Live-tank outdoor vacuum circuit breaker (OVCB) apparatus

Abstract

A live-tank outdoor vacuum circuit breaker (OVCB) apparatus 100 comprises a vacuum interrupter 102a-c; an insulating enclosure 103a-c containing the vacuum interrupter; a cabinet 109 adapted to suppor

Description

The present invention relates to a live-tank outdoor vacuum circuit breaker (OVCB) apparatus, and method of modifying an existing live-tank outdoor vacuum circuit breaker (OVCB) apparatus. Approximately 70% of global medium-voltage power distribution grids are in the form of overhead lines. These lines are generally classified by operating voltage, and are commonly seen strung between towers, such as pylons, and poles, in urban and rural areas. The operating voltage is typically a function of the distance over which power needs to be transmitted and / or the transmission of power to bulk consumers, such as factories. In the United Kingdom, for example, a transmission network operates at275kV and above, and transmits power over long distances to areas where it is required. A distribution network, which operates at 132kV and below, takes this electrical power and distributes it to an end user. Electrical sub-stations are used to convert incoming power into different voltages, for example, stepped up or stepped down, via a series of electrical transformers situated within the substation. Sub-stations on the transmission network convert incoming voltages, which may vary by source, into the required voltages for transmission. At the point electricity will leave the transmission network, the voltage is stepped down at a grid supply point, which may then transmit the stepped down voltage to an electrical sub-station on a distribution network. Here the voltage is stepped down again to ensure it is suitable to enter homes, and, where end-users are sending electricity back to the grid (for example, from domestic solar panel installations), the voltage may be stepped up for onward transmission. Each electrical sub-station, whether on the transmission grid or a local distribution grid, is provided with three elements: transformers, switching equipment and protection and control apparatus. Capacitors, reactors or static VAR compensators are typically used as voltage control and power factor correction devices, and phase-shifting transformers may be used to control power flow between adjacent power systems. Voltage and current transformers, relays and SCADA systems are used for protection and control. Circuit breakers are used to interrupt short circuits or overload currents that may occur on the network the sub-station is part of. In addition, a grounding or earthing system must be provided. Typically, an incoming voltage supply is connected to a disconnect switch, for isolation, and a circuit breaker, for load current interruption. If a large fault current flows through the circuit breaker, this is detected via a current transformer, the output of which trips the circuit breaker to disconnect the load. Substations may deal with one, two or three-phase voltages as required by the end-user. In distribution networks, two different types of circuit breaker are employed: live-tank circuit breakers and dead-tank circuit breakers. A live-tank circuit breaker uses an interrupter, 10 15 20 25 30 such as a vacuum interrupter, which is held within an insulating housing at electrical potential, and hence is live. A dead-tank circuit breaker also uses a vacuum interrupter, but in this case the interrupter is housed within an earthed metal enclosure. The embodiments of the present invention concentrate on issues associated with live-tank circuit breakers. Figure 1 is a schematic diagram of a prior art live-tank outdoor vacuum circuit breaker. The live-tank outdoor vacuum circuit breaker 1 comprises three vacuum interrupters 2a, 2b, 2c (generally indicated within the top half of an insulating enclosure but out of view), each housed within an insulating enclosure 3a, 3b, 3c. Each insulating enclosure 3a, 3b, 3c, is provided with an upper terminal plate 4a, 4b, 4c, a first portion 5a, 5b, 5c, a lower terminal plate 6a, 6b, 6c, a second portion 7a, 7b, 7c and a base 8a, 8b, 8c. The vacuum interrupters 2a, 2b, 2c are contained within the first portion 5a, 5b, 5c, between the upper 4a, 4b, 4c and lower 6a, 6b, 6c terminal plates. The insulating enclosures 3a, 3b, 3c are mounted on a cabinet 9 by means of a base frame 10. The cabinet 9 is adapted to support the insulating enclosures 3a, 3b, 3c containing the vacuum interrupters 2a, 2b, 2c and comprises a first enclosed chamber 11, the interior of which is adapted to be accessible via a door 12. The door 12 is mounted on the cabinet 9 by means of hinges 13, and is provided with a hasp 14 or other device to enable securing in closed position by means of a padlock (not shown) or similar. A plexiglass window 15 is provided to enable a worker