Date: July 7, 2023
Location: Wind farm near Balagong Town, Ordos City, Inner Mongolia
Testing Personnel: Li Hao, Zhang Zhenguo, Qiao Yifan
Cable Specification: YJV 3×240, 26/35 kV
Total Cable Length: 26 km (32 km provided by the client)
Fault Type: High-resistance leakage-to-ground fault (enclosed type)

1. Site Conditions:
(1) Cable ends: Both ends of the cable (specifically, the No. 5 incoming line running from the transformer to the power distribution room) have been disconnected.
(2) Cable route: The route is generally clear, with marker posts indicating the path.
(3) Cable joint locations: The locations of the joints are unknown; there is approximately one joint every 500 meters.
(4) Cable insulation resistance: Single-phase to ground (specific resistance value unknown).
Other: Power is available inside the distribution room, but a generator is required at the transformer end. Previous fault-finding efforts tentatively identified a joint at the 3 km mark as the likely fault location; however, excavation at that spot revealed neither the fault nor the cable joint.

II. Equipment used for testing:
(1) Insulation testing tool: Electronic insulation tester XHMR-5kV;
(2) High-voltage source: Control unit & test transformer XHYB-5-50, pulse energy storage capacitors (40/6 × 2);
(3) Rough ranging equipment: Cable fault tester XHGG-502;
(4) Pinpointing equipment: Pinpointer XHDD-503, Pinpointer XHDD-503D;
(5) Withstand voltage equipment: None;
(6) Other equipment: Cable/pipe locator XHGX-507;

III. Detailed Test Procedure:
(1) Insulation Test: Using the 5kV setting on an electronic insulation tester, the insulation resistance was measured between phases and between phases and ground; the resistance of Phase B to ground was found to be only 0.09 MΩ (at 500V), while all other readings exceeded GΩ levels.
(2) Route Tracing: The cable route was clearly identified on-site.
(3) High-Voltage Testing: Using a control unit, a test transformer, and a 40/6 capacitor, the fault point broke down at approximately 26 kV.
(4) Precise Pinpointing: No discharge sound was audible at the fault point when the high voltage was raised to 32 kV; two 40/6 capacitors were then connected in parallel, and the voltage was raised to approximately 30 kV, successfully locating the faulty joint at a distance of about 3,100 meters.
(5) Withstand Voltage Test: None performed.

IV. Test site images:
(1) Overview of the equipment: None
(2) Test site wiring diagram: None
(3) Diagram of specific pinpoint locations:

(4) Fault Excavation Diagram

(5) Fault waveform diagram

V. Summary of Insights from Testing:

When preparing the instrument, be sure to verify its accuracy and integrity.
Faults involving connector seal integrity produce very faint sounds—particularly at the constant-force spring—and result in non-standard waveforms. Given the presence of an external explosion-proof housing, vibration-based detection is a suitable method for identifying the faulty connector; relying solely on heat generation to locate the fault is insufficient. Pinpointing the fault requires patience and meticulous care to ensure the exact location is identified accurately.