Unmanned aerial vehicle for inspection and monitoring of electrical power transmission lines

Abstract

An unmanned aerial vehicle (UAV) 1002 to inspect and monitor electrical power transmission lines including measurement of S- parameters of a magnetic field to determine the permittivity of a medium, e

Description

CROSS-REFERENCE TO RELATED APPLICATION This application claims priority from United Kingdom patent application number 2311174.3 filed on 20 July 2023, which is incorporated by reference herein. FIELD This disclosure relates to an unmanned aerial vehicle (UAV) for inspecting and monitoring electrical conductors such as power transmission lines. It relates, in particular, to a UAV and associated system and method for use in the detection of corona discharge events associated with transmission lines, and for detecting faulty insulators. BACKGROUND UAVs have numerous applications including infrastructure inspection. One type of infrastructure inspection using UAVs is inspection of electrical power transmission lines. Power transmitted over transmission lines is typically at high voltage, which causes problems like corona discharge and increased leakage current in the insulator. UAVs have gained popularity for inspecting overhead transmission lines. Corona discharge can cause power losses and interference with radio signals. Corona discharge from transmission lines constitutes an economically significant waste of energy for utilities. It can also generate harmful ozone gas. Consequently, it is important to inspect transmission lines to detect and prevent corona discharge. Various methods are employed to detect corona discharge. The simplest approach involves visually checking for a bluish-purple glow surrounding the conductor. Additionally, corona discharge produces a hissing or crackling noise that can be detected using a stethoscope or other acoustic sensors. While this method is more sensitive than visual inspection, it may prove challenging to implement in noisy environments. Another method involves detecting the small amount of ionization generated by corona discharge using an ionization meter. However, this method is less sensitive compared to the other approaches. Whilst UAVs may be implemented in these known approaches to inspect transmission lines, limitations of UAVs may restrict their usefulness for these applications. UAVs are generally powered by electrical batteries and have limited flight time. To address this issue, one solution is to replace the UAV batteries when they are running low. Such a scenario costs the UAV an additional distance to be covered to recharge itself or carry extra weight for a power-backup recharging mechanism. An auxiliary charging mechanism is not only required to increase the time of flight, but in case of failure of any part of the UAV or complete battery depletion during the flight, the electronics components may also lose valuable data. Therefore, increasing the flight time for an extended duration through a supplemental charging mechanism is an area of interest. US 7,543,780 discloses an unmanned air vehicle system for transmission line field sensing. The system includes sensors responsive to electromagnetic fields, docking means and means for interrogating a global positioning system. Transducers comprising Hall effect sensors determine proximity to a current source. The resonance frequency of electrical transmission lines can be sensed. During operation, changes in magnetic field induce a current in the transducers, which can be used to charge a power source. US 2017 / 0285092 discloses a UAV for localizing power line corona discharges and electrical arcs. The UAV includes an array of ultraviolet point detectors. US 9,753,080 teaches a system for detecting partial discharge events using transducers. The preceding discussion of the background to the disclosure is intended only to facilitate an understanding of the present disclosure. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application. SUMMARY In accordance with an aspect of the disclosure there is provided an unmanned aerial vehicle (UAV) for inspecting and monitoring an electrical power transmission line, the UAV including a measurement component arranged to measure S-parameters of a magnetic field to determine the permittivity of a medium surrounding the transmission line. The UAV may include a transducer assembly comprising a plurality of transducers. The transducers may be configured to operate in a resonator mode wherein they act as resonators. The measurement component may be configured to measure the S-parameters when the transducers are operating in their resonator mode. At least one of the transducers may additionally be configured to operate in an inductor mode wherein it acts as an inductor. At least one of the transducers may be configured to operate selectively in either the resonator mode or the inductor mode. The UAV may include switch means configured to switch the at least one transducer between its resonator and inductor modes. The UAV may include means configured to match resonant frequencies of the transducers to the frequency of radiation from the transmission line. The transducer assembly may include a ground plane electrically connected to the transducers and separated from them by a substrate. The system may include vias connecting the transducers to the ground plane. The UAV may include locating means configured to determine and record its location relative to the transmission line. The locating means may include at least one distance sensor configured to measure a distance of the UAV from the transmission line. The UAV may include an alignment system configured to align the UAV relative to the transmission line. The alignment system may be arranged to operate with the transducers in their inductor mode. The alignment system may be arranged to align the UAV with reference to the transmission line by applying measured values of intensity of current induced in the transducers to determine proximity of the transducers to the transmission line and positioning the transducers relative thereto. The measurement component of the UAV may be arranged to measure the values of induced current in the transducers during operation in their inductor mode. In certain embodiments, the transducer assembly may be configured as an array of generally uniformly sized transducers. In certain embodiments, the transducers may each be shaped as a helical coil, for example, so that the transducer assembly comprises a helical array. In other embodiments, the transducers may each be shaped as a flat rectangular coil. Other shapes and configurations also fall within the scope of the disclosed technology. The UAV may include an onboard power source. The power source may be configured to transmit a current to one or more of the transducers in their resonator mode. The UAV may be configured such that the transducer to which the current is transmitted radiates a magnetic field to induce a current in at least a second transducer. The UAV may be configured to harvest wireless energy from magnetic fields surrounding the transmission line. The UAV may be configured to charge the power source using current induced in the transducers. The UAV may include means to configure the transducers to match the resonance frequency of the transmission line. The UAV may further include a docking means configured to dock the UAV on a transmission line. The docking means may comprise a clamp system. The clamp system may comprise at least one tilt mechanism. The disclosure extends to a transmission line inspection system comprising the disclosed UAV and a computing means. The computing means may be arranged to calculate values selected from the group consisting of permittivity, permeability, S-parameters, and any combination thereof, associated with a medium surrounding the transducers. The computing means may be arranged to solve for the permeability or permittivity with reference to fundamental mode S-parameter relationships. The computing means may further be arranged to compare the calculated values against a reference dataset of predetermined corresponding values associated with normal or abnormal functioning of the transmission line. The computing means may be arranged to thereby identify a corona discharge in the medium surrounding the transmission line, and optionally to classify its severity. The computing means may be arranged to manoeuvre the UAV to position the transducers on either side of the transmission line using the alignment system of the UAV, that is, to position one of more of the transducers on an opposite side of the of the transmission line from the other transducers. In accordance with a further aspect of the disclosure there is provided a method of inspecting a transmission line to detect an abnormal operating condition such as, but not limited to, corona discharge associated with the transmission line, the method comprising utilizing the disclosed system to transmit and receive a radio frequency (RF) signal using the transducers and to measure S-parameters of a magnetic field associated with the transmission line. The method may further comprise applying the measured S-parameters to solve