GB2628189A

GB2628189A - Disconnector and Earthing Switch with Telescopic Contact

Info

Publication number: GB2628189A
Application number: GB2306482.7A
Authority: GB
Inventors: Waghmore Minal; Kona Kaushik; Solase Rushikesh; Pawar Vishal; Pingle Mangesh
Original assignee: Eaton Intelligent Power Ltd
Current assignee: Eaton Intelligent Power Ltd
Priority date: 2023-03-14
Filing date: 2023-05-02
Publication date: 2024-09-18
Also published as: GB202306482D0

Abstract

A device 100 having one or more switching mechanisms 110 which disconnect a power supply from a load. A disconnector and earthing switch 330 is associated with each respective switching mechanism, each switch having a telescopic disconnector blade 332 with first 342 and second 334 ends. The disconnector blade pivots around the first end between three different positions: a first position in which the switch is closed, and the supply is connected to the load through the blade; a second isolation position in which the switch is open and the supply is disconnected from the load; and a third position in which the supply is disconnected from the load and a second end of the blade is electrically connected to an earthing contact 336. The disconnector blade may have an inner contact (402, figures 4A-B) which slides within an outer contact (404, figures 4A-B). The blade may have a compliant member (406, figures 4A-B), such as a compression spring, which is disposed within a guide hole of the outer contact, the member biasing the inner contact out of the guide hole. The device may have a housing 216 having first 216a and second side walls 216b, whereby the second wall has an insulating support 500 having a guide portion (662, figures 6A-B) and electrical contact (664, figures 6A-B).

Description

Disconnector and Earthing Switch with Telescopic Contact

Field

The present application relates to an earthing disconnection switch (also called herein a disconnector and earthing switch). In particular, the present application relates to an earthing disconnection switch having a telescopic or retractable contact. In some implementations, a three-position earthing disconnection switch (or three position disconnector and earthing switch, 3PS) can be provided within a compact footprint by way of said retractable contact.

Background

Switchgears and other switching devices are used to control and protect electrical equipment, such as equipment operated by utilities, commercial building owners, and operators of distributed renewable generation assets such as solar farms and wind turbines. Such switchgears include various medium voltage devices (e.g., devices rated for 12kV or 24kV) for a range of applications, such as a ring main unit (AMU).

For any given equipment specification or application, it is desirable to provide a reliable and compact switchgear with a small footprint. It is also desirable to provide an earthing disconnection switch (or disconnector and earthing switch) with three positions -on, off (or isolation), and earth -to facilitate in-situ testing of cable integrity and improve the ease of maintenance of the switchgear. It is particularly desirable to combine such a three-position disconnector and earthing switch or 3PS with a compact switchgear or switching device.

Summary

The matter for protection is set out in the appended claims.

Disclosed herein is a device comprising: one or more switching mechanisms configured to disconnect a power supply from a load; and one or more disconnector and earthing switches, each disconnector and earthing switch associated with a respective switching mechanism. Each disconnector and earthing switch comprising a telescopic disconnector blade having a first end and a second end, wherein the disconnector blade is configured to pivot around the first end between three different positions. The three positions comprise: a first position in which the disconnector and earthing switch is closed and the power supply is connected to the load through the disconnector blade; a second, isolation, position in which the disconnector and earthing switch is open and the power supply is disconnected from the load; and a third position in which the power supply is disconnected from the load and a second end of the disconnector blade is electrically connected to an earthing contact. Such a disconnector and earthing switch (also termed an earthing disconnection switch) can be termed a 3PS switch (three position disconnector and earthing switch).

The use of a disconnector and earthing switch with a telescopic or retractable contact (or disconnector blade) can facilitate provision of a reliable device with a small footprint and improved dielectric performance, which device can more easily and safely tested in-situ (thereby e.g., improve the ease of maintenance). For example, a 3PS can be provided within a small footprint, which can lead to smaller device architecture.

Tn some examples, the telescopic disconnector blade comprises an outer contact and an inner contact, a portion of the inner contact arranged to slide within the outer contact. Optionally, the outer contact comprises the first end of the disconnector blade and the inner contact comprises the second end of the disconnector blade. Optionally, the outer contact comprises a guide hole and the inner contact slides within the guide hole, the disconnector blade further comprising a compliant member disposed within the guide hole and configured to bias the inner contact out of the guide hole. Optionally, in response to an external force applied in a first direction and to the second end of the disconnector blade, the inner contact is configured to slide in the first direction within the guide hole of the outer contact and the compliant member is configured to bias the inner contact in a direction opposite the first direction. Optionally, the compliant member is a compression spring. Any other suitable compliant member can be used. The compliant member can be compliant through form and/or material.

