POWER FEEDER

Abstract: A power feeder for supplying electric power to a load such as a motor for driving a submerged pump that pumps liquid from a tank in which is stored a low-temperature liquid such as LNG. The power feeder has the structure in which a ceramic sleeve is fastened to a flange, a conductor is inserted in the ceramic sleeve, the ceramic sleeve and the conductor being airtightly coupled together inside the flange (inside the tank), and the outside (open air side) is sealed with a bellows having the shape of a half-mountain in cross section. The bellows has resiliency and is mounted between the ceramic sleeve and the conductor under the condition where the ceramic sleeve and the conductor undergoes linear expansion at a maximum practical temperature or at a temperature slightly higher than this temperature and where the bellows itself is displaced to its maximum length. The bellows absorbs the reaction of the conductor when it undergoes linear expansion and exerts compression only on the ceramic sleeve side but does not exert tensile stress.

Description: The present invention relates to a power supply unit which is employable for supplying power to such loads as a motor and so forth, to drive a submerged pump to serve to scoop up low temperature liquid as liquefied natural gas (LNG) which is stored inside a tank. Because it is the general practice to locate such a submerged pump near an end of a casing and inside the casing which has been vertically fixed inside the tank, the power supply unit to the motor for driving the pump is fitted airtight to a bulkhead by making use of a flange in the area where the casing extends from the tank into the atmosphere. The aforesaid power supply unit is subject to the following effects: a) The power supply unit is subject to a temperature roughly corresponding to ambient air temperature when the pump is not in operation. b) When the power supply starts to operate the pump, a conductor of the power supply which passes through the casing heats up to around 80° to 90° Celsius at an initial stage and when the scooping of low temperature liquid starts, the said conductor is cooled down rapidly under the influence of the low temperature liquid or gas in the tank. Since the conductor of the power supply unit is especially subject to such cyclic thermal influences, the said conductor is subjected to repeated linear expansion and contraction under these circumstances, and thereby such effects may cause impairment of the airtightness of the interface on the conductor due to the repetition of stress. In a conventional design as illustrated by Figure 5 of the accompanying drawings, a ceramic sleeve 4 is passed through and fixed to the inside surface of a mounting aperture 2 of flange 1 fitted to bulkhead (d) of the casing. Through the ceramic sleeve a conductor 5 is passed, the ceramic sleeve 4 being coupled airtight to the conductor 5 by making use of silver solder 7. with a metallic plate 6 inside the flange 1 (that is inside the casing), and in order to avoid stress acting especially on the ceramic sleeve 4 and the silver solder 7 with small tensile strength by allowing the outside of flange 1 and the inside of ceramic sleeve 4 to be free, and by diverting the linear expansion and contraction of the conductor 5 to the outside of flange 1. However, when the ceramic sleeve 4 is fitted airtight to the conductor 5, with only one portion inside the flange 1 in this manner, the low temperature liquid or gas may instantly leak out of the casing, creating a hazard if the sealed area should be damaged and the airtightness impaired. The present invention is proposed for correcting the defects of aforementioned conventional art. The first of its objects is to provide full sealing between the ceramic sleeve and the conductor at two locations inside and outside the flange, to allow the outside seal to prevent any leakage even if the sealing effectiveness is lost inside the sealed portion. Furthermore, the second of its objects is to provide such a prevention against the tensile stress influence on the ceramic sleeve side which is weak especially in tensile strength. Shortly, provided that the ceramic sleeve is fitted airtight to the conductor at two locations inside and outside the flange as described above, there may exist a difference in the heat expansion/contraction between the ceramic sleeve side, with extremely little heat expansion/contraction, and the conductor side with a large one. The stress focuses on the joint and sealed portions of both components, thus metal fatigue increases in the relevant joint and sealed portions and the said sleeve undergoes tensile stress. Finally, the third object is to miniaturise the unit, and to prevent the loss of function from any icing by the effect produced through miniaturising. According to the invention there is provided a power supply unit for supplying power to a load inside a casing and comprising a flange fitted to a bulkhead of said casing, a ceramic sleeve passed through an aperture in the flange and mounted airtight on the flange whereby a first end of the sleeve is disposed outside the casing and a second end of the sleeve is disposed inside the casing, and a conductor of the power supply inserted into the ceramic sleeve wherein the ceramic sleeve and the conductor are connected airtight to each other within the said casing at the said second end of the sleeve, characterised in that an airtight connection is secured between the said first end of the sleeve and the conductor by a tubular bellows of elastic material which is mounted around the conductor and the said first end of the sleeve, and wherein the said bellows is capable of elongating and contracting due to inherent elasticity over a range capable of fully absorbing the difference in linear expansion between the ceramic sleeve and the conductor over the range of temperatures expected during use, and wherein in mounting the bellows the ceramic sleeve and the conductor are linearly expanded by being heated to the maximum temperature expected during use or a temperature slightly higher than the said maximum temperature and wherein the bellows is connected, in a state of maximum elongation or in a state close thereto with the ceramic sleeve and the conductor. Preferably the bellows is mounted around the conductor and the said first end of the sleeve by two metal end members fitted around the conductor and the first end of the sleeve respectively. Preferably a metal plate is fixed around the said second end of the sleeve and the said metal plate is brazed to the sleeve and the conductor with silver solder and the two said metal end members are brazed to the sleeve and the conductor respectively with silver solder. The power supply may be used, where one end of the conductor is connected to the power source with a cable and the other end is connected to such a load as a motor and so forth, to drive a submerged pump positioned near a bottom portion inside a casing. The mounting conditions (mounting method) of the said bellows are as follows. The bellows must be such as to ensure that the compression/elongation is tolerated by its own elasticity and the difference generated when the ceramic sleeve and the conductor linearly expand or contract within a range of practical temperature. In mounting the bellows between the ceramic sleeve and the conductor, the ceramic sleeve and the conductor should be heated up to a practical maximum temperature or to a slightly higher temperature to allow the sleeve and conductor to expand linearly, and the bellows should be fixed in place to allow for the maximum compression/expansion envisaged. That is, the range for the bellows to transform by itself within its elasticity shall be set to the same value as the volume for the conductor to expand linearly at the practical maximum temperature or to a slightly higher value. As a result, the bellows under atmospheric temperature is in a state of accumulated pressure by the contraction of the conductor. For this reason, when the conductor generates a heat to be linearly expanded up to the limit or practical maximum temperature at the inception of the power supply, the bellows also transforms (elongated) by its own elasticity as the said linear expansion proceeds, not only for shrinking the linear expansion reaction force of the conductor through this displacement and for eliminating the reaction force at the ceramic sleeve side but also for producing a compression reaction force acting on the ceramic sleeve by the elasticity inherent to the bellows which has accumulated in pressure during the linear expansion of the conductor. When the scooping of low temperature liquid is started and the conductor is cooled down to transfer to contraction, the bellows transforms in pursuit of this contraction. During this operation, as a matter of course, the force of compression acts on the ceramic sleeve through the bellows. Brief description of the accompanying drawings. Figure 1 is an explanatory view showing an LNG storage tank, a casing for scooping LNG out of the said tank, a submerged pump inserted into the bottom portion inside the said casing, and a power supply unit for the motor to drive the said submerged pump. Figure 2 is a perspective view, in which a power supply unit is partially cut away to demonstrate its internal construction, Figure 3 is an explanatory sectional view showing the interrelationship of a ceramic sleeve, a conductor passing through the sleeve and a bellows by cross-sectioning part of a flange and the ceramic sleeve and bellows portions in a power supply unit, Figure 4 is an explanatory sectional view showing the means for mounting the bellows between the ceramic sleeve and the conductor in a power supply unit. Figure 5 is a cross-sectional view of a conventional power supply unit as previously described. Figure 1 is an example where a power supply unit relating to the present invention is applied to a scooping unit of LNG storage tank. Reference letter (a) denotes a LNG storage tank, (b) denotes a LNG receiving tube, (c) denotes a LNG scooping tube, (d) denotes a submerged pump which is inserted into the bottom portion of casing (d′) that is inserted inside the LNG storage tank (a), (e) denotes a power supply cable to supply power to a motor for driving a submerged pump (d) and (f) denotes a power supply unit for supplying power to the motor for driving the submerged pump (d) fixed to upper portion bulkhead (d″) of casing (d′), said power supply unit (f) being illustrated by Figures 2 to 4. In Figures 2 to 4 reference numeral 1 denotes a flange, and a sleeve-inserting port 2 is provided in this flange 1 and a mounting portion 3 is formed on its outside circumference wherein the flange 