for a value of at least one of permittivity and permeability of a medium surrounding the transducers and the transmission line. The method may include measuring inductance in at least one of the transducers and applying a value of the measured inductance to solve for the permeability of the surrounding medium. The method may include comparing the measured S-parameters, solved value of permittivity, or solved value of permeability against a dataset of predetermined corresponding values associated with normal or abnormal operating conditions of the transmission line, for example, corona discharge, thereby to detect if operation of the transmission line is in the abnormal condition. The method may include generating constructive or destructive interference between distinct pairs of transducers to promote enhanced accuracy of measurement of the S-parameters. The method may include positioning and aligning the UAV with reference to the transmission line prior to taking the measurements. Aligning the UAV may first involve positioning it to ensure that its extremities are clear of the transmission line. Alignment may then further involve measuring an induced current in each transducer, and if the current in one transducer exceeds that in each of the other transducers, rotating the UAV or the transducer assembly with respect to the transmission line; or if the current in each of a set of two adjacent transducers is approximately equal but exceeds the current in each of the other coils, moving the UAV in a direction of the higher current carrying coils. When the current in all of the coils is approximately matched, the position of the UAV may be adjusted until the transmission line extends through the transducer assembly at a level approximately midway between the two ends of each transducer. In accordance with a further aspect of the disclosure there is provided a method of detecting a faulty insulator which insulates a transmission line from a support structure, the method including the steps of: utilizing the disclosed system to measure a first intensity of current flowing in a portion of the transmission line extending from a first side of the insulator, and a second intensity of current flowing in a second portion of the line extending from a second side of the insulator; comparing the first and second current intensities, thereby to calculate a leakage current; and comparing the leakage current against a predetermined range of abnormal leakage current values indicative of a faulty insulator, thereby to establish that the insulator is faulty if the leakage current is within said range of values. The method may include docking the UAV on the transmission line while each of the respective first and second current intensities is measured. The docking may be performed by clamping the UAV to the transmission line using its clamp system. In accordance with a further aspect of the disclosure there is provided a method of harvesting wireless energy from an electrical power transmission line, the method comprising the steps of: positioning an unmanned aerial vehicle (UAV) in proximity with the transmission line, wherein the UAV includes at least two transducers acting as inductors which are configured to be positioned on either side of the transmission line; and utilising the transducers to harvest wireless energy using magnetic fields around the transmission line. The method may include a step of matching resonant frequencies of the transducers to the frequency of radiation from the transmission line. Embodiments of the technology will now be described, by way of example only, with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1 is an illustration of an exemplary embodiment of two conductors placed in the vicinity of each other; Figure 2 is a schematic diagram showing three different inductances; Figure 3 illustrates two uniformly sized rectangular coils placed at a certain distance from each other; Figure 4 illustrates two differently-dimensioned rectangular coils and resonance frequency matching circuits of both coils; Figure 5 shows isometric and side views of a rectangular coil operable selectively as either a resonator or an inductor; Figure 6 illustrates radiation and magnetic field patterns of the rectangular coil shown in Figure 5; Figure 7 is an isometric view of a three-dimensional helical coil; Figure 8 is a visual depiction of a helical array containing multiple three-dimensional helical coils; Figure 9 illustrates two helical array elements configured as a transmitter or receiver; Figure 10 illustrates a top view of a helical array showing interference of electric fields due to different and distinct array elements; Figure 11 illustrates an isometric view of an exemplary UAV control unit fitted with multiple distance sensors; Figure 12 is a three-dimensional view of an exemplary UAV having a measurement component comprising an array of helical transducer elements; Figure 13 illustrates misalignment of the helical array in which some elements are closer to the conductor than others; Figure 14 illustrates an alignment of the helical array in which each element is positioned a similar distance from the conductor under inspection; Figure 15 illustrates a UAV measuring a leakage current of an insulator while the UAV is operating in a clamp mode; Figure 16 illustrates a tilt mechanism of the UAV, for tilting transducers of the helical array relatively to one another; Figure 17 is a flow diagram depicting steps involved in performing various modes of operation of the UAV; Figure 18 is a flow diagram depicting a process for aligning and positioning of the UAV relatively to a transmission line, using a combination of sensors and current flowing in the helical array; Figure 19 is a flow diagram depicting a sub-process of energy harvesting using induction; Figure 20 is a flow diagram depicting insulator detection and leakage current measurement; and Figure 21 is a flow diagram depicting steps required to detect and / or measure corona discharge around a transmission line undergoing inspection. DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS Aspects of the present disclosure provide technology and techniques for interacting with, inspecting and monitoring electrical power transmission lines, and for harvesting wireless energy from them. An unmanned (uncrewed) aerial vehicle (UAV) is described which may include a measurement component arranged to measure S-parameters of a magnetic field to determine the permittivity of a medium surrounding the transmission line. The measured S-parameters may include S12-parameters. The UAV may include a transducer assembly comprising a plurality of transducers. The transducers may be provided as an ordered array of array elements. At least one of the transducers may be configured to operate in a resonator mode. The measurement component may be configured to measure the S-parameters of the magnetic field associated with a transmission line when said at least one transducer is operated in its resonator mode. In the resonator mode, the transducers may each be configured to operate as either a transmitter or a receiver. The transducers may be configured to operate in two modes: a resonator mode and an inductor mode. The disclosed UAV system may be configured with switch means for switching the transducers between the two modes. Thus, wt least one of the transducers may be configured to operate in an inductor mode. At least one of the transducers may be configured to operate selectively either in the resonator mode or the inductor mode. The UAV may be arranged to switch the at least one transducer between its resonator and inductor modes. The UAV may include means configured to match resonant frequencies of the transducers to the frequency of radiation from the transmission line. At least one of the transducers may be configured as a patch antenna. During operation of such an embodiment in resonator mode, the transducers may radiate in only one specific direction. The transducer assembly may include a ground plane electrically connected to the transducers and separated from them by a substrate. In the inductor mode, a current flows through a transducer coil, generating a magnetic field around it. The ground plane may deflect the magnetic field. The UAV may be configured to sense and locate transmission lines. The transducers may be configured to interact with a transmission line by positioning its transducers on either side of the line. The UAV may include locating means configured to determine and record its location relative to a transmission line suspended proximate to the UAV. The locating means may comprise at least one sensor configured to measure a position of the UAV relative to a reference point or region, for example, a region of a transmission line or a region of an insulator for a transmission line. The locating means may include at least one distance sensor. The sensor may be arranged to measure a relative distance of the UAV relative to the transmission line. The computing means may be arranged to determine the UAV’s location relatively to the transmission line based on said relative distance. The UAV may include multiple sensors which may be mounted on or