Vacuum insulated switching apparatus

Abstract: In a vacuum bulb 1 composed of a grounded metallic vessel 2, the reliability in monitoring and measuring the vacuum pressure can be improved by providing a vacuum pressure measuring terminal 30 at a side plane of the vessel 2 to electrically separate the main circuit 13 from the measuring terminal 30.

Description: Background of the invention The present invention relates to a vacuum insulated switching apparatus provided with a vacuum pressure measuring device. Switching performance and dielectric strength of a vacuum bulb is decreased rapidly when vacuum pressure is increased higher than 10 -4 Torr. Reasons of varying the vacuum pressure are such as vacuum leakage by generating cracks, release of gaseous molecules adsorbed onto metals and insulating materials, penetration of atmospheric gases, and others. In accordance with increasing size of the vacuum vessel accompanied with increasing the voltage of the vacuum bulb, the release of the adsorbed gas, and the penetration of atmospheric gas become not negligible. In accordance with a structure of the insulated switching apparatus as disclosed in JP-A-9-249076 (1997), wherein a breaker, a disconnector, and a ground switch are integrated in a single bulb, an addition of vacuum pressure checking function during operation, or of continuous pressure monitoring function is desirable, in order to ensure safety of operators for maintenance and inspection of load, or switching apparatus itself. Conventionally, vacuum bulbs provided with vacuum pressure measuring terminals such as those provided with an ionization vacuum gauge and a magnetron terminal, where vacuum pressure is determined by applying a voltage to a small gap provided in the vacuum vessel to cause discharge, are known. When considering insulation between a main circuit and a measuring terminal in the prior art, some problems occur as described below. If the measuring terminal is composed with an insulating cylinder separately from the main circuit, the size of the measuring terminal including the insulating cylinder becomes large up to the size of the vacuum bulb. Furthermore, electrons generated at the measuring terminal can enter into inside the vacuum bulb, collide with the insulating cylinder and generate secondary electrons resulting in a multiplication of the electron number. Therefore, deterioration of the insulating performance of the vacuum bulb is a problem. In accordance with the prior art, the size of the measuring terminal can be made small by making the insulating cylinder unnecessary with a method, wherein a line at power source side and an outer cylindrical electrode of the vacuum pressure measuring element are maintained at an equal potential and a voltage divided with a condenser is applied to an interior electrode. However, problems are caused such as the increasing size of the apparatus when insulation of the condenser with ground was considered, and further the reception of influences due to variations in voltage of the main circuit (for instance, a surge voltage and the like). Because the potential of the measuring element is equal to that of the line at power source side, insulating transformers and optical transmission are necessary for transmitting signals to relay circuits of the measuring apparatus, warning lamps, and warning buzzers. This results in the problem that the whole system becomes complex. An apparatus and a method for measuring gas pressure according to the preamble of claim 1 are disclosed in GB-A-2203282. The vacuum vessel therein is an insulator and not grounded. The measuring apparatus has to be connected to the high voltage applied portion. This requires the signal line to be of high dielectric strength. In addition, the size of the measuring apparatus becomes large due to the necessity of a large insulating distance between the grounded housing and the measuring apparatus. Summary of the invention The present invention is aimed at solving the above problems, and the object of the present invention is to provide a vacuum insulated switching apparatus provided with a reliable vacuum pressure monitoring and measuring function. This is achieved by the configuration described in the independent claim 1, where the vacuum bulb is composed of a grounded vacuum vessel and a vacuum pressure measuring apparatus is attached to the vacuum bulb. In accordance with the switching apparatus configured as above, the main circuit and the measuring element can be separated electrically, and safety of the switching apparatus can be ensured by increasing the reliability of the vacuum monitoring and measuring