CONTAINING TANK OF AN OIL IMMERSED POWER TRANSFORMER

Abstract: The subject of the invention is the containing tank of an oil immersed power transformer intended for use especially in large capacity power transformers. According to the invention, the containing tank of an oil immersed power transformer is a metal box to which, on its external circumference, acoustic screens (7) or (14) are attached. The longitudinal edges of the acoustic screens (7) or (14) are attached to the side walls (2) or (11) of the box. The lower and upper edges of the acoustic screens (7) are attached to the lower (4) or upper (5) flange of the box (1) respectively. The side edges of the acoustic screens (14) are suitably attached to the vertical brackets (13).

Description: CONTAINING TANK OF AN OIL IMMERSED POWER TRANSFORMER The subject of the invention is the containing tank of an oil immersed power transformer intended for use especially in large capacity power transformers. At present, in large capacity transformers metal tanks are used which consist of side walls, floor and cover, forming boxes in the shape of a rectangular prism. Such tank is filled with oil in which the column shaped core of the transformer with its windings is immersed. In order to reinforce the tank structure its side walls have brackets welded to them lengthwise, the brackets having usually the shape of T-bars or channel bars and being spaced depending on the power of the transformer and its size. These brackets, besides reinforcing the structure, dampen the vibrations caused mainly by the vibration of the transformer core. Acoustic waves arising from these vibrations propagate outside the transformer in all directions and are the source of noise arising during the operation of the transformer. Despite the use of the brackets attached to the side walls of the tank the problem of noise has not been adequately solved yet. However, there are known devices which are used in large capacity transformers to lower the noise level. The American patent specification No. US 4 558 296 describes a sound damping device which can be used to dampen sound in the containing tank of an oil immersed power transformer. The device consisting of a number of sound absorbing plates connected to one another along the circumference forms a plate of larger area which can be placed inside the transformer tank, between its core and the tank walls. Each single sound absorbing plate is a flat container tightly filled with gas of adequate characteristics, inside which there are placed structural elements which undergo an elastic strain when acoustic waves attack the surface of the plate. The device is characterised by a fairly complicated structure. The American patent specification No. US 4 514 714 describes a sound damping device which is used to dampen sound in the containing tank of an oil immersed power transformer. The device consists of a number of sound absorbing panels attached to steel brackets made in the form of channel bars which are vertically and horizontally welded by their edges to the side walls of the tank on its outer circumference. The steel channel bars form a lattice construction in whose empty spaces the above mentioned sound absorbing panels are placed, these panels being connected to weighting elements made in the form of a steel frame. To this frame are attached dynamic sound dampers positioned parallel to one another. Both the steel frame and the dynamic sound dampers are located in the empty spaces of the lattice construction, between the sound absorbing panels and the side walls of the tank. The frequency of the free vibrations of each sound damper is selected to counterbalance the frequency of vibrations of the weighting elements attached to the sound absorbing panels. In this way, the damping effect achieved by the use of the sound absorbing panels is intensified. Unexpectedly, it was found that a considerable reduction in the noise level created during the operation of an oil power transformer can be achieved by a simple modification of the structure of its tank. Mechanical waves created by the vibration of the transformer core undergo mainly internal reflections from the tank walls. A part of these waves cause the tank walls to vibrate, which in turn generates acoustic waves which propagate outside the tank. A reinforcement of the tank structure by its additional stiffening contributes to increased dampening of the vibration of the structure, but it barely contributes to the reduction of noise. The construction of the tank according to the invention causes that acoustic waves additionally undergo partial dampening outside the tank walls. The characteristic feature of the containing tank of an oil immersed power transformer in the form of a metal box, according to the invention, is that the box has acoustic screens preferentially formed as gutters which are