to see the status of the live-tank outdoor vacuum circuit breaker 1, showing a display that may read “SPRING CHARGED”, “SPRING DISCHARGED”, “CB OPEN” or “CB CLOSED”. The cabinet 9 is supported on a support frame 16. The support frame 16 has a distal end 17 on which the cabinet 9 is adapted to be mounted and a proximal end18 adapted to be secured to floor level 19. In this example, the support frame 16 comprises vertical legs 20a, 20b, 20c, 20d (two of which are hidden in the view shown) and cross bracing 21a, 21b. A control rod (not shown) runs between the vacuum interrupters 2a, 2b, 2c and the components within the cabinet 9. Given that it sits at the potential of the incoming power line a live-tank circuit breaker is subject to the same local electrical standards as the power lines themselves. In the United Kingdom, these is EN 50522:22 and ENA (Energy Networks Association) Technical Specification 43-8, which cover the clearance required by overhead lines. These requirements are in addition to any switchgear requirements in IEC 62271-100. In order to achieve compliance with the height requirements, live-tank outdoor vacuum circuit breakers in the United Kingdom are placed on a higher support frame or platform than those used in other European countries, for example, thus raising the vacuum interrupter to a safe height. However, the relevant standards do not just provide a requirement for the clearance of the live vacuum interrupter, but have an additional requirement regarding a safety clearance zone. This is based upon the need for a person carrying out maintenance or repair of a live-tank outdoor vacuum circuit breaker to be able to use a metal tool of up to 300mm in length. This additional requirement, therefore, places a further constraint on the design of live-tank outdoor vacuum circuit breakers for the United Kingdom, which is not met by merely raising the overall height. In addition, to maintain or repair existing live-tank outdoor vacuum circuit breakers it is necessary to impose an operational restriction to ensure that all apparatus is fully de-energised prior to any work being carried out. This increases the time required to repair the live-tank outdoor vacuum circuit breaker, which is detrimental to the ability of the distribution network to continue functioning, and places an unwanted burden on end-users waiting for the power supply to be restored. Consequently, a new approach to the design of live-tank outdoor vacuum circuit breakers in the United Kingdom is needed. The present invention aims to deliver this new approach by providing an live-tank outdoor vacuum circuit breaker (OVCB) apparatus comprising: a vacuum interrupter; an insulating enclosure containing the vacuum interrupter, wherein the enclosure is elongate; a cabinet adapted to support the insulating enclosure containing the vacuum interrupter and which comprises a first enclosed chamber, the interior of which is adapted to be accessible; and a support frame, having a distal end on which the cabinet is adapted to be mounted and a proximal end adapted to be secured to floor level; wherein the cabinet further comprises a second enclosed chamber located between the insulating enclosure and the first enclosed chamber, the interior of which is adapted to remain inaccessible. The advantage of the second enclosed chamber is that it provides a secure, inaccessible space that serves as the safety clearance zone in accordance with United Kingdom standards. In addition, it removes the need to fully de-energise the apparatus before any work is carried out, thus reducing critical maintenance and repair times. Preferably, the first enclosed chamber of the cabinet contains switchgear in electrical connection with the vacuum interrupter. Preferably, the second enclosed chamber of the cabinet preserves a safety clearance zone between the vacuum interrupter and the switchgear and does not contain any high voltage or low voltage components. Preferably, the first enclosed chamber comprises a door to enable access to its interior. Preferably, the second enclosed chamber comprises a sealed closure element to prevent access to its interior. Preferably, a mesh element is provided between the first enclosed chamber and the second enclosed chamber to form a physical barrier to the second enclosed chamber. Preferably, the mesh element also acts to allow air circulation and prevent condensation within the cabinet. 