DESC:
BACKGROUND

FIELD OF THE INVENTION

The present invention relates generally to a system for increasing the durability of a disconnector and earth switch assembly that is used in gas insulated switchgears (GIS). More particularly, the present invention relates to a system that eliminates electrical stresses caused by metal or non-metal particles within a gas-filled insulating chamber of a GIS.

DESCRIPTION OF THE RELATED ART

Gas insulated switchgear (GIS) is a control system that prevents faults and power fluctuations in electrical power plants. Switchgears can include a combination of circuit breakers, disconnectors, and switches. Disconnectors having earth switches are used to protect circuit breakers. The disconnectors are placed on either side of the circuit breakers. This prevents aging of the circuit breakers in high voltage electrical circuits, as the circuit breakers cannot withstand high voltages for prolonged time. Voltage ratings of the high voltage electrical circuits are typically in the range of kilovolts. These disconnectors are also termed as isolators. When maintenance work needs to be executed on the circuit breakers working under high voltages, the disconnectors are required to isolate and discharge the circuit breakers before maintenance work is executed.

The disconnectors may include disconnecting switch and earthing switch in a gas-filled insulating chamber. The gas-filled insulating chamber includes gas insulation materials, such as sulphur hexafluoride (SF6). Moving contacts are utilized to open and close the disconnecting switch and the earthing switch. Motion of the moving contacts is achieved by employing various mechanisms. Some of the mechanisms that are used to facilitate the motion of the moving contacts include rack and pinion, ball and screw, scotch and yoke, cams and, gears. The aforementioned mechanisms are used to drive the moving contacts of the disconnecting switch and earthing switch to their open, neutral, and closed configurations and are generally placed within the gas-filled insulating chamber. In an example, the rack and pinion mechanism is placed inside the gas-filled insulating chamber.

Due to friction, the aforementioned mechanisms result in wear and tear of the mechanical components. As a result, minute metallic particles are produced and deposited in the gas-filled insulating chamber of the disconnector. Electric charges get deposited on the minute metallic particles that are deposited inside the gas-filled insulating chamber. Therefore, electric stresses are generated on the minute metallic particles, thereby resulting in electrical breakdown of the gas insulation material that is included in the gas-filled insulating chamber.

Also, there exist other prior art mechanism, wherein a first position of contacts results in disconnecting switch closed configuration, a second position of contacts results in earthing switch closed configuration, and a third position of contacts, intermittently positioned between the first position and the second position, results in a neutral configuration.

In light of the foregoing discussion, there exists a need for a system that prevents deposition of minute metallic particles in the gas-filled insulating chamber, reduces dimensions of the gas-filled insulating chamber and hence, reduces the dimension of the housing of the disconnector, increases electrical stress handling capability and more importantly, increases the reliability of the overall switchgear system. The system should exercise a precise control to obtain fast and distinct switching between the disconnecting switch closed, earthing switch closed, and neutral configurations. Further, the switching mechanism should be less complex, should have fewer moving parts and, should have fewer joints (to reduce friction) that are required for achieving the open, closed and neutral configurations of the disconnector. Finally, the system should achieve various configurations of the disconnector switch using only one moving contact and one motor to drive the moving contact.

OBJECTS OF THE INVENTION

An object of the present invention is to provide a novel driving mechanism that prevents breakdown of gas insulation material inside the disconnector and earth switch assembly.

Another object of the present invention is to provide a disconnector and earth switch assembly that is less complex, involves fewer moving parts and, includes less number of joints that are required for achieving the open, closed and neutral configurations of the disconnector.

Another object of the present invention is to provide a disconnector and earth switch assembly that exercises a precise control to obtain fast and distinct switching between the disconnecting switch closed, earthing switch closed, and neutral configurations.

Yet another object of the present invention is to reduce the operation and replacement costs of the disconnecting switch and earth switch housed inside the gas-filled insulating chamber and provide a stable electrical environment in switchgear systems.

Embodiments of the invention provide a disconnector and earth switch assembly for metal encapsulated, gas insulated high voltage switchgear. The disconnector and earth switch assembly includes first, second and third fixed contacts connected to first, second and third terminals, respectively. A housing made up of a conducting material is connected to the second fixed contact. A moving contact is disposed inside the housing and is linearly movable therein along a movable path between first and third fixed contacts. The moving contact is in constant electrical connection with the housing. An operating mechanism provides a translational motion to the moving contact within the housing to achieve first, second, and third configurations. In the first configuration, the moving contact is electrically connected to the first fixed. In the second configuration, the moving contact is isolated from the first and third contacts. In the third configuration, the moving contact is connected to the third fixed contact.

BRIEF DESCRIPTION OF DRAWINGS

The features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. Embodiments of the present invention will hereinafter be described in conjunction with the appended drawings provided to illustrate and not to limit the scope of the claims, wherein like designations denote like elements, and in which:

Fig. 1A is a sectional view of disconnector and earth switch assembly along XY plane, in a disconnecting switch closed position, according to an embodiment of the present invention;
Fig. 1B is a sectional view of the disconnector and earth switch assembly along XY plane, in a neutral position, according to an embodiment of the present invention; and
Fig. 1C is a sectional view of the disconnector and earth switch assembly along XY plane, in an earth switch closed position, according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

As used in the specification, the singular forms “a”, “an” and “the” include plural references unless the context clearly dictates otherwise. For example, the term “an article” may include a plurality of articles unless the context clearly dictates otherwise.

