A sensor positioning apparatus

Abstract

A positioning apparatus 10 for positioning a sensor 12 relative to insulators 14 in an insulator stack 16 includes: a base 20, a support member 60 rotatably connected to the base, and a follower membe

Description

FIELD OF THE INVENTION The invention relates to a sensor positioning apparatus for positioning a sensor relative to insulators in an insulator stack. The apparatus may be used for sensors that monitor a condition of a stack of disc insulators in overhead transmission lines. In particular, the invention relates to a sensor positioning apparatus that moves to allow a sensor to monitor individual insulators in a stack. BACKGROUND TO THE INVENTION Insulators are critical components of high-voltage transmission and power distribution networks. Insulators prevent the flow of electricity between the conductor and the earth and are typically suspended from utility poles or transmission towers. Some insulators, such as disc insulators, are typically arranged end-to-end in an elongate stacked structure to aid withstanding high voltages. Insulator health can deteriorate due to environmental and other factors. Reduced capacity to withstand voltage may lead to power grid failure or other faults in the transmission lines. Therefore, inspection of disc insulators is crucial for ensuring the uninterrupted operation of electric substations and avoiding failures that might result in power outages. Insulator inspection may involve detection of surface contaminant build-up, defective insulation material, voltage flashovers, corona discharge, insulation material porosity, poor glazing, and mechanical loads on the insulators. Manual inspection of disc insulators is difficult, risky, and time-consuming due to the high voltages, the height of the towers, and other unfavourable environmental factors. Existing solutions for monitoring insulator health are expensive or cannot examine individual discs in a stack such that the precise location of a fault is identified, leading to sub-optimal operation of transmission lines, increased safety risks, and economic losses. There is accordingly room for improvement. The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. 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 OF THE INVENTION In accordance with an aspect of the invention there is provided a sensor positioning apparatus for positioning a sensor relative to insulators in an insulator stack, comprising: a base configured to be fixed to the stack and having a camming surface provided thereon; a support member rotatably connected to the base so as to be rotatable relative to the base about a first axis; an elongate follower member rotatably connected to the support member at a first end of the follower member so as to be rotatable relative to the support member about a second axis being perpendicular to the first axis, wherein the follower member bears on the camming surface between the first end and a second end of the follower member in use; a sensor mount located towards the second end of the follower member and being configured to support an insulator stack sensor in use; and, a drive unit configured to rotate the support member relative to the base about the first axis and in turn to displace the follower member along the camming surface, wherein the camming surface is configured to transform rotation of the follower member about the first axis into rotation of the follower member about the second axis, so as to move the sensor mount between a first position from which a first part of the insulator stack can be monitored in use and a second position from which a second part of the insulator stack can be monitored in use. The support member may be rotatably connected to the base by way of a connecting means in the base, the connecting means defining the first axis. The connecting means may be a protrusion extending from the base, the protrusion being configured to receive an end portion of the support member in use such that an inner surface of the end portion of the support member is slidably rotatable about an outer surface of the protrusion. The camming surface may surround and may be spaced apart from the first axis. The camming surface may be defined on a rim extending from a periphery of a first major surface of the base. The camming surface may be provided by formations corresponding to at least the first and second positions of a plurality of positions of the sensor mount. At least two of the formations of the camming surface have different elevations relative to each other. The formations of the camming surface define at least a rise condition and a return condition of the follower member during rotation of the follower member along the second axis. The rise position of the follower member may correspond to the first position of the sensor mount from which the first part of the insulator stack can be monitored in use, and the return position of the follower member may correspond to the second position of the sensor mount from which the second part of the insulator stack can be monitored in use. The first part of the insulator stack may be a first insulator, and the second part of the insulator stack may be a last insulator. The formations of the camming surface may define a dwell condition of the follower member. The formations may include a peak and a depression arranged in a smooth, continuous arrangement to provide the camming surface, the peak having a higher elevation relative to the depression. One of the formations may be an adjustable formation configured to have a relative elevation which may be adjustable by way of an adjustment means. The adjustable formation of the camming surface may include a first adjustable portion spaced apart from and displaceable relative to a second adjustable