Claims:WE CLAIM:

1. A device for indicating failure of a surge arrester, comprising:
- a first electrical end which is electrically connected to a ground terminal of the surge arrester;
- a second electrical end connected to a ground potential;
- a pair of electrodes maintaining a spark gap there between, the pair of electrodes are electrically connected to the first electrical end and the second electrical end of the device, such that an incident surge passes through the surge arrester to the ground potential passing through the spark gap;
- a resistor connected in parallel electrical circuit to the pair of electrodes between the first and the second electrical ends of the device, such that a leakage current flows through the resistor to the ground potential;
- a tape having a first end and a second end, the first end of the tape is attached to the resistor, such that it gets heated by a heated resistor when the leakage current flows through the resistor; and
- a dead weight hanging from the second end of the tape, such that when the resistor gets heated to a pre-defined temperature, the first end of the tape melts to detach and drop the dead weight.

2. The device according to claim 1, wherein the dropping of the dead weight is the indication of the surge arrester failure.

3. The device according to claim 1, wherein the pre-defined temperature is reached when the leakage current from the failed surge arrester reaches a pre-defined value that is indicative of the surge arrester failure.

4. The device according to claim 1, wherein the pre-defined temperature depends on at least one from a list including an electrical rating of the surge arrester, a dimension of the resistor, a material of the resistor, a material of the tape, a dimension of the spark gap, or a combination thereof.

5. The device according to claim 1, wherein the resistor is made from a high resistivity material.

6. The device according to claim 5, wherein the high resistivity material includes Kanthal, Nichrome.

7. The device according to claim 1, wherein the resistor is made as a coil of insulated wire.

8. The device according to claim 1, wherein the pre-defined temperature is more than a melting point of the tape.

9. The device according to claim 1, wherein the tape is made of a material having a melting point in a range of 65 degree Celsius to 140 degree Celsius.

10. The device according to claim 9, wherein the melting point is 74 degree Celsius.

11. The device according to claim 1, further including an insulated housing to enclose all components of the device and comprising a transparent portion located at bottom which holds the dead weight when it drops for visually indicating failure of the surge arrester.

12. A method of indicating failure of a surge arrester, comprising the steps of:
- making a leakage current from the surge arrester to flow through a resistor to a ground potential;
- providing a tape having a first end and a second end, such that it changes phase when heated above a pre-defined temperature;
- attaching the first end of the tape to the resistor, such that it gets heated by a heated resistor when the leakage current flows through the resistor;
- hanging a dead weight from the second end of the tape; and
- indicating the surge arrester failure when the first end of the tape melts thereby dropping the hanging dead weight.

13. The method according to claim 12, wherein the pre-defined temperature is reached when the leakage current from the failed surge arrester reaches a pre-defined value indicative of the surge arrester failure.

14. The method according to claim 12, wherein the pre-defined temperature depends on at least one from a list including an electrical rating of the surge arrester, a dimension of the resistor, a material of the resistor, a material of the polymeric tape, a dimension of the spark gap, or a combination thereof.
, Description:FIELD OF THE INVENTION

[001] The present invention relates to surge attesters used in electrical power distribution systems and more particularly, to devices and methods for indicating failure of a surge arrester.

BACKGROUND OF THE INVENTION

[002] Electrical equipment connected to the power line such as transformers, terminations, underground cables or splices are at the risk of getting damaged by a surge which results a high current overvoltage on the power transmission line. Surge arresters are installed between the power line and the ground of the electrical power system and are used to protect electrical equipment from overvoltage surges appearing thereon by bypassing the surge currents to the ground. The function of a surge arrester is to protect a power transmission system from overvoltage surges, typically caused by lightening, switching transients or faults.

[003] The surge arrester normally acts as an insulator, not allowing any current to pass through it, but when subjected to overvoltage the surge arrester becomes temporarily conductive. In the conductive state, the arrester will pass the high current surge directly to ground. After passage of the overvoltage surge, the surge arrester is designed to return to its non-conductive state and is ready for the next instance of an overvoltage surge. These opposing characteristics are typically achieved through the use of a Varistors, which have different resistances at different voltages.

[004] However, it is possible that the magnitude of the overvoltage surge may be such that the surge arrester fails, in which case the surge arrester continues to conduct current even after passage of the surge. Failure of the surge arrester may also be caused by moisture ingress into the surge arrester or contamination of the exterior of the arrester.

