FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION
Seismic proof power transformer
INVENTORS
Shendge Appaso Dattatraya and Lakhiani Virendra, both of Crompton Greaves Ltd, Transformer Division, Technology Department, Kanjur (E), Mumbai - 400042, Maharashtra, India, both Indian Nationals
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400025, Maharashtra, India, an Indian Company
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF INVENTION
This invention relates to a seismic proof power transformer.
This invention also relates to a method of making a seismic proof power transformer.
BACKGROUND OF INVENTION
A power transformer comprises a core coil assembly disposed in a metallic tank filled with oil. During earthquake or seismic conditions, a power transformer installed at site is subjected to bending, twisting and/or shearing forces and horizontal, vertical and/or rotational movements. Damage to the transformer will depend upon the intensity of the seismic waves. Fastenings employed at the foundation of the transformer are generally strong enough to withstand the forces acting on the transformer tank during seismic conditions but the forces get transferred onto the core coil assembly and the core coil assembly may bend, twist, shear or even overturn and get damaged. Overturning of the core coil assembly under seismic disturbances is commonly encountered. During seismic disturbances, oil sloshing will also occur and under the impact of oil sloshing damage can be caused to the transformer.
JP 56081910 describes a seismic proof transformer in which metal clamps at both sides of the lower part of the core coil assembly are provided with rigidity strengthening plates so as to restrict the metal clamps from deformation and increase the turning spring constant of the metal clamps under seismic conditions. Under seismic conditions, the clamps can break and damage the core coil assembly of the transformer unless the clamps are sufficiently strong. In order to increase the rigidity of the clamps, heavy metal
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stiffeners are to be used thereby increasing the cost and size of the transformer. Metal to metal contact of the clamps amplifies the intensity of the seismic waves to the other parts of the transformer and increases the severity of damage to the transformer, particularly because the core coil assembly is not supported in the tank at the top thereof. JP 2094409 relates to an anti seismic transformer in which the vertical sections or limbs of the iron core of the transformer are twisted to improve the flexural rigidity of the iron core and anti seismic property of the transformer. The core coil assembly is, however, freely supported in the metallic tank of the transformer. Therefore, it is free to move longitudinally, transversely and vertically and even overturn and can get damaged under seismic conditions. Depending upon the intensity of the seismic waves, oil sloshing will increase and damage the transformer.
OBJECTS OF THE INVENTION
An object of the invention is to provide a seismic proof power transformer, which
absorbs and damps seismic waves and shifts its natural frequency outside the seismic
frequency range under seismic conditions thereby protecting the transformer against
damages.
Another object of the invention is to provide a seismic proof power transformer, which absorbs and damps seismic waves and shifts its natural frequency outside the seismic frequency range of 5-35 Hertz under seismic conditions thereby protecting the transformer against damages.
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Another object of the invention is to provide a seismic proof power transformer, which is compact and simple in construction.
Another object of the invention is to provide a method of making a seismic proof power transformer, which method enables the transformer to absorb and damp seismic waves and shift the natural frequency of the transformer outside the seismic frequency range under seismic conditions thereby protecting the transformer against damages.
Another object of the invention is to provide a method of making a seismic proof power transformer, which method enables the transformer to absorb and damp seismic waves and shift the natural frequency of the power transformer outside the seismic frequency range of 5 to 35 Hertz under seismic conditions thereby protecting the transformer against damages.
Another object of the invention is to provide a method of making a seismic proof power transformer, which method is simple and easy to carried out and renders the transformer compact.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a seismic proof power transformer comprising a core coil assembly disposed in a metallic tank filled with oil, the core coil assembly being supported in the tank at the bottom thereof by vibration damping and
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movement limiting means and at the top thereof by vibration damping and movement restricting means, the damping factor of the vibration damping and movement limiting means being selected to shift the natural frequency of the transformer outside the seismic frequency range under seismic conditions.
According to the invention there is also provided a method of making a seismic proof power transformer, the method comprises supporting the core coil assembly of the transformer in the metallic tank thereof on the bottom plate of the tank by vibration damping and movement limiting means and at the top of the tank by vibration damping and movement restricting means, the damping factor of the vibration damping and movement limiting means being selected to shift the natural frequency of the transformer outside the seismic frequency range under seismic conditions.
According to an embodiment of the invention, the damping factor of the vibration damping and movement limiting means is selected to shift the natural frequency of the transformer outside the seismic frequency range of 5-35 Hertz under seismic conditions.
The following is a detailed description of the invention with reference to the accompanying schematic drawings, in which:
Fig 1 is front view of a seismic proof power transformer according to an exemplary embodiment of the invention;
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Fig 2 is side view of the power transformer of Fig 1;
Fig 3 is isometric view of the core coil assembly of the power transformer of Fig 1;
Fig 4 is bottom view of the core coil assembly of Fig 3;
Fig 5 is isometric view of an upright pin on the bottom plate of the tank of the transformer of Fig 1;
Fig 6 is isometric view of a rubber gasket of the transformer of Fig 1;
Fig 7 is a scrap cross-sectional view of an aperture in the top cover of the transformer of Fig 1 with a vertical pin engaged therein; and
Fig 8 is spectrum response of a typical seismic proof power transformer of Fig 1 with and without the rubber gaskets.
