WO1997022129A1

WO1997022129A1 - Attachment means for mounting a resistor in a sealing casing

Info

Publication number: WO1997022129A1
Application number: PCT/SE1996/001596
Authority: WO
Inventors: Tomas JIRÉNIUS
Original assignee: Asea Brown Boveri Ab
Priority date: 1995-12-08
Filing date: 1996-12-04
Publication date: 1997-06-19
Also published as: SE9504402D0; SE9504402L; SE504439C2

Abstract

The invention relates to attachment means for adjustably mounting a resistor (9) in a sealed casing, and is primarily intended for use in conjunction with start-up resistors in high power switch-gear, wherein the start-up resistancce is comprised of two mutually spaced resistor blocks which can be mutually coupled by means of a contact rod. The distance between the resistor blocks can be adjusted so as to adjust the start-up time of the start-up resistor. According to the invention, the attachment means is constructed to enable axial movement of one resistor block (9), by virtue of its attachment element being connected by screw threads with a casing cap or cover (14), so as to enable the longitudinal position of the resistor block to be adjusted by screwing the attachment element in or out. A sealing means is provided at the attachment element lead-through in the cap (14), such as to maintain the casing interior hermetically sealed. The position of the attachement element (13) is fixed by means of locking means (22).

Description

ATTACHMENT MEANS FOR MOUNTING A RESISTOR IN A SEALING CASING

The present invention relates to attachment means of the kind defined in the preamble of Claim 1.

Such attachment means are used primarily for the attachment of start-up resistances operating in high power switching gear. The start-up resistance is coupled in parallel with the switching gear itself and functions to dampen current transients when closing the switch gear, by virtue of the current being conducted via the start-up resistance prior to closing the main contact of the switch gear. The time required between activating the start-up resistance and closing the main contact is in the order of 5-15 ms.

One known start-up resistance of this kind is comprised of two mutually spaced resistor-packs and upon actuation a contact element, e.g. a rod-like element having a conductive part, is moved forwards so as to mutually connect the resistors and therewith switch-on the current. In order to avoid sparking, the resistors will preferably be spaced 85- 100 mm apart.

Manoeuvering of the contact element is coupled to the switch- gear manoeuvering mechanism such that current will begin to flow through the start-up resistance prior to closing the switch gear, the time required to this end corresponding to the aforesaid time range. This start-up time can be adjusted- by either adjusting the starting moment for manoeuvering the contact element in relation to manoeuvering of the switch gear and/or adjusting the speed at which the contact element moves. Alternatively, or complementary thereto, the distance between the two resistor blocks can be changed. Because this distance corresponds to the length of travel of the contact element, any adjustment will affect the operating time. The present invention is directed towards the adjustment possi¬ bility afforded by changing said distance. The start-up resistance is normally disposed in an hermeti¬ cally sealed casing made of electrically insulating material, usually porcelain, which encloses a gas of high dielectric strength, such as SFi , for instance. In known constructions for adjusting the distance between the resistor blocks, one resistor is dismantled from its fixed position in the casing and moved to a new position and fixed in said position with the aid of shims or the like, whereafter a gas-tight cap or cover is fitted onto the outside of the attachment. This method of adjustment requires the hermetic seal to be broken, therewith allowing the SF_j gas to escape and necessitating refilling of the casing. As a result, the adjustment proce¬ dure is both complicated and expensive.

Accordingly, the object of the present invention is to provide an adjustable resistor attachment means which enables the position of a resistor to be adjusted without emptying the casing of its gas content.

This object is achieved in accordance with the invention with an attachment means of the kind defined in the preamble of Claim 1 which includes the particular features set forth in the characterizing clause of said Claim.

As a result of the screw thread connection between the hole and the resistor attachment, the position of the resistor can be easily adjusted by turning the attachment in one or the other direction. Because the attachment element coacts sealingly with the hole, the position of the resistor can be adjusted without gas leaking from the container. The attach¬ ment element can then be readily fixed in position by locking means mounted on that part of the fastener element that extents out through the casing.

In a preferred embodiment of the invention, the seal is obtained with the arrangement of sealing means, preferably an O-ring, between the attachment element and the hole, wherein the attachment element will preferably have a smaller diameter in the region of the sealing element.

In another preferred embodiment, the locking means includes threads at the outer end of the attachment element, and a lock nut. These screw threads are preferably counter-directed to the adjustment threads, so as to obtain a counter locking effect. The screw threads may also have a different pitch and/or diameter or a complementary pitch and/or diameter.

To facilitate resistor adjustment, the outer end of the attachment element may have a profiled recess for receiving a turning tool ,

In still another preferred embodiment, the invention is applied in coaction with another resistor with which electri¬ cal connection can be achieved with the aid of an electric contact element and the distance to which can be regulated by said adjustment.