function. Brief description of the drawings FIG. 1 is a schematic illustration of the vacuum bulb and the vacuum pressure measuring terminal of an embodiment of the present invention; FIG.2 is a schematic illustration of the vacuum bulb and the vacuum pressure measuring terminal of an embodiment of the present invention; FIG. 3 is a vertical cross section of the vacuum pressure measuring terminal attached to the vacuum bulb of an embodiment of the present invention; FIG. 4 is a vertical cross section of another vacuum pressure measuring terminal attached to the vacuum bulb of an embodiment of the present invention; FIG. 5 is a vertical cross section of the vacuum bulb of an embodiment of the present invention; FIG. 6 is a vertical cross section of the vacuum bulb of an embodiment of the present invention; FIG. 7 is a vertical cross section of the vacuum bulb of an embodiment of the present invention; FIG. 8 is a vertical cross section of another vacuum pressure measuring terminal attached to the vacuum bulb of an embodiment of the present invention; FIG. 9 is a vertical cross section of another vacuum pressure measuring terminal attached to the vacuum bulb of an embodiment of the present invention; FIG. 10 is a vertical cross section of another vacuum pressure measuring terminal attached to the vacuum bulb of an embodiment of the present invention; FIG. 11 is a vertical cross section indicating another embodiment of the present invention; FIG. 12 is a vertical cross section indicating another embodiment of the present invention; FIG. 13 is a illustration of insulated switching apparatus of an embodiment of the present invention; FIG. 14 is a characteristic graph indicating a relationship between the pressure P and breaking performance/dielectric strength performance; FIG. 15 is a schematic illustration indicating a method for measuring the vacuum pressure of another embodiment of the present invention; Detailed explanation of the preferred embodiments of the invention Embodiments of the present invention are explained in detail referring to FIG. 1 to FIG. 15. (Embodiment 1) The first embodiment of the present invention is explained hereinafter. A cross sectional view of a vacuum bulb 1 and a vacuum pressure measuring terminal 30 is indicated in FIG. 1, and an insulated switching apparatus composed by mounting rotatably the movable conductor 21 to a main axis 20 is indicated in FIG. 12. The vacuum bulb is composed by attaching two bushings 3, 4 to periphery of a grounded metallic vessel 2. A fixed electrode 5 and a movable electrode 6 are arranged so as to be touchable/separable at inside the vacuum bulb 1 to switch on or off by making the electrodes touch or separate. The fixed electrode is fixed to the bushing 3, and a flexible conductor 8 extended from the movable electrode 6 is connected to the bushing 4. In accordance with the vacuum bulb 1 of the present embodiment, an electric current flows through a path in the order of bushing 3 - fixed electrode 5 - movable electrode 6 - flexible conductor 8 - bushing 4. The movable electrode 6 is connected with an insulating rod 9, and the insulating rod 9 is fixed to the metallic vessel 2 via a bellow 10. The reference numeral 11 indicates an arc shield for preventing an earth fault generated by touching an arc A to the metallic vessel 2. An operation of the vacuum bulb 1 is explained hereinafter referring to FIG. 13. FIG. 11 indicates a switching apparatus, wherein the vacuum bulb 1 is operated by an operating mechanism 25. The reference numeral 30 indicates a disconnecting spring, which generates a driving force by releasing a pressed insulating portion 31 by a trip mechanism provided separately, and the driving force is transmitted to the insulating rod 9 via a shaft 22. As the result, the insulating rod is moved upwards or downwards, and the fixed electrode 5 and the movable electrode 6 are touched or separated. The reference numeral 30 indicates a magnetron type measuring terminal, which is attached at a side plane of the metallic vessel 2. The structure of the measuring terminal 30 is indicated in FIG. 3. The measuring terminal 30 is composed of a coaxial electrode 32 and a coil 36 for generating a magnetic field arranged around periphery of the coaxial electrode 32. The coaxial electrode 32 is composed of a cylindrical outer electrode 33 and an inner electrode 34 penetrating the outer electrode. The outer electrode 33 and the inner electrode 34 are insulated each other by the insulating portion 31. A ring shaped permanent magnet 37 can be used instead of the coil 36 as indicated in FIG. 4. Additionally, N pole and S of the magnetic polarity of the