Dual Port Heat Pipe Structure For Switchgear

Abstract

A cooling apparatus is provided for a switchgear. The switchgear has an enclosure having a plurality of compartments. The cooling apparatus includes at least one evaporator constructed and arranged to be mounted in one of the compartments. The evaporator includes an evaporator plate having surfaces defining passage structure therein, and a cover plate covering a portion of the evaporator plate to seal the passage structure. A condenser is located at a higher elevation than the evaporator. First and second conduits fluidly connect the evaporator plate with the condenser. A working fluid is in the passage structure so as to be heated to a vapor state at the evaporator, with the first fluid conduit transferring the vapor to the condenser and with the second fluid conduit passively returning condensed working fluid back to the passage structure of the evaporator.

Description

FIELD

The invention relates to switchgear circuit breakers and, more particularly, to a cooling apparatus for preventing temperature rise in a compartment in a switchgear.

BACKGROUND

Switchgear configurations have current limits based on the heat rise over ambient room temperature. It is generally desired to limit the maximum temperature of the hottest spot on the switchgear main bus to 105° C. (a rise of 65° C. over an assumed ambient temperature of 40° C.), as directed by the standard IEEE 37.20.2. Typical medium and high-voltage metal-clad switchgear arrangements have maximum continuous current ratings of about 3000A, due to heat generation. It is desirable to increase this current rating. Heat produced by the electrical current in the main bus and breaker components can be cooled by the use of forced air cooling with fans mounted in every third or fourth switchgear frame. However, this solution is not practical in many cases, including in the case of arc-resistant switchgear, since the byproducts of an arc fault must be contained within the switchgear.

Thus, there is a need to provide a more effective and low cost method of moving interior heat in a switchgear to the ambient room environment.

SUMMARY OF THE INVENTION

An object of the invention is to fulfill the need referred to above. In accordance with the principles of the present invention, this objective is achieved by providing a cooling apparatus for a switchgear. The switchgear has an enclosure having a plurality of compartments including a circuit breaker compartment containing at least one circuit breaker, a main bus compartment housing a main bus that is connected with the circuit breaker, and a cable compartment. The cooling apparatus includes at least one evaporator constructed and arranged to be mounted in one of the compartments. The evaporator includes an evaporator plate having surfaces defining passage structure therein, and a cover plate covering a portion of the evaporator plate to seal the passage structure. A condenser is located at a higher elevation than the evaporator. A first fluid conduit fluidly connects the evaporator plate with the condenser. A second fluid conduit, separate from the first fluid conduit, fluidly connects the evaporator plate with the condenser. A working fluid is in the passage structure so as to be heated to a vapor state at the evaporator, with the first fluid conduit being constructed and arranged to transfer the vapor to the condenser and with the second fluid conduit being constructed and arranged to passively return condensed working fluid back to the passage structure of the evaporator.

In accordance with another aspect of the invention, a method of cooling a switchgear is provided. The switchgear has an enclosure having a plurality of compartments including a circuit breaker compartment containing at least one circuit breaker, a main bus compartment housing a main bus that is connected with the circuit breaker, and a cable compartment. The method provides at least one evaporator including an evaporator plate having surfaces defining passage structure therein, and a cover plate covering a portion of the evaporator plate to seal the passage structure. The evaporator is mounted in one of the compartments. A condenser is provided at a higher elevation than the evaporator, with first and second fluid conduits fluidly connecting the evaporator with the condenser. A working fluid is in the evaporator. Heat is transferred from the evaporator to the working fluid to cause the working fluid to evaporate with the evaporated vapor being delivered to the condenser via the first fluid conduit. The working fluid that condenses in the condenser is returned passively to the evaporator via the second fluid conduit.

Other objects, features and characteristics of the present invention, as well as the methods of operation and the functions of the related elements of the structure, the combination of parts and economics of manufacture will become more apparent upon consideration of the following detailed description and appended claims with reference to the accompanying drawings, all of which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the following detailed description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings wherein like numbers indicate like parts, in which:

FIG. 1 is a view of a cooling apparatus in the form of a heat pipe structure in accordance with an embodiment, shown mounted in a switchgear.

FIG. 2 is an enlarged view of the evaporator and fluid conduits of the heat pipe structure of FIG. 1, with the evaporator shown with a transparent cover plate for clarity of illustrating the internal passage structure thereof.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

With reference to FIG. 1, a cooling apparatus in the form of a heat pipe structure is shown, generally indicated at 10, mounted in a switchgear 12, generally indicated at 12. In the embodiment, the switchgear 12 is preferably an indoor, medium or high voltage metal-clad switchgear having a maximum continuous current ratings of about 4000 Amp. As used herein, the terms “medium voltage switchgear” and “high voltage switchgear” are used interchangeably, and refer to switchgear rated for operation at or exceeding 1 kV. In general, switchgear 12 comprises an enclosure, such as metal-clad enclosure 14, for housing the switchgear components. Enclosure 14 may contain one or more separate compartments, such as circuit breaker compartment 16, containing one or more circuit breakers 18, a main bus compartment 20 housing a main bus 22, and cable compartment 24. In the embodiment shown, circuit breaker 18 is a three-pole drawout type circuit breaker. Circuit breaker 18 is connected to primary contacts 27 that are supported by primary bushing plates 26a, 26b and that are connected to current-carrying bus bars 28 of the main bus 22.