Tn some examples, the telescopic disconnector blade is configured to move between an extended state and a compressed state, wherein the disconnector blade is in the extended state in the first position and the third position, and wherein the disconnector blade is in the compressed state in the second position.

In some examples, the device further comprises a housing having first and second side walls, wherein the telescopic disconnector blade is configured to rotate around the pivot 35 from the first position to the second position, wherein the rotation is towards the second side wall of the housing. The use of a telescopic or retractable blade as described herein -3 -can help maintain adequate between the second side wall and the tip or second end of the disconnector blade; this can help to reduce field intensity at the end of the blade and thereby help reduce or avoid the risk of dielectric failure between the housing and the blade.

Optionally, the second side wall comprises an insulating support configured to contact, when the disconnector blade is in the second position, the second end of said disconnector blade. The presence of the insulating support can act as an obstruction to help breakdown electrical current paths, and thereby help avoid dielectric failure by improving dielectric performance.

Optionally, the insulating support comprises a guide portion configured to cause the disconnector blade to move from the extended state to the compressed state as the disconnector blade pivots from the first position to the second position. Optionally, the guide portion is further configured to cause the disconnector blade to move from the compressed state to the extended state as the disconnector blade pivots from the second position to the third position.

In some examples, there is an electrical contact coupled to the insulating support, the electrical contact configured to contact the second end of the disconnector blade when the disconnector blade is in the second position. Optionally, the electrical contact comprises a partially spherical end configured to contact the second end of the disconnector blade when the disconnector blade is in the second position. The use of a spherical end can help to reduce field end effects.

In some implementations, each disconnector and earthing switch comprises two or more telescopic disconnector blades. By using two disconnector blades, two parallel paths are created for current flow. This can help to improve thermal performance. In other examples, each disconnector and earthing switch comprises a single telescopic disconnector blade.

Optionally, the device comprises a vacuum circuit breaker. Optionally, the one or more switching mechanisms comprise a vacuum interrupter.

In some examples, the device comprises a plurality of switching devices, each switching device comprising a plurality of poles, wherein each pole is associated with a respective -4 -switching mechanism of the one or more switching mechanisms and a respective disconnector and earthing switch of the one or more disconnector and earthing switches. A more compact device architecture maybe facilitated by the use of the telescopic or retractable blade described herein.

In some implementations, the telescopic disconnector blade comprises an outer contact and a plurality of contacts, a portion of a first inner contact arranged to slide within the outer contact and a portion of a second first inner arranged to slide within the first inner contact.

In some other implementations, the telescopic disconnector blade comprises an outer contact and an inner contact, a portion of the outer contact arranged to slide over the inner contact. The inner contact comprises the first end of the disconnector blade. The outer contact comprises the second end of the disconnector blade.

In some implementations, the telescopic disconnector blade comprises an outer contact and a plurality of inner contacts, a portion of the outer contact arranged to slide over a first inner contact, and a portion of the first inner contact arranged to slide over a second inner contact. The outer contact comprises the second end of the disconnector blade.

A method of operating an disconnector and earthing switch (or disconnection earthing switch) comprising a telescopic disconnector blade having a first end and a second end, wherein the disconnector blade is configured to pivot around the first end between three different positions. The method comprises pivoting the disconnector blade about the first end from a first position, in which the disconnector and earthing switch is closed and the power supply is connected to the load through the disconnector blade, to a second position, wherein the second position is an isolation position in which the disconnector and earthing switch is open and the power supply is disconnected from the load. The method further comprises pivoting the disconnector blade about the first end from the second position to a third position in which the power supply is disconnected from the load and a second end of the disconnector blade is electrically connected to an earthing contact.

In some examples, the disconnector and earthing switch is a 3PS switch (three position disconnector and earthing switch). -5 -

The method can further comprise compressing the disconnector blade as it pivots from the first position to the second position. The method can further comprise extending the disconnector blade as the disconnector blade pivots from the second position to the third position.

Also disclosed herein is a device comprising: one or more switching mechanisms configured to disconnect a power supply from a load; and one or more disconnector and earthing switches, each disconnector and earthing switch associated with a respective switching mechanism. Each disconnector and earthing switch comprising a telescopic disconnector blade having a first end and a second end, wherein the disconnector blade is configured to pivot around the first end between two or more different positions. The two or more positions comprise: a first position in which the disconnector and earthing switch is dosed and the power supply is connected to the load through the disconnector blade; and a second position in which the power supply is disconnected from the load and a second end of the disconnector blade is electrically connected to an earthing contact. This can be implemented as a two position earthing disconnection switch.

