Utility companies today install their cables underground to promote effective service provision. While this is an excellent option that's rarely affected by external environmental elements like the rain, wind, and sunlight, there is one major limitation the company has to handle to ensure the distribution system functions optimally – fault testing or detection. Because the cables are installed underground, mostly in pressurised ducts, damages can go unnoticed for long compared to overhead lines. For this reason, early detection of these faults should always be prioritised. This post will share common causes of underground cable faults and how cable locating experts detect them.
Open circuit fault
This fault occurs when the conductor breaks, leading to a discontinuity. The discontinuity may also occur once cables come out of their joints as a result of mechanical stress. To check this fault, a device known as a megger is used. Conductors at the end are bunched together (shortened) and connected to the ground (earthed). Then the megger is used to measure the resistance between every conductor and the surface (earth). In case the readings show zero resistance in the conductor's circuit, it will mean that it's still in excellent condition. However, if an infinite resistance is measured, you can be sure the conductor is broken and must be replaced.
Short circuit fault
This is a fault that affects multi-cored cables. An insulator fails when two conductors or the multi-core cable come into contact electrically. This leads to short-circuit failure. The fault often occurs once cable insulation gets damaged. This problem can be detected visually using a megger, so you won't have to worry about isolating the cables.
To get the readings, two megger terminals are linked to the two conductors. If the megger reveals a zero reading, then it means that a fault is detected. The same procedure is repeated by fixing the other two conductors at a time until all of them are tested.
Earth fault
Earth fault occurs whenever a cable conductor touches the earth surface. This happens when the conductor's outer sheath gets damaged by mechanical crystallisation and vibration or a chemical reaction with the soil. A megger can also be used to detect this type of fault.
To identify the fault, two megger terminals need to be connected to the ground and the conductor, respectively. If you get a zero reading, then an earth fault has occurred. The same process is repeated with the other conductors. New techniques of cable locating can also be used, but they involve the use of sophisticated technology. Contact an electrician for more information.