The aforedescribed embodiments and other advantageous embodiments of the invention will be apparent from the dependent Claims.

The invention will now be described in more detail with reference to a detailed description of a preferred embodiment of the invention and also with reference to the accompanying drawings, in which

Fig. 1 illustrates schematically a start-up resistance of the kind with which the invention can be suitably applied;

Fig. 2 is a longitudinal sectional view of an inventive attachment means;

Fig. 3 is an end view of the means shown in Fig. 2; and Fig. 4 is a longitudinal sectional view of an enlarged part of an attachment means according to a second embodiment of the invention.

Fig. 1 illustrates schematically a start-up resistance of the kind normally used in conjunction with switch gear for high- tension cables. The start-up resistance is adapted to be coupled in parallel to the switch gear itself, and switches- on the current immediately before the switch-gear is closed. The start-up time is in the order of 5-15 ms and results in reduced current surges when the switch gear is switched on.

The start-up resistance includes two resistor blocks 6, 9 which are mounted in a hermetically closed space 10 defined by an essentially cylindrical casing 11 made of an insulating material, normally porcelain. The space 10 is filled with a gas that has high dielectric strength, normally SF_j. The resistor blocks 6, 9 are fixed at respective ends of the casing 11 and are spaced apart at a distance sufficient to avoid sparking between the blocks, this distance being in the range of about 85-100 mm. The mutually facing ends of the resistor blocks 6, 9 are provided with electric contact elements 7 and 8 respectively.

The start-up resistance also includes an axially movable contact rod 3 by means of which the two resistor blocks can be mutually coupled. Fig. 1 shows the contact rod 3 in a non- circuit-making position. The contact rod 3 is made of conductive material and has an insulated part 4, shown furthest to the left in Fig. 1, and a non-insulated part 5 at its other end. Upon actuation of the start-up resistance, the contact rod 3 is moved to the right in Fig. 1 until its end reaches the contact element 8 of the right-hand resistor block 9, therewith coupling the resistor block 6, 9 through the medium of the two contact elements 7, 8 and the non- insulated part 5 of the conductive contact rod 3. Circuit-making movement of the contact rod 3 is achieved through the medium of a link arm 2 which is coupled mechani¬ cally with manoeuvering of the switch-gear via a manoeuvering mechanism 1, in a manner to obtain the aforesaid time difference. The manoeuvering mechanism may be of a known kind that finds use in conventional technics, and consequently its method of operation need not be known in detail in order to understand the present invention. The start-up time is influenced primarily by three parameters, namely the time at which movement of the contact rod 3 is started in relation to starting the switch-gear operating movement, the speed at which the contact rod moves, and the distance travelled by said rod. The first two parameters are determined by the design of the manoeuvering mechanism 1, while the last parameter is determined by the distance between the contact elements 7, 8 of respective resistor blocks 6, 9.

The manoeuvering mechanism can either be constructed so that the first two parameters will have a fixed, given value or to enable these values to be changed in given, predetermined steps. Both cases require the possibility of adjusting the distance between the resistor blocks. In the first-mentioned case, this is necessary to enable the start-up time to be changed, and in the second case in order to finely adjust the start-up time. The distance between the blocks is adjusted by adjusting the position of the resistor block 9 axially. Fig. 2 illustrates in more detail the manner in which this is achieved with the aid of the inventive attachment means for attachment of the resistor block 9.

Fig. 2 is an enlarged longitudinal sectional view of the resistor block attachment in a cap or cover 14 provided on the end wall of the casing 11. The cap is electrically conductive to allow current to flow through the start-up resistance to a conductor connection, not shown. The cap 14 is an integral part of the casing and sealed hermetically therewith. The cap 14 includes a hole 15 through which there extends an essentially cylindrical attachment element 13 which carries the resistor block 9 with the aid of a support tube 12 which is screwed firmly in a bore 16 provided in the inner end of the attachment element 13.

The attachment element is provided in the region of the inner wall of the cap 14 with external threads 19 which coact with corresponding internal threads 20 in the hole 15 provided in the cap. That part of the attachment element which lies axially outside the threaded section has a slightly smaller diameter and an axially inwards smooth section 18 and an axially outwards threaded section 28. Correspondingly, The hole 15 has a section of smaller diameter nearest the outer wall of the cap, where it sealingly embraces a corresponding section of the attachment element 13. That part of the hole of larger diameter is threaded solely in the vicinity of the inner wall of cap 14 and includes inwardly thereof a smooth section of sufficient length to embrace a part of the smooth element section of smaller diameter. In the illustrated case, the sealing element is an O-ring 21, which ensures that the lead-through is gas-tight.

