latest company case about Xi'an Xu&Hui Electromechanical Technology Co., Ltd. Certifications

At a glance

An industrial customer found an insulation anomaly on one cable circuit during preventive testing of its distribution system. The cable had operated normally before de-energization, but the insulation reading was outside the normal range. The cable length was approximately 1 km, and the route was basically clear. The objective was to locate the fault accurately along the cable route to support repair planning and reduce the risk of an unplanned outage.

Site and test conditions

• Test location: from an industrial substation to the plant area

• Cable ends: one end at the substation, the other end in the plant area

• Installation: buried conduit plus cable trench

• Route condition: basically clear; no additional route survey was required

• Customer: anonymized as an industrial customer

Equipment used

Test process

1. Fault nature assessment

The team used the XHMR-5000V insulation resistance tester on the 5,000 V range to measure A-to-ground, B-to-ground, C-to-ground, A-to-B, B-to-C, and A-to-C insulation resistance. The Phase A-to-ground reading was 3.2 MΩ at 2,489 V, while Phases B and C were normal. The fault was assessed as a high-resistance fault in the Phase A main insulation.

This type of fault is characterized by insulation that has not completely failed but has deviated from the normal range. The cable may still operate, but the fault point will not improve by itself.

2. Cable length measurement and fault pre-location

The XHGG501A2 cable fault tester was used with the low-voltage pulse method. The full-length waveform showed a cable length of 1,038.8 m.

Figure 1. Low-voltage pulse waveform showing the full cable length of 1,038.8 m.

A 3.2 MΩ fault is a high-resistance fault. Under the low-voltage pulse method, the reflection from such a fault is weak, so direct pre-location cannot provide a reliable result. High voltage was therefore required to make the fault location visible.

The team used the control box, XHYB-5/50 test transformer, XHCC-6/40 pulse energy-storage capacitor, and sphere gap to raise the voltage to approximately 26 kV. The fault did not break down at this stage.

To avoid a prolonged high-voltage breakdown process-especially considering possible large-area moisture or surface arcing/flashover at the fault point-the team used the XHSC-60Q digital burn-down bridge to reduce the fault resistance and establish a fault path. After burn-down resistance reduction, high-voltage impulse was applied again. The fault broke down at approximately 22 kV. The high-voltage flashover waveform from the XHGG501A2 indicated a fault distance of 345.7 m along the cable.

Figure 2. High-voltage flashover waveform indicating a pre-located fault distance of 345.7 m along the cable.

3. Fault pinpointing

The 345.7 m result is a distance along the cable, not a ground coordinate. Because the cable route was basically clear, no additional route survey was performed.

At the corresponding ground position, the team used the XHDD503E+ cable fault pinpointing instrument to move slowly along the cable route and listen for discharge sounds. Under the high-voltage flashover state, each breakdown at the fault point produced a discharge sound. At approximately 346 m, clear acoustic feedback was heard in the headphones, matching the pre-located distance.

Figure 3. Acoustic pinpointing near the 346 m mark; clear discharge feedback matched the pre-located distance.

Result

The cable fault was pre-located at 345.7 m along a 1,038.8 m cable and pinpointed at approximately 346 m by acoustic feedback under high-voltage flashover. The pinpointing result matched the pre-located distance.

Key takeaways

1. For cables that can still operate normally but show relatively low insulation resistance, the low-resistance phase should be investigated to reduce the risk of unplanned outages. In this type of case, the problem is often associated with an intermediate joint.

2. A fault that does not break down at the first high-voltage attempt may require burn-down resistance reduction to further lower the fault resistance and establish a fault path.

Why this matters

For cables that still operate but show reduced insulation resistance, early fault location helps support repair planning and reduces the risk of an unplanned outage. High-resistance faults may not break down at the first high-voltage attempt, so burn-down resistance reduction and high-voltage flashover methods may be required to obtain a reliable pre-location result.

Have a similar cable fault?

Send us the cable voltage level, cable length, insulation resistance readings, fault phase, and route information for a preliminary assessment.

Safety and compliance note

All high-voltage tests were performed by trained personnel under site safety procedures. Customer information has been anonymized. Images and test data should be approved and de-identified by the customer before publication.

Frequently Asked Questions

Q1: What is a high-resistance cable fault?

A high-resistance cable fault is an insulation fault with relatively high resistance, which may not produce a strong reflection under conventional low-voltage pulse testing.

Q2: Can a high-resistance cable fault be located using the low-voltage pulse method?

Not always. High-resistance faults may produce weak reflections, making direct pre-location difficult. High-voltage flashover methods may be required to obtain a measurable fault reflection.

Q3: What is cable fault burn-down?

Cable fault burn-down is a technique used to reduce the resistance of certain high-resistance faults, helping establish a conductive path for subsequent fault location.

Q4: What is the difference between cable fault pre-location and pinpointing?

Pre-location estimates the fault distance along the cable using electrical measurement methods. Pinpointing then identifies the approximate physical position of the fault on the ground using suitable detection techniques.