The power transformer 1 as illustrated in Figs 1 to 8 of the accompanying drawings comprises a core coil assembly 2 (core and coils marked 3 and 4, respectively) disposed in a metallic tank 5, preferably made of stainless steel. The tank is filled with oil (not shown). Mounting of the tank on a location is not illustrated and described as such is not necessary for understanding the invention. The metallic bottom plate 6 of the tank is provided with three longitudinally spaced rows of upright pins 7 across it. The upright
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pins are provided with tapered heads 8. Three elastic material gaskets 9 (preferably rubber gaskets) are disposed spacedly across the bottom plate of the tank and located on the bottom plate of the tank with the upright pins engaged in the corresponding openings 10 provided in the gaskets. Three metallic base plates 11 corresponding to the gaskets are fixed to the bottom of the core coil assembly and provided with slots 12 corresponding to the openings in the gaskets. The base plates are preferably made of stainless steel and are braced to the bottom of the core coil assembly with channel members 13. The core coil assembly is supported on the gaskets by locating the base plates against the gaskets with the upright pins engaged in the slots in the base plates. The taped heads of the upright pins facilite to slip down the gaskets and base plates through the respective openings and slots over the upright pins. Three vertical pins 14 projecting upwardly are provided on channel shaped brackets 15 fixed to the top of the core coil assembly. The vertical pins are as equally spaced as the rows of upright pins on the bottom plate of the tank. The vertical pins are disposed in apertures 16 provided in the top cover 17 of the transformer. The apertures correspond to the openings in the gaskets and slots in the base plates and are provided with protective caps 18. The vertical pins extend into the protective caps filled with damping material like fibrous material marked 19. The damping factor of the elastic material gaskets are selected by selecting the characteristics and dimensions of the elastic material gaskets such that under seismic conditions, typically under the general seismic frequency range of 5-35 Hertz, the gaskets absorb and damp the seismic waves and shift the natural or structural or fundamental frequency of the transformer outside the seismic frequency range thereby protecting the transformer against damage. As the seismic waves are absorbed and
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damped, oil sloshing is reduced and damage to the transformer under the impact of oil sloshing is eliminated. Because of the sandwiching of the elastic material gaskets between the metallic bottom plate of the tank and base plates, direct metal to metal contact and direct transfer of seismic waves to the core coil assembly is avoided. The core coil assembly is supported both at the bottom and top and is allowed only restricted and limited movement in the longitudinal and transverse directions permitted by the upright pins engaged in the openings and slots in the gaskets and base plates respectively and the vertical pins engaged in the apertures. In order to provide restricted and limited longitudinal and transverse movements to the core coil assembly, the openings and slots and apertures are made slightly larger than the respective pins by about 1.5 to 3mm. The seismic waves are also absorbed and damped by the damping material in the apertures. The vertical movement of the core coil assembly is restricted by the heads of the upright pins and by the caps in the top cover of the transformer in that the heads of the upright pins abut against the peripheries of the slots in the base plates and the vertical pins abut against the top inner surfaces of the respective caps. In order to allow restricted and limited vertical movement of the core coil assembly, slight clearances of the order of about 1.5 to 3 mm are provided between the top surfaces of the base plates and heads of the upright pins and the vertical pins and the top inner surfaces of the caps. As the core coil assembly is supported both at the bottom and top thereof, overturning of the core coil assembly is positively prevented. The invention avoids the use of heavy stiffeners for the core coil assembly thereby reducing the size of the core coil assembly and rendering it compact and also reducing cost. The invention is simple and is easy to carry out.
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The spectrum response of Fig 8 of the accompanying drawings illustrates the damping effects of a typical power transformer of 50MVA capacity under simulated seismic frequency range of 5-35 Hertz with and without rubber gaskets. Curve A represents the transformer with rubber gaskets and curve B represents the transformer without rubber gaskets. The rubber gaskets were made of acrylo nitrile butadine. There were four rubber gaskets each of length x width x thickness = 1000 mm x 420 mm x 22 mm, respectively. It is quite clear from Fig 8 that in the case of the transformer comprising rubber gaskets, the frequency of vibration is substantially reduced and is shifted outside the seismic frequency range.
The number of gaskets and corresponding number of rows of upright pins and number of base plates can vary. The gaskets, upright pins and base plates can lie longitudinally spaced in the tank. The core coil assembly can be of any known construction and configuration. The elastic material gaskets need not be rubber gaskets and instead can be of any other elastic material. Besides being stainless steel, the bottom plate of the tank and the base plates can be also made of any other metals. Such variations in the construction and configuration of the invention are obvious to those skilled in the art and are to be construed and understood to be within the scope of the invention.
