GB2338600A

GB2338600A - High voltage switchgear with earth switch connection

Info

Publication number: GB2338600A
Application number: GB9812677A
Authority: GB
Inventors: Stephen Eric Hibberson
Original assignee: Switchgear & Instrumentation L
Current assignee: Switchgear & Instrumentation L
Priority date: 1998-06-12
Filing date: 1998-06-12
Publication date: 1999-12-22
Anticipated expiration: 2018-06-12
Also published as: GB2338600B; GB9812677D0

Abstract

A high voltage switchgear comprises a user chamber 30, a circuit breaker chamber 40, and a main chamber 20 located between the user chamber 30 and the circuit breaker chamber 40. A current transformer bushing 100 traverses opposite walls of the main chamber 20 providing a user termination 102 in the user chamber 30 and a circuit breaker connector 104 in the circuit breaker chamber 40. A bushing conductor 106 electrically connects the user termination 102 to the circuit breaker connector 104. An earth switch 110 is operable to connect the bushing conductor 106 and the user termination 102 to earth via an electrical connector 120 connected between the earthing switch 110 and the end of the bushing conductor 106 in the main chamber 20. The input connector 104 and part of the electrical connector 120 are housed in an insulating housing, the housing comprising a recess adapted to receive the electrical connector 120.

Description

2338600 1 HIGH VOLTAGE SWITCHGEAR WITT1 SAFETY EARTH SWITCH CON =CTIO The

present invention relates to high voltage switchgear, 5 for example switchboards, and in particular to the provision of earthing facilities equipment for use in high voltage switchgear.

Switchboards are a type of switchgear. For the purposes of this description, the term Iswitchgear, should be taken to also include control gear, for example for use with contactors for the supply of power.

In high voltage switching operations, supply voltages of 15 many kilovolts are applied to conductors connecting equipment together. Before carrying out work on these conductors, it must be ensured that they are at a harmless voltage, and will remain so during the works.

It may be insufficient to simply disconnect the high supply voltage, as a dangerous voltage may be retained in the conductors by their inherent capacitance. There is also the risk that a conductor may inadvertently become live,, raised to several kilovolts, while it is being worked on.

Such may be the case in event of a fault in the switchgear, or any associated equipment, or in the case of a person unknowingly applying a high voltage to a conductor that is being worked upon.

It is safer to provide an earth switch, to provide a low resistance path from the conductor being worked on to an 2 earth voltage, for the duration of the works. In this way, one can be sure that the conductor being worked upon is at a safe voltage, and that it will remain at a safe voltage throughout the duration of the works. Preferably, it should be difficult for a user to disable this safety feature.

Accordingly, the invention aims to provide a high voltage switchgear which includes a switched connection to earth which is resistant to tampering.

The invention also aims to provide a high voltage switchgear with improved safety under normal and fault conditions.

The invention also aims to provide a high voltage switchboard which is relatively simple to manufacture.

The present invention provides a high voltage switchgear comprising a user chamber, a circuit breaker chamber, a main chamber located between the user chamber and the circuit breaker chamber, a bushing extending between a wall separating the main chamber from the user chamber, and a second wall separating the main chamber from the circuit breaker chamber, so as to provide a user termination in the user chamber and an input connector accessible from the circuit breaker chamber, and including a bushing conductor electrically connecting the user termination to the input connector, and an earthing means operable to connect the bushing conductor and the user termination to an earth, wherein an electrical connector is provided between the earthing means and the bushing conductor, the bushing conductor being connected to a first end of the electrical 3 connector within the main chamber.

Preferably, a second end of the electrical connector is connectable to the earthing means and is situated within the 5 main chamber.

Preferably, the bushing comprises a housing arranged to house the bushing conductor, the housing being adapted to receive the first end of the electrical connector.

Preferably, the housing comprises a recess within which the first end of the electrical connector is located.

Preferably, the first end of the electrical connector passes through a wall of the housing, so that the first end of the electrical connector is inaccessible from the user chamber.

The present invention also provides an electrical connector bushing comprising a bushing conductor and an input connector, an insulating housing being arranged to house the bushing conductor, the input connector and at least part of an electrical connector, the housing including a recess adapted to receive a first end of an electrical connector through a wall of the housing.