portion, and wherein the adjustment means may be configured to adjust a distance between the first and second adjustable portions to adjust the relative elevation of the adjustable formation. The adjustment means may be a screw provided between the first and second adjustable portions. The base may include an attachment formation configured to attach the base to the stack, the attachment formation provided on a second major surface of the base. The base may be formed of two base members configured to be removably attachable to each other in use. The base members may be removably attachable to each other by way of a friction fit. The base may be disc shaped and the base members may be semi-circular. The drive unit may be configured to harvest wind energy. The drive unit may include aerofoils. The aerofoils may be fixed to the support member by elongate members extending beyond the base such that the wind energy causes the aerofoils to rotate around the base and in turn rotate the support member about the first axis in use. The monitoring device may be a light-emitting sensor configured to monitor a condition of the insulators in the stack. Embodiments of the invention 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 a three-dimensional view of a sensor positioning apparatus attached to a stack of insulators in use according to aspects of the present disclosure; Figure 2 is an exploded three-dimensional view of the base members of the sensor positioning apparatus of Figure 1; Figure 3 is an exploded three-dimensional view of the sensor positioning apparatus of Figure 1; Figure 4 is a three-dimensional view of the sensor positioning apparatus of Figure 1; and Figure 5 is a block diagram illustrating components of an exemplary system for insulator stack monitoring according to aspects of the present disclosure. DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS An embodiment of a sensor positioning apparatus for positioning a sensor relative to insulators in an insulator stack is disclosed. The sensor positioning apparatus may be used in a system and method for insulator stack monitoring. The apparatus is configured to be fitted on top of a stack of insulators requiring monitoring. The apparatus has an arm with a mount for the sensor on its end which revolves around the stack and also moves to direct the sensor along the entire length of the stack. This way the whole stack of insulators can be assessed for a particular condition and a precise location of a fault can be identified for repair. The movement of the apparatus is driven by wind energy which drives rotation of the arm along the surface of the base about a first axis. The arm therefore rotates 360 degrees around the base. The surface of the base along which the arm slides has a contoured shape comprising peaks and troughs. The contoured surface causes the arm to rotate about a second axis and thus to direct the sensor up and down the length of the stack, so that the whole length of the stack may be monitored. The apparatus provides a simple, cost-effective solution for monitoring insulators. Referring to Figures 1 to 4, an embodiment of a sensor positioning apparatus (10) for positioning a sensor (12) relative to insulators (14) in an insulator stack (16) is shown. The apparatus (10) includes a base (20) with a camming surface (22), the base (20) being configured to be fixed to the stack (16). The camming surface (22) may be any surface configured to vary the motion of another part slidably moving along the surface. The apparatus (10) has a support member (60) rotatably connected to the base (20) so as to be rotatable relative to the base about a first axis (70). The apparatus further includes an elongate follower member (80) rotatably connected to the support member at a first end (82) of the follower member so as to be rotatable relative to the support member about a second axis (72) being perpendicular to the first axis (70). The follower member (80) may be an elongate arm, pole, or rod extending away from the support member and towards the camming surface. The follower member (80) bears on the camming surface (22) between the first end (82) and a second end (84) of the follower member in use. The follower member may rest on the camming surface and slidably move along the camming surface. The apparatus includes a sensor mount (100) located towards the second end (84) of the follower member (80), the sensor mount (100) being configured to support the insulator stack sensor (12) in use. The sensor mount (100) may be a bracket configured to hold the sensor (12) in use. The apparatus further includes a drive unit (120) configured to rotate the support member (60) relative to the base (20) about the first axis (70) and in turn to displace the follower member (80) along the camming surface (22). The camming surface (22) is configured to transform rotation of the follower member (80) about the first axis (70) into rotation of the follower member (80) about the second axis (72), so as to move the sensor mount (100) between a first position (102) from which a first part (17) of the insulator stack can be monitored in use and a second position (104) from which a second part (18) of the insulator stack can be monitored in use. In the present embodiment, the base (20) is provided by a disc-like body having a first major surface (24) and a second major surface (26). The first major surface (24) may be the upper surface, and the second major surface (26) may be the lower surface when the apparatus is in the operative position. The second major surface (26) of the base may include an attachment formation (28) configured to attach the base (20) to the insulator stack (16). The attachment formation (28) may be one or more clips, suction cups, magnets, adhesive formations or the