In some implementations, each disconnector and earthing switch comprises two or more telescopic disconnector blades.

In some examples, the two or more positions further comprise a third, isolation, position in which the disconnector and earthing switch is open and the power supply is disconnected from the load. In some examples, the disconnector and earthing switch (also called an earthing disconnection switch) is a 3PS switch.

Also disclosed herein is a switching device configured to disconnect a power supply from a load, the switching device comprising a telescopic disconnector blade having a first end and a second end, wherein the disconnector blade is configured to pivot around the first end between two or more different positions. The two or more positions comprise: a first position in which the power supply is connected to the load through the disconnector blade; and a second position in which the power supply is disconnected from the load. In the second position, a second end of the disconnector blade can optionally be electrically connected to an earthing contact. -6 -

Any of the features or examples discussed above can be combined in any suitable combination. For example, features of the device can be combined with features of the method, and vice versa. -7 -

List of Figures The following description is with reference to the Figures.

Figure 1 shows a front view of an example device having one or more switching mechanisms and one or more disconnector and earthing switches, as described herein. Figure 2: Figure 2A shows a front view of an illustrative disconnector and earthing switch in a first, on, position; Figure 2B shows a front view of the illustrative disconnector and earthing switch in a second, off or isolation, position; and Figure 2C shows a front view of the illustrative disconnector and earthing switch in a third, earth, position.

Figure 3: Figure 3A shows a perspective view of breakdown paths in an illustrative disconnector and earthing switch; and Figure 3B shows a front view of an illustrative disconnector and earthing switch clearance, illustrating clearance between the switch and a housing.

Figure 4: Figure 4A illustrates an example telescope or retractable blade in a first, extended or uncompressed position; and Figure 4B illustrates the blade of Figure 4A in a second, compressed position.

Figure 5: Figure 5A shows a front view of an exemplary disconnector and earthing switch having a telescopic blade in the first, on, position; Figure 5B shows a front view of the exemplary disconnector and earthing switch in the second, off or isolation, position (with a compressed telescopic blade); and Figure 5C shows a front view of the exemplary disconnector and earthing switch in the third, earth, position.

Figure 6: Figure 6A shows a perspective view of an insulating support, and Figure 6B shows a perspective view of the insulating support in combination with an exemplary disconnector and earthing switch.

Figure 7A and Figure 7B are schematic illustrations of other exemplary telescopic blades.

Detailed description

With reference to Figure 1, a device 100 comprising one or more switching mechanisms 110 configured to disconnect a power supply from a load and one or more corresponding disconnector and earthing switches 33o is described. Each disconnector and earthing switch is associated with a respective switching mechanism. In the examples described herein, the disconnector and earthing switch is a 3PS switch (three position disconnector and earthing switch), but it will be understood that the principles of the telescopic blade can be applied to other earthing disconnection switches (e.g. a two position earthing disconnection switch) and to other switch types more generally. -8 -

Device 100 maybe a switchgear or any other switching or disconnection device. The device can comprise a circuit breaker, optionally a vacuum circuit breaker VCB, or a load break switch, for example. In some examples, device 100 may comprise a plurality of switching devices, each switching device comprising a plurality of poles. For example, device 100 may be a three-way, three-Pole device. Each pole can be associated with a respective switching mechanism of the one or more switching mechanisms and associated with a respective disconnector and earthing switch of the one or more disconnector and earthing switches. Each of the plurality of switching devices may be optionally implemented as e.g. a vacuum circuit breaker VCB or a load break switch, for example. In the following examples, three switching mechanisms 110 are shown, but any suitable number of switching mechanisms (of any suitable type, e.g., mechanical, electromechanical and/or solid state) maybe used.

The switching mechanisms are provided within a housing 216. The housing has a first side 15 wall 216a and a second side wall 216b and a bottom plate 216c. The switching mechanisms shown here are arranged along a first axis 102 between the first and second side walls 216a, 216b of housing 216.

With further reference to Figure 1, each disconnector and earthing switch has a disconnector blade 332 which is pivotably connected, at a first end 342, to the associated switching mechanism. The disconnector blade 332 is the disconnector and earthing switch contact, which facilitates electrical connection of the load to the power supply via the disconnector and earthing switch. In the example of Figure 1, the first end 342 of the disconnector blade (or contact) is pivotably connected or coupled to a top of a housing enclosing the switching mechanism. The disconnector blade 332 also comprises a second end 334 opposite the first end.

