Common methods for locating faults in conduit cables

When a cable passes through a conduit, there are many types of faults, such as grounding, flashover, phase to phase, etc. Before testing, it is necessary to use an insulation meter or the high-voltage generator's withstand voltage burn through function to determine the nature of the fault and fully understand the fault type before testing.

 

What are the types of cable faults in conduit?

When a cable passes through a conduit, there are many types of faults, such as grounding, flashover, phase to phase, etc. Before testing, it is necessary to use an insulation meter or the high-voltage generator's withstand voltage burn through function to determine the nature of the fault and fully understand the fault type before testing.

 

How to accurately locate this type of fault?

Because it is a cable that passes through a conduit, there will be echo sound during high voltage discharge. When passing through a metal conduit, the sound transmission is more obvious and the metal conduit will conduct electricity. At this time, a positioning device with time difference method can be preferred for precise positioning.

 

Test site for cable faults in conduit (Part 1)

Location: Xi'an Qiyuan Jinyue (Jinye 5th Street);

Cable type: 380V cable fault location;

Cable burial method: buried directly in a conduit for 0.5 meters;

Fault type: Grounding fault through conduit;

Instruments used: QLD-301 Intelligent cable fault rangefinder, QLD8000 Cable route finder, QLD-M50 Cable Fault Test High -voltage Generator, QLD-D30 Multi functional cable fault precise fixer.

Testing process sharing:

Qilida's on-site technical engineer Mi Gong arrived at the cable fault testing site with testing equipment. The on-site staff described the cable laying situation in the community: the cable is a 380V cable, and the burial direction of the cable is unknown, about 200 meters, but the description of the cable length cannot guarantee accuracy.

(1)Determine the nature of the fault

The insulation resistance values ABCN of the faulty cable to ground were measured using a 2500V electronic insulation resistance tester, which were 260M Ω, 0M Ω, and 220M Ω, respectively. The resistance values between the 0M Ω items were A and B 450M Ω, A and C 420M Ω, and B and C 460 M Ω, respectively. Therefore, it is determined that the cable has grounding faults in items B and N.

 

(2)Test cable fault distance

Using the low voltage pulse method of QLD-301 Intelligent cable fault rangefinder, four sets of waveforms A C, A B, A N, and B N were analyzed to determine that the total length of the faulty cable is 346.15 meters and the fault distance is 106.425 meters.

(3) Cable routing and burial depth testing

Use the QLD8000 Cable route finder to measure the cable path, and click the direct reading test button to directly see that the cable is buried at a depth of 0.5 meters.

(4)Accurate positioning of cable path fault location

Using the QLD-D30 Multi functional cable fault precise fixer, go to a distance of 100 meters and turn on the locator. A faint sound can be heard, but the discharge sound will be very small due to the on-site environment. After adjusting the gain, the sound will increase significantly. According to the arrow on the locator display screen, move forward. At the location where the displayed fault distance is 0.35 meters, move forward to increase the distance. It is determined that the location where the displayed number is 0.35 meters is the fault point. After excavation, the cable is a through pipe cable, and there is a small break in the pipeline. After the pipeline breaks, the fault point is located at the break.

 

Test summary

After 2 hours, the rice worker successfully found the fault point. After the fault was repaired, the power supply in the community quickly returned to normal, effectively ensuring the normal use of electricity in the community.

The on-site environment is special, and the fault point is a grounding fault. The fault point is located in a green belt through a PVC pipe, and the cable has no steel strip. During impact discharge, high voltage can only be applied to the ground, and the discharge sound is very small. It may be difficult to accurately locate the location of the fault point using a conventional fixed-point instrument. The  QLD-D30 Multi functional cable fault precise fixer from Qilida has high anti-interference ability and multiple filtering frequency bands. Different filters can be selected according to different environments to filter various interference noises such as footsteps, car horns, conversations, etc., while only retaining the discharge sound. Digital compass guidance, no need for manual analysis, just follow the compass guidance to locate the fault, like a compass, guiding you to find the fault point. Real time indication of fault distance, displaying whether it is approaching or moving away from the fault point; Real time cable path guidance allows you to accurately locate without deviating from the cable. The fault distance is displayed digitally, in milliseconds, and the smaller the value, the closer it is to the fault point. Others may need an hour, but we only need twenty minutes to quickly and accurately locate the fault point.

Shaanxi Qilida Electronic Technology Co., Ltd. has always adhered to the concept of manufacturing high-quality pipeline (cable) fault testers, making cable fault testing simpler, more efficient, and more accurate! To provide better service for customers at home and abroad, when buying pipeline (cable) detection equipment, look for Qilida.

 

Contact Number：+86 15319759476（Miss Mi）

 

Shaanxi Qilida Electronic Technology Co., Ltd.

Building 1, Kyoto International, Changle East Road, Baqiao District, Xi'an City, China