The method of using the step voltage method to locate the fault of the street lamp cable

Author: Noyafa–CCTV Tester

Using the step voltage method to locate the fault of the street light cable The input port is connected; the receiver automatically switches to the A-frame for troubleshooting. Using the step voltage method to locate the fault of the street light cable inside the mounting screw holes; the output cable is connected to the receiver“External sensor input”port connection; the receiver automatically switches to the A-frame troubleshooting mode, and the signal used for the pipeline detector receiver troubleshooting interface is the 8Hz ultra-low frequency composite signal, which can determine the current direction by measuring the phase, while The current direction can represent the direction of the fault point. The pointer dial in the upper right corner of the screen shows the current phase, and the arrow to the left of it indicates the direction of the fault point. 2. It is recommended to perform a confirmatory test near the grounding solder before formally finding the fault point to judge whether this method can be used for this fault finding.

The signal is injected into the pipeline from the transmitter, and leaks to the surrounding ground at the fault point. The leakage current is finally collected at the grounding solder and returned to the transmitter. If the receiver can detect a strong enough signal near the grounding rod and respond in the correct direction, it means that the injected signal is strong enough to meet the needs of troubleshooting; the signal near the grounding rod is the strongest, if there is no correct response here, it means It is possible that the fault resistance is too high and the injection current is too small to be able to check the fault. Near-end test: back against the grounding rod and leave a distance of 2m, insert the A-frame probe into the ground in the direction that the red end of the A-frame points to the end of the pipeline.

After the insertion is firm, you should keep your hands away to avoid contact, to prevent interference caused by the electromagnetic field induced by the body, and to avoid the shaking of the A-frame. Adjust the gain of the receiver until the signal amplitude is large enough, observe the amplitude and phase, if they are relatively stable, it means the reception is normal. Observe the arrow, the arrow should point forward at this time, indicating that the fault point is towards the end and away from the grounding pin.

If the amplitude and phase are unstable, the change range is large, and the arrow cannot keep pointing forward (the end of the pipeline), but frequently changes up and down, it means that the injected signal is too small to be received normally. Surround test: If the reception is normal, according to the principle of black near red far, there should be a stable response around the grounding rod, and the arrow should always keep forward. Determine the response range: start from the near end of the pipeline, away from the transmitter, keep the red end of the A-frame forward to the end, and gradually move away from the transmitter for testing.

As the distance increases, the signal gradually decreases, and the gain needs to be gradually increased accordingly, and the signal amplitude and phase will gradually become unstable, and will eventually become indistinguishable. Record the position and receiver gain when the signal is just still correctly resolved. The distance from this position to the grounding pin is the maximum one-way response range of this fault.

Considering the environmental factors of pipeline burial (for example, the EHV cable is laid in the cable trench, but can only be tested outside the trench), the response range at the fault point is generally smaller than that at the grounding brazing. Therefore, it is recommended to use 1/3~1/2 of the measured response range as the test interval. For example, if the measured response range is 20m, the recommended test distance is 6~10m.

When this interval is used for troubleshooting test, it can avoid too large distance and miss the fault point, and can speed up the test speed. During the test, it is recommended to use the gain value recorded when determining the response range, so as not to miss small signals, and to avoid unnecessary noise response caused by the gain being too large. If the substation ground is used as the transmitter ground, the proof test will not be possible.

The recommended general test spacing is 3~5m, which can meet most needs without compromising efficiency. If the fault resistance value is high, reduce the test interval appropriately. 3. The obstacle detection test starts from the near end of the pipeline, faces the end, carries the receiver and the A-frame, keeps the red end of the A-frame forward (points to the end of the pipeline), and conducts the test with roughly equal spacing and receiving gain each time. Measurement.

At the beginning, the signal is strong and stable due to the closeness to the grounding pin, and the arrow points forward. As the distance increases, the signal gradually decreases until it becomes indistinguishable. Continue to test until you find a point where the signal amplitude, phase, and arrow direction are stable, indicating that the fault point is approaching.

Observe the direction of the arrow: if the fault point is ahead, the arrow is forward; if the fault point has been crossed, the arrow is backward. Approach to the fault point step by step according to the arrow direction. During the approach, the test interval should be gradually reduced, and the gain should be reduced accordingly to adapt to the gradually increasing signal. Eventually, when the fault point is right between the two probes of the A-frame, the signal strength will drop suddenly, and a slight movement will change drastically.

Move the A-frame with a small distance, and you will find a point with a sudden change in the direction of the arrow and the lowest signal strength, which is the fault point. If the path of the pipeline is not very clear, you can turn the A-frame to an angle perpendicular to the pipeline to test until you find the point where the arrow reverses. Approaching from multiple directions can determine the exact location of the fault point.

4. Precautions (1) When detecting, the operator must keep facing the end of the pipeline, the red end of the A-frame is in front (pointing to the end of the pipeline), and the direction of the receiver should be consistent (towards the end). (2) After firmly inserting the A-frame probe into the ground, keep your hands away to avoid contact, to prevent interference caused by the electromagnetic field induced by the body, and to avoid the A-frame shaking. (3) In the process of inserting and pulling out the soil of the A-frame, there will generally be a very large response. This is a false signal. After inserting it stably and removing the hand, observe the amplitude and direction of the signal.

(4) If the cable is laid in a cement cable trench and covered with a cement cover, it is better to probe on the soil next to the cable trench, rather than above the cement cover. (5) If the cable is under the hardened road, it is best to detect it in the grass/soil next to the road. If the land is too far from the cable, the detection effect will be poor, and the measured distance should be reduced to avoid missing the fault point. (6) The detection effect is poor directly on the dry hardened pavement (asphalt, cement or brick pavement), and the effect of wetting the ground with water will be improved to a certain extent.

(7) During the troubleshooting test, press“Measurement”The function of the key is also automatic gain. After inserting the A-frame probe firmly into the ground, use“Measurement”The key to automatically adjust the gain can speed up the detection speed.