HIGH POWER SWITCHING ARRANGEMENT

Abstract: A high power switching arrangement includes a compartment (2) which contains switching components together with insulating gas and a venting chamber (9) located beneath it. A vent (8) in a wall of compartment (2) causes gases produced during a catastrophic failure to be exhausted into the venting chamber which includes a plate (31) to give a turbulent flow to the gases and a plate (41) downstream of plate (31) to give a controlled directed flow towards an outlet port.

Description: High Power Switching Arrangement This invention relates to high power switching aιτangements 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 controlling release of 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 previous 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 invention there is provided a high power switching arrangement comprising a compartment filled with insulating gas and housing switchgear and a pressure relief vent which blows if pressure within the compartment exceeds normal operating values; and a venting chamber arranged to receive gases exhausted via the vent from the compartment, characterised in that the venting chamber comprises in series a turbulence inducing means to bring about a degree of turbulence in the flow of gases exhausted via the vent into the venting chamber and a gas flow directing means to direct the flow of gases towards an outlet of the venting chamber. 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 venting chamber, tend to billow around the switching arrangement, exposing the apparatus and any personnel in its vicinity to serious risks. By including a venting chamber in the switching arrangement as defmed above to receive the gases in a safe region away from equipment and personnel, the flow of gases is controlled and in addition any debris produced during the explosion is contained, thus significantly reducing the risks to nearby personnel. The venting chamber enables energy to be extracted from arc by-products in the case of failure of the switching unit. In a preferred arrangement the turbulence inducing means comprises a deflecting plate. The deflecting plate may have a slot extending therethrough, and the slot may be of sinuous form. In addition or alternatively, a part or the whole of at least one edge of the deflecting plate may be of saw-toothed formation, and the deflecting plate may incoφorate turbulence inducing vanes. It is further preferred that the gas flow directing means comprises a plate having at least one orifice therethrough, and the or each orifice may have a respective hollow tube mounted therein. A plurality of said tubes may be arranged at different angles relative to the plate with the angles selected to give a predetermined flow pattern of gases towards the output port; the angle of each tube may be adjustable. The arrangement may have a front part at or in which manual controls are located with the venting chamber outlet located at the rear of the arrangement. The venting chamber may be located on a wall ofthe compartment and may provide structural support to the compartment. An embodiment of the invention will now be 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 an enlarged view of the deflecting plate of Figure 2 as mounted in the venting chamber. 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, busbars 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. The switching unit may be free standing or may be suspended above the ground, being mounted on a transformer, say. A vent 8 is located in a wall 20 of the compartment 2 and comprises a membrane across an orifice in the compartment wall. A venting chamber 9 is located on the compartment wall 20 and has an aperture 10 which is aligned with the vent orifice 8 and is slightly larger than it. The venting chamber 9 includes turbulence inducing means which, as shown, take the form of at least one internal deflecting plate 31 which extends vertically in the chamber and across the chamber between the side walls thereof. The plate 31 will be fixed to the walls by any suitable means e.g. it may be welded thereto. As shown in Figure 3, the edges 33 of plate 31 adjacent the upper and lower walls of the chamber have a saw-toothed formation whereby a series of gaps 34 are formed between the plate 31 and the side walls. Spaced from the deflecting plate 31 is a gas flow directing means which in this embodiment takes the form of a flow control plate 41 also extending vertically from the top to the bottom of the chamber 9 and between the side walls thereof. The plate 41 abuts the top and bottom walls and the side walls of the chamber and is affixed thereto e.g. by welding, or by the use of bolts threadably engaged with the plate 41 and with (a) further component(s) welded to the side walls. For the purpose of allowing the flow of gases through the plate 41 in a controlled manner, the plate 41 is formed with a series of orifices 42 spaced horizontally across the plate 41 and each of which receives a hollow tube 43. Each hollow tube 43 may extend with its longitudinal axis at the same angle to the surfaces ofthe plate 41 and this may be a right angle, but it has been found particularly advantageous if each tube 43 is set at a different angle. For example, tube(s) close to one end of the plate 41 may be set at right angles, tube(s) in the intermediate region may be set at an angle of 82.5°, and tube(s) close to the other end of the plate 41 may be set at an angle of 75°, but other orientations are possible, and in certain circumstances only one tube 43 need be provided. The arrangement of the plate 41 and its associated tube(s) is selected to give a controlled flow of gases to the exhaust vent 20. During normal performance of the switching unit, the vent 8 remains intact and the venting chamber 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 directly or by a plate associated therewith, allowing the hot gases to be exhausted from the compartment 2 and into the venting chamber 9 via the aperture 10. The hot gases and any debris resulting from the explosion are initially channelled towards the front of the chamber 9. Any debris are impeded by plate 31, but the hot gases are allowed into a rear portion of the chamber 9 around the plate 31. The plate 31 , because of its form, gives a turbulent flow of the gases towards the plate 41. The plate 41 acts to give a controlled directed flow of gases towards the exhaust port of the venting chamber. Gases reaching this part of the chamber are released through a vent which may simply be the open end of the chamber 9 or an orifice therethrough; and the vent may comprise an angled deflector wall. In a further arrangement the gases blow a hinged vent flap open and are safely vented sideways and/or upwards. By virtue of their structure and arrangement the plates 31 and 41 and, especially the plate 41, act to restrict, diffuse and split the flow of exhausting gases in a controlled manner. They act to reduce the flow whereby a controlled pressure rise occurs in the venting chamber, thereby allowing time for the temperature in the chamber to rise and heat energy to be dissipitated in a controlled manner. Although the plates 31, 41 have been described and illustrated as being vertically mounted in chamber 9, any appropriate arrangement is possible, e.g. the plates may be angled relative to the top and bottom walls. Furthermore plate 31 may involve other means for inducing turbulent flow in addition or alternatively to the saw tooth formations, e.g. orifices of various shapes with associated turbulence inducing vanes. Although in the embodiment illustrated in Figures 1 and 2 the venting chamber is arranged to receive gases vented from the side of the compartment 2 and channel them in the manner described, other configurations are possible. For example, a pressure relief vent may be located in the bottom of the compartment 2 with a venting chamber arranged below the compartment whereby to direct gases expelled through the vent downwards away from the compartment 22. In a further embodiment, the venting chamber may be fitted above the compartment 2.