Those with ordinary skill in the art will appreciate that the elements in the figures are illustrated for simplicity and clarity and are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated, relative to other elements, in order to improve the understanding of the present invention.

There may be additional components described in the foregoing application that are not depicted on one of the described drawings. In the event such a component is described, but not depicted in a drawing, the absence of such a drawing should not be considered as an omission of such design from the specification.

Before describing the present invention in detail, it should be observed that the present invention constitutes a novel disconnector and earth switch assembly having disconnecting switch and earthing switch, wherein the disconnector and earth switch assembly has increased reliability. Such disconnector and earth switch assembly finds applications in gas insulated switchgears (GIS). Further, the disconnecting switch and the earthing switch in the disconnector and earth switch assembly protect vital electrical components like the circuit breakers that are in series with the disconnector and earth switch assembly. Accordingly, the components and the method steps have been represented, showing only specific details that are pertinent for an understanding of the present invention so as not to obscure the disclosure with details that will be readily apparent to those with ordinary skill in the art having the benefit of the description herein.

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting but rather to provide an understandable description of the invention.

It will be apparent to those skilled in the art that all the above mentioned components in a system are not restricted, as disclosed herein. This is done for illustrative purposes and also for ease of understanding. Hence, it should not be considered as a limitation in any way. The description relating to the functioning of the system as mentioned above follows the best mode of practicing the invention. The invention however, can be practiced in many ways other than the one disclosed.

Various embodiments of the invention described herein focus primarily on reducing the electrical stress caused by the metal particles in a sulfur hexafluoride (SF6) gas-filled insulating chamber of the disconnector and earth switch assembly, wherein the gas-filled insulating chamber houses the disconnecting switch and earthing switch. The objective of reducing the electrical stress in the SF6 gas-filled insulating chamber is achieved by modifying the control mechanism that achieves the switching between the states of disconnecting switch closed, earth switch closed and, neutral configurations of the disconnector and earth switch assembly.

Another embodiment of the present invention described herein focuses on reducing the complexity of the disconnector and earth switch assembly by employing a worm and roller rack mechanism to drive the disconnector and earth switch assembly to open, close and neutral positions. Further, by employing worm and roller rack mechanism, only one motor is required for the operation of the disconnector and earth switch assembly.

Referring now to FIG. 1A, a sectional view of the disconnector and earth switch assembly 100 along XY plane in a disconnecting switch closed position, according to an embodiment of the present invention is shown. The disconnector and earth switch assembly 100 includes an aluminium enclosure 102, a sulfur hexafluoride (SF6) gas-filled insulating chamber 104, a first fixed contact 106, a second fixed contact 108, a third fixed contact 110 (hereinafter referred to as “earth connection 110”), a housing 112, a moving contact 114, a roller rack 116, a worm drive 118, and a plurality of spacers including first through sixth spacers 120a-120f (collectively referred to as spacers 120). The moving contact 114 is utilised for achieving all the switching configurations of the disconnector and earth switch assembly 100. The disconnector and earth switch assembly 100 is placed on either side of a circuit breaker (not shown) to prevent aging of the components of the circuit breaker. Epoxy compounds and nozzles in the circuit breaker tend to age if kept under constant electrical stress caused due to prolonged exposure to high voltages. If the disconnector and earth switch assembly 100 is absent, the circuit breaker will be under constant load of high voltage which can damage the circuit breaker.

The aluminium enclosure 102 houses the SF6 gas-filled insulating chamber 104. The SF6 gas inside the gas-filled insulating chamber 104 is maintained at a pressure of 8 bar to provide the required insulation to a live connection inside the aluminium enclosure 102 as the aluminium enclosure 102 is connected to ground. The potential difference between the aluminum enclosure 102 and the live connection creates a high electric field region within the gas-filled insulating chamber 104. The spacers 120 provide support to the live connection from the aluminium enclosure 102 inside the disconnector and earth switch assembly 100. The spacers 120 also help in maintaining the pressure of the SF6 gas inside the gas-filled insulating chamber 104. Further, the moving contact 114, the housing 112, the roller rack 116 and the worm drive 118 are also placed inside the aluminium enclosure 102.

The worm drive 118 is connected to a motor (not shown) which rotates the worm drive 118. The worm drive 118 is made of an insulating material. The roller rack 116 is assembled inside the moving contact 114 by using one or more screws. The roller rack 116 has cylindrical teeth. The roller rack 116 along with the moving contact 114 moves toward and away from the first fixed contact 106 when the worm drive 118 rotates clockwise and anti-clockwise respectively. Thus, the worm drive 118 and the roller rack 116 provide reciprocating motion of the moving contact 114 along X’-X axis. The moving contact 114 is supported by the housing 112. The housing 112 is made up of a conducting material and is stationary. Subsequently, the housing 112 helps in achieving the connection with the second fixed contact 108. The first fixed contact 106 is connected to a live conductor (not shown), to which a high voltage is applied. The second fixed contact 108 is connected to the circuit breaker (not shown). However, it should be appreciated that the connections to the first and second fixed contacts 106 and 108 can be interchanged according to the requirements.

In an embodiment of the present invention, the disconnecting switch closed configuration is achieved when the moving contact 114 touches the first fixed contact 106. FIG. 1A illustrates the disconnecting switch closed configuration of the disconnector and earth switch assembly 100. In this configuration, the connection is achieved between the first fixed contact 106 and the second fixed contact 108 through the housing 112. Further, when the worm drive 118 rotates, the roller rack 116 carries the moving contact 114 along the X’-X axis towards the earth connection 110. When the moving contact 114 breaks the connection with the first fixed contact 106 and is only connected to the second fixed contact 108 through housing 112, the disconnector and earth switch assembly 100 is said to be in a neutral configuration. FIG. 1B illustrates the neutral configuration of the disconnector and earth switch assembly 100. As the worm drive 118 is further rotated, the moving contact 114 moves towards the earth connection 110 and touches the earth connection 110. This configuration in which the moving contact 114 touches the earth connection 110 is referred to as the earth closed configuration of the disconnector and earth switch assembly 100. FIG. 1C illustrates the earth closed configuration of the disconnector and earth switch assembly 100.

The worm drive 118 is made up of an insulating material whereas the roller rack 116 is made up of a conducting material. However, it should be appreciated that the material of the roller rack is not limited to a conducting material. As the switching configurations of the disconnector and earth switch assembly 100 are changed, the moving parts undergo wear and tear due to friction. The friction produces minute metallic particles inside the aluminium enclosure 102. However, since the moving contact 114 is inside the housing 112, the metallic particles generated due to friction fall inside the housing 112. The metallic particles are not deposited in the high electric field region of the gas-filled insulating chamber 104. This increases the reliability of the disconnecting and earth switches, and in turn increases the reliability of the disconnector and earth switch assembly 100. Thus, the electrical stress inside the gas-filled insulating chamber 104 is reduced.

Further, the worm drive 118 and roller rack 116 mechanisms have less friction, wear and tear as compared to the conventional mechanisms that drive the disconnecting and earth switches. Consequently, these aspects would result in fewer metallic particles inside the housing 112. As mentioned earlier, the roller rack 116 has cylindrical teeth. The cylindrical teeth reduce the friction caused by the contact between the worm drive 118 and the roller rack 116, as the moving contact 114 moves along the X’-X direction during switching operations. Further, only one moving contact 114 is included to achieve multiple switching configurations of the disconnector and earth switch assembly 100 resulting in fewer moving parts, less maintenance costs and compact design. As the reliability and durability of the disconnector and earth switch assembly 100 is increased, the disconnector and earth switch assembly 100 can be used for longer time and the amount of switching operations achieved by the disconnector and earth switch assembly 100 is also increased.

In another embodiment of the present invention, the disconnector and earth switch assembly 100 can also be used as only grounding switch when the first fixed contact 106 is open and the moving contact 114 connects the second fixed contact 108 and the earth connection 110.

The present invention has been described herein with reference to a particular embodiment for a particular application. Although selected embodiments have been illustrated and described in detail, it may be understood that various substitutions and alterations are possible. Those having ordinary skill in the art and access to the present teachings may recognize additional various substitutions and alterations are also possible without departing from the spirit and scope of the present invention.
,CLAIMS:What is claimed is:
1. A disconnector and earth switch assembly for metal encapsulated, gas insulated high voltage switchgear comprising:
first, second and third fixed contacts connected to first, second and third terminals, respectively;
a housing made up of conducting material wherein the housing is connected to the second fixed contact;
a moving contact, wherein the moving contact is disposed inside the housing and is linearly movable therein along a movable path between the first and third fixed contacts, and wherein the moving contact is in constant electrical connection with the housing;
an operating mechanism for providing a translational motion to the moving contact within the housing to achieve first, second, and third configurations, wherein in the first configuration, the moving contact is electrically connected to the first fixed contact, in the second configuration, the moving contact is isolated from the first and third fixed contacts, and in the third configuration, the moving contact is connected to the third fixed contact.

2. The disconnector and earth switch assembly according to claim 1, wherein the insulating gas is the sulfur hexafluoride gas (SF6).

3. The disconnector and earth switch assembly according to claim 1, wherein the first, second and third fixed terminals are live terminal, circuit breaker terminal, and earth connection, respectively.

4. The disconnector and earth switch assembly according to claim 1, wherein the operating mechanism is the worm and roller rack mechanism and the moving contact is conducting roller rack and wherein the moving contact is mounted on the insulating worm drive.

5. The disconnector and earth switch assembly according to claim 1, wherein the worm drive is made up of insulating material.

6. The disconnector and earth switch assembly according to claim 1, wherein the worm drive is driven by a motor.

7. The disconnector and earth switch assembly according to claim 1, the first, second, and third configurations are disconnector switch closed, neutral, and earth switch closed configurations, respectively.