Abstract:
A manufacturing method of ground-buried solid type insulation transformer is disclosed. According to the transformer manufactured by the method, electric shock to be given to human and animal that make contact with outer case due to electric field produced from winding wire within solid type insulation transformer, can be avoided, and even in case it is buried underground and it is used underwater for a long time, corrosion thereof can be avoided. The manufacturing method of ground-buried solid type insulation transformer comprises 9 processes in total.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a manufacturing method of a ground-buried type solid insulation transformer, and more particularly, to a manufacturing method of a ground-buried type solid insulation transformer in which solid is used as dielectric medium instead of liquid or gas. 
       BACKGROUND OF THE INVENTION 
       [0002]    Generally, it has been well known in the art that each of primary winding and secondary winding (coils) of a dry type transformer is treated with solid type cast material in order to provide a dry type transformer in which dielectric liquid or gas is used as an electrical insulating medium and for diffusing heat created in the windings (coils) or in the transformer core. 
         [0003]    In addition, an oil-filled transformer using liquid such as oil as dielectric material as an electrical insulating medium and for diffusing heat created in the windings (coils) or in the transformer core, classified as above-ground-type, overhead-type and underground-type, etc. Here, a dry type transformer using gas such as circulating air as dielectric material is classified as ground-type and underground-type, which generally raise drawbacks of not having resistance against natural chemical reaction when exposed to ground or underground surrounding. 
         [0004]    The manufacturing of the solid type or dry type transformer has been succeeded but is limited to transformer with relatively low power. Furthermore, the prior art of solid type or dry type transformer or a method of manufacturing of the same has some problems as follows. 
         [0005]    First, in case of the prior art of the solid type or dry type transformer the thermal diffusion through solid type dielectric material is limited and the accumulated heat inside windings can produced hot spots or high thermal gradients that can lead to cracks and produce electrical arcs in the solid insulation system. In particular, in some cases, the breakdown of the solid insulation of the transformer may lead to transformer failure to operate properly. The cracks produced in the transformer can make the transformer mechanically unstable (breakage of transformer coils) which can lead to further break down of the dielectric media between coils and within core or within coils. The electric arc produced within the solid insulation material weakens the dielectric strength of the solid type insulation material, causing break down of the solid insulation system leading to severe damages or even to the explosion of the transformer. In addition, oil-filled transformer using transformer oil as dielectric insulation material, can caused environmental contamination when oil leaks out of the transformer tank when the tank is damaged due to corrosion or when the tank is ruptured due to the transformer failure. 
         [0006]    A prior art manufacturing method of an above-ground dry type transformer requires a protective enclosure which is electrically connected to ground in order to eliminate risks of electric shocks to human beings or to animals wherein the protective enclosure is made of metal, such as steel, and large enough to cover the active part of the transformer (core and coils) and to provide enough electrical clearance between the active part and the grounded enclosure. The drawback of such a transformer arrangement is a large space requirement for installation which makes it difficult to install in small space. Additionally, the expansion and contraction due to the temperature variations within the coil cause mechanical stresses to the transformer coils. 
         [0007]    Furthermore, in the prior art of dry-type transformer, when a large transformer, such as a power distribution transformer, is manufactured using a dielectric cast resin material, it is difficult to cure the cast resin material uniformly in order to provide uniform physical and dielectric properties to the overall body of the transformer. 
         [0008]    Underground Oil-filled type, solid type or dry type transformer has been proposed in order to solve the aforementioned drawbacks of the above-ground type transformer, however, it has not solved the corrosion problem on its surface causing the oil leakage and etc. when it has been buried and operated in underground for a long time. 
         [0009]      FIG. 1  shows process order of prior manufacturing method of a transformer. As shown in  FIG. 1 , it includes low voltage winding process (S 10 ), high voltage winding process (S 20 ), core and coils assembling process (S 30 ), frame assembling process (S 40 ), final assembling process (S 50 ). However, according to the prior manufacturing method, it is difficult to manufacture solid type insulation, which may overcome drawbacks of solid type or dry type transformer. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention has been proposed to solve the aforementioned drawbacks of the prior art, and one object of the present invention relates to provide a manufacturing method of a ground-buried solid type insulation transformer whereby, in case of a physical contact by human or animals to the outer case, an electric shock due to the electric field produced from the windings&#39; wires within the solid type insulation transformer, can be avoided, and whereby even in case of being buried underground and submerged for long time underwater, corrosion can be avoided. 
         [0011]    In order to achieve the aforementioned object, the manufacturing method of ground-buried solid type insulation transformer includes nine processes. That is, the manufacturing method of ground-buried solid type insulation transformer comprises: producing a coil form into which an inner window is formed (first process); winding a low voltage coil and a high voltage coil on the coil form to produce a first coil part (second process); winding glass fiber on the first coil part to produce a second coil part and assembling a first mold into the inner window of the coil form and then pre-heating the second coil part (third process); putting the second coil part into a second mold and injecting epoxy resin and hardener between the second coil part and the second mold, and automatically casting and curing thereof under predetermined speed, vacuum degree, pressure and temperature to produce a third coil part on outer circumference of which an epoxy layer is formed (fourth process); separating the first mold from the inner window of the third coil part and then curing the third coil part (fifth process); cooling the after-treated and cured third coil part and sanding and washing the external epoxy layer, and applying semi-conductive coating material to the sanded part to produce a fourth coil part (sixth process); assembling a core to the fourth coil part to produce a fifth coil part and testing the fifth coil part (seventh process); and connecting the fifth coil part to a conductive mesh and shielding thereof, and then sealing outer side of the fifth coil part and filling silicone or high molecular weight compound between the fifth coil part and the shell made either of Vinlyester resin, Fiber Reinforced Polyester (FRP), or thermoplastic material to manufacture a transformer (eighth process); and final testing the transformer (ninth process). 