Preferably, in a bushing according to the invention, an end of the bushing conductor for connection to the input connector is located within the recess of the insulating housing.

Preferably, in a switchgear or a bushing according to the 4 invention, the electrical connection passes through a wall of the housing forming the recess.

Preferably, in a switchgear or a bushing according to the 5 invention, the electrical connection passes through a protrusion incorporated on the wall of the housing.

Preferably, in a switchgear or a bushing according to the invention, the electrical connector passes into the recess and is clamped between the bushing conductor and the input connector.

Preferably, in a switchgear or a bushing according to the invention, the electrical connector comprises a busbar having one or more holes through it in a connection region. The connection region of the busbar is preferably mounted between the bushing conductor and the input connector by means of one or more fasteners passing through the holes.

Preferably, the bushing is a current transformer bushing.

The housing preferably consists of moulding.

a single, integral The electrical connector is preferably attached to an end of the bushing conductor.

The electrical connector is preferably adapted to connect the bushing conductor to earth.

In a preferred embodiment of the invention, a three-phase switchgear comprises three bushings each traversing opposite walls of the main chamber. Each bushing provides a user termination in the user chamber and an input connector accessible from the circuit breaker chamber. Each bushing includes a bushing conductor electrically connecting a user termination to the corresponding input connector. At least one earth switch is included, operable to connect corresponding bushing conductors and corresponding user terminations to an earth. An electrical connector is provided between each earth switch and each bushing conductor.

Brief Description Qf_the Drawings

The present invention will be described in accordance with preferred embodiments, given by way of examples only, with reference to the accompanying diagrams, in which:

Figure 1 shows a side elevation of a high voltage switchboard according to an embodiment of the invention:

Figure 2 shows a rear elevation of the high voltage switchboard of Figure 1; Figure 3 shows a section along the line III-III of figure 1 and Figure 4 shows a current transformer bushing, earth switch and earthing busbar according to an aspect of the present invention.

Referring to figures 1-3, switchboard 10 includes a main 6 chamber 20, a user chamber 30 situated to the rear of the main chamber 20, a circuit breaker chamber 40 situated to the front of the main chamber, a low voltage chamber 42 situated adjacent to the circuit breaker chamber 40, and a VT chamber 45 situated to the front of the main chamber 20, below the circuit breaker chamber 40. A circuit breaker 50 is mounted on a circuit breaker cradle 60 and is located within the circuit breaker chamber 40. A circuit voltage transformer (VT) 70 is mounted on a VT cradle 80 and is located within the VT chamber 45. A busbar chamber 90 is contained within the main chamber 20. Within the busbar chamber, connectors 92 connect three-phase supply busbars 94 to internal busbars 96.

Although the main chamber 20 is preferably fully enclosed, one or more of the chambers referred to may be open on one or more sides.

As can be more readily seen in Figures 2, 3, in the example 20 shown, three sets of supply busbars 94, connectors 92 and internal busbars 96 are shown, for use with three phase electricity.

Each internal busbar 96 leads to a corresponding circuit 25 breaker input connector 98 which provides a connection accessible from the circuit breaker chamber 40, through a wall of main chamber 20. A current transformer bushing 100 traverses opposite walls of the main chamber 20, to provide a user termination 102 accessible from the user chamber and a circuit breaker output termination 104 accessible from the circuit breaker chamber 40, but recessed so as to be located 7 within the main chamber 20. A bushing conductor 106 electrically connects the user termination to the circuit breaker connector. Each current transformer (CT) bushing carries a current transformer 108. An earth switch 110 is electrically connected to the bushing conductor 106 of the CT bushing 100. The earth switch is further connected to an earth, and is operable to connect the bushing conductor 106 of the CT bushing 100 to the earth.

The earth switch 110 is electrically connected to the bushing conductor 106 by an earthing busbar 120, or three earthing busbars 120 for three phase operation. According to the present invention, a first end of each busbar connected to the bushing conductor(s) 106 is situated within the main chamber 20. Earthing busbars 120 are typically suitably shaped metal bars, and are preferably situated so as to be inaccessible from the user chamber 30.

