Power cable faults are one of the most common faults encountered during emergency power repairs. Due to the complex environment, detection can be challenging. While using a cable fault detector can reduce the difficulty of detection, other factors can also lead to mislocalization. To ensure accurate detection, it is crucial to follow the correct detection procedures when detecting a cable fault.
Cable Fault Locating Steps
① The first step is to measure the distance using a distance meter.
It is necessary to determine whether the cable fault is high resistance, low resistance, or ground fault, and to adopt different testing methods accordingly. If it is a ground fault, the distance can be directly measured using the distance meter's low-voltage pulse method. If it is a high-resistance fault, the distance can be measured using a high-voltage pulse discharge method. Using the high-voltage pulse discharge method to measure distance requires numerous auxiliary equipment, such as a high-voltage pulse capacitor, discharge bulb, current-limiting resistor, inductor coil, and signal sampler. This method is cumbersome, unsafe, and carries certain risks. Even more challenging is analyzing the sampled waveform, which requires advanced knowledge from the tester.
② The second step is to find the path (this step can be omitted if the path is clear).
To search for a path, a signal (path signal generator) is added to the cable. A receiver then receives the signal and walks along the signal path, thereby determining the cable's path. However, the path's range is approximately 1-2 meters, which is not particularly accurate.
③ The third step is to pinpoint the location based on the measured distance.
This method uses the sound produced by ignition and discharge. The fault point is located when the loudest sound is heard through the earphones of the pointing device. However, since it relies on sound, it takes a long time to find the sound due to ambient noise, and sometimes it can only be found at night. For cross-linked cables, this requires even more time, as cross-linked cables typically produce internal discharges, resulting in low, almost inaudible sound. Finally, only measurement is required.
Low-voltage cables have the following characteristics in actual use:
1. Laying is relatively random, and the path is not very clear.
2. When laying, do not bury the cable too deep after filling with sand and bricks, as is done with high-voltage cables. Shallow burial makes them more susceptible to external damage and destruction.
3. Cables are typically very short, ranging from tens to hundreds of meters, unlike high-voltage cables, which are typically hundreds to thousands of meters long.
Therefore, whether using or troubleshooting cables, it's crucial to follow the prescribed procedures and avoid any shortcuts, as this can lead to problems. The more knowledge you have about wires and cables, the better; it will always be useful in our daily lives.
