RU238937U1 - Self-diagnostic power cable - Google Patents

Abstract

The utility model relates to electrical engineering and the cable industry, in particular to the design of power cables intended for use in systems requiring increased reliability and continuous monitoring of the cable line's condition. The technical result consists of increasing the accuracy of converting complex mechanical deformations and temperature changes of the cable body into a single, spatially localized optical signal, providing the ability to obtain reliable information about the internal thermomechanical state of the cable along its entire length. This technical result is achieved by providing a monolithic connection between the sensor element and the cable structure. The cable, comprising a conductive insulated core and an outer protective sheath, also contains a sensor optical fiber with fiber Bragg gratings applied thereto. The optical fiber is integrated into the cable structure and arranged in a spiral, with the space around the sensor optical fiber filled with a hydrogel layer, over which an intermediate sheath is located. 4 fig.

Description

FIELD OF TECHNOLOGY TO WHICH THE UTILITY MODEL RELATES

This utility model relates to electrical engineering and the cable industry. Specifically, it concerns the design of single- and multi-core power cables intended for use in systems requiring increased reliability and continuous monitoring of cable line conditions. The introduction of a hydrogel filler layer further enhances vibration resistance and overall cable durability, which is critical in harsh operating conditions.

The main areas of application are:

Energy sector. For high-voltage underground and especially underwater power lines, the cost of failure and repair is colossal, and direct access for inspection is difficult or impossible. This technology enables continuous integrity monitoring, detecting ground movements, ship anchor impacts, localized overheating in couplings, and other anomalies before they lead to catastrophic failure. The immunity of fiber Bragg grating sensors to the strong electromagnetic fields inherent in high-voltage lines is a critical advantage here. A hydrogel layer provides additional waterproofing and damping, protecting the sensor fiber from dynamic loads and moisture.

Industrial automation and robotics. Cables connecting moving parts of robotic arms and other industrial equipment are subjected to millions of bending and torsion cycles, leading to fatigue failure. An integrated monitoring system based on fiber Bragg gratings (FBGs) can track fatigue stress accumulation in real time. The presence of a hydrogel ensures a perfect mechanical connection between the sensor and the cable's load-bearing elements, enabling highly accurate recording of even the slightest deformations. This allows for a transition from routine cable replacement (often premature) to replacement based on actual condition, preventing unexpected shutdowns of production lines.

LEVEL OF TECHNOLOGY

The prior art provides various designs of power cables equipped with monitoring systems to improve their operational reliability.

A technical solution known as an equivalent is patented by the Russian Federation for utility model RU 190398 U1 (IPC H01B 9/00, published July 1, 2019). This power cable contains a temperature sensor in the form of a standard optical fiber integrated into the strand of the conductive core. Temperature monitoring is performed using distributed temperature sensing (DTS) technology based on the Raman effect, which allows for a continuous temperature profile along the cable's length and increases its resistance to thermal damage. A disadvantage of this design is its monoparametric nature—the system can only measure temperature but cannot detect mechanical deformations (bending, torsion), which are a common cause of failure. Furthermore, DTS technology has low spatial resolution (approximately 1 meter), making it difficult to precisely localize point defects.

The utility model under Russian patent RU 195214 U1 (IPC H01B 11/22, published January 17, 2020) was selected as the closest analogue (prototype). This power cable, like the claimed solution, uses fiber Bragg grating (FBG)-based sensors integrated into the outer layer of the conductive core as control elements. The technical result of the prototype is increased operational reliability due to the ability to precisely (down to centimeters) localize existing faults, such as breaks, breakdowns, or localized heating.

The design of the prototype prevents it from achieving the technical result promised by the claimed utility model. The prototype utilizes a standard longitudinal arrangement of the optical fiber with a FBG, which is primarily sensitive to axial strain and temperature. This configuration only allows for the detection of the final result of mechanical failure (e.g., breakage), but is incapable of measuring and quantifying accumulated mechanical stresses from bending and torsion, which lead to fatigue failure of materials and are the primary cause of many failures. Furthermore, the prototype lacks a component that guarantees complete and stable transmission of strain from the cable's load-bearing elements to the sensor fiber, which could lead to measurement errors.

Thus, the prototype solves the problem of reactive fault detection, but does not solve the technical problem of creating a cable capable of comprehensive predictive monitoring of its entire thermomechanical state with high accuracy.

DISCLOSURE OF THE ESSENCE OF THE UTILITY MODEL

The technical result consists in converting complex mechanical deformations (bending, torsion, stretching) and temperature changes of the cable body into a single, spatially localized optical signal with increased accuracy due to the provision of a monolithic connection of the sensor element with the cable structure, providing the ability to obtain reliable information about the internal thermomechanical state of the cable in real time along its entire length.

The essential features characterizing a utility model include:

• The presence of at least one insulated conductive core.

• Presence of an external protective shell.

• The presence of a sensor optical fiber integrated into the cable design.

• The sensor optical fiber is made with fiber Bragg gratings applied to it.

• The sensor optical fiber is arranged in a spiral, which ensures its sensitivity to bending, twisting and stretching of the cable.

• The presence of a hydrogel filler layer located around the sensor optical fiber to provide reliable mechanical connection and additional protection.

• The presence of an intermediate shell located on top of the hydrogel layer.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 shows a section of a single-core structure.

Fig. 2 is a general view of a single-core structure illustrating the helical arrangement of the sensor fiber.

Fig. 3 shows a section of a multi-core structure.

Fig. 4 is a general view of a multi-core structure illustrating the helical arrangement of the sensor fiber.