Circuit breaker 50 is operable to electrically connect or 20 disconnect each circuit breaker input connector 98 to/from a circuit breaker output connector 104 and the associated bushing conductor 106 within a CT bushing. The circuit breaker 50 is moved into a service position on cradle 60. once in position, the electrical connection between input 98 and output 104 may be made. This connection may be broken by the circuit breaker 50 in the event of an electrical fault, for example when the current through the circuit breaker exceeds a predetermined limit.

In operation, the switchboard 10 serves to selectively connect busbars 94 to user terminations 102. Each user 8 termination 102 may carry fittings 109 (figure 1), which serve to enable connection of cables leading to switched equipment. For maintenance or modification purposes, it is sometimes necessary to work in the interior of the switchboard. In particular, the user of the switchboard must be able to safely work within the user chamber 30, to connect, disconnect or modify the cables connecting the switchboard to the switched equipment. This must be done in safety, without risk of electric shock from the high voltages present on busbars 94. It is not always possible to simply remove power voltages from busbars 94 to enable work to be carried out. Often, switchboards such as that described form a part of a large electrical system, and it would be unacceptable to shut down the entire system just to allow work to be carried out on one switchboard. Before working in the user chamber, the user will first ensure that all user terminations 102 are disconnected from busbars 94, by winding out, the corresponding circuit breakers 50.,Winding out' signifies the physical displacement of the circuit breaker 50 away from the circuit breaker connectors 98, 104 by withdrawing the circuit breaker cradle 60, which is provided with wheels. The action of winding out the circuit breaker activates a mechanical safety interlock device 130. Earth switch 110 is then able to be closed to connect the bushing conductor 106, and so also the user termination 102 and any user devices (not shown) connected to it, to earth. Additional such mechanical safety interlock devices may be provided that are activated by the opening of a door 132 enclosing the user chamber.

Mechanical interlock 130 is provided so that the earth 9 switch 110 may only be closed when the circuit breaker is displaced away from the connectors 98, 104. Similarly, the mechanical interlock only allows the circuit breaker to be reconnected to connectors 98, 104 when the earth switch 110 5 is open.

Advantageously, the earthing busbar 120 is situated within main chamber 20, preferably so as to be virtually completely inaccessible from the user chamber, for example by providing an earthing busbar having an end remote from the earth switch contained within the CT bushing 100. This may be achieved in several ways, though the preferred option, for simplicity, is to provide a number of holes in the end of the busbar, and to clamp the end of the busbar between the bushing conductor and the connector 104 using fasteners such as bolts or screws, passing through the holes in the end of the busbar. The earthing busbar may need to pass through a wall of the bushing.

Preferably, the earthing busbar is also inaccessible from the circuit breaker chamber, by providing that an end portion of the earthing busbar adjacent the earth switch, connectable with the earth switch, connects the earth switch within the main chamber 20. Thus, preferably, the earthing busbar is entirely contained within the main chamber 20.

One arrangement that had been previously proposed is to connect the earth switch to the user termination by providing an earthing busbar that traverses the rear wall of main chamber 20 into user chamber 30, and is connected to the user termination 102. A major disadvantage of this arrangement is that a user may, and in some instances is required to, disconnect this earthing busbar in order to connect the switched equipment to the CT bushing and so to the busbars 94. Not only does this make the connection more difficult, and there are more components to handle, but moreover it is possible that the user omits to reconnect the earthing busbar to the user termination, rendering ineffective the safety assurances provided by the earth switch 110. Further inconveniences of this arrangement are that the busbar is relatively long, and runs approximately parallel to the bushing conductor 106 and current transformer 108. Under fault conditions (e.g. when different phases are connected together, or to earth), a very large current will flow through the bushing conductor, and return through the earthing busbar, at least until this current causes the circuit breaker 50 to open. During the period of high current, strong electromechanical forces would act on both the earthing busbar and the bushing conductor, possibly leading to damage of the switchboard.

In addition, this arrangement requires the earthing busbar to traverse the rear wall of the main chamber 20, requiring insulation and the provision of a hole in that rear wall. These additional features add to the manufacturing cost of the switchboard. Also, the earthing busbar would be accessible to a user from the user chamber, even during the existence of a fault, which is clearly undesirable and a risk to the user.

On the contrary, the switchboard of the present invention uses only a short earthing busbar, running generally perpendicular to the bushing conductor 106. Under fault conditions, any large current that flows through the earthing busbar does not flow through the bushing conductor. The electromechanical forces acting on the switchboard of the invention are therefore much less.

