Radiant energy – Invisible radiant energy responsive electric signalling – With means to inspect passive solid objects
Reexamination Certificate
2000-08-31
2001-10-09
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
With means to inspect passive solid objects
C250S269600
Reexamination Certificate
active
06300634
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of material aging research and management, specifically to the in-situ monitoring and estimation of the condition of various degradable components used in a wide variety of applications (including, inter alia, electrical cable, process system valves, aircraft, spacecraft, and automobiles) via neutron activation techniques.
2. Description of Related Technology
The aging of degradable components (particularly those constructed in whole or in part of organic compounds such as polymers) is of great importance to modern society. Such degradable components comprise a significant fraction of what may be termed as “critical” components in use in many industrial, aerospace, and automotive applications, both commercial and military. Included in this category are components such as electrical cable insulation, valve internals, bushings, seals, and gaskets. Degradation and ultimate failure of these so-called critical components is of paramount importance in that such failures may result in the unanticipated maintenance costs, loss of operational capability and availability, and even loss of human life.
Several different approaches to managing the aging of such components exist. One approach involves 1) subjecting laboratory or in-situ specimens of a given component to a progressive regimen of aging stressors such as heat, radiation, electrical potential, chemicals, and/or oxygen present in the anticipated operating environment (known generally as “artificial aging”); 2) identifying a critical parameter of the component's function in the desired application (such as dielectric strength for an insulator); 3) determining a maximum or minimum acceptable value for the chosen parameter; 4) correlating the maximum or minimum acceptable value to a given installed lifetime (for example, via aging models such as the Arrhenius equation); and 5) removing the component from service when the installed lifetime is reached. Note, however, that this approach has the distinct disadvantage of not directly monitoring the condition of a given component, thereby introducing potentially significant variations in component condition across various applications. Specifically, some applications may have aged more or less than expected (due to a variety of factors such as radiant heat or radiation shielding, variations in oxygen/inert gas concentration, aging prior to installation, inaccuracies in the aging model used, etc.), and hence are being replaced either prematurely or too late. More effective condition monitoring programs will utilize a similar approach as that outlined above, yet instead of rotely replacing a component at a given point in life, will monitor the degradation of the component as a function of time to determine it's rate of aging as compared to the artificially (or naturally) aged specimen. The primary drawbacks of these latter condition monitoring programs include the costs of monitoring, component inaccessibility, and component/device downtime. For example, the condition monitoring of a fluoropolymer valve seat requires either remote inspection or disassembly of the valve, thereby removing the valve from service for a period of time. In such cases, simple periodic replacement of the component during other scheduled maintenance may be more cost effective. In some instances (such as electrical cable, described further below), no periodic maintenance or replacement is ever scheduled; hence condition monitoring of some sort is almost a necessity. The enormity of cost associated with replacement of cable in, for example, a commercial nuclear power facility, underscores the need for effective aging assessment and monitoring techniques.
Electrical Cable
As previously indicated, the aging and unanticipated failure of power, control, instrumentation, and data transmission cable may have significant adverse effects on plant operation and maintenance (O&M) costs and downtime. Electrical and optical cables have traditionally been considered long-lived components which merit little in the way of preventive maintenance or condition monitoring due to their generally high level of reliability and simplicity of construction. Like all other components, however, such cables age as the result of operational and environmental stressors. Aging effects may be spatially generalized (i.e., affecting most or all portions of a given cable equally, such as for a cable located completely within a single room of uniform temperature), or localized (i.e., affecting only very limited portions of a cable, such as in the case of a cable routed near a highly localized heat source). The severity of these aging effects depends on several factors including the severity of the stressor, the materials of construction and design of the cable, and the ambient environment surrounding the cable. Detailed discussions of electrical cable aging may be found in a number of publications including SAND96-0344 “Aging Management Guideline for Commercial Nuclear Power Plants—Electrical Cable and Terminations” prepared by Sandia National Laboratories/U.S. Department of Energy, September 1996. Discussions regarding optical cable aging may be found, inter alia, in Electric Power Research Institute (EPRI) publications and telecommunications industry literature. The following description will be limited to electrical cable, although it can be appreciated that the principles of aging and analysis described herein may also be largely applicable to optical cabling as well as many other types of polymeric components.
Electrical cables come in a wide variety of voltage ranges and configurations, depending on their anticipated uses. Existing prior art low- and medium-voltage power and control cables such as that shown in
FIGS. 1
a
-
1
d
are typically constructed using a polymer or rubber dielectric insulation
200
which is applied over a multi-strand copper or aluminum conductor
202
. The insulation is often overlaid with a protective polymer jacket
204
. In multi-conductor cables (such as those used in three-phase alternating current systems, as shown in
FIGS. 1
a
and
1
b
), a plurality of these individually insulated conductors are encased within a protective outer jacket
206
along with other components such as filler
208
and drain wires (not shown). These other components fulfill a variety of functions including imparting mechanical stability and rigidity to the cable, shielding against electromagnetic interference, and allowing for the dissipation of accumulated electrostatic charge. This general arrangement is used for its relatively low cost, ease of handling and installation, comparatively small physical dimensions, and protection against environmental stressors.
Current methods of evaluating electrical cable component aging generally may be categorized as electrical, physical, and microphysical. Electrical techniques involve the measurement of one or more electrical parameters relating to the operation of the cable, such as the breakdown voltage, power factor, capacitance, or electrical resistance of the dielectric. These methods have to the present been considered largely ineffective or impractical, in that they either do not show a good correlation between the parameter being measured and the aging of the dielectric, or are difficult to implement under normal operations. Furthermore, such techniques are often deleterious to the longevity of the insulation, and have difficulty determining localized aging within a given conductor.
Physical techniques including the measurement of compressive modulus, torsional modulus, or rigidity under bending often show a better correlation between the aging of the cable and the measured parameter (especially for low-voltage cable), and are more practical to apply during operational conditions. However, they generally suffer from a lack of access to the most critical elements of the cable, the individual electrical conductors and their insulation. For example, the measurement of compressive modu
Gagliardi Albert
Gazdzinski & Associates
Hannaher Constantine
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