CABLE FAULT ANALYSIS BY

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CABLE FAULT ANALYSIS BY

• UTMANCO SYSTEMS (P) LTD

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What is a Fault ?

• DEFECTWEAKNESSINCONSISTENCYOR NON-
  HOMOGENEITYTHAT AFFECTS THEPERFORMANCE OF THE
  CABLE

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COMMON TYPES OF FAULT

• CONTACT FAULTS (SHORT CIRCUIT FAULTS)
• BREAKS (OPEN CIRCUIT FAULT)

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CONTACT FAULT

• A connection or part connection between one core
  (conductor) and another or others or between
  core(s) and the metallic sheath.
• Value of fault resistance varies between zero
  ohms and many megohms.

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BREAK FAULT

• (OPEN CIRCUIT OR SERIES FAULT)
• CLEAN BREAK IN CONDUCTOR
• DIRTY BREAK
• PARTIAL BREAK

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CORRECT APPROACH TO CABLE FAULT LOCATION

• DIAGNOSIS
• PRE-CONDITIONING
• PRE-LOCATION
• PIN-POINTING

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DIAGNOSIS

1. Find out type of cable,length,time in service,
   how the fault occurred, protection operation etc.
2. Ensure both ends of the cable are disconnected
3. Test the insulation resistance between all
   conductors and sheath
4. Use an analog multimeter (avo) to measure the
   value of the fault resistance.
5. Check the continuity of all cores with the avo.

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PRE-CONDITIONING

• It may be necessary to alter the fault
  characteristics from a high resistance to low
  resistance or from an unstable flashing condition
  to a stable resistive fault
• How?
• Passing current through the fault to carbonise
  insulation (fault burner)
• Re-energising cable
• Leaving the cable dead for sufficient time to
  allow moisture to penetrate.

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PRE-LOCATION

• To determine the distance to fault either
  as a percentage of cable length or directly in
  units of distance.
• Utmanco offers two equipment for
  pre-location
• Pulse echo tester
• Digital cable fault locator.

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PIN-POINTING

• Positively confirms the exact position
  of fault
• 1. Test cable from both ends with cable fault
  locator . if the two readings add up to give the
  total length of cable, then the location of fault
  is confirmed.
• 2. Excavate cable at the distance obtained
  perhaps 3 metres on either side of fault
  position. Connect 230v phase to faulty core. Use
  utmanco non-contact voltage detector to detect
  voltage leakage point on the exposed cable to
  pin-point fault.