FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
An accelerated method for the manufacture of vacuum interrupter
INVENTORS
Joshi Sachin Sharad, More Sachin Vasant and Rajan Suresh, all of Crompton Greaves Limited, Corporate R&D and Quality Materials and Process Laboratory, Kanjur Marg (East), Mumbai 400 042, Maharashtra, India, all Indian National
and
Kulkarni Sandeep Prakash of Crompton Greaves Limited, Corporate R&D and Quality, Power Apparatus and System Laboratory, Kanjur Marg (East), Mumbai 400 042, Maharashtra, India, Indian National
APPLICANTS
CROMPTON GREAVES LIMITED, CG House, Dr Annie Besant Road, Prabhadevi, Mumbai 400025, Maharashtra, India, Indian Company
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF INVENTION
This invention relates to an accelerated method for the manufacture of vacuum interrupter. This invention also relates to a pressure vessel for use in the manufacture of vacuum interrupter.
PRIOR ART
A vacuum interrupter (VI) generally consists of a vacuum sealed switching chamber comprising an open ended ceramic housing sealed with seal cups and end plates at each end of the ceramic housing. A fixed electrode is fitted in one of the end plates with its one end extending into the ceramic housing and provided with a fixed contact. The other end of the fixed electrode protrudes outside the respective seal cup. A movable electrode is movably engaged in the other end plate with its one end protruding into the ceramic housing and the other end protruding out of the respective end plate. A moving contact is fixed to the movable electrode at its end protruding into the ceramic housing. The movable electrode is provided with bellows whose one end is sealed to the movable electrode and other end is sealed to the respective end plate. A center shield is provided over the contacts and fixed to the fixed or moving electrode to contain arcing at the contacts during opening and closing of the contacts. The centre shield can also be fitted at a floating potential by sandwiching it between a pair of ceramic half housing members forming the switching chamber. A bellows shield is provided over the bellows and fixed to the movable electrode to protect the bellows against arcing. The movable electrode is driven, for instance, by an electromagnetic or spring operated drive mechanism.
During operation of vacuum interrupters, the contacts thereof close and open generally with a force of 130 to 250 kg and speed of 0.5 to 1 m/s depending upon the current and voltage rating of the vacuum interrupters. The force of closing and opening gets transferred to all the sealing joints of the vacuum interrupters, namely joints of the seal cups with the end plates and the ceramic housing and the bellows with the moving electrode and respective end plate and induces stresses at the joints. The sealing joints which are inherently susceptible or prone to stresses will rupture and get damaged due to such stresses during
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operation of the vacuum interrupter thereby leading to leakage and premature failure of the vacuum interrupter. Typically, a vacuum interrupter is designed to withstand about 50000 mechanical close-open operations.
The various components of the vacuum interrupter are made of different metals having different thermal expansion coefficients. For instance, the end plates are made of stainless steel; seal cups are made of copper nickel; the fixed and moving electrodes are made of copper; the contacts are made of copper and chromium powder mix; the shields are made of stainless steel; and the bellows are made of stainless steel. Due to continuous flow of current through the vacuum interrupter, the temperature in the vacuum interrupter rises and the metallic components and the joints of the vacuum interrupter get heated up. As the metallic components have different thermal expansion coefficients, they expand and contract differently responsive to temperature rise and drop in the vacuum interrupter. This creates thermal stresses at the sealing joints because of which also the sealing joints are prone or susceptible to rupture and leakage causing premature failure of the vacuum interrupter.
