Electrical switching cap

Abstract

An electrical switching cap comprises a switching cover body formed of a first insulating material, the switching cover body having a closed first end; a protection cap disposed over the first end of the switching cover body and bonded to the switching cover body, the protection cap formed of a second insulating material; and sensing circuitry disposed over the protection cap such that the protection cap is disposed between the switching body cover and the sensing circuitry.

Description

[0001] Electrical Switching Cap

[0002] Field

[0003] The present disclosure relates to an insulating cover for an electrical switching cap and an electrical switching cap. In particular, the disclosure relates to an insulating cover comprising sensing circuitry for use in a medium voltage AC switching apparatus.

[0004] Background

[0005] SFe-Free medium voltage switching devices having insulated caps have been in use for several decades. There is now a desire for such switching device to include integrated sensing electronics to detect operating conditions of the switching device in use and communicate information to external devices. The use of sensing circuitry with existing medium voltage switching devices is not straightforward, as the provision of new electrical components alters the dielectric properties of the existing devices and creates new potential failure points. Furthermore, the power supply currents through the switching devices can interfere with the electronics of sensing circuitry. There is a need, therefore, to develop new insulated caps for switching devices that can safely and reliably incorporate sophisticated electrical circuitry.

[0006] Summary

[0007] Disclosed herein is an electrical switching cap, a switching arrangement, and a method of manufacturing an electrical switch cover.

[0008] An electrical switching cap comprises a switching cover body formed of a first insulating material, the switching cover body having a closed first end; a protection cap disposed over the first end of the switching cover body and bonded to the switching cover body, the protection cap formed of a second insulating material; and sensing circuitry disposed over the protection cap such that the protection cap is disposed between the switching body cover and the sensing circuitry.

[0009] The combination of insulating layers of the switching cover body and the protection cap provides highly effective insulation for preventing electrical discharge from medium voltage conductors to the sensing circuitry of the electrical switching cap.

[0010] In some examples, the protection cap comprises a rim portion and a flat portion, wherein the rim portion entirely surrounds an edge of the closed first end of the switching cover body and the flat portion covers faces the closed first end of the switching cover body.

[0011] Because the protection cap entirely surrounds a closed first end of the switching cover body, the protection cap and the end portion of the switching cover body form and effective insulating double layered barrier.

[0012] In some examples, the first insulating material is different to the second insulating material.

[0013] In some examples, the second insulating material is more ductile than the first insulating material.

[0014] The flexibility of the second insulating material allows the switching cover body to the cast using injection moulding over the protection cap without cracking of the protection cap.

[0015] In some examples, the first insulating material is a thermoset and the second insulating material is a thermoplastic. Preferably, the first insulating material is an epoxy resin.

[0016] The use of epoxy resin and thermoplastics as the first and second insulating materials provides effective dielectric properties and avoidance of cracking during the manufacture process.

[0017] In some examples, the electrical switching cap further comprising a conductive layer covering one side of the protection cap such that the conductive layer is disposed between the protection cap and the sensing circuitry.

[0018] The conductive layer protects the sensing circuitry from interference from electric fields.

[0019] In some examples, the conductive layer is electrically connected to a voltage source such that the conductive layer is held at a fixed electric potential.

[0020] By holding the conductive layer at a fixed electric potential, the sensing circuitry may be shielded from electric fields while avoiding shielding from magnetic fields. In some examples, the electrical switching cap further comprising a cover cap formed of an insulating material disposed over the sensing circuitry.

[0021] In some examples, the cover cap comprises a battery holder on an outer side of the cover cap, and a battery is held by the battery holder and is electrically connected to the sensing circuitry via electrical contacts that pass through the cover cap to an inner side of the cover cap.

[0022] In some examples, the sensing circuitry is configured to detect a magnetic field in order to indirectly sense an electrical current and / or a voltage in a conductor disposed inside the switching cover body.

[0023] In some examples, the switching cover body is integrally bonded to the protection cap.

[0024] In some examples, the electrical switching cap further comprises: a switching cap body disposed inside the switching cover body, the switching cap body comprising first and second electrical contacts disposed at an open second end of the switching cover body and a conductive contact bridge that forms a conductive path between the first and second electrical contacts, wherein a portion of the conductive contact bridge passes adjacent to the closed first end of the switching cover body such that a magnetic field produced by a current in the conductive contact bridge can be detected by the sensing circuitry.

