350m direct buried cable suddenly broke down! How to repair it?

In the early morning of April 8, 2025, our company received an urgent repair report from a water plant: a sudden failure of the power supply cable in the plant caused the equipment to stop operating. The repair team quickly arrived at the scene with a full set of professional equipment and successfully located the location after a hard fight. Witness the entire repair process in this race against time.

一、Sudden failure characteristics

Model: YJV 3120+295 direct buried cable (unarmored)
Symptoms: A/B phase and N line short circuit to ground, C phase insulation deterioration
Challenges: 350m direct buried section + complex factory environment + no armor interference

二、Four-step positioning method to solve the problem

1️⃣ Initial diagnosis: 502 cable fault tester low voltage pulse method quickly locked and measured the total length of 348.4 meters (with an error of only 0.5% from the file) and found abnormal waveforms at 55.7 meters of A/B/N phases. The fault point was roughly measured at about 55 meters and initially determined to be a multi-phase disconnection grounding fault.

2️⃣ Path tracking: 507C pipeline instrument accurately guides along the distribution room → factory wall → lawn to complete the path restoration, confirm the direct burial depth and direction, and eliminate interference from other pipelines. 507C pipeline instrument step voltage method
Detects abnormal potential difference in the 50-meter area and locks the 1-meter range through gradient changes. It is especially suitable for low-resistance faults without armor.

3️⃣ Cross-validation: 503E cable fault location device Acoustic-magnetic synchronization method double confirmation High voltage flash produces identifiable discharge signal 503E cable location device captures obvious shock wave Final location error <20cm

三、Repair experience worth collecting

① Use the single detection method with caution for unarmored cables

② It is recommended to use a voltage of less than 15kV for low-voltage cable faults

③ The step voltage method is preferred in wet lawn environments

④ When the high-voltage pulse waveform is abnormal, it is necessary to consider the possibility of multiple faults

Tips：Low-voltage cable repair golden 6 hours

When the insulation resistance is detected to be less than 0.1MΩ:

✅ Cut off the power supply immediately

✅ Record the initial test data

✅ Prioritize the protection of the non-faulty phase

✅ Select the pulse + step combination test solution