         [0012]    According to the ground-buried solid type insulation transformer manufactured by the present method, in case of a physical contact by human beings or animals to the outer case, an electric shock due to the electric field produced from the windings&#39; wires within the solid type insulation transformer, can be avoided 
         [0013]    In addition, windings are surrounded by the shell and silicone or high molecular compound and thus mechanically stable configuration can be obtained and even in case of being buried underground and being in underwater for a long time, corrosion can be avoided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  shows a manufacturing method and processing order in the prior art. 
           [0015]      FIG. 2  shows processing order of a manufacturing method of a ground-buried type solid insulation transformer according to one embodiment of the present invention. 
           [0016]      FIG. 3  shows schematically a holding device for insulation material being held according to another embodiment of the present invention. 
           [0017]      FIG. 4  shows schematically a finished coil form being used for a ground-buried type solid insulation transformer according to another embodiment of the present invention. 
           [0018]      FIG. 5  shows schematically a first coil part appearance implemented on an outer circumference of the coil form and a section of the first coil part. 
           [0019]      FIG. 6  shows schematically molds being inserted into an inner window of the coil form. 
           [0020]      FIG. 7  shows schematically a second coil part produced after a third process of a manufacturing method of a ground-buried type solid insulation transformer according to another embodiment of the present invention, and a section of the second coil part. 
           [0021]      FIG. 8  shows schematically the second coil part installed on the mold. 
           [0022]      FIG. 9  shows schematically a third coil part  300  manufactured through a fourth process of a manufacturing method of a ground-buried type solid insulation transformer according to another embodiment of the present invention, and a section of the third coil. 
           [0023]      FIG. 10  shows schematically a fourth coil part  400  manufactured through a sixth process of a manufacturing method of a ground-buried type solid insulation transformer according to another embodiment of the present invention, and a section of the fourth coil. 
           [0024]      FIG. 11  shows schematically a fifth coil part  500  manufactured through a seventh process of a manufacturing method of a ground-buried type solid insulation transformer according to another embodiment of the present invention. 
           [0025]      FIG. 12  shows schematically conductive mesh and the fifth coil part, which are disassembled. 
           [0026]      FIG. 13  shows schematically a transformer manufactured through the manufacturing method of a ground-buried type solid insulation transformer according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    The preferred embodiments of a manufacturing method of a ground-buried type solid insulation transformer according to the present invention will be described in detail referring to the accompanied drawings. However, it has to be understood that the present invention is not limited to the provided embodiments without departing from a spirit of the present invention. 
         [0028]    Referring again to accompanied drawings,  FIG. 2  shows schematically a processing order of a manufacturing method of ground-buried type solid insulation transformer according to one embodiment of the present invention. Referring to  FIG. 2 , the manufacturing method of a ground-buried type solid insulation transformer includes nine processes (S 100 -S 900 ). That is, each process of the nine processes (S 100 -S 900 ) is as follows: 
         [0029]    Through a first process S 100  a coil form  10  is provided in which an inner window  11  is formed. 
         [0030]    Through a second process S 200  a low voltage coil  20  and a high voltage coil  21  are wound on the coil form  10  to produce a first coil part  100 . 
         [0031]    Through a third process S 300  a glass fiber is wound on the first coil part  100  to produce a second coil part  200  and the second coil part  200  is pre-heated after a mold  30  which is formed corresponding to the inner window is assembled and inserted. 
         [0032]    Through a fourth process S 400  the second coil part  200 , into which the mold  30  is inserted, is placed in a mold  40  and epoxy resin and hardener are injected to the second coil part  200  through the extra part of the mold  40  and then automatically casted-cured to produce a third coil part  300  in predetermined speed, vacuum degree, pressure and temperature. 
         [0033]    Through a fifth process S 500  the third coil part  300  is separated from the mold  40  and the mold  30  is separated from the inner window  11  and then the third coil part  300  is after-treated and cured. 
         [0034]    Through a sixth process S 600  the third coil part  300  is cooled and then sanded and washed. A fourth coil part  400  is produced by applying a coating material  43  of semi-conductive on the sanded region of the third coil part  300 . 
         [0035]    Through a seventh process S 700  a core  50  is assembled to the fourth coil part  400  to produce a fifth coil part  500  and then the fifth coil part is tested. 
         [0036]    Through a eighth process S 800  a conductive mesh  51  is attached to the fifth coil part  500  and the fifth coil part  500  is shielded, and then a shell  52  is assembled thereto. The transformer  600  is produced by filling silicone or high molecular weight compound between the fifth coil part  500  and the shell  52 . 
         [0037]    Through a ninth process S 900  through the final test, the transformer  600  is completed. 
         [0038]    Hereinafter, more details are described, referring to the accompanying drawings. 
         [0039]      FIG. 3  shows insulation material which is held in a holding device.  FIG. 4  shows a finished coil form.  FIG. 5  shows an appearance of the first coil part and its cross section.  FIG. 6  shows a mold to be inserted into an inner window of the coil form. 