like that may securely attach the apparatus to the insulator stack (16). The attachment formation (28) may be removably attachable to the insulator stack or may be permanently attached to the insulator stack. The attachment formation (28) may be attached to the top of the insulator stack, on top of the first or uppermost insulator (14). Other embodiments may provide for the apparatus to be secured at the bottom, the side, or at another position on the insulator stack. The base (20) in the present embodiment is round and disc-shaped, but the base may be oblong or angular or another shape suitable for providing the camming surface (22) in other embodiments. The base may be formed of two base members (30, 31) configured to be removably attachable to each other in use. The base members may include a first base member (30) and a second base member (31) which may be separate, complementary pieces that a user may join to form the base during installation of the apparatus (10) on the insulator stack (16) in use. The detachable nature of the base members allows easier, more customisable installation of the apparatus to suit the size and shape of the insulator stack. This feature also allows easy disassembly and practical storage of the apparatus when not in use. The first base member (30) and the second base member (31) may be removably attachable to each other by way of a friction fit. This fit may be achieved with a mortise and tenon arrangement provided by a mortise (32) or recess located at each end of the first base member (30) and a tenon (34) or protrusion located at each end of the second base member (31). The tenon (34) may be configured to be complementary in shape to the mortise (32) such that the tenon fits tightly in the mortise in use. The mortise and tenon may be sized proportionally to the formations in which they are disposed to ensure a secure fit. For example, as illustrated, the mortise and tenon disposed in the join of a peak may be larger than the mortise and tenon joining together a depression. Where the base (20) is disc-shaped, the base members (31, 31) may be semi-circular. The support member (60) may be a hollow, elongate rod slotted or open along its length with a partially circular cross section. Other embodiments may include a hollow pipe, or a solid bar having a hollow end portion (62) for attachment to the base (20). The support member (60) may be rotatably connected to the base (20) by way of a connecting means in the base (20), the connecting means defining the first axis (70). The connecting means is provided in the centre of the base to define a central first axis (70) in the present embodiment but may be offset from the centre in other embodiments. The support member (60) may be pivotable relative to the base (20) to provide rotation of the support member. In the present embodiment, the connecting means is provided by a protrusion (68) extending from the base (20), the protrusion (68) having an outer surface (69) being configured to receive the support member (60) in use. The support member (60) may have an end portion (62), an inner surface (64) of which may be slidably rotatable about the outer surface (69) of the protrusion (68). The outer surface (69) of the protrusion (68) and the inner surface (64) of the support member (60) may be a smooth, low-friction surface to allow the support member to slide or glide about the protrusion in use. Similarly to the base members (30, 31), the support member may comprise two halves, namely a first support member part (61) and a second support member part (63) configured to be joined together to form the support member (60) during installation of the apparatus (10). The first support member part (61) and a second support member part (63) may be joined together by a mortise and tenon arrangement, or another suitable connection. The connecting means may further include a retaining formation to retain the support member on the protrusion. The retaining formation may for example be provided by a tongue and groove-type arrangement, or the like. The follower member (80) is provided by a pole or a beam, but may have other shapes suitable for sliding along the camming surface (22) in other embodiments. The follower member may be rotatably connected to the support member (60) by way of a hinge arrangement (86). The hinge arrangement (86) may be provided by projections (88) extending laterally from the sides of the first end of the follower member (80), the projections (88) being configured to be captured by corresponding receiving apertures (89) located near the end portion (62) of the support member (60). The projections (88) may be knobs, studs, or extensions that clip into or are otherwise received by the receiving apertures (89) by way of an interference or friction or other suitable fit. The follower member (80) may be pivotable about the second axis (72) by way of rotation of the projections (88) in and relative to the receiving apertures. Other embodiments may provide another connection that allows the follower member (80) to rotatably connect to the support member (60) such that it is movable about the second axis (72). The drive unit (120) may be configured to harvest wind energy. The drive unit (120) may include sails, blades, or other means suitable for catching, harnessing and / or transforming the kinetic energy of the wind into energy that drives rotation of the follower member about the first axis and in turn the second axis. The drive unit may include aerofoils (122) which may be suitably shaped members configured to produce lift and drag when moved through the air. The aerofoils (122) may be fixed to the support member (60) by elongate members (124) extending beyond the base such that the wind energy causes the aerofoils (122) to rotate around the base (20) and