Claims: CLAIMS 1. A high power switching arrangement comprising a compartment filled with insulating gas and housing switchgear and a pressure relief vent which blows if pressure within the compartment exceeds normal operating values; and a venting chamber arranged to receive gases exhausted via the vent from the compartment, characterised in that the venting chamber comprises in series a turbulence inducing means to bring about a degree of turbulence in the flow of gases exhausted via the vent into the venting chamber and a gas flow directing means to direct the flow of gases towards an outlet of the venting chamber. 2. An arrangement as claimed in Claim 1 wherein the turbulence inducing means comprises a deflecting plate. 3. An arrangement as claimed in Claim 2 wherein the deflecting plate has a slot extending therethrough . 4. An arrangement as claimed in Claim 3 wherein the slot is of sinuous form. 5. An arrangement as claimed in any one of Claims 2 to 4 wherein a part or the whole of at least one edge of the deflecting plate is of saw-toothed formation. 6. An arrangement as claimed in any one of Claims 2 to 5 wherein the deflecting plate incorporates turbulence inducing vanes. 7. An arrangement as claimed in any preceding claim wherein the gas flow directing means comprises a plate having at least one orifice therethrough. 8. An arrangement as claimed in Claim 7 wherein the or each orifice has a respective hollow tube mounted therein. 9. An arrangement as claimed in Claim 8 wherein a plurality of said tubes are arranged at different angles relative to the plate. 10. An arrangement as claimed in Claim 9 wherein the angles are selected to give a predetermined flow pattem of gases towards the output port. 11. An arrangement as claimed in either one of Claims 9 or 10 wherein the angle of each tube is adjustable. 12. An arrangement as claimed in any preceding claim wherein the arrangement has a front part at or in which manual controls are located and the venting chamber outlet is located at the rear of the arrangement. 13. An arrangement as claimed in any preceding claim wherein the venting chamber is located on a wall of the compartment. 14. An arrangement as claimed in any preceding claim wherein the venting chamber provides structural support to the compartment. 15. A high power switching arrangement substantially as illustrated in and described with reference to Figures 1, 2 and 3 of the accompanying drawings.

Inventors: WEBB DAVID ALBERT, WILKINSON ALLEN, WEBB, DAVID, ALBERT, WILKINSON, ALLEN
Applicants: GEC ALSTHOM T & D LONG AND CRA, GEC ALSTHOM T & D LONG AND CRAWFORD LIMITED
Application year: 1996
Main classification: H01H33
IPC codes: H01H33