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Topic Title: Can we pre-locate Shiel/Screen defects in MV Cables using TDR?
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Created On: 26 December 2012 09:23 AM
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 26 December 2012 09:23 AM
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Joined: 26 December 2012

Q.1 Can we use TDR (time domain reflectometry) to DETECT (pre-locate) DEFECTS (breakage of Shield/Screen wires of XLPE Cables and/or grounds through weak jacket) for Cable Shield?

NOTE: It is already established that the screen wires/shields are defective. The applied voltage in the Shield wires/Screen of the XLPE cable did not rise, even when the far end (other end) of the shield was open. Therefore, it is certain that shield wires are somewhere partially and/or completely broken AND GROUNDED. Please note that the likelihood of ingression of moisture in the shield wires and possibility of being corroded is also high. However, it is not sure that what is the extent of damage and at how manay places is the screen/schield wires affected.

CAN WE USE TDR IN THE ABOVE MENTIONED CASE TO ASSESS THE GENERAL HEALTH OF THE SCREEN, by injecting pulse in the screen and grounding both ends of the conductor, simultaneously connecting the ground wire of the test equipment with the conductor at the testing end.

What will be the difference (if any) IF Conductor is OPEN from both ends AND low voltage high rise time pulse is injected in the screen/shield wires with other end of the screen open while using substation ground for test equipment grounding and grounding of the shield wire of test lead.
 26 December 2012 02:28 PM
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Joined: 25 July 2008

It should not matter if the break is in the core or the shield of a coax: a TDR will show how far along the cable length the discontinuity due to the break occurs.

This may shed some light on your more specific questions:

This may also be of interest:

Andy Fierman


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