Title of Invention	ASSEMBLY AND METHOD FOR FORCED CONVECTION COOLING OF ELECTRICAL CONTACTS
Abstract	An assembly and method for forced convection cooling of electrical contacts are disclosed. The assembly comprises a rotating liquid metal pocket 1 with an annular opening 2 through which the electrical contacts 8 and 9 can enter. A motor assembly 5 includes a rotating motor spindle 4 that is connected to the rotating liquid metal pocket 1, where the motor assembly 5 is mounted on a translating arm 6. A control box mechanism 7 is configured to spin the rotating liquid metal pocket 1 when the electrical contacts 8 and 9 touch the liquid metal 3 in the rotating pocket 1. The control box mechanism 7 enables turbulent fluid flows of the liquid metal 3 to generate higher convection coefficients, which achieves direct heat removal from the contact regions of the electrical contacts 8 and 9.

Title of Invention

ASSEMBLY AND METHOD FOR FORCED CONVECTION COOLING OF ELECTRICAL CONTACTS

Abstract

An assembly and method for forced convection cooling of electrical contacts are disclosed. The assembly comprises a rotating liquid metal pocket 1 with an annular opening 2 through which the electrical contacts 8 and 9 can enter. A motor assembly 5 includes a rotating motor spindle 4 that is connected to the rotating liquid metal pocket 1, where the motor assembly 5 is mounted on a translating arm 6. A control box mechanism 7 is configured to spin the rotating liquid metal pocket 1 when the electrical contacts 8 and 9 touch the liquid metal 3 in the rotating pocket 1. The control box mechanism 7 enables turbulent fluid flows of the liquid metal 3 to generate higher convection coefficients, which achieves direct heat removal from the contact regions of the electrical contacts 8 and 9.

