RETROFITTABLE VOLTAGE SENSING DEVICE FOR POWER NETWORKS

Abstract

Voltage sensing device (1) for sensing an elevated voltage in a power distribution network, comprising a) a sensored insulation plug (10) comprising—a voltage sensor for sensing the elevated voltage, comprising a high-voltage contact; —a plug mating portion (50), shaped to mate the sensored insulation plug (10) with a corresponding socket mating portion of a separable connector, wherein the high-voltage contact is arranged in the plug mating portion (50) such that the high-voltage contact can be connected to the elevated voltage of the separable connector when the sensored insulation plug (10) is mated with the separable connector; b) a tubular insulating sleeve (20), comprising a socket mating portion (100) shaped as a socket mating portion of the separable connector and mated with the plug mating portion (50) of the insulation plug (10); c) a conductive rod (30) having a first end portion (120) for electrical connection to the power conductor, and an opposed second end portion, electrically connected to the high-voltage contact and arranged in the insulating sleeve (20).

Claims

1. Voltage sensing device for sensing an elevated voltage of a power conductor in a power distribution network of a national grid, comprising: a) a sensored insulation plug comprising a voltage sensor for sensing the elevated voltage, comprising a high-voltage contact for electrical connection to the power conductor; and a plug mating portion, shaped to mate the sensored insulation plug with a corresponding socket mating portion of a separable connector, wherein the high-voltage contact is arranged in the plug mating portion such that the high-voltage contact can be connected to the elevated voltage of the separable connector when the sensored insulation plug is mated with the separable connector; b) a tubular insulating sleeve, comprising a socket mating portion shaped as a socket mating portion of the separable connector and mated with the plug mating portion of the insulation plug; and c) a conductive rod having a first end portion for electrical connection to the power conductor, and an opposed second end portion, electrically connected to the high-voltage contact and arranged in the insulating sleeve.

2. Voltage sensing device according to claim 1, wherein the sensored insulation plug comprises an internal thread for engagement and electrical connection with the conductive rod.

3. Voltage sensing device according to claim 1, wherein the voltage sensor comprises a grounding contact for connection to ground and a signal contact for providing a divided voltage indicative of the elevated voltage, each arranged on the sensored insulation plug such as to be accessible after mating the sensored insulation plug with the insulating sleeve.

4. Voltage sensing device according to claim 1, wherein the voltage sensor comprises a voltage divider for sensing the elevated voltage of the power conductor, the voltage divider comprising the high-voltage contact, a grounding contact, a signal contact for providing a divided voltage indicative of the elevated voltage, and a plurality of discrete impedance elements, electrically connected in series between the high-voltage contact and the grounding contact, for dividing the elevated voltage and providing, at the signal contact, a signal voltage varying proportionally with the elevated voltage.

5. Voltage sensing device according to claim 4, wherein the plurality of discrete impedance elements is adapted such that the proportionality factor between the signal voltage and the elevated voltage is between 1:100 and 1:50'000 at an elevated voltage of 72 kilovolt and a frequency of 50 Hertz.

6. Voltage sensing device according to claim 1, wherein the plug mating portion of the insulation plug is mated with the tubular insulating sleeve releasably.

7. Voltage sensing device according to claim 1, wherein the tubular insulating sleeve comprises an electrical stress control layer.

8. Voltage sensing device according to claim 7, wherein the socket mating portion comprises a conductive or semiconductive layer on an outer surface of the socket mating portion, and wherein the electrical stress control layer is electrically connected to the conductive or semiconductive layer on the outer surface of the socket mating portion.

9. Voltage sensing device according to claim 1, wherein the socket mating portion comprises, on an inner surface of the socket mating portion, a conductive high-voltage electrode layer in electrical contact with the rod and forming a Faraday cage around an area in which the sensored insulation plug contacts the conductive rod.

10. Voltage sensing device according to claim 1, wherein the tubular insulating sleeve is radially expandable.

11. Voltage sensing device according to claim 1, wherein the tubular insulating sleeve comprises one or more polymeric rubber materials.

