Patent Publication Number: US-8110770-B2

Title: Vacuum circuit breaker of tank type

Description:
TECHNICAL FIELD 
     The present invention relates to a vacuum circuit breaker of a dead tank type for outdoor use in a substation to protect power equipment and for use of various other applications, and more specifically to an internal pressure structure in the tank. 
     BACKGROUND ART 
       FIG. 4  shows a vertical sectional front view of a dead tank type vacuum circuit breaker of earlier technology. A ground tank  2  is supported on a mount platform  1 . An operation box  4  is fixed to one end of the ground tank  2  through a support plate  3 . Operation box  4  includes therein an operation mechanism. An insulating support tube  5  is supported by the support plate  3  at one end in the horizontal direction in ground tank  2 , and a support insulating member  6  is supported at the other end in the horizontal direction in ground tank  2 . An electrically conductive movable-side contact case  8  is supported on the insulating support tube  5  through an insulating support member  7 . A fixed-side contact case  9  is supported on the support insulating member  6 . A vacuum interrupter  10  serving as a circuit breaking portion is supported horizontally at a movable-side end portion of the vacuum interrupter and a fixed-side end portion of the vacuum interrupter  10 , respectively, by the movable-side and fixed-side contact cases  8  and  9 . The operating mechanism in operation box  4  is connected with a movable lead  11  of vacuum interrupter  10  through a lever not shown in the figure and an insulating operating rod  12  extending through the insulating support tube  5  and the insulating support member  7 . The movable lead  11  of vacuum interrupter  10  is inserted in the movable-side contact case  8 , and electrically connected with the movable-side contact case  8 . A fixed lead  13  of vacuum interrupter  10  is electrically connected with fixed-side contact box  9 . Conductors  14  and  15  include lower ends electrically connected, respectively, with the contact cases  8  and  9 , and extend upward in an inclined state, from the inside of ground tank  2 . Conductors  14  and  15  are surrounded, respectively, by bushings  16  and  17 , which are supported, respectively, by bushing current transformers  18  and  19  mounted on the ground tank  2 . Bushing terminals  20  and  21  are provided, respectively, at upper ends of the conductors  14  and  15 . 
     Furthermore, SF 6  gas of about 0.15 MPa is filled in the ground tank  2  in order to insulate the high voltage main circuit section of conductors  14  and  15  and vacuum interrupter  10 , and the ground tank  2  at a ground potential or earth potential. Since the SF 6  gas is superior in insulating properties, the SF 6  gas can perform its function at a low pressure. 
       FIG. 5  shows a sectional view of the vacuum interrupter  10  of the earlier technology. A vacuum vessel is formed by hermetically closing both ends of a ceramic insulating tube  22  with a metallic fixed-side end plate  23  and a movable-side end plate  24 . One end of the fixed lead  13  is fixed to the center of the fixed-side end plate  23 . The movable lead  11  extends through a through hole  24   a  formed at the center of the movable-side end plate  24 . One end of a bellows  25  is fixed to the inner side of the movable-side end plate  24  around the through hole  24   a . The other end of bellows  25  is fixed to the movable lead  11 . Fixed electrode  26  and movable electrode  27  are fixed, respectively, to inner ends of fixed lead  13  and movable lead  11  so that the fixed electrode  26  and movable electrode  27  confront each other. A main shield  28  is provided on the inner side of insulating tube  22  at the middle in the length of insulating tube  22 . Terminal shields  29  and  30  are provided on the inner sides of end plates  23  and  24 , respectively. A bellows shield  31  is fixed to the movable lead  11  so as to cover a part of bellows  25 . 
     In the thus-constructed vacuum circuit breaker, closing and opening operations are performed in the following manner. When the operating mechanism is driven in response to a closing command in the case of the closing operation, the movable lead  11  is moved through the lever and the insulating operating rod  12 , and the movable lead  11  brings the movable electrode  27  into contact with fixed electrode  26 , and thereby makes connection between conductors  14  and  15 . When, in the case of the opening operation, the insulating operating rod  12  is pulled by the operating mechanism through the lever in response to an extracting command, the movable lead  11  is moved, and the movable lead  11  separates the movable electrode  27  from fixed electrode  26 , and thereby breaks the connection between conductors  14  and  15 . 
