BRAKING DEVICE FOR A TRANSFORMER IN THE FORM OF A NUCLEUS
FIELD OF THE INVENTION The invention relates generally to an electric transformer and, in particular, to an improved clamping device for retaining the windings of the transformer under the proper compressive force over the entire operational life of the transformer. BACKGROUND OF THE INVENTION Kernel-shaped energy transformers generally include a containment tank, a coil and an insulating assembly, a magnetic core, a static fastening system for maintaining the compression forces on the magnetic core and the coil assembly and insulator, and electrical conduction assemblies to connect the coils to the outside of the tank. After the assembly of most of the components, the containment tank is usually filled with an electric grade mineral oil that becomes an integral part of the transformer's electrical insulation, as well as a heat transfer medium. During the operation, the transformer periodically undergoes mechanical transient mechanical regimes as a result of contingencies of the electrical operation that occurs in the electrical power system to which the transformer is connected. One of the common contingencies in the energy system is that of short circuit faults. When a short circuit fault occurs in the power system, large currents flow from the different circuits to the place of the short circuit. If an energy transformer is connected in the high current circuit path, the high magnitude current flows through the power transformer and generates transient mechanical forces within the transformer components. Under the voltage of the short circuit currents, the magnetic interaction between the windings of the transformer increases the forces that tend to extend the windings axially and radially with respect to the core. The coil and insulator assembly is one of the components subjected to transient mechanical forces during a short circuit event. The coils are constructed of highly conductive copper or aluminum that is insulated with an electrically non-conductive material. For some decades, the prominent non-conductive material used in power transformers has been an electric-grade paper. It has been observed that many transformers have loose coil and insulator assemblies, which has been attributed to the shrinkage of insulating paper. If the coil and insulation assembly is loose and the transformer is subjected to a mechanical transient regime, the probability of failure of the transformer is much greater than if the assembly is properly adjusted. As such, the mechanical failure of a loose coil and insulator assembly is a common failure mechanism. As previously mentioned, the transformer includes a static clamping system which applies clamping pressure on the coil and insulator assembly. This fixed clamping system makes contact with the ends of the coil and insulator assembly. However, this fixed clamping does not perform the clamping function properly all the time because during the course of time the insulator shrinks. In this way, the force on the windings carried by this fixed clamping system is reduced, or even does not exist, so that the windings are no longer tightly secured in their position. Devices loaded with springs have also been used in the past to obtain reinforcing pressure in the windings. In these devices, springs are often large to directly resist the high deformation forces that result from short circuit currents. Also, in many cases, many springs are necessary to perform the function. Other dynamic clamping systems have been available in the market, such as the DynaComp® device manufactured by ABB of St. Louis, MO. However, this device will only be installed at the moment when the transformer is built and permanently attached to the clamping system. It was not designed to re-adjust existing transformers in the field. In addition, it is relatively large and requires substantial springs to perform the desired function. SUMMARY OF THE INVENTION The present invention is a spring-loaded damping device that can be adjusted in core-shaped transformers to restore the mechanical fit of the coil and insulation assembly that was present when the transformer was manufactured. The assembly of the invention includes a set of Belleville spring collars, a movable piston, and a cylinder. A small hole in the movable piston allows the cylinder to be filled with surrounding insulating oil when it is filled in the transformer container under vacuum. A load rod assembly is fixed to the mobile piston and fitted with the fixed fastening system of the transformer in the form of a core. The cylinder is placed against the coil and insulator assembly. Accordingly, the device of the invention is sandwiched between the fixed clamping system and the coil and insulator assembly. During the steady-state operation of the power transformer, the spring collars maintain compression forces on the coil and insulator assembly.