integrated into the top, bottom and sides of a control unit of the UAV to measure the distance between UAV and nearby objects. In certain embodiments, the transducer assembly (e.g. helical array) is mounted or integrated on the lower side of a control unit of the UAV. By using the combination of sensors and the helical array under the control of the control unit, the UAV may auto-align itself with the transmission line under inspection. The UAV may include an alignment system configured to align the UAV with reference to a suspended transmission line. The alignment system may be arranged to operate with the transducers in their inductor mode. The system may accordingly be configured such that the transducers in their inductor mode are used to determine proximity to a current source for positioning the transducers relative thereto. The alignment system may be arranged to compare intensities of induced current flowing in two or more of the transducers and to rotate the UAV based on the result of the comparison. The system may be arranged to rotate the UAV until a generally upright plane passing through two of the transducers aligns generally parallel to a linear axis of the conductor The system may be arranged to move the UAV sideways in a direction of a higher current carrying transducer. The alignment system of the UAV may also be configured to measure an operatively vertical height of the transmission line relatively to a length (height) dimension of the helical coils. In use, this information may be used for controlling the UAV to ascend or descend until the transmission line is vertically positioned approximately halfway up the height of the helical coils. The measurement component of the UAV may be arranged to measure values of induced current in the transducers during operation in their inductor mode. During use of the disclosed UAV and system, the measured values of inductance may be used as a supplementary basis for calculating the values of permeability, and for positioning and aligning the UAV relative to the transmission line. The transducer assembly may comprise an array of array elements. The array elements may comprise at least two transducers and an energy source configured to transmit a current to at least one of the transducers such that the transducer radiates a magnetic field around the transducer. In use, this may induce a current in at least a second transducer. The transducers can be configured to operate variably in either a resonator mode or an inductor mode. An electrical circuit composed of discrete components can act as a resonator when both an inductor and capacitor are included. An inductor consisting of a coil of wire is self-resonant at a certain frequency due to parasitic capacitance between its turns. In resonator mode, the transducers of the disclosed UAV may be used to detect radio frequency (RF) electromagnetic radiation. The transducers may be uniformly or differently sized. When the transducers have different dimensions, the UAV may include one or more capacitors configured to match the frequencies of the transducers. Portions of each transducer may have a shape selected from the group consisting of flat or three-dimensional coil shapes, spiral shapes, polygonal shapes, quadrilateral shapes including rectangular and square shapes, circular and elliptical shapes, and combinations of these shapes. Other shapes also fall within the scope of the disclosure. Coil-shaped transducers may, without limitation, have a helical, spiral, rectangular, circular, hexagonal, or pentagonal configuration. Some coil-shaped transducers may have a generally flat rectangular shape. In such embodiments, the transducers may be two uniformly sized rectangular coils which are placed near each other so as to maximize magnetic field interaction. Due to the uniformity of size, resonance frequency of both coils may be configured to match each other, which allows for wireless energy transfer. In embodiments where the coils may be of different dimensions, capacitors may be utilized to match the resonance frequencies of coils. In certain exemplary embodiments, each transducer, i.e. each array element, may comprise a helical coil. The transducer assembly may then be referred to as a helical array. The helical array may comprise four uniformly sized helical coils arranged as edges of a cube shape. The UAV may include an onboard power source. The power source may comprise a rechargeable electrical battery located aboard the UAV, the battery being connected or connectable to components of the UAV for selectively transmitting operational control signals to said components. The power source may be configured to transmit a current to one or more of the transducers in their resonator mode. The UAV may be configured such that the transducer to which the current is transmitted radiates a magnetic field to induce a current in at least a second transducer. The UAV may be configured to harvest wireless energy from magnetic fields surrounding the transmission line. The UAV may be configured to charge the power source using current induced in the transducers. The UAV may include means to configure the transducers to match the resonance frequency of the transmission line, such that a change in magnetic field associated with current flowing in the transmission line induces a current in the transducers. The UAV may include one or more capacitors configured to match the frequencies of the transducers and transmission line. The UAV may include a radio frequency (RF) port connected to each transducer. The system may include vias arranged to connect the transducers to the ground plane. The UAV may further include a docking means configured to dock the UAV on a transmission line. The docking means may comprise a clamp system. The clamp system may comprise at least one tilt mechanism. The tilt mechanism may comprise a transducer tilt mechanism configured to adjust an orientation of one or more of the transducers relatively one another. The transducer tilt mechanism may be configured to tilt at least one of the transducers relatively to another such that the transducers and hence the UAV may be operatively clamped onto the transmission line while measuring a current flowing therein. The UAV may include a propulsion apparatus. The invention extends to a UAV for inspecting and monitoring electrical power transmission lines, the UAV including a ground plane; a substrate; a sensor configured to measure a position of the UAV relative to a reference point; at least two transducers; and an energy or power source arranged to transmit a current to at least one of the transducers; wherein at least one of the transducers is configured to operate in either a resonator mode or an inductor mode. In the resonator mode, each transducer may be configured to operate as either a transmitter or a receiver. In resonator mode, the transducers may be configured to measure S-parameters, including permittivity, between two transducers. When the UAV is operating proximate a transmission line and the transducers are positioned on either side of the transmission line, this configuration may permit the transducers to measure S-parameters of the transmission line. For example, when the UAV is hovering proximate a transmission line and its transducers are positioned on either side of the transmission line, the transducers may be configured to measure S-parameters of a magnetic field to determine the permittivity of a medium surrounding the transmission line. The transducers in resonator mode may act as a patch antenna radiating in a single direction. The disclosure extends to a UAV for inspecting and monitoring electrical power transmission lines, the UAV including an array of at least two or more helical coils; at least one substrate and a ground plane; at least two vias connecting the coils to the ground plane; at least one distance sensor; and a control unit for controlling operation of the UAV with reference to measurements taken by the distance sensor. The disclosure extends to a transmission line inspection system comprising the disclosed UAV and a computing means. The computing means may be arranged to calculate values selected from the group consisting of permittivity, permeability, S-parameters, and any combination thereof, associated with a medium surrounding the transmission line and transducers. The computing means may be arranged to solve for the permeability or permittivity with reference to fundamental mode S-parameter relationships. The computing means may be arranged to compare the calculated values of permittivity, permeability, or S-parameters, against a reference dataset of predetermined corresponding values associated with normal or abnormal functioning of the transmission line. The computing means may be arranged to identify corona discharge in a medium surrounding the transmission line, and optionally to classify the severity of the corona discharge, by performing the described comparison. The system may include a data storage means arranged to store the reference dataset The computing means may be arranged to manoeuvre the UAV to position the transducers on either side of the transmission line using the alignment system of the UAV, that