Test time: November 13, 2020
Test site: The site of the third-stage expansion project of Binhai, Keqiao District, Shaoxing, Zhejiang
Test item: 110kV cable fault finding
Preparation before the test:
Both ends of the cable head are located at two temporary power distribution stations on the construction site, less than 100 meters apart. According to the description of the on-site specialists, the 110kV cable phase B cannot be tested normally, and phase A and phase C are normal.
Before the test, the two three phases were suspended separately, and the armor and copper shield were still grounded. Use a high-voltage megohmmeter to test, measure the insulation resistance of the cables A, B, and C relative to the main insulation, and then use a multimeter to measure the conduction between the three phases and the phases of the cable to facilitate preliminary judgment of cable faults Types of.
Insulation resistance test: (MΩ)
Multimeter conduction measurement:
According to the test results and phenomena, it is preliminarily judged that there is a fault in the B-phase of the cable, but the fault point and the fault phenomenon are still not obvious, and there is no obvious grounding phenomenon, so further testing and judgment are needed.
A phase full-length waveform
C-phase full-length waveform
B-phase suspected fault waveform
Through the low-voltage pulse method test, the length of the cable A and C phase is about 130 meters, which is basically in line with the actual situation. It is measured that there is a suspected fault waveform at about 55m of phase B, but the cause of the cable fault cannot be judged by the waveform, and an advanced test is required.
Accurate positioning by high pressure flashover method:
In order to ensure the precise location of the fault point, verification is carried out by the high-voltage flashover method ball gap DC discharge method, and the specific fault point location is determined through on-site sound monitoring of the high-voltage flashover discharge.
Investigation along the cable path revealed that there was a discharge phenomenon in one place, which basically coincided with the display position of the low-voltage pulse fault waveform at about 55m. The cable sheath was stripped on site and the cable armor was found to have been damaged.
Conclusion: The 110kV faulty cable has a total length of about 130 meters, of which phases A and C are normal, and phase B is faulty. After troubleshooting, the fault point was located and the excavation verified that the B-phase armor was damaged, causing the cable to fail to operate normally. It is recommended to repair the fault point in time to avoid affecting the daily power supply.