RÄTH, Bernd (Koalabärweg 3, Oberkrämer, 16727, DE)
PALAKURTHY, Ramamurthy (115/A, Satyanarayana Nagar Gudimalkapur, Hyderabad 8, 50002, IN)
RÄTH, Bernd (Koalabärweg 3, Oberkrämer, 16727, DE)
Patent claims
1. A switching device having a disconnecting mechanism (10) for detachably coupling a first (12) and a second (14) movable current path tube for controlling transfer of electrical current therebetween, said switching device comprising:
-a transfer contact system (26) for transferring electrical current from a rotatable terminal stem (30) to the first movable current path tube (12), said transfer contact system (26) further comprising at least one flexible braided conducting lead (36) rigidly fixed on both ends to said first current path tube (12) said at least one flexible braided conducting lead (36) being further in rigid contact with said terminal stem (30) at a point along its length intermediate to said ends.
2. The switching device according to claim 1, wherein said at least one flexible braided conducting lead (36) is formed from copper and comprises a tin plating.
3. The switching device according to any of the preceding claims, comprising a plurality of flexible braided conducting leads (36) rigidly fixed on both ends to said first movable current path tube (12) by tin plated lugs (38, 40) .
4. The switching device according to any of the preceding claims, wherein said terminal stem (30) are made of an aluminum alloy.
5. The switching device according to any of the preceding claims, further comprising a main contact system (16) adapted for electrically coupling said first (12) and second (14) movable current path tubes, said main contact system (16) further comprising:
- a female contact interface (18) associated with the first movable current path tube (12) and comprising a pair of contact fingers (50, 52), and - a male contact interface (20) associated with the second movable current path tube (14) and comprising a contact block (54) having a circumferential groove around its surface, adapted to provide two contact points (56 58) for transfer of electrical current to the female contact interface (18) .
6. The switching device according to claim 5, wherein said contact fingers (50, 52) and contact block (54) are formed from copper and coated with a material comprising silver, or graphite, or combinations thereof. |
Description
Disconnector for a switching device
The present invention relates to switchgears, particularly to a horizontal center-break type disconnecting mechanism for a switching device.
A disconnector is an assembly which, when installed in the head of a switchboard, has the function of assuring the interruption of the voltage supply line to the switchboard when the disconnector is open, thus isolating the switchboard from electric supply. A commonly known type of disconnector comprises a horizontal arrangement having a detachable current path, including pair of movable tubes or blades. The two moving blades are detachably coupled to each other and can occupy two positions, namely a closed position wherein the blades are in electrical contact with each other via a main contact system, and an open position wherein the two blades rotate about an axis perpendicular to their length such that the electrical contact between them is broken. The disconnector assembly also includes a pair of transfer contact systems for connecting the moving blades, at either ends, to the electricity supply and to the distribution bus bars of the switchboard.
In a typically known horizontal center-break type disconnecting mechanism, the main contact configuration consists of female contacts, provided on one of the moving blades, comprising helicoil springs (typically made of stainless steel) to exert a positive contact pressure for transfer of current and also to ensure proper contact to withstand to the electro-dynamic forces during the flow of fault current in the system. The female contacts are housed in the moving blade, which is generally made of an aluminum alloy. A male contact is provided on the other moving blade, and is formed out of two copper sheets and electro plated with silver coat to improve the conductivity and thermal
withstanding capability of contacts. However, this existing design of the main contact system has several disadvantages. During the open-close operation of the disconnector, the contacts are rubbed against each other during the course of motion of contacts, and requires lubrication to withstand to the frictional resistance. Unless this is lubricated at frequent intervals the silver layer gets eroded causing the damage to the contact. Further, the stainless steel helicoil springs used in the system also affects the functioning of the main contact system because, if the springs set permanently due to any reason over a period of time, the contact pressure will be lost causing the temperature rise thus burning the contact system itself.