Provision of the earthing busbar within the chamber 20 also avoids the need for providing insulation and a hole to allow the earthing busbar to traverse the rear wall of the chamber 20.

More importantly, in the switchboard and bushing of the present invention, it is difficult, and is indeed virtually impossible, for the user to disconnect the earthing busbar 120 at its end remote from the earth switch, since the end remote from the earth switch is preferably located within the circuit breaker output connector 104. The end adjacent to the earth switch is also virtually inaccessible, being preferably situated within the main chamber 20.

Figure 4 shows a current transformer (CT) bushing 100, earth switch 110 and earthing busbar 120, as used in the switchboard of figures 1-3.

CT bushing 100 comprises a bushing conductor 106 extending from the user termination 102 to the circuit breaker output connector 104. The shape of the circuit breaker output connector 104 is determined by the connectors available on the circuit breaker 50. In this preferred embodiment, a housing in the form of a single, integral moulding 101 houses the bushing conductor and the circuit breaker output 12 connector. User termination 102 protrudes from one end of the housing, while the circuit breaker output connector 104 is enclosed within a connection recess 103 defined in the housing 101. Connection recess 103 is designed to receive a connector of a circuit breaker 50. In use, the open end of connection recess 103 will be accessible from the circuit breaker chamber 40 and the user termination 102 will be accessible from the user chamber 30. The major, central, part C of the CT bushing will be located within the main chamber 20. Thus, in use, the circuit breaker output connector 104 is accessible from the circuit breaker chamber 40, although it is situated within main chamber 20.

In particular, and according to an aspect of the present invention, earthing busbar 120 passes through a wall forming the connection recess 103, and is electrically connected to the circuit breaker connector 104 and the bushing conductor 106, within the connection recess 103. This may be achieved by providing one or more holes in an end of the earthing busbar 120, placing the end of the busbar between the circuit breaker output connector 104 and the bushing conductor 106, and clamping the earthing busbar 120 between the circuit breaker connector 104 and the bushing conductor 106 using fasteners such as bolts or screws through the holes in the earthing busbar. The moulding 101 preferably comprises a protrusion 105 for receiving the earthing busbar and aligning it with the circuit breaker connector 104 and the bushing conductor 106.

Preferably, an end of the bushing conductor 106 terminates in an enlarged head 107, having an outer surface 13 approximately flush with an inner surface of recess 103. Tapped holes are preferably provided within the enlarged head, to receive fasteners 108 such as bolts or screws.

A hole is preferably provided in the wall of recess 103 to allow earthing busbar 120 to be inserted, to have one face adjacent to the outer surface of the enlarged head 107 of bushing conductor 106. For mechanical strength, and to aid alignment of the earthing busbar, a protrusion 105 is preferably provided extending outwards from the wall of the recess 103, to accommodate the hole.

The bushing of figure 4 may be constructed as follows. Bushing conductor 106 may be moulded, or turned, to include the enlarged head 107. Tapped holes may then be provided in the user termination end 102 and the enlarged head 107. Alternatively, the enlarged head 107 may be separately manufactured, and attached to the bushing conductor 106 using fasteners such as bolts or screws through the enlarged head into a tapped hole in the bushing conductor.

The bushing conductor 106, with its enlarged head 107, may then be placed in a mould, and housing 101 may be moulded on. Alternatively, the housing 101 may be separately moulded, or otherwise constructed, and the bushing conductor with the enlarged head inserted later.

After formation of the housing 101 around the bushing conductor 106, a first end of earthing busbar 120 may be inserted through the hole in the wall forming recess 103. The end of the earthing busbar lies adjacent to the surface 14 of the enlarged head 107. Preferably, the end of the busbar includes holes which align with the tapped holes in the enlarged head.

Finally, connector 104 is introduced into recess 103. The connector preferably includes holes which align with the holes in the earthing busbar and the holes in the bushing connector. Fasteners 108 such as bolts or screws are then applied through the holes in the connector 104 and the busbar 120 into the tapped holes in the enlarged head 107. The fasteners are then tightened to clamp the earthing busbar 120 between the bushing conductor 106 and the connector 104.

The CT bushing of figure 4 is a three-way connector, allowing simultaneous connection to the user termination 102, the earthing busbar 120 and the circuit breaker connector 104.

