Advantages of identifying live LV and MV electrical cables
Identification of live electrical cables, a need
The repair of breakdowns and maintenance works on electrical distribution cables in electrical sector is a very common task by the utilities and the companies that carry out these works for the utilities.
These Jobs may be a consequence of the deterioration of the cables, accidents when digging or simply due to a scheduled cable replacement activity, new client’s connection, splices, etc.
Historically, this task has caused numerous accidents, both for workers with disastrous consequences in the worst cases, as well as outages affecting to hundreds of customers. Mostly, these situations have been caused by the lack of cable identification procedures and adequate instruments to do so, causing confusion to the worker, and finally cutting the wrong cable.
Methods of energized cable identification
For some time now, electrical utilities have been increasingly aware of this problem and different identification methods have been established, including working with “Cable identifiers”, which identifies unambiguously the cable to be cut, injecting a specific signal at a known end of the cable and identifying it at the point where the cut is going to be made. Most of these devices work with de-energized cables, requiring the planning of a electric power cut to carry out the identification.
The usual operation of a cable cut consists in several phases, once the excavation is done and there is access to all the cables going through it:
(1) electrical power cut,
(2) identification of the cable,
(3) works to be done in the cable itself (replacement, repair, etc…) and
(4) commissioning and reconnection.
The operation of de-energizing a line often involves the cutting of the power supply to an important group of customers, consumers or more sensitive facilities such as factories, hospitals, etc…, with the corresponding damage.
For that reason, most of the time here is a limited and reduced space of time to carry out the tasks required on the cable and, therefore, the work must be carried out quickly and safely. The duration of the power interruptions has an impact on the service quality of the electrical utility (SAIDI) and can lead to penalties.
Energized cable identification
The Cable Identifiers devices that can operate under voltage, and perform the identification unambiguously have therefore certain advantages over those that only identify de-energized cables.
1/ The identification task, although it must be notified in advance to the company’s operating department of the electric network, it does not require a power supply cut nor much anticipation in the request for the said operation. This identification enables to locate the cable and mark/identify it prior to the power cut-off, so that the day of the works are carried out on the cable, with its corresponding power cut, it will be known in advance which cable it is, and a second identification can (and should) be done without voltage, ensuring the operators of the correct signaling of the cable and that no change has been made in the meantime. More safety for the worker, shorter power cur-off.
2/ Although the identification is carried out on live cables, isolated sensors are used without the need to access the conductive (live) part of the cable, although PPE corresponding to the voltage level of the lines must be used, It simply requires a direct low voltage connection from the transmitter to the line to be identified.
There is a very wide range of de-energized cable identifiers on the market, as well as energized cable identifiers. However, you can also find some more sophisticated equipment capable of performing the two types of identifications above.
Additionally, the company Merytronic developed a few years ago, in collaboration with an electricity company, a very versatile cable identifier that, in addition to identifying de-energized cables, can identify energized MV cables too, by injecting the signal through the LV side of the distribution transformer, reaching very long distances.
Benefits of using cable identification devices
The benefits provided by the use of this equipment in cable maintenance and repair operations are:
- Save time on the day of identification (where there is a stipulated cut-off with a start and end time).
- Carry out the identification exhaustively and without stress.
- Redundantly ensure that the cable to be cut is the “good” one.
- Guarantee the safety of workers and distribution networks
In conclusion, it can be said that the use of live cable identification devices by electric companies and their contractors not only offers advantages with respect to the safety of operators and networks, but also provides a reduction in labor costs of maintenance and an improvement in the management of its networks and quality of service.
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