vertically arranged on the external circumference of the box. The longitudinal edges of the acoustic screens are attached to the side walls of the box and their lower and upper edges are attached to the lower and upper flange of the box respectively. Each acoustic screen is preferentially formed of two flat bars joined to one another at an angle α > 90°. Each acoustic screen has vertical ribs fixed inside. These ribs are preferentially formed of two flat bars joined to one another at an angle αi < α and their top edge is attached inside the acoustic screen. The space between the side wall of the box and the internal walls of the acoustic screen is filled with sound absorbing material. Another embodiment of the invention is characterised in that the containing tank of an oil immersed power transformer has acoustic screens formed as gutters which are arranged horizontally on the external circumference of the box. The longitudinal edges of the acoustic screens are attached to vertical brackets. The acoustic screen is preferentially formed of two flat bars connected to one another at an angle > 90°. Each acoustic screen has longitudinal ribs fixed inside it. These ribs are preferentially formed either of two flat bars joined to one another at an angle αi < α, their top edge being attached inside the acoustic screen, or of a single flat bar which is situated perpendicular to the base of the acoustic screen. The space between the side wall of the box and the internal walls of the acoustic screen is filled with sound absorbing material. The advantage of the tank according to the invention is its simple construction permitting a considerable reduction of the level of noise occurring during the operation of the power transformer. A tank according to the invention is shown as an example embodiment in the drawing where fig. 1 shows the tank with vertically attached acoustic screens as a view in axonometric projection, fig. 2 shows a fragment of the tank wall from fig. 1 with an acoustic screen shown in cross-section, fig. 3 shows the tank with horizontally attached acoustic screens as a view in axonometric projection, fig. 4 shows a fragment of the tank wall with the acoustic screen from fig. 3 in cross-section, and fig. 5 shows a fragment of the tank wall fig. 3 with an acoustic screen in the other embodiment - also in cross section. As shown in fig. 1 , the containing tank of an oil immersed power transformer is made in the shape of a metal box ± by welding together side walls 2 and the floor 3 whose thickness and outer dimensions depend upon the size of the transformer and its capacity. The floor 3 is provided with a bottom flange 4 located on the outside of the side walls 2. To the side walls 2, in their upper part, there is welded the upper flange 5 to which the transformer cover, not shown in the drawing, is connected. To the outer surfaces of the side walls 2 are welded vertical metal brackets 6 in the form of channel bars. Instead of channel bars, T-bars may be used. The brackets 6 are spaced at a certain distance from one another, and their purpose is to reinforce the structure of the tank. Between the brackets 6, to the outer surfaces of the side walls 2 are vertically attached acoustic screens 7 which have a shape resembling a gutter and which are formed by welding together two flat bars at an angle α = 105°. These screens can be made of one piece of adequately bent steel sheet. The longitudinal edges of each screen 7 are attached to the side walls 2. The bottom edge of each screen 7 is connected with the upper surface of the lower flange 4, and the upper edge is connected with bottom surface of the upper flange 5. Fig. 2 shows a single acoustic screen 7 provided with vertical ribs 8 which are placed along the whole length of the screens 7 and they are made of flat bars welded with one another at an angle αi = 60° < . The top edge of so formed ribs 8 is joined to a screen 7 at the opening side of the angle . The space between the side wall 2 of the box and the internal walls of the acoustic screen 7 is filled with sound absorbing material 9 such as e.g. sand. Fig. 3 shows the containing tank of an oil immersed power transformer in the form of a metal box J_0 formed by welding together the side walls H and the floor 12 whose thickness and outside dimensions depend upon the size and power of the transformer. To each of the side walls V\_ axe welded vertical, metal brackets 13 which are arranged outside the box. The vertical brackets 13 in the example embodiment of the device have the form of flat bars. These brackets may have the form of angles and T-bars, which is not illustrated in the drawing. The brackets 13 are arranged at a certain distance from one another and their purpose is to reinforce the structure of the tank. Between the brackets 13, to the outer surfaces of the side walls H are horizontally connected