In case of the transfer contact system, the existing design provides rotary terminal contact jaws with flat spring exerting pressure on a terminal stem (typically made of copper) to achieve the proper contact to transfer the current. Herein, the contacts are typically silver plated and during the rotary motion while open-close operation of the disconnector the silver face gets rubbed against the terminal stem. It is hence necessary to maintain a proper pressure of contacts on to the terminal stem, in the absence of which, the silver layer existing on terminal stem as well as on terminal jaws gets eroded, thus reducing the thermal capability of the contacts and increasing the temperature rise beyond the specification limits at transfer point. Hence, in case the transfer contacts are not lubricated at frequent intervals, the contact surface experiences a lot of friction, causing the damage to the silver plating of contacts which reduces the functionality and life the contacts .
It is an object of the present invention to provide a switching device having an improved disconnecting mechanism.
The above object is achieved by a switching device having a disconnecting mechanism for detachably coupling a first and a
second movable current path tube for controlling transfer of electrical current therebetween, said switching device comprising:
-a transfer contact system for transferring electrical current from a rotatable terminal stem to the first movable current path tube, said transfer contact system further comprising at least one flexible braided conducting lead rigidly fixed on both ends to said first current path tube said at least one flexible braided conducting lead being further in rigid contact with said terminal stem at a point along its length intermediate to said ends..
The underlying idea of the present invention is to provide a switching device having a horizontal center-break type disconnecting mechanism wherein the transfer contact system does not have any relative rotary motion between the transfer contacts. In accordance with the present invention, transfer of current takes place through the flexible braided conducting lead, which is rigidly fixed to the movable current path tube and to the terminal stem.
In one embodiment, said at least one flexible braided conducting lead is formed from copper and comprises a tin plating. The above provides particularly improved conductivity for the flexible braided conducting lead.
In a further embodiment, the switching device comprises a plurality of flexible braided conducting leads rigidly fixed on both ends to said first movable current path tube by tin plated lugs. The above improves current carrying capacity of the transfer contact system.
In a preferred embodiment, said terminal stem is made of an aluminum alloy. The above advantageously ensures that requires no silver plating is required on the terminal stem and the moving current path tube, and hence, the cost of material and plating is reduced.
In a particularly preferred embodiment, the switching device further comprises a main contact system adapted for electrically coupling said first and second movable current path tubes, said main contact system further comprising: - a female contact interface associated with the first movable current path tube and comprising a pair of contact fingers, and
- a male contact interface associated with the second movable current path tube and comprising a contact block having a circumferential groove around its surface, adapted to provide two contact points for transfer of electrical current to the female contact interface.
The above design obviates the need for helicoil springs, and thus prevents damage due to malfunctioning of springs takes place,
In a further embodiment, said contact fingers and contact block are formed from copper and coated with a material comprising silver, or graphite, or combinations thereof. The coatings of silver & graphite improves the properties of conductivity and contact self lubrication respectively.
The present invention is further described hereinafter with reference to illustrated embodiments shown in the accompanying drawings, in which:
FIG 1 is a schematic front view a switching device having a horizontal center-break type disconnecting mechanism,
FIG 2, is a schematic cross-sectional view of the transfer contact system of said horizontal center-break type disconnecting mechanism,
FIG 3, is a schematic top view of a female contact interface of the main contact system of said horizontal center-break type disconnecting mechanism, and
FIG 4 is a schematic front view of a male contact interface of the main contact system of said horizontal center-break type disconnecting mechanism.
Referring now to FIG 1, a disconnector 10 for a switching device is illustrated having movable current path tubes 12 and 14. In the shown example, the current path tubes 12 and 14 are moving blades made of an aluminum alloy material, and having a rectangular cross-sectional profile. In an alternate embodiment, the moving blades 12 and 14 may also be made of a copper alloy. The moving blades 12 and 14 are detachably coupled to each other and are capable to rotation about the axes 19 and 21 respectively to occupy two positions, namely a closed position and an open position. The configuration shown in FIG 1 represents the closed position wherein the moving blades 12 and 14 are in electrical contact with each other via a main contact system 16. In the open position, the moving blades 12 and 14 rotate about the axes 19 and 21 respectively in the indicated direction, such that electrical contact between them is broken. The main contact system 16 comprises a female contact interface 18, fixed to the moving blade 12 by studs 24, and a male contact interface 20, fixed to the moving blade 14 by studs 22. Each of the moving blades 12 and 14 are connected to the to the electricity supply and to the distribution bus bars via transfer contact systems 26 and 28 having rotatable terminal stems 30 and 32 respectively. In the illustrated embodiment, the terminal stems 30 and 32 extend upwards from the moving blades 12 and 14 and are each further connected to a rotation unit (not shown) adapted for actuating rotation of the terminal stems 30 and 32 about the axes 19 and 21 respectively. Each rotation unit (not shown) incorporates a rotation mechanism typically comprising two ball-bearings and is designed for high mechanical loads.