[0025] A switching arrangement comprises: a base body comprising a power input terminal and a power output terminal, the power input terminal being electrically connected to a first fixed electrical contact and the power output terminal being electrically connected to a second fixed electrical contact; and a switching cap, wherein the switching arrangement is configured such that the first and second electrical contacts electrical switching cap respectively contact the first and second fixed electrical contacts of the base body when the switching cap is positioned on the base body.

[0026] A method of manufacturing an electrical switch cover is provided. The electrical switch cover comprises a switching cover body formed of a first insulating material and a protection cap formed of a second insulating material. The method comprises: forming the protection cap from the second insulating material; while the protection cap is positioned in an injection casting mould, forming the switching cover body by injection moulding of the first insulating material into the injection casting mould; subsequent to forming the switching cover body, attaching sensing circuitry to the protection cap.

[0027] In some examples, the method further comprises: subsequent to forming the protection cap, forming a conductive layer on one side of the protection cap by spraying a conductive material on one side of the protection cap.

[0028] Brief Description of the Figures

[0029] The detailed description is with reference to the following figures.

[0030] Figure 1 shows a schematic diagram of a switching arrangement comprising a base body and an electrical switching cap;

[0031] Figure 2a illustrates an example of an electrical switching cap in accordance with the disclosure;

[0032] Figure 2b illustrates a cross-sectional view of the electrical switching cap of Figure 2a; Figure 3a illustrates an example of an electrical switch cover accordance with the disclosure;

[0033] Figure 3b illustrates a cross-sectional view of the electrical switching cap of Figure 3a; Figure 4 shows a flowchart illustrating an example method of manufacturing an electrical switch cover.

[0034] Detailed Description

[0035] The present disclosure relates to an electrical switching cap 10 comprising an electric switch cover 100. The electrical switching cap 10 may be used as part of a switching device la for use in a switching arrangement, such as the switching arrangement 1 shown in Fig. 1. Though the electrical switching cap 10 and electrical switch cover 100 are illustrated in the context of a particular switching arrangement 1, the switching cap 10 and electrical switch cover 100 may be used in other switching arrangements and systems that are not discussed in detail herein. In general, the electrical switching cap 10 and the electric switch cover 100 are particularly suited for use in mediumvoltage switchgear arrangements. The switching arrangement 1 illustrated Fig. 1 comprises a base body 2 with one or more electrical terminals 8a, 8b, which may be power input terminals or power output terminals. An input terminal may be controllably connected to an output terminal via an electrical switching cap 10 connected to fixed contacts 9a, 9b. The switching arrangement 1 may comprise one or more switching devices la, where each switching device comprises an input terminal 8a, and output terminal 8band an electrical switching cap 10. The input terminal 8a of each switching device la is electrically connected to a first fixed electrical contact 9a, and the output terminal 8b of each switching device is electrically connected to a second fixed electrical contact 9b. When the switching cap 10 is connected to the base body 2, a conductive contact bridge 12 arranged in the switching cap 10 is connected at each end to a respective fixed electrical contact 9a, 9b such that the input terminal 8a and the output terminal 8b of the switching device la are electrically connected via the conductive contact bridge 12. When the switching cap 10 is pulled off the fixed contacts 9a, 9b, the switching device la is open, and when the switching cap 10 is placed on the fixed contacts 9a, 9b, the switching device la closed, and a current il..i3 may flow between the input 8a and output 8b terminals.

[0036] With reference to Figs. 2a and 2b, the electrical switching cap 10 of Fig. 1 is described in more detail. The electrical switching cap 10 comprises an electrical switch cover 100 at least partially surrounding a switching cap body 15. The switching cap body comprises first and second electrical contacts 11 configured to contact the fixed contacts 9a, 9b of the base body 2 when the electrical switching cap 10 is positioned on the base body 2 in the closed position, as described with reference to Fig. 1, and a conductive bridge portion 12. The first and second electrical contacts 11 are connected by the conductive bridge portion 12. The first and second electrical contacts 11 may be referred to as "moveable electric contacts 11", as the moveable electric contacts 11 move with respect to the fixed electric contacts 9a, 9b of the base body 2 when the switching cap 10 is removed from the base body 2.

