Patent Application
20080061037
The inventors of the present invention have innovatively recognized that it may be advantageous for an ablative material for use in an arc suppressing device to possess a desired arc energy absorption characteristic while providing a desired reduced ablation vapor pressure around the arc. For example, it has been experimentally observed that high vapor pressures, such as vapor pressures above 100 bars, resulting from ablation in a confined region, may limit arc cooling, resulting in undesirably longer arc extinguishing times. Such elevated vapor pressure may result from a choked exhaust flow condition wherein ablation vapors may not be evacuated from the confined region, resulting in the ablation vapors receiving more arc energy causing increased temperature and reduced arc quenching performance. Accordingly, the inventors have developed a composite arc suppression device that includes different regions providing different ablation characteristics to achieve desired arc energy absorption while providing reduced vapor pressure for continued suppression of the arc.
The ablative arc suppression device 10 may include a first region 16 having a first electrical arc ablation characteristic and a second region 18 having a second electrical arc ablation characteristic different than the first region 16. The first region 16 and the second region 18 may be to define the opening 22 that extends through the first region 16 and the second region 18. In an aspect of the invention, the opening 22 may be configured to extend through the first region 16 and the second region 18 perpendicularly with respect to respective region boundary surfaces 17, 19. As shown in
The first region 16 and the second region 18 may be further configured for defining the opening 22 so that the electrical arc 26 generated therein is exposed to both the first region 16 and the second region 18 before the arc 26 exits the opening 22 as shown in
In an aspect of the invention, the regions 16, 18 may be configured to have different arc reactive properties, for example, to achieve a desired arc quenching effect, such as to initially provide relatively high ablation, and later, as the arc 26 lengthens, to provide a relatively low ablation to limit a pressure increase in the opening 22 due to a build up of ablation vapors. For example, the first region 16 may comprise a material having a comparatively higher ablative vapor generation characteristic than the second region 18. Accordingly, upon initiation of an arc 26 within the opening 22, the arc 26 contacts the first region 16 and generates a relatively large volume of ablation vapors. The ablation vapors interact with the arc 26 and absorb the energy in the arc 26, resulting in a lower arc temperature and help to quench the arc 26. However, it has been observed by the inventors that a large ablation vapor volume generated within the opening 22 may adversely affect further arc quenching due to an ablation vapor-induced pressure build up within the opening 22, for example, due to a choked exhaust flow condition, for example, limiting exhaust of vapors from the arc confinement region 24 of the opening 22. When the opening 22 is configured to confine the arc 26 therein, such as by limiting a spacing 46, 48 of the surface portions 28, 30 of the opening 22 away from the contacts 12, 14, the inventors have experimentally determined that it is desired to keep the vapor pressure in the opening 22 under about 100 bars to achieve sufficient arc quenching. Accordingly, as the arc lengthens within the opening 22 and is exposed to the second region 18 having a comparatively lower ablative vapor generation characteristic, the arc 26 generates a reduced volume of ablation vapors compared to the volume produce when exposed to the first region 18. Consequently, pressure build up within the opening 22 is reduced compared to a case where the arc 26 is only exposed to the first region 16 having a comparatively higher ablative vapor generation characteristic as it lengthens, allowing arc quenching to proceed with less interference from an ablation vapor-induced pressure rise. In an aspect of the invention, the heights H1, H2 of the respective regions 16, 18 may be sized to achieve desired respective ablation and pressure reducing characteristics. For example, the first region 16 may be configured to have a height of between about 2 millimeters (mm) to about 5 mm for use with axial type contacts as shown in
For an ablative arc suppression device 10 accommodating axial type contacts as depicted in
A method for determining an effectiveness of an ablative for use in arc quenching may include first determining a heat of vaporization of a desired ablative material. Determining a heat of vaporization may include using a differential thermal analysis. An ablation rate may then be calculated using the determined heat of vaporization. Next, energy required for disassociation of molecules of the ablative and ionization of atoms and molecules of the ablative may be derived, for example, using a Specific Heat (Cp) versus temperature (T) curve, such as may be found in IEEE Transactions on Plasma Science, Vol. PS-12, No. 1, pp 38-42, March 1984, for the material in the temperature range of 5,000 to 24,000 Kelvin. A total dissipated energy for the ablative may be calculated as the product of the cumulative energies, for example, up to 24,000 Kelvin and an ablated mass. It has been determined by the inventors that ablation characteristics of an ablative material may be attributed to high energy absorption capabilities of the material that are primarily dictated by the material's hydrogen content. It has been further determined by the inventors that such ablative materials may be classified based on a product of enthalpy and ablative volume. The above method may be used, for example, in determining desired materials to be used in the above described arc suppression device 10.
Ablative materials such as polyoxymethylene, polymethylpentene, poly-methylacrylate, poly-amide, poly-butylene teraphthalate, polyester, and phenolic composite have been found to possess desired ablative characteristics for use in arc quenching. In particular, polymers such as DELRIN®, manufactured by E.I. du Pont de Nemours and Company, USA, and a phenolic composite known in the trade as HYLAM manufactured by Bakelite Hylam Limited, India, have been demonstrated to have desired ablation characteristics. For example, DELRIN® has a relatively higher energy absorption characteristic than HYLAM, thereby providing higher volume ablation suitable for arc quenching. Conversely, HYLAM has a relatively lower energy absorption characteristic than DELRIN®, thereby providing lower volume ablation than DELRIN® suitable for pressure reduction when used in associated with DELRIN®. For example, to achieve a desired level of arc cooling by the arc suppression device, the first region 16 may include a polymer material having a desired higher ablation characteristic, such as DELRIN® to achieve a desired high energy dissipation effect, and the second region 18 may include a phenolic composite having a desired lower ablation characteristic, such as HYLAM, to achieve a desired pressure controlling effect. Alternatively, the first region 16 may include a material having a relatively lower ablation characteristic, and the second region 18 may include may include a material having a relatively higher ablation characteristic.
In another example embodiment depicted in
The second region 18 and third region 20 may include an electrical arc ablation characteristic different than an electrical arc ablation characteristic of the first region 16. For example, the second region 18 and third region 20 may comprise comparatively lower ablative vapor generation characteristics than the first region 16. In such an embodiment, the arc suppression device 10 may include a HYLAM-DELRIN®-HYLAM sandwich. In another example embodiment, the second region 18 and third region 20 may comprise comparatively higher ablative vapor generation characteristics than the first region 16. In such an embodiment the arc suppression device 10 may include a DELRIN®-HYLAM-DELRIN® sandwich. In yet another embodiment, the second region 18 and third region 20 may comprise a thermo-set, composite, ceramic, or inorganic material. Such materials may be used to encapsulate the first region 16, except at the opening 22, as depicted in
In another example embodiment depicted in
While certain embodiments of the present invention have been shown and described herein, such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
