CA2205539C - Transformer testing method - Google Patents
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- CA2205539C CA2205539C CA002205539A CA2205539A CA2205539C CA 2205539 C CA2205539 C CA 2205539C CA 002205539 A CA002205539 A CA 002205539A CA 2205539 A CA2205539 A CA 2205539A CA 2205539 C CA2205539 C CA 2205539C
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- arrester
- isolator
- housing
- transformer
- coupling
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Abstract
Testing of a transformer in an oil filled housing is done by providing an external arrester insulator/isolator penetrating and making an electrical connection through the housing while preventing leaking of oil from said housing. An arrester inside said housing is electrically coupled between an interior end of arrester isolator and a predetermined potential point within the housing. An exterior end of said arrester isolator is removably and electrically coupled to a ground potential point. The ground coupling is removed from the exterior end of the arrester isolator and the transformer is tested by measuring electrical characteristics on transformer connections emerging from the housing. The ground coupling is reconnected to the exterior end of the arrester isolator after testing is completed. If required, an insulating cap may be applied to the external isolator to provide additional withstand capability to external flashover during the tests.
Description
Title - TRANSFORMER TESTING METHOD
This is a division of our copending Canadian Patent Application No. 2,004,444 filed December 1, 1989.
1. Field of the Invention This invention relates to devices for protecting single and multiphase high voltage apparatus to provide over-voltage protection and apparatus test, and more particularly, relates to the means for testing single and multiphase high voltage apparatus equipped with surge arresters or surge protectors and/or test the surge arrester without the necessity of disassembling the apparatus. wen more specifically, this invention relates to the testing of an oil filled apparatus such as a transformer having a surge arrester of the metal oxide varistor (MOV) type designed for under oil mounting and an external isolator.
This is a division of our copending Canadian Patent Application No. 2,004,444 filed December 1, 1989.
1. Field of the Invention This invention relates to devices for protecting single and multiphase high voltage apparatus to provide over-voltage protection and apparatus test, and more particularly, relates to the means for testing single and multiphase high voltage apparatus equipped with surge arresters or surge protectors and/or test the surge arrester without the necessity of disassembling the apparatus. wen more specifically, this invention relates to the testing of an oil filled apparatus such as a transformer having a surge arrester of the metal oxide varistor (MOV) type designed for under oil mounting and an external isolator.
2. Background Very often, it is necessary to test for any one of a number of reasons both in the field and prior to being shipped the single phase and multiphase voltage apparatus, i. e., transformer and/or its surge arrester. For example, after a transformer is subjected to high voltage transients, which could damage or destroy it, it may be necessary to conduct tests in order to determine whether a part should be replaced. During manufacture there could be faulty connections or the like. Therefore, it may be necessary to test the transformer of ter manufacture and before shipment. It may also be desirable, and often necessary, to conduct routine tests on CA 02205539 1997-06-16 ' the transformer in order to determine that it is in good working order.
Oil filled transformers and metal oxide varistor arresters are known. Generally, it is necessary to provide an arrester or a surge protector which protects the transformer against high voltage transients. For this reason, it is common practice to connect an arrester which will conduct transients from a power line to ground ahead of or at the transformer when high voltage occurs. The surge arrester may be mounted within the transformer tank.
High voltage surges actuate the arrester so that damaging electrical potentials are shunted to ground via the arrester before the transformer can be destroyed. Since the internally mounted arrester provides a path for shunting high voltage to ground, it also prevents a valid dielectric test of the transformer insulation system. Thus, it is not possible to test the transformer without disconnecting the internal arrester.
Therefore, the common practice is to disconnect the a.rrester, dielectrically test the transformer, and then reconnect the arrester or surge protector. In the case of an oil~filled transformer which has an arrester mounted therein, it is both awkward and costly to test the transformer and/or arrester. The transformer tank must be opened to so disconnect and reconnect the surge protector. This therefore substant-Tally eliminates field and/or installation evaluation of the transformer.
Still another condition which leads to cost problems and design restrictions is the need heretofore wherein an arrester failure should result in an open circuit fault. For example, most arresters are designed to melt open an isolating .fuse link or to fracture and result in an open circuit condition when a transient persists for a period of time.
Thereafter, it is necessary to disassemble the transformer and clean and remove all of the arrester parts from the trans-former housing. This is especially difficult when the transformer housing is filled with oil. Further, when an under oil arrester mounted in an oil filled transformer fails, - t=here is no readily visible means to indicate the arrester failure .
