Method and apparatus for measuring deterioration of power cable insulation
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United States of America Patent
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-
Nov 21, 1995
Grant Date -
N/A
app pub date -
Oct 22, 1993
filing date -
Oct 23, 1992
priority date (Note) -
Expired
status (Latency Note)
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Abstract
A system for detecting a power cable for water treeing and other forms of deterioration based on the dielectric loss of the insulation of the cable. An AC test signal is injected to the conductor of a sample of cable to be tested. The voltage drop appearing across a resistor connected to the insulation shield layer of the cable is measured by means of a lock-in amplifier. A phase shifter adds to the voltage drop a voltage signal that is 180 degrees out of phase with the reactive component of the voltage drop. The output of the lock-in amplifier is the active component of the voltage drop that is representative of the dielectric loss of the insulation of the cable. This approach permits an accurate and reliable detection of trees even if they have not spread out evenly in the power cable, as distinct from the conventional tan .delta. method.
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