         [0040]    Referring to  FIG. 3 , insulation material is cut to a desired size and then held on a holding device  60  to produce a coil form  10  inside which inner window  11  is formed under a first process S 100 . Through a second process S 200 , referring to  FIG. 5 , a low voltage coil  20  and a high voltage coil  21  are wound on an outer circumference of the produced coil form  10  to produce a first coil part  100 . 
         [0041]    Under a third process S 300  when the low voltage coil  20  is wound on the coil form  10 , at least two or more of copper sheet, Insulation paper or film, glass fiber  22  and semi-conductive paper  23  are further wound on outer side of the low voltage coil  20  and at the same time silicone or nitrile rubber are inserted and wound, together with the low voltage coil  20 , to mitigate thermal expansion of the low voltage coil  20 . 
         [0042]    Referring to high voltage coil  21  winding process, at least two or more copper wires, Insulation paper or film, Insulation spacer, glass fiber material and self-fusing tape are wound. In particular, the Insulation spacer is affixed longitudinally to Insulation paper or film at the predetermined distance in order to facilitate the epoxy resin and the hardener to infiltrate thereinto. Here, rectangular wire, round wire or flattened wire, made of aluminum or copper, is used to wind the high voltage coil  21 . The flattened wire and rectangular wire may be preferably used to minimize coil size and increase short circuit strength. 
         [0043]    Furthermore, the first mold  30  is assembled and inserted into the inner window  11 . And, the first mold  30  is composed of tapered parts in order to facilitate assembly and disassembly thereof. 
         [0044]      FIG. 7  shows an appearance of the second coil part and its cross section. Meanwhile, the second coil part  200  is pre-heated for 8-20 hours at temperature between 80° C. and 250° C. to evaporate moisture contained therein after the aforementioned processes are performed. 
         [0045]    Referring to the fourth process S 400 , the second coil part  200 , into which the first mold  30  is inserted, is arranged inside a second mold  40  and an epoxy layer  42  is formed on outer circumference using epoxy resin and hardener which are injected through an epoxy injection port  41  and then automatically casted and cured under predetermined speed, vacuum, pressure and temperature to produce a third coil part  300 . 
         [0046]      FIG. 8  shows an appearance of the second coil part installed on the second mold. Referring to  FIG. 8 , the second mold  40  is configured as a predetermined shape depending on a transformer shape. The second coil part  200  is assembled or installed into the second mold  40  and epoxy resin and hardener are injected automatically under computer control through the epoxy injection port  41  and then automatically casted and cured under predetermined speed, vacuum, pressure and temperature to produce the third coil part  300 , as shown in  FIG. 9 . 
         [0047]      FIG. 9  shows an appearance of the third coil part and its cross section. Here, epoxy resin and hardener are supplied through the epoxy resin injection port  41  formed on one side of the second mold  40  wherein the second mold  40  is kept at a temperature between 100° C. and 200° C., and epoxy resin and hardener is kept at a temperature between 50° C. and 150° C. and under vacuum level of 1 mbar to 80 mbar during filling and maintained at 2 bar to 20 bar of epoxy resin injection pressure within the second mold  40  for 30 min to 2 hr in order to make epoxy gel or gel state. 
         [0048]    In fifth process S 500 , the first mold  30  is separated from inner window  11  of the third coil part  300  and then after-treated and cured. Here, the third coil part  300  is cured at 60-250° C. to solidify the third coil part  300  in the after-treatment and curing process of the fifth process S 500 , and in particular the third coil part  300  may be cured preferably at a temperature between 100° C. and 200° C. 
         [0049]    In sixth process S 600  the third coil part  300  is cooled and then outer surface of epoxy layer  42  is sanded and washed so that epoxy paint (semi-conductive coating material  43 ) can be applied on epoxy layer  42  formed on outer surface of the third coil part  300 . In addition, the sanded part of epoxy resin is coated with semi-conductive epoxy paint to produce a fourth coil part  400 . 
         [0050]      FIG. 10  shows an appearance of the fourth coil part and its cross section. In the seventh process S 700 , a core  50  is assembled to the fourth coil part  400  to produce and test a fifth coil part  500 . 
         [0051]      FIG. 11  shows an appearance of the fifth coil part. In an eighth process S 800 , the fifth coil part  500  is attached with a conductive mesh  51  and shielded and then the shell  52  is assembled and silicone or high molecular weight compound is filled between the fifth coil part  500  and the shell  52 . 
         [0052]      FIG. 12  shows an attaching manner of the conductive meshes to the fifth coil part. Referring to  FIG. 12 , the conductive meshes  51  made of copper or aluminum are arranged over semi-conductive epoxy paint  43  of respective upper and lower part of the fifth coil part  500 . Also the conductive meshes  51  and the semi-conductive epoxy paint  43 , when the transformer operated in normal service conditions, are connected to the system ground providing an electrical shielding for the fifth coil part  500 . By grounding the conductive meshes  51  and the semi-conductive epoxy paint  43 , the electric field inside the fifth coil part  500 , which emanate from the windings, is confined inside the fifth coil part  500  and will not result in a shock hazard to human beings or animals coming in contact with the external shell surface. Also by grounding the conductive meshes  51  and the semi-conductive epoxy paint  43 , a path to ground for the fault current is provided in the event of an internal electrical fault inside the fifth coil part  500 . 
         [0053]      FIG. 13  shows a transformer manufactured through the manufacturing method of a ground-buried type solid insulation transformer according to the present invention. Referring to  FIG. 13 , the transformer  600  is manufactured finally such that the fifth coil part  500  which is attached with the conductive mesh  51  is assembled to the shell  52  made either of Vinlyester resin, Fiber Reinforced Polyester (FRP), or thermoplastic material At this time, silicone or high molecular weight compound is filled into the assembled shell  52  and thus after its solidification in a flexible material, the sealing and water-proofing of the transformer  600  can be obtained. 
         [0054]    The transformer  600  may be tested through a ninth process S 900 . 
         [0055]    A summary of a manufacturing method of ground-buried solid insulation transformer according to the present invention will be follows. 
         [0000]    1) Preparing insulation material (not shown) to be cut into desired size.
 
