Patent Application
20130319024
The invention relates to switchgear circuit breakers and, more particularly, to a cooling apparatus for preventing temperature rise in a compartment in a switchgear.
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.
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.
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:
With reference to
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
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
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.
