WO2015036897A1

WO2015036897A1 - A gear retainer assembly for a circuit breaker

Info

Publication number: WO2015036897A1
Application number: PCT/IB2014/064222
Authority: WO
Inventors: Krunal KANSARA; Amitabh KHANDKAR; Ashish Joshi; Kalpesh Chauhan; Navonil ROY
Original assignee: Abb Technology Ltd.
Priority date: 2013-09-13
Filing date: 2014-09-03
Publication date: 2015-03-19

Abstract

The invention relates to the field of electrical current interruption and provides a high voltage circuit breaker. The high voltage circuit breaker comprises a movable set of main (110) and arcing (120) contacts arranged at one end portion of a first metal tube (150) that is secured to one of a connection flange (155) of the high voltage circuit breaker. The high voltage circuit breaker has a cooperating and fixed set of main (130) and arcing (140) contacts, the arcing contact adapted to be displaced axially with help of a gear assembly (170), arranged at one end portion of a second metal tube (160) that is connected through a sliding contact means to another connection flange (165). A gear retainer (180) secured with the gear assembly (170) is provided in the high voltage circuit breaker wherein, the gear retainer is mechanically coupled to the second metal tube (160) using a pipe thread (310) on the gear retainer and on the second metal tube (160).

Description

A Gear Retainer Assembly for a Circuit Breaker

FIELD OF THE INVENTION:

The invention relates to the field of electrical current interruption. The present invention specifically relates to a gear retainer assembly for a high voltage circuit breaker.

BACKGROUND OF THE INVENTION:

A high voltage circuit breaker is used for current interruption in a high voltage system. A high voltage circuit breaker generally comprises an elongated casing of insulating material which is filled with a gaseous arc-extinguishing medium (example SF6) with connection flanges at the ends of the elongated casing to connect the ends of the line that needs to be interrupted or connected. The casing encompasses a contact device with cooperating fixed and movable main and arcing contacts.

The main contacts support the line current under normal operating conditions and the arcing contacts provides the current path during current interruption. The fixed contacts are arranged at one end portion of a first metal tube which is secured to one of the connection flanges of the circuit breaker, whereas the movable contacts are arranged at one end portion of the second metal tube, which is connected via an operating rod to an operating device (gear retainer) and, by means thereof, is axially displaceable in the casing between a closed and an open position. The second metal tube is permanently connected, via a sliding contact means and is secured to the other connection flange of the circuit breaker. The metal tubes form the high voltage tank that are maintained at electric potentials as that at the connection flanges and offers current path to the line current in normal operating conditions and during arc interruption.

The electric current path flowing through the circuit breaker is categorized as a lower current path through the first metal tube and upper current path through the second metal tube. The first and second metal tubes are in contact through contact fingers that are arranged in the second metal tube and carrying rated current. Therefore, the contact fingers are part of the upper current path. During current interruption, the moving contacts are operated that results in breaking causing an arc between arcing contacts. The arc current is passed through the second metal tubes connecting the arcing contact associated with the second metal tube. The arcing contact is operated by a moving gear which is housed in a gear retainer. The gear retainer transfers the arcing current from arcing contact to the second metal tube. Therefore the gear retainer should be capable of carrying the rated arc current during current interruption and also offer means to transfer the arcing current. It is to be recognized that the resulting current during arcing is very high in magnitude, in order of hundreds of Ampere to thousands of Ampere and therefore needs to be handled (carrying and transferring) effectively with means that offer current carrying capacity and less resistance in the current carrying (including transferring) path.

The present invention discloses a low cost arrangement for effectively transferring the arcing current from arcing contact to the second metal tube in a high voltage circuit breaker.

BRIEF DESCRIPTION OF THE INVENTION:

The main aspect of the invention is to provide a high voltage circuit breaker that offers easier manufacturability of its component and be also a low cost solution with performance being comparable with prior-art solutions. Specifically, the invention deals with manufacturability and coupling of aluminum upper current tube (second metal tube) with gear retainer which is part of the gear assembly used in the circuit breaker. The gear retainer is mechanically coupled to the second metal tube using a pipe thread on the gear retainer and on the second metal tube. The coupling is made such that the arcing current from the arcing contact of the circuit breaker is transferred to the second metal tube through the pipe thread coupling assembly and meet the specification defined for the circuit breaker.

The high voltage circuit breaker has the gear retainer secured with the gear assembly using screw joints. The threaded coupling between the gear retainer and the upper current tube is positioned with help of a shoulder step provided in the upper current tube to position the gear retainer inside the high voltage circuit breaker. The shoulder step also provides electrical contact with the gear retainer and contributes to transfer of arcing current from the arcing contact to the second metal tube. BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages will become apparent to those skilled in the art upon reading the description of the preferred exemplary embodiments in conjunction with the accompanying drawings, wherein;

Figure 1 illustrates a high voltage circuit breaker depicting major components;

Figure 2 illustrates a high voltage circuit breaker depicting (a) the flow of arcing current during current interruption and (b) crimping means to secure upper current tube to the gear retainer; and

Figure 3 illustrates a high voltage circuit breaker depicting (a) the flow of arcing current during current interruption and (b) threading means to secure upper current tube to the gear retainer; and

DETAILED DESCRIPTION OF THE INVENTION

An exemplary gas insulated high voltage circuit breaker as depicted in Figure 1. As described earlier, the casing (not shown in the figure) encompasses a contact device with cooperating movable (1 10, 120) and fixed (130, 140) main and arcing contacts.