     In the vacuum interrupter  10 , the bellows  25  capable of expanding and contracting maintains the vacuum in the vacuum vessel notwithstanding movement of the movable lead  11  in the closing and opening operations. Bellows  25  has a structure capable of bearing a pressure difference to some extent between the vacuum on the outer side and the pressure of the SF 6  gas on the inner side. However, when the pressure difference increases beyond a certain level, the bellows  25  may suffer phenomenon called buckling since bellow  25  is made of thin sheet of metallic material such as stainless steel. Accordingly, the pressure of the SF 6  gas on the inner side of bellows  25  needs to be lower than or equal to about 0.2 MPa. Moreover, for prevention of the global warming, it is required recently to reduce the quantity of usage of the SF 6  gas as much as possible because of its higher global warming potential. 
     A patent document 1 shows a technique to prevent damage of a bellows by decreasing the difference between the inner and outer pressures of the bellows by the setting of a vacuum on the outer side of the bellow and a low pressure gas or an atmospheric pressure on the inner side of the bellows. A patent document 2 shows a technique of making a space on an anti-vacuum side a sealed gastight chamber of a low pressure.
     Patent Document 1: Published Japanese Patent Application, Kokai No. 2004-220922   Patent Document 2: Published Japanese Patent Application, Kokai No. H06-208820   

     DISCLOSURE OF THE INVENTION 
     Problem to be Solved by the Invention 
     Dry air is effective for prevention of the global warming because of its approximately zero warming potential, and hence dry air is one conceivable candidate as a filler gas in a ground tank, substituting for the SF 6  gas. However, the dry air is inferior in insulating ability as compared to the conventional SF 6  gas. Therefore, it is necessary to improve the insulation by increasing the gas pressure to about 0.4˜0.5 MPa, and the bellows of the vacuum interrupter becomes one of the weakest portions with the increase of the gas pressure. To prevent buckling of the bellows, therefore, it is necessary to separate the portion of the bellows from the other portion of a high pressure, and to set the pressure in the portion of the bellows to a low pressure or the atmospheric pressure. Since the insulating performance becomes lower generally with decrease in the gas pressure, it is necessary to increase the total length of the insulating support tube and insulating operating rod which are part of the low pressure portion and which correspond to a portion defining an insulating distance between the high voltage portion and the earth portion or grounded portion. Therefore, there arises a problem that the length of the ground tank is increased as explained below with reference to  FIG. 6 . 
     In  FIG. 6 , a reference numeral  32  denotes a lever connecting the operating mechanism with the insulating operating rod  12 , a reference numeral  33  denotes ring contacts provided between the movable lead  11  of vacuum interrupter  10  and the movable-side contact case  8 , and a reference numeral  34  denotes a compression spring for pressing the movable electrode  27  onto the fixed electrode  26  and functioning to connect the insulating support tube  5  and the movable-side contact case  8  directly. Dry air is sealed at a high pressure in the ground tank  2 . In this case, the pressure in the insulating support tube  5  and movable-side contact case  8  is set at the atmospheric pressure (low pressure), and the bellows  25  is arranged so that the vacuum is on the outer side of the bellows and the atmospheric pressure (low pressure) is on the inner side. Therefore, this structure can reduce the pressure difference between the outer and inner sides of the bellows  25  as the structure of the patent document 1, and thereby prevent damage of bellows  25 . However, the length of the insulating support tube  5  and insulating operating rod  12  is increased to compensate for a decrease in the insulating ability. The long insulating support tube  5  and operating rod  12  causes an increase of the ground tank  2  and increases the size of the entire apparatus. When, on the other hand, the pressure in the bellows  25  is set at a high pressure, the bellows  25  should be constructed to have a structure withstanding the pressure difference between the inner and outer sides, and the cost is increased by the need for special material and special structure. In the case of the tank formed with a gas tight chamber of a low pressure on the anti-vacuum side as disclosed in the patent document 2, there is a possibility that the high pressure gas in the tank leaks gradually into the gas tight chamber, and increases the pressure gradually. 