in turn rotate the support member (60) about the first axis (70) in use. The elongate members (124) may be positioned perpendicular to the (122) as in the present embodiment or may be connected in another suitable arrangement for spacing the aerofoils apart from the base such that they orbit the base along a wider circumference. The drive unit may include a motor in other embodiments. The camming surface (22) on the base (20) may surround and may be radially spaced apart from the first axis (70). This way, the follower member (80) may move along the camming surface (22) by rotation of the support member (60) about the first axis (70). The camming surface (22) may be defined on a rim (36) extending from a periphery (38) of the first major surface (24) of the base (20). The rim (36) may be a raised portion extending from and generally perpendicularly to the first major surface (24). The periphery (38) may be a circumference of the base if the base is circular, or otherwise the outer edge or brink of the base. The camming surface (22) may be positioned closer to the support member (60) as opposed to the periphery (38) of the base in other embodiments. The camming surface (22) may be provided by formations (40), at least some of which correspond to a different position of the sensor mount for monitoring a different part of the insulator stack. There may for example be a formation for each of the first position (102), the second position (104) and so on for each of a plurality of positions of the sensor mount (100). The first position (102) corresponds to the first part (17) of the insulator stack which may be a first insulator. The second position (104) corresponds to the second part (18) of the insulator stack which may be a last insulator in the stack (16). The first and second parts of the insulator stack may be any portion of the stack that may be desirable to monitor with the sensor (12) from the plurality of positions in which the sensor mount may be placed. The first and second parts may both be on the same insulator or may be located on different insulators. At least two of the formations (40) may have different elevations (42) relative to each other, with formation having a higher elevation relative to another. An elevation (42) may be defined as the distance from the first major surface (24) of the base to the highest point of the formation. The formations (40) may include a peak (44) and a depression (46) arranged in a smooth, continuous arrangement to provide the camming surface (22), the peak (44) having a higher elevation (42) relative to the depression (46). The peak (44) may be a raised portion extending in a direction away from the first major surface (24) of the base. The depression (46) may be a trough or recess in the rim (36) that extends towards the first major surface (24) of the base. In the operative condition, the distance from the base parallel to the first axis to the highest point of the peak (44) is greater than the distance from the base parallel to the first axis to the highest point of the depression (46). One or more of the formations (44) may be an adjustable formation (48) configured to have a relative elevation which is adjustable by way of an adjustment means (54). All or a subset of the formations (44) may be adjustable formations (48). The adjustable formation (48) may include a first adjustable portion (50) spaced apart from and displaceable relative to a second adjustable portion (52). The adjustable formation (48) may be part of the rim (36) of the base (20) having a window or space therein, the size of which may be operatively adjusted by the adjustment means (54). One or both of the first and second adjustable portions may be movable. For example, the first adjustable portion (50) may be relatively moved closer to the second adjustable portion to decrease the elevation of the adjustable formation. As such, the range of motion of the follower member about the second axis would be limited. Such adjustment would be suitable to configure the follower member to position the sensor mount along a shorter insulator stack. To enable the sensor mount to reach all positions along a longer insulator stack, the adjustment means (54) may be operatively used to increase the elevation of the adjustable formation by moving the first and second adjustable portions further apart. The first adjustable portion (50) may be the upper portion and the second adjustable portion (52) may be the lower portion or vice versa. The adjustment means (54) may be configured to adjust a distance between the first and second adjustable portions to adjust the relative elevation of the adjustable formation. In the present embodiment, the adjustment means (54) is provided between the first and second adjustable portions. The adjustment means may be positioned on the one or both of the first and second adjustable portions that moves, or another position suitable to enable the adjustment means (54) to relatively move the first and second adjustable portions in other embodiments. The adjustment means (54) may be one or more screws provided between the first and second adjustable portions. The screw may be rotated in one direction by the user to relatively pull the first and second adjustable portions toward each other. Rotating the screw in the opposite direction by the user may push the first and second adjustable portions apart. The relative elevation of the adjustable formation (48) may be adjustable by the adjustment means (54) as a function of the flexibility of the material which the formation is made of. Alternatively, the adjustable formation (48) may be configured such that one or both of the first adjustable portion (50) and the second adjustable portion (52) is slidably adjustable or by another suitable adjustment means to