Description:“A PRIMARY CURRENT CARRYING CONDUCTOR WITH A DOUBLE POLYMER INSULATOR FOR A 220 KV CURRENT TRANSFORMER”

FIELD OF THE INVENTION:
The present invention relates in general to electric inductive apparatus, such as transformers, and more specifically to a new and improved 220 KV current transformers.

BACKGROUND OF THE INVENTION:
Background description includes information that may be useful in understanding the present invention.
Any electrical equipment must be provided with proper insulation otherwise the equipment may get damaged due to high voltage surges. Current transformers (CT) are an indispensable tool to aid in the measurement of AC current. Current Transformers installed at different sub stations / power stations are used to monitor the power flow and healthiness of the power system. Its main function is to supply proportional current of low value for measurement purpose. They also permit isolation of measuring circuits from high voltage and high current circuits avoiding hazardous conditions and allow usage of measuring instruments located on control panels in control rooms far away from the HT circuits. They also provide a means of scaling a large primary (input) current into a smaller, manageable output (secondary) current for measurement and instrumentation. A CT utilizes the strength of the magnetic field around the conductor to form an induced current on its secondary windings. This indirect method of interfacing allows for easy installation and provides a high level of isolation between the primary circuit and secondary measurement circuits. CTs are available in various sizes, designs and input ranges and output signal types.1
Porcelain is a ceramic made by heating various raw materials in a kiln. During this process the kiln can reach temperatures of up to 1500 degrees celsius. After baking, a glassy, translucent product is produced yielding high permeability and a white or off white color. Even though this material is known for its strength, it is very brittle. At least this is a reason for its cracking and breaking under extreme environments or if dropped from any height. However, unlike porcelain, polymers doesn't crack or break when dropped or submitted to extreme temperatures on both ends of the spectrum.
The lies a need for an improved insulator mechanism for current transformer.

OBJECTIVES OF THE INVENTION:
Some of the objects of the present disclosure, which at least one embodiment herein satisfy, are listed herein below.
At least an objective of the present subject matter is to propose a current transformer (100) with double polymer insulator (104) to enhance safety of nearby operator & equipment against explosion. Polymer insulator (104) do not shatter in case of explosion while porcelain insulator break/shatter in small pieces in case of explosion.
Yet another objective of the present subject matter is to increase the oil cooled capacity (103) for better heat dissipation/cooling by increasing effective dissipation area of insulator by utilization double insulator compared to current transformer with porcelain insulator.
Yet another objective of the present subject matter is to propose a new current transformer (100) having provision of separate bushing (108) for both primary legs which provide mechanical strength during short circuit or fault current during operation.
These and other objects and advantages will become more apparent when reference is made to the following description and accompanying drawings.

SUMMARY OF THE INVENTION:
The present invention proposes a novel 220 KV double polymer insulator (104) current transformer (100) over a porcelain insulator in a dead tank design where the top chamber (101) of elliptical base (105) increases the surface area of the top tank (101) for providing proper assembly of double insulators resulting in the increase of the surface area of the oil cooled arrangement (103). An improved oil cooled arrangement provides better heat dissipation/ cooling of the device. Also, separate bushing (108) for both primary legs is provided which further enhances the mechanical strength during short circuit or fault current during CT operation.
Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components

BRIEF DESCRIPTION OF DRAWINGS:
The illustrated embodiments of the subject matter will be understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and methods that are consistent with the subject matter as claimed herein, wherein:
Figure 1. illustrates a front view of the current transformer (100) in accordance with the present subject matter.
Figure 2. illustrates isometric or 3D angular view of the current transformer (100) insulator in accordance with the present subject matter.
Figure 3. illustrates isometric or 3D view of the top chamber (101) of the current transformer (100) in accordance with the present subject matter.
Figure 4. illustrates an isometric or 3D view of the bottom (102) of the current transformer (100) in accordance with the present subject matter.
Figure 5. illustrates a side view of the current transformer (100) in accordance with the present subject matter.