The spring washers are designed to maintain pressure throughout the service life of the transformer even if the insulating paper continues to shrink. The movement is sufficiently slow so that the displacement of the cylinder oil is not impeded by the small size of the hole in the cylinder. The expansion followed is based on the design and compression capacity of the device and can vary up to approximately 2.54 centimeters. Another important feature of the device is that it is not compressed during mechanical transient events. During these transients, it is necessary that the device acts as a rigid component instead of as a spring. Because the transient events are too short in length of time to allow sufficient oil flow through the small hole in the cylinder, the volume of oil inside the cylinder is an incompressible volume that prevents rapid movement of the piston which, in turn, prevents rapid expansion or compression of the spring. Therefore, the device becomes a rigid component during the transient mechanical events and the compression force is maintained on the coil and insulator assembly. The device is relatively small and occupies a volume of less than 2458.1 cm3 while administering up to 27.216 kilograms of force. A device that delivers 6,804 kilograms of force will occupy less than 573.5 cm3. The device incorporates compression-retaining bolts that keep the spring collars under proper pressure when assembled. After installation in the transformer, the compression bolts are removed so that the force of the spring washers is applied to the windings. In this way, the field installation of the present invention is quite simple. In summary, this invention provides an ecocal solution for restoring adequate compression on the coil and insulator assembly of core-shaped energy transformers, maintaining compression, and dampening axial movement. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Figure 1 is a cross-sectional view through the dynamic coil holding device of the present invention. Figure 2 is a top view of the piston of the dynamic coil holding device of Figure 1. Figure 3 is a side view of the piston of the dynamic coil holding device of Figure 1. Figure 4 is a top view of the cylinder of the dynamic coil holding device of Figure 1. Figure 5 is a side view of the cylinder of the dynamic coil holding device of Figure 1. Figure 6 illustrates a side view of a typical core-shaped transformer; and Figure 7 illustrates the transformer of Figure 6 with the inventive coil holding device of Figures 1-5 installed therein. DETAILED DESCRIPTION OF THE DRAWINGS Initially referring to Figures 1-5, a dynamic coil holding device 10 includes a cylinder 12 and a piston 14 positioned within the cylinder 12. The lower surface of the piston 14 and the lower inner surface of the cylinder 12 define a chamber 15. At the base of the cylinder 12 and inside the chamber 15, a plurality of spring washers 16 are provided. The spring washers 16 (e.g., disk springs) are brought into contact with the inner surface bottom of the cylinder 12 and also with the bottom surface of the piston 14. An alignment pin 18 is placed inside the cylinder 12 and is the structure around which the spring collars 16 are placed. Although the alignment pin 18 is shown as a separate piece, can be formed integrally with the cylinder 12. A load rod assembly 20 is located at the upper end of the coil holding device 10.? The loading rod assembly 20 includes a bent rod 22 around which an upper nut 24 and a lower nut 26 are screwed in a threaded manner. Due to the inherent vibration (for example, 60 hertz) which is present in a transformer, each of the nuts 24 and 26 includes a fixed screw 28 which is adjusted after the coil holding device 10 is installed in the transformer as will be described in greater detail with reference to Figures 6 and 7. The threaded rod 22 could also be formed integrally on the piston 14. Due to the need to make each electrically conductive component of a transformer is connected to ground, a spring 30 is located between the alignment pin 18. and the piston 14 to ensure that the alignment pin 18 maintains mechanical contact with either the piston 14 or the cylinder 12. The spring 30 is a steel compression spring. The cylinder 12 and the piston 14 are also generally made of steel, such as the alignment pin 18. Additionally, the components of the loading rod assembly 20 are also preferably made of steel. The coil holding device 10 can be made relatively small while providing a substantial amount of force, for example, of up to 27,216 kilograms of force. The external diameter of the cylinder 12 is, for example, from about 17.78 to 20.32 centimeters. The height of the cylinder 12 is approximately 10.16 centimeters. In this way, it occupies approximately 2458.1 cm3. The distance that the load rod assembly 20 extends over the surface of the piston 14 in this device is approximately 5.08 centimeters. A device 10 that delivers 6.804 kilograms of force would have a cylinder 12 with an outer diameter of approximately 10.2 cm and a cylinder height of 7 cm. In this way, the device 10 administering approximately 6.804 kilograms occupies approximately 573.5 cm3. This load rod would have a height of approximately 2.54 centimeters. As best shown in Figures 2 and 3, the piston 14 includes an alignment recess 42 that receives the alignment pin 18. The alignment recess 42 is also the internal structure of the piston 14 that receives the spring 30. A recess of rod 44 is located on the uppermost surface of the piston 14 so as to receive the loading rod assembly 20. The rod recess 44 of the piston 14 is used primarily to center the loading rod assembly 20 on the piston 14. As shown, the hollow of the rod 44 is not strung. However, the recess of the rod 44 could be strung to securely