FIG 2 is a cross-sectional view illustrating the components of the transfer contact system 26. It may be appreciated that a similar description may apply to the transfer contact
system 28. As shown, the transfer contact system 26 is partially contained in a housing 42 which is fixed to the moving blade 12 via studs 43 and 45. Insulation of the terminal stem 30 is provided by bushings 39, typically formed from nylon. In the transfer contact system 26, current is transferred from the rotatable terminal stem 30 to the moving blade 12 by one or more highly flexible braided conducting leads 36. In the illustrated embodiment, the conducting leads 36 are made of copper and comprise a tin plating. Unlike in existing designs, in this embodiment no silver coating is required. Silver plating incurred additional material cost in the existing designs. Further consequently, this embodiment does away with erosion that generally takes place in the silver coating. Also, the terminal stem 30 in the shown example is made of an aluminum alloy material, whereby no silver plating is required, thus further reducing material cost .
Single or multiple flexible braided conducting leads may be provided based upon the required amperage. The flexible braided conducting leads 36 are rigidly fixed on both ends to the moving blade 12 by tin plated lugs 38 and 40. The flexible braided conducting leads 36 extend in a generally horizontal orientation, extending upwards to be in rigid contact with the terminal stem 30 via washer 41. In the shown embodiment, the point of rigid contact of the flexible conducting leads 36 with the terminal stem 30 is about the center of the length of the flexible conducting leads 36. This provides two parallel paths for transfer of current between the terminal stem 30 and the moving blade 12, thus enhancing the current carrying capacity of the transfer contact system 26. This design employing flexible conducting leads ensures that the transfer contact system 26 does not have any relative rotational motion between the transfer contacts (between the terminal stem 30 and the conducting leads 36, and between the conducting leads 36 and the moving blade 12) . The above-described design advantageously provides easy assembly of the components and cheaper manufacturing
obviating the need for CNC. Further, the design maximizes surface dissipation of heat. Unlike in existing designs, the illustrated embodiment obviates the need for terminal jaws or any contact pressure since both ends are rigidly fixed of the conducting leads 36 are fixed. Further, since the conducting leads 36 are flexible, no helicoil springs are required, thus obviating any manufacturing inconsistency or damage to the transfer contacts.
Components of the main contact system 16 are illustrated referring to FIG 3 and FIG 4. Referring to the top view in FIG 3, a female contact interface 18 comprises fingers 50 and 52 fitted in finger blocks 53. The contact fingers 50 and 52 are typically made of copper. Referring to the front view in FIG 4, the male contact interface 20 includes a contact block 54 that fits between the contact fingers 50 and 52 during closed operation of the disconnector. The male contact block 54 has a V-groove around its circumference, such that the contact block 54 has two contact points 56 and 58 for transfer of current for each finger when the disconnector is in a closed position. The male contact block 54 may also be formed of copper. The contact fingers 50 and 52 and the male contact block 54 are may be with silver & graphite for improving the conductivity and contact self lubrication respectively. The above advantageously reduces the maintenance and servicing of the main contact system. Further, in the illustrated embodiment, no helicoil stainless steel springs are required, and hence, no damage due to malfunctioning of springs takes place.
Summarizing, the present invention deals with a switching device having a disconnecting mechanism for detachably coupling a first and a second movable current path tube, for controlling transfer of electrical current therebetween. The switching device comprises a transfer contact system for transferring electrical current from a rotatable terminal stem to the first movable current path tube. The transfer contact system comprises at least one flexible braided
conducting lead rigidly fixed on both ends to the first current path tube. The flexible braided conducting lead is further in rigid contact with the terminal stem at a point along its length intermediate to said ends.
Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the spirit or scope of the present invention as defined.