In some examples, each switching mechanism has a fixed contact and a moveable contact, and an actuating mechanism comprising a shaft 214 (extending into the page, here perpendicular to axis 102) and drive rod 344. The shaft is configured to rotate (here around a rotation axis arranged perpendicular to the first axis 102) to transfer an external input force to move the moveable contact and open or close the switching mechanism. The drive rod 344 is connected to the shaft 214 to transfer the rotation of the shaft 214 in response to an external input force into movement of the moveable contact along a second axis 106 perpendicular to the first axis. The second axis is also referred to herein as the operating axis. The moveable contact is moveable by the drive rod 344 of the actuating -9 -mechanism and is arranged between the fixed contact and the shaft 214 of the actuating mechanism. Each disconnector and earthing switch 33o is arranged between the active part of the switching mechanism no (here the moving and fixed contacts) and the shaft 214 along the second axis 106.

In some particular examples, the switching mechanism 110is implemented as, or comprises, a vacuum interrupter (or VI). The VI can be implemented as part of a VCB or other circuit breaker, or as part of any other type of switching device (such as a load break switch or LBS). The top contact of the vacuum interrupter VI is the moveable contact, moveable by the actuating mechanism is response to rotation of the shaft 214. With reference to Figure 1, the fixed contact of the vacuum interrupter VI is fixed to the bottom plate 216c of the housing 216 via a support plate (not shown). The bottom plate 216c and first and second sidewalls 216a, 216b at least partially define a switching compartment of the switchgear 100, 200. The switching compartment described herein is air insulated, however any other insulating medium which fulfils the required dielectric / thermal requirements (such as a vacuum, pressurised air, SF6 (sulphur hexafluoride) or other gaseous dielectric medium, or inert gas) may be provided within the switching compartment.

A housing of the VI covers the fixed and moving contacts and is bolted to the support plate. Column supports formed of an insulating material (not shown) can be bolted between the support plate and the bottom plate 216c to hold the support plate within the switching compartment of the housing 216. In this particular example, the VI is mounted on a bushing 350. The bushing 35o is bolted to the bottom plate 216c and is fixed to the support plate with epoxy.

The VI housing here acts as a support for the hinge or pivot point at the first end 342 of the disconnector blade 332. The first end of each disconnector blade is pivotably coupled to the switching mechanism no. The first end of the disconnector blade 342 can be 3° pivotably coupled to the switching mechanism between the moveable contact and the shaft 214. In this particular example, the first end of the disconnector blade 342 is pivotably coupled to a top of the VI housing which surrounds the fixed and moveable contacts of the switching mechanism 110.

A metallic shield (not shown) can be provided within the VI housing, placed between the moveable contact and the first end of the disconnector blade. The metallic shield acts to help shield the disconnector blade and the hinge/pivotable coupling from any electric field within the vacuum interrupter. As discussed above, the moving contact moves within the VI housing in response to actuation/rotation of the shaft 214. In particular, rotation of the shaft 214 actuates the drive rod 344 of the actuating mechanism, pulling the moveable contact along the operating axis towards the shaft 214 and opening the switch 212.

The disconnector blade of each disconnector and earthing switch 33o is arranged to pivot around the first end to move between three different positions, as is further illustrated in Figure 2.

With reference to Figure 2A, the disconnector blade 332 is arranged in a first position in which in which the disconnector and earthing switch is closed and the power supply is connected to the load through the disconnector blade. In this first position, current flows through the device 100 via the switching mechanism 110 and the disconnector blade 332.

In response to user actuation of a direct break mechanism (not shown), the disconnector blade is moved from the first position to a second position, which is shown in Figure 2B. The direct break mechanism comprises a second shaft and a second actuating mechanism which is operated by rotation of the second shaft. A user can rotate the second shaft by turning or rotating an external handle, and the second actuating mechanism is rotated in response to rotation of the shaft. In this example, the second actuating mechanism is a four-bar crank rocker mechanism 348, but any suitable actuating/driving mechanism may be used. In particular, in response to rotation of the second shaft of the direct break mechanism, the disconnector blade is configured to rotate around the pivot from the first position to the second position, wherein the rotation is towards the second side wall 216b of the housing.