12. Voltage sensing device according to claim 1, wherein the length of the tubular insulating sleeve is thirty centimeters or more.

13. Voltage sensing device according to claim 1, wherein the conductive rod further comprises a middle portion connecting the first end portion and the second end portion, and wherein the middle portion is arranged in, and enveloped by, the insulating sleeve.

14. Medium-voltage or high-voltage switchgear or medium-voltage or high-voltage transformer for a power distribution network of a national grid comprising a power conductor, such as a busbar, on elevated voltage when in use, and a voltage sensing device according to claim 1, wherein the first end portion of the conductive rod is electrically connected to the power conductor.

15. Power distribution network in a national grid comprising a power conductor and a voltage sensing device according to claim 1, wherein the first end portion of the conductive rod is electrically connected to the power conductor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0057] The invention will now be described in more detail with reference to the following Figures exemplifying particular embodiments of the invention:

[0058] FIG. 1 Perspective view of a first voltage sensor according to the present disclosure before mating the sensored insulation plug with the insulating sleeve; and

[0059] FIG. 2 Sectional view of the first voltage sensor, after mating the sensored insulation plug with the insulating sleeve.

DETAILED DESCRIPTION

[0060] The perspective view of FIG. 1 illustrates a first voltage sensor 1 according to the present disclosure. It is suitable for sensing an elevated voltage of a power conductor in a power distribution network and comprises a sensored insulation plug 10, a tubular insulating sleeve 20 and a conductive rod 30.

[0061] The sensored insulation plug 10 is shown separate from the insulating sleeve 20 and the rod 30, i.e. before the insulation plug 10 is mated with the insulating sleeve 20. The insulation plug 10 comprises a plug body 40 of an electrically insulating hardened resin with a voltage sensor embedded in the plug body 40.

[0062] In the embodiment shown in FIG. 1, the plug body 40 has an elongated shape defining a high-voltage end portion 70, oriented towards the rod 30 on elevated voltage when mated, and a low-voltage end portion 80, oriented generally away from the rod 30 on elevated voltage when mated. At the high-voltage end portion 70, the plug body 40 comprises a plug mating portion 50 which can be received in a corresponding socket mating portion of a separable connector and equally in the corresponding socket mating portion 100 of the insulating sleeve 20. The plug mating portion 50 has a generally frustro-conical shape, adapted for mating the insulation plug 10 with a separable connector or with the insulating sleeve 20.

[0063] The insulation plug 10 comprises, in the plug mating portion 50, a high-voltage contact (not visible in FIG. 1) for connection of the voltage sensor to the elevated voltage of the power conductor. The insulation plug 10 also comprises a grounding contact 60 for connection of the voltage sensor to electrical ground, and a signal contact (not visible in FIG. 1, shown in FIG. 2) for making the signal voltage, i.e. the output voltage of the voltage sensor, available outside of the plug body 40 for sensing the elevated voltage. Both the grounding contact 60 and the signal contact are arranged at the low-voltage end portion 80 of the plug body 40.

[0064] Turning now to the tubular insulating sleeve 20, the function of this sleeve 20 is to electrically insulate the conductive rod 30, which is on elevated voltage when in use, and the high-voltage contact of the insulation plug 10, so as to reduce the risk of electrical discharges between these components and elements on ground in the vicinity of the voltage sensor 1. The sleeve 20 will be explained in more detail below. However, FIG. 1 illustrates that the sleeve 20 comprises a socket mating portion 100 which is shaped identical to a socket mating portion of the separable connector for which the shape of the sensored insulation plug 10 was intended and designed to mate with. In particular it is the shape of the aperture of the sleeve 20 which is to receive the plug mating portion 50 of the insulation plug 10. It is thus particularly the inner surface of the socket mating portion 100 of the sleeve 20 which is shaped suitably to be mated with an insulation plug, and with the sensored insulation plug 10, while the outer surface of the socket mating portion 100 is, at least in the embodiment shown in FIG. 1, not critical for mating with the insulation plug 10.

