Patent Application
20170012413
This invention addresses inspection robots for live transmission line cables in general, and in particular inspection robots for live transmission line cables that could be installed using an insulating rod.
Power lines consist of conducting cables that carry electrical current. These cables are subject to the effects of weathering, such as corrosion of their elements, cracks caused by wind vibration and damage due to atmospheric discharges [lightning bolts]. As these cables are normally live and installed at great heights, it is hard for the concessionaire electrician to access them for the purposes of inspection or even repair. It must be noted that such inspections are necessary in order to avoid the cable breaking, with consequences that could be very serious, such as power outages for large segments of the population and/or accidents involving vehicles and people, should the cable fall onto a highway or in an inhabited area.
Consequently, the need arises for a tele-controlled robot that could be installed on the conductor and inspect it. An initial device was developed by the authors of this invention, whose main innovative aspects were claimed through an application for a patent of invention filed with the INPI on Aug. 6, 2007 [1]. However, in order to install this device, the power line cannot be live. This constitutes a constraint on the use thereof, as planning is required for tasks involving several agents, due to the need to switch off the line that will be inspected. In order to overcome this flaw, a new device was developed that operates when the line is live. However, a difficulty arose over how to install the robot on the conductor, when it is live at high voltages.
Several possible alternatives encompass those normally used for working on live power lines, such as accessing the conductor by helicopter or by truck with an insulating crane. However, the costs and constraints on access through these solutions significantly lessen the advantages of having a tele-controlled robot. In other words, once the difficulty of getting one or more electricians up to the live conductor has been dealt with, they can carry out several inspection tasks. Even for inspections where the use of a tele-controlled robot is required, the cost of its installation and removal from the conductor undermines the feasibility of using this technique on a large scale.
As demonstrated, there are clear advantages in developing a robot that could be installed on the conductor from the pylon, using an insulating rod for this purpose. This invention shows how this technique was successfully implemented on a tele-controlled robot used for corrosion inspections on steel-core aluminum conductors (SCC). Several aspects of the robot are fundamental for allowing this type of installation, such as its shape, the guide system for fitting it onto the conductor, light weight so it can be supported by the rod, adjustment of its centre of gravity in order to maintain stability and the design of the sensor that automatically clips onto the conductor. These aspects are described in this document and constitute the main claims of this invention.
There are several types of power line inspection robots on the market. In general, these devices may be classified into three categories. The first consists of flying robots, which may be in the shape of tele-controlled aircraft or helicopters carrying video cameras and flying along the monitored power line [2]-[3].
The second category consists of manually operated robots [4]-[5]. These are not actually robots, but are rather tele-controlled inspection devices that require an operator in order to travel along the conductor. One of these robots is the manually operated robot made by Fujikura [4] which is conducted along a power line by the operator (see
More common, the third category consists of crawler robots that move along the conductor being inspected [6]-[16]. One of these robots is the crawler robot made by Kinectrics [16] that is installed on the conductor by a truck with an insulating crane (see
An electro-mechanical design for a live power line cable inspection robot that can be installed on the cable from the pylon, using an insulating rod.
Constraints of Products Currently Available on the Market
The most obvious disadvantage of flying robots is the risk of a defect in the robot damaging the supervised line, in addition to other consequences (meaning the robot could fall on inhabited areas). Another disadvantage is that this type of inspection is limited to visual inspections or those using thermographic imaging, as a sensor cannot be coupled to the conductor.
The clear disadvantage of manually operated robots is the need for the operator to accompany the robot during inspections. In addition to the risks of industrial accidents inherent to this activity, the weight of the operator prevents such inspections from being conducted on lines whose conductors are installed vertically.
Crawler robots do not present the disadvantages of flying robots, but they can conduct accurate inspections of conductors only when their support is ensured by such conductors. Similarly, crawler robots do not require an operator to accompany the robot, as is the case with manually operated robots. However, crawler robots offer the disadvantages of having to be installed on the conductor, with difficulties in getting past obstacles (such as splices in the conductor and clamps holding it to the pylon).