'Summa~.y .o.f '.the. .Tri~enti:on According to the present invention, we provide a ' method of testing a transformer in an oil filled housing, comprising the steps of: (a) providing an external arrester i.nsulator/isolator penetrating said housing for making an electrical connection through the housing while preventing a leaking of oil from said housing; (b) electrically coupling a.n arrester inside said housing between an interior end of said arrester isolator and a predetermined potential point within said housing; (c) removably and electrically coupling an exterior end of said arrester isolator to a ground potential point; (d) removing said ground coupling from said exterior end of said arrester isolator; (e) testing said transformer by
Oil filled transformers and metal oxide varistor arresters are known. Generally, it is necessary to provide an arrester or a surge protector which protects the transformer against high voltage transients. For this reason, it is common practice to connect an arrester which will conduct transients from a power line to ground ahead of or at the transformer when high voltage occurs. The surge arrester may be mounted within the transformer tank.
High voltage surges actuate the arrester so that damaging electrical potentials are shunted to ground via the arrester before the transformer can be destroyed. Since the internally mounted arrester provides a path for shunting high voltage to ground, it also prevents a valid dielectric test of the transformer insulation system. Thus, it is not possible to test the transformer without disconnecting the internal arrester.
Therefore, the common practice is to disconnect the a.rrester, dielectrically test the transformer, and then reconnect the arrester or surge protector. In the case of an oil~filled transformer which has an arrester mounted therein, it is both awkward and costly to test the transformer and/or arrester. The transformer tank must be opened to so disconnect and reconnect the surge protector. This therefore substant-Tally eliminates field and/or installation evaluation of the transformer.
Still another condition which leads to cost problems and design restrictions is the need heretofore wherein an arrester failure should result in an open circuit fault. For example, most arresters are designed to melt open an isolating .fuse link or to fracture and result in an open circuit condition when a transient persists for a period of time.
Thereafter, it is necessary to disassemble the transformer and clean and remove all of the arrester parts from the trans-former housing. This is especially difficult when the transformer housing is filled with oil. Further, when an under oil arrester mounted in an oil filled transformer fails, - t=here is no readily visible means to indicate the arrester failure .
'Summa~.y .o.f '.the. .Tri~enti:on According to the present invention, we provide a ' method of testing a transformer in an oil filled housing, comprising the steps of: (a) providing an external arrester i.nsulator/isolator penetrating said housing for making an electrical connection through the housing while preventing a leaking of oil from said housing; (b) electrically coupling a.n arrester inside said housing between an interior end of said arrester isolator and a predetermined potential point within said housing; (c) removably and electrically coupling an exterior end of said arrester isolator to a ground potential point; (d) removing said ground coupling from said exterior end of said arrester isolator; (e) testing said transformer by
3 ?7326-65D
measuring electrical characteristics on transformer connections emerging from said housing; and (f) reconnecting said ground coupling to said exterior end of said arrester isolator after said testing is completed. If required, an insulating cap may be applied to the external isolator to provide additional withstand capability to external flashover during the tests.
The arresters or surge protectors of the oil filled high voltage apparatus do not have to be disconnected in order to test the transformer either in the factory after manufacture and before shipment or in the field during operation. There preferably is included means for remotely separating or isolating the apparatus from the surge protector.
It is desirable to provide a visual indication of the destruction of a surge arrester mounted within a transformer housing so that workers in the field can quickly tell if a transformer must be tested and repaired or replaced. An internally mounted arrester no longer has to fail in an open circuit condition. Here, an arrester may fail in a short circuit mode and still give ample "open circuit" isolation.
An oil filled transformer has suitably mounted in its transformer housing a surge arrester of the metal oxide varistor type. An isolator is externally mounted on the transformer housing and has an external visible link thereon.
The visible ground wire connected to the isolator is connected to a ground point outside the housing. The other end of the isolator is connected to the arrester inside the housing. Thus, the arrester is connected from a ground point outside
measuring electrical characteristics on transformer connections emerging from said housing; and (f) reconnecting said ground coupling to said exterior end of said arrester isolator after said testing is completed. If required, an insulating cap may be applied to the external isolator to provide additional withstand capability to external flashover during the tests.