10 15 20 Preferably, the live-tank outdoor vacuum circuit breaker (OVCB) apparatus further comprises a base frame located between the insulating enclosure and the cabinet. Preferably, the insulating enclosure comprises an upper terminal plate, a first portion, a lower terminal plate, a second portion and a base, and wherein the vacuum interrupter is contained within the first portion, between the upper and lower terminal plates. Preferably, the lower terminal plate is positioned at a minimum clearance above the floor in accordance with a local electricity standard. Preferably, there are three insulating enclosures, each containing a vacuum interrupter. Preferably, the live-tank outdoor vacuum circuit breaker (OVCB) apparatus further comprises a base frame mounted between the second enclosed chamber and the insulating enclosure containing the vacuum interrupter. The present invention also provides a method of modifying an existing live-tank outdoor vacuum circuit breaker (OVCB) apparatus to form the live-tank outdoor vacuum circuit breaker (OVCB) apparatus as described above, wherein the existing live-tank outdoor vacuum circuit breaker comprises a cabinet having a single, first enclosed chamber only, comprising: replacing the cabinet of an existing live-tank outdoor vacuum circuit breaker (OVCB) with a cabinet sized to accommodate the first enclosed chamber and the second enclosed chamber; mounting the door of the existing live-tank outdoor vacuum circuit breaker (OVCB) onto the cabinet in order to access the interior of the first enclosed chamber; and providing a sealed closure member over the second enclosed chamber to prevent access into the interior of the second enclosed chamber. The present invention will now be described by way of example only, and with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a prior art live-tank outdoor vacuum circuit breaker in 25 accordance with an embodiment of the present invention; Figure 2 is a schematic diagram of a live-tank outdoor vacuum circuit breaker in accordance with an embodiment of the present invention; Figure 3 is a schematic diagram of modifying a live-tank outdoor vacuum circuit breaker in accordance with an embodiment of the present invention; and 30 Figure 4 is a flowchart outlining the steps for retrofitting an existing live-tank outdoor vacuum circuit breaker that does not meet local standards without fully de-energising for maintenance work. The embodiments of the present invention take the approach that the requirement to preserve a safety clearance zone for workers under the relevant United Kingdom standards can 35 be met by providing a sealed space between the cabinet and the insulating housings of the vacuum interrupters. This sealed space is preferably does not contain any high voltage or low 10 25 30 voltage components. It may contain an operating rod extending between the vacuum interrupters and the controls in the cabinet. By providing a secure safety clearance zone there is no need to de-energise the live-tank outdoor vacuum circuit breaker before work can be carried out safely, thus reducing maintenance and repair times for distribution network operators. The live-tank outdoor vacuum circuit breaker apparatus comprises a vacuum interrupter, and an insulating enclosure containing the vacuum interrupter, wherein the enclosure is elongate. The insulating enclosure takes the form of existing insulating enclosures as illustrated in Figure 1 and described with reference to Figure 2 below. A cabinet adapted to support the insulating enclosure containing the vacuum interrupter is provided, which comprises a first enclosed chamber. This first enclosed chamber has an interior that is adapted to be accessible, for example, by means of a lockable door. A support frame is also provided, having a distal end on which the cabinet is adapted to be mounted and a proximal end adapted to be secured to floor level. Unlike existing live-tank outdoor vacuum circuit breaker apparatus, the embodiments of the present invention have a cabinet that further comprises a second enclosed chamber located between the insulating enclosure and the first enclosed chamber. The interior of this second enclosed chamber is adapted to remain inaccessible, in order to preserve the safety clearance zone required in the United Kingdom. Figure 2 is a schematic diagram of a live-tank outdoor vacuum circuit breaker in accordance with an embodiment of the present invention. The live-tank outdoor vacuum circuit breaker 100 comprises three vacuum interrupters 102a, 102b, 102c, (generally indicated within the top half of an insulating enclosure but out of view) each housed within an insulating enclosure 103a, 103b, 103c. Each insulating enclosure 103a, 103b, 103c, is provided with an upper terminal plate 104a, 104b, 104c, a first portion 105a, 105b, 105c, a lower terminal plate 106a, 106b, 106c, a second portion 107a, 107b, 107c and a base 108a,108b, 108c. The vacuum interrupters 102a, 102b, 102c are contained within the first portion 105a, 105b, 105c, between the upper 104a, 104b, 104c and lower 106a, 106b, 106c terminal plates. The insulating enclosures 103a, 103b, 103c are mounted on a cabinet 109 by means of a base frame 110. The cabinet 109 is adapted to support the insulating enclosures 103a, 103b, 103c containing the vacuum interrupters 102a, 102b, 102c and comprises