FIELD OF THE INVENTION

[001] The present invention is related to gas insulated switchgear. More specifically, the present invention is related to reducing abrasive wear of components in kinematic chains of such switchgear.

BACKGROUND OF THE INVENTION

[002] A gas insulated switchgear typically comprises one or more equipment such as, but not limited to, a circuit breaker, an interrupters, and a resistor. These equipment are enclosed in a sealed tank and the insulation is provided with an insulating gas such as SF ₆ . Switches of such equipment can be operated with kinematic chains. For example, there could be a switch which has a movable contact and a fixed contact, wherein the movable contact is connected with a kinematic chain.

[003] The kinematic chain can have different components such as a mechanism for driving (e.g. a drive), and connections for transmitting motion from the driving mechanism to the corresponding switching contact. These connections may include, but need not be limited to, connecting rods, rollers, levers and links. In regular operation, these components may interface with each other for opening or closing corresponding switches. As a result of such interaction, there could be abrasive wear of such components resulting in generation of metal particle. There is a chance of leakage of such metal particles into the housing or other components of the switchgear. This could be detrimental for the gas insulated switchgear.

[004] Consider a gas insulated switchgear, where a circuit breaker is used to do switching of current both in normal and abnormal condition. Sometimes such a circuit breaker comes with a combination of a main switch and a closing resistor switch in order to have an additional function to overcome electrical stresses. Such stresses may come for example from switching of overhead long distance transmission lines. The closing resistor switch typically consists of a mechanism housing, in which the closing resistor switch mechanism runs in order to delay contact closing/opening of the resistor switch with respect to main switch. There is generally at least one roller and one lever in the closing resistor switch mechanism to transmit motion from a drive to a switching contact during closing operation.

[005] In full open condition of the switch, the roller and the lever are completely separated from each other. When the mechanism starts to move towards the close position, the roller hits onto the lever and pushes the lever towards the close position and during this operation the roller rubs over the lever surface. Both of these components are generally made out of high carbon steel and have hardness of around 70 HRC. High voltage circuit breakers need to be tested for mechanical endurance of around 10,000 close & open operations. During the test, this mechanism is operated 10,000 times and after some operations, the contact surfaces of roller and lever start to erode due to higher operating velocity and contact pressure, causing lots of metal particle generated in the vicinity.

[006] These metal particles tend to spread around the circuit breaker chamber during switching or gas handling. Presence of these kind of metal particles reduces dielectric strength between live and earth part significantly inside such a circuit breaker chamber. In order to reduce generation of such metal particles, the components of kinematic chain are typically coated with zinc phosphate. However, even when coated with zinc phosphate, as mentioned after some operations, metal particles are generated. Further, if zinc phosphate is used, the material needs to be greased (approximate 1 micron).

[007] In place of zinc phosphate, other coating materials such as hard chrome, or chrome carbide weld overlay may be used. Alternately the kinematic chain component may be prepared from materials such tool steel, cemented carbide etc. However, even when these alternatives are used, the components have a higher abrasive wear rate (e.g. for about 6000 cycles).

[008] In view of the above, there is a need for improving the components of such kinematic chains, to minimize abrasive wear, thereby minimizing generation of metal particles.

SUMMARY OF THE INVENTION

[009] Various embodiments of the present invention relate to a switchgear with a kinematic chain for operating a switch of the switchgear. The switchgear can be a gas insulated switchgear. The switch can be a closing resistor switch, a switch of an intermpter and so forth.

[0010] In accordance with various embodiments, the kinematic chain comprises a roller assembly, and a lever and link assembly. The roller assembly comprises a roller that is attached with a rod. The rod is in turn connected with a drive such that the drive can transmit motion to a switching contact of the switch during switching via the rod and the roller.

[0011] In an embodiment, the roller is attached with a bracket for rolling about an axis of the bracket. This bracket is in turn attached with the rod (e.g. with a screw). The connection is such that the drive can impart a translational motion to the rod about a first axis. This translational motion causes the roller to come in contact with and move with a corresponding component of the lever and link assembly.

[0012] The lever and link assembly is connected with the switching contact. The lever and link assembly comprises one or more levers and links. For example, the lever and link assembly can have one lever and one link, or one lever two links, or two or more levers / links and such variations will be readily apparent to one of ordinary skill in the art. [0013] In an embodiment, the lever and link assembly comprises one lever and one link. The lever is mechanically coupled with the movement of the roller. For example, the translational motion of the rod can cause the roller to come in contact with and move the lever. Further, the lever can be pivoted at an end, such that the lever can rotate about an axis as a result of the coupling with the roller.

[0014] The link is mechanically coupled with the movement of the lever. In an embodiment, the link is attached to the lever at a portion of the lever. In accordance with the embodiment, the link has two arms attached with the lever. For example, the link arms can be attached with the lever using a pin. Thus, when the roller causes the lever to rotate about the pivot, the lever pushes the link (arms). In accordance with the embodiment, the switching contact is mechanically coupled with the movement of the link. The switching contact can be a movable contact (e.g. pin or tulip), connected with the link. Thus, the feed from the drive can lead to closing the switch (e.g. closing resistor switch, interrupter switch etc.).

[0015] Thus, various components of the kinematic chain interact during opening / closing of the switch. In particular, there is contact between the roller(s) and the lever(s), which can cause wear and tear of these components. In the present invention, in accordance with various embodiments, an outer surface of the roller and an outer surface of the lever comprises tungsten carbide/carbon (also referred as‘tungsten carbide carbon’ or‘WC/C’). In an embodiment, the roller and the lever are machined out of wrought high carbon steel. This provides a roughness value required to coat the corresponding components with tungsten carbide/carbon.

[0016] The contact surfaces of the roller(s) and the lever(s) comprise tungsten carbide/carbon. In an embodiment, the outer surface of the roller is a cylindrical surface that contacts with a corresponding planar surface of the lever. In accordance with the embodiment, the planar surface of the lever is the outer surface comprising tungsten carbide/carbon. [0017] In an embodiment, each outer surface, i.e. the outer surface of the roller (e.g. cylindrical surface) and the outer surface (e.g. the planar surface) of the lever, has a coating of tungsten carbide/carbon. Further, the coating is such that it has certain desired properties including one or more of, but not limited to, a micro hardness of 1500 (HK 0.01), a coating thickness of 1 - 4 (pm), and a co-efficient of friction against steel of 0.1 - 0.2.

[0018] In an embodiment, each of the roller and the lever is coated with zinc phosphate and tungsten carbide/carbon. In accordance with the embodiment, the component is first coated with zinc phosphate, wherein a coating thickness of 5 (pm) is maintained. Thereafter, the coating of tungsten carbide/carbon is applied.

[0019] Thus, each of the roller and lever at least has an outer surface having tungsten carbide/carbon. Further, the roller and / or lever surface may have both zinc phosphate and tungsten carbide/carbon, wherein the component can be machined out of wrought high carbon steel.

BRIEF DESCRIPTION OF DRAWINGS

[0020] The subject matter of the invention will be explained in more detail in the following text with reference to exemplary embodiments which are illustrated in attached drawings in which:

[0021] FIG. 1 is an assembly view of a closing resistor switch mechanism in an open position inside a housing of a switchgear, in accordance with an embodiment of the invention;

[0022] FIG. 2 is an isometric view of a roller assembly, and a lever and link assembly, of the closing resistor switch mechanism, in accordance with the embodiment; [0023] FIG. 3 is an assembly view of the closing resistor switch mechanism in a close position inside the housing, in accordance with the embodiment;

[0024] FIG. 4 shows a kinematic chain mechanism, in accordance with another embodiment of the invention; and

[0025] FIG. 5 is a two dimensional view illustrating coatings on surfaces of a lever and a roller, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

[0026] Various embodiments of the present invention relate to a switchgear with a kinematic chain for operating a switch of the switchgear. The switchgear can be a gas insulated switchgear. The switch can be a closing resistor switch, a switch of an intermpter and so forth.

[0027] FIG. 1 is an assembly view of a closing resistor switch mechanism (100), in accordance with an embodiment of the invention. In FIG. 1 the switch is in an open position inside a housing (102) of the switchgear.

[0028] The kinematic chain shown in FIG. 1 comprises a roller assembly, and a lever and link assembly. As shown, the roller assembly comprises a roller (104) that is attached with a rod (106). The rod is in turn connected with a drive (not shown in figures) such that the drive can transmit motion to a switching contact (not shown for embodiment of FIGS. 1 - 3) of the switch during switching via the rod and the roller.

[0029] The roller is attached with a bracket (108), as shown in FIG. 2. Here, the roller is mounted on a pin, for rolling about an axis (110) of the bracket. This bracket is attached with the rod (e.g. with a screw). The connection is such that the drive can impart a translational motion to the rod about a first axis (112). This translational motion causes the roller to come in contact with and move with a corresponding component of the lever and link assembly.

[0030] In the embodiment of FIG. 1 , the lever and link assembly comprises a lever (114) and a link (116). The lever is pivotally connected (118) with the mechanism housing, and it can freely rotated once the drive (not shown here) force comes through the roller assembly. The lever is further connected with the link as shown. The link is an intermediate connection between the switching contact (e.g. a moving pin or tulip, not shown in FIG. 1) and the lever.

[0031] Once the roller assembly starts to move towards the lever, both lever and roller slides through a lever surface (120). FIG. 3 is an assembly view of the mechanism inside the mechanism housing in a close position. Until the close position, the roller always has a rotating movement and connection with a corresponding surface of the lever.

[0032] In the embodiments shown in FIGs. 1 - 3, the roller assembly has one roller, and the lever and link assembly has one lever and one link (see Fig. 2). The link has two arms (202a, 202b) attached with the lever (e.g. with a pin at (204)) such that the link has a translational motion proportional to the movement of the rod (i.e. controlled with the drive), leading to operating the switching contact.

[0033] There could be variations in the kinematic chain mechanism, and there could be differences in the roller assembly, the lever and link assembly, and connections thereof. For example, there could be multiple rollers, levers and links, and such variations will be apparent to those of ordinary skill in the art. FIG. 4 shows a kinematic chain mechanism, in accordance with another embodiment of the invention. In the embodiment of FIG. 4, there are two rollers (402a, 402b), and two levers (404a, 404b).

[0034] The rollers are provided on a slider (406), which is attached with an interrupter rod (not shown here). Here, the intermpter rod can drive the slider, causing the slider to move along a first axis (408), as per the movement of the interrupter rod during opening/closing of the interrupter. The slider can be in the shape of a substantially hollow cylinder such that it can slide over a substantially cylindrical member.

[0035] As shown, the lever and link arrangement comprises two levers (404a, 404b), symmetrically arranged, which can be used as cam to provide desired operation. For example, each lever can be pivoted as shown at 410, and connected to its respective links (e.g. 411, 412) at a portion (414) to transfer motion from the lever(s) to a moving contact (416) of a resistor switch, which in this case is an arcing pin.

[0036] At one end, the levers are connected to the slider through the pair of rollers (402a, 402b), which are symmetrically arranged about the slider. The pair of rollers are arranged such that when the slider is driven by the interrupter rod of the interrupter, the pair of rollers come in contact with and push the levers. In other words, the rollers are physically separated from the lever in the beginning and push the levers later as a result of the translational motion of the slider. The lever and link arrangement enables the movable contact of the switch to move proportionally in response to movement of the intermpter.

[0037] As the various components of the kinematic chain interact during opening / closing of the switch, there is contact between different components. For example, there is contact between the roller(s) and the lever(s), which can cause wear and tear of these components. Further, there could be difference in the amount of contact forces in different positions, interactions. For example, at the close position shown in FIG. 3, the contact force between the roller and lever surfaces could be the highest.

[0038] In accordance with the present invention, outer surfaces of the roller(s) and the lever(s) are made using tungsten carbide/carbon. In one embodiment, the roller(s) and the lever(s) are machined out of wrought high carbon steel. This provides a roughness value required to coat the corresponding components with tungsten carbide/carbon. [0039] The outer surfaces made using tungsten carbide/carbon are the surfaces of the roller(s) and the lever(s) that contact during switching. For example, in the embodiment shown in Figs. 1 - 3, the outer surface of the roller and the lever can be coated with tungsten carbide/carbon. Here, as shown in Fig. 5, the outer surface of the roller is a cylindrical surface that contacts with a corresponding planar surface (refer 120, Fig. 1) of the lever. The cylindrical surface of the roller and the planar surface of the lever are the outer surfaces are coated with tungsten carbide/carbon, in accordance with the embodiment. The other outer surfaces of the lever may be masked during the coating process.

[0040] The table below shows coating parameters of the tungsten carbide/carbon coating, in accordance with the embodiment:

[0041] The outer surfaces may be coated with one or more materials. For example, the roller(s), lever(s) surfaces (of wrought high carbon steel) may be coated with zinc phosphate and tungsten carbide/carbon.

[0042] In one embodiment, the outer surfaces of the roller and the lever are coated with zinc phosphate and tungsten carbide/carbon. In accordance with the embodiment, the component (roller, lever etc.) is first coated with zinc phosphate (502a, 502b), wherein a coating thickness of 5 (pm) is maintained. Thereafter, the coating of tungsten carbide/carbon (504a, 504b) is applied. Here, the coating parameters of the coating of tungsten carbide/carbon are those as shown in the table above.

[0043] Thus, in accordance with the present invention, tungsten carbide/carbon is used on linkage surfaces. Further, such usage may be as a coating, in conjunction to a zinc phosphate coating. As a result of the same, there is reduction in friction coefficient, leading to reduction in abrasive wear. This improves life of mechanism components. Also, the surface on which the coating is applied has good surface finish (e.g. machined wrought high carbon steel), thereby achieving low coefficient of friction. Further, greasing is not required while applying tungsten carbide/carbon.