The arresters or surge protectors of the oil filled high voltage apparatus do not have to be disconnected in order to test the transformer either in the factory after manufacture and before shipment or in the field during operation. There preferably is included means for remotely separating or isolating the apparatus from the surge protector.
It is desirable to provide a visual indication of the destruction of a surge arrester mounted within a transformer housing so that workers in the field can quickly tell if a transformer must be tested and repaired or replaced. An internally mounted arrester no longer has to fail in an open circuit condition. Here, an arrester may fail in a short circuit mode and still give ample "open circuit" isolation.
An oil filled transformer has suitably mounted in its transformer housing a surge arrester of the metal oxide varistor type. An isolator is externally mounted on the transformer housing and has an external visible link thereon.
The visible ground wire connected to the isolator is connected to a ground point outside the housing. The other end of the isolator is connected to the arrester inside the housing. Thus, the arrester is connected from a ground point outside
4 the transformer housing through the isolator. High voltage transients are conducted to ground via the arrester. As stated above, the arrester may be activated or destroyed by high voltage and high current transients. When the energy level of the transient is sufficient to damage the arrester, it will also be sufficient to blow off the visible ground lead and disconnect the external ground connection. Thus a man in the field can readily see when the arrester internally mounted in a transformer tank has been damaged.
Further, the externally mounted isolator enables the i=ransformer to be readily tested. If required, an insulating 4a E r cap can be placed over the isolator to provide greater insulation to ground during the dielectric tests.
~3RIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention are shown in the attached drawings, wherein:
Fig. 1 schematically illustrates a two coil transformer in an oil filled housing with an under oil arrester in a veri~ical position between transformer coils;
Fig. 2 is a cross-section taken along line 2-2 of Fig. 1;
Fig. 3 is a cross-section which shows a wall or cover mounted feed-through bushing isolator and arrester insulator;
and Fig. 4 is a schematic illustration of a single coil transformer having a horizontal surge arrester;
Fig. 5 is a cross-section taken along line 5-5 of Fig. 4;
and Fig. 6 is a graph showing a typical arrester isolator disconnect characteristics that are used by the invention. .
DETAINED DESCRIPTION OF THE INVENTION
Figs. 1 and 2 show a transformer housing 20 coupled to a high voltage line 22 via a primary insulated bushing 24. The housing is substantially full of oil, up to level 26 or other insulating;media. Oil is commonly used within the housing to provide the required dielectric strength.
Inside the housing, an oil insulated transformer is provided in any conventional design. We illustrate here two coils 28, on a core 2.9 in a conventional manner. The exact design of the transformer is not relevant to our invention.
<35950113.SPC> 5 - ~ CA 02205539 1997-06-16 The transformer has a primary wire 22 connected to an insulated bushing 24 on the exterior of tank 20. The external connections 22 and point G are available for conducting specified dielectric tests.
Enclosed within tank 20 is any suitable and known arrester or surge protector 30 which is designed to protect the transformer from high voltage. The preferred arrester is a mental oxide varistor type which provides a non-linear resistance that decreases under over voltage conditions. If the voltage transient is high enough, the resistance of arrester 30 significantly decreases, limiting the over voltage applied to the potential point P1, thereby protecting the transformer winding 28.
The arrester 30 is preferably positioned within the tank 20 in a position which minimizes the length of the lead lines 31, while placing the arrester in a mechanically safe and fully protected position. The short lead lines are desirable primarily to prevent their impedance from increasing the. ~-overvoltage stress on the winding 28.
The arrester 30 is grounded at point G, via a through the wall. external insulator/isolator 32 and connected, to a high potential point P1. High potential point P1 is between primary bushing 24 and transformer coil 28.
Under normal operating conditions, the arrester resistance is high and has no significant effect upon the potential at point P1. However, if lightning, for example, should strike the primary feed line 22, the resulting high voltage transient significantly reduces the resistance of <35950113.SPC> 6 .. .
arrs~ster 30 in order to conduct the transient to ground and remove the current surge that might damage the coil 28. Upon cessation of the overvoltage, a sharp increase in resistance of i~he arrester takes place and the current through the arrester 30 returns to the magnitude typical for normal service.
Referring to Fig. 3, the external wall or cover mounted arrester insulator/isolator 32 is shown in a partial cross seci~ional view as mounted on the transformer tank 20. The insulator/isolator 32 may have any appropriate configuration.