Full Text	ASSEMBLY AND METHOD FOR FORCED CONVECTION COOLING OF ELECTRICAL CONTACTS FIELD OF THE INVENTION The present invention relates to the fields of electrical contacts in medium voltage (MV) technology. The present invention specifically relates to an assembly and method for forced convection cooling of electrical contacts. BACKGROUND OF THE INVENTION Different technologies are developed for fabricating and designing electrical contact switches in medium voltage (MV) technology for various switching applications. Such contact switches are used in typical electrical devices such as circuit breaker, switches, contactors, vacuum interrupters, etc. These technologies rely on solid, mechanical contacts that are alternatively actuated from one position to another to make and break electrical contact for switching. Such mechanical contacts are prone to wear and tear. Such wear and tear increases the contact resistance that the product performance in greatly imparted by the poor contacts. Also, such contacts result in arcing, which reduces the life of the product exponentially. In some cases, in order to minimize mechanical damage imparted to switch contacts, the switches are fabricated using liquid metals to wet the movable mechanical structures for preventing solid-to-solid contact. Generally, the MV technology can utilize spring-loaded contacts as the electrical contacts, where the contacts are enabled and/or disabled by activation and deactivation of a spring mechanism on the spring-loaded contacts. Even though such technology is robust in terms of its shorter time frames for making and breaking the contacts, the heat is developed at the contact region, which causes considerable temperature rise at the joints of the electrical contacts. In MV technology, the contact resistance of a product on an average is between 10 uQ and 30 uQ, such that at least 10 - 30°C temperature rise is formed at the contact points due to this resistance. In some cases, even temperature rise of 5°C is found to be highly critical when it is operating close to the temperature rise limits defined by standards. Such high temperature development at the contact region is due to the very small surface areas coming in contact, i.e. in the order of 10~6 mm2, in both 'point contact' and 'line contact' type electrical contacts. Additionally, the key factors, like surface roughness and surface irregularities of the contact surfaces, can also increase the amount of heat at the contact points. Further, the torque of the spring(s) can make the contacts to butt against each other. Since the torque of the spring is directly proportional to the contact pressure, the contact pressure builds at the contact surfaces, i.e. more the contact pressure less the heat generation. This temperature rise can cause damage to the electrical contacts, which leads to degradation in the life span of the electrical contacts. Furthermore, simulation studies on the MV products show the criticality of the contact temperature rise problem. This states that the temperature rise at the contact regions can impact the thermal design of the product adversely, especially when the design is already ciose to the temperature limits offered by the standards. For example, a sample simulation study resulting from a typical MV cubicle is examined to show the maximum temperatures attained by the product when the cabinet is provided with no vents. Assume that the contact resistance per contact is around 6 uQ and totally four contact locations in the vacuum interrupter and disconnector. This essentially states that the heat developed at the contacts alone is around 12 Watts. The convection coefficients measured at the contact region showed with natural convection in the air medium values can be as low as 5-10 W/m2K. All these factors cause the contact temperature to be as high as 113°C, where the maximum temperature limit for the product as per standards is only 105°C. Such higher temperatures in the MV electrical contacts can lead to the need of improved contact designs, which can withstand all thermal constraints posed by the standards. In general, such contact designs should maintain compactness of the product, i.e. it should not increase size, shape or weight of the contacts. The design should be more robust, cost effective and simpler in terms of operation. It should be maintenance-free application. US20060191778 describes a liquid metal micro-switch provided with a main channel that is partially filled with a single droplet of liquid metal. Such single droplet of liquid metal on the electrical contacts can slightly prevent temperature rise, but it does not provide permanent solution for the temperature rise. In some of the conventional micro-switch construction, the electrical contacts are arranged with a liquid metai solution provided within the micro-switch. During activation and/or deactivation of the switch, the contacts are inserted into and/or removed from the liquid metal solutions, respectively, which eliminates temperature rise in the contacts. However, in such arrangements, due to the low thermal and electrical conductivity of the liquid metal solutions and due to its more number of switching operations, the liquid metal solutions are heated up to a certain temperature, which causes decrease in life span of the switch. Therefore, it is desirable to provide an improved assembly and method for preventing temperature rise in the contacting points of the electrical contacts. OBJECT OF THE INVENTION An object of the present invention is to provide a rotating liquid metal pocket assembly for forced convection cooling of electrical contacts. Another object of the present invention is to provide a liquid metal pocket assembly with a spinning disk for forced convection cooling of electrical contacts. A further object of the present invention is to provide a method for forced convection cooling of electrical contacts. A further object of the present invention is to provide a liquid metal pocket assembly capable of reducing temperature rise in contacting points of the electrical contacts. SUMMARY OF THE INVENTION According to one aspect, the present invention, which achieves this objective, relates to a rotating liquid metal pocket assembly for forced convection cooling of electrical contacts comprising a rotating liquid metal pocket with annular openings through which the electrical contacts enters. A motor assembly includes a rotating motor spindle that is connected to the rotating liquid metal pocket, where the motor assembly is mounted on a translating arm. A control box mechanism is configured to spin the rotating liquid metal pocket when the electrical contacts touch the liquid metal in the rotating pocket. The control box mechanism enables turbulent fluid flows of the liquid metal to generate higher convection coefficients, which achieves direct heat removal from the contact regions of the electrical contacts. According to another aspect, the present invention, which achieves this objective, relates to a liquid metal pocket assembly for forced convection cooling of electrical contacts comprising a liquid metal pocket with a spinning disk that is connected to a motor spindle of a motor assembly. The spinning base and a wall of the metal pocket can arrest the liquid metal using non-contact or contact seals, where the electrical contacts can be submerged in the liquid metal through annular openings in the metal pocket. A control box mechanism is configured to spin the spinning disk when the electrical contacts touch the liquid metal in the pocket. The control box mechanism enables turbulent fluid flows of the liquid metal to generate higher convection coefficients. Such higher convection coefficients can reduce temperature rise in the contact regions of the electrical contacts. According to further aspect, the present invention, which achieves this objective, relates to a method for forced convection cooling of electrical contacts, involving: mounting a liquid metal pocket assembly that is filled with the liquid metal. The pocket assembly and the electrical contacts are connected such that the electrical contacts are in contact with the liquid metal. The liquid metal pocket or the spinning disk is rotated using the motor assembly actuated by the control box mechanism, causing high velocity rotational movement of the liquid metal to generate higher convection coefficients, which results in effective forced convection cooling of the electrical contacts. Moreover, during beginning of the operation, the spinning base liquid metal pocket assembly and the electrical contacts are separated from each other. After activation of the metal pocket assembly, the spinning mechanism enables high velocity rotational movement in the liquid metal to generate convection coefficients as high as 1000 - 20,000 W/m2K. In natural convection with air, the maximum possible convection coefficients are around 10 W/m2K only. This high convection coefficient is a function of spinning speed of the rotating liquid metal pocket or the spinning disk as well as thermal-fluid properties of the liquid metal. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be discussed in greater detail with reference to the accompanying Figures. FIG. 1 shows a cross-sectional view of a rotating liquid metal pocket assembly, in accordance with one embodiment of the present invention. FIG. 2 is a cross-sectional view of a liquid metal contact switch with the rotating liquid metal pocket assembly of FIG. 1, showing that the contact switch is in 'ON' state. FIG. 3 is a cross-sectional view of a liquid metal contact switch with the rotating liquid metal pocket assembly of FIG. 1, showing that the contact switch is in 'OFF' state. FIG. 4 shows a cross-sectional view of a liquid metal pocket assembly with a spinning disk, in accordance with another embodiment of the present invention. FIG. 5 is a cross-sectional view of a liquid metal contact switch with the liquid metal pocket assembly of FIG. 4, showing that the contact switch is in 'ON' state. FIG. 6 is a cross-sectional view of a liquid metal contact switch with the liquid metal pocket assembly of FIG. 4, showing that the contact switch is in 'OFF' state. FIG. 7 illustrates a flowchart of a method for forced convection cooling of electrical contacts, in accordance with an exemplary embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows a cross-sectional view of a rotating liquid metal pocket assembly in accordance with one embodiment of the present invention. The liquid metal pocket assembly comprises a rotating liquid metal pocket 1 filled with a liquid metal 3 that can be arrested within a wall 1a of the rotating liquid metal pocket 1. The liquid metal 3 can act as a contacting agent as well as cooling agent for switching applications. The liquid metal 3 can be selected from a group consisting of Gallium, Indium, Tin, Bismuth and other combinational alloys such as Gallium-lndium-Tin, Gallium-lndium-Zinc, etc. Such liquid metals 3 are good electrical conductors (approximately 14.oE-8 Ohms-m) and viscous in nature, and have very good thermal conductivity. Moreover, all these liquid metals 3 can melt in the range of 10 - 150°C, which increases thermal gain of the product by an appreciable margin especially at its critical working range. Some good examples of combinational alloys within the melting range of 10-150°C are 45%Bi 5%Cd 19%in 23%Pb 8%Sn = 47°C, 75%Ga 24.5%ln = 15.7°C, and 62.5%Ga 21.5%ln 16%Sn = 10.7°C. Additionally, Gallium alloys boiling (evaporation) point is in the range of 2204°C, which retires the risk that Gallium alloy may evaporate during the normal operation of the liquid metal switch. The liquid metal pocket 1 exhibits an annular opening 2 at the top through which electrical contacts 8 and 9, as shown in FIG. 2 and FIG. 3, can enter into it in order to make a contact with the liquid metal 3 in the pocket 1. The rotating liquid metal pocket 1 can be connected to a motor spindle 4 of a motor assembly 5 such that the liquid metal pocket 1 starts to spin as per the activation of the motor 5. A control box mechanism 7 spins the pocket 1 when the electrical contacts 8 and 9 touch the liquid metal 3. The control box mechanism 7 can be fitted with a translating arm 6, which provides physical support to the control box mechanism 7. Such control box mechanism 7 causes high velocity movement (turbulent fluid flows) in the liquid metal 3 to generate higher convection coefficients as high as 1000 - 20,000 W/m2K. The higher convection coefficients can achieve dramatically high heat removal rates in order to reduce temperature rise in contacting points of the electrical contacts 8 and 9 in MV technology. In natural convection with air, the maximum possible convection coefficients are around 10 W/m2K only. Referring to FIG. 2, a cross-sectional view of a liquid metal contact switch with the rotating liquid metal pocket assembly of FIG. 1 is illustrated, which shows that the contact switch is in 'ON' state. The metal contact switch comprises an input terminal 8 and an output terminal 9, which act as electrical contacts for switching applications. The input and output terminals 8 and 9 can be arranged to contact the liquid metal 3 provided in the rotating liquid metal pocket 1. Initially, the input and output terminals 8 and 9 are not in touch with the liquid metal 3 in the liquid metal pocket 1 during the beginning of the operation of the contact switch, i.e. the switch is in 'OFF' state, as shown in FIG. 3, which illustrates a cross-sectional view of the liquid metal contact switch in 'OFF' condition. When the contact switch is in 'ON' state, the spring loaded control box mechanism 7 connecting the rotating liquid metal packet assembly to the input and output terminals 8 and 9 in such a way that both the input and output terminals 8 and 9 can simultaneously touch the liquid metal 3 via the annular openings 2, as shown in FIG. 1. The motor 5 is mounted on the translating arm 6 that is connected to the control box mechanism 7. The control box mechanism 7 actuates the motor 5 to rotate and spin the rotating liquid metal pocket 1, after the terminals 8 and 9 contacts the liquid metal 3. Such rotational movement of the liquid metal pocket 1 causes a high velocity fluid rotation of the liquid metal 3, which exhibits the convection coefficients up to 1000 - 20,000 W/m2K. This high convection coefficient is a function of spinning speed of the rotating liquid pocket 1 and thermal-fluid properties of the liquid metal 3. Such very high convection coefficients can enable designing of high rating circuit breakers, which achieves direct forced convection cooling of the electrical contacts 8 and 9 in the MV technology. Similarly, FIG. 4 shows a cross-sectional view of a liquid metal pocket assembly with a spinning disk 12, in accordance with another embodiment of the present invention. The liquid metal pocket assembly comprises a liquid metal pocket 11 having a spinning base or disk 12 that is placed within the liquid metal pocket 11 in an inverted T shape. The spinning disk 12 and a wall 11a of the metal pocket 11 can arrest the liquid metal 14 using non-contact or contact seals 15. These non-contact or contact seals 15 can be designed to avoid spill out of the liquid metal 14 during operation. The liquid metal pocket 11 exhibits two annular openings 13 at the top through which electrical contacts 20 and 21, as shown in FIG. 5 and FIG. 6, can enter into it in order to make a contact with liquid metal 14 filled in the metal pocket 11. Furthermore, the spinning disk 12 can be connected to a motor spindle 16 of a motor 17 such that the spinning disk 12 starts to spin as per the activation of the motor 17. The liquid metal pocket assembly also includes a control box mechanism 19 that is fitted to a translating arm 18, where the translating arm 18 supports the control box mechanism 19 and the motor assembly 17. The control box mechanism 19 is configured to spin the spinning disk 12 when the electrical contacts 20 and 21 touch the liquid metal 14. Such spinning movement of the disk 12 causes high velocity movement (turbulent fluid flows) in the liquid metal 14 to generate higher convection coefficients as high as 1000 - 20,000 W/m2K. These higher convection coefficients can reduce temperature rise in contacting points of the electrical contacts 20 and 21 in MV technology. Referring to FIG. 5, a cross-sectional view of a liquid metal contact switch with the liquid metal pocket assembly of FIG. 4 is illustrated, which shows that the contact switch is in 'ON' state. The metal contact switch is provided with a liquid metal pocket assembly, an input terminal 20 and an output