The method for the manufacture of vacuum interrupter comprises first making the contacts by the steps of powder mixing, compacting, initial sintering, repressing, final sintering and machining. Subassemblies of the components are made by brazing. The assembly of the subassemblies is made by brazing the subassemblies in a vacuum furnace at 800-1000°C and 1 x 10"5 to 1 x 10"7 mbar pressure to form the vacuum interrupter. The ends of the fixed and moving electrodes protruding outside the vacuum interrupter are electroplated and the pressure within the vacuum interrupter is determined by the magnetron procedure. If the pressure within the vacuum interrupter is less than 10-4 Torr, the vacuum interrupter is subjected to power frequency voltage withstand test and impulse voltage withstand test. If the pressure within the vacuum interrupter is greater than 10-4 Torr, the vacuum interrupter is rejected. Vacuum interrupters passing the power frequency voltage withstand test and impulse voltage withstand test are subjected to hammer test which comprises closing and opening of the contacts generally about 100 times at a force of 130-250kg with a speed of 0.5 to 1 m/s depending upon the current and voltage rating of the vacuum
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interrupter. The hammer test is usually carried out using a pneumatic arrangement comprising a pneumatic cylinder.
Vacuum interrupters which have passed the power frequency voltage withstand test and impulse voltage withstand test and hammer test are subjected to the pressure vessel test for early detection of their susceptibility to infant mortality or early failure. The pressure vessel test comprises storing the vacuum interrupters in the closed condition of the contacts thereof in a vessel at a pressure between 2 to 3 kg/cm for about 168 hours. After the pressure vessel test, the pressure in the vacuum interrupters is again measured by the magnetron procedure. If the pressure within the vacuum interrupter is greater than 10"4 Torr the vacuum interrupter is rejected. If the pressure within the vacuum interrupter is less than 10"4 Torr, the vacuum interrupter is subjected to power frequency voltage withstand test and mV drop measurement test successively. If it passes both the tests, it is considered to be healthy for use. Vacuum interrupters are randomly selected from a given batch and subjected to mechanical endurance test which comprises 50,000 close-open operations with a force of 130-250 kg and a speed of 0.5 to 1 m/s depending on the current and voltage rating of the vacuum interrupters.
As the pressure vessel test duration during manufacture of the vacuum interrupters is generally 168 hours, the manufacturing time for the vacuum interrupters is correspondingly increased and productivity and efficiency of production and economics of production are reduced. The hammer test and pressure vessel test help to identify vacuum interrupters with sealing joints prone or susceptible to early or premature rupture or failure due to mechanical stresses and eliminate them at the manufacturing stage. Although the sealed joints of vacuum interrupters are also inherently prone or susceptible to leakage and rupture due to thermal stresses, the effect of thermal stresses is not evaluated at the manufacturing stage of the vacuum interrupters. Therefore, infant mortality of the vacuum interrupters due to thermal stresses can occur to the vacuum interrupters during the operation thereof thereby reducing the life of the vacuum interrupters.
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OBJECTS OF INVENTION
An object of the invention is to provide an accelerated method for the manufacture of vacuum interrupter, which method reduces the manufacturing time thereby increasing productivity and production efficiency and economics of production of vacuum interrupters.
Another object of the invention is to provide an accelerated method for the manufacture of vacuum interrupter, which method besides evaluating the effect of mechanical stresses also evaluates the effect of thermal stresses at the sealing joints of the vacuum interrupter and eliminates vacuum interrupters having sealing joints prone or susceptible to rupture due to both mechanical and thermal stresses at the manufacturing stage thereof thereby preventing both mechanical and thermal stresses induced infant mortality of the vacuum interrupters and improving the life of the vacuum interrupters.
Another object of the invention is to provide an accelerated method for the manufacture of vacuum interrupter, which method facilitates to carry out the hammer test during the pressure vessel test.
Another object of the invention is to provide a pressure vessel for use in the manufacture of vacuum interrupter which reduces the manufacturing time of vacuum interrupters thereby increasing productivity and production efficiency and economics of production of vacuum interrupters.
Another object of the invention is to provide a pressure vessel for use in the manufacture of vacuum interrupter, which besides evaluating the effect of mechanical stresses also evaluates the effect of thermal stresses at the sealing joints of the vacuum interrupter and eliminates vacuum interrupters having sealing joints prone or susceptible to rupture due to both mechanical and thermal stresses at the manufacturing stage thereof thereby preventing both mechanical and thermal stresses induced infant mortality of the vacuum interrupters, and improving the life of the vacuum interrupters.
