WO2022003559A1

WO2022003559A1 - System and method for dinamic monitoring of a high-tension electric line

Info

Publication number: WO2022003559A1
Application number: PCT/IB2021/055809
Authority: WO
Inventors: Elsa De Sá Caetano
Original assignee: Universidade Do Porto
Priority date: 2020-06-29
Filing date: 2021-06-29
Publication date: 2022-01-06

Abstract

The present invention relates to a system and to a method for dynamic monitoring of a high-tension electric line (HTEL). The system comprises a fibre-optic based transducer node consisting of a moulded base in fiberglass that takes the shape of the cable, properly adjusted to its outside surface, in which three integrated sensors, two strain gauges FBG1 and FBG2 are located inside and the thermometer FBG3 is located on the surface. The system allows to identify and measure the dynamic factors that are in the origin of vibrations occurring in HTELs, thereby resulting in damage at connections, cables, and other parts of EHTELs. The present invention is in the technical field of electricity, high-tension electric lines, and related measurements.

Description

DESCRIPTION

SYSTEM AND METHOD FOR DINAMIC MONITORING OF A HIGH-TENSION

ELECTRIC LINE

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a system and to a method for dynamic monitoring of a high-tension electric line (EHTEL).

The system comprises a fibre-optic based transducer node consisting of a moulded base in fiberglass that takes the shape of the cable, properly adjusted to its outside surface, in which three integrated sensors, two strain gauges FBG1 and FBG2 are located inside and the thermometer FBG3 is located on the surface.

The system allows to identify and measure the dynamic factors that are in the origin of vibrations occurring in EHTELs, thereby resulting in damage at connections, cables, and other parts of EHTELs.

The present invention is in the technical field of electricity, high-tension electric lines, and related measurements.

BACKGROUND OF THE INVENTION

Overhead power transmission lines are classified in the electrical power industry by the range of transmission voltages. High-Tension transmission lines transport bulk quantities of electricity over long distances at voltages greater than H OkV. Because of the long transport distances, large spans are used. Despite the high degree of standardisation reached at international level in the design of these lines, important uncertainties still exist related with the characterisation of wind loads, of the structural behaviour of the conductor/tower system and of the dissipation capacity of the devices used commonly to prevent and mitigate vibrations .

As a consequence, incidents and failures in HTELs are still too frequently reported related with damage of conductor wires and fittings, as well as in towers, which can cause a disturbance in the distribution of electricity with significant economic repercussions.

Despite the high level of standardization currently implemented in high-tension transmission lines transport systems some aspects of their characterization remain unknown, such as the effects of wind action, the structural behaviour of conductors and their dynamic interaction with the posts, and also the definition of damping levels to be guaranteed in service and extreme conditions.

On the other hand, the difficulties related to the instrumentation of live lines have strongly limited the experimental characterization of the behaviour of these structures . In particular, monitoring of conductors from transmission lines has been insufficiently addressed due to the difficulty of instrumenting a line in tension and at height. Consequently, the assessment of vibrations has been limited and this has also restrained developments in the understanding of their sources and those of local and global failures of wires and conductors .

At the present moment, the monitoring of vibration in transmission lines is based on devices based on a compact autonomous mounting on the conductors. These transducers have autonomy for operation over a period (typically of 3 months), but they cannot operate continuously on the line and no real time information can easily be obtained, at least on a systematic basis due to limitations in the battery capacity. This may limit the assessment of fatigue required for estimation of the service life of a cable.

DESCRIPTION OF THE FIGURES

Figure 1 schematically represents a cross section of the conductor and the position of the 3 sensors on the transducer according to one embodiment of the invention, wherein

1 is a conductor,

2 is a fiberglass sleeve,

3 sensors, wherein the 1^st sensor (FBG1) and 2^nd sensor (FBG2) are strain gauges, and the 3^rd sensor (FB3) is a thermometer. Figure 2 represents the positioning of the three sensors; 2 strain gauges, FBG1 and FBG2 (Fibre Bragg G), for measuring the deformation of the conductor, which are placed in the inner part of the fibre glass sleeve (2), and the thermometer FBG3 for measuring its temperature, which is placed at the surface of the fibre glass sleeve (2).

Figure 3 represents the optical fibres (4) connecting the Bragg sensors of a transducer according to one embodiment of the invention, wherein each sensor (FBG) is connected by an incoming and outgoing optical fibre. In the present embodiment, the transducer comprises 6 fibre optic cables, wherein each one of the three sensors (FBG1, FBG2 and FBG3) have two corresponding fibre optic cables.

Figure 4 represents the transducer of the invention after extrusion of a polymeric layer (5), which is applied to the surface of the several elements of the transducer for protection and easy mounting on the cable.

DESCRIPTION OF THE INVENTION

The present invention relates to a system and to a method for dynamic monitoring of a high-tension electric line (HTEL).

The system comprises a fibre-optic based transducer node consisting of a moulded base in fiberglass that takes the shape of the cable, properly adjusted to its outside surface, in which three sensors, two strain gauges (inside) and the thermometer (on the surface) are integrated.

The system allows to identify and measure the dynamic factors that are in the origin of vibrations occurring in HTELs, thereby resulting in damage at the connections, cables, and other parts of HTELs. 1 . Characteristics of the optical transducer

The optical transducer of the invention comprises a conductor (1), a fiberglass sleeve (2), 3 sensors being two of them strain gauges (FBG1, FBG2) placed inside the fiberglass sleeve (4) and a third sensor (FBG3) a temperature sensor, placed on the outer surface of the fiberglass sleeve.

The Bragg sensors are on the inner side of the fiberglass sleeve because once glued to the cable they deform together with the cable. The temperature sensor is deforming freely and therefore it is mounted on the outer surface of the fiberglass sleeve. Therefore, the measured variations in the temperature sensor are only due to temperature variations. These are used both to compensate the strain gauges for temperature effects and to measure the conductor temperature, which constitutes another relevant measure for the management of electricity in the line.

The optical transducer is formed from the embedding of three optical fibres with Bragg gratings in a partial glass fibre moulded sleeve (2) having its inner diameter identical to that of the conductor to monitored.

Each sensor (FBG1, FBG2 and FBG3) is connected by an incoming and an outgoing optical fibre (4). In this way, each transducer has 6 fibre optic cables, 2 for each of the 3 sensors as shown in Figure 3.

The sensors FBG1, FBG2 allow the measurement of the longitudinal deformation on the outside of the cable (4) in two orthogonal transversal directions, with an angular spacing of 90° (2 strain gauges). The third sensor FBG3 allows the measurement of the temperature at the surface of the cable (4).

The robustness and durability of the transducer are ensured by a layer of a polymeric material (5), preferably polyurethane applied over its entire surface, while the optical cables have characteristics that allow easy handling without prejudice to the quality of the signals.

In a preferred embodiment for being implemented onto a 24 mm diameter conductor (1), the transducer has the following dimensions: 150mm encasing length, 100 mm length of fiberglass sleeve and 6 mm thickness.

The transducers nodes are designed so that they can be mounted on high voltage cables by nonspecialized instrumentation personnel by applying an adhesive material, such as glue along the contact surface.

In the scope of the present invention, high voltage cables are cables that allow voltages in the range over 110 kV.

The adhesive material also serves as a filling material between the voids of the conductor wires. The application of this material should be followed by mechanical fastening at the ends, which is required until the cure of the adhesive.

The setup is endowed with such durability that it allows its continuous exposure to the elements for a minimum period of two years, both at the level of the transducers and the optical fibres and their connections. In a preferred embodiment, the adhesive material is an epoxy product designed for use with optical fibres with adequate properties namely as regards the operational temperatures (it should be considered that temperatures of 100°C can be present in the line.

2. Method of monitoring the vibrational behaviour of a high- tension electric line

In order to monitor a high-tension line, one or more sensor nodes should be glued to the conductor at specific distances from the isolators. These sensors need to be electrically isolated, considering that the optical fibers need to be transported along the cable to the tower and connected to a 3- channel interrogator.

The interrogator is normally located in a cabinet fixed to one of the supports close to the ground and needs to be electrically powered.