     The present invention is aimed to meet such a problem, and its object is to provide a dead tank type vacuum circuit breaker to hold the stress applied to the bellows at a low level even if the pressure of the insulating to gas enclosed in the ground tank is increased so as to prevent decrease of the dielectric strength. 
     Means for Solving the Problem 
     According to one embodiment, a vacuum circuit breaker comprises: a ground tank filled with an insulating gas at a pressure higher than the atmospheric pressure; a vacuum interrupter which includes a vacuum vessel, electrodes which are supported, respectively, by a movable lead and a fixed lead in the vacuum vessel, and which are arranged so that the electrodes can be contacted with each other and separated from each other, and a bellows to retain the vacuum between the movable lead and the vacuum vessel; movable-side and fixed-side contact cases which are supported, respectively, through insulating members in the ground tank, and which are provided on both sides of the vacuum interrupter; movable-side and fixed-side conductors which are connected, respectively, with the movable-side contact case and the fixed side contact case, and which are extended through bushings provided in the ground tank, to the outside; and an insulating operating rod ( 12 ) extending through the before-mentioned insulating member ( 7 ) and connecting the movable lead ( 11 ) with an operating mechanism ( 4 ) outside the ground tank. In this vacuum circuit breaker, the movable-side conductor is tubular or in the form of a pipe, there is formed a chamber which communicates with a space on an anti-vacuum side of the bellows and which is isolated from a space filled with the insulating gas in the ground tank by a sealing device or sealing means, and the chamber is communicated, through an inside cavity of the movable-side conductor, with the atmosphere. 
     According to another embodiment, a vacuum circuit breaker comprises: a ground tank filled with a high pressure dry air; a vacuum interrupter which includes a movable-side end portion supported by a movable-side contact case supported in the ground tank through an insulating support tube through which an insulating operating rod is inserted, and an insulating support member, and a fixed-side end portion supported by a fixed-side contact case, and which further includes a bellows provided at the movable-side end portion, and so arranged that the vacuum is on an outer circumferential side of the bellows; and a movable-side conductor which includes a lower end connected with the movable-side contact case and an upper end connected with a bushing terminal and which is surrounded by a bushing, and a fixed-side conductor which includes a lower end connected with the fixed-side contact case and an upper end connected with a bushing terminal and which is surrounded by a bushing. In this vacuum circuit breaker, the movable-side conductor is tubular or in the form of a pipe, the inside of the movable-side conductor, the inside of the support member, the inside of the movable-side contact case and the inside of the bellows of the vacuum interrupter are communicated with one another, the upper end of the movable-side conductor is opened to the atmosphere, and there is provided, between the support member and the insulating operating rod, a gas tight seal portion to hold the high pressure dry air in the insulating support tube. 
     In the vacuum circuit breaker according to another embodiment, there is provided a filter in a vent hole of the movable-side bushing terminal opening to the atmosphere. 
     EFFECT OF THE INVENTION 
     Because of the high pressure insulating gas enclosed in the ground tank, it is possible to secure the insulating performance even if the length of the insulating operation rod etc., is decreased, and thereby to reduce the size of the entire apparatus. Moreover, because of the arrangement in which the atmospheric pressure is applied to the anti-vacuum side of the bellows, the pressure difference between the pressure on the outer side and the pressure on the inner side of the bellows is decreased, and the bellows is protected against damage or impairment. 
     Because of the arrangement in which the higher pressure of the dry air is applied to the portion, such as the insulating support tube and the insulating operation rod, where the electric field is high, the vacuum circuit breaker can retain the insulating performance even if the length of the portion including these members is decreased, and hence make it possible to reduce the entire size. Moreover, the bellows is so arranged that the atmospheric pressure is applied on the inner side of the bellows while the vacuum is on the outer side of the bellows. This arrangement can decrease the pressure difference between the pressure on the outer side and the pressure on the inner side of the bellows, and protect the bellows against damage or impairment. In order to apply the atmospheric pressure in the inside of the bellows, the atmospheric pressure is further applied to the space which communicates with the inside of the bellows and which is formed by the inside of the movable-side conductor, the inside of the insulating support member and the inside of the movable-side contact case. Because these members are members to which no high field is applied and which are equal in the potential, these members do not require high insulating ability. Furthermore, the gas sealed in the ground tank is the dry air having a small global warming potential, so that the vacuum circuit breaker is helpful to the prevention of the global warming. 