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We claim
1. A seismic proof power transformer comprising a core coil assembly disposed in a
metallic tank filled with oil, the core coil assembly being supported in the tank at
the bottom thereof by vibration damping and movement limiting means and at the
top thereof by vibration damping and movement restricting means, the damping
factor of the vibration damping and movement limiting means being selected to
shift the natural frequency of the transformer outside the seismic frequency range
under seismic conditions.
2. A seismic proof power transformer as claim in claim 1, wherein the damping
factor of the vibration damping and movement limiting means is selected to shift
the natural frequency of the transformer outside the seismic frequency range of 5-
35 Hertz under seismic conditions.
3. A seismic proof power transformer as claimed in claim 1 or 2, wherein the vibration damping and movement limiting means comprises a plurality of elastic material gaskets sandwiched between metallic plates and having damping factor selected to shift the natural frequency of the transformer outside the seismic frequency range under seismic conditions.
4. A seismic proof power transformer as claimed in claim 1 or 2, wherein the vibration damping and movement limiting means comprises a plurality of elastic gaskets sandwiched between metallic plates and having damping factor selected
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to shift the natural frequency of the transformer outside the seismic frequency range of 5-35 Hertz under seismic conditions.
5. A seismic proof transformer as claimed in claim 3 or 4, wherein the elastic material gaskets are rubber gaskets such as acrylo nitrile butadine.
6. A seismic proof power transformer as claimed in claim 1 or 2, wherein the vibration damping and movement limiting means comprises a plurality of elastic material gaskets disposed spacedly across the metallic bottom plate of the tank, the bottom plate of the tank being provided with a plurality of longitudinally spaced rows of upright pins across it, the upright pins being provided with tapered heads, the gaskets being located on the bottom plate of the tank with the upright pins engaged in corresponding openings provided in the gaskets, the openings in the gaskets being slightly larger than the size of the upright pins and a plurality of metallic base plates corresponding to the number of gaskets disposed above the gaskets and fixed to the bottom of the core coil assembly, the base plates being provided with slots slightly large than the size of the upright pins and corresponding to the openings in the gaskets, the core coil assembly being supported on the gaskets by locating the base plates against the gaskets with the upright pins engaged in the slots in the base plates, a clearance being provided between the top surfaces of the base plates and the heads of the upright pins and the vibration damping and movement restricting means comprises a plurality of vertical pins projecting upwardly from the top of the core coil assembly as equally spaced as the rows of upright pins on the bottom plate of the tank, the vertical pins being disposed in apertures provided in the top cover of the
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transformer, the apertures being slightly larger than the size of the vertical pins and corresponding to the openings in the gaskets and the apertures being provided with protective caps, the vertical pins extending into the protective caps filled with a damping material and a clearance being provided between the vertical pins and the top inner surfaces of the caps.
7. A seismic proof power transformer as claim in claim 6, wherein the openings in the elastic material gaskets, slots in the base plates and apertures in the top cover are larger than the upright pins and vertical pins respectively by 1.5 to 3 mm and the clearances between the top surfaces of the base plates and heads of the upright pins and between the vertical pins and top inner surfaces of the caps is 1.5 to 3 mm.
8. A seismic proof transformer as claimed in claim 6 or 7, wherein the elastic material gaskets are rubber gaskets such as acrylo nitrile butadine.
9. A seismic proof power transformer as claimed in claim 6, wherein the damping material comprises fibrous material.
10. A method of making a seismic proof power transformer, the method comprises supporting the core coil assembly of the transformer in the metallic tank thereof on the bottom plate of the tank by vibration damping and movement limiting means and at the top of the tank by vibration damping and movement restricting means, the damping factor of the vibration damping and movement limiting means being selected to shift the natural frequency of the transformer outside the seismic frequency range under seismic conditions.
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11. A method as claim in claim 10, wherein the damping factor of the vibration damping and movement limiting means is selected to shift the natural frequency of the transformer outside the seismic frequency range of 5-35 Hertz under seismic conditions.
12. A method as claim in claim 10 or 11, wherein the vibration damping and movement limiting means comprises a plurality of elastic material gaskets sandwiched between metallic plates and having damping factor selected to shift the natural frequency of the transformer outside the seismic frequency range under seismic conditions.
13. A method as claimed in claim 10 or 11, wherein the vibration damping and movement limiting means comprises a plurality of elastic material gaskets sandwiched between metallic plates and having damping factor selected to shift the natural frequency of the transformer outside the seismic frequency range of 5-35 Hertz under seismic conditions.
14. A method as claimed in claim 12 or 13, wherein the elastic material gaskets are rubber gaskets such as acrylo nitrile butadine.
Dated this 19th day of February 2007

(Jose M A)
Agent for the Applicants
Khaitan & Co
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Abstract
A seismic proof power transformer (1) and a method of making the same. The transformer comprises a core coil assembly (2) disposed in a metallic tank (5) filled with oil. The core coil assembly is supported in the tank at the bottom thereof by vibration damping and movement limiting means (7, 9, 11, 12) and at the top thereof by vibration damping and movement restricting means (14, 16, 19). The damping factor of the vibration damping and movement limiting means is selected to shift the natural frequency of the transformer outside the seismic frequency range under seismic conditions (Fig 1).