[0037] The electrical switch cover 100 comprises a switching cover body 20 that substantially surrounds the switching cap body and a protection cap 25. The switching cover body 20 and the protection cap 25 are shown in more detail with reference to Figs. 3a and 3b. The switching cover body 20 is formed of a first insulating material. Preferably, the first insulating material is a thermoset material, such as a quartz filled epoxy resin or polyurethane. The switching cover body 20 is preferably formed with a protection grade PA in accordance with IEC 62271-201 Annex D. The switching cover body 20 comprises a closed first end 20a (or "end wall") and an open second end 20b (or "end opening"). The closed first end 20a comprises a substantially flat surface. A side wall 20c extends from the first end 20a and ends at the open second end 20b. The first and second electrical contacts of the switching cover body 20 are disposed adjacent to the open second end 20b of the switching cover body 20. At least part of the conductive bridge portion 12 passes adjacent to the closed second end 20a of the switching cover body 20.

[0038] A protection cap 25 is disposed over the closed first end 20a of the switching cover body 20. The protection cap 25 is formed from a second insulating material. Preferably the second insulating material is a different material from the first insulating material and may be a thermoplastic, such as thermoplastic elastomer TPE, thermoplastic polyurethane TPU, or polyamide PA. Preferably, the protection cap 25 is formed with a protection grade PB in accordance with IEC 62271-201 Annex D. The protection cap 25 comprises a flat portion 25a that is parallel to and in contact with the closed first end 20a of the switching cover body 20. The protection cap 25 further comprises a rim portion 25b that surrounds the edge of the first end portion 20a of the switching cover body 20. The rim portion 25a may surround a part of the side wall 25c of the switching cover body 20.

[0039] The protection cap 25 is bonded to the closed first end 20a of the switching cover body 20 along a first side of the flat portion 25a and an inner surface of the rim portion 25b. The protection cap 25 may be integrated with the switching cover body 20. As described in more detail below with reference to Fig. 4, the switching cover body 20 may be cast by injection moulding with the previously formed protection cap 25 inserted in the injection casting mould. Preferably the protection cap 25 is formed of a second insulating material having a lower hardness and / or a lower brittleness than the first insulating material. During injection moulding of the switching cover body 20, the protection cap 25 may be elastically deformed by the pressure of the epoxy material without cracking.

[0040] A conductive layer 26 may be disposed on a second side of the flat portion 25a of the protection cap 25. As such, the flat portion 25a of the protection cap 25 is disposed between the end wall 20a of the switching cover body 20 and the conductive layer 26. The end wall 20a of the switching cover 20a is disposed between the flat portion 25a of the protection cap 25 and the switching cap body. Sensing circuitry 22 is disposed adjacent to the conductive layer 22 in a cavity formed by a cover cap 21. The sensing circuitry 22 may, for example, be mounted on a circuit board. The cover cap 21 has the form of a cap with an open end and a closed end and is disposed such that the protection cap 25 and at least part of the switching cover body 20 are enclosed by the cover cap 21. The cover cap may be formed of a thermoplastic material. The cover cap 21 comprises a battery holder 23 on an outside surface of the cover cap 21. The sensing circuitry 22 is powered by a battery (not shown) that is disposed in the battery holder 23 in use and is electrically connected to the sensing circuitry 22 via electrical contacts that pass through the cover cap 21. The sensing circuitry 22 may comprise one or more of a current sensor and / or a voltage sensor. The sensing circuitry 22 may comprise a pick-up coil with or without a ferro-magnetic core and / or a Hall sensor. The sensing circuitry 22 may indirectly detect a current and / or a voltage in the conductive bridge portion 12 by directly detecting a magnetic field generated in the vicinity of the sensing circuitry 22.

[0041] The sensing circuitry 22 is separated from the conductive bridge portion 12 by successive layers comprising the closed first end 20a of the switching cover body 20, the flat portion 25a of the protection cap 25, and the conductive layer 26. The closed first end 20a of the switching cover body 20 and the flat portion 25a of the protection cap 25 provide electrical insulation between the conductive bridge portion 12 and the sensing circuitry 21. The conductive bridge portion 12 carries a medium voltage power supply current when in use. As the sensing circuitry 22 is electrically connected to the battery on the exterior of the cover cap 21, it is important that the sensing circuitry is well insulated from the conductive bridge portion 12 to avoid electrical discharge from the conductive bridge portion 12 to the exterior of the switching device 10. The multilayer insulating structure of the electrical switch cover 100 of the present disclosure provides improved protection from electrical discharges from the main power supply current to external entities in comparison known electrical switch caps.