permanent magnet pole can be reversible. Operation of the measuring terminal 30 is explained hereinafter referring to FIG. 3. A negative direct current is applied to the inner electrode 34 by an electric power source circuit 40. An alternating current, or voltage pulses also can be used. The electrons e released from the inner electrode 34 receive Lorentz force by a magnetic field B applied by an electric field E and the coil 36, and move rotatively around the periphery of the inner electrode 34. The rotating electrons e collide with residual gases to ionize them, and generated anions I flow into the inner electrode 34. The ionized current j varies depending on the amount of the residual gases, that is a pressure. Therefore, the pressure can be measured by determining the voltage V generated between the both ends of the resistance R. When the pressure must be monitored continuously, a relay may be operated to turn on a warning lamp, or to generate a warning sound based on the voltage at the both ends of the resistance R. As the graph shown in FIG. 14 indicates, the disconnecting performance and the insulating performance of the vacuum bulb 1 is rapidly deteriorated when the pressure is increased equal to or more than 10 -4 Torr. The vacuum pressure measuring terminal 30 indicated in the present embodiment is detectable till approximately 10 -6 Torr, and sufficiently effective for monitoring the vacuum pressure. Advantages of the present embodiment are explained hereinafter. Because the measuring terminal 30 is provided to the grounded metallic vessel 2, the power source circuit for the measuring terminal 30 can be separated from the main circuit 13. Therefore, malfunction caused by a surge from the main circuit 13 can be avoided, and reliability of the switching apparatus is improved. Because signals are transmitted directly from the resistance R to measuring instruments or relay circuits, the measuring system can be small in size and simplified. In accordance with the present invention, the measuring terminal 30 is fixed directly to the metallic vessel 2. Therefore, in comparison with the prior art, wherein the measuring terminal was fixed via an insulating cylinder, the number of electrons entering into the vacuum bulb 1 is small, and an advantage to avoid deterioration of the disconnecting performance and the insulating performance of the vacuum bulb 1 can be realized. FIG.5 shows an example of a magnetron using metallized part of the ceramics to release electrons. A coaxial electrode 32 and outer electrode 33 are connected to negative polarity and the inner electrode 34 is connected to positive polarity. Therefore, the polarity is the reverse to FIG.4. The electric field becomes high near the thin metallized part 43 of the ceramics 31 for connecting the outer electrode 33 with the ceramics 31, and therefore, the electron emission coefficient becomes large. As a result, the sensitivity of the magnetron is improved. The position for fixing the measuring terminal 30 is preferably at an outside of the arc shield 11 as indicated in FIG. 6. Because metallic particles, electrons, and ions released from the electrode at a disconnecting time do not enter into the measuring terminal 30, and the reliability can be maintained. The shield 12 can be provided separately in the vacuum bulb 1 as indicated in FIG. 7. In this case, the coil 36 can be arranged far from the electrode, and decrease of the disconnecting performance by the magnetic field can be avoided. The coil 36 is not necessarily provided at all times, but it may be provided at only pressure measuring time, in order to avoid the influence of the magnetic field to the disconnecting performance. It is natural that the present invention is applicable not only to the magnetron terminal, but also to measuring terminals such as ionization vacuum gauge terminal, discharging gap measuring terminal, and the like. The reliability of all the measuring terminal can be improved by attaching to the grounded metallic vessel 2, because the measuring system and the main circuit can be separated. (Embodiment 2) The second embodiment of the present invention is explained referring to FIG.2. In accordance with the present embodiment, the measuring terminal 30 indicated in FIG.1 is attached to the metallic vessel 2 of the vacuum bulb 1 through an insulating member 50. In case the thickness of the insulating member 50, electrons from the sensor repeat to collide with the insulating member 50 and multiplied electrons by the secondary electron multiplication enter into the vacuum vessel 1. As a result, the insulation performance reduces. Therefore, the appropriate