A conservator device for use with an offshore electrical induction device

Abstract

A conservator device (1) for use with an electric induction device (2), said electric induction device comprising a liquid-filled volume. The conservator device (1) comprises: a tank (3), one or more wall members (4) provided within an inner volume of the tank (3), said one or more wall members (4) being adapted to horizontally divide the inner volume of the tank (3) into a plurality of compartments (C). One or more of said compartments (C) is provided with a respective barrier (6) being flexible and attached to the tank (3) such that the barrier (6) fluidly separates a dry portion of the inner volume of the tank (3) from a remaining portion of the inner volume of the tank (3), wherein each dry portion of the inner0 volume of the tank (3) is fluidly connected to ambient air by a first port (8) of the tank (3). The tank (3) comprising a second port (7) adapted to enable a liquid connection between said remaining portion of the inner volume of the tank (3) and a liquid-filled volume of the electric induction device (2). Further, the one or more wall members (4) are liquid-permeable.

Description

[0001] A CONSERVATOR DEVICE FOR USE WITH AN OFFSHORE ELECTRICALINDUCTION DEVICETechnical fieldThe present invention relates to a conservator device for use with an electricalinduction device in offshore conditions. The electrical induction device may be atransformer or a shunt reactor and the electrical device comprises a chamberbeing at least partly filled with a liquid, such as oil. Temperature changes makethe liquid expand and contract and the conservator device is provided to receiveand hold a portion of the liquid in response to increased temperature forcing liquidout of the chamber.BackgroundOffshore substations are for example used to transfer power to shore fromoffshore wind farms. The offshore substations comprise liquid-immersed inductiondevices such as power transformers and shunt reactors. The induction devicesare immersed in an insulation liquid that changes volume depending on itstemperature. Each induction device is therefore fitted with a conservator device tocontain the additional volume of liquid as it expands.The induction device comprises cellulose insulation with material properties thatdegrade in the presence of oxy-gen. To prevent influx of oxygen from theatmosphere into the insulation liquid, the conservator device may be fitted with abarrier separating the insulation liquid from air. The barrier can be a flexiblebladder or diaphragm, where the space inside the bladder or above thediaphragm is in communication with the atmosphere. Alternatively, theconservator device can be sealed from the atmosphere and filled with nitrogen, inwhich case no flexible bladder or diaphragm is needed.The offshore substation may be assembled far from the final installation site andtransported to the final offshore installation site by sea. In deep water, the offshoresubstation may be placed on a floating platform. The conservator device may beexposed to sea wave motion creating a sloshing movement of the liquid inside theexpansion tank. The sloshing movement involves large forces that may damagethe bladder or diaphragm. Further, oil sloshing inside the conservator maydamage the barrier or other components, such as an oil level indicator. Further,sloshing may cause false alarm in a Buchholz relay. Accordingly, sloshing of theinsulation liquid should be avoided in order to mitigate failure of the electricinduction device.An object of the present invention is thus to provide an improved conservatordevice suitable for offshore use.SummaryAccording to a first aspect of the invention, this and other objects are achieved bya conservator device according to claim 1 with alternative embodiments defined inthe dependent claims. The conservator device comprises: a tank, and one ormore wall members provided within an inner volume of the tank. The one or morewall members are adapted to horizontally divide the inner volume of the tank intoa plurality of compartments. One or more of said compartments are provided witha respective barrier. Each respective barrier is flexible and attached to the tanksuch that the barrier fluidly separates a dry portion of the inner volume of the tankfrom a remaining portion of the inner volume of the tank. Further, each dry portionof the inner volume of the tank is fluidly connected to ambient air by a first port ofthe tank. Accordingly, the remaining portion of the inner volume of the tank istypically all of the inner volume of the tank except for the volume occupied by thebarrier(s) and air. The tank further comprises a second port adapted to enable aliquid connection between said remaining portion of the inner volume of the tankand a liquid-filled volume of the electric induction device. The one or more wallmembers are liquid-permeable.The conservator device is used to act as a conservator device for liquid of theelectric induction device. Upon expansion of liquid in the electric induction devicecaused by heating of the liquid, liquid flows into the inner volume of the tank of theconservator device, forcing the flexible barrier to deform, thus forcing air out of thetank and vice versa. The liquid is typically an insulation liquid, such as a suitableoil.The barrier prevents air from mixing with liquid inside the tank. By horizontallydividing the inner volume into compartments using the wall members, movementof liquid within the tank is mitigated by the wall members, thus reducing sloshingmotions of liquid inside the tank.The liquid-permeability of the wall members enable a restricted flow of liquidthrough the whole wall member, thus mitigating any need of leaving a gapbetween the tank and the respective wall member for liquid to flow through andfurther enables improved damping of local pressure build-up by the wall membersupon acceleration of the tank.The provision of multiple compartments reduces the size of each barrier neededand thus reduces its tendency to move upon sloshing, thus mitigating fatigue ofthe barrier. Reduced fatigue of the barrier mitigates rupture of the barrier. Ruptureof the barrier would cause severe failure due to contamination with oxygen.Presence of oxygen in insulation oil will accelerate degradation and mightirreversibly damage the insulation system and increase risk of fire hazard. Toreplace a barrier and decontaminate liquid / oil would be very costly in off-shoreinstallations and cause severe consequences due to interruption in operation ofthe electrical induction device. Furthermore, mitigating sloshing of liquid in thetank reduces stress on the conservator and the electrical induction device causedby sloshing forces. Thus, a reduction of sloshing will increase system stability.Further, the sloshing movement is severe at resonance frequency. The liquid hasan effective mass (convective mass + impulsive mass). Impulsive mass is relatedto rigid-motion and convective mass is associated with flexible-mass. Theconvective mass is the mass that is moving and creating the sloshing. Dividingthe conservator into several compartments will reduce the convective mass andthereby reduce the sloshing. Hence, a suitable horizontal division of the innervolume of the tank into compartments will mitigate resonance frequency effectson sloshing.The wall member(s) are made of porous material providing said liquid-permeability.The porous material enables an even flow of liquid over the whole surface of eachwall member.The one or more wall members may be plates.The plates are easy to produce and provide a planar support for the barrier, thusreducing wear and risk of failure of the barrier. Plate-formed wall members alsoprovide improved stiffness.The at least one wall member may extend from an upper portion of the tanktowards a lower portion of the tank.The at least one wall member may extend substantially vertically.The vertical direction refers to the direction after installation of the conservatordevice, i.e. in use (in still weather conditions).Each wall member may cover a respective whole cross-section of the tank.By covering a whole cross-section of the tank, the wall member providesimproved rigidity to the tank.The barrier may comprise a bladder.As an alternative, or compliment to a bladder, the barrier may comprise adiaphragm being attached to the tank around a circumferential portion of therespective diaphragm, said attachment being formed by a direct attachmentbetween the tank and at least a portion of the respective diaphragm and / or by anattachment between the one or more wall members and least a portion of therespective diaphragm.The walls of the bladder or the diaphragm provide said fluid separation, whilstenabling a variable volume on each side of the bladder or diaphragm to accountfor varying amounts of liquid and air in the tank.A second aspect of the invention relates to a system comprising an electricinduction device and the conservator device described above.The electric induction device may be a transformer or a shunt reactor.Brief description of drawingsFigs. 1-5 are schematic illustrations not drawn to scale.Fig. 1 shows a cross-sectional side view of a system comprising an electricinduction device and a conservator device according to an embodiment in whichthe barrier comprises a bladder.Fig. 2 shows a top view of the system device also shown in fig. 1.Fig. 3 show an embodiment of a wall member comprising an array of throughopenings.Fig. 4 shows an alternative embodiment of the system also shown in fig. 1. In fig.4, the conservator device of the system comprises a higher number ofcompartments.Fig. 5 shows a top view of the system also shown in fig. 4.Fig. 6 shows a cross-sectional side view of a system comprising an electricinduction device and a conservator device according to an embodiment in whichthe barrier comprises a diaphragm.Fig. 7 shows a top view of the system device also shown in fig. 6.Detailed descriptionEmbodiments of the present invention will hereinafter be described with referenceto the appended drawings.As shown in fig. 1, a conservator device 1 is suitable for use with an electricinduction device 2, such as a transformer or a shunt reactor. The electric inductiondevice 2 comprises a liquid-filled volume. Temperature variations of the liquid inthe liquid-filled volume causes the liquid to expand and contract and theconservator device 1 forms an expansion chamber for liquid of the liquid-filledvolume of the electric induction device 2.It is an object of the invention to improve longevity of the conservator device 1when used at sea, i.e. in conditions at which the conservator device 1 is exposedto accelerations.The conservator device 1 comprises a tank 3, and one or more wall wall members4 provided within an inner volume V of the tank 3. The one or more wall members4 are adapted to horizontally divide the inner volume V of the tank 3 into aplurality of compartments C.Accordingly, a plurality of compartments distributed in a horizontal plane areformed, thereby reducing the maximum horizontal distance between wallstructures of the conservator device 1.One or more of said compartments C are provided with a respective barrier 6comprising a bladder.The bladder 6 may be formed as a bag or other structure with flexible wallsenabling a volume of the bladder 6 to adapt in response to liquid being forced intoor out of the tank 3.Each respective bladder 6 is attached to the tank 3 such that an inner volume ofthe bladder 6 is fluidly separated from a remaining portion of the inner volume Vof the tank 3, and each bladder 6 is fluidly connected to ambient air by a first port8 of the tank 3.For example, the bladder 6 may comprise an opening or port provided with asuitable fitting which seals to the tank 3 or to a conduit leading out of the tank 3.The bladder 6 may be attached to the tank 3 by any suitable means, such as bysaid fitting or conduit. The conduit may comprise a header fluidly connectingmultiple bladders 6 to the first port 8 of the tank 3. By fluidly connecting eachbladder 6 to an outside of the tank 3 such that each bladder 6 is exposed toatmospheric pressure, the volume of each bladder 6 adapts to changes of liquidvolume in the tank 3. The use of a header inside the tank 3 enables use of onlyone port 8 of the tank 3 for all bladders 6, thus simplifying production andassembly of the conservator device 1.The tank 3 further comprises a second port 7 adapted to enable a liquidconnection between the remaining portion of the inner volume of the tank 3 and aliquid-filled volume of the electric induction device 2.Here, the remaining portion refers to the portion of the inner volume of the tank 3fluidly separated from the inner volume of the bladders 6.The tank 3 may be formed in any suitable way, such as by welding togetherstructural members of a suitable metal or plastic material, or using fiber-reinforcedplastics. The tank 3 may be formed from two or more parts joined together usingflanges and mechanical fasteners. The tank 3 may be an elongated body adaptedto be installed with a longitudinal axis of the tank 3 oriented substantiallyhorizontally. The elongated body may be cylindrical. The tank 3 is typicallyinstalled on top of the electrical induction device 2 such that gravity is able toforce liquid from the tank 3 into the electrical induction device 2. It should beunderstood that the orientation of the tank 3 may vary slightly without departingfrom the scope of the invention. Generally, the tank should exhibit a certainminimum volume by design, and by orienting the tank 3 horizontally, the totalheight of the installation is reduced.In the embodiment of figs. 12, 6 and 7, the wall member(s) is / are made of porousmaterial providing said liquid-permeability. In other embodiments the wallmembers 4 could have any other suitable configuration. For example, the wallmembers 4 could comprise an array of through openings 5 providing said liquid-permeability, as shown in fig. 3.In this embodiment, the wall members 4 are plates but in other embodiments anyother suitable form of the wall members may be used instead, such as a suitablesheet material.In this embodiment, the at least one wall member 4 extends from an upper portionof the tank 3 towards a lower portion of the tank 3.In this embodiment, the at least one wall member 4 extends substantiallyvertically but may in other embodiments extend obliquely between an upperportion of the tank 3 and a lower portion of the tank 3.The vertical extent is the extent when the conservator device is oriented in itsintended orientation in use, which is typically evident by studying the position ofthe port for liquid (downwards) and the port for air to the bladder(s) 6 (upwards).In this embodiment, each wall member 4 covers a respective whole cross-sectionof the tank 3 but may in other embodiments cover only a portion of the cross-section of the tank 3. For example, for a cylindrical tank 3, each wall member maybe substantially circular and thus cover the entire cross-section of the tank 3.The wall members are 4 attached to the tank 3 by welding but may in otherembodiments be attached in any other suitable way, such as by adhesive or byusing mechanical fasteners.The embodiment shown in figs. 6 and 7 corresponds to the one of figs. 1 and 2,except for the barrier 6 comprising a diaphragm instead of a bladder. In thisembodiment, only one diaphragm is shown but in other embodiments two or morediaphragms may be provided instead.The diaphragm is attached to the tank 3 around a circumferential portion of thediaphragm. The attachment is formed by a direct attachment between the tank 3and the respective diaphragm. Portions of two or more diaphragms may beinterconnected or formed in one piece to provide a liquid seal between thediaphragms.The present invention also relates to a system S comprising an electric inductiondevice 2 and the conservator device 1 described above. The electric inductiondevice 2 may be a transformer or a shunt reactor.

[0002] 1 conservator device2 electric induction device3 tank4 wall members5 array of through openings6 barrier7 second port of tank (for liquid)8 first port of tank (for air)V inner volume of tankC compartmentsTable of reference numerals

Claims

Claims1. A conservator device (1) for use with an electric induction device (2), said electricinduction device comprising a liquid-filled volume, andsaid conservator device (1) comprising:a tank (3),one or more liquid-permeable wall members (4) provided within an inner volumeof the tank (3), said one or more wall members (4) being adapted to horizontallydivide the inner volume of the tank (3) into a plurality of compartments (C),wherein the wall member(s) is / are made of porous material providing said liquid-permeability, said one or more of said compartments (C) being provided with a respectivebarrier (6) being flexible and attached to the tank (3) such that the barrier (6)fluidly separates a dry portion of the inner volume of the tank (3) from a remainingportion of the inner volume of the tank (3), wherein each dry portion of the innervolume of the tank (3) is fluidly connected to ambient air by a first port (8) of thetank (3),said tank (3) comprising a second port (7) adapted to enable a liquid connectionbetween said remaining portion of the inner volume of the tank (3) and a liquid-filled volume of the electric induction device (2),2. The conservator device according to any one of claims 1, wherein the one ormore wall members are plates.

3. The conservator device according to claim any one of claims 1-2, wherein the atleast one wall member extends from an upper portion of the tank towards a lowerportion of the tank.

4. The conservator device according to any one of claims 1-3, wherein the at leastone wall member extends substantially vertically.

5. The conservator device according to any one of claims 1-4, wherein each wallmember covers a respective whole cross-section of the tank.

6. The conservator device (1) according to any one of claims 1-5, wherein thebarrier (6) comprises a bladder.

7. A system comprising an electric induction device and the conservator deviceaccording to any one of the preceding claims.

8. The system according to claim 7, wherein the electric induction device is atransformer or a shunt reactor.

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