Common methods for locating dead grounding cable faults

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.

 

 

Common methods for locating dead grounding cable faults

What is dead grounding?

Dead grounding refers to a fault where a metallic short circuit occurs between the steel strip and the ground, with a resistance of 0 ohms.

1. Ground subsidence The steel strip overlaps with the phase line.

2. Instantaneous fusion of high current faults.

3. The cable has been running for a long time due to aging, resulting in large-scale faults (low resistance faults equivalent to dead connections for lengths over 2 meters).

 

What is the basis for determining dead ground faults?

The insulation resistance tester tests 0 megohms, and then uses a multimeter to test the resistance value to be close to 0 ohms, determining it as a dead connection.

 

How to test for this type of malfunction?

When encountering a dead ground fault, use a wave reflection rangefinder to test the entire length, and use a bridge to test the cable fault distance. The first choice is to use a positioning device with a step method for fault location, and choosing the electromagnetic mode of the D30 fixed-point device for fault location is more efficient.

 

Test Site for Dead Grounding Cable Fault (Part 1)

Location: International Art City, Weiyang District, Xi'an City;

Cable type: 380V cross-linked cable fault location;

Cable burial method: direct burial of 1.15 meters on land;

Fault type: metal short circuit and grounding;

Instruments used: QLD-301 intelligent cable fault rangefinder, QLD8000 cable routing instrument, QLD-K10 direct buried grounding cable fault fast side instrument.

Testing process sharing:

（1） Understand the on-site situation

Qilida's on-site technical engineer Mi Gong arrived at the cable fault testing site with testing equipment. The on-site staff described that the sales department has been experiencing intermittent power outages for two days. The electrician has determined the location based on experience and has dug three locations, none of which are faulty. The cable is a 380V cable, and the burial direction of the cable is unknown.

（2） Determine the nature of the fault

Using a 2500V electronic insulation resistance tester, the insulation resistance values ABCN of the faulty cable to ground were measured to be 0M Ω, 20M Ω, 0M Ω, and 25M Ω, respectively. Continuing to use a multimeter to test the phase continuity, A and C phases were directly connected, thus determining that the cable is a metallic short-circuit grounding fault.

（3） Test cable fault distance

Using the low voltage pulse method of QLD-301 intelligent cable fault rangefinder, analyze three sets of waveforms A, C, BC, and AB, where BC and AB are full-length waveforms and AC is a short-circuit waveform with obvious branching points. According to three sets of waveforms, the total length distance of the faulty cable is 179.5 meters, and the fault distance is 68.8 meters.

（4） Accurate positioning of cable paths and fault locations

Based on the nature of the fault, the technical personnel chose to use the step voltage method to locate the fault point, because the M30 integrated high-voltage generator is used for impulse discharge of the metal short circuit fault at the fault point. The QLD-D20 cable fault locator has almost no sound for accurate positioning near the fault point, making it impossible to locate. So the rice worker directly chose to use the QLD-K10 cable fault tester to find the fault point while searching for the path, and the tester accurately located the fault point in about forty minutes. The cable is buried under the cement ground, and the one click depth measurement function of QLD8000 cable pathfinder is used to measure the burial depth of the cable at this location, which is 1.05 meters. Mark the location and depth of the fault point and wait for excavation.

  

Test Summary

After more than an hour, the rice worker successfully found the fault point. The master used a water drill to dig open the cement layer and find the cable. The cable had obvious damage. After pulling it open, the core wire at the fault point was completely overlapped, and the fault point was under the cement ground. The grounding fault detector could not be directly grounded, and the test signal was very small. Water was poured into the cement gap for conduction. After multiple judgments, the fault point was located. If the efficiency of locating the fault point with a conventional step voltage fixed-point instrument is low, using the QLD-D30 multifunctional cable fault precise locator electromagnetic mode of Qilida can synchronously receive the voltage signal generated by high-voltage discharge, which is 100 times that of ordinary step voltage signals, effectively avoiding interference. It can quickly and accurately test the grounding faults of high and low voltage cables, without being limited by the environment, making it easier to solve the problem of locating high resistance grounding faults. Real time indication of the direction of the fault point and cable orientation can ensure no deviation from the cable, quickly determine the location of the fault point, and shorten the positioning time by more than 5 times. The original positioning time was 1 hour, but now it takes 10 minutes.

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.

 

 

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