allow the user to freely set the height of the adjustable formation. The formations (40) of the camming surface (22) define at least a rise condition and a return condition of the follower member (80) during rotation of the follower member (80) along the second axis (72). The rise condition may be defined as movement of that part of the follower member (80) which bears on the camming surface in a direction away from the base. Such movement would in turn move the sensor mount up the stack to direct the sensor towards a topmost insulator thereof. The follower member may be in the rise condition when moving along a peak (44) towards the highest point. The follower member may be in the return condition when the part of the follower member which bears on the camming surface moves in a direction towards the base, for example when moving along a depression (46) towards its lowest point. Such movement would in turn move the sensor mount down the stack to direct the sensor towards a lowermost insulator thereof. The rise position may correspond to the first position of the sensor mount (100) from which the first part (17) of the insulator stack (16) can be monitored in use. The return position of the follower member may correspond to the second position of the sensor mount from which the second part (18) of the insulator stack can be monitored in use. The formations (40) of the camming surface may define one or more dwell conditions of the follower member. The follower member may be in the dwell condition when moving in a direction parallel to the base. The dwell condition may allow the follower member to position the sensor mount (100) to rotate about the first axis only such that the one insulator or part of the stack of interest may be monitored for an extended period. The sensor mount (100) may provide a connection to a sensor that may be movable about the connection, such as a hinge arrangement, or may be fixed to the mount. The sensor (12) may be a light-emitting sensor configured to monitor a condition of the insulators (14) in the stack (16). The sensor may monitor one or more health parameters of the insulators such as corrosion, electric stress, mechanical stress, heat emission from damaged discs, gas reflectance, flashover currents due to contamination, and ionization of air molecules. A schematic block diagram depicting a system (1000) for insulator stack monitoring according to aspects of the present disclosure is shown in Figure 5. The sensing node (1002) includes a sensor that allows the direct or indirect monitoring of disc insulators. Inspection of the electric or mechanical stress, corrosion formed on the disc, the misalignment caused due to the mechanical stresses, and so on calls for the direct sensing of the disc insulators. In contrast, the emission of heat into the surrounding air, the reflectance of gases from the disc’s surfaces and the ionizing of the surrounding air in the event of a corona discharge demand indirect sensing. The sensing node transfers its data to a Digital Signal Processing (DSP) unit (1004), which includes a microcontroller, memory storage device, and an ADC / DAC for data conversion. The processed data may be sent spontaneously for access to the Human Machine Interface (HMI) unit (1006), which has a range of user interface choices for accessing the data. A power management unit (1008) driven by wind energy may power up all the modules. In use, the apparatus (10) may be attached to an insulator stack (16) for monitoring by way of the attachment formation (28). The wind may be caught by the aerofoils (122) which harness the kinetic energy of the wind to move. Movement of the aerofoils (122) which are fixed to the support member (60) results in rotation of the support member (60) about the protrusion (68) in the base (10) about the first axis (70). As a function of rotation of the support member, the follower member (80) connected to the support member (60) likewise rotates about the first axis (70), sliding along the camming surface (22) of the base. This positions the sensor mount (100) at a plurality of positions along a 360-degree path surrounding the insulator stack (16). Due to the peaks (44) and depressions (46) of the camming surface (22), the follower member (80) also moves about the second axis (72) such that the sensor mount (100) may be positioned at a plurality of positions to monitor along the length of the insulator stack. The elevations of at least one of the formations (44) of the camming surface (22) may be adjusted to change the path of the sensor mount (100) about the second axis (72). As such, the whole insulator stack may be monitored by a sensor attached to the mount. The ability to position a sensor to monitor all parts of the insulator stack ensures that faults may be located and repaired timeously to minimise damage and enhance safety. The sensor positioning apparatus provides a cost-effective solution with its simple mechanical design. Additionally, the apparatus moves a single sensor to monitor all parts of the stack, negating the need for multiple sensors. The apparatus may be customisable to any insulator stack as a user can alter the camming surface to adapt to the dimensions of the stack. The harnessing of wind energy results in a sustainable solution for monitoring which may be desirable to carry out regularly. The foregoing description has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the invention 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. The language used in the specification has been principally selected for readability and 5 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 invention be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims. 10 Finally, throughout the specification and 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. 15

Claims

1. A sensor positioning apparatus for positioning a sensor relative to insulators in an insulator stack, comprising:a base configured to be fixed to the stack and having a camming surface provided thereon;a support member rotatably connected to the base so as to be rotatable relative to the base about a first axis;an elongate follower member rotatably connected to the support member at a first end of the follower member so as to be rotatable relative to the support member about a second axis being perpendicular to the first axis, wherein the follower member bears on the camming surface between the first end and a second end of the follower member in use;a sensor mount located towards the second end of the follower member and being configured to support the sensor in use; and,a drive unit configured to rotate the support member relative to the base about the first axis and in turn to displace the follower member along the camming surface, wherein the camming surface is configured to transform rotation of the follower member about the first axis into rotation of the follower member about the second axis, so as to move the sensor mount between a first position from which a first part of the insulator stack can be monitored in use and a second position from which a second part of the insulator stack can be monitored in use.

2. The sensor positioning apparatus as claimed in claim 1, wherein the support member is rotatably connected to the base by way of a connecting means in the base, the connecting means defining the first axis.

3. The sensor positioning apparatus as claimed in claim 2, wherein the connecting means is a protrusion extending from the base, the protrusion being configured to receive an end portion of the support member in use such that an inner surface of the end portion of the support member is slidably rotatable about an outer surface of the protrusion.

4. The sensor positioning apparatus as claimed in claim any one of claims 1 to 3, wherein the camming surface surrounds and is spaced apart from the first axis.

5. The sensor positioning apparatus as claimed in any one of claims 1 to 4, wherein the camming surface is defined on a rim extending from a periphery of a first major surface of the base.

6. The sensor positioning apparatus as claimed in claim 5, wherein the camming surface is provided by formations corresponding to at least the first and second positions of a plurality of positions of the sensor mount.

7. The sensor positioning apparatus as claimed in claim 6, wherein at least two of the formations of the camming surface have different elevations relative to each other.

8. The sensor positioning apparatus as claimed in claim 6 or 7, wherein the formations of the camming surface define at least a rise condition and a return condition of the follower member during rotation of the follower member along the second axis.

9. The sensor positioning apparatus as claimed in claim 8, wherein the rise position of the follower member corresponds to the first position of the sensor mount from which the first part of the insulator stack can be monitored in use, and the return position of the follower member corresponds to the second position of the sensor mount from which the second part of the insulator stack can be monitored in use.

10. The sensor positioning apparatus as claimed in claim 9, wherein the first part of the insulator stack is a first insulator, and the second part of the insulator stack is a last insulator.

11. The sensor positioning apparatus as claimed in any one of claims 6 to 10, wherein the formations of the camming surface define a dwell condition of the follower member.

12. The sensor positioning apparatus as claimed in any one of claims 6 to 11, wherein the formations include a peak and a depression arranged in a smooth, continuous arrangement to provide the camming surface, the peak having a higher elevation relative to the depression.

13. The sensor positioning apparatus as claimed in any one of claims 6 to 12, wherein one of the formations is an adjustable formation configured to have a relative elevation which is adjustable by way of an adjustment means.

14. The sensor positioning apparatus as claimed in claim 13, wherein the adjustable formation of the camming surface includes a first adjustable portion spaced apart from and displaceable relative to a second adjustable portion, and wherein the adjustment means is configured to adjust a distance between the first and second adjustable portions to adjust the relative elevation of the adjustable formation.

15. The sensor positioning apparatus as claimed in claim 13 or 14, wherein the adjustment means is a screw provided between the first and second adjustable portions.

16. The sensor positioning apparatus as claimed in any one of claims 1 to 15, wherein the base includes an attachment formation configured to attach the base to the stack, the attachment formation provided on a second major surface of the base.

17. The sensor positioning apparatus as claimed in any one of claims 1 to 16, wherein the base is formed of two base members configured to be removably attachable to each other in use.

18. The sensor positioning apparatus as claimed in claim 17, wherein the base members are removably attachable to each other by way of a friction fit.

19. The sensor positioning apparatus as claimed in claim 17 or 18, wherein the base is disc shaped and the base members are semi-circular.

20. The sensor positioning apparatus as claimed in any one of claims 1 to 19, wherein the drive unit is configured to harvest wind energy.

21. The sensor positioning apparatus as claimed in claim 20, wherein the drive unit includes aerofoils.

22. The sensor positioning apparatus as claimed in claim 21, wherein the aerofoils are fixed to the support member by elongate members extending beyond the base such that the wind energy causes the aerofoils to rotate around the base and in turn rotate the support member about the first axis in use.

23. The sensor positioning apparatus as claimed in any one of claims 1 to 22, wherein the sensor is a light-emitting sensor configured to monitor a condition of the insulators in the stack.16