hold the threaded rod 22 of the load rod assembly 20. The piston 14 includes a circumferential recess 45 which receives a seal 46. The seal 46 (Figure 1) inhibits that the fluid flows between the outer circumference of the piston 14 and the inner wall of the cylinder 12. Around its circumference, the piston 14 also includes a plurality of diminished recesses 47. Each of the diminished recesses 47 receives a compression retention bolt 48. as shown in Figure 1. The compression retention bolts 48 are strung through the correspondingly aligned stringer holes 52 in the cylinder 12, as shown in Figures 4 and 5. The compression retention bolts 48 are used. during the assembly process to maintain the coil holding device 10 in a steady state force condition prior to installation. In this way, when adequate compression force of the spring collars 16 is achieved, the compression retaining bolts 48 are inserted in a strung fashion through the cylinder 12 and engage the piston 14 to hold the assembly in a convenient position for its storage and transport. The piston 14 also includes a fluid conduit 60 that includes a large region 62 and a small region 64. Because this coil holding device 10 is installed in a transformer having an insulating fluid in all its internal workings, the device Clamp 10 will be exposed to this insulating fluid. As such, when the transformer is filled with vacuum oil with the insulating fluid (eg, mineral oil) the fluid is allowed to flow from the outside of the piston 14 through the conduit 60 in the chamber 15 where the spring collars are located 16. The insulating fluid would also flow along the alignment gap 42 to the region occupied by the spring 30. Include an incompressible fluid within the chamber 15 and provide the glued region 64 in the conduit 60 (eg, 0.1524 centimeters of diameter) allows the coil holding device 10 to act as a rigid member when the transformer is subjected to transient mechanical shocks. The spring washers 16 can include multiple sets of washers. For example, as shown in Figure 1, the spring washer 16 includes a first set of Belleville washers 72 and a second set of Belleville washers 74 placed around the alignment pin 18. The dimensions of the second set of the Belleville 74 cranks are such that they fit within the ring-shaped hollow defined by the alignment pin 18 and the first set of Belleville 72 cranks after the first set of Belleville 72 crankshafts has been placed on cylinder 12 Also, the spring washers 16 can be replaced by standard springs. Referring now to Figure 6, a core-shaped transformer 110 containing a container 112 and a coil assembly 114 is illustrated which is comprised of a plurality of windings of an electrical conductive wire and its associated insulation. An upper coil support 116 is located on the coil assembly 114 and a support block 118 is located above the upper coil support 116. Because the coil assembly 114 has a round cross-sectional shape, as does the upper coil support 116, the support blocks 118 are usually placed in a circumferentially symmetrical manner around the upper coil support 116. It should be noted that the transformer 110 includes a lower coil support similar to the upper coil support 116. However , in the drawings of Figure 6, only the upper coil support 116 is shown. The entire coil assembly 114 is held in compression by a static fastening system 120 when manufactured. The static clamping system 120 includes an upper clamp 122 and a corresponding lower clamp which is not shown in Figure 6. The upper and lower clamps are connected via an axially extending tie rod. During the assembly of a typical transformer, the static clamping system 120 is positioned to fit the coil assembly 114 under a predetermined amount of force. To accomplish this, an appropriately sized support piece 124 is placed on the support block 118 under the upper fastener 122. In this way, the static fastening system 120 provides a known amount of force on the coil assembly 114. The static clamping system 120 is also used to compress a yoke assembly of the magnetic core that is not shown in Figure 6. It should be noted that in some transformers, jack screws are used instead of support pieces 124. Due to the electromagnetic nature of the transformer 110, the upper coil support 116 and the support blocks 118 are made of an electrically insulating material. Examples of this material include wood, Spauldite® manufactured by Spaulding Corporation, Lebanite®, high-density pressed wood manufactured by Weidmann, or Pernawood® manufactured by Pernali Corporation. Additionally, the support piece 124 is often a piece of wood. As previously mentioned, the windings of the coil assembly 114 are metallic structures having an insulating material around it. As well, the coil assembly 114 may be composed of multiple sets of concentric windings. Between these concentric windings, coil 114 would include electronically insulating material extending axially to what is commonly referred to as "filler material". Also, the entire contents of the transformer 110 located within the container 112 are surrounded by an insulating fluid 130. In the course of time, the insulating material associated with the windings of the coil assembly 114, the insulating material of the upper coil holder 116, and / or the material comprising the support block 118 begins to shrink. In addition, the