Over time, the world has adopted the idea of underground cables. You won’t find many electric poles with loosely connected cables and wires on the street. This may have given the idea that underground cables are safe as no one has to feel threatened by broken poles with loose electric-powered cables on the road. Well, truth be told, that’s not the case.
Nowadays, underground cable faults have emerged to be triggering concern due to their more significant risks. Excavation, water damage, and poor installation can cause such a risk, especially at residential, commercial, and mining sites. Although the risk is significant, several underground cable fault locating companies have stepped up to make things less complicated.
Today, we will discuss the dangers of underground cable faults and ways to locate the faults, along with solutions for them. So, let’s dive in.
Any damage to underground power cables can result in injuries. This typically happens due to the associated fire and explosive impact of the arcing current. It mainly occurs when the conductor insulation and the cable cover case gets perforated by any sharp item. Another reason may be the excess pressure that results in the cable getting crushed severely and enabling contact between the conductor(s) and the overlayer.
The repercussion of such an incident results in severe and probably fatal burns to the body, face, or hands. Another danger associated with underground cable faults is direct electric shock. Moreover, some high-voltage underground cables are oil-filled, so any fault may result in ignition. If the damage from such electrical fire extends to nearby gas stations or gas pipes, the outcome can turn out to be catastrophic.
Although the possibility of experiencing underground cable faults is low, these cables can become a big-budget replacement if the issue doesn’t get resolved as soon as possible. That’s why getting in contact with a professional underground cable fault locating company has become the best solution to avoid such catastrophic repercussions and costly replacements in the first place.
Engineers who prefer circular connectors for cable joints are the same type of people who contributed to the innovation of a megger, which made things easier for underground cable fault locating companies. However, special techniques remain the topmost requirement for determining the exact location of the underground cable fault. The two most popular techniques to locate faults in underground cables are Murray and Varley loop tests.
Keeping aside the mainstream techniques, we will talk about some other popular techniques, which includes:
By definition, a cable thumper is considered a compact and portable surge generator with a high-voltage capacity. It usually serves the purpose of inserting a DC surge of about 25 kV into the underground cable with fault. With the high voltage supply, a high-current arc will be generated by breaking the open-circuit fault. The high-current arc produces a distinctive thumping sound on the exact cable fault location.
To determine the underground cable fault location, the professional sets a thumper to hit the ground constantly. Then, the professionals walk along the cable path to hear this thumper-produced sound. The higher the DC voltage, the more the thumping sound. This is an effective method to resolve issues associated with shorter cables. However, this method becomes obsolete when it comes to longer cable faults.
A TDR or Time Domain Reflectometer plays a crucial role in sending an ephemeral and temporary low-energy signal (50V) into the underground cable while maintaining a high repetition rate. The signal gets reflected back from the point where there’s a hindrance in the underground cable (fault).
The principle of work of TDR is somewhat similar to that of the principle of RADAR. With TDR, professionals determine the time required for the signal to come back from the point of change in hindrance (fault).
The elapsed (passed) time and the amplitude of the reflections get tracked down via graphical display. The distance of the fault location is directly proportional to the elapsed time. If the signal experiences a high hindrance or open circuit, the amplitude encounters deflection upward. However, the amplitude undergoes negative deflection on the graphical display for short-circuit failure.
The inability of the low-voltage TDR method to identify the high-resistance underground cable faults has made it limited in use for the locating services. To get rid of such limitations, some advanced high voltage RADAR methods were introduced. They are:
- Arc Reflection Method: This method revolves around the application of TDR with a thumper and filter. An arc is created over the shunt fall using the thumper, resulting in a temporary short-circuit. This leads the TDR to effectively exhibit a downward deflection. Moreover, the TDR stays protected against the high voltage surge from the thumper via the arc reflection filter.
- Surge Pulse Reflection Method: The use of a storage oscilloscope (analyzer), a thumper, and a current coupler become essential for this method. This method is crucial when the long cables with faults become troublesome to arc over, even with the arc reflection method. In the surge pulse reflection method, there’s no filter and the cable is directly connected to the thumper. This way, you can limit the application of both the current and voltage to the cable fault. A high voltage pulse gets inserted into the cable via the thumper to create an arc across the fault.
- Voltage Decay Reflection Method: In this method, a storage oscilloscope (analyzer), a dielectric test set, and a voltage coupler is needed. When it comes to transmission class cables, this method stands out as the most effective one. It resolves the issue with transmission class cables when the arc generation at the cable fault needs a tremendous amount of breakdown voltage than what any surge generator or thumper can provide. Here, the reflections generated from the flashover of DC voltage at the cable fault gets sensed and detected by the voltage coupler.
With the rapid technological advancement in the electrical world, several companies have started to provide underground cable fault locating services. However, it’s best to seek services from the one who uses the latest technologies and machines like the Frame Fault Finder locating device.
Also, most importantly, the service provider must have knowledge and skills to implement all these above-mentioned techniques. So, have a good read and let’s meet again with some enticing articles.