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How to Find Underground Cable Faults?

Views:222     Author:Site Editor     Publish Time: 2020-10-13      Origin:Site


At present, power cables are the main equipment for power transmission. Once the cable fails, it will affect the normal transmission of power and cause immeasurable economic losses. But now most cables are buried under the ground, so it is more difficult to find cable dead short circuit points. So how can we find the short circuit and overloading faults of buried cables simply and quickly?


short circuit and overloading fault indicator



1. Segmentation

The segmentation is the oldest and simplest method to detect the location of electric wire short circuit faults in underground cables. As the name suggests, it requires cutting and physically splicing cables. Usually, the cable is cut into smaller parts, and each component is tested with an ohmmeter or tester. By testing each piece of the cable, you can narrow down the exact parts that need to be repaired. The only major disadvantage of this cable fault detection method is that it is laborious and means that underground cables are repeatedly excavated.

 

For example, at a length of 500 feet, you can cut the cable into two 250-feet sections and use an ohmmeter or a high-voltage insulation resistance (IR) tester to measure. The defective part shows a lower IR than the good part. You will repeat this procedure until you find the electronic short circuit fault part.

 

 

2. Heavy Hit

When you supply high voltage to a faulty cable, the high current arc generated will produce noise to allow you to hear the sound on the ground. Although this method avoids the cutting and splicing, it has its own disadvantages. At voltages up to 25kV, a heavy hit requires about tens of thousands of amperes of current to make underground noise loud enough so that you can hear the sound on the ground.

 

Heating from this high current often leads to some degradation of the cable insulation. If you are proficient in the thumping method, you can limit the damage by reducing the power sent through the cable to the minimum required to perform the test. Although moderate testing may not have a noticeable impact, continuous or frequent testing can cause the cable insulation to degrade to an unacceptable state.


ground fault indicators



3. TDR

Time Domain Reflectometer (TDR) sends low-energy signals through cables without causing insulation degradation. A theoretically perfect cable returns this signal in a known time and a known profile. The impedance change in the "real world" cable will change the time and profile, and the TDR screen or printout is graphically represented. This graph (called "trace") provides users with approximate distances from "landmarks" such as openings, connectors, Y-faucets, transformers, and water inlets.

 

One of the weaknesses of TDR is that it does not detect the ground short circuit fault. TDR is accurate to about 1% of the test range. Sometimes, this information is sufficient. Other times it still needs to make a more precise heavy hit. However, this increased accuracy can greatly save cost and time. The typical result is "438 feet 510 feet". If the fault is located at 440 feet, you only need the distance from 428 feet to 448 feet, not the entire distance of 440 feet.

 

Another weakness of TDR is that the reflectometer cannot see the ground ac short circuit fault, and the resistance is much greater than 200 ohms. Therefore, in the case of a "bleeding fault" rather than a power short circuit or close to a cable short circuit, TDR is blind.

 

 

We can provide you with professional ground fault indicators and line fault indicators to help you find underground cable faults more accurately.


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