The data acquisition can be made from the USB port of the interrogator to a laptop. Upon application of the temperature compensation to the FBG1 and FBG2, time records of deformation and temperature of the conductor can be obtained.

These time records can be used to characterize the conductor vibrations and installed force.

In particular, the application of fatigue damage algorithms to the collected records over a relevant time enables the characterization of the fatigue life of the conductor. Frequency analysis of the records enables the identification of the frequency range of vibrations and the design of adequate mitigation measures, namely the adequate choice of dampers.

EXAMPLES

Example 1. Production of an optical transducer

The transducer is produced with a diameter identical to that of the cable to monitor. It consists of a moulded base in fiberglass that takes the shape of the cable, properly adjusted to its outside surface, in which the strain gauges (inside) and the thermometer (on the surface) are integrated.

Two of the sensors allow the measurement of the longitudinal deformation on the outside of the cable in two orthogonal transversal directions, with an angular spacing of 90° (2 strain gauges), and a third allows the measurement temperature (1 thermometer). Because this sensor is mounted on the outer surface of the fiberglass sleeve, it is isolated from deformation.

Each sensor is connected by an incoming and an outgoing optical fibre. In this way, each transducer has 6 fibre optic cables, 2 for each of the 3 sensors.

Example 2. Implementation of an optical transducer into a conductor on a test bench

The transducer as described in Example 1 was mounted on a 16.5m conductor with 24 mm diameter and tested on a test bench.

The tested conductor was of the type BEAR-ACSR 325 supplied by Rede Eletrica Nacional (REN).

Since the conductor is made from two materials, steel and aluminium, it was necessary to ensure that the anchorage was made in a similar form as on site so that the force distribution between wires of the internal steel core and the outer aluminium layers would take place in a similar way as on site.

In order to simulate the site conditions, the 16.5 m conductor was mounted on the test bench and tensioned to the force measured on site on an identical conductor.

After application from one of the anchorages of several loading / unloading cycles, designed to reduce the relaxation effects of the conductor, a load of 2330 daN was installed, identical to the one identified in the prototype conductor to be later instrumented. This load was kept constant over two days, what enabled the gluing of the optical transducer node and cure of the glue.

With this level of tension, the optical transducer was glued, at a section distant of about 4 m from the active anchorage. This operation implied the following steps:

- Removal of any paint or primer, as well as any encrustation or rust on the surface of the outer wires in the bonding area with a fine sanding sheet.

- Cleaning of the bonding surface using acetone, first, and, secondly, isopropanol, in order to eliminate impurities, oils and fats present.

- Application of the epoxy-based structural adhesive SikaFast 5211 acquired to HBM.

- Application of ties along the sensor node in order to position the sensor and guarantee the cure. A 1-day adhesive cure time was indicated by the glue manufacturer. However, for the sake of safety, it was decided to carry out the test two days later, maintaining the applied force in the amount of 2330 daN throughout that time.

Claims

1. An optical transducer for high-tension electric lines, characterized by comprising a fiberglass sleeve (2), three sensors (3) being two of them strain gauges (FBG1, FBG2) and a third sensor (FBG3) a temperature sensor, six optical fibres (4) and a polymeric layer, wherein:

- the strain gauges (FBG1, FBG2) are located in the inner part of the optical transducer having an angular spacing between each other of 90°, and the temperature sensor (FBG3) is located at the surface of the optical transducer,

- each sensor (FBG1, FBG2 and FBG3) is connected by an incoming and an outgoing optical fibre,

- the optical fibres are embedded in a partial glass fibre moulded sleeve (2) having its inner diameter identical to that of the conductor to monitored,

2. An optical transducer according to claim 1 characterized by having a polymeric layer (5) applied to its surface.

3. An optical transducer according to claim 2 characterized by the polymeric layer comprises polyurethane.

4. An optical transducer according to claim 1 characterized by a connection to the conductor with an adhesive material as filling material between the voids of the conductor wires.

5. A method of monitoring the vibrational behaviour of high- tension electric lines characterized by comprising the following steps: a) Assembling an optical transducer as the one described in any of the claims 1 to 4 into a high-tension electrical conductor, b) Connecting the optical transducer to an interrogator, c) Connecting the interrogator to a laptop to record data.