In the second position of Figure 2B, the disconnector and earthing switch is open and the power supply is disconnected from the load (the current path between the load and the power supply through the disconnector blade 332 is broken). This second, intermediate position is an isolation position in which the disconnector and earthing switch is "off'. The disconnector blade 332 can be moved into this "off' or isolation position without a corresponding actuation of the switching mechanisms 110 (i.e., independent of rotation of the shaft 214) in some implementations. However, in other implementations this operation is dependent on the position of the switching mechanism 11o. For example, where the disconnector and earthing switch is an off load 3PS arranged in series with the switching mechanism, the off load 3PS switch can only be operated when the switching mechanism (optionally a VCB) is in an open state. This can be achieved by way of interlock / interlocking mechanisms: the 3PS direct break mechanism will interlock with the switching mechanism to ensure the device is operated as per mechanical interlock requirements.

In response to further user actuation of the second shaft of the direct break mechanism in the same direction of rotation, the disconnector blade is moved from the second position to a third position, which is shown in Figure 2C. In particular, the disconnector blade is configured to rotate around the pivot from the second position to the third position, wherein the rotation is again towards the second side wall 216b of the housing. In the third position, the power supply is disconnected from the load and a second end 334 of the disconnector blade is electrically connected to an earthing contact 336. The disconnector blade 332 can be moved into this earthed position without a corresponding actuation of the switching mechanisms no (i.e., independent of rotation of the shaft 214) in some implementations. However, in other implementations, as discussed above, this operation is dependent on the position of the switching mechanism 110. For example, where the disconnector and earthing switch is an off load 3PS arranged in series with the switching mechanism, the off load 3PS switch can only be operated when the switching mechanism (optionally a VCB) is in the open state.

The disconnector and earthing switch 33o can thus be activated or controlled independently of the shaft 214 which controls or actuates the moving contact of the switches. In the example described above, the disconnector blade 332 is coupled to a fixed component (e.g., the housing of the VT) and is therefore decoupled from the actuation of the switching mechanism 110; in other words, actuation of the device loo via shaft 214 does not actuate the disconnector and earthing switch 33o. However, it will be understood that in other examples the second actuating mechanism (of the disconnector and earthing switch) can be configured such that, when the moving contact is opened by shaft 214 to disconnect the power supply from the load, the disconnector blade 332 of the disconnector and earthing switch is correspondingly moved to the third, earthed, position. In this way, the current path through each switching mechanism 110 is automatically opened in two different locations when the switching mechanism is opened. In other examples, interlock mechanisms can prevent actuation of the direct break mechanism if the switching device is open.

-12 -As discussed above, device too comprises a three-position disconnector and earthing switch 33o. It is desirable to provide a disconnector and earthing switch with three positions -on, off (or isolation), and earth -to facilitate in-situ testing of cable integrity and improve the ease of maintenance of the switchgear. It is particularly desirable to combine a three-position disconnector and earthing switch with a compact switchgear, as is discussed below with reference to Figure 3.

It will be recognised that the device housing 216 (also termed enclosure) is always at ground potential (earthed). In the third position the disconnector plate is also earthed, to but in the second, "off" or isolated, position the disconnector blade 332 is at a live potential. As per 1EC62271 standard for metal-enclosed switchgear, an off' position isolation test should be conducted at 85kVp (or 85 Kilovoltage peak) impulse voltage and 32kV power frequency withstand voltage (maximum rms value of voltage that the device can withstand permanently). However, since the disconnector blade tip (otherwise referred to as the second end 334) is free in air when in the second position, end effects lead to a high intensity electric field being generated at the second end of the disconnector blade 332. This can lead to dielectric failure of the system and the formation of electric breakdown paths 36o between the disconnector blade 332 and the second side wall 216b of the device too (as shown in Figure 3A).

It is therefore desirable that the field intensity should be reduced, and adequate clearance d should be maintained to between the second side wall 216b and the tip or second end 334 of the disconnector blade (see Figure 3B) to avoid such dielectric failure between the housing or enclosure 216. Directly increasing the clearance d by moving the side wall 216b away from the switching mechanism 110 and disconnector and earthing switch 33o will increase the overall dimensions of the device too, hindering the provision of a compact device too. It is therefore desirable to increase clearance d and achieve better dielectric performance within a compact device footprint in order to provide a reliable device with a small footprint which can be provided which can more easily and safely tested in-situ (thereby e.g., improve the ease of maintenance).

