Patent Description:
With the development of transmission grid, requirements of the transformer capacity for power transformers increase constantly. As a critical component for power transformer, the high voltage transformer bushing is required to have a high current class so that it is reliable enough during its lifetime to ensure the security of the transformer and power grid. The cable lead bushing does not meet these requirements, and therefore more bushings are used with the central conductor.

For a bushing in service, a length of components of the bushing might change due to temperature changes. Normally, the larger the current of the bushing is, the higher the temperature rises, and due to the thermal expansion and contraction of conductor, the central conductor will change in the length. In addition, the length of a conductor also increases with the temperature rise during the daytime and decreases with the temperature fall during the night. Thus, a periodic temperature change may occur during a day. The similar change might occur due to seasonal temperature variations as well. Those changes in the length of the conductor will in turn cause a relative movement between internal central conductor and the sealing element. Such a relative movement would cause wear, especial wear of the sealing element due to an impact of tension load.

For now, there are mainly two types of sealing methods to deal with the thermal expansion and contraction of the central conductor in the market. One is to use a simple dynamic sealing system and the other is to apply a multi-contact and static system. However, none of these solutions is effective enough to deal with the thermal expansion and contraction as well as the sealing problems.

<CIT> describes a bar run for electrical transformers.

<CIT> describes an electric bulkhead feedthrough.

<CIT> describes a wall bushing for an electrical conductor.

<CIT> describes a seal for a bushing on a transformer with fluid insulation.

<CIT> describes a pressure-tight cable entry for single-core or multi-core cables in a housing.

Therefore, in the art there is a need for a new sealing arrangement for bushing.

Various embodiments of the present disclosure mainly aim at providing a solution for a sealing arrangement for bushing to solve or at least partially mitigate at least a part of problems in the prior art. Other features and advantages of embodiments of the present disclosure will also be understood from the following description of specific embodiments when read in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of embodiments of the present disclosure.

According to a first aspect of the present disclosure, there is provided a sealing arrangement of a bushing for a power electrical device. The sealing arrangement may comprise a top cover; a central conductor going through the top cover; a guide element having a cylinder portion and a flange portion extended from a middle part of the cylinder portion, wherein the cylinder portion is arranged between the top cover and the central conductor, and the flange portion is connected onto the top cover; a static sealing structure provided between the guide element and the top cover; and a dynamic sealing structure provided between the guide element and the central conductor.

In an embodiment of the present disclosure, the dynamic sealing structure may comprise at least one dynamic sealing O-ring between the guide element and the central conductor.

In another embodiment of the present disclosure, the dynamic sealing structure may comprise at least one dynamic sealing O-ring between the guide element and the central conductor.

In a further embodiment of the present disclosure, the at least one dynamic sealing O-ring may be made of fluorine silicone rubber.

In a still further embodiment of the present disclosure, the dynamic sealing structure may further comprise a wear ring arranged between the guide element and the central conductor.

In a yet further embodiment of the present disclosure, the at least one dynamic sealing O-ring may comprise two dynamic sealing O-rings, and wherein the wearing ring may be arranged between the two dynamic sealing O-rings.

In another embodiment of the present disclosure, the wear ring may be made of poly tetra fluoroethylene.

In a further embodiment of the present disclosure, the dynamic sealing structure (<NUM>) may further comprise a wiper ring arranged between the guide element and the central conductor, at an upper portion of the guide element.

In a still further embodiment of the present disclosure, the wiper ring may be made of polyurethane.

In yet further embodiment of the present disclosure, the sealing arrangement may comprise a protective cap covering a top portion of the guide element to protect the sealing arrangement from an external environment and wherein the central conductor goes through the protective cap.

In another embodiment of the present disclosure, the sealing arrangement may further comprise a further O-ring arranged between the protection cap and the central conductor.

In a further embodiment of the present disclosure, the further O-ring may be made of chloroprene rubber (CR).

In another embodiment of the present disclosure, the central conductor may have a chrome-plating surface.

In another embodiment of the present disclosure, the guide element may have an anodic oxidation surface.

According to the invention, the static sealing element comprises a static sealing O-ring and a gasket arranged between the guide element and the top cover. One or both of the static sealing O-ring and a gasket may be made of nitrile butadiene rubber (NBR).