We use an insulator/isolator 32 having a feed-thru bushing insulator 40 with an appropriate isolator 51 mounted thereon.
The isolator has an appropriate disconnector 52 releasably mounted thereon. The insulator bushing 40 is made of any appropriate insulating material. The insulating material and insulating characteristics of the insulator bushing are such that, with the ground lead removed from the isolator, standard dielectric high potential tests may be run on the transformer.
In some cases it may be desirable to encase the external isolator 51 with an insulating cap (not shown) to provide additional voltage withstand capability.
In general, there is a hole in the wall or cover of the transformer tank 20 through which the insulator bushing 40 may pass. Threads T are formed on the inside end of insulator bushing 40. A compression gasket 42 is trapped between insulator 40 and tank 20 on one side and a compression nut 44 is i~hreaded onto the -threaded end of insulator 40 on the inside of the tank 20. When compression nut 44 is tightened, <35950113.SPC> 7 _ CA 02205539 1997-06-16 the gasket 42 forms an oil tight seal between tank 20 and ' insulator 40. The oil seal is necessarv to arevent oil leakage or moisture ingress.
Extending through insulator 40 is a threaded stud 46 which has a threaded receiver hole 49. The isolator 51 has a threaded terminal 50 that is screwed into the hole 49. An advantage of this construction is that the isolator 51 and/or disconnector 52 may be replaced without having to either open tank 20 or break the oil seal at gasket 42. The arrester 30 is connected to stud 46 via wire 31 (Fig. 1). A ground.wire 56 is connected from ground point G to a stud 58 (Fig. 3) on the arrester disconnector.
The disconnector 52 may be operated by a blank 22-cal.
cartridge or other means such that the frangible housing of disconnector 52 is broken and the lead connected to 58 is disconnected from the arrester. The disconnector 52 is actuated when enough heat is generated to ignite the powder (no-t shown) in the disconnector 52. The heat occurs w responsive to the high current conducted by the arrester during or after conditions such as voltage transients.
Although we have described the use of a powder charge disconnector, any suitable thermal type release disconnector may be used.
In order to test the transformer without involving the arrester or surge protector 30, the ground wire 56 (Fig. 1) is disconnected from the lug 58, thereby removing ground from the arreater, which open.circuits the arrester 30. -The test may then be carried out by simply measuring the electrical <35~50113.SPC> 8 characteristics on the transformer wire emerging from the housing 20 and point G. An insulating cap can be placed over the insulator/isolator so that the open circuited arrester 30 has no effect upon the testing. After the test is completed, ground wire 56 is reconnected to the lug 58.
Another embodiment is shown in (Figs. 4, 5) where the insulator/isolator 32 is mounted in the tank wall instead of in i~he cover. Here, the same reference numerals are used to identify the same parts that are shown in Figs. 1, 2.
Therefore, they will not be described a second time.
For this type of transformer, the arrester 30 is shown mounted horizontally on insulated brackets 62, 64 which are secured to the transformer core/coil assembly 29a.
Heretofore, arresters were usually designed to fail in an open circuit mode. This requirement caused arresters to be designed to fall apart or otherwise destroy themselves in order to be certain that there is a physical gap in the circuit after a failure has occurred. As a result, after a°
failure, the broken parts of-the perished arrester remained in the transformer tank.
According to the invention, when a disconnector 52 (Fig.
3) operates, the frangible section ruptures and the ground wire 56 is-blown off along with the arrester ground stud 58, thereby producing an open circuit between potential point P1 and ground G. This means that the arrester may now be either a short or an open circuit. Therefore, it is more probable that the arrester may. not fall apart. Thus the whole arrester <35950113.SPC> 9 may be removed and the transformer placed back in service after replacing the arrester, and changing the oil.
Fig. 6 illustrates the desired disconnecting fault curi_-ent-time characteristic for a disconnector 52. Some high voltage conditions (such as lightning strokes) do not last long enough to generate a current which is heavy enough to destroy the arrester 30. Therefore, it would not be either necessary or desirable to actuate the disconnector 52. On the other hand, if the energy level is high enough, it might be desirable to have an instantaneous disconnect.
The horizontal axis of Fig. 6 indicates the root mean square amperage of the fault current. The vertical axis indicates the time required to ignite an explosive charge after the indicated amperage occurs. The operating range or band 70 indicates the allowable variance V for disconnector operation.
