FIELD OF THE INVENTION
[001] The present disclosure, in general, relates bushing in transformers. The present disclosure, in particular, relates to protection of transformers from bursting of oil filled high voltage bushing during failure conditions.
BACKGROUND OF THE INVENTION
[002] Electric power is the most common form of energy which can be generated, transmitted and utilized for different applications in Industry and Society. Electric power is generated in a power station by harnessing the kinetic energy of Water, Steam or Gas. The kinetic energy of the water or Steam or Gas rotates the Turbine. The Shaft of the turbine is coupled with the shaft of an electric machine called Electric Generator. The rotation of the turbine rotates the generator thus producing electric power.
[003] This electric power is generated at low voltage in the range of 11 KV to 15.75 KV or 21 kV. The generated power is converted to higher voltages such as 132 kV or 220 kV or 400 kV (or still higher voltages) using a transformer which is then transmitted to distant load centre. The generated power is fed to the transformer at Low voltage terminal. This power at low voltage is converted to power at high voltage. The converted high voltage power is transmitted from the transformer through High voltage bushing which are connected to transmission lines of the GRID.
[004] Referring to Figure 1, illustrating connections of transformer 100 to bushings 101 as per general practice. In a large sub-station large bulk of A C power is handled for which high voltage large power transformers 100 are installed. The transformer 100 are oil filled equipment installed at outdoor switch-yards and provided with high voltage bushings 101 at their HV side connected to the power transmission grid through long transmission line. There are other equipment like Reactors, circuit breakers, CT, PT, Isolators and many other components connected to the transmission line. Depending upon the load requirements and the system disturbances these equipment are made to be ON or OFF generating different types of high voltage surges on the system.
[005] The surges, that are generated by lightening (thundering) or by any system disturbances, travel through the transmission line and strike the transformer 100 causing higher stress in the winding, winding connections and the bushing 101. The insulation system of winding and bushing 101 can be some times over stressed. This phenomena could generate gas inside the bushing 101, beyond a limit the gas pressure inside the bushing 101 could burst the porcelain housing 102 of the bushing 101.
[006] The broken parts of the blasted bushing 101 can cause damage to the adjacent equipment and can also harm people working around. The breakage of the bushing 101 can cause damage to other bushings in the proximity and cause oil leakage. It can easily happen to the bushing of other phases of the transformer 100 and associated equipment, like CT / VT in the sub-stations.
[007] Referring to Figure 2 illustrating fire hazard in sub-station owing to failure of bushing 101. The gushed out hot oil from the ruptured bushing 101 can also cause fire hazard and lead to catastrophic failures like burning of the transformer 100and associated other equipment in the vicinity of the transformer 100 in the sub-station. The failure of the bushing 101 and the transformer 100 causes interruption of power supply. The replacement of the bushing 101 and the transformer 100require huge costs in terms of money and is also time consuming.
[008] Besides fire hazard, bursting of bushing 101 can also cause other damages because the fragmented pieces of insulation can damage the nearby equipment. On few occasions, it has caused damage to human life as well.
[009] Therefore, there is a need to develop a bushing to provide protection to transformer 100 during failure conditions which can obviate the drawbacks mentioned above.
OBJECT OF THE INVENTION
[0010] It is therefore an object of the present invention, to solve the aforementioned and other drawbacks existing in the existing bushings of the transformers.
[0011] Another primary object of the present invention is to provide a bushing to protect transformers during failure conditions.
[0012] Yet another objective of the present invention is to provide a bushing to enhance the safety of the people working in the sub-station at the time of failure of the bushing.
[0013] Yet another object of the present invention is to provide a bushing to increase the availability of power supply by avoiding fire hazard.
[0014] Yet another object of the present invention is to provide a bushing which is economical.
SUMMARY OF THE INVENTION
[0015] One or more drawbacks of conventional bushings, and additional advantages are provided through the bushing as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be a part of the claimed disclosure.
[0016] The present subject matter relates to a bushing to provide protection to a transformer during failure conditions. The bushing comprises a central metallic tube carrying a conductor, a porcelain insulator surrounding, a bushing head, an oil gauge and a pressure relieving arrangement. The central metallic tube passes the current from winding of the transformer to the outside bushing terminal. The porcelain insulator surrounds the central metallic tube. Paper insulations and metallic conductive foils are provided between the central metallic tube and the porcelain insulator to provide insulations and to produce a capacitive effect which dissipates the electrical energy evenly throughout the paper insulations. The bushing is full with insulating oil owing to the dielectric requirements .The oil level gauge is provided on the bushing head to indicate and ascertain the level of oil inside the transformer. There is a pressure relieving arrangement provided between the bushing head and the oil level gauge. This arrangement creates a radial opening between the oil level gauge and the bushing head so as to release gas generated inside the bushing during bushing over-stress/failure condition.