[0065] In the embodiment shown in FIGS. 1 and 2 the tubular sleeve 20 has a length of about 40 centimetres (cm), which provides that non-insulated components on elevated voltage, e.g. the cable lug 110 at the opposed end of the rod 30, are sufficiently far removed from the low-voltage end portion 80 of the plug body 40 and the grounding contact 60 arranged therein.

[0066] The insulating sleeve 20 envelopes a major portion of the conductive rod 30. The rod 30 is a metallic rod 30 of elongated shape, of which only the first end portion 120 forming the cable lug 110 is visible in FIG. 1, while a middle portion 125 and a second end portion 130 (the end portion 130 which is in the vicinity of the sensored insulation plug 10 when mated) are arranged and enveloped in the sleeve 20 and hence not visible in FIG. 1. As will be explained in the context of FIG. 2, at its second end portion 130 the rod 30 comprises an external thread 140 which can engage with an internal thread 150 in a conductive metal inlay 160 in the high-voltage end portion 70 of the sensored insulation plug 10. The metal inlay 160 establishes the electrical connection of the voltage sensor of the sensored insulation plug 10, via the rod 30 and its cable lug 110, with the elevated voltage of the power conductor to which the conductive rod 30 is connected when in use. The metal inlay 160 is the high-voltage contact 160 of the voltage sensor.

[0067] The insulating sleeve 20 is made of rubber. To envelope the rod 30, the rubber material can be molded around the rod 30, or at least around a portion of the rod 30. Alternatively, a rubber sleeve 20 forming a cavity or a through hole can be manufactured separately, and the rod 30 is pushed into the cavity or the through hole. In either case the rod 30 is held in its position in the insulating sleeve 20 at least by friction between the outer surface of the rod 30 and the inner surface of the sleeve 20.

[0068] The first end portion 120 of the rod 30 is not enveloped by the insulating sleeve 20 but protrudes from the sleeve 20. This, in conjunction with a mounting hole 170 in the first end portion 120, facilitates electrical and mechanical connection of this first end portion 120 to the power conductor, such as, for example to a busbar of a switchgear or of a transformer.

[0069] FIG. 2 is a sectional view of the first voltage sensor 1 of FIG. 1, with the sensored insulation plug 10 mated with the tubular insulating sleeve 20 and electrically connected with the conductive rod 30. The insulating sleeve 20 comprises the socket mating portion 100 and an insulation section 90.

[0070] Looking first at the sensored insulation plug 10, the sectional view illustrates the grounding contact 60 and the signal contact 240. Elements of the voltage sensor in the sensored insulation plug 10 are illustrated as elements of a circuit diagram, namely a high-voltage capacitor 250, electrically connected to the rod 30 on elevated voltage via the metal inlay 160, and a low-voltage capacitor 260, electrically connected to the grounding contact 60. The high-voltage capacitor 250 and the low-voltage capacitor 260 form a capacitive voltage divider, connected between the elevated voltage and ground, for sensing the elevated voltage. The signal contact 240 is electrically connected between the high-voltage capacitor 250 and the low-voltage capacitor 260, so that it picks up a divided voltage. This divided voltage is the signal voltage which varies proportionally with the elevated voltage, the proportionality factor being the dividing ratio of the voltage divider which can be calculated from the ratio of the impedance of the high-voltage capacitor 250 to the combined overall impedance of the voltage divider.

[0071] The dividing ratio is generally chosen such that the signal voltage is a few Volt, but mostly below 50 Volt, so that commercially available electronic circuitry can measure and process the signal voltage, and thereby determine the elevated voltage of the power conductor.

[0072] It should be noted that instead of a single high-voltage capacitor 250, a plurality of serially-connected high-voltage capacitors 250 can be used to form a high-voltage portion of the voltage divider. Similarly, instead of a single low-voltage capacitor 260, a plurality of serially-connected low-voltage capacitors 260 can be used to form a low-voltage portion of the voltage divider.