terminal 21. The input and output terminals 20 and 21 are arranged in such a way to contact the liquid meta! 14 in the liquid metal pocket assembly. When the contact switch is in 'ON' state, the spring loaded control box mechanism 19 connects the packet assembly to the input and output terminals 20 and 21 in such a way that both the input and output terminals 20 and 21 can simultaneously touch the liquid metal 14 via the annular openings 13, as shown in FIG. 4. The connection of the terminals 20 and 21 and the liquid metal 14 can be done either by moving the liquid metal pocket assembly upwards or else by moving the terminals 20 and 21 downwards. Thereafter, the control box mechanism 19 directs the motor 17 to rotate or spin the spinning disk 12 of the liquid metal pocket 11, after the terminals 20 and 21 touch the liquid metal 14. Such spinning movement of the spinning disk 12 causes a high velocity fluid rotation of the liquid metal 14 to achieve higher convection coefficients. This high convection coefficient is a function of spinning speed of the spinning disk 12 and thermal-fluid properties of the liquid metal 14. Such very high convection coefficients can achieves direct forced convection cooling of the electrical contacts 20 and 21. When the contact switch is in 'OFF' state, the liquid metal pocket assembly and the terminals 20 and 21 are moved apart from each other, which disconnects contacts between the terminals 20 and 21 and the liquid metal 14 in the liquid metal pocket 1, as shown in FIG. 6, which illustrates a cross-sectional view of the liquid metal contact switch in 'OFF' condition. By default, the motor assembly 7 stops its activation in order to stop the movement of the spinning disk 12 in the liquid metal pocket 11 while disconnecting the terminals 20 and 21 and the liquid metal 14 in the pocket 11. Similarly, the disconnection of the terminals 20 and 21 and the liquid metal 14 can be done either by moving the liquid metal pocket assembly downwards or else by moving the terminals 20 and 21 upwards. In MV applications, the MV cubicles are never tilted during operation, such that it is easy to mount the liquid metal pocket assembly to avoid spill out of the liquid metal 14. Since the liquid metal 14 exhibits a fluid of good viscosity, it flows into the surface irregularities on the contact surfaces of the input and output terminals 20 and 21, such that the contact resistance value of the input and output terminals 20 and 21 can be nullified. Thus, the contact temperatures in the input and output terminals 20 and 21 and the liquid metal 14 can be lowered to achieve longer life of the input and output terminals 20 and 21, i.e. less wear and tear of the terminals 20 and 21. Also, thermal safety of the contact switch is ensured at all mean and peak current ratings. FIG. 7 illustrates a flowchart of a method for forced convection cooling of electrical contacts, in accordance with an exemplary embodiment of the present invention. As depicted at step 710, the liquid metal pocket assembly filled with the liquid metal 3 or 14 is mounted. The pocket assembly and the electrical contacts 8 and 9 or 20 and 21 are connected such that the electrical contacts 8 and 9 or 20 and 21 are in contact with the liquid metal 3 or 14, as shown at step 720. As indicated at step 730, the liquid metal pocket 1 or the spinning disk 12 can be rotated using the motor 5 or 17 actuated by the control box mechanism 7 or 19, causing high velocity movement of the liquid metal 3 or 14 to generate higher convection coefficients in order to directly cool the contact regions of the electrical contacts 8 and 9 or 20 and 21. Finally, as illustrated at step 740, the rotation of the liquid metal pocket 1 or the spinning disk 12 is terminated before disconnecting the contact between the liquid metal 3 or 14 and the electrical contacts 8 and 9 or 20 and 21. WE CLAIM: 1. An assembly for forced convection cooling of electrical contacts, comprising: a rotating liquid metal pocket having one or more openings through which a plurality of electrical contacts enters; a motor assembly including a rotating motor spindle connected to said rotating liquid metal pocket, the motor assembly being mounted on a translating arm; and a control box mechanism configured to spin said rotating liquid metal pocket when said plurality of electrical contacts touches liquid metal in the said rotating pocket, wherein said control box mechanism enables turbulent fluid flows of the liquid metal to generate higher convection coefficients, thereby achieving direct heat removal from a plurality of contact regions of the said plurality of electrical contacts. 2. The assembly of claim 1, wherein said rotating liquid metal pocket starts to spin as per the activation of said motor assembly directed by the said control box mechanism. 3. The assembly of claim 1, wherein said assembly is used as a liquid metal contact switch for switching applications. 4. The assembly of claim 1, wherein the liquid metal is selected from a group consisting of Gallium, Indium, Tin, Bismuth and other combinational alloys such as Gallium-Indium-Tin and Gallium-Indium-Zinc. 5. The assembly of claim 1, wherein said translating arm is connected to the said control box mechanism. 6. An assembly for forced convection cooling of electrical contacts, comprising: a liquid metal pocket having a spinning disk and one or more openings through which a plurality of electrical contacts enters; one or more seals fitted between said spinning disk and a wall of the said liquid metal pocket; a motor assembly including a rotating motor spindle connected to said spinning disk of said liquid metal pocket, the motor assembly being mounted on a translating arm; and a control box mechanism configured to spin said spinning disk when said plurality of electrical contacts touches liquid metal in the said pocket, wherein said control box mechanism enables turbulent fluid flows of the liquid metal to generate higher convection coefficients, thereby achieving direct heat removal from a plurality of contact regions of the said plurality of electrical contacts. 7. The assembly of claim 6, wherein said spinning disk starts to spin as per the activation of said motor assembly directed by the said control box mechanism. 8. The assembly of claim 6, wherein said one or more seals prevent spilling out of the liquid metal during operation. 9. The assembly of claim 6, wherein the liquid metal is selected from a group consisting of Gallium, Indium, Tin, Bismuth and other combinational alloys such as Gallium-Indium-Tin and Gallium-Indium-Zinc. 10. The assembly of claim 6, wherein said translating arm is connected to the said control box mechanism. 11. A method for forced convection cooling of electrical contacts, comprising the steps of: mounting a liquid metal pocket assembly that is filled with liquid metal; connecting the pocket assembly and a plurality of electrical contacts such that said plurality of electrical contacts are in contact with the liquid metal; and rotating a liquid metal pocket or a spinning disk using a motor assembly actuated by a control box mechanism, causing high velocity movement of the liquid metal to generate higher convection coefficients in order to directly cool a plurality of contact regions of the said plurality of electrical contacts. 12. The method of claim 11, wherein the higher convection coefficients are a function of speed of said spinning disk and a thermal-fluid property of the liquid metal. 13. The method of claim 11, further comprising: terminating the rotation of said liquid metal pocket or said spinning disk and disconnecting the contact between the liquid metal and the said plurality of electrical contacts. 14. The method of claim 11, wherein said motor assembly terminates the movement of said spinning disk before disconnecting the contact between the liquid metal and the said plurality of electrical contacts. 15. The method of claim 11, wherein the liquid metal provides uniform contact between the said plurality of electrical contacts by flowing into the surface irregularities on the said plurality of electrical contacts. 16. The method of claim 11, wherein said liquid metal is selected from a group consisting of Gallium, Indium, Tin, Bismuth and other combinational alloys such as Gallium-Indium-Tin and Gallium-Indium-Zinc.