thickness of the insulating member 50 is 2 to 3mm. According to the present embodiment, the main circuit and measuring system are separated, and therefore, it is capable of avoiding the failure of measuring system caused by the surge current from the main body. The vacuum measuring apparatus is able to be equipped at the wall of the grounded vacuum vessel (metallic vessel) 2 as well as any place distant from the vacuum vessel 2 as shown in FIG. 15. That is, it is possible to install the vacuum measuring apparatus at anywhere in the vacuum vessel if the pressure is able to be measured. (Embodiment 3) The third embodiment of the present invention is explained hereinafter referring to FIG. 8. In accordance with the present embodiment, the measuring terminal 30 indicated in FIG. 7 is attached to the metallic vessel 2 in the vacuum bulb 1 indicated in FIG. 1. The measuring terminal 30 is composed of an outer electrode 33, an inner electrode 34, and a third electrode 39 having an equal potential to the outer electrode 33 provided facing to the inner electrode 34. Accordingly, the electrons e released from a top end of the inner electrode 34 are captured by the electrode 39, entering the electrons e into inside of the vacuum bulb can be decreased, and decrease of the insulating performance of the vacuum bulb 1 can be avoided. The same effect as above can be obtained by providing a hole 15 to the metallic vessel 2, and attaching the coaxial electrode 32 thereon as indicated in FIG. 9. As shown in FIG.10, a hole 51 smaller than the inside of outer electrode 33 is provided at the metallic vessel 2. The electrons e2 emitted from the top end of the inner electrode 34 receive Lorentz force by the electric field E and magnetic field B, and move along a spiral locus 44 and reach to the metallic vessel 2. When the electron e2 repeat to collide with residual gases, ion current j flows. In addition to the current by the electron e1, the sensitivity is improved by the effect of electrons e2. (Embodiment 4) The fourth embodiment of the present invention is explained hereinafter referring to FIG. 9. In accordance with the present embodiment, the measuring terminal 30 indicated in FIG. 11 is attached to the metallic vessel 2 in the vacuum bulb 1 indicated in FIG. 1. The measuring terminal 30 comprises an outer electrode composed of a metallic plated film 52 on an inner side plane of a cup shaped ceramic body 51. In accordance with the embodiments 1 and 2 as shown in FIG.3, the insulating portion 31 and the outer electrode 33 were manufactured separately. However, in accordance with the present embodiment, the insulating portion and the outer electrode can be manufactured as an integrated member. Therefore, the numbers of parts and brazing portions can be decreased. (Embodiment 5) The fifth embodiment of the present invention is explained hereinafter. In accordance with the present embodiment indicated in FIG. 11, the measuring terminal 30 indicated in FIG. 11 is attached to the metallic vessel 2 in the vacuum bulb 1 indicated in FIG. 1. The measuring terminal 30 comprises the inner electrode 34 having a screw portion, which improves a sensitivity of the measurement by enhancing a local electric field at surface of the inner electrode 34 to increase the amount of electrons released from the inner electrode 34. Naturally, the same effect as above can be obtained by providing any protrusion at the inner electrode 34. (Embodiment 6) The sixth embodiment of the present invention is explained hereinafter referring to FIG. 15. The measuring terminal 30 is attached at the side plane of the metallic vessel 2 as same as the embodiment 1 indicated in FIG. 1. In accordance with the present embodiment, generation of a direct current voltage applied to the measuring terminal 30 and measurement of the ionic current are performed using a megohmmeter 41, i.e. an insulation resistance tester. The megohmmeter 41 is a handy type tester for measuring M Ω level resistance by applying a direct current voltage of several kV to an insulator and measuring a leak current, and one of instruments, which are generally owned by personal in charge of maintenance and control of high voltage apparatus. Voltage terminals 42 of the megohmmeter 41 are connected with the coaxial electrode 32 of the measuring terminal 30, and a resistance R is measured by applying a voltage V. The leaking current (I = V/R ) determined by the voltage V and the resistance R corresponds to the ionic current I depending on the pressure P. Accordingly, if a relationship between the resistance R and the pressure P is determined previously, the pressure can be readily