[005] There are two principal type of surge arresters namely Metal Oxide Varistor (MOV) arresters and silicon carbide gapped arrester. However now most of the new surge arresters are MOV based and the utilities are also insisting on replacing silicon carbide based surge arresters with MOV type surge arresters. Generally, a MOV surge arrester is made up of two parts an active part consisting of one or more piled up MOV and an insulating housing, which provides both insulation and mechanical strength.The MOV surge arrester consists of multiple MOV disks inside a metallic cage, which is further enclosed in a polymeric bushing. The surge arrester has end fitting at both of its longitudinal ends allowing it to make electrical connection with other conductors. The MOV disk is a semiconductor that is sensitive to voltage. At normal voltages, the MOV disk is an insulator and will not conduct current, however at higher voltages caused by switching it becomes a conductor.

[006] Since the surge arrester is connected between a power line and a ground, some amount of leakage current always flows through it to the ground. In case of failure of surge arresters, a leakage current of value about thousand times than the normal leakage current flows through the surge arrester thereby indicating a failure. The leakage current is considered as one of the parameter for detecting failure of surge arresters by different methods. The high leakage current deteriorates the MOV disk which leads to increase in leakage current, which then further deteriorates the MOV and this vicious cycle goes on till the surge arrester fails completely thereby losing its property to perform its intended function.

[007] When a surge arrester fails, the equipment being protected is subjected to very high risk of damage by any future incident surge on the power line. It is very important to know if a surge arrester has failed and to take necessary action on detection of failure.

[008] A variety of surge arrester failure indicators are available in the art and it has been a common practice to provide a disconnector along with the indicator. On detection of surge arrester failure, the indicator disconnects the power line form the equipment as a precaution to avoid any future surge to reach the equipment. A prior art surge arrester failure indicator includes a resistor being heated by the leakage current and the heated resistor ignites an explosive that will disconnect the power line from the ground when the surge arrester fails. The indicator not only disconnects the failed surge arrester from the power system, but also provides a visible indication to a lineman that the surge arrester has failed.

[009] The disadvantage of above type of surge arrester, is that the protected equipment no longer has protection after the failed arrester has been disconnected; however, electrical service continues to be provided to the customer. In some utility systems, however, there is a requirement that, not only should a visible signal be given that an arrester has failed, but also a current carrying conductive path to system ground should be maintained until the failed arrester is removed and replaced.

[0010] In view of the limitations inherent in the available devices and methods for indicating failure of a surge arrester, there exists a need for an improved device and method for indicating failure of a surge arrester, which overcomes the disadvantages of the prior art and which can be used in a simple, cost effective, reliable, secure and environmental friendly manner.

[0011] The present invention fulfils this need and provides further advantages as described in the following summary.

SUMMARY OF THE INVENTION

[0012] In view of the foregoing disadvantages inherent in the prior arts, the general purpose of the present invention is to provide an improved combination of convenience and utility, to include the advantages of the prior art, and to overcome the drawbacks inherent therein.

[0013] A primary objective of the present invention is to provide a device and method for indicating failure of a surge arrester in an electrical system which is simple and cost effective.

[0014] In one aspect, the present invention provides a device for indicating failure of a surge arrester. The device comprises a first electrical end which is electrically connected to a ground terminal of the surge arrester, a second electrical end connected to a ground potential, a pair of electrodes maintaining a spark gap there between, the pair of electrodes are electrically connected to the first electrical end and the second electrical end of the device, such that an incident surge passes through the surge arrester to the ground potential passing through the spark gap, a resistor connected in parallel electrical circuit to the pair of electrodes between the first and the second electrical ends of the device, such that a leakage current flows through the resistor to the ground potential, a tape having a first end and a second end, the first end of the tape is attached to the resistor, such that it gets heated by a heated resistor when the leakage current flows through the resistor and a dead weight hanging from the second end of the tape, such that when the resistor gets heated to a pre-defined temperature, the first end of the tape melts to detach and drop the dead weight.

[0015] In another aspect of the present invention, the dropping of the dead weight is the indication of the surge arrester failure.

[0016] I another aspect of the present invention, the resistor is made as a coil of insulated wire of a high resistivity material such as Kanthal, Nichrome.

[0017] In yet another aspect of the present invention, the pre-defined temperature is reached when the leakage current from the failed surge arrester reaches a pre-defined value that is indicative of the surge arrester failure.

[0018] In another aspect of the present invention, the pre-defined temperature depends on at least one from a list including an electrical rating of the surge arrester, a dimension of the resistor, a material of the resistor, a material of the tape, a dimension of the spark gap, or a combination thereof.

[0019] In a further aspect of the present invention, the pre-defined temperature is more than a melting point of the tape.