Full Text

ASSEMBLY AND METHOD FOR FORCED CONVECTION COOLING OF
ELECTRICAL CONTACTS

FIELD OF THE INVENTION

The present invention relates to the fields of electrical contacts in medium voltage (MV) technology. The present invention specifically relates to an assembly and method for forced convection cooling of electrical contacts.

BACKGROUND OF THE INVENTION

Different technologies are developed for fabricating and designing electrical contact switches in medium voltage (MV) technology for various switching applications. Such contact switches are used in typical electrical devices such as circuit breaker, switches, contactors, vacuum interrupters, etc. These technologies rely on solid, mechanical contacts that are alternatively actuated from one position to another to make and break electrical contact for switching. Such mechanical contacts are prone to wear and tear. Such wear and tear increases the contact resistance that the product performance in greatly imparted by the poor contacts. Also, such contacts result in arcing, which reduces the life of the product exponentially. In some cases, in order to minimize mechanical damage imparted to switch contacts, the switches are fabricated using liquid metals to wet the movable mechanical structures for preventing solid-to-solid contact.

Generally, the MV technology can utilize spring-loaded contacts as the electrical contacts, where the contacts are enabled and/or disabled by activation and deactivation of a spring mechanism on the spring-loaded contacts. Even though such technology is robust in terms of its shorter time frames for making and breaking the contacts, the heat is developed at the contact region, which causes considerable temperature rise at the joints of the electrical contacts. In MV technology, the contact resistance of a product on an average is between 10 uQ and 30 uQ, such that at least 10 - 30°C temperature rise is formed at the contact points due to this resistance. In some cases, even temperature rise of 5°C is found to be highly critical when it is operating close to the temperature rise limits defined by standards.

Such high temperature development at the contact region is due to the very small surface areas coming in contact, i.e. in the order of 10~6 mm2, in both 'point contact' and 'line contact' type electrical contacts. Additionally, the key factors, like surface roughness and surface irregularities of the contact surfaces, can also increase the amount of heat at the contact points. Further, the torque of the spring(s) can make the contacts to butt against each other. Since the torque of the spring is directly proportional to the contact pressure, the contact pressure builds at the contact surfaces, i.e. more the contact pressure less the heat generation. This temperature rise can cause damage to the electrical contacts, which leads to degradation in the life span of the electrical contacts.

Furthermore, simulation studies on the MV products show the criticality of the contact temperature rise problem. This states that the temperature rise at the contact regions can impact the thermal design of the product adversely, especially when the design is already ciose to the temperature limits offered by the standards. For example, a sample simulation study resulting from a typical MV cubicle is examined to show the maximum temperatures attained by the product when the cabinet is provided with no vents. Assume that the contact resistance per contact is around 6 uQ and totally four contact locations in the vacuum interrupter and disconnector. This essentially states that the heat developed at the contacts alone is around 12 Watts. The convection coefficients measured at the contact region showed with natural convection in the air medium values can be as low as 5-10 W/m2K. All these factors cause the contact temperature to be as high as 113°C, where the maximum temperature limit for the product as per standards is only 105°C.

Such higher temperatures in the MV electrical contacts can lead to the need of improved contact designs, which can withstand all thermal constraints posed by the standards. In general, such contact designs should maintain compactness of the product, i.e. it should not increase size, shape or weight of the contacts. The design should be more robust, cost effective and simpler in terms of operation. It should be maintenance-free application.

US20060191778 describes a liquid metal micro-switch provided with a main channel that is partially filled with a single droplet of liquid metal. Such single droplet of liquid metal on the electrical contacts can slightly prevent temperature rise, but it does not provide permanent solution for the temperature rise. In some of the conventional micro-switch construction, the electrical contacts are arranged with a liquid metai solution provided within the micro-switch. During activation and/or deactivation of the switch, the contacts are inserted into and/or removed from the liquid metal solutions, respectively, which eliminates temperature rise in the contacts. However, in such arrangements, due to the low thermal and electrical conductivity of the liquid metal solutions and due to its more number of switching operations, the liquid metal solutions are heated up to a certain temperature, which causes decrease in life span of the switch.

Therefore, it is desirable to provide an improved assembly and method for preventing
temperature rise in the contacting points of the electrical contacts.

OBJECT OF THE INVENTION

An object of the present invention is to provide a rotating liquid metal pocket assembly for forced convection cooling of electrical contacts.

Another object of the present invention is to provide a liquid metal pocket assembly with a spinning disk for forced convection cooling of electrical contacts.

A further object of the present invention is to provide a method for forced convection cooling of electrical contacts.

A further object of the present invention is to provide a liquid metal pocket assembly capable of reducing temperature rise in contacting points of the electrical contacts.

SUMMARY OF THE INVENTION

According to one aspect, the present invention, which achieves this objective, relates to a rotating liquid metal pocket assembly for forced convection cooling of electrical contacts comprising a rotating liquid metal pocket with annular openings through which the electrical contacts enters. A motor assembly includes a rotating motor spindle that is connected to the rotating liquid metal pocket, where the motor assembly is mounted on a translating arm. A control box mechanism is configured to spin the rotating liquid metal pocket when the electrical contacts touch the liquid metal in the rotating pocket. The control box mechanism enables turbulent fluid flows of the liquid metal to generate higher convection coefficients, which achieves direct heat removal from the contact regions of the electrical contacts.