is, to position one of more of the transducers on an opposite side of the of the transmission line from the other transducers. The computing means may include an onboard computing device located aboard the UAV, energized by the onboard power source. The computing means may include a remote computing apparatus located remotely from the UAV, e.g. at a base station. The onboard computing device may be arranged to control operational aspects of the UAV, for example, operation of the measurement component, resonance matching means, alignment system, docking apparatus, flight surface control apparatus, and / or propulsion apparatus. The disclosed system may include switching means for switching operation of the transducers between their resonator and inductor modes. In resonator mode, the disclosed UAV is operable as a detection means for sensing corona discharge in electrical transmission lines. Accordingly, the operation of the UAV can be switched from a corona detection mode to an inductor mode. The disclosure extends further to a method of determining S-parameters of magnetic fields associated with electrical power transmission lines, the method comprising the steps of: utilizing a UAV which includes at least two transducers, at least one of which is configured to act as a resonator; positioning the UAV with the transducers on either side of the transmission line; measuring S-parameters between the transducers to determine the S-parameters of the transmission line; and recording the S-parameters in a database. The database may be stored locally aboard the UAV or transmitted to a storage means at a remote location such as a base station. The method may include comparing the S-parameters against a dataset of predetermined values associated with normal or abnormal functioning of the transmission line. The method may include detecting a corona discharge from the conductor based on said comparison. The predetermined values may be selected from the group consisting of permittivity, permeability, S-parameters, and any combinations thereof. The disclosure extends to a method of inspecting a transmission line to detect an abnormal operating condition, such as a corona discharge, associated with the transmission line. The method may comprise utilizing the disclosed UAV system to transmit and receive an RF signal using the transducers; and measuring S-parameters associated with the transmission line. The method may further comprise applying the measured S-parameters to solve for a value of at least one of permittivity and permeability of a medium surrounding the transducers and the transmission line. The method may also include measuring inductance in at least one of the transducers and applying a value of the measured inductance to solve for the permeability of the surrounding medium. The determined permittivity of the medium provides information regarding the level of corona discharge. The method may include comparing the measured S-parameters, solved value of permittivity, or solved value of permeability against a dataset of predetermined corresponding values associated with normal or abnormal operating conditions of the transmission line, thereby to detect if operation of the transmission line is in the abnormal condition. The method may include generating constructive or destructive interference between distinct pairs of transducers to promote enhanced accuracy of measurement of the S-parameters. The method may include positioning and aligning the UAV with reference to the transmission line prior to taking the measurements. The distance sensors of the UAV may be used to measure the distance between the UAV and the transmission line. Aligning the UAV may first require positioning it to ensure that its extremities are clear of the transmission line. By way of example, for embodiments of the UAV having a downwardly projecting helical array, this step may involve adjusting the altitude of the UAV (moving it upwardly) so that a measured distance of the UAV from the transmission line exceeds the length of the helical array. Once the distance from the line is greater than the length of the array, the UAV can proceed with the following further steps. The induced current in each transducer can then be measured, and if the current in one transducer exceeds that in each of the other transducers, the UAV or the transducer assembly can be rotated with respect to the transmission line; or if the current in each of a set of two adjacent transducers is approximately equal but exceeds the current in each of the other coils, the UAV can be moved in a direction of the higher current carrying coils. When the current in all of the coils is approximately matched, the position of the UAV may be adjusted until the transmission line extends through the transducer assembly at a level approximately midway between the two ends of each transducer. For embodiments of the UAV having a downwardly projecting helical array, this step may involve adjusting the altitude of the UAV (moving it downwardly) until the transmission line is at a level approximately half the length (height) of the transducers. Once aligned, the tilt mechanism of the helical array may be used to operate the UAV in a clamp mode. The clamp mode may be activated to calculate the leakage current through any insulator, as described in more detail below with reference to Figure 15. This disclosure therefore also teaches a method of detecting a faulty insulator, the method comprising utilizing the disclosed UAV system to measure a first intensity of current flowing in a portion of the transmission line extending from a first side of the insulator, and a second intensity of current flowing in a second portion of the line extending from a second side of the insulator; comparing the first and second current intensities, thereby to calculate a leakage current; and comparing the leakage current against a predetermined range of abnormal leakage current values indicative of a faulty insulator, thereby to establish that the insulator is faulty if the leakage current is within said range of values. The method may include docking the UAV on the transmission line while each of the respective first and second current intensities is measured. The docking may be performed by clamping the UAV to the transmission line using its clamp system. Also disclosed is a method of harvesting wireless energy from an electrical power transmission line using magnetic fields around the line. Wireless energy may be harvested from the line by positioning transducers (e.g. helical coils) of the UAV, acting as inductors, on either side of the transmission line and utilising the transducers to harvest the energy from the transmission line. The method may include a step of matching resonant frequencies of the transducers to the frequency of radiation from the transmission line. The wireless energy is harvested after the matching of resonance frequencies. The UAV may then be charged by storing the harvested wireless energy in an onboard electrical battery system. Figures 1 to 21 illustrate example embodiments of the above-described UAV and methods according to aspects of the present disclosure. In Figure 1, the basic phenomenon 100 of induction is shown where two conductors 102,104 are placed in the vicinity of each other. The distance 106 between two conductors 102, 104 should be selected in such a way that the magnetic field 108 due to the current 110 passes through the second conductor 104. Due to the magnetic field 108, a current 112 is induced in the second conductor 104, having the opposite direction to its source current 110. Figure 2 illustrates three different inductances 204, 208, 210 induced in conducting coils located proximate conductors 202, 204. The shorter conductor 202 produces a lesser inductance 204 due to its short length. The relatively longer conductor 206 produces a higher inductance 208 than the the conductor 204. A greater value of inductance 210 can be achieved by increasing the number of turns of the coiled conductor. Required inductance can be achieved with reference to the following equation: N2iiQiirA Figure 3 illustrates two uniformly sized and configured rectangular coils 302, 304 postioned at a distance 306 from each other, showing a basic wireless power transfer mechanism. The dimensions of the coils 302, 304 are equal, and the resonance frequency of both rectangular coils 302, 304 is matched. The rectangular coils 302, 304 may have various shapes or configurations, including but not limited to circular, pentagonal, hexagonal or any other suitable shape. Magnetic field lines 308 produced by the first coil 302 are shown passing through the second coil 304. Conversely, the field lines (not shown) produced by the second coil 304 pass through the first coil 302. Figure 4 illustrates a wireless power transfer setup 402 for transmitting power between two differently sized rectangular coils 404, 406. The distance 408 between the coils determines the efficiency of the wireless power transfer setup. The dimensions 410,412 of the coils are not equal, so capacitors 418,424 are required to match the resonance frequency of the two rectangular coils 404, 406. The values of Li (412), Ci (414), L2 (414) and C2 (420) are selected in a way to match the resonance frequency of both the rectangular coils 404, 406. To achieve resonant coupling, the coils can be capacitive loaded so as to form a tuned LC circuit. The resonance frequency of any LC circuit may be determined using the following equation: 1 fr =---1= ZnjLC An LC circuit is discussed above for simplicity, but various other resonance circuit architectures can be used with the UAV. The resonance circuit may, for example, comprise an inductor-capacitor-inductor (LCL) resonance architecture, switched inductor-capacitor (SLC) resonance architecture, or High-gain resonance architecture instead of an LC circuit. Selection can be based on availability and use. Figure 5 illustrates an isometric view 502 and a side view 504 of a rectangular coil 506 that may operate as either a resonator or an inductor with a ground plate or plane 508 and an intervening substrate 510. An RF port 512 is connected to the coil 506 and ground plane 508. In the embodiment 501 shown in Figure 6, a radiation pattern 503 and a magnetic field pattern 509 produced by a rectangular coil 506 are shown. In the resonator mode, the radiation pattern 503 is emitted. The depicted pattern has a major or main lobe 505 and a back lobe 507. The size of the main lobe 505 in this example is greater than that of the back lobe 507, so the depicted pattern has a directivity in one direction, that is, the resonator is radiating more power in one direction than in the other. The depicted radiation pattern 503 has a higher ratio of front-to-back radiation. The radiation pattern 503 may be enhanced by reducing the size of the back lobe 507 through any suitable method. The size of the back lobe 507 mainly depends upon the size of the ground plane and the design of the resonator. The larger the size of the ground plane 508, the smaller the size of the back lobe 507. In the inductor mode, the magnetic field pattern 509 is produced as induced current flows in the rectangular coil 506. As current passes through the rectangular coil 506, it generates magnetic fields 511. The divergence of magnetic fields is due to the ground plane 508. In an exemplary embodiment 600 shown in Figure 7, a three-dimensional helical coil 602 that may act as a resonator or an inductor is disclosed. The helical coil 602 placed on a substrate 606 may connect to a ground plane 604 through a via 608. This configuration may be suitable for implementing the resonator mode. Figure 8 illustrates a helical array 702 comprising four helical elements or coils of the type 602 shown in Figure 7. A substrate 706 is disposed between the helical array 702 and a ground plane 704. The distance 718 between array elements 708, 714 should be greater than 2 / 4. The distance between each pair of the other elements 708, 710, 712, 714 of the helical array 702 may also be greater than 2 / 4. All of the elements 708, 710, 712, 714 of the helical array 702 are connected to the ground plane 704 through vias 716. Figure 9 illustrates two array elements 708, 710 configured respectively as a transmitter and receiver. Any element 708, 710, 712, 714 of the helical array 702 may be arranged and configured to act as either a transmitter or receiver. The wireless RF signals 802 move from 708 towards 710. Using this setup, S-parameters are measured to determine the permittivity of a medium 804. During operation of the disclosed UAV in a medium present around a transmission line, measurement of the permittivity of the medium in this way may permit corona discharge around the line to be detected. Figure 10 illustrates a top view of the helical array 702, showing array elements 708, 710, 712, 714. The diagonally opposed elements 708, 712 are configured as transmitter or receiver. An electric field 805 is obtained by applying a potential difference between the two diagonally opposed elements 708, 712. The electric field 807 due to 710 and 714 may cause constructive or destructive interference to the existing field 805 generated between elements 708, 712. By applying a voltage difference on 710 and 714, constructive interference may be achieved to enhance measurement of the S-parameters of 708 and 712. The disclosed UAV system may provide an airborne detection means for sensing corona discharge in electrical transmission lines. In certain embodiments, S-parameters can be measured between an array of two or more helical elements while the UAV hovers in a corona discharge medium. The disclosed technology can promote enhanced accuracy of measurement of S-parameters to evaluate corona discharge by utilizing the array of helical elements for constructive interference as explained above. Moreover, the UAV system may incorporate means for switching operation between the mode suitable for sensing and measuring corona discharge, and the inductor mode suitable for aligning the UAV or charging its batteries. This switchable functionality therefore enables a same, single array of transducers to support positioning the UAV relative to a conductor, measuring a corona discharge, and charging the UAV. In the embodiment 900 of Figure 11, an isometric view 902 of a control unit 904 is displayed. The shape of the control unit 904 is not limited to that of the displayed embodiment. Sensors 906 may be mounted on the top and bottom surfaces of the control unit 904. Other sensors 906 may be positioned on sides of the control unit 904. The sensors 906 may, for example, be distance sensors. These may be configured to measure the distance of different sides of the UAV from a transmission line while aligning the UAV over the transmission line. Figure 12 shows an exemplary embodiment 1002 of the disclosed UAV. The UAV 1002 includes a helical array 702 attached to an underside of a control unit 904 of the UAV, for inspection of transmission lines. Sensors are fitted on the operatively top (910), bottom (not shown) and sides (914) of the control unit 904 to measure the distance between the UAV 1002 and any nearby object. The UAV is configured so that the connected helical array 702 may be switched between resonator and inductor modes, according to whether the UAV 1002 is to be used for detection of corona discharge or for charging of the UAV’s batteries by inductance. The shape and configuration of the disclosed UAV 1002 is not limited to that shown in the drawing. Figure 13 illustrates an alignment system and procedure 1100 for aligning the disclosed UAV relatively to a conductor such as, but not limited to, a transmission line. The diagram shows two separate rotational alignments of the UAV. In the alignment setup 1102 shown on the left, the flow of current 1106 through a conductor 1104 induces current in the helical array elements or coils 708, 710, 712, 714. The intensity of the induced current varies with the distance 1108, 1110, 1112 of the coils from the conductor 1104. The helical array element 710 may have greater current owing to its lesser distance 1110 from the conductor 1104. The coils 708, 712, 714 may have lesser induced current due their relatively greater distances 1108,1112 from the conductor 1104. With reference to these distances, the UAV system may be controlled to rotate the UAV clockwise 1114 in a horizontal plane, so that the adjacent coils of the pair 708, 710 and of the pair 712, 714 are brought into an orientation in which the adjacent coils of each pair are located the same distance from the conductor 1104. In certain embodiments of the UAV system, the distances 1108, 1110, 1112 between the UAV and the conductor 1104 may be measured using the sensors 906. In other embodiments of the UAV system, the angle of rotation of the UAV relative to the conductor can be inferred and adjusted by comparing the proportional intensity of current flowing in each of the two adjacent coils of a pair. In such embodiments, the UAV could be rotated until the current flowing in each of the coils of that pair is matched, i.e., the current in each is approximately the same. The alignment setup 1116 depicted on the right of Figure 13 illustrates the result of the alignment procedure. The rotational orientation of the UAV has been adjusted so that the distances 1120, 1122 of the adjacent coils 708, 710 of the helical array 702 match each other. In so doing, the UAV has been aligned generally parallel to the conductor 1104. The distances 1118, 1124 between the conductor 1104 and the pair of adjacent coils 714, 712 are relatively greater than the distances 1120, 1122 of the pair 708 and 710. The magnitude of the current flowing in the coils 708, 710 will be relatively greater than that flowing in the coils 712, 714, from which the closeness of the coils 708, 710 to the conductor 1104 can be inferred. Figure 14 shows a front view of a part 1101 of an exemplary embodiment of the disclosed UAV. The UAV is shown positioned over a conductor 1104. The conductor is surrounded by magnetic fields 1103. Following the parallel alignment of the embodiment 1101, the UAV may be controlled to move sideways towards the pair of coils 708, 710 which are carrying the higher current, until the UAV is positioned such that the conductor runs between centre of the helical array, that is, with the conductor being