The CT bushing as described has advantages in that it is impossible to inadvertently disconnect the earthing busbar 120. To disconnect the earthing busbar, it would be necessary to remove the associated circuit breaker to gain access to the connection recess 103, to remove the circuit breaker connector 104 and withdraw the earthing busbar 120 from the moulded protrusion improvement over the known and in some instances is earthing busbar in order to Use of the CT bushing of resistance of the safety 105. This provides a significant CT bushings, where a user may, required to, disconnect the connect the switched equipment. figure 4 increases the tamper- earth switching feature. In is particular, preferably the central portion C of the CT bushing, including protrusion 105 and earthing busbar 120, is to be located within the main chamber 20, making it practically impossible for a user to tamper with the earth 5 switch safety device.

The CT bushing of figure 4 also has the advantage of providing a simple means for locating at least a first end of the earthing busbar 120 within the main chamber 20, according to an aspect of the present invention.

Although the present invention has been described with reference to certain particular embodiments, many variations and alterations to the invention are possible. For example, the invention may be applied to switchgear other than switchboards, for example, to control gear for use with contactors for the supply of power.

Claims

CLAIMS:

16 1. A high voltage switchgear comprising: a user chamber, 5 a circuit breaker chamber, a main chamber located between the user chamber and the circuit breaker chamber, a bushing extending between a wall separating the main chamber from the user chamber, and a second wall separating the main chamber from the circuit breaker chamber, so as to provide a user termination in the user chamber and an input connector accessible from the circuit breaker chamber, and including a bushing conductor electrically connecting the user termination to the input connector, an earthing means operable to connect the bushing conductor and the user termination to an earth, wherein an electrical connector is provided between the earthing means and the bushing conductor, the bushing conductor being connected to a first end of the electrical connector within the main chamber.

2. A switchgear according to claim 1, in which a second end of the electrical connector is connectable to the earthing means and is situated within the main chamber.

3. A switchgear according to claim 1 or claim 2 wherein the bushing comprises a housing arranged to house the bushing conductor, the connection between the connector and the bushing conductor being situated within the housing.

17 4. A switchgear according to claim 3 wherein the first end of the electrical connector passes through a wall of the housing, so that the first end of the electrical connector is inaccessible from the user chamber.

5. An electrical connector bushing comprising a bushing conductor and an input connector, an insulating housing being arranged to house the bushing conductor, the input connector and at least a part of an electrical connector, the housing including a recess adapted to receive a first end of the electrical connector through a wall of the housing.

6. A switchgear or a bushing according to any of claims 3- 5, in which the insulating housing comprises a recess within which an end of the bushing conductor for connection to the input connector is located.

7. A switchgear or bushing according to claim 6, in which the electrical connection passes through a wall of the housing forming the recess.

8. A switchgear or bushing according to claim 7, in which the electrical connection passes through a protrusion incorporated on the wall of the housing.

9. A switchgear or bushing according to claim 7 or claim 8 in which the electrical connector passes into the recess and is clamped between the bushing conductor and the input connector.

18 10. A switchgear or bushing according to claim 9 wherein: the electrical connector comprises a busbar having one or more holes through it in a connection region; the connection region of the busbar is mounted between the bushing conductor and the input connector by means of one or more fasteners passing through the holes.

11. A bushing according to any of claims 5-10, being a current transformer bushing.

12. A bushing according to any of claims 5-12 in which the housing consists of a single, integral moulding.

13. A bushing according to any of claims 5-12 wherein the electrical connector is attached to an end of the bushing conductor.

14. A bushing according to any of claims 5-12 wherein the electrical connector is adapted to connect the bushing conductor to earth.

15. A three-phase switchgear according to any of claims 1-3 or 6-10, comprising: three bushings each traversing opposite walls of the main chamber, and each providing a user termination in the user chamber and an input connector accessible from the circuit breaker chamber, and each including a bushing conductor electrically connecting a user termination to the corresponding input connector, at least one earth switch, operable to connect bushing conductors and corresponding user corresponding 19 terminations to an earth, wherein an electrical connector is provided between each earth switch and each bushing conductor.

16. A switchgear substantially as described, with reference to the drawings.

17. A bushing substantially as described, with reference to figure 4 of the drawings.