acoustic screens 4 which have a shape resembling a gutter, and which are formed by welding together two flat bars at an angle α = 105°. These screens can be made of one adequately bent steel sheet. The longitudinal edges of each acoustic screen 14 are horizontally welded to the side walls JM . The side edges of each screen 14 are connected with the side surfaces of the metal brackets 13. As shown in fig. 4, each acoustic screen 14 is provided with longitudinal ribs 15 which are located along the whole length of the screens 14 and which are made from flat bars welded with one another at an angle αi = 60° < α. The top edge of so formed ribs 15 is joined to a screen 14 at the opening side of the angle α. The space between the side wall H of the box and the internal walls of the acoustic screen T4 is filled with a sound absorbing material 1_6 such as e.g. sand. Fig. 5 shows the longitudinal walls of the acoustic screen 14^ which can also have the form of a single flat bar J7 attached to the screen 14 and arranged perpendicular to the base of that screen. The space between the side wall 11 of the box and the internal walls of the acoustic screen 14 is filled with sound absorbing material 16. That space can be filled with the sound absorbing material 16 under pressure through openings (not shown in the drawing) made in the metal brackets 13. The openings may be blinded with rubber stoppers. During the operation of the power transformer the acoustic wave created as a result of the core vibration causes vibration of the side walls 2 or JJ . of the tank. The walls, in turn, transfer the vibrations to the screens 7 or 14. The vibrations are dampened on the brackets 6 or J3, acoustic screens 7 or 14 and on their ribs 8, J_5 or 17, as well as inside the sound absorbing material 9 or 16. As the result of the application of such a solution the amplitude of vibrations on the outer surface of the screens 7 or 14 is much smaller than on the side walls 2 or 1J . of the tank. Acoustic pressure generated outside the tank is much lower than pressure which is generated by the vibrations of a tank without the acoustic screens 7 or 14.

Claims: CLAIMS 1. A containing tank of an oil immersed power transformer in the form of a metal box, characterised in that the box has acoustic screens (7) preferentially formed as gutters, which gutters are arranged vertically on the external circumference of the box (1), and the longitudinal edges of the acoustic screens (7) are attached to the side walls (2) of the box (1), and their lower and upper edges are attached to the lower (4) and upper (5) flange of the box (1) respectively. 2. A tank as per the claim 1 characterised in that the acoustic screen (7) is formed of two flat bars joined to one another at an angle ( ) > 90°. 3. A tank as per the claim 1 characterised in that the acoustic screen (7) has vertical ribs (8) attached inside the said screen. 4. A tank as per the claim 3 characterised in that the vertical ribs (8) are formed of two flat bars joined to one another at an angle (αi) < ( ), and the top edge of the ribs (8) is fixed inside the acoustic screen (7). 5. A tank as per the claim 1 characterised in that the space between the side wall of the box (1) and the internal walls of the acoustic screen (7) is filled with a sound absorbing material (9). 6. A containing tank of an oil immersed power transformer in the form of a metal box characterised in that the tank has acoustic screens (14) formed as gutters, which gutters are arranged horizontally on the external circumference of the box, and the longitudinal edges of the said acoustic screens (14) are attached to the side walls (H) of the box, whereas the side edges of the said acoustic screens (14) are suitably attached to the vertical brackets (J3). 7. A tank as per the claim 6 characterised in that the acoustic screen (14) is formed of two flat bars joined to one another at an angle (α) > 90°. 8. A tank as per the claim 6 characterised in that the acoustic screen (14) has longitudinal ribs (15) fixed inside the said screen (14). 9. A tank as per the claim 8 characterised in that the longitudinal ribs (15) are formed of two flat bars joined to one another at an angle (αjj < ( ), their top edge being fixed inside the acoustic screen (14). 10. A tank as per the claim 8 characterised in that the longitudinal ribs are formed of a single flat bar (17) which is situated perpendicular to the base of the acoustic screen (14). 11. A tank as per the claim 6 characterised in that the space between the side wall (H) of the box and the internal walls of the acoustic screen (14) is filled with a sound absorbing material (16).

Inventors: NOWAK DARIUSZ, NOWAK TOMASZ, ZBUDNIEWEK ANTONI, NOWAK, DARIUSZ, NOWAK, TOMASZ, ZBUDNIEWEK, ANTONI
Applicants: ABB ELTA SP Z OO, ABB ELTA SP. Z.O.O.
Application year: 1999
Main classification: H01F27
IPC codes: H01F27