Original scientific paper
Use Of Micro-Void Content Growth Rates To Validate And Add Value To Electrical Insulation Tan-Delta Aging Testing
Greg A. Horvath
; Tetra Tech Advent PO Box 555, Ann Arbor, MI 48106-0555, USA
Greg M. Hostetter
; Tetra Tech Advent PO Box 555, Ann Arbor, MI 48106-0555, USA
Abstract
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.
Keywords
Hrčak ID:
199041
URI
Publication date:
31.7.2017.
Visits: 757 *