GB2237149A - Air gap arrangement - Google Patents

Abstract

For acting as a back-up for an excess voltage arrestor that has one terminal connected to a stud terminal (1) and another terminal connected to ground an air gap arrangement (10) is provided as part of an assembly that includes the terminal (1). In a particular embodiment, the air gap arrangement (10) includes a flanged sleeve (14) of insulating material mounted on the terminal (1) and having mounted en it a first conductive washer (15A) in electrical contact with the terminal (1), a second conductive washer (15B) held out of electrical contact with the terminal (1) but in contact with a grounded connector tag (17), and an insulating washer (16) sandwiched between the first and second washers (15A, 15B). The aperture in the insulating washer (16) is over-size as compared with the sleeve (14) so that there is an air gap (20) between the first and second conductive washers (15A, 15B). Current flow is normally from the stud terminal (1) to the excess voltage arrestor. In use, should the arrestor fail to operate to protect against excess voltage, discharge to ground takes place across the air gap arrangement. <IMAGE>

Description

AIR GAP ARRANGEMENT This invention relates to an air gap arrangement in an otherwise electrically conductive line for permitting a current flow at voltages above a predetermined value, in particular in a line in which there is connected an excess voltage arrestor.

As excess voltage arrestor can be, for example, a gas-filled enclosure and a pair of electrodes housed within the enclosure and defining a discharge gap.

Such an arrestor is connected across equipment that it is desired to protect against excess voltage, the discharge gap breaking down on the occurrence of excess voltage. It is desirable that there should be back-up protection to be effective should the arrestor fail to operate to protect the equipment.

According to the present invention there is provided an air gap arrangement in an otherwise electrically conductive line for permitting current flow at voltages above a predetermined value, the air gap arrangement comprising two apertured electrically conductive members in series in the line and held in non-conducting relationship by an apertured first electrically insulating member, all three members being mounted on a second electrically insulating member passed through the apertures in the other members, the aperture in the first insulating member being over-size with respect to the second insulating member so that there is an air gap between the first and second insulating members, the apertures in the two electrically conductive members being smaller than the aperture in the first electrically insulating member so that this air gap is bounded on each side by the two electrically conductive members, the distance between the two electrically conductive members being such that current flow from one to another across the air gap will take place at voltages higher than the predetermined value. In use in a line in which there is connected an excess voltage arrestor one of the two conductive members is connected to the line and the other is connected to ground so that the air gap arrangement is in parallel with the arrestor. Should the voltage arrestor fail to operate to protect against excess voltage, discharge to ground will take place across the air gap arrangement.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawing, in which: Figure 1 is a sectional side view of a connector assembly; and Figure 2 is a sectional side view of part of the assembly of Figure 1, drawn to a larger scale.

The connector assembly shown in the Figures has two threaded stud terminals 1,1 mounted in a housing 2 formed of electrically insulating material. Within the housing 2 there is an excess voltage arrestor 3 potted in potting material 4 which can be, for example, an epoxy compound. Line connection leads 5,5 from the arrestor 3 are connected to line tags 6,6 that are in electrical contact with the stud terminals 1,1. A ground connection lead 7 from the arrestor 3 is connected to a ground terminal 8 mounted in the housing 2. From this ground terminal 8 there also extend ground connection leads 9,9 of an air gap arrangement 10, at each of the stud terminals 1,1, which will now be described with reference to Figure 2.

As shown in Figure 2, each stud terminal 1 is made fast to the housing 2 by nuts 11A, 11B sandwiching between them a wall of the housing. A connector arrangement 12 and lock nut 13 therefor on each stud terminal 1, shown in Figure 1, are omitted from Figure 2.