[0017] In an aspect, the pressure relieving arrangement comprises springs provided on each mounting screw of the oil gauge flange to create the opening between the oil level gauge and the bushing head to release the gas.
[0018] In an aspect, the springs compresses when the pressure, generated by the gas inside the bushing, increases to a pre-set limit to create the opening between the oil level gauge and the bushing head to release the pressure.
[0019] In an aspect, after the pressure release the springs decompresses when the pressure inside the bushing reaches below the pre-set limit.
[0020] In an aspect, a hood is provided over the oil gauge to restrict the released gas from going towards bushing top.
[0021] In an aspect, the transformer is an oil filled power transformer.
[0022] In an aspect, the metallic conductive foil is aluminum foil.
[0023] In order to further understand the characteristics and technical contents of the present invention, a description relating thereto has been made with reference to the accompanying drawings. However, the drawings are illustrative only but not used to limit scope of the present subject matter.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0024] Further objects and advantages of this invention will be more apparent from the description when read in conjunction with accompanying drawings of exemplary embodiments of invention and wherein:
[0025] Figure 1 illustrates connections of transformer to bushings as per general practice;
[0026] figure 2 illustrating fire hazard in sub-station owing to failure of bushing;
[0027] Figure 3 illustrates construction of a bushing according to existing art;
[0028] Figure 4 illustrating arrangement of insulating layers inside bushing as per existing art;
[0029] Figure 5 illustrates a bushing equipped with pressure relieving arrangement in accordance with proposed present subject matter;
[0030] Figure 6 illustrates pressure relieving arrangement according to one of the embodiment of proposed present subject matter; and
[0031] Figure 7a and 7b illustrates states of the spring during normal condition and failure condition according to one of the embodiment of proposed present subject matter.
DETAILED DESCRIPTION OF THE INVENTION
[0032] The present invention discloses a bushing to provide protection to a transformer during failure condition.
[0033] Referring to Figure 3 illustrating construction of a bushing 101 according to the existing art. The bushing 101 comprises a porcelain insulator 301, a central metallic tube 302 carrying a conductor, a bushing head 303, an oil level gauge304, paper insulations, and other metal parts etc., immersed in oil. The bushing 101 for high voltage operations are oil filled generally.
[0034] When the transformer 100 is energized and connected to outside network through HV or LV terminal bushings, the central metallic tube 302 inside the porcelain insulator 301is also energized to the voltage of the network (HV OR LV). So, the insulations viz. oil and paper insulations get stressed by virtue of the electrical field around the conductor.
[0035] The paper insulation used is hygroscopic in nature and absorbs moisture during manufacturing. Moisture is detrimental to insulation because it deteriorates paper insulation. So, moisture is removed by heating and are impregnated either with oil or with resin. Accordingly the bushing 101 is called OIP (Oil impregnate) or Resin impregnate (RIP) type bushing.
[0036] Referring to figure 4 illustrating arrangement of insulating layers inside bushing 101 as per existing art. To improve the performance of paper insulated bushings 101, metallic conductive foils separated by layers of paper 401 (refer fig.4) are inserted during the winding process of manufacture of bushings. The inserted conductive foils produce a capacitive effect which dissipates the electrical energy more evenly throughout the insulated paper and reduces the electric field stress between the energised conductor and any earthed material. With increase in the strength of the electrical field, the intensity of leakage paths increases within the insulation. When the energy of the leakage path overcomes the dielectric strength of the insulation, it punctures the insulation and allow the electrical energy to conduct to the nearest earthed material causing burning and arcing.
[0037] The current passes through central metallic tubes from the winding of the transformers to outside bushing terminal and vice versa. During the flow of current (when transformer is loaded) there is a rise in temperature of the conductor carrying current, which simultaneously, increase the temperature of the central metallic tube that houses the conductor. There is a rise in the temperature of oil and paper insulations, which are already stresses due to the electrical field caused by charging of the transformer. This causes continuous deterioration of the insulation system of the bushing. With time, these deterioration give rise to more severe type of deterioration like partial discharge in the oil – paper combination which rapidly grows to dangerous level and could puncture the insulation of bushing causing arcs and spark inside the bushing. This arc and spark burns the oil and paper inside the bushing and will generate gas inside the bushing which results in bursting of bushes.
[0038] Referring to Figure 5 illustrating a bushing 500 equipped with pressure relieving arrangement in accordance with present subject matter. According to present subject matter, the oil level gauge 504 is mounted on the bushing head 503 firmly.
[0039] Referring to Figure 6 illustrating pressure relieving arrangement 600 according to one of the embodiment of present subject matter. The pressure relieving arrangement 600 creates an opening between the oil gauge 504 and the bushing head 503 to release gas generated inside the bushing 500during failure condition. The pressure relieving arrangement 600 comprises spring 602 provided on each mounting screw 603 of the oil gauge flange601 to create the opening between the oil gauge504 and the bushing head503 to release the gas. A hood 701 is provided over the oil gauge 504 to restrict the released gas from going towards the bushing top.
[0040] Referring to figure 7a and 7b illustrating states of the springs 602 during normal condition and failure condition, respectively, according to one of the embodiment of proposed present subject matter. During failure condition, the springs 602 compress when the pressure, generated by the gas inside the bushing 500, increases to a pre-set limit to create the opening between the oil gauge 504 and the bushing head 503 to release the pressure.
[0041] After release of pressure, the springs 602 decompresses when the pressure inside the bushing500 reaches below the pre-set limit. In this way, the proposed bushing 500 never let pressure inside it to raise to dangerous levels. This eliminates the bursting of bushing 500 due to high pressure and other associated problems.
[0042] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”
[0043] It will be further appreciated that functions or structures of a plurality of components or steps may be combined into a single component or step, or the functions or structures of one-step or component may be split among plural steps or components. The present invention contemplates all of these combinations. Unless stated otherwise, dimensions and geometries of the various structures depicted herein are not intended to be restrictive of the invention, and other dimensions or geometries are possible. In addition, while a feature of the present invention may have been described in the context of only one of the illustrated embodiments, such feature may be combined with one or more other features of other embodiments, for any given application. It will also be appreciated from the above that the fabrication of the unique structures herein and the operation thereof also constitute methods in accordance with the present invention. The present invention also encompasses intermediate and end products resulting from the practice of the methods herein. The use of “comprising” or “including” also contemplates embodiments that “consist essentially of” or “consist of” the recited feature.

Claims:
We claim:
1. A bushing (500) to provide protection to a transformer (100) during failure conditions, the bushing (500) comprises:
a central metallic tube (502) carrying a conductor to pass the current from winding of the transformer (100) to the outside bushing terminal;
a porcelain insulator (501) surrounding the central metallic tube (502) wherein paper insulations and metallic conductive foils are provided between the central metallic tube (502) and the porcelain insulator (501) to provide insulation and to produce a capacitive effect which dissipates the electrical energy evenly throughout the paper insulations;
a bushing head (503) operating as an oil compensator;
an oil gauge (504) provided on the bushing head (503) to indicate the level of oil inside the transformer (100); and
a pressure relieving arrangement (600) to create an opening between the oil gauge (504) and the bushing head (503) to release gas generated inside the bushing (500) during failure conditions.
2. The bushing (500) as claimed in claim 1, wherein the pressure relieving arrangement (600) comprises springs (602) provided on each mounting screw (603) of the oil gauge flange (601) to create the opening between the oil gauge (504) and the bushing head (503) to release the gas.
3. The bushing (500) as claimed in claim 1 or 2, wherein the springs (602) compresses when the pressure, generated by the gas inside the bushing (500), increases to a pre-set limit to create the opening between the oil gauge (504) and the bushing head (503) to release the pressure.
4. The bushing (500) as claimed in claim 1 or 2, wherein the springs (602) decompresses when the pressure inside the bushing (500) reaches below the pre-set limit.
5. The bushing (500) as claimed in claim 1, wherein a hood (701) is provided over the oil gauge (504) to restrict the released gas from going towards bush top.
6. The bushing (500) as claimed in claim 1, wherein the transformer (100) is an oil filled power transformer.
7. The bushing (500) as claimed in claim 1, wherein the metallic conductive foil is aluminium foil.