     In one embodiment, the movable-side bushing terminal is formed with a vent hole opening into the atmosphere, and a filter is provided in the vent hole. This arrangement is effective to prevent penetration of rain water or other foreign object into the tubular movable-side conductor. 
    
    
     BEST MODE(S) FOR CARRYING OUT THE INVENTION 
     The following is explanation on one or more best modes for carrying out the present invention with reference to the drawings.  FIG. 1  is an enlarged vertical sectional front view of a main portion of a dead tank type vacuum circuit breaker according to one best mode for carrying out the present invention.  FIG. 2  is a vertical sectional front view of the dead tank type vacuum circuit breaker.  FIG. 3  is an enlarged vertical sectional view of a part of a movable-side conductor of the dead tank type vacuum circuit breaker. In  FIGS. 1 and 3 , hatching indicates portions of the atmospheric pressure. In the figures, dry air is sealed, as a high pressure insulating gas, in a ground tank  2 . The high pressure dry air is also filled in bushings  16  and  17 . A support plate  3  is fixed at one horizontal end in the ground tank  2 . A movable-side contact case  8  is supported on the inner side of support plate  3  through an insulting support tube  5  and an insulating support member  7 . At the other horizontal end in ground tank  2 , a fixed-side contact case  9  is supported through a support insulating member  6 . A movable-side end portion of a vacuum interrupter  10  is supported on a tubular metal member  8   b  of movable-side contact case  8 . A fixed-side end portion of the vacuum interrupter  10  is supported on fixed-side contact case  9 . A movable lead  11  of vacuum interrupter  10  is inserted through the movable-side contact case  8  via ring contacts  33 , and connected with an insulating operating rod  12  extending through the insulating support tube  5  and insulating support member  7 . Between a movable-side end plate  24  of the vacuum interrupter  10  and the movable lead  11 , there is provided a bellows  25  surrounded by a vacuum applied on the outer side of the bellows  25 . 
     A reference numeral  35  denotes a movable-side conductor which is tubular or shaped in the form of a pipe. A lower end of the movable-side conductor  35  is connected with the movable-side contact case  8 . A lower end of a fixed-side conductor  15  is connected with the fixed-side contact case  9 . The conductors  15  and  35  extend upwards in oblique directions from the inside of ground tank  2 . Conductors  15  and  35  are surrounded, respectively, by bushings  16  and  17  provided on bushing current transformers  18  and  19 . Bushing terminals  20  and  21  are connected with the upper ends of conductors  15 ,  35 . The movable-side bushing terminal  20  has a vent hole  20   a  for leading to the atmosphere, and a filter  36  is provided in this vent hole  20   a  of the movable-side bushing terminal  20 . 
     In order to set the atmospheric pressure on the inner side of bellows  25  of vacuum interrupter  10 , the atmospheric pressure is applied in a portion leading to the inner side of bellows  25  and receiving no high electric field. More concretely, the atmospheric pressure is introduced in the inside space of the movable-side conductor  35 , the inside space of the insulating support member  7  and the inside space of the movable-side contact case  8 . To achieve this atmospheric pressure portion, there are provided high temperature seal portions (portions for sealing at high temperatures)  37 ˜ 39 , as gastight seal portions, between the outer circumference of movable-side conductor  35  and a tubular portion  8   a  of the movable-side contact case  8 , between the insulating support member  7  and the movable-contact case  8 , and between the movable-side contact case  8  and a tubular metal member  8   b  (welded to the end plate  24 ) of the contact case  8 . Moreover, to provide a high pressure dry air in the insulating support tube  5 , there are provided rectilinear seal portions  40  and  41 , as gas tight seal portions, between the insulating operating rod  12  and the support member  7  and between the insulating operating rod  12  and the through hole  3   a  of the support plate  3 . 