In general, the physical aspects of manually operated and crawler robots (such as weight, manner of installation, slotting in the sensor) require installation on conductors by one or more electricians (see
Causes of the Constraints of Products Currently Available on the Market
The main problems associated with flying and manually operated robots are inherent to their conceptualizations, while the problems associated with crawler robots are related to design aspects. On the other hand, difficulties in getting past obstacles is related to the electro-mechanical design of crawler robots. In fact, as shown by the references [6]-[12], a series of steps may be used that allow a crawler robot to get past obstacles along the length of the conductor.
Similarly, difficulties in installing the robot on the conductor by a rod are also related to its electro-mechanical design. The main causes of this problem are:
Technical, Commercial and Economic Advantages of the Invention
The main technical advantage of installing the robot by a rod is the possibility of inspecting conductors on spans of lines that are not accessible through the current inspection robot installation methods. For example, there are many spans of power lines in mountainous areas that are not accessible for trucks with insulating cranes used to install inspection robots. Similarly, line conductors installed in power line corridors (several power lines in parallel) are not accessible by helicopter.
The main commercial advantage is a significant reduction in inspection costs, as the installation of a robot using a rod requires only a small live line team travelling in a regular vehicle owned by the concessionaire. Final access to the foot of the pylon can be achieved through any available means, including by foot.
Finally, the economic advantage is reflected in the benefits arising from the inspection conducted. For an inspection designed to assess the remaining useful life of the conductor, the economic benefits consist of lower power line maintenance costs (OPEX) and avoidance of outlays arising from falling conductors (fine, loss of profits and emergency repair costs).
The crawler robot addressed by this paper was developed for inspecting live power lines, based on the assumption that it would be installed on the conductor by an insulating rod. To do so, the following steps were taken:
Weight Reduction
Several techniques were used to lower the weight of the robot, such as using aluminum to make most of its parts, for example, as this is some three times less dense than steel. The mechanical devices on the robot were also made more compact, in order to reduce its size and consequently its weight. The final dimensions of the robot are: width 27 cm×length 45 cm×height 36 cm, weighing 16 kg
Slotting onto the Conductor¶
In contrast to other crawler robots that fit on to the conductor along the side, the robot addressed by this invention is slotted onto the conductor vertically, similar to the manner in which a saddle is placed on a horse.
The roller guide mechanism is shown in 8A and 8B, where the worm thread axis (8.1) may be seen, together with the springs that press the roller guides against the conductor (8.2). Each roller guide has ball bearings (8.3) installed along its central axis, allowing it to spin freely as the robot moves along the conductor.
The gap between the roller guides is adjusted previously by a disc (8.4) that triggers a worm thread mechanism, in order to size its opening to the gauge of the conductor that will be inspected. This adjustment system is fitted with springs that press the roller guides against the conductor. At the same time as this keeps the robot aligned on the conductor, these springs endow the roller guides with sufficient flexibility to adapt to minor local variations in the diameter of the conductor.
Adjustment of the Centre of Gravity
The robot design follows a plan based on vertical symmetry, with the centre of gravity of the robot located above the conductor axis. To do so, asymmetrical components such as the motor and electronic circuit were arrayed on opposite sides, in order to preserve an even balance. The robot is powered by two batteries installed in its lower section (one on each side) in order to lower its centre of gravity. Furthermore, fine-tuning battery positions allows the robot to be balanced evenly, ensuring that its centre of gravity coincides with the axis of the conductor. In other words, adjusting the position of the batteries offsets the differences between the asymmetrical components and allows the centre of gravity of the robot to be outlined with the axis of the conductor.
As shown in
Opening and Closing the Sensor
In order to ensure that the robot can be installed through the use of a rod, it is important that the sensor closes automatically over the conductor. To do so, a mechanism is coupled to the hoisting eyebolt, in a manner whereby the sensor opens to receive the conductor when this eyebolt is pulled. When the robot is supported by the conductor and the eyebolt loosens, a spring pushes the sense or into its closing position.
Example of a Robot Installation Using a Rod
Once the robot is ready to be installed on the power line by a rod, several techniques can be developed by the concessionaire for its installation. For example, the robot can be hoisted to the top of the pylon by a rope tied to its central eyebolt, as shown in