As noted above, the main bus 22 of the switchgear 12 has temperature rise restrictions that are measured relative to the ambient temperature. In accordance with the embodiment, the heat pipe structure 10 applies an evaporative recycling cooling arrangement with an evaporator 30 located at convenient and critical points associated with the main bus 22, bus bars 23, risers, cable connections, and/or primary contacts 27, preferably where the conventional copper space plate is currently employed.

The heat pipe structure 10 operates to cool a first location by transporting heat from the first location to a second location via the use of a working fluid. Referring to FIGS. 1 and 2, the heat pipe structure 10 includes a plurality of evaporators 30. Each evaporator 30 of the heat pipe structure 10 is placed in thermal contact with a first location to be cooled (e.g., near the heat generating components associated with the main bus 22 such as coupled with the bus bars 23 in the main bus compartment 20, or in the cable compartment 24). A first fluid conduit 32 connects each evaporator 30 to a condenser 34 (FIG. 1). Working fluid 36 resides in the evaporator 30 and settles near a bottom portion 38 thereof. Heat from the first location causes the liquid working fluid 36 to evaporate, primarily at evaporator 30. Thereafter, the working fluid 36 (in a gaseous or vapor state) travels upstream through the first fluid conduit 32 to the condenser 34, where the heat is released as a substantial portion of the evaporated working fluid condenses back to a liquid state (although some condensation and evaporation may also occur in the first fluid conduit 32). The condensed (e.g., liquid) working fluid 36 then travels downstream through a second fluid conduit 40, separate from the first fluid conduit 32, back to the evaporator 30 to complete a cooling cycle. The condenser 34 is preferably mounted to the enclosure 14 and can be located on the exterior, interior or partially on both the interior and exterior of the enclosure 14 so that the condenser 34 can exchange heat with abundant ambient airflow.

The heat pipe structure 10 is advantageously in the form of a thermosiphon—a term connoting that condensed working fluid is transported from the condenser 34 to each evaporator 30 primarily by operation of gravity. As such, in a thermosiphon generally, the condenser 34 is arranged at a higher elevation (in the gravitational field) than each evaporator 30, and a vertical drop should be present between the condenser 34 and the evaporator 30.

With reference to FIG. 2, in the embodiment, each evaporator 30 is approximately 4″×4″×0.75″ and comprises two copper plates. A first or evaporator plate 42 is generally rectangular and has sufficient thickness to allow for passage structure 44 in which the working fluid 36 will evaporate, and to allow connection of the first and second fluid conduits 32, 40, respectively. In the embodiment, the passage structure 44 is formed by surfaces 45 to define a continuous, generally serpentine passage extending from the bottom portion 46 to the top portion 48 of the evaporator plate 42 so that the working fluid 36 changes direction multiple times in the passage structure 44 prior to reaching the first conduit 32. Thus, the serpentine passage structure 44 increases the surface area in contact with the working fluid 36 to heat the working fluid to the vapor state. A second or cover plate 50 (shown transparent in FIG. 2 so that the passage structure 44 can be seen) covers a portion of the evaporator plate 42 to seal the passage structure 44 while providing addition heat transfer surface area. A gasket or seal (not shown can be provided about the periphery of the cover plate 50 and sandwiched between the cover plate 50 and the evaporator plate 42 when the cover plate 50 is coupled to the evaporator plate 42. Mounting holes 51 can be provided for receiving fasteners to secure the cover plate 50 to the evaporator plate 42. Alternatively, the periphery of the cover plate 50 can be welded or adhered to the evaporator plate 42, without a gasket.

The copper evaporator plate 42 and copper cover plate 50 can include additional gating to provide more effective heat transfer to the working fluid 36. An inlet 52 of the second fluid conduit 40 that returns the working fluid 36 to the evaporator 30 is preferably located at the bottom portion 46 of the evaporator plate 42. An outlet 54 of the first fluid conduit 32 that delivers vapor to the condenser 34 is preferably located at the top portion 48 of the evaporator plate 42. However, it can be appreciated that the connection of the first and second fluid conduits 32, 40 with the evaporator plate 42 can be located to optimize and control working fluid flow and levels within the evaporator 30. The use of separate fluid conduits 32 and 40 provides the needed fluid/vapor flow separation and prevents vapor locks and is also less costly than pipe-in-pipe arrangements.