[0042] The conductive layer 26 shields the sensing circuitry 22 from electric fields produced by the power supply current in the conductive bridge portion 12. Preferably, the conductive layer 26 does not shield the sensing circuitry 22 from magnetic fields produced by the power supply current in the conductive bridge portion 12. The conducive layer 26 may be held at a constant voltage in order to shield electric fields without shielding magnetic fields. Preferably, the conductive layer 26 may be held at a fixed potential via an electrical connection with the battery. For example, the conductive layer 26 may be connected to a null terminal of the battery. As such, the sensing circuitry 22 is capable of making sensitive measurements magnetic fields generated by currents in the conductive bridge portion 12 without interference from electrical fields. Because the conductive layer 26 is electrically connected to the battery on the exterior of the insulating electrical switch cover 100, it is important that the conductive layer 26 is well insulated from the conductive bridge portion 12 to avoid electrical discharge from the conductive bridge portion 12 to the exterior of the switching device 10. The multilayer insulating structure of the electrical switch cover 100 of the present disclosure provides improved protection from electrical discharges from the main power supply current to external entities in comparison known electrical switching caps.

[0043] With reference to Figure 4, a method of manufacturing an electrical switch cover 100 is described. The electrical switch cover 100 may be the electrical switch cover 100 described with reference to Figs. 1, 2a, 2b, 3a and 3b.

[0044] At operation S10 the protection cap 25 is formed from the second insulating material. The second insulating material may be a thermoplastic material. The protection cap 25 may be formed by injection moulding or another suitable method of thermoplastic moulding. A conductive layer 26 is provided on one side of the protection cap 25. The conductive layer may be added to the protection cap 25 after the protection cap 25 has been formed. In one example, the conductive layer 26 may be applied as a spray onto the surface of the protection cap 25 after it has been formed (or after operation S20 described below). Alternatively, the conductive layer 26 may be provided as an inmould label that is bonded to the protection cap when the protection cap 25 is formed.

[0045] At operation S20, the switching cover body 20 is formed by injection moulding of the first insulating material in an injection casting mould. The protection cap 25 formed during operation S10 is positioned in the injection casting mould when the resin for forming the switching cover body 20 is injected into the injection casting mould. The protection cap 25 may be formed in the same injection casting mould as the switching cover body 20. In this example, the protection cap 25 may already be positioned in the injection casting mould when it is formed in operation S10. Alternatively, the switching cover body 20 and the protection cap 25 are formed in different injection moulding casts. In such examples, the protection cap 25 is placed in the injection casting mould for casting of the switching cover body 20 subsequent to operation S20. During the injection casting of the switching cover body 20, the switching cover body 20 adheres to the protection cap 25 forming an integral unit.

[0046] Preferably the second insulating material is suitably ductile or flexible that it does not crack under the pressure of the injection moulding of the switching cover body 20. The second insulating material may be a thermoplastic material. Preferably the second insulating material is more ductile or flexible than the first insulating material. The first insulating material may be an epoxy resin such as a quartz filled epoxy. When an epoxy resin and a thermoplastic are used, the pressure during the casting process of the protection cap 25 may be significantly greater than the pressure during the injection moulding process for the switching cover body 20. For example the pressure during the casting process of the protection cap 25 may be around 400 bar, whereas the pressure during the injection moulding process for the switching cover body 20 may be around 6 bar. As such, damage of the protection cap 25 may be avoided during the subsequent formation of the switching cover body 20. The use of an epoxy resin as the first insulating material and a thermoplastic as the second insulating material ensures good adhesion of the switching cover body 20 to the protection cap 25 during casting of the switching cover body 20.

[0047] In operation S30, subsequent to forming the switching cover body, sensing circuitry 22 is attached to the protection cap 25. The sensing circuitry 22 may be mounted on a circuit board and fixed either to the protection cap 25 or to a cover cap 21 that is moulded separately.

[0048] Subsequent to operation S30, the switching cap body, including the conductive bridge portion, may be placed inside the switching cover body 20 and the cover cap 21 may be placed over the protection cap 25 and sensing circuitry 22 to form an electrical switching cap 10.

