Aging Of Electrical Insulation Research Articles

Use Of Micro-Void Content Growth Rates To Validate And Add Value To Electrical Insulation Tan-Delta Aging Testing

Our research as well as others has shown that micro-void content in electric insulation polymers grows in a way that can be correlated to the degree of aging. Specific results of our experiments combined with research by others have led us to conclude that a promising technique for predicting remaining life in electric cable insulation, based on micro-void content and proximity to void limiting parameters, can be developed. This approach involves use of acoustic or optical microscopy to establish an estimate of void content in polymers by determining micro-void sizes and density. Separate research is used to establish limiting values for percent void content correlating to material failure. The mode of failure varies depending on the applied voltage regime. For example, at medium and high voltage levels, partial discharge detection can be considered indicative of pending end of life. Whereas for low voltage regimes, brittleness to the point of cracking susceptibility would allow the potential for moisture ingress and shorting and can be considered end of life. It has been separately shown that void growth rate is a function of temperature and radiation dose rate both during normal and nuclear accident conditions and is predictable based on the known polymer chemical degradation equations, which produce gaseous products in the form of oxygen, water vapor, carbon dioxide, and carbon monoxide. Thus if end of life void content is known, the degree of void content growth occurring during a design basis accident is properly accounted for, and void content growth rates during normal temperature and radiation conditions are considered, then remaining life in electrical insulation can be accurately predicted. In recent years, several techniques have been proposed to assess electrical insulation aging. One of the more promising approaches for use with medium voltage cable is the tan-delta technique. This paper will demonstrate how the mirco-void content approach can be used to validate other techniques such as tan-delta and add additional meaning and value not otherwise available from tan-delta alone.

A Review of Aging Models for Electrical Insulation in Power Cables

Electrical insulation is an integral part of power components. The aging of electrical insulation is an undeniable fact that limits the operational lifetime of power components. Apart from regular aging, abnormal stresses and the development of defects are real threats because of their contribution in accelerating the aging rate and thereby leading to a premature failure of the power components. Over the decades, various studies have been carried out to understand the aging behavior of electrical insulation mainly considering electrical and thermal stresses. Similarly, a number of mathematical (aging) models have been developed based on the theoretical and experimental investigations and evidences. However, a dependable formulation of the models that can provide more practical estimation of the insulation degradation profile has not been achieved yet. This paper presents a comprehensive review of the aging models considering single and multistress conditions. Further, the paper discusses possible challenges and barricades averting the conventional models to achieve a suitable accuracy. Finally, suggestions are provided that can be considered to improve the modeling approaches and their performance.

Life and reliability models for high voltage DC extruded cables

Aging of electrical insulation is the irreversible degradation of its dielectric properties due to applied stresses. Aging eventually leads to insulation failure, which in practice means breakdown. In this framework, a “life model” is a mathematical relationship between time to failure, also referred to as “life” of the insulation, and the levels of applied stresses. Insulation life modeling consists of finding the most appropriate life model for a given insulation, i.e., the life model that is the best in predicting accurately the life of that insulation as a function of applied stress levels.

The aging of electrical insulation at cryogenic temperatures

The author points out that the application of superconductive conductors requires the development of electrical insulation capable of operating for many years at temperatures as low as 4 K and ranging to approximately 100 K for the most recent superconductors. The insulation is subjected to stresses caused by the cryogenic environment, possibly high pressures and radiation, in addition to the electrical stresses associated with service. Experimental results of aging tests for small samples are reported, and operating experiences with superconducting devices in service for about a decade are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Thermal Aging of Electrical Insulation - Technology and Standardization

Thermal Aging of Electrical Insulation - Technology and Standardization

Bibliography on Thermal Aging of Electrical Insulation

This collection of references on Thermal Aging of Electrical includes those in books, technical standards and guides, and individual articles in periodicals during the time period 1897 to 1968. Most of the sources are from the U.S.A. and Canada; many from Europe, and some from Japan. This bibliography was prepared by the author for his own company's use initially. It has now been made available to the Electrical Insulation Group.

Diffusion Couples as Electrical Insulation Aging Monitors

Most aging phenomena are temperature dependent as indicated by the Arrhenius equation. Knowledge of probable aging rates is necessary for practical engineering design of equipment, and aging rates of many electrical insulation systems have been studied in detail. Service life expectancies can therefore be confidently estimated for particular insulation systems in specific thermal environments. However, it is not possible to assure that all electrical equipments will be operated within the design environments and ratings. Thus, variations in service life performance of electrical equipments often reflect variations in operating conditions. It has not been economically feasible to measure actual conditions of use and exposure of most electrical equipments. An inexpensive monitor of thermal exposures has been recently developed. The resistance changes of bimetallic elements are in accord with the Arrhenius model for normal diffusion. Selection of metals that interdiffuse with temperature sensitivity equivalent to that of an insulation system of known thermal aging behavior allows use of the bimetallic diffusion couple as an indirect monitor of the actual insulation thermal degradation. A preferred form of the bimetal is a composite wire, comprising alternate concentric layers of two pure metals. The diffusion couple must be placed in a location which exhibits a representative, if not identical, thermal exposure of the insulation system to be monitored. The monitors may be built-in and read in-situ or they may be inserted as replaceable probes which can be retrieved and returned to a central test facility for evaluation.