[0073] It should also be noted that instead of capacitors 250, 260, other impedance elements can be used to form the voltage divider. Other impedance elements may, for example, be resistors or inductors. In certain embodiments, the low-voltage portion of the voltage divider (i.e. the portion electrically arranged between the signal contact and electrical ground) comprises one or more discrete resistors, and the high-voltage portion of the voltage divider (i.e. the portion electrically arranged between the signal contact and elevated voltage) comprises one or more discrete resistors.

[0074] The high-voltage capacitor 250 and the low-voltage capacitor 260 can be formed in various different ways, and independently from each other. The high-voltage capacitor 260, for example, may be formed by a plate-like electrode that is arranged opposite to the metal inlay 160, so that the plate-like electrode and the metal inlay 160 form the electrodes of the high-voltage capacitor 250, and a portion of the plug body 40 forms the dielectric between the electrodes. Alternatively, the high-voltage capacitor 250 may be a single discrete capacitor 250, as is shown in FIG. 2

[0075] The low-voltage capacitor 260 may be, for example, a discrete capacitor 260, mounted on a PCB, and arranged in a cavity formed in the plug body 40. Its connection to the grounding contact 60 may be achieved by, for example, a wire or a piece of metal.

[0076] The sensored insulation plug 10 is shown mated with the insulating sleeve 20, with the plug mating portion 50 inserted into the socket mating portion 100 of the sleeve 20.

[0077] The socket mating portion 100 of the sleeve 20 comprises an insulating body portion 270 which is provided with an electrically conductive outer surface layer 220 which is held on ground to provide a certain amount of shielding for the voltage sensor. On an inner surface of the socket mating portion 100, a conductive high-voltage electrode layer 230 is arranged which is in contact with the rod 30 on elevated voltage. The high-voltage electrode layer 230 is made of a conductive rubber material. It forms a Faraday cage around the area in which the sensored insulation plug 10 contacts the conductive rod 30 to prevent partial discharges in this area.

[0078] The insulation section 90 of the insulating sleeve 20 comprises four layers, arranged on top of each other: The innermost layer is an inner stress control layer 180, which is in surface contact with the conductive rod 30. It comprises a high-permittivity material such as carbon-filled silicone rubber, its permittivity Er is between about 15 and about 40. The inner stress control layer 180 is an optional layer, and may be omitted if, for example, the high-voltage electrode layer 230 in the socket mating portion 100 is shaped to form a stress control funnel.

[0079] The next layer is an inner insulating layer 190 comprising a non-conductive polymeric rubber material, thick enough to provide reliable electrical insulation of the elevated voltage of the rod 30 against ground. The third layer is an outer stress control layer 200 of about 3 millimeter thickness, made of a material (such as a carbon particle loaded silicone) of high electrical permittivity Er, such as having an Er of >10, to further reduce the risk of excessive concentration of electrical field lines and of related electrical discharges. The outermost layer 210 is an outer insulation layer 210, again of a non-conductive rubber material.

[0080] The outer stress control layer 200 and the outer insulation layer 210 help prevent partial discharges at the end of the conductive outer surface layer 220 of the insulating sleeve 20. For that purpose, the outer stress control layer 200 is in electrical contact with the conductive outer surface layer 220 of the sleeve 20.

[0081] Optionally, the outer stress control layer 200 and the outer insulation layer 210 can be manufactured as a single co-extruded two-layer tube, that may be pushed over the insulation section 90 and a part of the socket mating portion 100 to form the insulating sleeve 20 as shown in FIGS. 1 and 2.

[0082] For mating, the plug mating portion 50 of the sensored insulation plug 10 is inserted into the socket mating portion 100. By turning the sensored insulation plug 10, the internal thread 150 in the conductive metal inlay 160 in the high-voltage end portion 70 of the sensored insulation plug 10 engages the external thread 140 of the rod 30. This establishes a reliable electrical and mechanical connection between the sensored insulation plug 10, the rod 30 and the insulating sleeve 20.