Characterization of conductor by alternating current potential-drop method with a four-point probe

A method of determining material parameters associated with a conductor using four points includes injecting and extracting alternating current into the plate using current-carrying wires operatively connected to two of the four points, measuring potential drop between the remaining two of the four points, and calculating the material parameters. The conductor can be of a homogenous material, a stratified material, or other type of material. The conductor can have any number of geometries, including that of a plate, a cylinder, a tube, a stratified cylinder or other shape

Negative Refractive Index Composite Metamaterials for Microwave Technology

Materials that exhibit negative index (NI) of refraction have several potential applications in microwave technology. Examples include enhanced transmission line capability, power enhancement/size reduction in antenna applications and, in the field of nondestructive testing, improved sensitivity of patch sensors and detection of sub-wavelength defects in dielectrics by utilizing a NI superlens

Dielectric and Mechanical Behavior of Thermally Aged EPR/CPE Cable Materials

Power and instrumentation cables play a crucial role in the safe operation of Nuclear Power Plants (NPPs). Thermal and other stressors present in the reactor environment cause the cable materials to degrade. In this work, dielectric and mechanical properties of cable insulation and jacket materials are studied as they are thermally aged, supporting development of non-destructive evaluation sensors for monitoring cable aging. Materials selected for this study are found in certain types of single-core unshielded power cables. These utilize ethylene propylene rubber (EPR)-based insulation material and chlorinated polyethylene (CPE)-based jacket material. Flat mats of these materials were obtained from the cable manufacturer and thermally aged at 140 °C in an air-circulating oven. Elongation-at-break was measured on tensile specimens stamped from the aged mats, and dielectric properties were measured from 100 Hz to 100 kHz using a parallel plate capacitor and precision LCR meter. In the case of aged EPR-based materials, rapid decrease in elongation at break indicating end of useful life was accompanied by a significant increase in dissipation factor, D, measured at 100 kHz. Capacitive measurement of D shows promise, therefore, as a non-destructive indicator of corresponding mechanical property changes in thermally-aged EPR-based insulation materials

Quantitative analysis of changes in antioxidant in crosslinked polyethylene (XLPE) cable insulation material exposed to heat and gamma radiation

Quantitative analysis of the antioxidant poly(1,2-dihydro-2,2,4-trimethylquinoline) (pTMQ) was conducted on pristine, thermally-aged, and gamma radiation-aged commercial cross-linked polyethylene-(XLPE-)based cable insulation material aged at temperatures 60, 90, and 115 °C, with gamma radiation exposure dose rates of 0, 120, 300, and 540 Gy/h for 15 days. The quantification of antioxidant was performed using pyrolysis gas chromatography-mass spectrometry (Py-GCMS). Oxidation induction time (OIT) was measured using differential scanning calorimetry (DSC) and correlation was made between the quantified depletion of antioxidant and measured OIT. It was observed that, in the case of isothermal aging, the quantity of antioxidant and OIT decreased with increasing gamma radiation dose. In the case of samples exposed to the same gamma radiation dose, the quantity of antioxidant and OIT were observed to decrease with increasing aging temperature. Depletion in the quantity of antioxidant relative to that in the pristine material ranged from 7 to 93% for differently aged samples. The measured decline in OIT ranged from 0 to 80%. Change in the quantity of antioxidant in the material was observed to follow the same trend as the change in OIT when the samples were aged under various conditions. The observations are explained in terms of the reaction between the antioxidant and free radicals created during exposure of the samples to thermal and gamma radiation

Capacitive Sensing for Nuclear Power Plant Cable Insulation Assessment

The ability to evaluate, nondestructively, the material state of insulation polymers widely employed in aged control and power cables has been identified as important In the process of routine safety inspection and safety inspection for license renewal of aging Light Water Reactor Nuclear Power Plants (NPPs) in the United States [1]. The present industry standard is that the insulation polymer breaking strain (or elongation-at-break, EAB) should be no less than 50% of that value measured on the pristine material, for the aged insulation polymer to be fit for service. Measurement of EAB is destructive, the method requires a relatively large quantity of sample material, and the results exhibit large uncertainty, however. Here, the ability of a capacitive sensor to indicate, nondestructively, the state of the insulation polymer is explored. The insulation material most commonly employed in U.S. NPPs, cross-linked polyethylene (XLPE), is aged simultaneously at elevated temperature and by exposure to gamma radiation. XLPE- coated wire samples are aged at 90 °C or 115 °C with a combination of three dose rates (0, 19, or 54 krad/h) and two exposure durations (10 or 25 days) to give different total doses that range between 0 Mrad, for a pristine sample, and approximately 32 Mrad, for the most severely aged sample in this set. An inter-digital capacitive sensor that conforms to the curved surface of the insulated wire [2] is used to assess the dielectric properties of the samples. The breakdown voltage of the wire insulation is measured by means of a custom-designed electrode setup. Correlation values are computed between capacitance, dissipation factor, breakdown strength, and EAB measured on the aged samples, in order to assess the effectiveness of the nondestructive capacitive method for indicating the state of the wire insulation after aging

Design of interdigital spiral and concentric capacitive sensors for materials evaluation

This paper describes the design of two circular coplanar interdigital sensors with i) a spiral interdigital configuration and ii) a concentric interdigital configuration for the nondestructive evaluation of multilayered dielectric structures. A numerical model accounting for sensor geometry, test-piece geometry and real permittivity, and metal electrode thickness has been developed to calculate the capacitance of the sensors when in contact with a planar test-piece comprising up to four layers. Compared with a disk-and-ring coplanar capacitive sensor developed previously, the interdigital configurations are predicted to have higher signal-to-noise ratio and better accuracy in materials characterization. The disk-and-ring configuration, on the other hand, possesses advantages such as deeper penetration depth and better immunity to lift-off variations

Interdigital Capacitance Local Non-Destructive Examination of Nuclear Power Plant Cable for Aging Management Programs

This Pacific Northwest National Laboratory milestone report describes progress to date on the investigation of non-destructive test methods focusing on local cable insulation and jacket testing using an interdigital capacitance (IDC) approach. Earlier studies have assessed a number of non-destructive examination (NDE) methods for bulk, distributed, and local cable tests. A typical test strategy is to perform bulk assessments of the cable response using dielectric spectroscopy, Tan , or partial discharge followed by distributed tests like time domain reflectometry or frequency domain reflectometry to identify the most likely defect location followed by a local test that can include visual inspection, indenter modulus tests, or Fourier Transform Infrared Spectroscopy (FTIR) or Near Infrared Spectroscopy FTIR (FTNIR). If a cable is covered with an overlaying jacket, the jacket’s condition is likely to be more severely degraded than the underlying insulation. None of the above local test approaches can be used to evaluate insulation beneath a cable jacket. Since the jacket’s function is neither structural nor electrical, a degraded jacket may not have any significance regarding the cable’s performance or suitability for service. IDC measurements offer a promising alternative or complement to these local test approaches including the possibility to test insulation beneath an overlaying jacket