DETAILED DESCRIPTION OF THE EMBODIMENT:
The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.
The terms “comprises”, “comprising”, or any other variations thereof used in the disclosure, are intended to cover a non-exclusive inclusion, such that a device, system, assembly that comprises a list of components does not include only those components but may include other components not expressly listed or inherent to such system, or assembly, or device. In other words, one or more elements in a system or device proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or device.
145/245 KV Current Transformers installed at different sub stations / power station are used to monitor the power flow and healthiness of the power system to supply proportional current of low value for measurement purpose. They also permit isolation of measuring circuits from high voltage and high current circuits avoiding hazardous conditions and allow use of measuring instruments located on control panels in control rooms far away from the HT circuits. Such transformer is of single phase, oil immersed, 145/245 KV class suitable for Outdoor applications.
Presently BHEL manufactures 220 KV current transformer of dead tank design with porcelain insulator. In dead tank CT, the core and secondary winding is housed in the bottom tank which is earthed or dead. In dead tank CT, the primary winding is brought down to the bottom tank and it is insulated from the earthed tank and cores. The primary has to pass through the porcelain insulator and the larger length of the primary conductor produces maximum mechanical force during short time dynamic current which might damages the insulation.
A 220 KV Current Transformer with polymer insulator (104) is in demand for some time now since it provides better insulation compared to porcelain. Yet, the current dead tank design current transformers require hollow insulator with higher outer & inner diameter. At least a problem associated with this state of the art is that the availability of higher outer/inner diameter polymer insulator is limited and time consuming, which further effect the delivery of current transformers of polymer insulation.
To overcome the above-mentioned problem, a 220 KV, 1600A current transformer with double polymer insulator (104) having small inner/outer diameter is proposed. This current transformer (100) has two polymer insulator (104) of small inner/outer diameter for each inner/outer current lags of primary winding copper tube to provide mechanical strength during short circuit test.
A polymer insulator employed in CT has two parts, one is a glass fiber reinforced epoxy resin rod-shaped core and the other is a silicone rubber or EPDM (Ethylene Propylene Diene Monomer) made weather sheds. The rod-shaped core is covered by weather sheds. Weather sheds protect the insulator core from the outside environment. As it is made of two parts, core and weather sheds, polymer insulator is also called a composite insulator. The rod-shaped core is fixed with Hop dip galvanized cast steel made end fittings on both sides.
Additionally, polymer insulator is very lightweight compared to porcelain and glass insulator. As the composite insulator is flexible the chance of breakage becomes minimum because of lighter in weight and smaller in size, this insulator has lower installation costs. It has a higher tensile strength compared to a porcelain insulator. Its performance is better, particularly in polluted areas. Due to lighter weight polymer insulator imposes less load to the supporting structure less cleaning is required due to the hydrophobic nature of the insulator2.
Figure 1. illustrates a front view of the current transformer (100) in accordance with the present subject matter. In this new design, top tank (top chamber (101)) for supporting primary winding of elliptical base (105) increases the surface area of the top tank (101) for providing proper assembly of double insulators & terminal connection. The elliptical base (105) however is a non-limiting example and the present description may be covered to cover other analogues such as arcuate shape, parabolic, hemispherical etc.
Furthermore, oil cooled capacity (103) is increased to dissipate thermal energy by increasing the effective dissipated area of the top tank (101) through an elliptical or arcuate shape as compared to complete-circular design in a porcelain insulator current transformer.
The current transformer (100) has provision of separate bushing (108) as illustrated in Figure 1. for both primary legs which provide mechanical strength during short circuit or fault current during operation
Figure 2. illustrates isometric or 3D angular view of the current transformer (100) in accordance with present subject matter. The figure illustrates the plurality of layers (104) which are separated by a visible-margin or gap between the layers (104). In another scenario, the layers (104) may also abut each other within the insulation arrangement (104,105,106) to achieve a flush and seamless outer surface thereof.