[0020] In one aspect of the present invention, the tape is made of a material having a melting point in a range of 65 degree Celsius to 140 degree Celsius.

[0021] In another aspect of the present invention, the melting point of the tape is 74 degree Celsius.

[0022] In another aspect of the present invention, the device further includes an insulated housing to enclose all components of the device and comprising a transparent portion located at bottom which holds the dead weight when it drops for visually indicating failure of the surge arrester.

[0023] In a further aspect, the present invention provides method of indicating failure of a surge arrester that comprises making a leakage current from the surge arrester to flow through a resistor to a ground potential, providing a tape having a first end and a second end, such that it changes phase when heated above a pre-defined temperature, attaching the first end of the tape to the resistor, such that it gets heated by a heated resistor when the leakage current flows through the resistor, hanging a dead weight from the second end of the tape and indicating the surge arrester failure when the first end of the tape melts thereby dropping the hanging dead weight.

[0024] These together with other aspects of the invention, along with the various features of novelty that characterize the invention, are pointed out with particularity in the description annexed hereto and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be made to the accompanying drawings and descriptive matter in which there are illustrated exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The advantages and features of the present invention will become better understood with reference to the following more detailed description taken in conjunction with the accompanying drawings in which:

[0026] FIG. 1 illustrates an electrical circuit of a device for indicating failure of a surge arrester, according to one embodiment of the present invention;

[0027] FIG. 2 illustrates a schematic view of the housing, according to one embodiment of the present invention;

[0028] FIG. 3 illustrates shows an exploded view of the device with housing parts, according to one embodiment of the present invention;

[0029] FIG. 4 illustrates a sectional view of the device with housing parts, according to one embodiment of the present invention; and

[0030] FIG. 5 illustrates a flowchart of a method of indicating failure of a surge arrester according to one embodiment of the present invention.

[0031] Like reference numerals refer to like parts throughout the several views of the drawings.

DETAILED DESCRIPTION OF THE DRAWINGS

[0032] In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details.

[0033] As used herein, the term ‘plurality’ refers to the presence of more than one of the referenced item and the terms ‘a’, ‘an’, and ‘at least’ do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.

[0034] Reference herein to “one embodiment” or “another embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Further, the diagrams representing one or more embodiments of the invention do not inherently indicate any particular order nor imply any limitations in the invention.

[0035] Referring to FIG. 1, which illustrates an electrical circuit of a device 10 for indicating failure of a surge arrester. The device 10 comprises a first electrical end 12, a second electrical end 16, a pair of electrodes 20 maintaining a spark gap there between, a resistor 22 connected in parallel electrical circuit to the pair of electrodes 20, a tape 24 having a first end 24F and a second end 24S, the first end 24F of the tape is attached to the resistor 22 and a dead weight 26 is hanging from the second end 24S of the tape.

[0036] The surge arrester is electrically connected with the main supply line at one end which also goes to the equipment being protected by the surge arrester. The other end called ground terminal 14 of the surge arrester is connected to the ground potential 18.

[0037] The first electrical end 12 of the device is connected to the ground terminal 14 of the surge arrester and the second electrical end 16 is connected to the ground potential 18, such that the device 10 is electrically between the ground potential 18 and the surge arrester. The other electrical connections of the main supply line to the equipment being protected by the surge arrester remain as in the prior art and are not disturbed due to installation of the device 10.

[0038] The pair of electrodes 20 are electrically connected to the first electrical end 12 and the second electrical end 16 of the device. One of the electrode is connected to the first electrical end 12 and other electrode is connected to the second electrical end 16 of the device. There is a spark gap between the pair of electrodes, such that an incident surge passes through the surge arrester to the ground potential 18 passing through the spark gap.

[0039] The resistor 22 is connected between the first and the second electrical ends 12 and 16 of the device in parallel electrical connection with the pair of electrodes 20, such that a leakage current from the surge arrester flows through the resistor 22 to the ground potential 18. The resistor 22 is adapted to get heated when the leakage current flows through the resistor 22. 5. In one embodiment of the present invention, the resistor 22 is made from a high resistivity material including but not limited to Kanthal and Nichrome. The resistor 22 may be made as a coil of insulated wire to have very high resistance and short dimensions.

[0040] The first end 24F of the tape is wrapped over the resistor 22 such that it gets heated by the heated resistor 22 when the leakage current flows through the resistor 22. When the resistor 22 gets heated to a pre-defined temperature, the first end 24F of the tape melts to detach and drop the dead weight 26 thereby indicating failing of the surge arrester.