a first enclosed chamber 111, the interior of which is adapted to be accessible via a door 112. The first enclosed chamber 111 of the cabinet 109 contains switchgear (not shown) in electrical connection with the vacuum interrupter 102a, 102b, 102c. The door 112 is mounted on the cabinet 109 by means of hinges 113, and is provided with a hasp 114 or other device to enable securing in closed position by means of a padlock (not shown) or similar. A plexiglass window 115 is provided to enable a worker to see the status of the live-tank outdoor vacuum circuit breaker 100, showing a display that may read “SPRING CHARGED”, “SPRING DISCHARGED”, “CB OPEN” or “CB CLOSED”, or include a mechanical operation counter for each time the vacuum interrupter has been tripped. The cabinet 109 is supported on a support frame 116. The support frame 116 has a distal end 117 on which the cabinet 109 is adapted to be mounted and a proximal end118 adapted to be secured to floor level 119. In this example, the support frame 5 116 comprises vertical legs 120a, 120b, 120c, 120d, again, two of which are hidden in the view shown. 10 25 Unlike the prior art live-tank outdoor vacuum circuit breaker shown in Figure 1, the embodiment of the present invention illustrated in Figure 2 has been modified to meet the requirements of the standards for the United Kingdom. The cabinet 109 further comprises a second enclosed chamber 121 located between the insulating enclosure 103a, 103b, 103c and the first enclosed chamber 111, the interior of which is adapted to remain inaccessible. This second enclosed chamber 121 of the cabinet 109 preserves a safety clearance zone between the vacuum interrupter 102a, 102b, 102c and the switchgear and does not contain any high voltage or low voltage components. Such components include high voltage components connected directly to the vacuum interrupter 102a, 102b, 102c, and low voltage components include additional items such as heaters used to prevent condensation within the cabinet 109. This enables a worker who is maintaining or repairing the live-tank outdoor vacuum circuit breaker 101 to work safely with no risk of inadvertently placing either their hand or a tool into the safety clearance zone. If high voltage or low voltage components were to be included in the safety clearance zone then there would be a requirement for any operator to carry out maintenance on these components. However, this would require fully de-energising the apparatus to avoid any intrusion into the safety clearance zone, and effectively be the same as the prior art solution illustrated in Figure 1. But by providing a second enclosed chamber 121 that does not contain any high voltage or low voltage components, it is no longer necessary for the live-tank outdoor vacuum circuit breaker 100 to be fully de-energised before work can be carried out since the safety clearance zone is protected and cannot be accessed. The control rod (not shown) between the vacuum interrupters 102a, 102b, 102c and components within the first enclosed chamber 111 runs through the second enclosed chamber 121 and can be accessed from the first enclosed chamber 111. Whilst the first enclosed chamber 111 30 comprises a door 112 to enable access to its interior, the second enclosed chamber 121 comprises a sealed closure element 122 to prevent access to its interior. This sealed closure element 122 may be a blanking plate that is screwed (using security screws), bolted or welded to the cabinet 109. Preferably, the second enclosed chamber 121 should have a height that meets the requirements of a local electricity standard when installed. In the United Kingdom 35 this is at least 300mm, to match the additional distance required by EN 50522 in relation to allowing a worker to use a metal tool safely. A mesh element 123 is provided between the first 10 25 30 enclosed chamber 111 and the second enclosed chamber 121 to form a physical barrier to the second enclosed chamber 121 and this preserve the safety clearance zone when any work is carried out on components provided in the first enclosed chamber 111. The mesh element 123 is formed from a metal material (either a metal such as aluminium or an alloy such as stainless steel), which may be the same as or different to the cabinet 109 material, and may be painted or coated, for example, powder coated. The use of a mesh element 123 rather than a solid element between the first 111 and second 121 enclosed chambers provides additional air circulation benefits, enabling both the removal of heat from either the first 111 or the second 121 enclosed chamber, and ventilation to avoid moisture issues from ambient humidity. Such a mesh element 123 therefore also removes the need to include any low voltage components within the second enclosed chamber 121. Thus, due to the presence of the mesh element 123 and the sealed closure element 122, the second enclosed chamber 121 cannot be accessed by anyone carrying out maintenance or repair. The mesh element 123 may be a sheet of material with a regular array of apertures included, for example, circular, square, rectangular, triangular or any other regular polygonal shape. Alternatively, the mesh element 123 may be formed from a grid of elongate elements creating an array of apertures, such as a wire mesh. Consequently, as well as providing a physical barrier, the mesh element 123 also acts to allow air circulation and prevent condensation within the cabinet. In the example illustrated in Figure 2, the lower plate 106a, 106b, 106c is positioned at a minimum clearance above the floor in accordance with local electricity standards, such as EN 50522. As a non-limiting example, the overall height between the lower plate 106a, 106b, 106c and the ground in Figure 2 is nominally between 3.435m and 3.436m, depending on how the support frame 116 is fixed to the ground. This meets the minimum requirement of a clearance of 3.2m given in the standard for a live-tank outdoor vacuum circuit breaker having an operational voltage between 33kV and 66kV, as found typically in a distribution network. Figure 3 is a schematic diagram of modifying a live-tank outdoor vacuum circuit breaker in accordance with an embodiment of the present invention. As shown in Figure 1, an existing live-tank outdoor vacuum circuit breaker comprises a cabinet having a single, first enclosed chamber 11 only. In order to modify this to meet local electricity standards such as EN 50522, the cabinet 9 is replaced with a cabinet 109 sized to accommodate the first enclosed chamber 111 and the second enclosed chamber 121 of the live-tank outdoor vacuum circuit breaker illustrated in Figure 2. Once this is done, the door 12 of the existing live-tank outdoor vacuum circuit breaker (OVCB) is mounted on the cabinet 9 in order to access the interior of the first enclosed chamber 111. Finally, a sealed closure member 122 is provided over the second 35 enclosed chamber to prevent access into the interior of the second enclosed chamber. This is preferably the blanking plate that is screwed (using security screws), bolted or welded to the 10 25 30 cabinet 109. By utilising existing components and replacing only the cabinet it is possible to retrofit existing live-tank outdoor vacuum circuit breakers that do not meet local standards without fully de-energising for maintenance work in the field, or to modify existing live-tank outdoor vacuum circuit breakers originally manufactured for installation in other countries to meet United Kingdom standards. The steps required for this to happen at an existing installation of live-tank outdoor vacuum circuit breakers of the type illustrated in Figure 1 are outlined below with respect to Figure 4, Figure 4 is a flowchart outlining the steps for retrofitting an existing live-tank outdoor vacuum circuit breaker that does not meet local standards without fully de-energising for maintenance work. The method 400 begins with a site power outage to de-energise the live-tank outdoor vacuum circuit breaker 1. Next, at step 402, a replacement live-tank outdoor vacuum circuit breaker 100 to be retrofitted is moved into a licensed closed area as per any factory-imposed clean assembly requirements in the field. These are to avoid any environmental outdoor impacts on the live-tank outdoor vacuum circuit breaker 100 during the retrofitting procedure. At step 404, the required parts are gathered and taken to the live-tank outdoor vacuum circuit breaker 1 to be retrofitted. At step 406, the existing live-tank outdoor vacuum circuit breaker 1 is stripped of all of its operating mechanism, leaving the cabinet 9 empty. This is then removed and replaced with a taller cabinet 109 in step 408. The closure member 122 in the form of a blanked off section and longer operating rod are then fitted at step 410, with the operating mechanism replaced at step 412. Once the retrofitted live-tank outdoor vacuum circuit breaker 100 is assembled, it requires retesting (such as repeated high-voltage and insulation resistance tests) and recalibration (to meet angular speed of operation and stroke force requirements) to meet local standards at step 414, such as IP55 regulations for water ingress and to ensure that the overall height of the live-tank outdoor vacuum circuit breaker 100 meets the requirements of EN50522 with regards to the provision of a safety clearance zone. Finally, when successful testing is complete, at step 416 the retrofitted live-tank outdoor vacuum circuit breaker 109 is commissioned, signed off, and re-energised for service. Thus, it is possible, according to the embodiments of the present invention, to install new live-tank outdoor vacuum circuit breakers 100 or to retrofit existing live-tank outdoor vacuum circuit breakers 1, that meet local standards, such as EN50522.

Claims

1. A live-tank outdoor vacuum circuit breaker (OVCB) apparatus comprising: a vacuum interrupter;an insulating enclosure containing the vacuum interrupter, wherein the enclosure is elongate;a cabinet adapted to support the insulating enclosure containing the vacuum interrupter and which comprises a first enclosed chamber, the interior of which is adapted to be accessible; anda support frame, having a distal end on which the cabinet is adapted to be mounted and a proximal end adapted to be secured to floor level;wherein the cabinet further comprises a second enclosed chamber located between the insulating enclosure and the first enclosed chamber, the interior of which is adapted to remain inaccessible.

2. A live-tank outdoor vacuum circuit breaker (OVCB) apparatus as claimed in claim 1, wherein the first enclosed chamber of the cabinet contains switchgear in electrical connection with the vacuum interrupter.

3. A live-tank outdoor vacuum circuit breaker (OVCB) apparatus as claimed in claim 2, wherein the second enclosed chamber of the cabinet preserves a safety clearance zone between the vacuum interrupter and the switchgear and does not contain any high voltage or low voltage components.

4. A live-tank outdoor vacuum circuit breaker (OVCB) apparatus as claimed in claim 1, 2, or 3, wherein the first enclosed chamber comprises a door to enable access to its interior.

5. A live-tank outdoor vacuum circuit breaker (OVCB) apparatus as claimed in any preceding claim, wherein the second enclosed chamber comprises a sealed closure element to prevent access to its interior.

6. A live-tank outdoor vacuum circuit breaker (OVCB) apparatus as claimed in any preceding claim, wherein a mesh element is provided between the first enclosed chamber and the second enclosed chamber to form a physical barrier to the second enclosed chamber.

7. A live-tank outdoor vacuum circuit breaker (OVCB) apparatus as claimed in claim 6, wherein the mesh element also acts to allow air circulation and prevent air condensation within the cabinet.

8. A live-tank outdoor vacuum circuit breaker (OVCB) apparatus as claimed in any preceding claim, further comprising a base frame located between the insulating enclosure and the cabinet.

9. A live-tank outdoor vacuum circuit breaker (OVCB) apparatus as claimed in any preceding claim, wherein the insulating enclosure comprises an upper terminal plate, a first portion, a lower terminal plate, a second portion and a base, and wherein the vacuum interrupter is contained within the first portion, between the upper and lower terminal plates.

10. A live-tank outdoor vacuum circuit breaker (OVCB) apparatus as claimed in claim 8, wherein the lower terminal plate is positioned at a minimum clearance above the floor in accordance with a local electricity standard.

11. A live-tank outdoor vacuum circuit breaker (OVCB) apparatus as claimed in any preceding claim, comprising three insulating enclosures, each containing a vacuum interrupter.

12. A live-tank outdoor vacuum circuit breaker (OVCB) apparatus as claimed in any preceding claim, further comprising a base frame mounted between the second enclosed chamber and the insulating enclosure containing the vacuum interrupter.

13. A method of modifying an existing live-tank outdoor vacuum circuit breaker (OVCB) apparatus to form the live-tank outdoor vacuum circuit breaker (OVCB) apparatus as claimed in any of claims 1 to 12, wherein the existing live-tank outdoor vacuum circuit breaker comprises a cabinet having a single, first enclosed chamber only, comprising:replacing the cabinet of an existing live-tank outdoor vacuum circuit breaker (OVCB) with a cabinet sized to accommodate the first enclosed chamber and the second enclosed chamber;mounting the door of the existing live-tank outdoor vacuum circuit breaker (OVCB) onto the cabinet in order to access the interior of the first enclosed chamber; andproviding a sealed closure member over the second enclosed chamber to prevent access into the interior of the second enclosed chamber.

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