After the cable fault has been located, can we directly start excavation? Why is the fault distance indicated by the instrument very clear, but no obvious fault is found at the site? During the cable maintenance and emergency repair process, cable fault location does not mean that the fault point has been 100% confirmed. The distance obtained by the tester is usually the electrical distance from the test end to the suspected fault location. However, the cable at the site may have bends, joints, path deviations, and data errors. Therefore, after completing the cable fault location, further confirmation is needed through methods such as synchronous sound-magnetic positioning, on-site path verification, and electrical re-measurement to minimize accidental excavation and repeated construction.
Cable fault location generally includes two stages: pre-location and more precise point determination. Pre-location mainly uses the cable fault tester to determine the approximate distance of the fault point, helping the staff to narrow down the investigation range. More precise point determination is to further confirm the specific location based on the pre-location results. These two stages are not mutually exclusive but are sequential. If only the distance measurement is completed without conducting on-site more precise point determination, it is not advisable to directly determine the excavation location based on a single distance value.
After cable fault location, the first step is to compare the distance measured by the instrument with the actual cable laying data. Check the cable route, starting and ending positions, and confirm whether there are intermediate joints, cable wells, branches, and turning positions along the line. If the tester indicates that the fault point is approximately 500 meters from the test end, and the on-site data shows that there is a cable intermediate joint exactly 450 meters away, then it is necessary to further determine whether the reflection at this position comes from the joint or the actual fault. The cable fault location result cannot be judged independently of the on-site data.
Secondly, it is necessary to check the waveform of the cable fault tester. If using the pulse reflection method for pre-location, changes in the emitted waveform and reflected waveform can be used to determine whether there is a clear fault reflection. The reflection characteristics of normal cables, open circuits, short circuits, and different types of insulation faults may differ. For inexperienced operators, it is not recommended to judge the fault point based solely on a certain peak on the screen, but to conduct a comprehensive analysis combining the cable type, testing method, and historical waveforms.
If conditions permit, the reverse test can be conducted from the other end of the cable. For example, if the suspected fault point distance measured from end A is 800 meters, and the distance measured from end B is 200 meters, and the actual length of the cable is approximately 1000 meters, then the two measurement results can form a good correspondence. By measuring from both ends, the influence of terminal, joint, and wave speed parameter errors caused by single-end testing can be reduced, and it is also a practical cross-validation method in cable fault location.
After pre-location, on-site more precise point determination usually requires the use of synchronous sound-magnetic positioning methods. For faults suitable for impulse discharge testing, if the safety conditions are met and the test plan is clear, the fault point can be located on-site based on the discharge signal generated by the fault point. When the fault point discharges, it will produce propagable sound waves and electromagnetic signals. The on-site positioning equipment can determine the approximate location of the fault point based on the arrival time and strength changes of the two types of signals.
In actual operation, staff usually come to the suspected fault area according to the distance obtained by the cable fault tester and then narrow the range for point-by-point scanning. As the positioning equipment gradually approaches the fault point, the signal usually shows significant changes. By comparing multiple measurement points, the location of the fault point can be further determined, rather than making a conclusion based solely on a single signal peak.
However, not all cable faults can be located directly using the sound-magnetic method. For some high-resistance faults, if a stable and obvious discharge signal cannot be formed, it may be necessary to first perform fault handling or use other suitable more precise point determination methods. Therefore, the verification methods for cable fault location need to be selected based on the type of fault, and it should not be assumed that the same steps are applicable for all faults.
For low-resistance faults or obvious short-circuit faults, additional verification can be conducted by combining test results such as insulation resistance and conduction status. For example, if an instrument has pre-located a certain section of the cable, and on-site inspection reveals that the insulation condition of this section is significantly abnormal compared to other sections, then the fault range can be further narrowed. However, the verification of electrical parameters is mainly for auxiliary judgment and should not simply replace professional fault precise location with a single insulation resistance test.