[0041] In normal situations, the surge arrester acts as an insulator and the current from main supply line flows to the equipment and the device 10 is not exposed to any current flow through it. However in surge situation, the surge arrester becomes electrically conducting and the current flows from the surge arrester to the ground and passes through the device 10 of the present invention.

[0042] When a surge occurs a very high voltage is momentarily generated which switches the function of the surge arrester from insulator to conductor and the current flows from the surge arrester to the ground potential 18 and also passes from the device 10. The high voltage also lets the current to jump through the spark gap to flow to the ground potential 18. The high current due to surge is passed to the ground and the equipment is protected. This is the normal functioning of the surge arrester.

[0043] In case of surge arresters available in market, a disconnector also disconnects the main supply to the equipment which is not desirable in some situations.

[0044] During normal situations without any surge, there is some amount of leakage current always flowing from the surge arrester to the ground potential 18. Since the device 10 is connected in the path, the leakage current flows via the resistor 22 to the ground potential 18. The surge arrester goes through multiple surges to protect the equipment, however after prolong use, the surge arrester gradually starts failing and loses its capacity to effectively switch from insulator to conductor as per its design. This is indicated by the increase in the amount of leakage current from the surge arrester. More amount of leakage current starts flowing from the surge arrester which eventually flows via the resistor 22 to the ground potential 18. This constitutes a vicious cycle where more leakage current deteriorates the surge arrester functionality, which eventually increases the leakage current, till a point when the surge arrester fails completely and cannot switch to becoming conductor when a surge occurs.

[0045] When a surge arrestor fails due to repeated surges or a single very high energy surge, the leakage current through the surge arrestor increases. This leakage current can reach a few tens of milli amperes for example 30-40 milli amperes. This current may be used to heat up the resistor which in turn can be harnessed to change the state of any matter. In the present invention the resistive heating is used to melt the tape made of polymer or lower melting metal alloys and release a weight attached to the tape. The weight becomes visible from a distance when it drops and thus it act as a visual indicator.

[0046] The resistor keeps the connection to the ground working for some more time, thus not disconnecting the whole system immediately.

[0047] A spark gap is also incorporated in the system such that any regular surges experienced by the arrester during its working life gets transmitted to the spark gap, instead of the resistor.

[0048] The value of leakage current which is reported an indication of surge arrester is as a starting point and the resistor 22 is designed to have a particular resistance, such that sufficient heating takes place to melt the tape 24 material. When the resistor 22 gets heated to a pre-defined temperature, the first end 24F of the tape melts. In one embodiment of the present invention, the pre-defined temperature is reached when the leakage current from the failed surge arrester reaches a pre-defined value that is indicative of the surge arrester failure.

[0049] In an embodiment of the present invention, the pre-defined temperature of the heated resistor 22 at which the tape 24 melts depends on electrical rating of the surge arrester, dimension of the resistor, material of the resistor, material of the tape, dimension of the spark gap, or a combination of one or more of these parameters. The pre-defined temperature is determined and the resistor 22 is designed to have such resistance to get heated to that pre-defined temperature when the leakage current value which indicates surge arrester failure is reached.

[0050] In one embodiment of the present invention, the pre-defined temperature is more than the melting point of the tape. This makes sure that the tape 24 melts when the resistor 22 is heated to pre-defined temperature. The tape may be made of a material having a melting point in a range of 65 degree Celsius to 140 degree Celsius. In one preferred embodiment of the present invention, the melting point of the tape 24 is 74 degree Celsius. In one embodiment of the present invention, the material used for tape 24 includes low melting metal alloys and polymers. For example polyolefins

[0051] In one embodiment of the present invention, the device 10 further includes an insulated housing 30 to enclose all components of the device. Referring to FIG. 2 that shows a schematic view of the housing 30, according to one embodiment of the present invention. The housing 30 includes a transparent portion 32 located at bottom which contains the dead weight 26 when it drops for visually indicating failure of the surge arrester. This makes the detection of surge arrester failure easily identifiable from a distance. Thus there is no need to test the surge arrester electrically to detect its failure.

[0052] The electrical circuit and components as shown in FIG. 1 are inside the housing 30. As seen in FIG. 2, the top bolt acts as the first electrical end 12 and is connected to the ground terminal 14 of the surge arrester.