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Another object of the invention is to provide a pressure vessel for use in the manufacture of vacuum interrupter, which facilitates to carry out the hammer test during the pressure vessel test.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided an accelerated method for the manufacture of vacuum interrupter comprising subjecting the vacuum interrupter passing the power frequency voltage withstand test and impulse voltage withstand test to the pressure vessel test, which comprises subjecting the vacuum interrupter to the hammer test in a vessel at atmospheric pressure by keeping the vacuum interrupter fixed in position and closing and opening the moving contact of the vacuum interrupter 100 to 150 times at a force of 130-250 kg with a speed of 0.5 to 1 m/s and storing the vacuum interrupter subjected to the hammer test in the vessel at a pressure of 2 to 3kg/cm with the vacuum interrupter fixed in position and the moving electrode of the vacuum interrupter being kept pulled away from the vacuum interrupter at a force of 130 to 250 kg with simultaneous heating of the seal cups of the vacuum interrupter at 130 to 160°C for period of 65 to 75 hours.
According to the invention there is also provided a pressure vessel for use in the manufacture of vacuum interrupter comprising a vessel connected to an air supply and fitted with a pressure gauge and a pressure relief valve, the vessel having a platform provided therein for supporting at least one vacuum interrupter, fixing means for firmly holding the vacuum interrupter in position and pulling means for closing and opening the moving contact of the vacuum interrupter at a force of 130-250 kg with a speed of 0.5 tol m/s and for keeping the moving electrode pulled at a force of 130 to 250 kg and heating means for simultaneously heating the seal cups of the vacuum interrupter at 130 to 160°C for 65 to 75 hours.
According to an embodiment of the invention, the seal cups of the vacuum interrupter are electrically heated and the heating means comprises an electric heater comprising a pair of ring shaped heater elements each being removably fitted over each of the seal cups and connected to an AC power supply through an electric control.
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According to an embodiment of the invention, the moving electrode of the vacuum interrupter is pneumatically pulled and the pulling means comprises a pneumatic cylinder mounted on the platform and connected to a pneumatic supply through a pneumatic control provided with a cyclic counter, the piston rod of the pneumatic cylinder being coupled to the moving electrode of the vacuum interrupter.
According to an embodiment of the invention, the fixing means comprises a channel shaped bracket mounted on the platform and a bolt secured to the fixed electrode of the vacuum interrupter at its end protruding outside the respective seal cup in thread engagement therewith the bolt passing through a hole in the web portion of the bracket with the head of the bolt abutting against the web portion of the bracket.
The following is a detailed description of the invention with reference to the accompanying drawings in which :
Fig 1 is schematic front elevation of a pressure vessel for use in the manufacture of vacuum interrupters according to an embodiment of the invention; and
Fig 2 is schematic top view of the pressure vessel of Fig 1 without the top wall thereof and without the pneumatic and electric controls.
