How Is An Underground Cable Fault Detected?

Rohan Mathew

With the development of the power grid and internet, underground cable systems have gained prominence. The underground cable systems save space as one doesn’t have to deal with wires above the surface. Moreover, safety hazards with underground cables are considerably less. This is because the chances of a human being coming into contact with underground cables are almost nil. Like all cable systems, underground cables are also prone to damage due to a variety of factors. These factors include wear and tear, rodents, and harsh underground conditions. The damage to a cable is called a fault. With underground cable systems, detection of faults is not an easy task. If the fault is detected, the repair person will only dig up that area to fix the cable. Otherwise, the whole line has to be dug up. There are many companies that can help with underground cable fault detection. HV Diagnostics is one such company. This company specializes in high voltage test equipment.


Underground cable faults and their detection

Underground cable faults are preferred because they’re quite protected from events above the surface, such as rains, thunderstorms, pollution, etc. The fact that they are underground prevents them from being damaged easily. However, one major downside to underground cable systems is fault detection. Detecting a fault in an underground cable system is a very difficult task. Unlike overhead cables, one cannot simply look and locate the fault.

The detection of a fault depends upon the type of fault that has occurred. The causes of these faults can be many. These may include mechanical injuries during their handling and transportation, damage due to moisture in the insulation, damages due to stress, and damage to the lead sheath caused by soil, water, or crystallization of lead. However, overall, the causes of damage for underground cables are still fewer than for overhead cables

There are three types of faults that can occur in underground cables:

  • Short Circuit Faults
  • Open Circuit Faults
  • Earth Faults

Short Circuit Fault:

This type of fault can only occur in multi-core cables. This fault occurs when two or more conductors that belong to the same cable come into contact with each other. This fault cannot be detected by the naked eye. In order to detect it, the cable has to be taken apart. This fault occurs when the individual insulation of the cable is damaged by coming into contact with another cable. The usual method to detect this fault involves the use of a megger.

A megger is an instrument that is used to measure the resistance of electrical resistance. As any expert will tell you, a short circuit is characterized by zero resistance. To detect the fault, the resistance between any two conductors is measured with a megger. The whole process of fault detection involves measuring the resistance between all the conductors, two at a time. If there is a short circuit fault, the megger will read zero. That would indicate that there is a short circuit fault between those two conductors.

Open Circuit Fault

An open-circuit fault occurs when there is an open circuit in the conductors. An open-circuit fault occurs when one or more conductor cores break. This leads to a discontinuity. This discontinuity can also happen if a cable comes out of its joint. That can happen due to mechanical injuries or stress. Unlike a short circuit, an open circuit is characterized by infinite resistance. The conductors at the far end are taken together, bunched, and then earthed. The resistance between each of these conductors is measured with the help of a megger. If the megger reads infinite resistance between a conductor and the earth, it is concluded that there is an open circuit fault.

Earth Faults

An earth fault occurs when any conductor comes into contact with the earth. An earth fault often occurs due to a damaged outer sheath. When the outer sheath is damaged, the cable can be exposed to the earth, and its chances of coming in contact with it increase. The lead sheath that prevents this from happening can either be damaged by agents such as water and soil or due to the crystallization of lead. The detection process of this fault is similar to those of other faults and can be completed using a megger. Similar to the short circuit fault, if the reading of the megger is nearly zero, it is concluded that there is an earth fault.

Once the fault is detected, the repair persons can easily dig up that area and fix the issue.