The main contacts (1 10, 130) support the line current under normal operating conditions and the arcing contacts (120, 140) provides the current path during current interruption. "The set of movable contacts are arranged at one end of a first metal tube 150 which is secured to the first connection flange 155 of the circuit breaker. The set of movable contacts are axially displaceable in the elongated casing between a closed and an open position. The fixed contact 130 is arranged at one end of the second metal tube 160. The arcing contact 140 which is also arranged in metal tube 160 is connected via an operating rod to an operating device 170 (gear assembly comprising of a gear and drive mechanism to move the contacts during opening and closing operation of the circuit breaker). The first metal tube 150 is permanently connected, via a sliding contact means (not shown in the figure) to the second connection flange 155 of the circuit breaker. The metal tubes are maintained at electric potentials as that at the connection flanges and offers current path to the line current in normal operating conditions and during arc interruption. The main purpose of a gear retainer (180) in a circuit breaker is to hold gear assembly and to have means to transfer the arc current from the arcing contact (140) to the upper current tube (160). The means to transfer the arc current from the arcing contact to the upper current tube needs to be efficient to ensure minimal contact resistance. The various components that take part as a current carrying component are designed to be capable to carry the specified current in normal operating conditions including arc interruption and fault conditions. Prior-art methods include use of metallic (example aluminium, copper or alloys) components secured to each other with use of screw joints, a large number of screws may be used to reduce contact resistance; or secured with crimps.

To concept designed for securing with multiple screw joints commonly have flanged provided for placement of the multiple screws used for joining. Space and assembly wise, a crimping method may be more efficient. As an example, a design of tube providing upper current path with copper alloy and crimping is shown in Figure 2. The arcing current path is shown in Figure 2(a) with numeral 210; where 210a represents the current path through the arcing contact (140), the current path through the gear retainer is represented with 210b, and the current path through the tube (second metal tube) is represented with 210c.

In this example, the gear retainer (180) is made of rolled in (crimping) process and gets its position to hold the gear assembly (170) as shown in Figure 2. The second metal tube provides an upper current path (210c) and is made of copper alloy to have good conductivity since it needs to carry the rated current. This is also crimped (220) to assemble onto the gear retainer (180) as shown in Figure 2(b). Copper is an expensive material and the crimping process is very complex, thereby the manufacturing expertise may be limited to selected vendors. This makes the entire product quite expensive, especially for cost sensitive markets.

To drive the cost effective measure and manufacturing friendly design, the second metal tube providing the upper current path has been converted to aluminium alloy, and the crimping process is removed. This leads to a design change of gear retainer. The new design with aluminium alloy is made equivalent in performance i.e. it needs to carry the specified current offering about the same electrical contact resistance for the arc current. The new design (refer Figure 3) using aluminium alloy is made with introduction of a pipe thread (310) in the gear retainer for fixing the gear assembly (170) with the aluminium tube (second metal tube, 160) providing the upper current path (210c) and carrying the arc current. This is made possible as a design using aluminium alloy is thicker compared with designs using copper alloy to have equivalent electrical resistance. Also a shoulder step (320) has been provided as a stopper arrangement to make sure positioning of the gear assembly inside interrupter.

The complexity of the assembly has been reduced by introduction of pipe thread (310) on the gear retainer (180) as well as upper current tube (160). These two parts are now coupled together by threading (310). Thereby the crimping process is completely removed. Special tool is used to make the assembly easier with proper torque. Also, the design is not based on securing the gear retainer with the upper current tube based on multiple screw joints.

In a prior-art design with crimping process, the arc current was passing through the crimped joint (220) between the gear retainer and the upper current tube (second metal tube). In the new design, the current is required to pass through the joint achieved through threading (310) without compromising the rated performance of the breaker. The contact area in the joint is accordingly designed to ensure effective joining during the entire duration of the passage of arc current. The butt joint (330) with the stopper (320) is also contributing to the passage of arc current as the joint provides a contact pressure similar to that through multiple screw joints when tightened through the threads.

Thus, the new gear retainer is designed in such a way that it is seated along its position through pipe threading with the upper current tube for carrying the arc current.

The solution leads to a simpler, cost effective and manufacturing friendly design which takes care of technical feature like carrying the rated arc current and proper positioning of the gear assembly inside interrupter. The key advantage is to get rid of expensive and complex crimping process without compromising on technical performance.

The invention is not limited to the embodiments shown, but several modifications are possible within the scope of the following claims.

Claims

CLAIMS:

1. A high voltage circuit breaker having connection flanges to connect in series in a high voltage line, the high voltage circuit breaker comprising: a movable set of main (110) and arcing (120) contacts arranged at one end portion of a first metal tube (150) that is secured to one of the connection flanges (155) of the high voltage circuit breaker; a cooperating and fixed set of main (130) and arcing (140) contacts, the arcing contact adapted to be displaced axially with help of a gear assembly (170), arranged at one end portion of a second metal tube (160) that is connected through a sliding contact means to the other connection flange (165); and a gear retainer (180) secured with the gear assembly (170); wherein, the gear retainer is mechanically coupled to the second metal tube (160) using a pipe thread (310) on the gear retainer and on the second metal tube (160).

2. The high voltage circuit breaker as claimed in claim 1 , wherein the gear retainer transfers the arcing current from the arcing contact to the second metal tube through the pipe thread.

3. The high voltage circuit breaker as claimed in claim 1, wherein the second metal tube is substantially made from aluminum.

4. The high voltage circuit breaker as claimed in claim 1, wherein the gear retainer is secured with the gear assembly using screw joints.

5. The high voltage circuit breaker as claimed in claim 1, wherein the second metal tube is provided with a shoulder step to position the gear retainer inside the high voltage circuit breaker.

6. The high voltage circuit breaker as claimed in claim 5, wherein the shoulder step provides electrical contact with the gear retainer and contributes to transfer of arcing current from the arcing contact to the second metal tube.