According to the invention, there is provided a bushing comprising a sealing arrangement for the bushing according to any of the first aspect.

In a further embodiment of the present disclosure, the bushing is a transformer bushing, especially, an oil-immersed paper transformer bushing.

With the new sealing structure design, it could provide a good sealing performance so that the bushing can be used in various environments. Specially, the dynamic structure could provide a good sealing performance. The wear ring could provide good anti-eccentricity and anti-wear properties. Chrome-planting on copper conductor surface can effectively prevent the copper conductor from abrasion. Anodic oxidation for guide's face can effectively prevent electrochemical corrosion between copper and aluminum, and meanwhile, the anodic oxide planting of aluminum has an insulating effect, it can effectively prevent the virtual connection and unnecessary diversion circuit. The entire sealing system may be further protected by a protection cap, which can effectively prevent the sliding sealing structure from dust, rain and snow erosion. In addition, the adoption of new structures does not increase the cost significantly or cause any substantial complexity.

The above and other aspects, features, and benefits of various embodiments of the present disclosure will become more fully apparent, by way of example, from the following detailed description with reference to the accompanying drawings, in which like reference numerals or signs are used to designate like or equivalent elements.

Hereinafter, the principle of the present disclosure will be described with reference to illustrative embodiments. It shall be understood, all these embodiments are given merely for one skilled in the art to better understand and further practice the present disclosure, but not for limiting the scope of the present disclosure, which is defined by the appended claims. In the interest of clarity, not all features of an actual implementation are described in this specification.

References in the specification to "one embodiment," "an embodiment," "an example embodiment," etc. indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic.

It shall be understood that, although the terms "first" and "second" etc. may be used herein to describe various elements, these elements should not be limited by these terms.

It will be also understood that the terms "connect(s)," "connecting", "connected", etc. when used herein, just means that there is an electrical connection between two elements and they can be connected either directly or indirectly, unless explicitly stated to the contrary.

As mentioned in Background, the bushing conductor temperature will rise when the bushing is in service, and the ambient temperature of the bushing may also change, all of which cause changes in the length of conductor in service. Currently, there are mainly two common types of top structure systems for the transformer bushing. One is to use a simple dynamic sealing system, and other is to use a multi-contact and static system.

As to the first type of top structure system, there are many similar bushings available in the market, but they all use a simple top sealing structure which is unreliable enough. For illustrative purposes, description will be first made to <FIG> to briefly introduce an existing sealing arrangement, wherein <FIG> illustrates an example sealing arrangement for transformer bushing in the prior art.

As illustrated in <FIG>, the transformer bushing <NUM> includes a central conductor <NUM>, a top chamber <NUM> (only a part thereof is illustrated), a cover plant <NUM> and a dynamic sealing system including a first O-ring <NUM> and a second O-ring <NUM>. The central conductor <NUM> is used to transfer high-voltage power. The central conductor <NUM> goes through the top chamber <NUM> and enters the bushing. The top chamber <NUM> is the top portion of the bushing oil chamber, in which insulation liquid such as oil is filed. The central conductor <NUM> also goes through the cover plate <NUM>, which is connected onto the top cover by bolts <NUM>. The first O-ring <NUM> is arranged between the central conductor <NUM> and the top chamber <NUM>, and the second O-ring <NUM> is arranged between the top chamber <NUM> and the cover plate (<NUM>). The first O-ring <NUM> forms a dynamical sealing system and the second O-ring <NUM> forms a static sealing system. The contraction of the central conductor can be adjusted by the dynamic sealing structure so as to reduce the risk of leakage. However, such a dynamical top sealing structure is too simple to provide enough reliability and thus it still has a risk of oil leakage.

On the other hand, the multi-contact and static system uses multiple contacts to form a sealing structure, which means a quite complex structure. Such a system not only increases the cost of production but also fails to reduce wear of sealing rings and conductors as well.

In addition, the traditional structure systems also have many other problems. As an example, the central conductor will be eccentric when the outer terminal of the bushing is subjected to a lateral force or when the outer wire is subjected to a wind force. As another example, an electrochemical corrosion might exist between different metal sealing surface due to lack of protection for the sealing system. These problems have a great negative effect on the sealing performance of the sealing ring and also increase the risk of internal oil leakage.