equidistant from the two pair of adjacent coils 708, 710 (not shown) and 712, 714 (not shown). In this orientation and position, the induced current in the adjacent pairs of coils may be equal. The conductor 1104 is shown positioned between the coils 708 and 714. The UAV may then also be controlled to descend until the conductor 1104 is positioned at half the length (height) of a transducer, e.g. a helical coil. Figure 15 illustrates the working of an exemplary embodiment 1002 of the UAV during inspection of a transmission line, including detecting and assessing the health of insulators 1208. A conductor comprising a transmission line 1206 is shown suspended from transmission towers 1202, 1204. The combination of distance sensors and helical array 702 may be used for detecting the presence and health of the insulator 1208. The UAV 1002 may be operated and controlled to travel along the conductor 1206 then switch to a clamp mode to measure the current in the line. In this mode, the UAV can be clamped onto the transmission line at locations along its length. This functionality may be used for detecting leakage current, which in turn may be useful for assessing the health of insulators supporting the line. In the clamp mode, the UAV may be temporarily clamped onto a transmission line so that the intensity of current flowing in the line may be measured at that location. The UAV may then be clamped onto the line at a second location, for example, a location on the other side of an intervening insulator, so that the current flowing there can be measured and compared against the first measurement. Leakage current, if any, caused by the insulator may accordingly be calculated by accurately measuring current flowing in the line at separate locations before and after the position of an insulator. This information can then be applied to predict the health of the insulator. The clamp mode relies on a tilt mechanism fitted to the UAV, which may be activated to tilt at least one of the helical coils 708, 714 with respect to the others. The UAV system may then calculate a leakage current 1210 by measuring intensity of the current in the line both before and after the position of detection of the insulator 1208 along the line and comparing these values according to the following equation: heakage current — In ^n+1 Where, ln and ln+i denotes the current before and after the detection of the insulator, respectively. The current is measured according to the principle of electromagnetic induction. The order of leakage current is in mA, which requires higher accuracy. Using the clamp mode, the UAV can stay still and take precise measurements of the current before and after the detection of the insulator. The measurement accuracy can be further increased by using the readings of multiple tilting array elements. Each pair of array elements can operate in a clamp mode, and hence, different current measurements can be taken with multiple array elements. Figure 16 illustrates an exemplary embodiment 1203 of a clamp system which includes a tilt mechanism of the UAV. The drawing shows how the angular orientation of one of the helical coils can be adjusted relative to another. This may permit the UAV to be switched to the clamp mode. The drawing displays the movement of the coil 708 by an angle 1205. Certain embodiments of the tilt mechanism may be designed in such a way that the movement is made by either of the two coils in a pair (for example, either of the pair 708 and 710) while the other two coils (for example, 712 and 714) remain fixed at a right angle relative to the body of the UAV. The position of coil 714 is shown by a right angle 1207. The tilt mechanism 1203 may not require any electrical power but may, for example, rely on a mechanical or hydraulic mechanism and hinge to work. In alternative embodiments the tilt mechanism may be electrically powered. Figure 17 illustrates a workflow involved in the monitoring of transmission lines using the device disclosed in Figure 12. The workflow begins with a sub-process involving the alignment of the UAV 1302. This may be followed by checking the battery status of the UAV 1304. Based on this information, it may take a decision 1306 regarding initiating the energy harvesting mode 1308 or checking the mode of operation of the UAV 1310. The present disclosure may be divided into two main modes; the leakage current measurement 1314 and the corona discharge inspection 1316. Depending upon the selected mode, the process may lead to the particular sub-process. Figure 18 illustrates a sequence of steps for positioning and aligning an embodiment of the disclosed UAV, such as the UAV shown in Figure 12. Initially, the distance is measured 1402 by using sensors 906 mounted on the control unit 904. For purposes of this exemplary scenario, the UAV is considered to be hovering on the side of the conductor. Based on the comparison of the distance between helical coils and conductor, as depicted in 1404, the UAV is moved upward 1406. Subsequently, the current in each coil is measured 1408. Block 1410 illustrates the closeness of the coil with the conductor as the current in any one of the coils is greater than the others. If this is the event, this may lead to the rotation of the UAV in a clockwise direction 1412. On the contrary, the process may enter another conditional state 1414 where the current in adjacent coils of both sides is compared, suggesting that the one adjacent side of the coils is in close proximity to the conductor. Assuming this is the case, the UAV may move in the direction of the conductor 1416. To align the UAV, it may be controlled to move upwardly or downwardly 1418 until the distance between the conductor and the control unit is half the length of the coils. After alignment, the distance between the conductor and each coil may be equal. Figure 19 illustrates a workflow for charging the UAV. The procedure may rely on resonant inductive energy transfer. The procedure involves matching the resonance frequency of the helical coils and the conductor. Accordingly, in 1502, the resonance frequency is matched, followed by initiating the charging of the device 1504. Another verification is implemented in 1506 to determine if the battery is fully charged. If the battery is not yet charged, the charging process may continue. However, if the battery is fully charged, the process may be terminated so that the UAV can continue its monitoring. The use of resonant inductive energy transfer provides certain benefits. Unlike mains-wired equipment for charging, no direct electrical connection is needed and hence equipment can be sealed to minimize the possibility of electric shock or water damage. Furthermore, if resonance circuitry is not included in an inductive power transfer system, its performance and power transfer efficiency suffer. Using resonance can help improve efficiency. Figure 20 illustrates a workflow for detecting and measuring leakage current. The measured value of the leakage current may then be applied to check the health of insulators used to suspend transmission lines from support structures. After measuring the current 1602, the UAV checks whether an insulator is detected or not 1604. If no insulator is detected, the UAV may continue to move along the conductor 1606. However, if an insulator is detected, the UAV again measures 1608 the current after the insulator. The leakage current is calculated 1610 before the process is concluded. In case of any anomaly in the leakage current, the system notifies operators that the insulator may be damaged. Figure 21 illustrates a workflow used to detect corona discharge in transmission lines. In a first step, the helical array is initialized or activate 1702 to send and receive RF signals 1704. This transmission and receiving of RF signals can be applied to measure the S-parameters which in turn may be used to calculate the permittivity of the surrounding environment 1706. Following this, RF signal generation is deactivated as the inductance in each coil is measured 1708. This may lead to the calculation of the permeability of the surrounding environment 1710. Predetermined or pre-defined values of permittivity and permeability associated with normal conditions, when there is no corona discharge, may be stored as a dataset accessible by the UAV system. In block 1712, the UAV system may compare the measured values of permittivity and permeability with the predetermined or pre-defined data set. Following the comparison, the condition is evaluated to determine the presence and level of corona discharge 1714. In the event of severe corona discharge, the system may notify 1716 a base station otherwise the process is terminated. Various components may be provided for implementing the system and method described above. The computing means may comprise onboard or remote computing devices including a processor (not shown) for executing the functions of components described herein, which may be provided by hardware or by software units executing means for comparing measured values against the dataset of values, and for controlling operation of the UAV. The software units may be stored in a memory component and instructions may be provided