Figure 3. illustrates an isometric or 3D view of the top chamber (101) mounted atop the double polymer insulator (104) of the current transformer (100) in accordance with the present subject matter. The double polymer insulation arrangement (104,105,106) is suspended from the elliptical base (105) of the top chamber (101) and supported upon the elliptical bottom (106) tank, both suspension and supporting having been through removable fasteners (107). Further an oil cooled arrangement (103) is provided at the top chamber (101) for heat dissipation/cooling through a wide surface area provided by the elliptical base (105) of the top chamber (101).
Figure 4 (a and b) illustrates an isometric or 3D view of the bottom dead tank (102) which is a steel tank having an elliptical top (106) or the elliptical base (106) to receive the insulation arrangement (104,105,106) of the current transformer (100) in accordance with present subject matter. The double polymer insulation arrangement (104,105,106) is mounted atop the elliptical top (106) through twelve removable fasteners (107) per insulator enclosed by twenty-four equispaced holes (107) for better insulation arrangement (104,105,106).
Figure 5. illustrates a 3D side view of the current transformer (100) in accordance with present subject matter.
In the transformer (100), the fabricated steel tank (102) at bottom supports a hair pin condenser primary which passes through the porcelain housing mounted on top (106) of the bottom tank cover and terminates in a top chamber (101). The condenser primary passes through the ring type secondary core and windings which are placed in bottom tank (102) and suitably clamped against any movement during transit or use. The leads of the secondary windings are connected to the inner side terminals of the epoxy terminal board located in a weather proof terminal box on the side of the tank. The tank is complete with one power factor terminal along with cap, valves for filling, draining and sampling of oil, rating and diagram plate, sling guides etc. The stud type primary terminals project from the top chamber. The top tank or chamber (101) of the CT (100) also act as an expansion vessel for the oil. The current transformer (100) after a careful dry out is filled with high quality degassed oil under vacuum and to seal the space left for the expansion on the top chamber (101) is filled with dry and pure nitrogen through a Schrader valve at a predetermined pressure. The current transformer (100) is normally supplied filled with dry nitrogen from the factory and does not require to be filled again at the site. However, where it is suspected that the gas has leaked out, its pressure can be checked by fixing a pressure gauge to the Schrader valve.
The current transformer (100) was successfully tested for all routine, type tests including short circuit test, temperature rise & impulse test including mechanical & seismic tests. The present 220 KV double polymer insulator (104) current transformer (100) exhibits an increased oil cooled capacity for better heat dissipation and further provides mechanical strength during short circuit or fault current during operation, by providing separate bushing (108) for both primary legs. The current transformer (100) with double polymer insulator (104) enhances safety of nearby operator and equipment against explosion as polymer insulator (104) do not shatter in case of explosion while porcelain insulator break/shatter in small pieces.
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 polymer insulation based current transformer (100) comprising:
a top chamber (101) for supporting primary winding;
a steel tank (102) for supporting secondary winding and the core; and
an insulation arrangement (104,105,106) suspended from the top chamber (101) and supported upon the bottom tank (102),
wherein the insulation arrangement (104,105,106) comprises a plurality of layers of polymer insulator (104) suspended from an elliptical base (105) of the top chamber (101).

2. The current transformer (100) as claimed in claim 1, wherein the top chamber (101) is a steel/aluminum top chamber (101) defined as a dead tank and mounted atop the double polymer insulator (104).

3. The current transformer (100) as claimed in claim 1, wherein the bottom tank (102) is a steel tank defined as a dead tank having an elliptical top (106) to receive the insulation arrangement (104,105,106).

4. The current transformer (100) as claimed in claim 1, wherein the plurality of layers (104) abut each other within the insulation arrangement (104,105,106) to achieve a flush outer surface thereof.

5. The current transformer (100) as claimed in claim 1, wherein the insulation arrangement (104,105,106) is held between the top chamber (101) and the bottom tank (102) through twelve equispaced removable fastener (107) per insulator enclosed by twenty-four equispaced holes (107) for better insulation arrangement (104,105,106).

6. The double polymer insulator (104) 220 KV dead tank current transformer (100) as claimed in claim 1, further comprising an oil cooled arrangement (103) provided at the top chamber (101) for heat dissipation/cooling through a wide surface area provided by the elliptical base (105) of the top chamber (101).

7. The dead tank current transformer (100) as claimed in claim 1, wherein the current transformer is a 220 KV dead tank current transformer (100) with double bushing (108).