The components making up the air gap arrangement 10 associated with each of the stud terminals 1 include a flanged sleeve 14 of insulating material mounted on the stud terminal 1 within the housing 2. The unflanged end of this sleeve 14 bears on the nut 11B that is also within the housing 2 and on this end of the sleeve 14 there is mounted a first washer 15A of electrically conductive material. Sandwiched between this first washer 15A and a second washer 15B of electrically conductive material is a washer 16 of electrically insulating material. Sandwiched between the second washer 15B and the flange 14A of the sleeve 14 is a ground connector tag 17 of the ground connector lead 9 (Figure 1), not shown in Figure 2. Between the sleeve flange 14A and a washer 18 there is the line tag 6 shown also in Figure 1.All of the components 18, 6, 14A, 17, 15B, 16, 15A and 14 are held in closely abutting relationship with each other and (in the case of the washer 15A and the unflanged end of the sleeve 14) with the nut 11B within the housing 2 by a further nut 19 screwed onto the inner end of the stud terminal 1.

The aperture in the washer 16 of electrically insulating material through which the sleeve 14 passes is over-sized as compared with the sleeve 14 so that there is an air gap 20 between the insulating washer 16 and the sleeve 14. The sleeve 14 is, however, a close fit in the apertures through which it passes in the washers 15A and 15B so that these washers, which are of electrically conductive material, bound the air gap 20 on either side.

The washer 15A, held in abutting relationship with the nut 11B, is thereby in electrical contact with the stud terminal 1, the nut 11B being of electrically conductive material. The washer 15B and the ground connector tag 1 7 are electrically insulated from the stud terminal 1 by the electrically insulating washer 16 and the insulating sleeve 14. The line tag 6 is in electrical contact with the stud terminal 1. Thus there is a permanent line from the stud terminal 1 via the line connector tag 6 to the excess voltage arrestor 3.

In the event of excess voltage, the excess voltage arrestor 3 will normally operate to connect the line to ground at the ground terminal 8. Should the excess voltage arrestor fail to do so, discharge to ground, at a sufficiently high voltage, will then take place across the air gap 20, which thus gives a back-up protection. Typical dimensions to give the desired back-up protection are 0.06mum - 0.1 mm for the electrically insulating washer 16, 7.00mm - 7.25mm aperture diameter in this member 16 and 6.50mm - 6.55mm outside diameter for the part of the sleeve 14 that passes through this aperture.

It is to be noted that the air gap arrangement 10 is provided as a part of an assembly that includes the stud terminal, and that any component for which the protection offered by the air gap arrangement is required can be connected to the line tag 6.

Claims (5)

1. An air gap arrangement in an otherwise electrically conductive line for permitting current flow at voltages above a predetermined value, the air gap arrangement comprising two apertured electrically conductive members in series in the line and held in non-conducting relationship by an apertured first electrically insulating member, all three members being mounted on a second electrically insulating member passed though the apertures in the other members, the aperture in the first insulating member being over-size with respect to the second insulating member so that there is an air gap between the first and second insulating members, the apertures in the two electrically conductive members being smaller than the aperture in the first electrically insulating member so that this air gap is bounded on each side by the two electrically conductive members, the distance between the two electrically conductive members being such that current flow from one to another across the air gap will take place at voltages higher than the predetermined value.

2. An air gap arrangement as claimed in claim 1, wherein the second electrically insulating member is a sleeve that is mounted on an electric terminal and is held thereon by retaining means serving to maintain the two apertured electrically conductive members and the first electrically insulating member in abutting relationship with one of the apertured electrically conductive members in electrical connection with the terminal, the other apertured electrically conductive being held out of conducting relationship with the terminal by the sleeve.

3. An air gap arrangement as claimed in claim 2, wherein said other of the apertured electrically conductive members is for connection in a circuit arrangement in parallel with an electrical component connected to the terminal whereby current flow is normally via the component, but is across the air gap to bypass the component if the component does not operate in a predetermined manner.

4. An air gap arrangement as claimed in claim 3, wherein the electrical component is an excess voltage arrestor having a terminal connected to ground, and wherein the connection of said other conductive member is to ground.

5. An air gap arrangement substantially as hereinbefore described with reference to the accompanying drawing.