[0049] The above method of manufacturing an electrical switch cover 100 provides an electrical switch cover 100 with improved insulation over known switching cap covers while avoiding cracking of elements of the switching cap cover during injection moulding processes.

[0050] The improved electrical insulation properties and electric field shielding of the electrical switching cap in the above disclosure allows the sensing circuitry to be used to sense operating conditions of medium voltage power supply devices without the risk of electrical discharge faults.

Claims

Claims1. An electrical switching cap, the electrical switching cap comprising: a switching cover body (20) formed of a first insulating material, the switching cover body having a closed first end (20a); a protection cap (25) disposed over the first end of the switching cover body (20) and bonded to the switching cover body (20), the protection cap (25) formed of a second insulating material that is different to the first insulating material; and sensing circuitry (22) disposed over the protection cap (25) such that the protection cap (25) is disposed between the switching body cover (20) and the sensing circuitry (22).

2. The electrical switching cap of claim 1, wherein the protection cap (25) comprises a rim portion (25a) and a flat portion (25b), wherein the rim portion (25a) entirely surrounds an edge of the closed first end (20a) of the switching cover body and the flat portion covers (25a) faces the closed first end (20a) of the switching cover body (20).

3. The electrical switching cap of claim 1, wherein the second insulating material is more ductile than the first insulating material.

4. The electrical switching cap of any preceding claim, wherein the first insulating material is a thermoset and the second insulating material is a thermoplastic.

5. The electrical switching cap of any preceding claim, further comprising a conductive layer (26) covering one side of the protection cap (25) such that the conductive layer (26) is disposed between the protection cap (25) and the sensing circuitry.

6. The electrical switching cap of claim 5, wherein the conductive layer (26) is electrically connected to a voltage source such that the conductive layer is held at a fixed electric potential.

7. The electrical switching cap of any preceding claim, further comprising a cover cap (21) formed of an insulating material disposed over the sensing circuitry (22).

8. The electrical switching cap of claim 7, wherein the cover cap (21) comprises a battery holder (23) on an outer side of the cover cap (21), and wherein a battery is held by the battery holder (23) and is electrically connected to the sensing circuitry (22) via electrical contacts that pass through the cover cap (21) to an inner side of the cover cap (21).

9. The electrical switching cap of any preceding claim, wherein the sensing circuitry (22) is configured to detect a magnetic field in order to indirectly sense an electrical current and / or a voltage in a conductor disposed inside the switching cover body (20).

10. The electrical switching cap of any preceding claim, wherein the switching cover body (20) is integrally bonded to the protection cap (25).

11. The electrical switching cap of any preceding claim, further comprising: a switching cap body disposed inside the switching cover body (20), the switching cap body comprising first and second electrical contacts disposed at an open second end (20b) of the switching cover body (20) and a conductive contact bridge (12) that forms a conductive path between the first and second electrical contacts, wherein a portion of the conductive contact bridge (12) passes adjacent to the closed first end (20a) of the switching cover body (20a) such that a magnetic field produced by a current in the conductive contact bridge (12) can be detected by the sensing circuitry.

12. A switching arrangement comprising: a base body (2) comprising a power input terminal (8a) and a power output terminal (8b), the power input terminal being electrically connected to a first fixed electrical contact (9a) and the power output terminal being electrically connected to a second fixed electrical contact (9b); and the switching cap (10) according to claim 11, wherein the switching arrangement is configured such that the first and second electrical contacts electrical switching cap respectively contact the first and second fixed electrical contacts of the base body (2) when the switching cap (10) is positioned on the base body (2).

13. A method of manufacturing an electrical switch cover comprising a switching cover body (20) formed of a first insulating material and a protection cap (25) formed of a second insulating material that is different to the first insulating material, the method comprising:forming the protection cap (25) from the second insulating material; while the protection cap (21) is positioned in an injection casting mould, forming the switching cover body (20) by injection moulding of the first insulating material into the injection casting mould; subsequent to forming the switching cover body (20), attaching sensing circuitry to the protection cap (21).

14. The method of claim 14, further comprising: subsequent to forming the protection cap (25), forming a conductive layer (26) on one side of the protection cap (25) by spraying a conductive material on one side of the protection cap (25).

Images