With reference to Figure 4, a telescopic or retractable contact / disconnector blade 432 is described that can help achieve some of the above advantages. The telescopic contact or blade 432 is configured to move between an extended state, shown in Figure 4A, and a 35 compressed or retracted state, shown in Figure 4B. Any suitable arrangement of -13 -telescopic or retractable blade can be provided. The telescopic blade 432 is a particular embodiment of the disconnector blade 332 described above.

With particular reference to the example of Figure 4, the telescopic disconnector blade 332, 432 comprises an outer contact 404 and an inner contact 402, a portion of the inner contact arranged to slide within the outer contact. These features of the blade 332, 432 are referred to as "contacts" because they are electrically connecting (to facilitate connection of the supply to the load via the disconnector and earthing switch 330). In other words, the inner contact 402 can be inserted into the outer contact 404 and can slide uo relative to the outer contact. The outer contact comprises the first end 342, 442 of the disconnector blade (the end around which the disconnector blade is configured to pivot. The inner contact comprises the second end 334, 434 of the disconnector blade (the free end, or tip).

With further reference to Figure 4A, the outer contact 404 comprises a guide hole and the inner contact 402 slides within the guide hole. The disconnector blade further comprises a compliant member 406 disposed within the guide hole and configured to bias the inner contact 402 out of the guide hole. In other words, the inner contact can be configured to retract into the outer contact, and the complaint member acts to counter the retraction.

The compliant member 406 of Figure 4 is shown as a compression spring, but any other compliant member may be used. The compliant member can be compliant through form and/or material.

As shown in Figure 4B, in response to an external force F applied in a first direction 408 and to the second end 434 of the disconnector blade 432, the inner contact 402 is configured to slide in the first direction 408 within the guide hole of the outer contact 404. The compliant member compresses in response to the movement of the inner contact in the first direction 408. The compressed compliant member is then configured to urge the inner contact 404 away from the outer contact in a direction opposite the first direction.

In this way, the disconnector blade 432 can be in the extended state of Figure 4A in the absence of a force F. The disconnector blade is configured to move into the compressed state of Figure 4B in response to an external force. From the compressed state, the disconnector blade is configured to move back to the extended state of Figure 4A by way of the biasing or urging of the compliant member 406.

-14 -With further reference to Figure 5, the disconnector blade 432 is in the extended state in the first position and the third position (of Figures 2A, 5A and Figures 2C, 5C, respectively), and the disconnector blade 432 is in the compressed state in the second position (of Figures 2B, 5B). In particular, as can be seen in Figures 4 and 5, in the first "on" position and the third "earthed" position, the disconnector blade 432 is in the extended state and has an overall length of! r. In contrast, in the second "off' position, the disconnector blade 432 is in the compressed (or retracted) state and has an overall length of 1 2. The particular lengths I_1 and 1_2 can be determined by the device size and application requirements, and the stiffness of the compliant member 406, but L_2 is less to than 1 1. In this way, a greater clearance d can be provided for "off' or isolation tests, without increasing the overall footprint of the device loo. A reliable device with a small footprint and improved dielectric performance can therefore be provided by use of an disconnector and earthing switch with a telescopic or retractable contact (or disconnector blade), which device can more easily and safely tested in-situ (thereby e.g., improve the ease of maintenance). It will be understood that the telescope blade described herein can also be used with any other form of disconnection and/or earthing switch.

As is also shown in Figure 5, the second side wall 216b can further comprise an insulating support 500 configured to contact, when the disconnector blade is in the second position (with length 1_2), the second end 434 of the retracted / compressed disconnector blade 432. This insulating support 500 is discussed further in Figure 6 (Figures 6A, 6B).

With reference to Figure 6A, the insulating support 50o comprises an insulating guide portion 662 configured to cause the disconnector blade 432 to move from the extended state to the compressed state as the disconnector blade pivots from the first position to the second position. A section 662a of the guide portion 662 is shaped to gradually decrease the distance between the (fixed length) outer contact 404 and the guide portion 662, thereby causing an increasing displacement of the inner contact 402 of the blade 432 along the first direction 408 as the blade pivots (and increasing compression of the compliant member). The reaction force F exerted by the guide portion 662 on the second end 434 of the blade is greater than the reaction force from compression of the compliant member 406, and therefore the disconnector blade retracts.

The insulating guide portion 662 can be further configured to cause the disconnector blade to move from the compressed state to the extended state as the disconnector blade pivots from the second position to the third position. In this example, a section 662b of the -15 -guide portion is shaped to gradually increase the distance between the (fixed length) outer contact 404 and the guide portion 662, thereby allowing the inner contact 402 of the blade 432 to slide in a direction opposite the first direction 408 as the blade pivots in response to the biasing or urging of the compliant member 406 (and extension of the compliant member). The reaction force F exerted by the guide portion 662 on the second end 434 of the blade is less than the urging force from compression of the compliant member 406, and therefore the disconnector blade extends.

