessment technique is highly desirable to evaluate the cable status and to predict the remaining life of a cable. In this paper, the capability of joint time-frequency domain reflectometry (JTFDR) as such a condition assessment technique is studied. The health status of three popular insulations in power system cables - cross-linked polyethylene, ethylene propylene rubber, and silicone rubber - is monitored using the JTFDR in a thermal accelerated aging test. The experimental results show that the JTFDR can successfully monitor the aging process of all three insulations. Then, the results from the JTFDR are compared with the results from the elongation at break (EAB); the results show that the JTFDR technique is comparable with the EAB and has a great potential as a nondestructive and nonintrusive condition assessment technique.

Health Monitoring of Power Cable via Joint Time-Frequency Domain Reflectometry

Dielectric spectroscopy as a condition monitoring technique for cable insulation based on crosslinked polyethylene

An approach for reliability prediction of instrumentation & control cables by artificial neural networks and Weibull theory for probabilistic safety assessment of NPPs

Four crosslinked polyethylene (XLPE) and ethylene propylene rubber (EPR) insulated cables were subjected to accelerated thermal, radiation, and sequential radiation and thermal exposure to simulate 20, 30, and 40 yr in-service environments in Ontario Hydro Nuclear Plants. Two sets of samples were evaluated. The first set contained 15 cm cable specimens in tubular form with the conductors removed, while the second set was made up of 4.3 m cable samples wound on mandrels. The cable samples were sequentially irradiated and thermally aged and subjected to an additional accident radiation exposure followed by a simulated loss of coolant accident (LOCA)/main steam line break (MSLB) steam test. During the steam test, samples were energized and their electrical characteristics continuously monitored. The material performance of the insulation was assessed using the 15 cm specimens during the various stages of aging exposure by conventional elongation measurement and by the use of micro-specimens with differential scanning calorimeter (DSC), oxidation induction time (OIT) and infrared carbonyl absorption techniques. The results from these samples were compared with the electrical performance of the cable samples wound on mandrels that had been subjected to the LOCA/MSLB steam test. The test results indicate that with the use of micro-specimens meaningful changes were obtained until the elongation values of the samples were reduced to 50% absolute. Electrical test data obtained for XLPE and EPR during the steam tests indicate that 50% absolute elongation values provide sufficient margin to withstand additional accident radiation, and to function electrically during design basis events.

W. Seidl

Papers

Condition assessment of cable insulation systems in operating nuclear power plants