The pressure vessel 1 as illustrated in Figs 1 and 2 of the accompanying drawings comprises a vessel 2 connected to an air supply (not shown) through port 3. The vessel is fitted with a pressure gauge 4 and pressure relief valve 5. The vessel is also provided with a platform 6 supported on support members 6a and 6b and having three spaced brackets 7a, 7b and 7c. Each of the brackets is channel shaped and is provided with a hole (not shown) in the web portion 8 thereof. 9a, 9b and 9c are three vacuum interrupters which have passed the power frequency voltage withstand test and impulse voltage withstand test. The seal cups and end plates at each end of the vacuum interrupters are marked 10, 10 and 11, 11, respectively. The fixed electrode is marked 12. The vacuum interrupters 9a, 9b and 9c
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are aligned with the brackets 7a, 7b and 7c, respectively. Each of the vacuum interrupters is supported and fixedly or firmly held on the platform in position by a bolt 13 secured to the fixed electrode 12 at its end protruding outside the respective seal cup in thread engagement therewith. The bolt 13 passes through the hole in the web portion of the respective bracket and its head abuts against the web portion of the bracket thereby firmly holding the vacuum interrupter in position against the respective bracket on the platform. 14a, 14b and 14c are pneumatic cylinders mounted on the platform aligned with the vacuum interrupters 9a, 9b and 9c and brackets 7a, 7b and 7c, respectively. The piston rods 15a, 15b and 15c of the pneumatic cylinders are coupled to the moving electrodes 16a, 16b and 16c of the vacuum interrupters by couplings marked 17a, 17b and 17c, respectively. The pistons of the pneumatic cylinders are marked 18. The cylinder side port 19 and piston side port 20 of each of the pneumatic cylinders are connected to a pneumatic control 21 through ports 22 and 23, respectively. The pneumatic control is provided with a cyclic counter 24. The seal cups of the vacuum interrupters are provided with ring shaped electric heater elements 25a and 25b, respectively removably fitted over them. The heater elements are connected to an AC power supply (not shown) through an electric control 26.
The vacuum interrupters are subjected to the hammer test in the vessel at atmospheric pressure by closing and opening the moving contacts of the vacuum interrupters for instance 100 to 150 times at a force of 150-250kg with a speed of 0.5 - 0.1 m/s by alternating the air supply to the cylinder side and piston side of the pneumatic cylinder by operating the pneumatic control. The cyclic counter of the pneumatic control keeps a count of the number of closing and opening of the moving contacts of the vacuum interrupters and indicates the same to the operator. It is to be understood that the number of times of the closing and opening of the moving contacts for the hammer test can vary. The pistons and piston rods reciprocate in the pneumatic cylinders to move the moving electrodes of the vacuum interrupters back and forth. Following this, the vessel is pressurized to 2-3kg per cm2 by allowing air to enter the vessel through port 3. The vacuum interrupters are stored in the vessel at a pressure of 2-3 kg per cm2 with the moving electrodes of the vacuum interrupters kept pulled away from the vacuum interrupters at a force of 130-250kg by operating the pneumatic control and pressurizing the cylinder side of
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the pneumatic cylinders through parts 19. On pressurizing the cylinder side of the pneumatic cylinders, the pistons and piston rods of the pneumatic cylinders move in and keep the moving electrodes pulled. Simultaneously the heater elements are heated to a temperature of 130-160° by operating the electric control. The moving electrodes of the vacuum interrupters are subjected to pulling and the seal cups of the vacuum interrupters are subjected to heating simultaneously continuously for a period of 65 to 75 hours under pressure of 2-3 kg cm2. While the moving electrodes of the vacuum interrupters are kept continuously pulled at a force of 130-250kg and the seal cups are kept continuously heated at 130-160°C, the sealing joints of the vacuum interrupters are continuously subjected to both mechanical stresses and thermal stresses. This helps to detect susceptibility of the vacuum interrupters to mechanical and thermal stresses and their susceptibility to early or premature failure due to such stresses and their elimination at the manufacturing stage itself within the reduced time duration of 65 to 72 hours. The air pressure in the vessel is monitored through the pressure gauge. At the end of the pressure vessel test the air relief valve is opened to release the air pressure in the vessel. The heating of the end plates of the vacuum interrupters is discontinued. Air supply to the piston side of the pneumatic cylinders is resumed and air in the cylinder side of the pneumatic cylinders is released through the respective ports 20 and 19. The pistons and piston rods of the pneumatic cylinders move out thereby releasing the pulling force on the moving contacts of the vacuum interrupters. Once the end plates of the vacuum interrupter have cooled down, the vacuum interrupters are unfastened from the brackets by removing the bolts. The moving electrodes of the vacuum interrupters are released from the piston rods of the pneumatic cylinders by removing the couplings. The vacuum interrupters are taken to the next tests namely power frequency voltage withstand test and mV drop measurement test and mechanical endurance test at random as desired.
