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800V PV Station Cable Fault Detection — YJLV 3×120 B-Phase Short Circuit Pre-Location at QinYuan Solar Plant

2026-07-23

800V PV Station Cable Fault Detection — QinYuan Solar Plant, Tongchuan

Project: Tongchuan Huangbao Town QinYuan PV Station 800V Low-Voltage Cable Fault Detection

Test Personnel: Ge Haojie, Qiao Yifan, Gao Fei | Date: June 9-10, 2026

1. Project Background

The QinYuan Photovoltaic Station in Huangbao Town, Tongchuan, experienced an operational outage on one of its 800V low-voltage collector cables connecting a transformer to the PV array inverters. The site engineering team requested professional cable fault detection services to locate and identify the fault, enabling targeted excavation and repair with minimal impact on power generation.

Site Parameter	Details
Cable Type	YJLV-3×120 (Aluminum conductor, XLPE insulated, PVC sheathed)
Cable Length	Approximately 260 meters
Operating Voltage	800V DC / Low-voltage AC
Routing	Transformer → buried path → PV array inverters; cables intact, armor bonding properly grounded
Site Conditions	Nearby inverters continuously operating, generating strong electromagnetic interference

2. Fault Diagnosis — Insulation Testing

Initial insulation resistance measurements were conducted using a 1000V megohmmeter across all three phases (A, B, C) referenced to the cable armor:

Test Point	Result
Phase A to Armor	>1 GΩ — healthy, no insulation degradation detected
Phase B to Armor	0 Ω — direct short circuit confirmed; digital multimeter measured 24Ω on resistance range, continuity mode indicated conduction
Phase C to Armor	>1 GΩ — healthy, no insulation degradation detected

Fault Nature Confirmed: Single-phase (B-phase) low-resistance short circuit to cable armor. The 24Ω resistance value classified this as a low-resistance fault rather than a dead short, which would later prove significant for acoustic pinpointing difficulty.

Testing from the transformer side, the cable fault distance is approximately 185 meters.

3. Fault Pre-Location — Low-Voltage Pulse Waveform Method

Fault distance pre-location was performed using the low-voltage pulse reflection method (TDR). A low-voltage pulse was injected into the B-phase conductor from both cable ends to cross-validate the fault distance measurement:

Test Direction	Measured Distance to Fault
From Transformer End (LV distribution cabinet)	185 meters
From PV Inverter End (reverse verification)	85 meters
Total Cable Length (verified)	260 meters (185m + 85m ≈ 260m — cross-validation consistent)

The low-voltage pulse waveform clearly displayed the fault reflection point, with the total cable length waveform confirming the 260m overall distance. The bi-directional measurements yielded consistent results: 185m from the transformer side and 85m from the inverter side, with the combined distances matching the known cable length — confirming the pre-location accuracy.

4. Fault Pinpointing — Challenges and Solutions 4.1 Initial Approach: High-Voltage Impulse Discharge

Fault pinpointing was attempted using the XHHV515-8L high-voltage pulse generator in conjunction with an operating control box and test transformer. Based on the pre-location results, the fault was approximately 85m from the inverter end. However, several field conditions complicated the acoustic-magnetic pinpointing process:

Low-Resistance Fault Behavior: The 24Ω fault presented low impedance, resulting in weak discharge acoustic signals at the fault point — the arc energy dissipated across the low-resistance path produced insufficient acoustic output for reliable surface detection
Multiple Armor Discharge Points: The cable armor exhibited discharge activity at multiple locations along the route, creating false acoustic indications that could mislead the pinpointing operator
Continuous Inverter Operation: Nearby inverters remained in operation throughout the test, generating strong electromagnetic field interference that degraded the magnetic component of the acoustic-magnetic synchronization method

4.2 Alternative Approach: 507 Pipeline Locator Audio Frequency Method

Given the acoustic-magnetic method limitations under the site conditions, the team deployed the XHHV507 pipeline and cable locator in audio frequency mode as an alternative pinpointing technique:

The 507 receiver traced the cable path from the inverter end toward the transformer end, monitoring audio signal amplitude along the route
At approximately 85m from the inverter — consistent with the TDR pre-location result — a significant signal attenuation and characteristic distortion pattern was observed, indicating the fault location
The audio frequency method proved more resistant to inverter electromagnetic interference than the acoustic-magnetic method, as the narrow-band audio receiver filtered out broadband power electronic noise

5. Equipment Deployed

Instrument	Role in Fault Detection Process
XHGG502 Cable Fault Locator (TDR)	Low-voltage pulse pre-location — cable length measurement and fault distance determination
503 / 503C / 503E Series	Supplementary fault pre-location and waveform analysis
XHGX507 Pipeline & Cable Locator	Audio frequency cable tracing and fault point identification under inverter interference conditions
XHHV515-8L HV Pulse Generator	High-voltage impulse discharge for acoustic-magnetic fault pinpointing
Operation Box + Test Transformer (5/50)	High-voltage power supply and control for impulse discharge system
Pulse Energy Storage Capacitor (40/6)	Energy storage for high-voltage impulse discharge
515-8L Insulation Resistance Tester	Pre-test cable insulation assessment (1000V megohmmeter range)
Digital Multimeter	Resistance measurement and continuity verification (24Ω fault confirmation)

6. Results and Recommendations

Finding	Detail
Fault Type	B-phase low-resistance short circuit to cable armor (24Ω)
Fault Location	85m from PV inverter end / 185m from transformer end — confirmed by bi-directional TDR and audio frequency tracing
Probable Cause	Insulation damage at a single point on B-phase conductor, likely from external mechanical stress or manufacturing defect manifesting under thermal cycling during station operation
Repair Action	Excavate at identified location (85m from inverter end), expose cable, cut out damaged section, install inline cable joint with proper insulation restoration and armor rebonding

7. Operational Lessons Learned

Low-Resistance Fault Pinpointing: Faults in the 20-30Ω range produce weak acoustic signatures during impulse discharge. When acoustic-magnetic pinpointing is compromised, audio frequency injection via a pipeline/cable locator provides a viable alternative more tolerant of EMI from nearby operating equipment
Bi-Directional TDR Verification: Measuring from both cable ends and cross-validating combined distances against the known cable length is a critical QA step — the 185m + 85m = 260m match provided high confidence in the pre-location result before committing to excavation
PV Station Operating Constraints: Unlike utility substations where circuits can be fully de-energized, PV station cable fault detection often proceeds with adjacent inverters online. Test crews should anticipate EMI and prepare alternative pinpointing methods — in this case, the 507 audio frequency receiver provided the decisive measurement
Multi-Instrument Synergy: The combination of TDR pre-location (502), impulse discharge (518-8L), and audio frequency tracing (507) formed a complementary toolkit — each instrument compensated for the limitations of the others under challenging field conditions