During the cable fault location process, the actual length of the cable is also an important reference factor. If the cable data records are incomplete, or the line has undergone multiple renovations, the length recorded in the archives may not be completely consistent with the actual length of the cable laid on site. At this time, even if the distance measurement of the cable fault tester is accurate, there may still be a situation where “the instrument says it’s here, but there is no fault on site”. Therefore, when conditions permit, it is necessary to conduct a comprehensive verification by combining cable path measurement, joint position, and cable well position.
The accuracy of testing the wave velocity also directly affects the judgment of the fault distance. The cable fault tester usually converts the distance based on the propagation speed of electromagnetic waves in the cable, and for cables with different structures and insulating materials, their actual wave velocities are not exactly the same. If the input wave velocity parameters have a large deviation, the measured fault distance will also have corresponding errors. Therefore, when inconsistencies between the distance found during cable fault location and the actual situation are discovered, it is necessary to first check the cable parameters and wave velocity settings rather than directly denying the test results.
For long-distance buried cables, it is recommended to use multiple information cross-validation during the location process. For example, first complete the distance pre-location using the cable fault tester, then confirm the corresponding section based on the cable drawings, then conduct a more precise on-site location using the acoustic-magnetic synchronous positioning equipment, and finally confirm the final result by combining on-site excavation or partial inspection. Through multiple stages of mutual verification, the probability of misjudgment can be significantly reduced.
The LD-2004 cable fault tester developed by Wuhan Guodian Xigao Electric Co., Ltd. can be used for fault detection and distance pre-location of power cables and buried cables. When using the LD-2004 for cable fault location in actual applications, it is recommended to take the instrument’s distance measurement results as one of the important bases for more precise on-site location, and then combine the cable path data, forward and reverse tests, and corresponding precise location equipment for confirmation. This is more reliable than simply relying on a single distance measurement result.
After completing the fault distance test using the LD-2004, if no obvious fault location can be found immediately on site, there is no need to rush to conduct a large-scale re-examination. One can first confirm whether the test waveform is stable, then check the test lines, grounding, and cable parameters, and simultaneously verify the actual cable length. If conditions permit, re-test from the other end and compare the distance results from both directions. When the two test results can be well matched, it indicates that the pre-location result has a high reference value.
During more precise on-site location, it is also necessary to pay attention to the influence of the environment on the location results. Underground cables may be surrounded by other cables, metal pipes, communication lines, and large electrical equipment, which may all cause interference to the positioning signal. Therefore, the locator needs to select an appropriate test position based on the on-site situation and repeat measurements at multiple points to observe the trend of signal changes, rather than measuring only one point.
After finally confirming the fault point, appropriate maintenance methods need to be adopted based on the on-site conditions. For damage to the cable body, it is necessary to further confirm the damaged location and fault nature; for faults at intermediate joints, it is necessary to focus on checking the construction quality, insulation status, and grounding condition of the joint; for terminal faults, it is necessary to check the terminal head and related connection parts. Only by confirming the specific type of fault can the subsequent maintenance be targeted.
It should be particularly noted that the fault location and impact test involving high-voltage cables are professional electrical testing tasks. Before the test, safety measures such as power-off, voltage verification, grounding, and isolation must be completed. The test must be carried out strictly in accordance with the equipment manual and on-site testing procedures. After the fault location is completed, one cannot directly contact or disassemble the cable just because the fault distance indicated by the instrument is clear. On-site personnel must confirm that the cable is in a safe state before proceeding with the next operation.
From practical experience, the more reliable cable fault location process should be “instrument pre-location – data verification – reverse verification – relatively precise on-site location – fault confirmation”. The cable fault location solves the problem of “where is the fault approximately”, the relatively precise location solves the problem of “which specific position is it”, and the final fault confirmation answers “why did the fault occur”. By doing these steps well, the efficiency of cable fault repair can be truly improved.
Therefore, after cable fault location, do not rush to excavate, and do not simply assume that the fault point has been determined based on a single distance value. After pre-location is completed using the LD-2004 cable fault tester, combined with waveform analysis, forward and reverse tests, cable data, and relatively precise on-site location for cross-validation, the fault location judgment can be made more reliable, and unnecessary excavation and maintenance work can be reduced.
Post time: Sep-17-2026