2) Holding the insulation material on a holding device  60  and producing a coil form  10  into which inner window  11  is formed.
 
3) Winding low voltage coil  20  on an outer circumference of the coil form  10 .
 
4) Winding glass fiber  22  and semi-conductive paper  23  on an outer circumference of the low voltage coil  20 .
 
5) Winding high voltage coil  21 .
 
6) Winding glass fiber  22  (second coil part  200 )
 
7) Separating the second coil part  200  from the holding device  60  and assembling and inserting a first mold  30  into the inner window  11  of the second coil part  200 .
 
8) Pre-heating the second coil part  200 .
 
9) Putting the pre-heated second coil part  200  into a second mold and injecting epoxy resin and hardener thereto and further controlling inside the second mold to predetermined speed, vacuum degree, pressure and temperature and automatically casting and curing, and producing a third coil part  300  of an epoxy layer being formed on outer part of the second coil part  200 .
 
10) After-treating and curing the third coil part  300 .
 
11) Cooling the third coil part  300  and applying semi-conductive coating material  43  (semi-conductive epoxy paint) to produce a fourth coil part  400 .
 
12) Assembling a core  50  to the fourth coil part  400  to produce a fifth coil part  500  and testing the fifth coil part  500 .
 
13) Attaching a conductive mesh  51  to the fifth coil part  500 .
 
14) Assembling a shell  52  to an outer circumference of the fifth coil part  500  and filling silicone or high molecular weight compound between the fifth coil part  500  and the shell  52  to produce a transformer.
 
15) Testing the produced transformer.
 
         [0056]    While the present invention is described referring to the preferred embodiment, the present invention is not limited thereto, and thus various variation and modification can be made without departing from a scope of the present invention.