1 is fitted to bulkhead (d″) of casing (d′) at this mounting portion 3. Reference numeral 4 denotes a ceramic sleeve, and this ceramic sleeve 4 has a plurality of metal plate rings 2′ fitted into its outside circumference. The sleeve 4 is inserted into the sleeve mounting port 2 through these metal plate rings 2′ and fixed airtight on both inside and outside faces of flange 1. Reference numeral 5 represents a conductor inserted into the ceramic sleeve 4, the conductor 5 being brazed airtight with silver solder to the ceramic sleeve 4 by use of a metal plate 6 below flange 1 (inside the casing (d′)) and is engaged airtight with use of bellows 8 of hemispherical cross-section which is fitted with both end metal fittings 6′ on both the ends above flange 1 (on the atmosphere side). Reference numeral 7 denotes silver solder which connects both end metal fittings 6′ with the ceramic sleeve 4 and the conductor 5. Likewise, the bellows 8 is joined by welding with both end metal fittings 6′. The mounting conditions of the bellows 8 are described as follows: The bellows 8 can adapt to a range of linear expansion and contraction in a practical temperature range. The temperature of conductor 5 rises from under -162° to 100° Celsius, in the case of the submerged pump (d) in the embodiment. Moreover, when fixing the bellows 8 around the ceramic sleeve 4 and the conductor 5 exploiting both end metal fittings 6′, at least the conductor 5 should be heated up to a temperature level of around 100° Celsius to allow some linear expansion and the bellows 8 should further be linearly expanded to allow for displacement to the longest or equivalent state due to its inherent elasticity to allow nearly maximum expansion. Figure 4 is a view showing an example of a method for fixing the said bellows 8 by use of silver solder 7, where the silver solder 7 should be deposited on the insides of metal plate 6 and both end metal fittings 6′, and with the bellows 8 expanded to near the maximum length due to its elasticity, this bellows 8 in expansion should be fixed with a jig 9. The bellows should be put into a furnace to heat around 800° Celsius. The ceramic sleeve 4 and the conductor 5 expand linearly due to this heating because of the larger linear expansion of the conductor 5 than that of the ceramic sleeve 4, the conductor 5 elongates, sliding inside both end metal fittings 6′. Silver solder 7 fuses at around 780° Celsius, this temperature should be maintained for about fifteen minutes before the temperature is lowered. The silver solder 7 solidifies in the falling phase of temperature, and the ceramic sleeve 4 adheres to the conductor 5, with the metal plate 6 below the flange 1 while both end metal fittings 6′ adhere respectively to the ceramic sleeve 4 and the conductor 5 above the flange 1. As a result, the bellows 8 is fitted to one end of the ceramic sleeve 4 and the conductor 5. The jig 9 should be removed from both end metal fittings 6′ at a temperature of 100° Celsius, a slightly higher temperature than the practical maximum, to allow the conductor 5 to shrink freely. Therefore, the conductor 5 is hindered from contracting between the metal plate 6 and the bellows 8 until the temperature inside the furnace falls to around 100° Celsius, staying elongated. After the jig 9 is removed, the conductor 5 keeps shrinking until its temperature level reaches the atmospheric temperature. However, the degree of deformation of the bellows 8 still stays within a tolerable range though it would follow the contraction of the said components. The jig 9 was removed at a temperature around 100° Celsius in the case of this embodiment, in which the value of 100° Celsius was selected to allow for a margin on designing safety against a temperature 80° to 90° Celsius of the conductor at the inception of power supply. Thus power supply unit (f) is fabricated at a factory and the unit is bolted, placing the upper side of bellows 8 upward (to the atmosphere), on the bulkhead (d′′) of casing (d′) of submerged pump (d) by making use of mounting portion 3 of flange 1, the power supplying cable (e) being connected to the conductor 5. When the submerged pump (d) starts to operate the LNG goes up inside the casing (d′) and discharges from scooping tube (c) because during the operation the LNG contacts the inside of the flange 1 during which it is subjected to quenching at a temperature of -162° Celsius, the ceramic sleeve 4 and the conductor 5 contract, and particularly the conductor 5 contracts with the practical maximum variation. In this case, because the conductor 5 is fixed on the inside of the flange 1 with the use of the metal plate 6, it contracts against the elasticity of the bellows 8 on the side of the outer bellows 8. The bellows 8 changes it shape following this contraction, but this change in shape stays within permitted displacement range of bellows 8. By this action, the shrinkage force of conductor 5 acts as a compression force onto the ceramic sleeve 4 through the bellows 8. Next, when the operation of the submerged pump (d) stops, the entire power supply unit (f) goes up in temperature to the ambient atmospheric temperature. As a result, the ceramic sleeve 4 and the conductor 5 linearly expand in gradually releasing the bellows 8 from compression (displacement), and the linear expansion comes to an end as soon as the ambient temperature is reached, but even then the displacement of the bellows 8 remains in a tolerable range and within the maximum displacement permitted. As a result, the elastically reactive force from the bellows 8 is transmitted to the ceramic sleeve 4 while the force dies down, and acts as a compression force on the ceramic sleeve 4. Industrial Application: The present invention has an industrial application as described below. 