[0053] Referring to FIG. 3 that shows an exploded view of the device 10 with housing 30 parts, according to one embodiment of the present invention. The housing 30 includes a top enclosure 34, a top cover 36, a bottom enclosure 38 containing the transparent portion 32, a circular plate 40 between the top enclosure 34 and the bottom enclosure 38 and a metallic strip 42 which is mounted on the circular plate 40. Referring to FIG. 4 that shows a sectional view of the device 10 with housing 30 parts, according to one embodiment of the present invention. In one embodiment of the present invention, the pair of electrodes 20 are made as one upper electrode 20U and one lower electrode 20L (shown in FIG.4) with a spark gap between them. The upper electrode 20U is in the form of a conical shape and the lower electrode 20L is in the form of a circular plate which fits inside the top enclosure 34. The metallic strip 42 is made as two pieces joined electrically by the resistor 22 in between such that the metallic strip 42 forms the section of the circuit of FIG. 1 which connects the resistor 22 with the first electrical end 12 on one side and with the second electrical end 16 from another side. The first end of the tape 24F is wrapped over the resistor and the dead weight ball 26 hangs from the second end of the tape 24S. The metallic strip 42 is connected to the ground potential 18 from one end as shown using a wire which acts as the second electrical end 16 of the device. A wire (not shown) also connects the first electrical end 12 to another side of the metallic strip 42. A bolt 44 electrically connects the lower electrode 20L with the metallic strip 42, such that it forms the section of the circuit where one of electrodes 20L is connected to the second electrical end 16 of the device which eventually is connected to the ground potential 16.

[0054] All the components of the housing are connected with each other by nuts and bolts. The electrical connections between the device 10 components is such that it makes the circuit of FIG. 1.

[0055] The device 10 is now connected to the between the surge arrester and the ground potential. Now during surge striking the pair of electrodes 20 pass the high energy to the ground 18. When eth surge arrester fails, it starts leaking current which is sufficient to heat the resistor 22, so that it melts the tape 24 thereby dropping the dead weight 26 into the transparent portion 32. Any personal on seeing the ball 26 in the transparent portion, can know that the surge arrester has failed and can take necessary action of replacing the surge arrester.

[0056] The device 10 of the present invention, does not disconnect the surge arrester and keeps the main line supply ON.

[0057] Referring to FIG. 5 that illustrates a flowchart of a method 100 of indicating failure of a surge arrester according to one embodiment of the present invention. The method 100 starts with step 110 of making a leakage current from the surge arrester to flow through a resistor 22 to a ground potential 18. The surge arrester ground terminal 14 carries the leakage current to the ground potential 18, this is made to flow from the resistor 22 of the device 10, such that it gets heated due to the leakage current flow. Now in step 120 a tape 24 having a first end 24F and a second end 24S is provided which is made of a low melting alloy, such that it changes phase when heated above a pre-defined temperature. In step 130 the first end 24F of the tape is attached to the resistor 22, such that it gets heated by a heated resistor 22 when the leakage current flows through the resistor 22. Now a dead weight 26 is hanged from the second end 24S of the tape in step 140. This makes the electrical circuit such that when the leakage current passes through the resistor 22, it will heat it and also heats the first end 24F of the tape. As the surge arrester fails, the leakage current increases and the heating is more. When the heating temperature reaches a pre-defined temperature which is indicative of the surge arrester failure, the first end 24F of the tape melts thereby dropping the hanging dead weight 26 which indicates the failure of the surge arrester visually in step 150.

[0058] In one embodiment of the present invention, the pre-defined temperature is reached when the leakage current from the failed surge arrester reaches a pre-defined value indicative of the surge arrester failure. The pre-defined temperature depends on one from electrical rating of the surge arrester, dimension of the resistor, material of the resistor, material of the polymeric tape, dimension of the spark gap, or a combination of one or more of these parameters.

[0059] The device 10 of the present invention is very much suited for manual inspection to detect the surge arrester failure systems, however the device 10 may be combined with sensors to detect the ball 26 and convert it into a digital signal and transferred to a remote location via communication means to remotely inspect the surge arrester for failure. The device 10 may also be supplemented with other sensors for measuring the leakage current, partial discharge, rise in electrical conductivity of the surface, rise in surface temperature etc to monitor the working and predicting life of the surge arrester.

[0060] Although a particular exemplary embodiment of the invention has been disclosed in detail for illustrative purposes, it will be recognized to those skilled in the art that variations or modifications of the disclosed invention, including the rearrangement in the configurations of the parts, changes in steps and their sequences may be possible. Accordingly, the invention is intended to embrace all such alternatives, modifications and variations as may fall within the spirit and scope of the present invention.

[0061] The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching.

[0062] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims.