GB2252671A

GB2252671A - High power switching arrangement

Info

Publication number: GB2252671A
Application number: GB9102654A
Authority: GB
Inventors: David Albert Webb
Original assignee: Long and Crawford Ltd
Current assignee: Long and Crawford Ltd
Priority date: 1991-02-07
Filing date: 1991-02-07
Publication date: 1992-08-12
Anticipated expiration: 2011-02-07
Also published as: GB2252671B; GB9102654D0

Abstract

A high power switching arrangement comprises a compartment 2, which contains switching components and insulating gas, and a baffle box 9, wherein vent 8 in compartment 2 causes gases produced during a catastrophic failure to be exhausted into baffle box 9 where they are directed along channel 12 and upwardly over baffle plate members 14 (also Fig. 3). The gases are vented to the atmosphere via vent flap 18 and any debris produced in the explosion is collected at the front and bottom of the box 9. Relief vent (21) may be in the side of the compartment (Fig. 4). <IMAGE>

Description

High Power Switching Arrangement This invention relates to high power arrangements and is particularly, but not exclusively, suitable for use with a ring main switch unit.

In one type of high power switching arrangement,a sealed compartment containing switchgear is filled with an insulating gas such as SF6. Under some conditions, faults or overloads can occur which result in arcing between components housed in the compartment. If this arcing continues the insulating gas will be heated causing it to expand and the pressure within the compartment to rise rapidly. Unless some way of controllably releasing this pressure exists the compartment may explode, resulting in destruction of the compartment and possibly endangering personnel standing nearby.

One way in which pressure within a switching compartment may be relieved is described in our co-pending application, published under serial No. GB-A-2235582. That application describes a vent arrangement comprising a membrane sealing an orifice in the compartment wall. The membrane is supported by a plate retained in the orifice by lugs. As the pressure increases the plate is forced through the orifice and the membrane ruptures, allowing the products of arcing to be expelled through the orifice.

According to the present invention there is provided high power switching apparatus comprising: a compartment housing switchgear and a pressure relief vent which blows if pressure within the compartment exceeds normal operating values; and a baffle box arranged to receive gases exhausted via the vent from the compartment and direct them over baffle surfaces within the box prior to exhausting them at an output port. By high power it is meant high voltage or high current or a combination of the two. The invention is particularly applicable to ring main switching units.

It has been found that, under catastrophic failure, gases released from the compartment by the vent are extremely hot and, in the absence of the baffle box, tend to billow around the switching arrangement, exposing the apparatus and any personnel in its vicinity to serious risks. By including a baffle box to receive the gases in a safe region away from equipment and personnel, the temperature of the vented gases is reduced and any debris produced during the explosion is contained, thus significantly reducing the risks to nearby personnel.

The baffle box enables energy to be extracted from arc by-products in the case of failure of the switching unit.

The baffle surfaces within the box are arranged to absorb heat from hot gases flowing over them and enables controlled expansion of the gases to be achieved.

In one advantageous embodiment of the invention, the arrangement has a front portion at which manual controls are located and the output port of the box is located at the rear of the arrangement, ensuring that when the gases leave the box they are remote from where any personnel are likely to be standing.

In another embodiment, the output port is to the side of the arrangement. - The output port may open direct to the atmosphere but it may be advantageous in some arrangements to include additional boxes through which gases pass.

Advantageously, the baffle box is located under the compartment and it may be preferred that it provides structural support to the compartment.

In one preferred embodiment of the invention, the baffle surfaces are arranged so that exhaust gases are directed to the front and downwardly and subsequently to the rear and upwardly of the baffle box. Other configurations may be used depending on the situation and type of switching unit. For example if the switching unit is connected to a transformer at the rear, the baffle box could be configured so as to expel gases to the side of the unit.

Advantageously, the baffle box includes a deflecting baffle plate defining with one wall of the baffle box a channel which is extensive from the pressure relief vent to substantially midway along the height of the baffle box.

Where the gases are firstly deflected forwards and downwardly, the said one wall is the front wall, but it could be a side wall if the gases are expelled to the side of the baffle box. Also, it is preferred that a plurality of substantially planar baffle plate members are included, being arranged with their main surfaces substantially parallel to one another and orthogonal to upper and lower walls of the baffle box.

In a preferred embodiment of the invention, the baffle plate members are equi-distantly spaced apart. However, different arrangements may be used and the baffle plate members need not be planar.

Some ways in which the invention may be performed are now described by way of example with reference to the accompanying drawings in which: Figure 1 schematically shows a high power switching unit in accordance with the invention; Figure 2 illustrates part of the unit of Figure 1 in greater detail and in section; Figure 3 is a schematic sectional view along line III-III on Figure 2; and Figure 4 is a schematic front elevation of another arrangement in accordance with the invention.

With reference to Figure 1, a high power switching arrangement 1 includes a compartment 2 housing a number of electrical components such as fuses, switches, earth switches and test devices. This compartment 2 is gas tight and filled by an insulating gas, SF6, which is present to suppress arcing between the high power components.

Hatches 3 and 4 permit access to components such as fuses, which might need replacing, and to switches which can be operated manually. These areas are isolated from the rest of the compartment 2 in order that the insulating gas does not escape when the hatches 3 and 4 are opened.

Electrical power is fed into the arrangement 1 via an input unit 5 at 6. The power is then transmitted via switchgear and other components within the compartment 2 to the output at a transformer cable box 7.

In this embodiment of the invention the switching unit is free standing but in other arrangements the unit is suspended above ground, being mounted on a transformer, say.

A vent 8 is located in the base of the compartment 2 and comprises a membrane across an orifice in the compartment wall, the membrane being supported by a plate. A baffle box 9 is located beneath the compartment 2 and has an aperture 10 in its top wall which is aligned with the vent orifice and is slightly larger than it.

The baffle box 9 includes an internal deflecting baffle plate 11 which is downwardly extensive from the top of the box 9 over approximately half of the its height and extends substantially entirely across its width. The baffle deflecting plate 11 is shaped so as to form a channel 12 with the front wall 13 of the baffle box 9 at the front of the baffle box 9, the channel 12 extending from the vent 8 and aperture 10.

A plurality of substantially planar baffle plate members 14 are also located in the baffle box 9, being arranged substantially parallel to one another and behind the deflecting baffle plate 11. The baffle plate members 14 are held in position by means of slotted steel strips 15 and 16 and by the deflecting baffle plate 11 which has location slots in which the members 14 are fitted. In this embodiment of the invention, the baffle plate members 14 are regularly spaced apart across the width of the baffle box 9.

A second aperture 17 is included in the upper wall of the baffle box 9 and to its rear such that it is located behind the compartment 2, and is covered by a flap 18 which is welded into position.

A channel 20 is located over the aperture 17 and defines a path from the aperture 17 in the baffle box 9 to the side of and away from the switching unit.

During normal performance of the switching unit, the vent 8 remains intact and the baffle box 9 is not involved in its operation. However, if there is catastrophic failure within the compartment 2 which causes rapid heating and expansion of the insulating gas, the membrane of the vent 8 is ruptured by its plate, allowing the hot gases to be exhausted from the compartment 2 and into the baffle box 9 via the aperture 10. The hot gases and any debris resulting from the explosion are channelled towards the front of the box 9 and downwardly by the deflector plate 11. Any debris falls to the bottom and front of the baffle box 9 where it remains, and the hot gases are directed rearwardly to the baffle plate members 14 as shown by the arrows on Figure 2.

The gases are caused to flow upwards by the configuration of surfaces within the box 9 and pass over the baffle plate members 14. The baffle plate members 14 absorb heat from the gases and direct them, in a controlled path, upwards and towards the rear of the baffle box 9. The vent flap 18 is blown open, hinging at 19, and the gases are safely vented upwards where there are directed by the channel 20 to the side and away from the switching unit.

Although in the embodiment illustrated in Figures 1, 2 and 3 the baffle box is arranged to receive gases vented from the bottom of the compartment 2 and channel them in the manner described, other configurations are possible. For example, as shown schematically in Figure 4, the pressure relief vent 21 is located in the side of the compartment 22 and the baffle box 23 is arranged to direct gases expelled through the vent 21 sideways away from the compartment 22, as shown by the broken arrows.

Claims

1. A high power switching arrangement comprising: a compartment housing switchgear and a pressure relief vent which blows if pressure within the compartment exceeds normal operating values; and a baffle box arranged to receive gases exhausted via the vent from the compartment and direct them over baffle surfaces within the box prior to exhausting them at an output port.

2. An arrangement as claimed in claim 1 wherein the arrangement has a front part at which manual controls are located and the baffle box output port is located at the rear of the arrangement.

3. An arrangement as claimed in claim 1 or 2 wherein the baffle box is located substantially under the compartment.

4. An arrangement as claimed in claim 1, 2 or 3 wherein the baffle surfaces are arranged to direct exhaust gases along a convoluted path.

5. An arrangement as claimed in any preceding claim wherein the baffle box includes baffle surfaces arranged such that exhaust gases are directed initially to the front of the box and downwardly and subsequently to the rear of the box and upwardly.

6. An arrangement as claimed in claim 1, 2, 3 or 4 wherein the exhaust gases are directed initially in a sideways direction way from the compartment.

7. An arrangement as claimed in any preceding claim wherein the baffle box includes a deflecting baffle plate defining, with a wall of the baffle box, a channel extensive from the pressure relief vent to substantially midway along the height of baffle box.

8. An arrangement as claimed in claim 5, 6 or 7 and including a plurality of substantially planar baffle plate members arranged with their main surfaces substantially parallel to one another and orthogonal to the upper and lower walls of the baffle box.

9. An arrangement as claimed in claim 8 wherein the baffle plate members are equi-distantly spaced apart.

10. An arrangement as claimed in claim 8 or 9 wherein the baffle plate members are held in position by at least one locating strip extensive across the width of the baffle box.

11. An arrangement as claimed in any preceding claim wherein the baffle box provides structural support to the compartment.

12. A high power switching arrangement substantially as illustrated in and described with reference to Figures 1, 2 and 3 or Figure 4 of the accompanying drawings.