adjacent winding turns, which are of rectangular cross-section, can be loosely untied in relation to one another over time. This phase shift may cause additional shrinkage in the spool assembly 114. Any shrinkage will result in loss of material that is being clamped in a compressible manner which inherently reduces the compressive force on the spool assembly 114. When minimal shrinkage occurs, the support piece 124 can lose contact with the upper fastener 122 as shown in general with the line 132 (the distance is not to scale) so that the coil assembly 114 is no longer held under the compression force of the system static clamping 120. The gap left between the upper clamp 122 and the support part 124 due to shrinkage (i.e. the distance of the line 132 to the upper clamping 122) is usually from about 0.0508 millimeters to about 0.0762 millimeters. Consequently, any electrical transient that is present can cause a high magnetic force in the coil assembly 114 and result in displacement of the coil assembly 114. This occurrence will inevitably result in damage to the transformer 110. The present invention as described previously with respect to Figures 1-5 remedies the situation when installed in the transformer 110. In particular, the coil holding device 10 can be retro-fitted into existing transformers after the aforementioned shrinkage occurs, which usually happens several years after the transformer 110 has been placed in the field. When retrofitting is needed, a field service technician places a jack or jacks between the upper holder 122 and the upper coil holder 116 after the fluid 130 has been drained from the transformer 110. It may be possible to remove the support parts 124 even before using the jacks. However, if the support pieces 124 are still held in place, the activation of the jacks creates a force tending to separate the upper coil support 116 from the upper fasteners 122, thereby allowing the support pieces to be removed. easily. Referring now to Figure 7, as soon as the support pieces 124 are removed and the coil assembly 114 is held in compression by the jacks, the technician then develops a shallow, generally cylindrical recess 140 in each support block 118. Shallow recess 140 has a diameter slightly larger than the diameter of the cylinder 12 and serves to keep the dynamic clamping device 10 in place on the support block 118. The technician can develop these recesses 140 with a simple cutting tool such as a chisel At this time, the dynamic clamping devices 10 are placed in the recesses 140. The loading rod assembly 20 is placed in the recess of rod 44 on the piston 14. The lower nut 26 is rotated to make its lower surface it fits with the upper surface of the piston 14. The upper nut 24 is rotated so that its upper surface is in tight contact with the upper holder 122. The fixed screws 28 (Figure 1) are tightened to hold the lower and upper nuts 26 and 24 instead. This process is repeated for each dynamic clamping device 10 in the transformer 110. Finally, the compression retaining bolts 48 are removed at the same time as they reduce the jacks pressure so that the force of the spring collars 16 are now on the coil assembly 114. As soon as the force is entirely on the coil assembly 114, the jacks are removed from the transformer 110. After the installation process is completed, the container 12 of the transformer 110 is filled to the vacuum with fluid 130 which also enters the chambers 15 of each device 10 via its conduits 60 (FIG. 3) . Because the dynamic clamping device 10 will be used in a variety of types of transformers, each of which has its unique recommended preload making force, the present invention contemplates providing a set that includes several sets of dynamic clamping devices. 10. For example, a first set can have four devices 10, each of which provides 18,144 kilograms of force. In this way, this assembly can be used in transformers with four support posts 118 that require approximately 72,576 kilograms of force in their coil assembly 114. The device 10 allows up to 2.54 centimeters of expansion. A second set can have four devices, each of which administers 13,608 kilograms of force. Together, this second set could administer 54,432 kilograms of force. The devices of a third set can each have 11,340 kilograms of force. The invention also contemplates proper labeling, either by color coding or by simple alpha numeric declarations, which reflect the available strength of each specific device 10. Due to the use of compression retention bolts 48, the dynamic clamping device 10 can be Preload for easy transportation. In this way, the device 10 can be shipped to transformer manufacturers for easy placement in new transformers, in addition to the aforementioned retrofit application. The dynamic clamping device 10 can be installed between the static clamp and the upper coil support, as previously described without being fixedly attached to any structure. In other words, the dynamic clamping device 10 would be sandwiched between the two structures in a newly manufactured transformer. Although the present invention has been described with reference to one or more preferred embodiments, those skilled in the art will recognize that many changes can be made thereto without departing from the spirit and scope of the present invention which is set forth in the following claims.