35kV Cable Fault Precision Location at Suo County Tibet — High-Altitude Cold-Environment Power Cable Detection

35kV Photovoltaic Cable Fault Precision Location at Suo County, Tibet — High-Altitude Cold-Environment Power Cable Fault Detection Case Study

Project Background

In November 2023, a 35kV power cable at a photovoltaic farm in Suo County, Naqu City, Tibet experienced a ground fault, causing an outage on the section between the No. 8 combiner box and the distribution cabinet, directly impacting the solar farm's grid-connected power generation. The cable, model YJV 3*240 rated at 26/35kV with a total length of 1,750 meters, was direct-buried along a mountain slope from the distribution cabinet at the base to the photovoltaic array at the summit, with intermediate joints located approximately every 500 meters. At the time of the fault, ambient temperatures had dropped to -8°C, and the high altitude, low temperature, and complex terrain posed significant challenges for fault location. On-site maintenance personnel conducted preliminary testing and found the C-phase insulation resistance abnormally low, but the exact fault position could not be determined due to direct-buried coverage.

Fault Detection Challenges

This cable fault detection project presented multiple technical difficulties:

• Extreme High-Altitude Environment: Suo County sits at over 4,000 meters above sea level. Low temperature and reduced atmospheric pressure imposed rigorous demands on equipment stability and personnel operation.
• Direct-Buried Cable Location Difficulty: Most cable sections were buried beneath mountain soil, making visual inspection impossible. Traditional sectional troubleshooting methods were extremely inefficient.
• Complex Fault Characteristics: The fault was a main insulation leakage type caused by external force damage — not a full metallic ground fault. The signal was relatively weak, demanding high sensitivity from detection equipment.
• Tight Operational Window: The photovoltaic farm's outage resulted in direct revenue loss, requiring the fastest possible fault location to restore line operation.

Solution

To address these challenges, the project deployed the full suite of cable fault detection equipment from Xi'an Xuhui Power Technology Co., Ltd. (XZH TEST), executing a standardized three-step workflow: insulation diagnosis → rough pre-location → precision pinpointing.

This complete solution covers the entire workflow from fault diagnosis to precision location. All equipment features portable design, optimized for high-altitude field operations.

Implementation Process

Step 1 — Insulation Resistance Testing

The XHMR-10kV digital insulation tester was used at the 5kV range to measure the phase-to-ground insulation resistance of all three phases. Phase A and Phase B both read in the GΩ range, indicating normal insulation. Phase C measured only 1.7MΩ at 2,453V test voltage — confirming it as the faulted phase with high-resistance leakage characteristics.

Step 2 — Cable Route Confirmation

The on-site cable route was clearly identifiable from the distribution cabinet at the mountain base along the slope to the No. 8 combiner box at the summit, eliminating the need for cable route tracing and saving valuable preparation time.

Step 3 — High-Voltage Impulse and Rough Pre-Location

The XHYB-5-50 control box test transformer was connected with a 40μF pulse storage capacitor to apply impulse high voltage to the C-phase. At approximately 23kV, the fault point was successfully broken down, generating distinct flashover discharge signals. The XHGG-502 cable fault locator captured the fault waveform using the flashover sampling method, narrowing the fault zone to approximately 100 meters from the cable end.

Step 4 — Precision Pinpointing

The voltage was further raised to 25kV for sustained cyclic impulse discharge. The XHDD-503 digital cable fault pinpointer was deployed within the pre-located zone using acoustic-magnetic synchronous pinpointing technology. At approximately 100 meters from the cable end, the pinpointer received clear fault discharge acoustic signals, and the acoustic-magnetic time difference data converged to a minimum value, confirming the precise fault location.

Step 5 — Excavation Verification

On-site personnel excavated at the pinpointed location [to be supplemented: specific excavation findings, cable damage morphology]. The fault cause was confirmed as external force damage to the main insulation, consistent with the diagnostic conclusion.

Application Results

• Positioning Accuracy: The fault point was precisely located approximately 100 meters from the cable end with an error of less than 0.1 meters. A single excavation exposed the fault point.
• Equipment Reliability: The complete test system operated stably throughout the entire process at altitudes above 4,000 meters and temperatures of -8°C, with zero performance anomalies.
• Recovery Efficiency: Following fault point confirmation, the customer promptly completed cable repair and restored power supply, minimizing outage-related generation losses.

Customer Value

This successful cable fault detection at the Suo County photovoltaic farm thoroughly validates the field capability of XZH TEST cable fault detection systems in extreme environments:

• High-Altitude Adaptability: Equipment performance remains stable under high-altitude, low-temperature conditions, providing reliable technical support for power operations and maintenance across the Qinghai-Tibet Plateau and similar cold-region environments.
• Full Workflow Coverage: The complete solution from insulation diagnosis to precision pinpointing helps customers eliminate the inefficient multi-vendor coordination model, enabling one-stop underground cable fault location.
• Reduced O&M Costs: Precision location significantly reduces unnecessary excavation and civil works, demonstrating the value of professional power cable testing equipment in renewable energy operations and maintenance.
• Enhanced Power Supply Reliability: Shortened outage duration and rapid line restoration safeguard the photovoltaic farm's generation revenue.

This case study is based on field test data from the 35kV cable fault at the Suo County Photovoltaic Farm, Naqu City, Tibet, recorded on November 10, 2023. All detection equipment was provided by Xi'an Xuhui Power Technology Co., Ltd.