The use of one or more insulating or isolating features such as the insulating support 500 may improve electrical safety during the isolation, second, position by improving dielectric performance. In particular, the insulating support 500 can help to reduce field end effects at the second end 334 of the disconnector blade 332 and provide a dielectrically better performance compared to a high electric field in air. The insulating support Soo be provided individually, or in combination with one or more other insulating features (including features not described herein).

In some examples, an insulating sheet 55o may be provided. The insulating sheet 55o can be formed from any suitable insulating material. The insulating sheet 55o need not contact the second end 434 of the disconnector blade 432 when the blade is in the second position. The presence of the insulating sheet 55o, even without physical contact, acts as an obstruction to breakdown electrical current paths and can help avoid dielectric failure, thereby improving dielectric performance.

The use of the insulating support 500 and/or the insulating sheet 55o on the second side wall 216b of the housing / enclosure facilitates use of a three-position disconnector and earthing switch 33o within a compact device footprint. A more compact, reliable device may therefore be provided by use of the insulating features provided herein.

In the example of Figure 6B, the disconnector and earthing switch 33o comprises two disconnector blades 434, disposed either side of the second actuating mechanism 348. In other words, each disconnector and earthing switch can comprise two or more telescopic disconnector blades. By using two disconnector blades, two parallel paths are created for current flow. This can help to improve thermal performance. In such implementations, two guide portions 662 are also provided; one guide portion is provided for each disconnector blade. However, it will be understood that other arrangements are possible.

For example, a single telescopic blade can be provided. In such an implementation, the -16 -size/shape of the contacts in the on / off /earth positions can be implemented as e.g. a Jaw contact to facilitate good electrical connection between the blade and the contacts.

The disconnector blade can be operated or actuated by operation of the second actuating mechanism 348. However, as described above, in this example the disconnector blade will be operated by the second actuating mechanism only when the switching mechanism is open. In other words, the actuating mechanisms are interlocked such a way that the disconnector and earthing switch or 3PS can be operated only when the switching mechanism (such as the VCB) is in the open state. In this example, the second actuating mechanism is implemented as a four-bar crank rocker mechanism (i.e., the telescopic disconnector blade is operated by a four-bar crank rocker mechanism).

Tn some examples, an electrical contact 664 is coupled the insulating support 500 and configured to contact the second end(s) 434 of the disconnector blade(s) 432 when the disconnector blade(s) are in the second position. When two disconnector blades are provided, the electrical contact 664 is configured to be disposed between the second ends 434 of the respective blades 432. The electrical contact 664 is disposed between the two guide portions 662. The electrical contact 664 can comprise a partially spherical end. The use of a spherical (i.e., curved) portion at the second end of the electrical contact 664 acts to reduce or avoid high fields at the electrical contact 664. Dielectric performance may therefore be further improved.

In the examples described herein, the telescopic contact or blade of the disconnector and earthing switch 33o comprises two contacts, one moveable relative to the other. However, in other implementations there may be more than two moveable contacts, as is illustrated in Figure 7A. Tn this example, there are two inner contacts 4o2a, 4o2b, and an outer contact 404. The inner contacts 402a, 402b are configured to slide relative to each other and relative to the outer contact to provide the telescopic blade 432. Two compliant members 4o6a, 4o6b may be provided to facilitate the return of the telescopic blade 432 to the extended state (of e.g. Figure 4A). The compliant members can be disposed in respective guide holes. In some other examples, more than two inner contacts and corresponding compliant members may be provided.

In another example implementation, shown in Figure 7B, the inner and outer contacts may be arranged in an alternate manner to form a telescopic blade 432. The outer contact 404 comprises the second end 334, 434 of the disconnector blade (the free end, or tip).

-17 -The inner contact 402b comprises the first end 342, 442 of the disconnector blade (the end around which the disconnector blade is configured to pivot. In this arrangement, the outer contact slides over the inner contacts (rather than the inner contact(s) sliding into the outer contacts, as in Figure 4 and Figure 7A).

Other arrangements of a telescopic blade as described herein may also be provided. It should be realised that the foregoing embodiments are not to be construed as limiting and that other variations, modifications and equivalents will be evident to those skilled in the art and are intended to be encompassed by the claims unless expressly excluded by the claim language.