According to another aspect, the present invention, which achieves this objective, relates to a liquid metal pocket assembly for forced convection cooling of electrical contacts comprising a liquid metal pocket with a spinning disk that is connected to a motor spindle of a motor assembly. The spinning base and a wall of the metal pocket can arrest the liquid metal using non-contact or contact seals, where the electrical contacts can be submerged in the liquid metal through annular openings in the metal pocket. A control box mechanism is configured to spin the spinning disk when the electrical contacts touch the liquid metal in the pocket. The control box mechanism enables turbulent fluid flows of the liquid metal to generate higher convection coefficients. Such higher convection coefficients can reduce temperature rise in the contact regions of the electrical contacts.

According to further aspect, the present invention, which achieves this objective, relates to a method for forced convection cooling of electrical contacts, involving: mounting a liquid metal pocket assembly that is filled with the liquid metal. The pocket assembly and the electrical contacts are connected such that the electrical contacts are in contact with the liquid metal. The liquid metal pocket or the spinning disk is rotated using the motor assembly actuated by the control box mechanism, causing high velocity rotational movement of the liquid metal to generate higher convection coefficients, which results in effective forced convection cooling of the electrical contacts.

Moreover, during beginning of the operation, the spinning base liquid metal pocket assembly and the electrical contacts are separated from each other. After activation of the metal pocket assembly, the spinning mechanism enables high velocity rotational movement in the liquid metal to generate convection coefficients as high as 1000 - 20,000 W/m2K. In natural convection with air, the maximum possible convection coefficients are around 10 W/m2K only. This high convection coefficient is a function of spinning speed of the rotating liquid metal pocket or the spinning disk as well as thermal-fluid properties of the liquid metal.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be discussed in greater detail with reference to the accompanying Figures.

FIG. 1 shows a cross-sectional view of a rotating liquid metal pocket assembly, in accordance with one embodiment of the present invention.

FIG. 2 is a cross-sectional view of a liquid metal contact switch with the rotating liquid metal pocket assembly of FIG. 1, showing that the contact switch is in 'ON' state.

FIG. 3 is a cross-sectional view of a liquid metal contact switch with the rotating liquid metal pocket assembly of FIG. 1, showing that the contact switch is in 'OFF' state.

FIG. 4 shows a cross-sectional view of a liquid metal pocket assembly with a spinning disk, in accordance with another embodiment of the present invention.

FIG. 5 is a cross-sectional view of a liquid metal contact switch with the liquid metal pocket assembly of FIG. 4, showing that the contact switch is in 'ON' state.

FIG. 6 is a cross-sectional view of a liquid metal contact switch with the liquid metal pocket assembly of FIG. 4, showing that the contact switch is in 'OFF' state.

FIG. 7 illustrates a flowchart of a method for forced convection cooling of electrical contacts, in accordance with an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a cross-sectional view of a rotating liquid metal pocket assembly in accordance with one embodiment of the present invention. The liquid metal pocket assembly comprises a rotating liquid metal pocket 1 filled with a liquid metal 3 that can be arrested within a wall 1a of the rotating liquid metal pocket 1. The liquid metal 3 can act as a contacting agent as well as cooling agent for switching applications. The liquid metal 3 can be selected from a group consisting of Gallium, Indium, Tin, Bismuth and other combinational alloys such as Gallium-lndium-Tin, Gallium-lndium-Zinc, etc. Such liquid metals 3 are good electrical conductors (approximately 14.oE-8 Ohms-m) and viscous in nature, and have very good thermal conductivity.

Moreover, all these liquid metals 3 can melt in the range of 10 - 150°C, which increases thermal gain of the product by an appreciable margin especially at its critical working range. Some good examples of combinational alloys within the melting range of 10-150°C are 45%Bi 5%Cd 19%in 23%Pb 8%Sn = 47°C, 75%Ga 24.5%ln = 15.7°C, and 62.5%Ga 21.5%ln 16%Sn = 10.7°C. Additionally, Gallium alloys boiling (evaporation) point is in the range of 2204°C, which retires the risk that Gallium alloy may evaporate during the normal operation of the liquid metal switch.

The liquid metal pocket 1 exhibits an annular opening 2 at the top through which electrical contacts 8 and 9, as shown in FIG. 2 and FIG. 3, can enter into it in order to make a contact with the liquid metal 3 in the pocket 1. The rotating liquid metal pocket 1 can be connected to a motor spindle 4 of a motor assembly 5 such that the liquid metal pocket 1 starts to spin as per the activation of the motor 5. A control box mechanism 7 spins the pocket 1 when the electrical contacts 8 and 9 touch the liquid metal 3. The control box mechanism 7 can be fitted with a translating arm 6, which provides physical support to the control box mechanism 7.

Such control box mechanism 7 causes high velocity movement (turbulent fluid flows) in the liquid metal 3 to generate higher convection coefficients as high as 1000 - 20,000 W/m2K. The higher convection coefficients can achieve dramatically high heat removal rates in order to reduce temperature rise in contacting points of the electrical contacts 8 and 9 in MV technology. In natural convection with air, the maximum possible convection coefficients are around 10 W/m2K only.

Referring to FIG. 2, a cross-sectional view of a liquid metal contact switch with the rotating liquid metal pocket assembly of FIG. 1 is illustrated, which shows that the contact switch is in 'ON' state. The metal contact switch comprises an input terminal 8 and an output terminal 9, which act as electrical contacts for switching applications. The input and output terminals 8 and 9 can be arranged to contact the liquid metal 3 provided in the rotating liquid metal pocket 1. Initially, the input and output terminals 8 and 9 are not in touch with the liquid metal 3 in the liquid metal pocket 1 during the beginning of the operation of the contact switch, i.e. the switch is in 'OFF' state, as shown in FIG. 3, which illustrates a cross-sectional view of the liquid metal contact switch in 'OFF' condition.

When the contact switch is in 'ON' state, the spring loaded control box mechanism 7 connecting the rotating liquid metal packet assembly to the input and output terminals 8 and 9 in such a way that both the input and output terminals 8 and 9 can simultaneously touch the liquid metal 3 via the annular openings 2, as shown in FIG. 1. The motor 5 is mounted on the translating arm 6 that is connected to the control box mechanism 7. The control box mechanism 7 actuates the motor 5 to rotate and spin the rotating liquid metal pocket 1, after the terminals 8 and 9 contacts the liquid metal 3.

Such rotational movement of the liquid metal pocket 1 causes a high velocity fluid rotation of the liquid metal 3, which exhibits the convection coefficients up to 1000 - 20,000 W/m2K. This high convection coefficient is a function of spinning speed of the rotating liquid pocket 1 and thermal-fluid properties of the liquid metal 3. Such very high convection coefficients can enable designing of high rating circuit breakers, which achieves direct forced convection cooling of the electrical contacts 8 and 9 in the MV technology.

Similarly, FIG. 4 shows a cross-sectional view of a liquid metal pocket assembly with a spinning disk 12, in accordance with another embodiment of the present invention. The liquid metal pocket assembly comprises a liquid metal pocket 11 having a spinning base or disk 12 that is placed within the liquid metal pocket 11 in an inverted T shape. The spinning disk 12 and a wall 11a of the metal pocket 11 can arrest the liquid metal 14 using non-contact or contact seals 15. These non-contact or contact seals 15 can be designed to avoid spill out of the liquid metal 14 during operation. The liquid metal pocket 11 exhibits two annular openings 13 at the top through which electrical contacts 20 and 21, as shown in FIG. 5 and FIG. 6, can enter into it in order to make a contact with liquid metal 14 filled in the metal pocket 11.

Furthermore, the spinning disk 12 can be connected to a motor spindle 16 of a motor 17 such that the spinning disk 12 starts to spin as per the activation of the motor 17. The liquid metal pocket assembly also includes a control box mechanism 19 that is fitted to a translating arm 18, where the translating arm 18 supports the control box mechanism 19 and the motor assembly 17. The control box mechanism 19 is configured to spin the spinning disk 12 when the electrical contacts 20 and 21 touch the liquid metal 14. Such spinning movement of the disk 12 causes high velocity movement (turbulent fluid flows) in the liquid metal 14 to generate higher convection coefficients as high as 1000 - 20,000 W/m2K. These higher convection coefficients can reduce temperature rise in contacting points of the electrical contacts 20 and 21 in MV technology.

Referring to FIG. 5, a cross-sectional view of a liquid metal contact switch with the liquid metal pocket assembly of FIG. 4 is illustrated, which shows that the contact switch is in 'ON' state. The metal contact switch is provided with a liquid metal pocket assembly, an input terminal 20 and an output terminal 21. The input and output terminals 20 and 21 are arranged in such a way to contact the liquid meta! 14 in the liquid metal pocket assembly. When the contact switch is in 'ON' state, the spring loaded control box mechanism 19 connects the packet assembly to the input and output terminals 20 and 21 in such a way that both the input and output terminals 20 and 21 can simultaneously touch the liquid metal 14 via the annular openings 13, as shown in FIG. 4. The connection of the terminals 20 and 21 and the liquid metal 14 can be done either by moving the liquid metal pocket assembly upwards or else by moving the terminals 20 and 21 downwards.

Thereafter, the control box mechanism 19 directs the motor 17 to rotate or spin the spinning disk 12 of the liquid metal pocket 11, after the terminals 20 and 21 touch the liquid metal 14. Such spinning movement of the spinning disk 12 causes a high velocity fluid rotation of the liquid metal 14 to achieve higher convection coefficients. This high convection coefficient is a function of spinning speed of the spinning disk 12 and thermal-fluid properties of the liquid metal 14. Such very high convection coefficients can achieves direct forced convection cooling of the electrical contacts 20 and 21.

When the contact switch is in 'OFF' state, the liquid metal pocket assembly and the terminals 20 and 21 are moved apart from each other, which disconnects contacts between the terminals 20 and 21 and the liquid metal 14 in the liquid metal pocket 1, as shown in FIG. 6, which illustrates a cross-sectional view of the liquid metal contact switch in 'OFF' condition. By default, the motor assembly 7 stops its activation in order to stop the movement of the spinning disk 12 in the liquid metal pocket 11 while disconnecting the terminals 20 and 21 and the liquid metal 14 in the pocket 11. Similarly, the disconnection of the terminals 20 and 21 and the liquid metal 14 can be done either by moving the liquid metal pocket assembly downwards or else by moving the terminals 20 and 21 upwards.

In MV applications, the MV cubicles are never tilted during operation, such that it is easy to mount the liquid metal pocket assembly to avoid spill out of the liquid metal 14. Since the liquid metal 14 exhibits a fluid of good viscosity, it flows into the surface irregularities on the contact surfaces of the input and output terminals 20 and 21, such that the contact resistance value of the input and output terminals 20 and 21 can be nullified. Thus, the contact temperatures in the input and output terminals 20 and 21 and the liquid metal 14 can be lowered to achieve longer life of the input and output terminals 20 and 21, i.e. less wear and tear of the terminals 20 and 21. Also, thermal safety of the contact switch is ensured at all mean and peak current ratings.

FIG. 7 illustrates a flowchart of a method for forced convection cooling of electrical contacts, in accordance with an exemplary embodiment of the present invention. As depicted at step 710, the liquid metal pocket assembly filled with the liquid metal 3 or 14 is mounted. The pocket assembly and the electrical contacts 8 and 9 or 20 and 21 are connected such that the electrical contacts 8 and 9 or 20 and 21 are in contact with the liquid metal 3 or 14, as shown at step 720. As indicated at step 730, the liquid metal pocket 1 or the spinning disk 12 can be rotated using the motor 5 or 17 actuated by the control box mechanism 7 or 19, causing high velocity movement of the liquid metal 3 or 14 to generate higher convection coefficients in order to directly cool the contact regions of the electrical contacts 8 and 9 or 20 and 21. Finally, as illustrated at step 740, the rotation of the liquid metal pocket 1 or the spinning disk 12 is terminated before disconnecting the contact between the liquid metal 3 or 14 and the electrical contacts 8 and 9 or 20 and 21.

WE CLAIM:

1. An assembly for forced convection cooling of electrical contacts, comprising:

a rotating liquid metal pocket having one or more openings through which a plurality of electrical contacts enters;

a motor assembly including a rotating motor spindle connected to said rotating liquid metal pocket, the motor assembly being mounted on a translating arm; and

a control box mechanism configured to spin said rotating liquid metal pocket when said plurality of electrical contacts touches liquid metal in the said rotating pocket, wherein said control box mechanism enables turbulent fluid flows of the liquid metal to generate higher convection coefficients, thereby achieving direct heat removal from a plurality of contact regions of the said plurality of electrical contacts.

2. The assembly of claim 1, wherein said rotating liquid metal pocket starts to spin as per the activation of said motor assembly directed by the said control box mechanism.

3. The assembly of claim 1, wherein said assembly is used as a liquid metal contact switch for switching applications.

4. The assembly of claim 1, wherein the liquid metal is selected from a group consisting of Gallium, Indium, Tin, Bismuth and other combinational alloys such as Gallium-Indium-Tin and Gallium-Indium-Zinc.

5. The assembly of claim 1, wherein said translating arm is connected to the said control box mechanism.

6. An assembly for forced convection cooling of electrical contacts, comprising:

a liquid metal pocket having a spinning disk and one or more openings through which a plurality of electrical contacts enters;

one or more seals fitted between said spinning disk and a wall of the said liquid metal pocket;

a motor assembly including a rotating motor spindle connected to said spinning disk of said liquid metal pocket, the motor assembly being mounted on a translating arm; and

a control box mechanism configured to spin said spinning disk when said plurality of electrical contacts touches liquid metal in the said pocket, wherein said control box mechanism enables turbulent fluid flows of the liquid metal to generate higher convection coefficients, thereby achieving direct heat removal from a plurality of contact regions of the said plurality of electrical contacts.

7. The assembly of claim 6, wherein said spinning disk starts to spin as per the activation of said motor assembly directed by the said control box mechanism.

8. The assembly of claim 6, wherein said one or more seals prevent spilling out of the liquid metal during operation.

9. The assembly of claim 6, wherein the liquid metal is selected from a group consisting of Gallium, Indium, Tin, Bismuth and other combinational alloys such as Gallium-Indium-Tin and Gallium-Indium-Zinc.

10. The assembly of claim 6, wherein said translating arm is connected to the said control box mechanism.

11. A method for forced convection cooling of electrical contacts, comprising the steps of:

mounting a liquid metal pocket assembly that is filled with liquid metal;

connecting the pocket assembly and a plurality of electrical contacts such that said plurality of electrical contacts are in contact with the liquid metal; and

rotating a liquid metal pocket or a spinning disk using a motor assembly actuated by a control box mechanism, causing high velocity movement of the liquid metal to generate higher convection coefficients in order to directly cool a plurality of contact regions of the said plurality of electrical contacts.

12. The method of claim 11, wherein the higher convection coefficients are a function of speed of said spinning disk and a thermal-fluid property of the liquid metal.

13. The method of claim 11, further comprising:

terminating the rotation of said liquid metal pocket or said spinning disk and disconnecting the contact between the liquid metal and the said plurality of electrical contacts.

14. The method of claim 11, wherein said motor assembly terminates the movement of said spinning disk before disconnecting the contact between the liquid metal and the said plurality of electrical contacts.

15. The method of claim 11, wherein the liquid metal provides uniform contact between the said plurality of electrical contacts by flowing into the surface irregularities on the said plurality of electrical contacts.

16. The method of claim 11, wherein said liquid metal is selected from a group consisting of Gallium, Indium, Tin, Bismuth and other combinational alloys such as Gallium-Indium-Tin and Gallium-Indium-Zinc.

Documents:

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Patent Number

271311

Indian Patent Application Number

752/CHE/2009

PG Journal Number

08/2016

Publication Date

19-Feb-2016

Grant Date

16-Feb-2016

Date of Filing

31-Mar-2009

Name of Patentee

SCHNEIDER ELECTRIC INDUSTRIES SAS

Applicant Address

89 BOULEVARD FRANKLIN ROOSEVELT, F-92500 RUEIL MALMAISON

Inventors:

#	Inventor's Name	Inventor's Address
1	ARUNVEL THANGAMANI	GLOBAL TECHNOLOGY CENTRE, #88(P), II FLOOR, "SAHASRA SHREE", EPIP INDUSTRIAL AREA, NEXT TO VYDEHI HOSPITAL, WHITEFIELD, BANGALORE-560066
2	OLIVIER DUJEU	GLOBAL TECHNOLOGY CENTRE, #88(P), II FLOOR, "SAHASRA SHREE", EPIP INDUSTRIAL AREA, NEXT TO VYDEHI HOSPITAL, WHITEFIELD, BANGALORE-560066

PCT International Classification Number

F24C

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA