Date of Award
Open Access Dissertation
Power plants, power distribution and transmission networks, automobiles, aircrafts, trains, industrial manufacturing plants etc. use a variety of cables and wires. The insulation and jacket polymer materials of cables can degrade over time due to operational stressors and environmental conditions. Materials may age, corrode, get chaffed and go missing which if remain undetected and unaddressed can result in major failures. Insulation degradation or damage detection from a distance normally involves the application of direct contact reflectometry techniques. This requires the cable to be disengaged and a diagnostic signal to be directly applied to a cable with a return path. While examples of non-conductor contact capacitive coupling associated with reflectometry and surface wave reflectometry have been proposed they are limited to detecting open or short circuit faults that result in reflected signals with large amplitudes and phase reversals. Such approaches are not suitable for insulation damage detection at various distances (and of various sizes and shapes) along the length of a cable.
This dissertation addresses that knowledge gap by focusing on studying, designing, and developing a non-conductor contact microwave surface wave reflectometry type cable diagnostic method to detect missing or damaged insulation and jacket materials on unshielded cables.
The key innovation proposed for insulation damage detection is to use a monopole type surface wave launcher (SWL) operating at high enough frequency (GHz range) that has sufficient bandwidth and that can ensure high electromagnetic (EM) energy localization within the insulation material. A sinusoidal swept frequency broadband signal with appropriate frequency range is excited which causes the generation of surface waves that propagate along the length of the cable. The surface waves, upon reaching the location of the damaged insulation are reflected and then subsequently picked up by the SWL. The results are measured by a vector network analyzer (VNA) as one-port complex scattering (S) parameters as function of frequency. Further processing e.g., windowing and inversefast-Fourier transform is performed on the S parameters to determine the location and extent of the insulation damage. For example, the detection of a 4 cm-long insulation damage at 40m distance on a 50m long cable (2.44cm diameter) is demonstrated with the help of a 0.7-1.1 GHz surface wave launcher. Similarly, a 1-cm long quarter circumferential insulation damaged region is detected on a 0.3cm diameter and 61cm long wire with the help of a 5.5-8.5 GHz wave launcher. The proposed approach may be implemented on live cables as a nondestructive evaluation (NDE) method since it may be applied to the outer jacket/insulation and requires no contact to the conductor.
A second innovative aspect of this dissertation is the study, design, and development of a conformal SWL array that can be used on large diameter power cables to detect miniature insulation or jacket damage. The efficacy of the proposed approach is demonstrated by multiple simulations and experiments on a variety of cables (single conductor, multiconductor, with/without semiconducting screen etc.). Although utilization of microwave frequencies limits the distance over which the proposed method is effective, its ability to detect miniature cracks or damages without directly connecting to the conductor makes it an excellent candidate for future cable NDE applications including online monitoring
The proposed SWL being conformal easily lends to be mounted to the outer surface of the cable and can detect damages as small as the size of a slit (0.2cm width, 1cm length) on a 1.98 cm diameter cable with 0.58 cm thick insulation. Effects of damage detection feasibility in the presence of other cables in proximity and for cables containing semiconducting screen are also demonstrated.
Arman, A. S.(2022). Non-intrusive Microwave Surface Wave Technique For Cable Damage and Aging Detection. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/6927