Damage to LV and MV cable insulation in densely developed areas entails the risk of costly, misdirected excavations. The answer to this challenge is the LKR-2500 A-Frame from Sonel. Thanks to digital operator support, this tool allows for the precise determination of fault locations and revolutionizes modern cable diagnostics.

Challenges in power line diagnostics: the "potential funnel" problem

When the insulation of LV, MV, and other power lines is damaged, it becomes crucial to precisely determine the point of current leakage to earth. In practice, this means the necessity of locating the so-called "potential funnel", i.e., the point where energy "escapes" from the conductor and dissipates in the ground.
 
In the reality of a densely developed area, even a small location error leads to costly excavations, interference with the surface, and the risk of damaging accompanying infrastructure. Therefore, professional diagnostics cannot end solely with determining the cable route.

A-Frame vs. classic locators

The answer to these challenges is the LKR-2500 A-Frame from Sonel. It is a tool designed to precisely determine the fault location of sheaths and insulation. Unlike classic electromagnetic locators, the system uses the earth potential difference method, allowing the operator to actually track and follow the fault current.

Operating principle of the Sonel LKR-2500 system: potential difference and phase shift

The operating principle of the system is based on injecting a measurement signal into the tested cable from the Sonel LKN-2500 transmitter, with frequencies of 263 Hz + 526 Hz or 512 Hz + 1024 Hz, depending on the selected operating mode. At the fault location, a characteristic potential distribution (earth potential gradient) is created, which is detected by the A-Frame equipped with two measurement electrodes. 

The condition for obtaining correct readings is guiding the A-Frame along the route of the tested cable. A significant deviation from the cable axis causes a change in the potential distribution measured by the electrodes, which may lead to signal attenuation and misinterpretation of directional indications.

The device records not only the potential difference but also analyzes the phase shift of the signal. This allows for the unambiguous identification of the leakage current and distinguishing it from passive interference or induction. On this basis, the system precisely indicates the direction to the insulation fault location.

Safe excavations and high accuracy in the fault zone

As you approach the fault location, the measurement values increase, and after passing it, the direction of indications is immediately reversed. The change in direction and signal characteristics allows for unambiguously determining the fault zone with an accuracy corresponding to the spacing of the A-Frame's electrodes. In practice, this means indicating an area with a width of just over a dozen centimeters, which ideally matches the width of narrow backhoe excavator buckets.

This precision allows for the safe removal of the topsoil layer using heavy equipment only down to the level of the marker tape. Further work, directly by the cable, should be carried out manually, which eliminates the risk of accidentally cutting the insulation with an excavator bucket. An excavation prepared in this way not only marks the fault location but also provides the fitter with the necessary space to move freely and correctly make a repair joint.

Potential distribution analysis: locating the zero-crossing point

As the operator nears the fault location, the measurement values increase dynamically, peaking just prior to the fault. This process is depicted by a characteristic curve, popularly termed the “mustache curve”, showing the ground potential distribution. Right at the fault point (peak), the reading crosses zero, and immediately reverses direction once the point is passed.

It is worth emphasizing that the precise visualization is the result of the operation of the full Sonel LKZ-2500 Pro set (integration of the LKR A-Frame with the LKD detector). Thanks to this fusion, the user sees on the tablet screen not only the direction to the leakage but also confirmation of the cable route, which is manifested by a change in the color and direction of the arrow exactly at the zero-crossing point. Such a characteristic allows for flawless "centering" of the instrument over the insulation defect.

In practice, the user sees this on the tablet screen as a change in the color and direction of the arrow, e.g., from green to red, when moving the A-Frame just a few centimeters along the cable axis. Such a characteristic allows for precise "centering" of the instrument exactly over the insulation defect.

Digital signal processing and full measurement automation

A key advantage of the Sonel LKR-2500 is its modern signal processing architecture. The applied algorithms perform digital correlation in real time, analyzing the signal with a very high time resolution. In practice, this translates into a high signal-to-noise ratio (a higher SNR means better quality, a clearer signal, and less interference) and the stability of indications even at very low signal levels. This eliminates the phenomenon of "floating" readings and significantly improves the comfort of work in difficult field conditions.

Importantly, the device operates fully automatically. When working with the LKR or LKD system, the operator does not have to waste time on manual adjustment of the signal gain. This intelligent automation provides a much lower entry barrier for inexperienced or novice workers, allowing them to perform tasks flawlessly and effectively from the very first day of working with the equipment.

Remote control and hardware optimization with the Sonel LKZ Mobile app

The system was designed according to the "point and find" philosophy. Thanks to full integration with the Sonel LKZ Mobile app, the user receives unambiguous directional indications in the form of dynamic arrows, which eliminates the need to interpret raw data and reduces the risk of errors. 

The entire system is controlled remotely using a smartphone or tablet. In terms of hardware, the manufacturer provides the user with full flexibility: a dedicated mobile device can be purchased in a ready-made set, or the equipment that employees already have at their disposal can be used. Such unification makes it possible to reduce the number of devices taken to the field and significantly optimizes implementation costs.

However, the capabilities of the application itself go far beyond the measurement itself. The system allows for the digital recording of the entire cable route along with the applied results from the LKR A-Frame. At the point where an earth fault is detected, the operator can create a precise measurement point, enriched with photo documentation, voice notes, and exact GPS coordinates.

A report prepared in this way can be immediately shared with repair teams. Importantly, this is a much more reliable method than traditional ground markers (paint, pegs), which can be washed away by rain or displaced during field work. Thanks to the function of navigating to a saved point, the repair team can return to exactly the same place even after a long time, retracing the route and using the saved fault as a routing target. 

Maximum immunity to urban interference thanks to data fusion

In an urban environment, immunity to interference becomes particularly important. However, it should be remembered that every location method, regardless of the class of the device used, is subject to limitations resulting from the laws of physics and the specific nature of a given environment. Factors such as extreme soil mineralization, rapid changes in its moisture content, or extreme density of conductive underground infrastructure can affect signal stability and, in specific conditions, even make precise cable tracing impossible.

The Sonel system solves this problem through advanced data fusion, namely the ability of the A-Frame to work simultaneously with the LKD-2500 detector. In this configuration, the A-Frame pinpoints the earth fault based on the voltage gradient, while the detector verifies the route by analyzing the parameters of the magnetic signal. Such measurement redundancy provides the operator with additional diagnostic data, allowing for a reliable assessment of the situation where single methods fail.

This approach allows for effectively distinguishing a real fault from stray currents or induction in neighboring installations. The system makes it possible to detect both severe short circuits and early, high-resistance insulation faults that are just beginning to develop.

The integration of location functions enables simultaneous tracking of the cable route and determination of the fault location during a single measurement pass. This significantly increases work efficiency and shortens the fault location time.

Ergonomics, IP67 protection, and professional field documentation

The ergonomics of use are also of great importance. The lightweight, folding design of the A-Frame and wireless Bluetooth communication eliminate the limitations typical of older wired solutions and significantly facilitate operating the equipment in the field. In addition, the high IP67 protection rating ensures the reliable operation of the structure even in the harshest weather conditions, such as heavy rain or mud.

Modern diagnostics also means full documentation. The system allows for recording results along with GPS location, photos, and field notes. As a result, each fault can be precisely documented and forwarded to service teams as a complete set of data to undertake repair actions.

Summary: higher operational efficiency and quick return on investment

The use of the LKR-2500 A-Frame means transitioning from approximate location to precise pinpointing of the fault location. Reducing the scope of excavations, shortening repair times, and increasing work safety ensure that the investment in the system pays for itself quickly and provides measurable operational benefits.