measured with the megohmmeter. It is not necessary to prepare a special electric power source for measuring pressure, and the pressure can be readily measured with a low cost. (Embodiment 7) The seventh embodiment of the present invention is explained hereinafter. The present embodiment is a countermeasure for prevent the magnetic field B generated at the measuring terminal 30 from entering into the vacuum bulb 1. The composition is as same as the embodiment 1 indicated in FIG. 1. In accordance with the present embodiment, the metallic vessel 2 indicated in FIG. 1 is made of a magnetic material such Monel (a Cu-Ni alloy) and the like, in order to avoid decrease of disconnecting performance with entering a magnetic field by shielding the magnetic field generated at the measuring terminal with the metallic vessel 2. The present invention can be applied to a rotary operation type vacuum bulb indicated in FIG. 12. The movable electrode 6 is rotated with a main axis 20 as a supporting point to be contacted or separated with the fixed electrode 5. The fixed electrode 5 is insulated by an insulating cylinder 16A, and the movable electrode 6 is insulated by an insulating cylinder 16B, from the grounded metallic vessel 2, respectively. In accordance with the present embodiment, the hole 15 is added in order to compose a small size switching apparatus comprising a breaker, a disconnector, and ground switch, by making the movable electrode 6 stop at each of four positions, i.e. a closing position Y1, an opening position Y2, a disconnected position Y3, of which insulating is not broken with thunder and the like, and grounding position Y4. In accordance with adding the vacuum pressure measuring terminal 30 of the present invention to the vacuum bulb 1 having a function as a disconnector, safety of operators for maintenance and inspection can be ensured, and the reliability of the switching apparatus can be improved. As explained above, in accordance with the present invention, reliability in monitoring and measuring the vacuum pressure is improved by providing the vacuum pressure measuring terminal to the grounded metallic vessel, and as the result, a vacuum insulated switching apparatus having a high safety can be provided.

Claims: A vacuum insulated switching apparatus comprising: a vacuum vessel (2), a switch comprising a fixed electrode (5) attached to said vessel (2) and a movable electrode (6) attached to said vessel (2) and facing said fixed electrode (5), and a vacuum pressure measuring apparatus (30) for measuring the pressure in said vessel (2), characterized in that said vacuum vessel (2) is grounded and made of metal and the fixed and movable electrodes (5,6) are attached to the vessel (2) via insulation (3,4,9). The apparatus of claim 1, wherein said vacuum pressure measuring apparatus (30) is capable of detecting a pressure in the range of 13 to 0.13 mPa (10 -4 to 10 -6 Torr). The apparatus of claim 1, wherein said vacuum pressure measuring apparatus (30) comprises a coaxial electrode (32) and a magnetic field generating apparatus (36) arranged around said coaxial electrode (32). The apparatus of claim 3, wherein an arc shield (11) is disposed around the electrode arranged in said vessel (2), and said coaxial electrode (32) is provided outside of said arc shield in the vessel (2). The apparatus of claim 3, including a shielding means (11) provided in said vessel (2) for preventing metallic particles released by electrode contact at the switching time from entering said coaxial electrode (32). The apparatus of any one of claims 3 to 5, including an electrode (39) having the same potential as the outer electrode (33) of said coaxial electrode (32) and facing the central electrode (34) of said coaxial electrode (32). The apparatus of any one of claims 3 to 5, wherein said coaxial electrode (32) is composed of a cup shaped ceramic cylinder (51) the inside of which is plated with metal (52), and a central electrode (34) penetrating the ceramic cylinder (51). The apparatus of any one of claims 3 to 7, wherein a protrusion is provided on the central electrode (34) of said coaxial electrode (32) for enhancing the electric field. The apparatus of any one of claims 3 to 7, wherein a megohmmeter (41) is used as an electric power source of said vacuum pressure measuring apparatus (30). The apparatus of any one of claims 3 to 9, wherein said vacuum vessel (2) is composed of a magnetic material.

Inventors: MORITA AYUMU, NATSUI KENICHI, TANIMIZU TORU, MORITA, AYUMU, NATSUI, KENICHI, TANIMIZU, TORU
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1999
Main classification: H01H33
IPC codes: G01L21, H01H33