Patent Abstract:
A gas-insulated switchgear includes a sealed vessel filled with an insulating gas, a circuit breaker held in the sealed vessel, and a branch pipe attached to a lower part of the sealed vessel right below the circuit breaker. The branch pipe defines a hand hole for use in inspecting the circuit breaker, provides a place for installing an absorbent container and forms a foreign matter collecting space.

Full Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a highly reliable gas-insulated switchgear and, more particularly, to a gas-insulated switchgear suitable for use as a puffer type gas-blast circuit breaker. 
     A general gas-insulated switchgear has a breaker including a stationary contact and a movable contact, a sealed vessel containing the breaker and filled with an insulating gas, such as sulfur hexafluoride gas (SF 6 ), a contact operating device disposed outside the sealed vessel to operate the movable contact, a high-tension conductor connected to the breaker, an insulating spacer connected to the breaker, and buses. 
     It is possible that foreign matters are produced in the sealed vessel during the assembly of the gas-insulated switchgear or when the breaker exercises its function. If the foreign matters produced in the sealed vessel are conductive, it is possible that the dielectric ability of the insulating gas and the surfaces of insulators is deteriorated. 
     Various methods have been proposed to prevent the adverse effect of conductive foreign matters on the performance of the breaker in a case where the conductive foreign matters are produced in the sealed vessel. For example, a method proposed in JP-A No. 234113/1998 installs foreign matter catching vessels at a plurality of parts of a sealed vessel filled with an insulating gas and holding a breaker therein, corresponding to nodes of vibration to catch foreign matters when the sealed vessel is shook by the circuit-breaking action of the breaker. 
     Foreign matters produced in the sealed vessel tend to gather in the nodes of vibration. Therefore, the foreign matters are caught efficiently by the foreign matter catching vessels disposed at the nodes and, consequently, the deterioration of the dielectric ability by conductive foreign matters can be prevented. 
     However, the prior art method does not give any consideration to a fact that the sealed vessel of the gas-insulated switchgear needs many incidental devices, and have problems in manufacture and cost. Although the prior art method disposes the foreign matter catching vessels at the nodes of vibration, the gas-insulated switchgear needs an absorbent to be placed in all the gas compartments, and the gas-insulated switchgear must be provided with a hand hole for inspecting the breaker. 
     Nevertheless, the prior art method does not give any consideration to providing the absorbent and forming a hand hole. Thus, some other parts for holding the absorbent must be formed by connecting branch pipes or the like to the sealed vessel, which makes the construction of the gas-insulated switchgear complicated and invokes problems in manufacture and cost. Many branch pipes connected to the sealed vessel spoils the appearance of the gas-insulated switchgear. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a gas-insulated switchgear capable of being easily and economically manufactured and of facilitating work for maintenance and inspection, and excellent in electrical insulating performance. 
     A gas-insulated switchgear according to one aspect of the present invention includes a sealed vessel filled with an insulating gas; a circuit breaker held in the sealed vessel; and a branch pipe attached to a lower part of the sealed vessel right below the circuit breaker; wherein the branch pipe defines a hand hole for use in inspecting the circuit breaker, provides a place for installing an absorbent container and forms a foreign matter collecting space. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal sectional view of a gas-insulated switchgear in a preferred embodiment according to the present invention as a puffer type gas-blast circuit breaker. 
     FIG. 2 is a longitudinal sectional view of a gas-insulated switchgear in a modification of the gas-insulated switchgear shown in FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the FIG. 1 showing a gas-insulated switchgear in a preferred embodiment according to the present invention as a puffer type gas-blast circuit breaker, a sealed vessel  1  containing an insulating gas is supported by support members  2  on a base E or on an apparatus. A puffer type gas-blast circuit breaker  3  is built in the sealed vessel  1 . 
     The puffer type gas-blast circuit breaker  3  has a stationary-contact unit including a stationary contact  4  and a main stationary contact  5  surrounding the stationary contact  4 . The stationary contact  4  and the main stationary contact  5  are attached to a free end of a stationary conductor  6 . The stationary conductor  6  is electrically connected to a bus supported on insulating support members not shown in the figure. 
     The gas-blast circuit breaker  3  has a movable-contact unit including a movable contact  8  formed integrally with a puffer cylinder  7 . An insulator-operating rod  9  is connected to the puffer cylinder  7 . An insulating nozzle  10  is attached to the puffer cylinder  7  so as to surround the movable contact  8 . 