If the heat pipe structure 10 cooling system is intended to form an electrical isolation gap, the working fluid 36 needs to be electrically insulating. Examples of suitable working fluids 36 are refrigerants such as hydrofluorocarbons (e.g. R134a, R245fa), fluorketones (e.g., NOVEC-649™, commercially available from 3M), and hydrofluoroethers (e.g., HFE-7100™, commercially available from 3M). In addition, portions of the fluid conduits 32, 34 can be made of electrically insulating materials.

The foregoing preferred embodiments have been shown and described for the purposes of illustrating the structural and functional principles of the present invention, as well as illustrating the methods of employing the preferred embodiments and are subject to change without departing from such principles. Therefore, this invention includes all modifications encompassed within the spirit of the following claims.

Claims

1. A cooling apparatus for a switchgear, the switchgear having an enclosure having a plurality of compartments including a circuit breaker compartment containing at least one circuit breaker, a main bus compartment housing a main bus that is connected with the circuit breaker, and a cable compartment, the cooling apparatus comprising:

at least one evaporator constructed and arranged to be mounted in one of the compartments, the at least one evaporator comprising: an evaporator plate having surfaces defining passage structure therein, and a cover plate covering a portion of the evaporator plate to seal the passage structure,

a condenser located at a higher elevation than the evaporator,

a first fluid conduit fluidly connecting the evaporator plate with the condenser,

a second fluid conduit, separate from the first fluid conduit, fluidly connecting the evaporator plate with the condenser, and

a working fluid in the passage structure so as to be heated to a vapor state at the evaporator, with the first fluid conduit being constructed and arranged to transfer the vapor to the condenser and with the second fluid conduit being constructed and arranged to passively return condensed working fluid back to the passage structure of the evaporator.

2. The cooling apparatus of claim 1, wherein the evaporator plate has a top portion and a bottom portion, the first fluid conduit being coupled to the top portion and the second fluid conduit being coupled to the bottom portion.

3. The cooling apparatus of claim 2, wherein the passage structure extends from the bottom portion to the top portion of the evaporator plate.

4. The cooling apparatus of claim 3, wherein the passage structure is defined by surfaces so as to form a continuous, serpentine passage between the bottom portion and the top portion of the evaporator plate so that the working fluid must change direction multiple times in the passage prior to reaching the first conduit.

5. The cooling apparatus of claim 1, wherein the evaporator plate and the cover plate are each composed of copper.

6. The cooling apparatus of claim 1, wherein the working fluid is selected from the group consisting of hydrofluorocarbon, fluoroketone, and hydrofluoroether refrigerants, and any mixtures thereof.

7. The cooling apparatus of claim 1, in combination with the switchgear, wherein the at least one evaporator is mounted in the main bus compartment.

8. The cooling apparatus of claim 7, where a plurality of evaporators are connected with the condenser, each evaporator being adjacent to an associated bus bar of the main bus.

9. The combination of claim 7, wherein the condenser is mounted to the enclosure.

10. The cooling apparatus of claim 1, wherein the condenser is constructed and arranged to exchange heat with ambient air to cause the vapor to condense to liquid working fluid.

11. A method of cooling a switchgear having an enclosure having a plurality of compartments including a circuit breaker compartment containing at least one circuit breaker, a main bus compartment housing a main bus that is connected with the circuit breaker, and a cable compartment, the method comprising the steps of:

providing at least one evaporator comprising an evaporator plate having surfaces defining passage structure therein, and a cover plate covering a portion of the evaporator plate to seal the passage structure,

mounting the evaporator in one of the compartments,

providing a condenser at a higher elevation than the evaporator, with a first and second fluid conduits fluidly connecting the evaporator with the condenser, and with a working fluid in the evaporator,

permitting heat transfer from the evaporator to the working fluid to cause the working fluid to convert form a liquid to a vapor state, with the vapor being delivered to the condenser via the first fluid conduit, and

passively returning the working fluid that condenses in the condenser to the evaporator via the second fluid conduit.

12. The method of claim 11, wherein the step of providing the evaporator includes providing the evaporator plate to have a top portion and a bottom portion, the first fluid conduit being coupled to the top portion and the second fluid conduit being coupled to the bottom portion.

13. The method of claim 12, wherein the passage structure extends from the bottom portion to the top portion of the evaporator plate.

14. The method of claim 13, wherein the passage structure is defined by surfaces so as to form a continuous, serpentine passage between the bottom portion and the top portion of the evaporator plate so that the working fluid must change direction multiple times in the passage prior to reaching the first conduit.

15. The method of claim 11, wherein the evaporator plate and the cover plate are provided from copper.

16. The method of claim 11, wherein the working fluid is selected from the group consisting of hydrofluorocarbon, fluoroketone, and hydrofluoroether refrigerants, and any mixtures thereof.

17. The method of claim 11, wherein the evaporator is mounted in the main bus compartment.

18. The method of claim 17, wherein a plurality of evaporators is provided and each evaporator is mounted adjacent to an associated bus bar of the main bus.

19. The method of claim 1, wherein the condenser is mounted on the enclosure.