According to the invention the manufacturing time of the vacuum interrupters during the pressure vessel test is reduced from about 168 hours to about 65 to 75 hours. Therefore, the productivity and production efficiency and economics of production of vacuum interrupters are increased. Besides, evaluating the susceptibility of the sealing joints of the vacuum interrupters to mechanical stresses in an accelerated manner within the reduced
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time, the method of the invention also evaluates the susceptibility of sealing joints of the vacuum interrupters to thermal stresses simultaneously in an accelerated manner within the reduced time. Therefore, according to the invention it is possible to detect early susceptibility of the vacuum interrupters to both mechanical and thermal stresses at the manufacturing stage itself and prevent infant mortality of the vacuum interrupters due to both the mechanical and thermal stresses and improve the life of the vacuum interrupters. It is also possible according to the invention to carry out the hammer test in the pressure vessel itself.
The performance of vacuum interrupters (VI) manufactured according to the conventional method and the method of the invention were evaluated and were as shown in the following Tables 1 and 2
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Table 1
(conventional method)
Sr VI Pre pressure vessel test Pressure Vessel Test Post pressure vessel test
No rating
Vacuum Power mV drop 50,000
Vacuumlevel in Power frequency Impulsevoltage Hammertest of VI Pressure vessel test Pressure inthe pressurevesselkg/cm2 level in VI frequency voltage test measurement test mechanical operations
VI voltage withstand Y/N duration (mbar) withstand Y/N withstand
(mbar) withstand test of VI 100 times (hours) Y/N test
test of VI Y/N Y/N
Y/N
1 12 kV, lxl0-6 Y Y Y lxl0-6 Y Y Y
2
1250 A, 20 kA 1xl0-6 Y Y Y 168 2 lxl0-5 Y Y Y
3 5xl0-6 Y Y Y Lxl0-5 Y Y Y
Table 2
(method of invention)
SrNo VI rating Pre pressure vessel test Pressure Vessel Test Post pressure vessel test
Vacuum Power Impulse Hammer test Pressure Temperature Pulling Pressure Vacuum Power mV drop 50,000
level in frequency voltage Of VI in the in the of heater force of vessel level in Frequency measurement mechanical
VI voltage with stand vessel at pressure elements moving test VI voltage test operationswithstandtestY/N
(mbar) withstand test of atmospheric vessel OC contact duration (mbar) withstand Y/N
test of VI pressure kg/cm2 Of VI (hours) test
VIY/N Y/N 100 timesY/N Y/N
4 12 kV, 1250A, 20 kA Lx0-5 Y Y Y 2 150 250kg 72 Lxl0-5 Y Y Y
5 Lx0-6 Y Y Y 150 250kg Lxl0-6 Y Y Y
150 250kg Lxl0-4 Y Y Y
6 Lx0-5 Y Y Y

It is quite clear from the Tables 1 and 2 that the performance of the vacuum interrupters manufactured according to the method of the invention was comparable to the performance of the vacuum interrupters manufactured by the conventional method.
The pressure vessel can be designed to hold one or two or more than 3 vacuum interrupters. The platform for mounting the vacuum interrupters and pneumatic cylinders may be of different configuration or construction. Besides the bolt and bracket arrangement for fixing the vacuum interrupters in position, other fixing means can be used. Instead of pneumatic cylinder, hydraulic cylinder can be used to keep the moving contacts of the vacuum interrupters pulled or to carry out the hammer test. The hammer test can be carried out outside the pressure vessel. The heating elements can be of a different configuration. Such variations of the invention are to be construed and understood to be obvious to those skilled in the art and within the scope of the invention.