The advantages of the invention should now be clear. It is possible to conduct testing upon the transformer after ._ manufacture and before shipment without having to either open the cover or disconnect the arrester. In the event of arrester failure, blowing off the ground wire 56 gives a visual indication to a lineman so that he will know that maintenance is required, and to take the proper safety precautions. The failure of an arrester no longer must be an open circuit failure; therefore, it may not be necessary to design an arrester to have an internal disconnecting feature.
For convenience of description, this specification referred to "oil filled transformers°'. However, it should be <35950113.SPC> 10 . CA 02205539 1997-06-16 i~
understood that the principles of our inventian may also be applied to many other types of transformers or other high voltage devices with other insulating systems which may require similar protection and testing. Therefore, the invention is to be construed broadly enough to cover all equivalent structures including both single and three phase devices .
Those who are skilled in the art will readily perceive how to modify the invention. Therefore, the appended claims are to be construed to cover all equivalent structures which fall within the true scope and spirit of the invention.
<35950113.SPC> 11
Further, the externally mounted isolator enables the i=ransformer to be readily tested. If required, an insulating 4a E r cap can be placed over the isolator to provide greater insulation to ground during the dielectric tests.
~3RIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention are shown in the attached drawings, wherein:
Fig. 1 schematically illustrates a two coil transformer in an oil filled housing with an under oil arrester in a veri~ical position between transformer coils;
Fig. 2 is a cross-section taken along line 2-2 of Fig. 1;
Fig. 3 is a cross-section which shows a wall or cover mounted feed-through bushing isolator and arrester insulator;
and Fig. 4 is a schematic illustration of a single coil transformer having a horizontal surge arrester;
Fig. 5 is a cross-section taken along line 5-5 of Fig. 4;
and Fig. 6 is a graph showing a typical arrester isolator disconnect characteristics that are used by the invention. .
DETAINED DESCRIPTION OF THE INVENTION
Figs. 1 and 2 show a transformer housing 20 coupled to a high voltage line 22 via a primary insulated bushing 24. The housing is substantially full of oil, up to level 26 or other insulating;media. Oil is commonly used within the housing to provide the required dielectric strength.
Inside the housing, an oil insulated transformer is provided in any conventional design. We illustrate here two coils 28, on a core 2.9 in a conventional manner. The exact design of the transformer is not relevant to our invention.
<35950113.SPC> 5 - ~ CA 02205539 1997-06-16 The transformer has a primary wire 22 connected to an insulated bushing 24 on the exterior of tank 20. The external connections 22 and point G are available for conducting specified dielectric tests.
Enclosed within tank 20 is any suitable and known arrester or surge protector 30 which is designed to protect the transformer from high voltage. The preferred arrester is a mental oxide varistor type which provides a non-linear resistance that decreases under over voltage conditions. If the voltage transient is high enough, the resistance of arrester 30 significantly decreases, limiting the over voltage applied to the potential point P1, thereby protecting the transformer winding 28.
The arrester 30 is preferably positioned within the tank 20 in a position which minimizes the length of the lead lines 31, while placing the arrester in a mechanically safe and fully protected position. The short lead lines are desirable primarily to prevent their impedance from increasing the. ~-overvoltage stress on the winding 28.
The arrester 30 is grounded at point G, via a through the wall. external insulator/isolator 32 and connected, to a high potential point P1. High potential point P1 is between primary bushing 24 and transformer coil 28.
Under normal operating conditions, the arrester resistance is high and has no significant effect upon the potential at point P1. However, if lightning, for example, should strike the primary feed line 22, the resulting high voltage transient significantly reduces the resistance of <35950113.SPC> 6 .. .
arrs~ster 30 in order to conduct the transient to ground and remove the current surge that might damage the coil 28. Upon cessation of the overvoltage, a sharp increase in resistance of i~he arrester takes place and the current through the arrester 30 returns to the magnitude typical for normal service.
Referring to Fig. 3, the external wall or cover mounted arrester insulator/isolator 32 is shown in a partial cross seci~ional view as mounted on the transformer tank 20. The insulator/isolator 32 may have any appropriate configuration.
We use an insulator/isolator 32 having a feed-thru bushing insulator 40 with an appropriate isolator 51 mounted thereon.
The isolator has an appropriate disconnector 52 releasably mounted thereon. The insulator bushing 40 is made of any appropriate insulating material. The insulating material and insulating characteristics of the insulator bushing are such that, with the ground lead removed from the isolator, standard dielectric high potential tests may be run on the transformer.
In some cases it may be desirable to encase the external isolator 51 with an insulating cap (not shown) to provide additional voltage withstand capability.
In general, there is a hole in the wall or cover of the transformer tank 20 through which the insulator bushing 40 may pass. Threads T are formed on the inside end of insulator bushing 40. A compression gasket 42 is trapped between insulator 40 and tank 20 on one side and a compression nut 44 is i~hreaded onto the -threaded end of insulator 40 on the inside of the tank 20. When compression nut 44 is tightened, <35950113.SPC> 7 _ CA 02205539 1997-06-16 the gasket 42 forms an oil tight seal between tank 20 and ' insulator 40. The oil seal is necessarv to arevent oil leakage or moisture ingress.
Extending through insulator 40 is a threaded stud 46 which has a threaded receiver hole 49. The isolator 51 has a threaded terminal 50 that is screwed into the hole 49. An advantage of this construction is that the isolator 51 and/or disconnector 52 may be replaced without having to either open tank 20 or break the oil seal at gasket 42. The arrester 30 is connected to stud 46 via wire 31 (Fig. 1). A ground.wire 56 is connected from ground point G to a stud 58 (Fig. 3) on the arrester disconnector.
The disconnector 52 may be operated by a blank 22-cal.
cartridge or other means such that the frangible housing of disconnector 52 is broken and the lead connected to 58 is disconnected from the arrester. The disconnector 52 is actuated when enough heat is generated to ignite the powder (no-t shown) in the disconnector 52. The heat occurs w responsive to the high current conducted by the arrester during or after conditions such as voltage transients.
Although we have described the use of a powder charge disconnector, any suitable thermal type release disconnector may be used.
In order to test the transformer without involving the arrester or surge protector 30, the ground wire 56 (Fig. 1) is disconnected from the lug 58, thereby removing ground from the arreater, which open.circuits the arrester 30. -The test may then be carried out by simply measuring the electrical <35~50113.SPC> 8 characteristics on the transformer wire emerging from the housing 20 and point G. An insulating cap can be placed over the insulator/isolator so that the open circuited arrester 30 has no effect upon the testing. After the test is completed, ground wire 56 is reconnected to the lug 58.
Another embodiment is shown in (Figs. 4, 5) where the insulator/isolator 32 is mounted in the tank wall instead of in i~he cover. Here, the same reference numerals are used to identify the same parts that are shown in Figs. 1, 2.
Therefore, they will not be described a second time.
For this type of transformer, the arrester 30 is shown mounted horizontally on insulated brackets 62, 64 which are secured to the transformer core/coil assembly 29a.
Heretofore, arresters were usually designed to fail in an open circuit mode. This requirement caused arresters to be designed to fall apart or otherwise destroy themselves in order to be certain that there is a physical gap in the circuit after a failure has occurred. As a result, after a°
failure, the broken parts of-the perished arrester remained in the transformer tank.
According to the invention, when a disconnector 52 (Fig.
3) operates, the frangible section ruptures and the ground wire 56 is-blown off along with the arrester ground stud 58, thereby producing an open circuit between potential point P1 and ground G. This means that the arrester may now be either a short or an open circuit. Therefore, it is more probable that the arrester may. not fall apart. Thus the whole arrester <35950113.SPC> 9 may be removed and the transformer placed back in service after replacing the arrester, and changing the oil.
Fig. 6 illustrates the desired disconnecting fault curi_-ent-time characteristic for a disconnector 52. Some high voltage conditions (such as lightning strokes) do not last long enough to generate a current which is heavy enough to destroy the arrester 30. Therefore, it would not be either necessary or desirable to actuate the disconnector 52. On the other hand, if the energy level is high enough, it might be desirable to have an instantaneous disconnect.
The horizontal axis of Fig. 6 indicates the root mean square amperage of the fault current. The vertical axis indicates the time required to ignite an explosive charge after the indicated amperage occurs. The operating range or band 70 indicates the allowable variance V for disconnector operation.
The advantages of the invention should now be clear. It is possible to conduct testing upon the transformer after ._ manufacture and before shipment without having to either open the cover or disconnect the arrester. In the event of arrester failure, blowing off the ground wire 56 gives a visual indication to a lineman so that he will know that maintenance is required, and to take the proper safety precautions. The failure of an arrester no longer must be an open circuit failure; therefore, it may not be necessary to design an arrester to have an internal disconnecting feature.
For convenience of description, this specification referred to "oil filled transformers°'. However, it should be <35950113.SPC> 10 . CA 02205539 1997-06-16 i~
understood that the principles of our inventian may also be applied to many other types of transformers or other high voltage devices with other insulating systems which may require similar protection and testing. Therefore, the invention is to be construed broadly enough to cover all equivalent structures including both single and three phase devices .
Those who are skilled in the art will readily perceive how to modify the invention. Therefore, the appended claims are to be construed to cover all equivalent structures which fall within the true scope and spirit of the invention.
<35950113.SPC> 11
Claims (6)
1. A method of testing a transformer in an oil filled housing, comprising the steps of:
(a) providing an external arrester insulator/isolator penetrating said housing for making an electrical connection through the housing while preventing a leaking of oil from said housing;
(b) electrically coupling an arrester inside said housing between an interior end of said arrester isolator and a predetermined potential point within said housing;
(c) removably and electrically coupling an exterior end of said arrester isolator to a ground potential point;
(d) removing said ground coupling from said exterior end of said arrester isolator;
(e) testing said transformer by measuring electrical characteristics on transformer connections emerging from said housing; and (f) reconnecting said ground coupling to said exterior end of said arrester isolator after said testing is completed.
(a) providing an external arrester insulator/isolator penetrating said housing for making an electrical connection through the housing while preventing a leaking of oil from said housing;
(b) electrically coupling an arrester inside said housing between an interior end of said arrester isolator and a predetermined potential point within said housing;
(c) removably and electrically coupling an exterior end of said arrester isolator to a ground potential point;
(d) removing said ground coupling from said exterior end of said arrester isolator;
(e) testing said transformer by measuring electrical characteristics on transformer connections emerging from said housing; and (f) reconnecting said ground coupling to said exterior end of said arrester isolator after said testing is completed.
2. The method of claim 1, wherein an insulating cap is applied to the external isolator to provide additional withstand capability to external flashover during the tests.
3. The method of claim 1 or claim 2, further comprising the added step of providing a coupling between said arrester isolator and said seal to said housing whereby said arrester isolator may be replaced without entering said housing or breaking said seal.
4. The method of claim 1 or claim 2, further comprising the added step of providing means associated with said arrester isolator for blowing away said removable electrical coupling of step (c) in response to an arrester failure.
5. The method of claim 4, further comprising the added step of positioning said removable electrical coupling of step (c) in a location which gives a visible indication responsive to said blowing away of said electrical coupling to indicate that said arrester failed.
6. The method of any one of claims 1 to 5, further comprising the added step of supporting said arrester in a mechanically protected position where lead lines from said arrester are relatively short.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/394,523 US4975797A (en) | 1989-08-16 | 1989-08-16 | Arrester with external isolator |
| US07/394,523 | 1989-08-16 | ||
| CA002004444A CA2004444C (en) | 1989-08-16 | 1989-12-01 | Arrester with external isolator |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002004444A Division CA2004444C (en) | 1989-08-16 | 1989-12-01 | Arrester with external isolator |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2205539A1 CA2205539A1 (en) | 1991-02-16 |
| CA2205539C true CA2205539C (en) | 2001-02-13 |
Family
ID=25673812
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002205539A Expired - Fee Related CA2205539C (en) | 1989-08-16 | 1989-12-01 | Transformer testing method |
| CA002206716A Expired - Fee Related CA2206716C (en) | 1989-08-16 | 1989-12-01 | Arrester with external isolator |
Family Applications After (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002206716A Expired - Fee Related CA2206716C (en) | 1989-08-16 | 1989-12-01 | Arrester with external isolator |
Country Status (1)
| Country | Link |
|---|---|
| CA (2) | CA2205539C (en) |
-
1989
- 1989-12-01 CA CA002205539A patent/CA2205539C/en not_active Expired - Fee Related
- 1989-12-01 CA CA002206716A patent/CA2206716C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2206716A1 (en) | 1991-02-16 |
| CA2205539A1 (en) | 1991-02-16 |
| CA2206716C (en) | 1999-12-21 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |