SE1400342A1

SE1400342A1 - Arrangement for cooling electrial components of a subsea electric system

Info

Publication number: SE1400342A1
Application number: SE1400342A
Authority: SE
Inventors: Adrian Zuckerberger; Fabio Bolgiani; Raphael Cagienard; Thomas Gradinger; Thomas Wagner
Original assignee: Abb Technology Ltd
Priority date: 2014-07-04
Filing date: 2014-07-04
Publication date: 2014-07-08

Description

15 20 25 30 Because of the high reliability requested for the subsea converters, it may be advantageous to have a passive cooling system for the subsea converter, i.e., a cooling system without the need for a pump. The oil in the tank and in any oil-to-sea-water heat exchanger can be moved by natural convection. Also the sea water cooling the oil-to-sea-water heat exchanger may be moved by natural convection. Ideally it may thus be desirable to move the oil by natural convection only, to eliminate the pump as a component that has a ﬁnite lifetime and that may fail. One issue with oil-natural-convection cooling is, however, the limited efñciency.

Generally, dielectric ﬂuids such as mineral oil have high viscosity and low thermal conductivity. Furthermore, the natural convection ﬂow rate of a typical dielectric ﬂuid in a heat exchanger is generally in the laminar regime.

Typical cooling systems for subsea power-electronic equipment are thus limited by the high thermal resistance between the cooling ﬂuid and the wall necessitating a large heat-transfer surface.

US 20130056181 discloses a deionized-water cooling system for electrical equipment, connected electrically to a primary power supply. The system includes a main circuit to channel and cool the deionized water intended to circulate within the electrical equipment; a main pumping system; a main power source; a deionization circuit connected at two points to the main circuit and including a deionizer; a secondary pumping system to circulate the deionized water in the deionizer, and a secondary power source, which secondary power source has less power than the main power source.

US 20120189472 discloses a hydraulic power unit for subsea use. The power unit includes a tank containing a ﬂuid, an electric motor mounted in the tank, a distribution pump, a heat exchange unit provided externally to the tank and at least one distribution conduit in ﬂuid communication with the heat exchange unit and the tank While such systems may be thermally efﬁcient, they require oil channels to be built around the components to cool, or the heat sinks to which they are 10 15 20 25 30 attached. The oil in the channels is under overpressure with respect to the oil around the channels. So, the channel walls need to be strong and tight enough to sustain this overpressure. In addition, the channel walls must be thermally insulating to limit the heat transfer from high-loss components that may get hotter, to low-loss components that are more temperature sensitive. This signiﬁcantly adds to the mechanical complexity of the system.

Consequently, the cooling efﬁciency is limited, and the design of an economical cooling system may thus be challenging. Hence there is a need for efﬁcient subsea cooling of electric components in subsea applications.

SUMMARY An object of embodiments herein is to provide efficient mechanisms for subsea cooling of electric components in subsea applications.

Particularly, according to a ﬁrst aspect there is presented an arrangement for cooling electrical components of a subsea electric system. The arrangement comprises a tank filled with a dielectric ﬂuid. The arrangement comprises at least one electric component located in the tank. The arrangement comprises a thermal conductor located inside the tank and in thermal contact with the tank and at least one of the at least one electric components. The arrangement comprises an extension wall placed outside the tank and arranged parallel to an adjacent wall of the tank, wherein said extension wall and the adjacent wall deﬁne side walls of a channel for, in use, receiving seawater. The arrangement comprises ﬂow generating means for generating a ﬂow of the seawater inside the channel, thereby causing the seawater to ﬂow through the channel and cool the at least one electric component.

Advantageously, such an arrangement enables efficient subsea cooling of electric components in subsea applications. Advantageously, such an arrangement enables reduced ageing of temperature sensitive electric components.

According to a second aspect there is presented a subsea power-electronic converter unit comprising an arrangement according to the ﬁrst aspect. 10 15 20 25 Advantageously, the subsea power-electronic converter unit can have a high power rating.

It is to be noted that any feature of the ñrst or second aspects may be applied to any other aspect, wherever appropriate. Likewise, any advantage of the ﬁrst aspect may equally apply to the second aspect, and vice versa. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical ﬁeld, unless explicitly deﬁned otherwise herein. All references to "a/ an/ the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is now described, by way of example, with reference to the accompanying drawings, in which: Figures 1 and 2 schematically illustrate arrangements for cooling electrical components of a subsea electric system according to embodiments.

DETAILED DESCRIPTION The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout the description. 10 15 20 25 30 Cooling systems for electric equipment, and speciﬁcally for subsea electric system, are used to cool down electric components, such as power electronic building blocks (PEBBs), semiconductor modules, connectors and capacitor units. Such electric components generate heat that needs to be dissipated by the cooling system. The cooling systems of subsea power-electronic converter units are usually designed in a simple manner avoiding any unnecessary parts and mechanisms. Generally it is desirable to have passive cooling systems, thus cooling systems without any driven or powered parts, such as for example without pumps, to cool down the electric equipment. In some cases natural convection is used but it has a low efficiency. Cooling by natural convection uses the heat transfer from the cooling liquid to the surrounding sea water to generate circulation within the cooling system and thus within the electric installation and the subsea power-electronic converter unit.

Reference is now made to Figures 1 and 2. F igures 1 and 2 are cross-sectional side views illustrating arrangements 1a, 1b for cooling electrical components of a subsea electric system.

In general terms, there is provided an arrangement 1a, 1b for cooling electrical components of a subsea electric system. The arrangement 1a, 1b comprises a tank 2. The tank 2 is ﬁlled with a dielectric ﬂuid 3. The dielectric ﬂuid can contain oil, mineral oil, an oil containing silicon or silicone, and/ anv other suitable dielectric ﬂuid such as. for example, liquid esters. The arrangement 1a, 1b further comprises at least one electric component 4, 5, 6.

The at least one electric component 4, 5, 6 is located in the tank 2. The arrangement 1a, 1b further comprises a thermal conductor 7. The thermal conductor 7 is located inside the tank 2. The thermal conductor 7 is in thermal contact with the tank 2 and at least one of the at least one electric components 4, 5, 6. The arrangement 1a, 1b further comprises an extension wall. The extension wall 17 is placed outside the tank 2 and arranged parallel to an adjacent wall 18 of the tank 2. The extension wall 17 and the adjacent wall 18 deﬁne side walls of a channel 9. The channel 9 is provided-før, in use, to receive seawater 14. The arrangement 1a, 1b further comprises ﬂow generating means 13. The ﬂow generating means 13 is provided for 10 15 20 25 30 generating a ﬂow 10 of the seawater 14 inside the channel 9, thereby causing the seawater 14 to ﬂow through the channel 9 and cool the at least one electric component 4, 5, 6.

Thermal losses 8 are thereby evacuated from the tank 2 by the seawater 14 through the thermal conductor 7. The seawater in the channel 9 is “replaced” by fresh seawater by the ﬂow 10 forced by the ﬂow generating means 13. By using forced cooling, the seawater ﬂow will pass from bei_ng1aminar to turbulent. This will increase the efficiency of the cooling. Thus, the target of the the ﬂow generating means 13 is to increase the speed of the water ﬂow 10 until it becomes turbulent.

Particular details of arrangements 1a, 1b for cooling components of a subsea electric system will now be disclosed.

In use, components such as electric components 4, 5, 6 generate heat. In general terms, for some electric components 4, 5, 6 increased temperature is a common stress factor. In subsea environments, such as in subsea power- electronic converter units, which require high reliability, the thermal stress should thus be limited to a minimum. In the at least one electric component 4, 5, 6 energy is dissipated during operation. This energy is conducted to the outer walls of the at least one electric component 4, 5, 6, where it is transported to the surroundings, such as to a dielectric ﬂuid 3, such as oil, surrounding the at least one electric component 4, 5, 6. From the dielectric ﬂuid 3 heat is transferred to the surrounding seawater 14 through the walls of the tank 2. Flow of the dielectric ﬂuid 3 inside the tank 4 may thus be by natural convection.

However, such cooling may not be enough to cool the at least one electric component 4, 5, 6. The arrangement 1a, 1b therefore comprises at least one thermal conductor 7 for leading heat from the at least one electric component 4, 5, 6 to a particular wall of the tank 2, namely the so-called “adjacent wall” 18. This adjacent wall 18 deﬁnes one sidewall of the channel 9 through which seawater 14 ﬂows with the aid of the ﬂow generating means 13. This enables 10 15 20 25 efﬁcient cooling of the at least one electric component 4, 5, 6. Efﬁcient cooling of the at least one electric component 4, 5, 6 enables the at least one electric component 4, 5, 6 hotspot temperature to be limited.

Embodiments relating to further details of the arrangements 1a and 1b for cooling components of a subsea electric system will now be disclosed.

The thermal conductor 7 may be attached to the extension wall 18. This may minimize any thermal losses between the thermal conductor 7 and the extension wall 18.

The arrangement 1a, 1b may, in use, be arranged such that the extension wall 18 is vertically arranged. The extension wall 18 may thus be a sidewall of the tank 2. Alternatively, the arrangement 1a, 1b may, in use, be arranged such that the extension wall 18 is horizontally arranged (not shown in the ﬁgures).

The extension wall 18 may thus be a top-wall of the tank 2.

There are different types of ﬂow generating means 13 for causing the ﬂow 10 inside the channel 9. For example, the ﬂow generating means 13 may be provided as at least one pump. In the embodiments of Figures 1 and 2 there are three such pumps. For generating a turbulent ﬂow 10 with a water speed in the range of about 5o-2oomm/ s pumps with a nominal power of in the range of about 1-2 kW may be needed.

There are different possible locations for where the ﬂow generating means 13 may be placed. In general terms, the ﬂow generating means 13 may be placed outside and adjacent the channel 9. For example, the ﬂow generating means 13 may be located adjacent the outlet 15 of the channel 9 (as in the embodiment of Figure 1). For example, the ﬂow generating means 13 may be located adjacent the inlet 16 of the channel 9 (as in the embodiment of Figure 2).

The arrangement 1a, 1b may further comprise guiding means 12. The guiding means 12 may be provided as ﬁns. The guiding means 12 may be arranged for guiding seawater 14 out of the channel 9 (as in the embodiment of Figure 1). 10 15 20 25 Additionally or alternatively the guiding means 12 may be arranged for guiding seawater 14 in to the channel 9 (as in the embodiment of Figure 2).

The extension wall 17 and the adjacent wall 18 may be joined by an inlet 16 of the channel 9 and an outlet 15 of the channel. The inlet 16 and/ or outlet 15 may comprise means for hindering foreign objects tofrom entering enterthe channel 9. This means may be provided as a netone or more of a vane, a net. a ﬁlter, or a membrane. The mmm, ﬁlter, or membrane thus allows seawater 14 to enter and exit the channel 9 but may hinder other objects, such as small rocks, animals, etc. from entering, and possibly clogging, the channel 9.

There may be different types of electric components 4, 5, 6. For example, the at least one electric component 4, 5, 6 may be an electrical module comprising a capacitor 4, a semiconductor element 5, such as being part of an insulated gate bipolar transistor (IGBT), and a connector 6.

The arrangement 1a, 1b may comprise a plurality of vertically stacked such electrical modules. In the embodiments of Figures 1 and 2 three such electrical modules are shown. Each electrical module may be in thermal contact with its own thermal conductor 7. Further, each electrical module may have its own bus bar 19. Hence, the electric components 4, 5, 6 of each electrical module may be electrically connected to the bus bar 19 of that electrical module.

The tank 2 further may comprises a pressure compensator 11. The pressure compensator 11 may be arranged for pressure compensating the tank 2. This may make the tank 2 suitable for subsea applications.

There may be different types of thermal conductors 7. For example, the thermal conductor 7 may be an electrically insulator with a good thermal conductivity. For example, the thermal conductor 7 may be made from Aluminium nitride (AlN) or Silicon carbide (SiC).

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as deﬁned by the appended patent claims.

For example, although oil has been used as an example of the dielectric ﬂuid 3, it is understood that any suitable dielectric ﬂuid 3 could be used.

Claims

10 15 20 25 10 CLAIMS

1. An arrangement (1a, 1b) for cooling electrical components of a subsea electric system, comprising: a tank (2) ﬁlled with a dielectric ﬂuid (3); at least one electric component (4, 5, 6) located in the tank; a thermal conductor (7) located inside the tank and in thermal contact with the tank and at least one of the at least one electric components; an extension wall (17) placed outside the tank and arranged parallel to an adjacent wall (18) of the tank, wherein said extension wall and the adjacent wall define side walls of a channel (9) for, in use, receiving seawater (14); and ﬂow generating means (13) for generating a ﬂow (10) of the seawater inside the channel, thereby causing the seawater to ﬂow through the channel and cool the at least one electric component.

2. The arrangement according to claim 1, wherein the thermal conductor is attached to the extension wall.

3. The arrangement according to any one of the preceding claims, wherein the arrangement, in use, is arranged such that the extension wall is vertically arranged.

4. The arrangement according to any one of the preceding claims, wherein the ﬂow generating means (13) is at least one pump.

5. The arrangement according to any one of the preceding claims, wherein the extension wall and the adjacent wall are joined by an inlet (16) of the channel and an outlet (15) of the channel, and wherein the inlet comprises a net, a ﬁlter, or a membrane for hindering foreign objects to enter the channel.

6. The arrangement according to claim 5, wherein the outlet comprises a vane, net, a ﬁlter, or a membrane for hindering foreign objects to enter the channel. 10 15 20 11

7. The arrangement according to any one of the preceding claims, wherein the ﬂow generating means (13) is located adjacent an outlet (15) of the channel.

8. The arrangement according to any one of the preceding claims, further comprising guiding means (12) for guiding seawater out of the channel.

9. The arrangement according to any one of claims 1 to 6, wherein the ﬂow generating means (13) is located adjacent an inlet (16) of the channel.

10. The arrangement according to claim 9, further comprising guiding means (12) for guiding seawater in to the channel.

11. The arrangement according to any one of the preceding claims, wherein the at least one electric component is an electrical module comprising a capacitor (4), a semiconductor element (5), such as being part of an insulated gate bipolar transistor, IGBT, and a connector (6).

12. The arrangement according to claim 11, wherein the arrangement comprises a plurality of vertically stacked electrical modules, each electrical module being in thermal contact with its own thermal conductor.

13. The arrangement according to claim 11 or 12, wherein each electrical module has its own bus bar (19).

14. The arrangement according to any one of the preceding claims, wherein ﬂow of the dielectric ﬂuid inside the tank is by natural convection.

15. The arrangement according to any one of the preceding claims, wherein the tank further comprises a pressure compensator (11) for pressure compensating the tank.