To this end, the present invention provides a new-type sealing arrangement of the bushing for a power electrical device to address or at least mitigate at least one of problems mentioned above. Hereinafter, reference will be made to <FIG> to describe example sealing arrangements for a transformer according to embodiments of the present disclosure. It shall be appreciated that the example sealing arrangements are only given to illustrate the principle of the tying device proposed herein and the present disclosure is not limited thereto. In addition, the bushing can be a transformer bushing, a wall bushing, or any other type of bushing for a power electrical device that is required to be insulated. In addition, the bushing can be a dry-type bushing or a liquid-filled bushing.

Reference is made to <FIG>, which schematically illustrates a diagram of an example sealing arrangement for transformer bushing according to an embodiment of the present disclosure. In <FIG>, the appearance is illustrated in the left half of the drawing and an inner sectional view is illustrated in the right half of the drawing. As illustrated in <FIG>, the example sealing arrangement <NUM> for bushing is a top sealing structure, which comprises a central conductor <NUM>, a top cover <NUM>, a guide element <NUM>, and a protective cap <NUM>.

The central conductor <NUM> is a conductor for transferring the high-voltage power, which is usually made of copper. The top cover <NUM> is the top portion of the bushing. Specifically, for the dry-type bushing, the top cover <NUM> is the top plate of the expansion space; for a liquid-filled bushing, the top cover <NUM> is the top chamber of the bushing. The guide element <NUM> is arranged between the central conductor <NUM> and the top cover <NUM> and is connected onto the top cover <NUM> by bolts <NUM>. As illustrated in <FIG>, the central conductor <NUM> also goes through the guide element <NUM> and thus the guide element <NUM> is arranged between the central conductor <NUM> and the top cover <NUM> in the radial direction of the central conductor. The guide element <NUM> can be made of for example aluminum (AL). The guide element <NUM> is different from the cover plate <NUM> in the existing top structure, and in fact, they have different structures and different functions. Reference can be made to <FIG>, which illustrates a sectional view of the guide element <NUM> according to an embodiment of the present disclosure.

As illustrated in <FIG>, the guide element <NUM> have a cylinder portion 203a and a flange portion 203b extended from a middle part of the cylinder portion 203a. The cylinder portion 203a is the main body of the guide element <NUM> and the central conductor can go through the cylinder portion 203a. The guide element <NUM> further has installation holes 203c on the flange portion 203b and the guide element can be connected onto the top cover <NUM> by means of the installation holes 203c and bolts <NUM>. Thus, different from the cover plate <NUM> in the existing top structure, the guide element have a cylinder body, which provide a possibility to design more effective sealing structure and provide a basis to address further problems, like electrochemical corrosion, and etc..

Referring back to <FIG>, as illustrated, there is provided a new sealing structure <NUM>. Partial enlarged view of the sealing structure <NUM> is further illustrated in <FIG>. As illustrated in <FIG>, the guide element <NUM> is connected onto the top cover <NUM> by bolts and there is arranged a static sealing structure <NUM> between the guide element <NUM> and the top cover <NUM>. The static sealing structure includes an O-ring <NUM> and a gasket <NUM>. The O-ring <NUM> is arranged between the guide element <NUM> and the top over <NUM>. The gasket <NUM> is arranged between the guide element <NUM> and the top over <NUM> as well but located over the O-ring <NUM>. Both the inner side and the top side of the gasket <NUM> are contacted with the guide element <NUM>. The bolts <NUM> can connect the guide element <NUM> onto the top cover <NUM> by means of via holes in the guide element, which could effectively provide a sealing force. The O-ring <NUM> and the gasket <NUM> work together to provide a static sealing between the top cover <NUM> and the guide member <NUM>. The O-ring <NUM> and the gasket <NUM> can be made of for example nitrile butadiene rubber (NBR), which can ensure a good sealing performance.

In addition to the static sealing structure <NUM>, there is further provided a dynamic sealing structure <NUM> between the guide element <NUM> and the central conductor <NUM>. The dynamic sealing structure <NUM> includes a first O-ring <NUM> and a second O-ring <NUM>, which are arranged between the guide element <NUM> and the central conductor <NUM>. The O-ring <NUM>, <NUM> are arranged at the upper side and the lower side of flange portion 203b. The O-ring <NUM>, <NUM> are used together to guarantee no leakage of top sealing structure. The O-rings <NUM>, <NUM> can be made of for example Fluor silicone rubber/gum (FVMQ), NBR, poly tetra fluoroethylene (PTFE), or any other suitable material. Preferably, the O-rings are made from the FVMQ material since it has a better resistance to high temperature and low temperature, ranging from -<NUM> to <NUM> and thus could provide desirable sealing performance. It shall be noticed that the number of O-rings can be less or more, which is dependent actual applicant requirements.

The dynamic sealing structure <NUM> may also comprise a wear ring <NUM> arranged between the guide element <NUM> and the central conductor <NUM>. The wear ring <NUM> may be arranged between the two O-rings <NUM>, <NUM>. The wear ring <NUM> can be configured to provide anti-eccentricity and anti-wear properties. The wear ring <NUM> can be made of PTFE, FVMQ, NBR, or any other suitable material. Preferably, the wear ring <NUM> is made of PTFE due to its better wear resistance and self-lubricating properties. Due to such properties, the wear ring could reduce wear, especial wear of the sealing element due to an impact of tension load; and meanwhile it could provide enough tightening force, by means of the sealing force provided by the guide element, to hold the central conductor tightly, and therefore no eccentricity occurs even when relative movements occur between the central conductor and the guide element.

The dynamic sealing structure <NUM> may further comprise a wiper ring <NUM> arranged between the guide element <NUM> and the central conductor <NUM> at an upper portion of the guide element <NUM>. The wiper ring <NUM> is used to seal the upper portion of the guide element so that the dust cannot enter gaps between the guide element <NUM> and the top cover <NUM>. The wiper ring <NUM> may be made of for example polyurethane (PU), or any other material.

Above the upper portion of the guide element, the protective cap <NUM> is further provided. The protective cap <NUM> can be connected to the copper central conductor by, for example, threads. The protective cap <NUM> can be used to protect the sealing arrangement from the external environment, such as dust, rain, and snow. The protective cap <NUM> can be made of, for example, stainless steel, brass, aluminum, which could substantially reduce the electrical electrochemical corrosion between the central conductor and the protective cap <NUM>. Between the central conductor <NUM> and the protective cap <NUM> is further arranged an O-ring to provide a further sealing therebetween. The O-ring could be made of chloroprene rubber (CR).

In addition, the central conductor <NUM> may have a chrome-plating surface 201a, especially at the area that abrasion is likely to happen. The chrome-planting of copper conductor surface can effectively prevent the copper conductor from abrasion. Further, the guide element may have an anodic oxidation surface 202d, especially at the contact between the guide element and the central conductor <NUM>. The anodic oxidation for guide element surface can effectively prevent electrochemical corrosion between copper central conductor and aluminum guide element. The anodic oxide planting of aluminum guide element has an insulating effect and meanwhile it can also effectively prevent a virtual connection and unnecessary diversion circuit.

In order to verify the functionality of the sliding sealing arrangement to be used on high current bushings, the sealing arrangement <NUM> was tested through verification tests, which will be described hereinafter.

<FIG> illustrates a test sliding mounting of the sealing arrangement <NUM>. During the sliding cyclic test, a terminal plate <NUM> is clamped to a copper rod <NUM> for applying a cantilever load. The relative distance between the terminal plate <NUM> and sliding surface was kept the same as that for the bushing. A cycle for the test was defined as moving upward <NUM> from a neutral position, going back to the neutral position, then moving downward <NUM> and going back to the neutral position again. Thus, the stroke is <NUM> and a cycle travel is <NUM>.

The copper rod <NUM> was further connected to hydraulic actuator, by which a 3000N transversal load was continually applied to the sample sealing arrangement during sliding cyclic test to simulate a lateral force from wind. The test was performed with a cycle frequency of <NUM>, i.e. at a moving speed of <NUM>/s. In addition, the sliding was performed twenty hundred times to simulate the sliding in thirty years of lifetime.

After the sliding cyclic test, tightness tests were further performed in <NUM> groups, the tightness tests include two kinds of tests, i.e., overpressure tightness tests, and tests on vacuuming helium for leakage.

During the over tests, the test sample was installed to a device which was firmly fixed to the ground, and a transversal load of 3000N was applied to terminal plate, filled with compressed air to the device by controlling the pressure up to <NUM>. 4MPa, the inlet of the air was shut off and the pressure was maintained for <NUM> minutes. During the test, the joint interface with liquid soap and the change in pressure were observed.

Test conditions were listed as follows: <NUM>) Ambient temperature: <NUM>; <NUM>) Relative humidity: <NUM>%. The overpressure tightness tests results are shown in Table <NUM>.

These results show that no any leakage was observed and no any pressure drop occurred, which means a good sealing performance.

During the Vacuuming helium for leakage test, a test sample was installed to a test device, applied transversal load to the terminal plate, with the outlet of the test device connected to a helium mass spectrum leak detector, and vacuumed the test device, meanwhile continually jetting helium to the sealing interfaces.

During the leakage test, all <NUM> samples were applied to the transvers load of 3000N, and one of them was tested with transvers load of 4000N.

Test conditions are as follows: ambient temperature <NUM>; relative humidity: <NUM>%. The vacuuming helium for leakage tests results are shown in Table <NUM>.

These results show that no leakage was observed and no any pressure drop occurred, which means a good sealing performance.

Through the tests, it can be seen that the new top sliding sealing structure can effectively prevent eccentricity. Despite the frequent expansion of the rod, the tightness can be still guaranteed. Chrome-planting (copper conductor surface) can effectively prevent the copper conductor from abrasion. Anodic oxidation for guide's face can effectively prevent electrochemical corrosion between copper and aluminum, and meanwhile, the anodic oxide planting of aluminum has an insulating effect, it can effectively prevent the virtual connection and unnecessary diversion circuit. The entire sealing system is further protected by protection cap, which can effectively prevent the sliding sealing structure from dust, rain and snow erosion. Beside, despite the adoption of new structures and new materials, the cost has not increased significantly and the assembly is not complex either.

Therefore, unlike the traditional structure, the example sealing arrangement can not only be adapted for large changes in temperature, but also be used under bad conditions such as conductor eccentricity, large lateral load, sandstorm.

In another aspect of the present disclosure, there is also provided a bushing comprising a sealing arrangement <NUM> for the bushing as described hereinabove. The bushing can be for example transformer bushing, especially an oil-immersed paper transformer bushing.

It shall be noted that the example sealing arrangement is illustrated only for illustrative purposes and the present disclosure is not limited thereto. For example, in the illustrated dynamic sealing structure, there are two O-rings arranged above and under the wear ring respectively. In fact, the number of the O-rings can be less or more and the arrangement of the O-rings is not limited to the arrangement as illustrated. For another example, the illustrated example has various features to achieve corresponding advantages; however, these features can be use separately to achieve respective functionalities.

It shall also be noted that the present application is applicable to various bushings, like dry-type bushing, liquid-filled bushing. In addition, the bushing can be transformer bushing or wall bushing, or any other bushing to the OIP transformer bushing. The present application can be used in OIP transformer bushing but is not limited thereto.

Claim 1:
A bushing for a power electrical device, comprising a sealing arrangement (<NUM>) comprising:
a top cover (<NUM>);
a central conductor (<NUM>) going through the top cover (<NUM>);
a guide element (<NUM>) having a cylinder portion (203a) and a flange portion (203b) extended from a middle part of the cylinder portion (203a), wherein the cylinder portion (203a) is arranged between the top cover (<NUM>) and the central conductor (<NUM>),
a static sealing structure (<NUM>) provided between the guide element (<NUM>) and the top cover (<NUM>); and
a dynamic sealing structure (<NUM>) provided between the guide element (<NUM>) and the central conductor (<NUM>), wherein
the static sealing element (<NUM>) comprises a gasket (<NUM>),
characterized in that
the static sealing element (<NUM>) further comprises an O-ring (<NUM>), whereby the O-ring (<NUM>) is arranged between the guide element (<NUM>) and the top cover (<NUM>), the gasket (<NUM>) is arranged between the guide element (<NUM>) and the top cover (<NUM>) and located over the O-ring (<NUM>), both the inner side and the top side of the gasket (<NUM>) are contacted with the guide element (<NUM>), and in that the flange portion (203b) is connected by bolts (<NUM>) onto the top cover (<NUM>) by means of via holes in the guide element (<NUM>).