Full Process for Accurate Cable Fault Location: Practical Operation Guide for Test Equipment

Full Process for Accurate Cable Fault Location: Practical Operation Guide for Test Equipment

Cable fault testing focuses on one core goal: precisely locating the fault point. Success depends on phased troubleshooting, selecting the right test method, and avoiding interference. The key points are as follows:

1. Pre-Test Diagnosis: Identify the Fault Type and Nature

Before testing, determine basic fault information to avoid blind testing, including:

  • Fault type identification: use an insulation resistance tester (megohmmeter) or multimeter for a preliminary assessment, such as:
    • Low-resistance faults (resistance to ground or between phases < 100 Ω)
    • High-resistance faults (> 100 Ω)
    • Open-circuit faults
    • Flashover faults
  • Faulted phase confirmation: use a multimeter to measure continuity and insulation between each phase conductor and ground, and between phase conductors, to identify the specific faulted phase (e.g., Phase A to ground).
  • Basic information collection: confirm the cable type, length, installation method (directly buried, cable tray, duct), and fault history to support later location. If multiple cables need to be distinguished or their energized status confirmed, use the S20 cable identifier. Before excavation, verify the cable is de-energized and use the Z20 cable safety piercing device to ensure work safety.

2. Core Testing Stage: Select Test Methods Step by Step

Follow the "coarse measurement → fine measurement → pinpointing" three-step workflow and select supporting equipment according to the fault type:

Step 1: Coarse Measurement (Determine Fault Distance)

Measure the approximate distance from the fault point to the test end.

Recommended main units:

Step 2: Fine Measurement (Narrow the Fault Range)

Further narrow the fault location to a 1–3 meter range based on the coarse measurement distance.

Standard equipment:

Acoustic-magnetic synchronous method: apply high voltage to the cable (the G35 provides the impulse discharge). When the fault point breaks down, it generates mechanical vibration (sound) and electromagnetic signals. The C11 synchronously collects both signals and uses BNR intelligent noise reduction with three-band filtering to remove environmental noise and lock onto the approximate fault zone.

Step 3: Pinpointing (Precise Location)

For directly buried cables, determine the exact surface coordinates of the fault point.

  • If the fault sound is clear: use the C11 acoustic-magnetic synchronous pinpointer with the listening method, moving close to the ground surface to detect the fault discharge sound.
  • If plant or road noise is high: use the step-voltage method with the R30 underground cable and pipeline locator. Measure the voltage difference between two points on the ground surface; the point with the peak voltage indicates the fault location.
  • For cables installed in ducts or trays where listening is not possible: first use the R30 underground cable and pipeline locator to scan the full cable route and burial depth, then check section by section along the route.

3. Key Precautions: Avoid Test Errors and Safety Risks

Safety preparation before testing

  • Disconnect power and loads at both ends of the cable, post "Do Not Close" warning signs, and confirm the cable is completely de-energized.
  • When multiple cables run in parallel, use the S20 cable identifier to distinguish the target cable. After confirming the correct cable, use the Z20 cable safety piercing device for double verification that it is de-energized before excavation.
  • When testing high-resistance or flashover faults, high-voltage equipment such as the G35 fault location power supply and MB10 high-voltage bridge must be reliably grounded. Operators must stay away from the high-voltage output area. The instruments are equipped with emergency stop and automatic discharge protection.

Reducing test errors

  • Correctly set the cable wave velocity in the A10, A50, or A52 portable/trolley-mounted main unit (copper-core PVC cables: approximately 160 m/μs; aluminum-core cables: approximately 140 m/μs). An incorrect wave velocity directly causes distance measurement deviation.
  • Distinguish test waveforms: intermediate joints and terminations generate spurious reflections. Compare waveforms with a healthy cable of the same specification to distinguish joint reflections from fault reflections. Adding the A30D multi-impulse generator significantly weakens joint interference waveforms.

Special scenario handling

  • Ultra-long cables (over 1000 m): use the double-ended test method. Test from both ends using A52 trolley-mounted systems and average the two distance measurements to offset wave velocity errors. For stubborn high-resistance faults, use the MB10 bridge to burn down and reduce the fault resistance, then retest.
  • Cable tray/duct cables and severe noise environments: first use the R30 underground cable and pipeline locator to map the complete cable route, then use the C11 pinpointer section by section along the route with synchronized acoustic-magnetic detection.
  • GIS cables and cables with cross-bonded sheaths: use the extended portable cable fault test system, which supports distance measurement without removing terminations or dismantling cross-bonding devices.
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