to the processor to carry out the functionality of the described components. In some cases, for example in a cloud computing implementation, software units arranged to manage and / or process data on behalf of the system may be provided remotely. Some or all of the components may be provided by a software application downloadable onto and executable on the computing device. The computing device may be embodied as any form of data processing device including a personal computing device (e.g. laptop or desktop computer), a server computer (which may be self-contained, physically distributed over a number of locations), a client computer, or a communication device, such as a mobile phone (e.g. cellular telephone), satellite phone, tablet computer, personal digital assistant or the like. Different embodiments of the computing device may dictate the inclusion or exclusion of various components or subsystems described below. The computing device may be suitable for storing and executing computer program code. Various participants and elements may use any suitable number of subsystems or components of the computing device to facilitate the functions described herein. The computing device may include subsystems or components interconnected via a communication infrastructure (for example, a communications bus, a network, etc.). The computing device may include one or more processors and at least one memory component in the form of computer-readable media. The one or more processors may include one or more of: CPUs, graphical processing units (GPUs), microprocessors, field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs) and the like. In some configurations, a number of processors may be provided and may be arranged to carry out calculations simultaneously. In some implementations various subsystems or components of the computing device may be distributed over a number of physical locations (e.g. in the UAV and a distributed, cluster or cloud-based computing configuration) and appropriate software units may be arranged to manage and / or process data on behalf of remote devices. The memory components may include system memory, which may include read only memory (ROM) and random access memory (RAM). A basic input / output system (BIOS) may be stored in ROM. System software may be stored in the system memory including operating system software. The memory components may also include secondary memory. The secondary memory may include a fixed disk, such as a hard disk drive, and, optionally, one or more storage interfaces for interfacing with storage components, such as removable storage components (e.g. magnetic tape, optical disk, flash memory drive, external hard drive, removable memory chip, etc.), network attached storage components (e.g. NAS drives), remote storage components (e.g. cloud-based storage) or the like. The computing device may include an external communications interface for operation of the computing device in a networked environment enabling transfer of data between multiple computing devices and / or the Internet. Data transferred via the external communications interface may be in the form of signals, which may be electronic, electromagnetic, optical, radio, or other types of signal. The external communications interface may enable communication of data between the computing device and other computing devices including servers and external storage facilities. Web services may be accessible by and / or from the computing device via the communications interface. The external communications interface may be configured for connection to wireless communication channels (e.g., a cellular telephone network, wireless local area network (e.g. using Wi-Fi™), satellite-phone network, Satellite Internet Network, etc.) and may include an associated wireless transfer element, such as an antenna and associated circuitry. The external communications interface may include a subscriber identity module (SIM) in the form of an integrated circuit that stores an international mobile subscriber identity and the related key used to identify and authenticate a subscriber using the computing device. One or more subscriber identity modules may be removable from or embedded in the computing device. The computer-readable media in the form of the various memory components may provide storage of computer-executable instructions, data structures, program modules, software units and other data. A computer program product may be provided by a computer-readable medium having stored computer-readable program code executable by the central processor. A computer program product may be provided by a non-transient or non-transitory computer-readable medium, or may be provided via a signal or other transient or transitory means via the communications interface. Interconnection via the communication infrastructure allows the one or more processors to communicate with each subsystem or component and to control the execution of instructions from the memory components, as well as the exchange of information between subsystems or components. Peripherals (such as printers, scanners, cameras, or the like) and input / output (I / O) devices (such as a mouse, touchpad, keyboard, microphone, touch-sensitive display, input buttons, speakers and the like) may couple to or be integrally formed with the computing device either directly or via an I / O controller. One or more displays (which may be touch-sensitive displays) may be coupled to or integrally formed with the computing device via a display or video adapter. The peripherals and I / O devices may be configured to communicate to a user pertinent information relating to the detection of a corona discharge, the comparison of measured S-parameters or values of permittivity or permeability against the predetermined dataset, or information on the health of insulators, for example. The UAV may include a geographical location element which is arranged to determine the geographical location of the UAV. The geographical location element may for example be implemented by way of a global positioning system (GPS), or similar, receiver module. In some implementations, the geographical location element may implement inertial navigation to track and determine the geographical location of the UAV using an initial set point and inertial measurement data. The presently disclosed technology differs in important respects from prior systems. For example, the technology is not dependent for its operation on Hall effect sensors such as those described in US 7,543,780. Moreover, the technology does not rely on electromagnetic field signal sensing by transducer elements of the type taught by that patent. The foregoing description has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the technology to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure. Any of the steps, operations, components or processes described herein may be performed or implemented with one or more hardware or software units, alone or in combination with other devices. Components or devices configured or arranged to perform described functions or operations may be so arranged or configured through computer-implemented instructions which implement or carry out the described functions, algorithms, or methods. The computer-implemented instructions may be provided by hardware or software units. In one embodiment, a software unit is implemented with a computer program product comprising a non-transient or non-transitory computer-readable medium containing computer program code, which can be executed by a processor for performing any or all of the steps, operations, or processes described. Software units or functions described in this application may be implemented as computer program code using any suitable computer language such as, for example, Java™, C++, or Perl™ using, for example, conventional or object-oriented techniques. The computer program code may be stored as a series of instructions, or commands on a non-transitory computer-readable medium, such as a random access memory (RAM), a read-only memory (ROM), a magnetic medium such as a hard-drive, or an optical medium such as a CD-ROM. Any such computer-readable medium may also reside on or within a single computational apparatus, and may be present on or within different computational apparatuses within a system or network. Flow diagrams are used herein to illustrate methods and workflows. Each block of the flow diagrams and combinations of blocks in the flow diagrams may provide functions which may be implemented by computer readable program instructions. In some alternative implementations, the functions identified by the blocks may take place in a different order to that shown in the flow diagrams. The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the present disclosure be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the present disclosure is intended to be illustrative, but not limiting, of the scope of any accompanying claims. Finally, throughout the specification and any accompanying claims, unless the context requires otherwise, the word ‘comprise’ or variations such as ‘comprises’ or ‘comprising’ will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