A lock nut 22 is screwed onto the outer part of the attach¬ ment element and the end surface of said element has an hexagonal hole into which an hexagonal spanner or Allen key can be inserted for turning the attachment element. The threads 19, 20 operative in securing the attachment element 13 to the cap or cover 14 are directed oppositely to the threads 28 that coact with the lock nut 22.

The described attachment means functions as follows: When it is seen that the distance between the resistor blocks 6, 9 needs adjusting, the lock nut 22 is loosened from its abutment with the cap 14. The attachment element 13 can now be moved axially, by turning the element with a tool fitted into the hexagonal hole. The attachment element 13 is either screwed inwardly or outwardly on the threads 19, 20 to a position corresponding to the desired adjustment. The seal is maintained intact during this adjustment, by virtue of the O-ring 21. Subsequent to having made the adjustment, the nut 22 is screwed into abutment with the cap 14, so as to fix the attachment element 13 in its new position.

The threaded section 19 on the attachment element part of larger diameter has a length sufficient to provide the necessary adjustment range. The contact rod 3 will typically move at a speed of about 6 mm/ms, which requires an adjusting length of about 20 mm in order to change the start-up time by 3 ms.

The drawings also show an alternative possibility of locking the lock nut 22, wherein a nut-carried flange 24 is provided with arcuate slots 25 through which bolt fasteners 26 are screwed into the cap 14.

In the embodiment shown in Fig. 4, the smooth section of the attachment element has two part-sections 18a, 18b of mutually different diameters. The part-section 18a has the larger diameter which corresponds as close as possible to the inner diameter of the hole, so as to obtain a sealing function. The part-section 18b outwards of the part-section 18a has a slightly smaller diameter so as to form a gap between said section and the hole, this gap receiving a sealing O-ring 21. Mounted on the attachment element is a ring 27 which func¬ tions to hold the O-ring 21 in position relative to the attachment element 13 as said element is moved axially. Such a retaining ring may also be included in the embodiment illustrated in Fig. 2.

Claims

1. An attachment means for a resistor (9) mounted in a sealing casing (11, 14), and functioning to enable the resistor (9) to be adjustably mounted on one wall (14) of the casing (11, 14), wherein the attachment means includes

- an attachment element (13) having an essentially cylindri¬ cal part;

- an essentially cylindrical hole (15) provided in the casing (14) and through which the cylindrical part of the attachment element (13) extends;

- a locking means (19, 22, 26) functioning to secure the attachment element (13) in an axial direction; characterized in that - said cylindrical part and said hole (15) have mutually coacting first threads (19, 20) in the vicinity of the inner wall of the casing (14);

- said cylindrical part includes axially outside said first threads (19, 20) a smooth section (18, 18a, 18b) which coacts sealingly with said hole (15);

- and in that the attachment element (13) has a locking means receiving part on the outside of the casing (14).

2. Attachment means according to Claim 1 provided with sealing means (21) between said smooth section and said hole

(15).

3. Attachment means according to Claim 2 wherein said sealing means includes at least one O-ring (21).

4. Attachment means according to any one of Claims 1-3 wherein said smooth section (18) has a smaller diameter than the attachment element part provided with said first threads (19, 20).

5. Attachment means according to any one of Claims 1-3 wherein said smooth section has at least two part-sections (18a, 18b) of mutually different diameters.

6. Attachment means according to any one of Claims 1-5 wherein said locking means receiving part has second threads (28) and wherein said locking means (19, 22, 26) include a nut (22).

7. Attachment means according to Claim 6, wherein said first (19, 20) and said second threads (28) differ from one another with respect to at least one of the following: thread direction, thread pitch and thread diameter.

8. Attachment means according to Claim 6, wherein said means include means (26) for fixing the nut (22) in a position of rotation.

9. Attachment means according to any one of Claims 1-8, wherein that part of the attachment element which is located on the outside of the casing (14) has turning-tool receiving means (23).

10. Attachment means according to Claim 9, wherein said tool-receiving means comprises a profiled recess (23) in one end surface of the attachment element.

11. Attachment means according to any one of Claims 1-10, wherein said adjustable resistor (9) is adapted to coact with a further resistor (6), wherein both resistors (6, 9) are spaced from one another and can be coupled by means of a movable contact element (3), and wherein the distance between said adjustable resistor (9) and said other resistor (16) can be adjusted by adjusting the position of the adjustable resistor (9).

12. Attachment means according to Claim 11, wherein the distance travelled by the contact element (3) can be adjust¬ ed.

13. Attachment means according to any one of Claims 1-12, wherein said casing (11, 14) is at least partially comprised of an insulating material, preferably porcelain, and its interior is filled with gas, preferably SF_fi.