On March 16, 2024, the technical team of XZH TEST completed a 10kV cable fault detection project in Chonburi Province, Thailand, successfully pre-locating a leakage-type low-resistance fault on an underground power distribution cable. Using a combination of insulation resistance testing, the low-voltage pulse method and the high-voltage flashover method, the team located the fault point at 172 meters from the test end, providing a reliable basis for subsequent excavation and repair works. This case demonstrates the practical efficiency of XZH TEST cable fault locating solutions in overseas distribution network maintenance.

The faulty cable is a YJV-8.7/10 3×240mm² XLPE insulated underground power cable serving a distribution network in an industrial zone of Chonburi Province. A ground fault tripped the protection device and interrupted power supply, but visual inspection could not reveal the fault position. Because the cable route runs through a busy industrial area, blind excavation was not acceptable, and XZH TEST engineers were called in to perform precise fault pre-location before excavation.

Step 1: Insulation Resistance Test — Using an insulation resistance tester at the 2500V range, the team measured the insulation condition of all three phases to ground. The results were as follows: Phase A to ground 0.03MΩ (169V), Phase B to ground 0.04MΩ (155V), and Phase C to ground 0.01MΩ (146V). The extremely low insulation values indicated a leakage-type low-resistance fault, and the similarity of the three-phase readings suggested a common fault location.

Step 2: Low-Voltage Pulse Method — The low-voltage pulse method was then applied to measure the cable length and obtain an initial fault distance estimate. The measurement showed that the cable length of Phase C was 177m, and Phases B and C both measured 177m as well. The fact that the pulse method displayed the fault distance confirmed that the fault resistance was already very low.

Step 3: High-Voltage Flashover Method — To confirm the distance, the team applied the high-voltage flashover method at 28kV, which located the fault point at 172m from the test end.

• Comprehensive Diagnosis Workflow: Insulation resistance testing first confirmed the fault nature, then the low-voltage pulse method provided the cable length, and finally the high-voltage flashover method delivered the accurate fault distance.
• Cross-Validation of Two Methods: The pulse method result of 177m and the flashover method result of 172m cross-validated each other, greatly improving the confidence of the pre-location before excavation.
• Handling of Low-Resistance Leakage Faults: For leakage-type faults with very low resistance, the discharge sound at the fault point can be extremely small, requiring careful and patient pinpointing during the final location stage.
• Minimum Disruption: Accurate pre-location minimized excavation in a busy industrial zone, reducing downtime and repair costs.