     The insulator-operating rod  9  is extended through an end part on the side of the movable-contact unit of the sealed vessel  1  and is connected to a movable contact-operating device  11  disposed outside the sealed vessel  1 . The movable contact operating device  11  moves the insulator operating rod  9  in axial directions, i.e., lateral directions as viewed in the figure, to bring the movable contact  8  into contact with the stationary contact  4  and to disconnect the movable contact  8  from the stationary contact  4 . 
     A stationary piston  12  is attached to a conductive member  13  of the movable-contact unit so as to define a puffer chamber together with the puffer cylinder  7 . The conductive member  13  of the movable-contact unit has one end on the side of the movable-contact unit fixedly attached to an insulating holding tube  14  fixed to the end part on the side of the movable-contact unit of the sealed vessel  1 . A main movable contact  15  is attached to the other end of the conductive member  13 . A high-tension conductor  16  is attached to an upper part of the conductive member  13  of the movable-contact unit so as to extend upward. 
     An upper branch pipe  17  is extended upward from an upper part of the sealed vessel  1 . The conductive member  13  is connected to a gas bus or a bushing by the high-tension conductor  16 . 
     A short lower branch pipe  20  provided with a flange  21  is extended downward from a lower part of the sealed vessel  1  corresponding to the puffer type gas-blast circuit breaker  3 . A lid  22  is detachably attached to the flange  21  to close the open end of the lower branch pipe  20 . An absorbent container  23  is detachably attached to the inner surface of the lid  22 . 
     The lower branch pipe  20  is formed in a size and a shape (a circular shape in most cases) such that the operator&#39;s hand or arm can be inserted through the lower branch pipe  20  in the sealed vessel  1  to take parts out of and to put parts into the sealed vessel when the operator changes parts of the circuit breaker. Thus the lower branch pipe  20  serves also as a hand hole. The absorbent container  23  is a perforated box capable of containing a sufficient quantity of an absorbent for absorbing moisture contained in the sealed vessel  1  and cracked gases produced in the sealed vessel  1 . 
     The respective sizes of the lower branch pipe  20  and the absorbent container  23  are determined so that a gap G of a predetermined size is formed between the outside surface of the absorbent container  23  and the inside surface of the lower branch pipe  20 . 
     The operation of the gas-insulated switchgear in the preferred embodiment will be explained hereinafter. When breaking a circuit, the puffer type gas-blast circuit breaker  3  blows the compressed insulating gas, such as sulfur hexafluoride gas (SF 6 ) against an electric arc formed between the stationary contact  4  and the movable contact  8  in the puffer cylinder  7  to intercept an electric current. 
     Therefore the movable-contact-operating device  11  needs to exert a considerably large operating force on the operating rod  9 . Consequently, the puffer type gas-blast circuit breaker  3  and the movable contact-operating device  11  vibrate when the movable contact-operating device  11  operates to break the circuit. The vibration of the puffer type gas-blast circuit breaker  3  and the movable contact operating device  11  is transmitted to the sealed vessel  1 . If conductive foreign matters are contained in the sealed vessel  1 , the conductive foreign matters will move around in the sealed vessel when the sealed vessel vibrates. 
     Since the components including the puffer type gas-blast circuit breaker  3  and held in the sealed vessel are charged at a high voltage, the conductive foreign matters will float in the sealed vessel. 
     In the gas-insulated switchgear in the embodiment, the lower branch pipe  20  is connected to the lower part of the sealed vessel  1  right below the puffer type gas-blast circuit breaker  3  so as to define the gap G. Therefore foreign matters once fall into the lower branch pipe  20  and accumulate in the gap G and will not be cause to float again by the vibration transmitted to the sealed vessel  1  and the puffer type gas-blast circuit breaker  3  charged at a high voltage. 
     The length of the lower branch pipe  20  is determine such that the gap G has a depth that is effective in preventing foreign matters accumulated in the gap G from being caused to float again by the vibration transmitted to the sealed vessel  1  and the puffer type gas-blast circuit breaker  3  charged at a high voltage. 
     Thus, conductive foreign matters moving in the sealed vessel  1  fall into the lower branch pipe  20  attached to the lower part of the sealed vessel  1  right below the puffer type gas-blast circuit breaker  3  and are collected easily in the gap G. Since the gap G extends over the lid  22  attached to the lower end of the lower branch pipe  20 , the same can be formed in a considerably big depth, and hence the foreign matters accumulated in the gap G are not caused to move by the high voltage applied to the puffer type gas-blast circuit breaker  3 . 
     The gas-insulated switchgear has a highly reliable insulating ability. Since the lower branch pipe  20  can be used as a hand hole for use in insecting the puffer type gas-blast circuit breaker  3 , the sealed vessel  1  does not need any other hand hole. 
     The absorbents container  23  containing the absorbent for absorbing moisture and cracked gases is placed in the lower branch pipe  20  and is attached to the inner surface of the lid  22 . Therefore the sealed vessel  1  does not need any other branch pipe for containing the absorbent. Thus, the gas-insulated switchgear of the present invention is simple in construction and is capable of being easily and economically manufactured. 
     Since the absorbent container  23  is detachable from the lid  22 , the absorbent container  23  can be easily replaced with a new one, when necessary, by removing the lid  22  from the lower branch pipe  20  to maintain the high reliability of the gas-insulated switchgear. 
     A gas-insulated switchgear in a modification of the gas-insulated switchgear shown in FIG. 1 will be described with reference to FIG. 2, in which parts like or corresponding to those of the gas-insulated switchgear shown in FIG. 1 are denoted by the same reference characters and the description thereof will be omitted. 
     Referring to FIG. 2, a stationary conductor  6  is connected to a conductor  37 . The conductor  37  is supported in a sealed vessel  1  by an insulating support  40  to hold the stationary conductor  6  fixedly in the sealed vessel  1 . A stationary contact  4  is supported on the stationary conductor  6 . The stationary conductor  6  has an opening  30 . An insulating gas, such as SF 6  gas, blowing toward the stationary conductor  6  when a movable contact  8  is disconnected from the stationary contact  4  flows through the opening  30 . An opening  31  is formed in a part on the side of a base E of the stationary conductor  6 . 
     The insulating gas generated when the movable contact  8  is disconnected from the stationary contact  4  passes through the opening  30  and blows against the wall, connected to the conductor  37 , of the stationary side conductor  6 , thereby being deflected to flow through the opening  31  into the sealed vessel  1 . Since the insulating gas flows through the opening  31  toward a branch pipe  20 , foreign matters produced when the movable contact  8  is disconnected from the stationary contact  4  are carried by the insulating gas into a gap G. 
     A puffer cylinder  7  is provided with an opening  32 . A stationary piston  12  is provided with an opening  33 , and a movable conductor  13  is provided with an opening  34 . 
     The insulting gas blows toward an insulating nozzle  10  when the movable contact  8  is disconnected from the stationary contact  4 , and the insulating gas flows through a central part of a puffer cylinder  7  toward an operating rod  9 . The insulating gas blows against the wall, connected to the operating rod  9 , of the puffer cylinder  7 , thereby being deflected. The deflected insulating gas flows through the opening  32  of the puffer cylinder  7 , the opening  33  formed in the stationary piston  12  and the opening  34  formed in the movable conductor  13  into the sealed vessel  1 . 
     The insulating gas flowing through the opening  34  flows toward the branch pipe  20 . Consequently, foreign matters produced when the movable contact  8  is disconnected from the stationary contact  4  is carried by the insulating gas into the gap G. 
     Although the insulating gas flows from the puffer cylinder  7  via the stationary piston  12 , and the opening  34  of the movable conductor  13  in this embodiment, the movable conductor  13  may be provided with two openings arranged in a vertical direction with respect to the base E, and two openings arranged in a horizontal direction with respect to the base E may be formed in the puffer cylinder  7  and the stationary piston  12  to make the insulating gas flowing through the openings  32  and  33  of the puffer cylinder  6  and the stationary piston  12  flow through the opening  34  of the movable conductor  13  into the sealed vessel  1  in order that the foreign matters produced when the movable contact  8  is disconnected from the stationary contact  4  can be removed from the insulating gas. 
     When the openings of the movable conductor  13  are arranged in a horizontal direction and the openings of the puffer cylinder  7  and the stationary piston  12  are arranged in a vertical direction, foreign matters contained in the insulating gas can be collected in the gap G. 
     Thus, foreign matters produced when the movable contact  8  is disconnected from the stationary contact  4  can be carried by the insulating gas from both the stationary conductor and the movable contactor into the gasp G. 
     Since the sealed vessel  1  is provided only with the upper branch pipe  17  and the lower branch pipe  20 , the gas-insulated switchgear has a simple, aesthetically satisfactory appearance from the viewpoint of industrial design. 
     Although the invention has been described in its preferred embodiment with a certain degree of particularity, obviously many changes and variations are possible therein. It is therefore to be understood that the present invention may be practiced otherwise than as specifically describe herein without departing from the scope and spirit thereof.

Technology Classification (CPC): 7