Moreover, the disclosure of the present application should be understood to include any novel features or any novel combination of features either explicitly or implicitly disclosed herein or in any generalisation thereof. Claims may be formulated to cover any such 15 features and/or combination of such features derived therefrom.

Claims

Claims 1. A device (too, 200) comprising: one or more switching mechanisms (no) configured to disconnect a power supply 5 from a load; and one or more disconnector and earthing switches (33o), each disconnector and earthing switch (33o) associated with a respective switching mechanism (no), each disconnector and earthing switch (33o) comprising a telescopic disconnector blade (332, 432) having a first end (342, 442) and a second end (3345434)5 wherein the disconnector blade (332, 432) is configured to pivot around the first end (342, 442) between three different positions, the three positions comprising: a first position in which the disconnector and earthing switch (33o) is closed and the power supply is connected to the load through the disconnector blade (332, 432); a second, isolation, position in which the disconnector and earthing switch (33o) is open and the power supply is disconnected from the load; and a third position in which the power supply is disconnected from the load and a second end (334, 434) of the disconnector blade (332, 432) is electrically connected to an earthing contact (336).
2. The device (too, 200) of claim 1, wherein the telescopic disconnector blade (332, 432) comprises an outer contact (404) and an inner contact (402), a portion of the inner contact (402) arranged to slide within the outer contact (404).
3. The device (too, 200) of claim 2, wherein the outer contact (404) comprises the first end (342, 442) of the disconnector blade (3325432) and the inner contact (402) comprises the second end (3345434) of the disconnector blade (332, 432).
4. The device (too, 20o) of claim 2 or claim 3, wherein the outer contact (404) comprises a guide hole and the inner contact (402) slides within the guide hole, the disconnector blade (332, 432) further comprising a compliant member (406) disposed within the guide hole and configured to bias the inner contact (402) out of the guide hole.
5. The device (too, 20o) of claim 4, wherein, in response to an external force applied 35 in a first direction (408) and to the second end (334, 434) of the disconnector blade (332, 432), the inner contact (402) is configured to slide in the first direction (408) within the -19 -guide hole of the outer contact (404) and the compliant member is configured to bias the inner contact (402) in a direction opposite the first direction (408).
6. The device (too, 20o) of claim 4 or claim 5, wherein the compliant member is a compression spring.
7. The device (too, 200) of any preceding claim, wherein the telescopic disconnector blade (332, 432) is configured to move between an extended state and a compressed state, wherein the disconnector blade (332, 432) is in the extended state in the first position and the third position, and wherein the disconnector blade (332, 432) is in the compressed state in the second position.
8. The device (too, 200) of any preceding claim, further comprising a housing (216) having first (216a) and second (216b) side walls, wherein the telescopic disconnector blade (332, 432) is configured to rotate around the pivot from the first position to the second position, wherein the rotation is towards the second side wall (216b) of the housing (216).
9. The device (too, zoo) of claim 8, wherein the second side wall (216b) comprises an insulating support (500) configured to contact, when the disconnector blade (332, 432) is in the second position, the second end (334, 434) of said disconnector blade (332, 432).to.
The device (too, 200) of claim 9, wherein the insulating support (5oo) comprises a guide portion (662) configured to cause the disconnector blade (332, 432) to move from the extended state to the compressed state as the disconnector blade (332, 432) pivots from the first position to the second position.it.
The device (too, 200) of claim to, wherein the guide portion (662) is further configured to cause the disconnector blade (332, 432) to move from the compressed state to the extended state as the disconnector blade (332, 432) pivots from the second position to the third position.
12. The device (too, zoo) of any of claims 9 to 11, further comprising an electrical contact (664) coupled to the insulating support (500), the electrical contact (664) configured to contact the second end (334, 434) of the disconnector blade (332, 432) when the disconnector blade (332, 432) is in the second position.
13. The device (ioo, 200) of claim 12, wherein the electrical contact (664) comprises a partially spherical end configured to contact the second end (334, 434) of the disconnector blade (332, 432) when the disconnector blade (332, 432) is in the second position.
14 The device (t00, 20o) of any preceding claim, wherein each disconnector and earthing switch (33o) comprises two or more telescopic disconnector blades (332, 432).
15. The device (loo, zoo) of any preceding claim, comprising: a plurality of switching devices, each switching device comprising a plurality of poles, wherein each pole is associated with a respective switching mechanism of the one or more switching mechanisms (no) and a respective disconnector and earthing switch (33o) of the one or more disconnector and earthing switches (33o).