Construction: 1 - conductive core, 2 - insulation, 3 - sensor optical fiber with fiber Bragg gratings applied to it, 4 - hydrogel filler layer, 5 - intermediate shell, 6 - outer shell.

IMPLEMENTATION OF THE UTILITY MODEL

The claimed self-diagnosing power cable can be made in various design variants, including single-core or multi-core designs, as demonstrated by examples of its possible implementation below.

Example 1. Single-core construction (Fig. 1, 2).

The cable contains a central conductive core (1), which can be made of any suitable electrically conductive material.

The core (1) can be either solid or stranded to provide the required flexibility.

The core (1) is covered with a layer of insulation (2) made of a dielectric material with sufficient electrical strength and heat resistance.

A sensor optical fiber (3) coated with fiber Bragg gratings is arranged in a spiral around the insulation layer (2). The space around the sensor fiber (3) is filled with a hydrogel layer (4), which provides its fixation, protection, and ensures the precise transmission of all mechanical and thermal effects from the cable structure to the sensor. An intermediate sheath (5) is located on top of the hydrogel layer, providing additional fixation and protection for the internal components. The entire structure is enclosed in an outer protective sheath (6).

For applications requiring increased electromagnetic compatibility or additional mechanical strength, the design may optionally include a screen in the form of a braid of tinned copper wires (not shown in the drawings) located under the outer protective shell (6).

The intermediate and outer sheaths are made of polymeric materials selected based on the cable's operating conditions (e.g., to protect against mechanical damage, moisture, and ultraviolet radiation). Examples of materials used include PVC, polyethylene, or halogen-free compounds.

Example 2. Multi-core structure (Fig. 3, 4)

The cable contains two or more conductive conductors (1), each covered with a layer of insulation (2), twisted into a core. A sensor optical fiber (3) with a FBG is spirally wound over the core formed by the conductive conductors. The spiral winding converts bending and torsional strains of the entire cable into axial tension/compression of the optical fiber, enabling their effective detection.

The entire interveinal space, including the area around the sensor fiber (3), is filled with a layer of hydrogel (4). In this case, the hydrogel not only ensures the integrity of the structure for precise deformation transfer but also serves as a seal and prevents longitudinal moisture spread.

The design also contains an intermediate (5) and outer protective (6) shell, the materials and purpose of which are similar to those described in Example 1.

Also, similar to the single-core design, for special operating conditions the cable can be additionally equipped with an optional shielding layer.

The operation of the device is based on the physical properties of fiber Bragg gratings (FBGs) and is independent of the specific cable design.

1) The fundamental principle of the VBR.

A fiber Bragg grating is a periodic structure with a variable refractive index created in the core of an optical fiber. This structure acts as a highly selective mirror, reflecting light only at a specific wavelength, known as the Bragg wavelength (λ _B ).

It is described by the fundamental relationship:

λ _B =2n _eƒƒ Λ,

where n _eƒƒ is the effective refractive index of the fiber core, and Λ is the grating period (the refractive index modulation step). Any external influence capable of changing n _eƒƒ or Λ will result in a measurable shift in the reflected wavelength.

2) Mechanisms for converting physical effects into an optical signal.

The VBR is sensitive to two key parameters simultaneously: mechanical deformation and temperature.

Strain response: When a section of fiber is subjected to axial tension or compression, its physical length changes, which directly affects the grating period Λ. Additionally, due to the photoelastic effect, the refractive index n _eƒƒ also changes. The combined effect results in a shift in the Bragg wavelength, which is directly proportional to the applied strain.

Temperature response: A change in temperature causes two effects: thermal expansion of the fiber material (changes Λ) and the thermo-optic effect (changes n _eƒƒ ). As a result, a linear shift of the Bragg wavelength is observed with changes in the ambient temperature.

3) The operation of a self-diagnostic power cable is a cyclic process of interrogation and analysis, which can be divided into several stages:

Stage 1. Interrogation. An external device, called an "analyzer (interrogator)," is connected to the optical fiber. This device generates and sends a broadband light pulse into the fiber.

Stage 2. Wavelength-specific reflection. Light propagating through the fiber reaches each of the fiber Bragg gratings. Each FBG has a unique period in its structure and, as a result, reflects light back to the interrogator only in a very narrow spectral range—its so-called Bragg wavelength. The rest of the light spectrum passes on to the next grating.

Stage 3. Wavelength shift under stress. When a section of the cable is subjected to mechanical deformation or temperature change, the hydrogel layer (4) ensures instantaneous and precise transmission of this stress to the sensor fiber (3). This change in the grating period results in a proportional shift in the reflected Bragg wavelength. The advantage of the hydrogel is that it transmits deformation without loss or distortion, significantly increasing the accuracy and sensitivity of the entire monitoring system.

Stage 4. Detection and localization. The interrogator receives signals reflected from all FBGs. It analyzes their spectrum and detects the wavelength shift from each specific grating, allowing the magnitude of the impact (degree of deformation or temperature change) to be determined. Simultaneously, by measuring the delay time between the transmission of the pulse and the reception of the reflected signal from each FBG, the interrogator accurately calculates the location of each grating and, accordingly, the coordinates of the event along the cable. This dual capability—quantification and precise localization—is the essence of the technical result achieved.

Claims (1)

A self-diagnosing power cable comprising at least one conductive core, its insulation and an outer protective sheath, characterized in that it is additionally provided with at least one sensor optical fiber with fiber Bragg gratings applied thereto, integrated into the cable structure and arranged in a spiral, wherein the space around the sensor optical fiber is filled with a hydrogel layer, on top of which an intermediate sheath is located.