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We Claim
1. An accelerated method for the manufacture of vacuum interrupter comprising subjecting the vacuum interrupter passing the power frequency voltage withstand test and impulse voltage withstand test to the pressure vessel test, which comprises subjecting the vacuum interrupter to the hammer test in a vessel at atmospheric pressure by keeping the vacuum interrupter fixed in position and closing and opening the moving contact of the vacuum interrupter 100 to 150 times at a force of 130-250kg with a speed of 0.5 to 1 m/s and storing the vacuum interrupter subjected to the hammer test in the vessel at a pressure of 2 to 3kg/cm with the vacuum interrupter fixed in position and the moving electrode of the vacuum interrupter being kept pulled away from the vacuum interrupter at a force of 130 to 250 kg with simultaneous heating of the seal cups of the vacuum interrupter at 130 to 160°C for period of 65 to 75 hours.
2. An accelerated method as claimed in claim 1, wherein the moving electrode of the vacuum interrupter is pneumatically pulled.
3. An accelerated method as claimed in claim 1, wherein the seal cups of the vacuum interrupter are electrically heated.
4. A pressure vessel for use in the manufacture of vacuum interrupter comprising a vessel connected to an air supply and fitted with a pressure gauge and a pressure relief valve, the vessel having a platform provided therein for supporting at least one vacuum interrupter, fixing means for firmly holding the vacuum interrupter in position and pulling means for closing and opening the moving contact of the vacuum interrupter at a force of 130-250 kg with a speed of 0.5 to 0.1 m/s and for keeping the moving electrode pulled at a force of 130 to 250 kg and heating means for simultaneously heating the seal cups of the vacuum interrupter at 130 to 160°C for 65 to 75 hours.
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5. A pressure vessel as claimed in claim 4, wherein the fixing means comprises a
channel shaped bracket provided on the platform and a bolt secured to the fixed electrode
of the vacuum interrupter at its end protruding outside the respective seal cup in thread
engagement therewith, the bolt passing through a hole in the web portion of the bracket
with the head of the bolt abutting against the web portion of the bracket.
6. A pressure vessel as claimed in claim 4, wherein the pulling means comprises a
pneumatic cylinder mounted on the platform and connected to a pneumatic supply through
a pneumatic control provided with a cyclic counter, the piston rod of the pneumatic
cylinder being coupled to the moving electrode of the vacuum interrupter.
7. A pressure vessel as claimed in claim 4, wherein the heating means comprises an
electric heater comprising a pair of ring shaped heater elements each being removably
fitted over each of the seal cups and connected to an AC power supply through an electric
control.
Dated this 31st day of March 2006

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ABSTRACT
An accelerated method for the manufacture of vacuum interrupter. The vacuum interrupter passing the power frequency voltage withstand test and impulse voltage withstand test is subjected to the pressure vessel test by subjecting the vacuum interrupter to the hammer test in a vessel at atmospheric pressure by keeping the vacuum interrupter fixed in position and closing and opening the moving contact of the vacuum interrupter 100 to 150 times at a force of 130-250kg with a speed of 0.5 to 1 m/s. The vacuum interrupter subjected to the hammer test is stored in the vessel at a pressure of 2 to 3kg/cm2 with the vacuum interrupter fixed in position and the moving electrode of the vacuum interrupter being kept pulled away from the vacuum interrupter at a force of 130 to 250 kg with simultaneous heating of the seal cups of the vacuum interrupter at 130 to 160°C for period of 65 to 75 hours. Also a pressure vessel for use in the manufacture of vacuum interrupter comprising a vessel (1) connected to an air supply and fitted with a pressure gauge (4) and a pressure relief valve (5). The vessel has a platform (6) provided therein for supporting at least one vacuum interrupter (9a, 9b, 9c). The vessel is provided with fixing means (7a, 7b, 7c, 13) for firmly holding the vacuum interrupter in position and pulling means (14a, 14b, 14c, 21, 24) for closing and opening the moving contact (16a, 16b, 16c) of the vacuum interrupter at a force of 130-250 kg with a speed of 0.5 to 0.1 m/s and for keeping the moving electrode (16a, 16b, 16c) pulled at a force of 130 to 250 kg. Heating means (25a, 25b, 26) are provided for simultaneously heating the seal cups (10, 10) of the vacuum interrupter at 130 to 160°C for 65 to 75 hours.