1. An unmanned aerial vehicle (UAV) for inspecting and monitoring an electrical power transmission line, the UAV including a measurement component arranged to measure S-parameters of a magnetic field to determine the permittivity of a medium surrounding the transmission line.

2. The UAV according to claim 1, which includes a transducer assembly comprising a plurality of transducers configured to operate in a resonator mode, and wherein the measurement component is arranged to measure the S-parameters between at least two of the transducers.

3. The UAV according to claim 2, wherein at least one of the transducers is configured to operate in an inductor mode.

4. The UAV according to claim 3, wherein at least one of the transducers is configured to operate selectively either in the resonator mode or the inductor mode, and the UAV includes switch means configured to switch the at least one transducer between its resonator and inductor modes.

5. The UAV according to any one of claims 2 to 4, which includes means configured to match resonant frequencies of the transducers to a frequency of radiation from the transmission line.

6. The UAV according to any one of claims 2 to 5, wherein the transducer assembly includes a ground plane separated from the transducers by a substrate, and vias connecting the transducers to the ground plane.

7. The UAV according to any one of claims 2 to 6, which includes locating means configured to determine and record a location of the UAV relative to the transmission line, the locating means comprising at least one distance sensor.

8. The UAV according to any one of claims 2 to 7, which includes alignment means arranged to align the UAV with reference to the transmission line by applying measured values of intensity of current induced in the transducers to determine proximity of the transducers to the transmission line and positioning the transducers relative thereto.

9. The UAV according to any one of claims 2 to 8, wherein the transducer assembly isconfigured as an array of generally uniformly sized transducers selected from the group consisting of helical coils and flat rectangular coils.

10. The UAV according to any one of claims 2 to 9, which includes a docking means configured to dock the UAV on the transmission line, the docking means comprising a clamp system which includes a transducer tilt mechanism.

11. A transmission line inspection system comprising the UAV according to any one of claims 2 to 10 and a computing means arranged to:calculate values selected from the group consisting of permittivity, permeability, S-parameters, and any combinations thereof, associated with a medium surrounding the transducers of the UAV; andcompare the calculated values against a reference dataset of predetermined corresponding values associated with abnormal functioning of the transmission line.

12. The system according to claim 11, wherein the computing means is arranged to manoeuvre the UAV to position the transducers on either side of the transmission line using the alignment system of the UAV.

13. A method of inspecting a transmission line to detect an abnormal operating condition associated with the transmission line, comprising utilizing the system according to claim 11 or claim 12 to:transmit and receive a radio frequency signal using the transducers;measure S-parameters of a magnetic field associated with the transmission line;apply the measured S-parameters to solve for a value of at least one of permittivity and permeability of a medium surrounding the transducers; andcompare the measured S-parameters, solved value of permittivity, or solved value of permeability against a dataset of predetermined corresponding values associated with the abnormal operating condition, thereby to detect if operation of the transmission line is in the abnormal operating condition;wherein the abnormal operating condition comprises corona discharge.

14. The method according to claim 13, which includes measuring inductance in at least one of the transducers and applying a value of the measured inductance to solve for the permeability of the surrounding medium.

15. The method according to claim 13 or claim 14, which includes generating constructive ordestructive interference between distinct pairs of the transducers to promote enhanced accuracy of measurement of the S-parameters.

16. The method according to any one of claims 13 to 15, which includes positioning and aligning the UAV with reference to the transmission line by performing one or more of the following steps:positioning the UAV to ensure that its extremities are clear of the transmission line;measuring an induced current in each transducer, and if the current in one transducer exceeds that in each of the other transducers, rotating the UAV or the transducer assembly with respect to the transmission line; or if the current in each of a set of two adjacent transducers is approximately equal but exceeds the current in each of the other coils, moving the UAV in a direction of the higher current carrying coils; andwhen the current in all of the coils is approximately matched, adjusting the position of the UAV until the transmission line extends through the transducer assembly at a level approximately midway between the two ends of each transducer.

17. A method of detecting a faulty insulator which insulates a transmission line from a support structure, the method including the steps of:utilizing the system according to claim 11 or claim 12 to measure a first intensity of current flowing in a portion of the transmission line extending from a first side of the insulator, and a second intensity of current flowing in a second portion of the line extending from a second side of the insulator;comparing the first and second current intensities, thereby to calculate a leakage current; andcomparing the leakage current against a predetermined range of abnormal leakage current values indicative of a faulty insulator, thereby to establish that the insulator is faulty if the leakage current is within said range of values.

18. The method according to claim 17, which includes docking the UAV on the transmission line while each of the respective first and second current intensities is measured.

19. A method of harvesting wireless energy from an electrical power transmission line, the method comprising positioning an unmanned aerial vehicle (UAV) in proximity to the transmission line, wherein the UAV includes at least two transducers acting as inductors which are configured to be positioned on either side of the transmission line; and utilising the transducers to harvest wireless energy using magnetic fields around the transmission line.

20. The method according to claim 19, which includes a step of matching resonant frequencies of the transducers to the frequency of radiation from the transmission line.

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