1) Because the ceramic sleeve 4 and the conductor 5 are doubly sealed both on the inside and outside of the flange 1, the outer sealing obviates any fear of the leakage of liquid or gas and the unit is safe even if the inner sealing should be damaged. 2) Not only the ceramic sleeve 4 and the conductor 5 are sealed by the bellows 8 on the outside of the flange 1 but the said bellows 8 is also fixed around the ceramic sleeve 4 and the conductor 5, capable of changing its shape within a displacement up to a maximum length due to its elasticity, at a location where the conductor 5 has expanded linearly at the practical maximum temperature or at a location where the temperature is slightly larger than the above mentioned. As a result, because, for example, in brazing the bellow in a heated furnace, the extent of displacement in the contraction portion from around 700° Celsius at which the solder solidifies down to, for instance, 100° Celsius which is the practical maximum temperature usable, taking into account safe operation; the bellows 8 can be miniaturised and moreover the power supply unit (f) can be a miniaturised unit at the said contraction portion. 3) The bellows 8 has elasticity and is fixed between fully elongated (displaced) state or the situation closer to the said state to an area round the ceramic sleeve 4 and the conductor 5. As a result, not simply when the conductor shrinks but also when it linearly expands, the bellows 8 offsets the linear expansion of the conductor, and furthermore the reaction force being generated from the elastic elongation acts, as compression, against the ceramic sleeve 4. Namely, because all the reaction forces act as compressions against the ceramic sleeve 4, in no case would the ceramic sleeve 4 be damaged. 4. Because the displacement limits of the bellows 8 becomes much less, the bellows 8 can be designed to a hemispherical form. Consequently, if the bellows 8 has a valley area, icing may appear on this valley portion to hinder its action, especially the contraction action, but no ice adheres to such a bellows having a hemispherical form, and moreover any ice formed can be removed without any difficulty, so there is no fear of the hindrance of the contraction action. The power supply unit (f) in accordance with this invention can be utilised in a wide range as another power supply unit for supplying power to other loads, through a bulkhead, in addition to a supply of power to a motor for driving a submerged pump (d).

Claims: A power supply unit for supplying power to a load (d) inside a casing (a,d′) and comprising a flange (1) fitted to a bulkhead (d″) of said casing (d′), a ceramic sleeve (4) passed through an aperture (2) in the flange (1) and mounted airtight on the flange (1) whereby a first end of the sleeve (4) is disposed outside the casing (d′) and a second end of the sleeve (4) is disposed inside the casing (d′), and a conductor (5) of the power supply inserted into the ceramic sleeve (4) wherein the ceramic sleeve (4) and the conductor (5) are connected airtight to each other within the said casing (d′) at the said second end of the sleeve (4), characterised in that an airtight connection is secured between the said first end of the sleeve (4) and the conductor (5) by a tubular bellows (8) of elastic material which is mounted around the conductor (5) and the said first end of the sleeve (4), and wherein the said bellows (8) is capable of elongating and contracting due to inherent elasticity over a range capable of fully absorbing the difference in linear expansion between the ceramic sleeve (4) and the conductor (5) over the range of temperatures expected during use, and wherein in mounting the bellows (8) the ceramic sleeve (4) and the conductor (5) are linearly expanded by being heated to the maximum temperature expected during use or a temperature slightly higher than the said maximum temperature and wherein the bellows (8) is connected, in a state of maximum elongation or in a state close thereto with the ceramic sleeve (4) and the conductor (5). A power supply unit according to Claim 1, wherein the bellows (8) is mounted around the conductor (5) and the said first end of the sleeve (4) by two metal end members (6′) fitted around the conductor (5) and the first end of the sleeve (4) respectively. A power supply unit according to Claim 2, wherein a metal plate (6) is fixed around the said second end of the sleeve (4) and the said metal plate (6) is brazed to the sleeve (4) and the conductor (5) with silver solder (7) and the two said metal end members (6′) are brazed to the sleeve (4) and the conductor (5) respectively with silver solder (7).

Inventors: AIZAWA IKUO, AOKI NOBUO, NEGISHI H F ELEC CO LTD, YOKOI KEISUKE, AIZAWA, IKUO, AOKI, NOBUO, NEGISHI, H F. ELEC. CO., LTD., YOKOI, KEISUKE
Applicants: FURUKAWA ELECTRIC CO LTD, TOKYO GAS CO LTD, FURUKAWA ELECTRIC CO., LTD.
Application year: 1990
Main classification: H02G3
IPC codes: H02G3, H01B17