     In the above-mentioned best mode, the high field portion including members, such as the insulating support tube  5  and insulating operating rod  12 , receiving the application of high electric field is arranged so that the high pressure dry air is applied to the high field portion. This arrangement can ensure the insulating performance even if the lengths of these parts, and hence makes it possible to reduce the size of the ground tank  2  and to reduce the size of the vacuum circuit breaker as a whole. The bellow  25  is arranged so that the atmospheric pressure is on the inner side of bellows  25  while the vacuum is on the outer side, and the pressure difference between the inner side and the outer side of bellows  25  is reduced. Therefore, this arrangement can prevent damage or impairment of the bellows, eliminate the need for a structure for withstanding a greater pressure difference between the inner side and outer side of the bellows, and hence reduce the cost by allowing the use of a structure adequate for mass production. 
     Although the bellows  25 , movable-side conductor  35 , support member  7  and movable-side contact case  8  are arranged so that the atmospheric pressure is applied in the inside space of bellows  25 , the inside space of movable-side conductor  35 , the inside space of support member  7  and the inside space of movable-side contact case  8 , these parts are equal in potential and free from high electric field, and therefore these parts do not require a high pressure and a high insulating performance. The dry air sealed in ground tank  2  is small in the global warming potential, and therefore the vacuum circuit breaker can add a contribution to the prevention of the global warming. Moreover, the movable-side bushing terminal  20  includes the vent hole  20   a  which communicates with the atmosphere, and which is provided with the filter  36 . Therefore, the filter can prevent rain water from flowing into the inside cavity of the hollow movable-side conductor  35 . 
     As the high pressure insulating gas for improving the dielectric strength, the above-mentioned best mode employs dry air. However, instead of the dry air, it is possible to employ SF6 gas, CF3I gas, N2 gas etc. With the use of these high pressure insulating gases, the arrangement including the atmospheric pressure chamber formed on the anti-vacuum side opposite to the vacuum side of the bellows  25  can reduce the pressure difference between the inner side and outer side of bellows  25  and reduce the level of the stress applied to bellows  25  as in the case of the dry air. Especially, the use of the SF6 gas having a great dielectric strength makes it possible to reduce the size of the ground tank  2  when the gas pressure is set at a high pressure of about 0.17˜0.4 MPa. Even in the event of leakage in the high temperature seal portions  37 ˜ 39 , the pressure in the inside space of movable-side contact case  8  (the inside space of tubular metallic member  8   b ) is held at the atmospheric pressure, so that the bellows  25  receives no adverse influence. 
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is an enlarged vertical sectional front view or elevation of a main portion of a dead tank type vacuum circuit breaker according to one best mode for carrying out the present invention. 
       FIG. 2  is a vertical sectional front view or elevation of the dead tank type vacuum circuit breaker according to the best mode for carrying out the present invention. 
       FIG. 3  is an enlarged vertical sectional view of a part of a movable-side conductor of the dead tank type vacuum circuit breaker according to the best mode for carrying out the present invention. 
       FIG. 4  is a vertical sectional front view of a dead tank type vacuum circuit breaker of earlier technology. 
       FIG. 5  is a sectional view of a vacuum interrupter of earlier technology. 
       FIG. 6  is a vertical sectional front view of a dead tank type vacuum circuit breaker of earlier technology in which a dry air of a high pressure is filled in a ground tank, and the pressure is set at the atmospheric pressure in an insulating support tube, a movable-side contact case and a bellows. 
     EXPLANATION OF REFERENCE NUMERALS 
     
         
           2  . . . ground tank 
           3  . . . support plate 
           5  . . . insulating support tube 
           6  . . . support insulating member 
           7  . . . support member 
           8 ,  9  . . . contact cases 
           10  . . . vacuum interrupter 
           11  . . . movable lead 
           12  . . . insulating operating rod 
           13  . . . fixed lead 
           15 ,  35  . . . conductor 
           16 ,  17  . . . bushings 
           20 ,  21  . . . bushing terminals 
           20   a  . . . vent hole 
           23 ,  24  . . . end plates 
           25  . . . bellows 
           36  . . . filter 
           37 ˜ 39  . . . high temperature seal portion(s) 
           40 ,  41  . . . linear seal portion(s)