Abstract:
Apparatus for cooling a conventional oil filled electrical transformer by using a conventional refrigeration unit. The transformer liquid coolant may be either circulated through a remotely located heat exchanger cooled by an electrical refrigeration unit, or the heat exchanger may be directly located within the transformer&#39;s housing and within its liquid coolant.

Description:
BACKGROUND OF THE INVENTION.  
         [0001]    1. Field of the Invention  
           [0002]    The invention pertains to cooling systems for liquid cooled electrical transformers.  
           [0003]    2. Description of the Related Art  
           [0004]    Large electrical transformers commonly use a liquid coolant, usually oil, to dissipate the heat generated during the operation of the transformer. The cooling oil may substantially fill the transformer housing and, in most cases, convection circulation of the oil produces the cooling action. The transformer housing may include a sinuous configuration to define the surface area to increase heat dissipation to the atmosphere, and in some transformer designs, conduits vertically extending along the transformer exterior communicating with the transformer housing upper and lower regions permits the coolant to be effectively dissipated to the atmosphere. However, in some applications, particularly when electrical circuits are operating at maximum potential, the coolant may reach a temperature higher than that desired lowering the efficiency of the transformer and threatening the transformer&#39;s operation. The need for cooling systems for electrical apparatus has been known for some time, and various solutions have been proposed as shown in U.S. Patent Nos. 3,371,298; 3,524,327; 4,394,635; 4,467,305 and 4,485,367. However, a practical and cost effective system for cooling electrical transformers, particularly under extreme conditions, has not previously been available.  
         OBJECTS OF THE INVENTION  
         [0005]    It is an object of the invention to provide a cooling system for electrical transformers utilizing a liquid coolant wherein a standard refrigeration unit may be used to lower the temperature of the liquid coolant.  
           [0006]    Another object of the invention is to provide a cooling system for liquid cooled electrical transformers wherein substantially conventional components may be utilized and relatively minor modifications to the transformer housing are required.  
           [0007]    An additional object of the invention is to provide a cooling system for liquid cooled electrical transformers which may be rapidly transported to the location needed and refrigeration units may be quickly connected to the transformers.  
         SUMMARY OF THE INVENTION  
         [0008]    The concepts of the invention may be practiced with a wide variety of liquid cooled transformers wherein a liquid coolant, such as oil, is in contact with the transformer coils wherein heat generated by the transformer operation is transferred to the oil for dissipation. Liquid cooled transformers come in a variety of configurations and coolant path systems whereby the heated coolant circulates within the transformer housing due to convection transferring heat to the housing permitting such heat to be dissipated to the atmosphere. The transformer housing may be sinuously configured to increase the surface area, and rate of heat dissipation, and/or vertically extending conduits may be exteriorly located of the housing communicating with the upper and lower housing regions through which coolant will flow under convection aiding heat transfer to the atmosphere. Also, it is known to utilize small pumps to augment the coolant movement.  
           [0009]    In the practice of the invention, the transformer liquid coolant is exposed to the heat removing abilities of a heat exchanger receiving a refrigerant from an electrically operated refrigeration unit of conventional construction. Such a refrigeration unit would include a refrigerant compressor, a condenser dissipating the heat of the refrigerant, and an expansion coil absorbing heat. The expansion coil is located within a heat exchanger through which the transformer liquid coolant is circulated wherein the refrigerant will absorb the heat of the transformer and provide a more effective and efficient cooling of the transformer liquid coolant than is provided by coolant convection circulation and exposure to ambient temperatures. For instance, high electrical loads are experienced during hot days due to heavy air conditioner usage, and such high ambient temperatures reduce the efficiency of heat transfer between a transformer&#39;s liquid coolants and the atmosphere. The practice of the invention permits transformer liquid coolants to be effectively cooled even under high ambient atmosphere temperatures.  
           [0010]    The heat exchanger may either be located adjacent the refrigeration unit and the transformer liquid coolant pumped from the transformer housing through the heat exchanger, or the heat exchanger may be located within the transformer housing in contact with the liquid coolant. Both systems have advantages and disadvantages. For instance, when the heat exchanger is located exteriorly of the transformer, no significant modifications to the transformer are required. When the heat exchanger is located within the transformer housing, the transformer housing design must accommodate this added component.  
           [0011]    As the need for the high transformer cooling capacity of the invention may only be occasional, it is contemplated that the refrigeration units may be mounted upon trucks or trailers to be quickly located at electrical substations having the greatest need for transformer cooling. By the use of quick connect couplings attached to conduits communicating with the transformer liquid coolant, it is possible to quickly connect the portable heat exchanger to the transformers by means of flexible hose, and a single refrigeration unit may be used to cool several transformers.  
           [0012]    As the heat exchangers and refrigeration units are of conventional construction, little specialized engineering is required to use the concepts of the invention with conventional liquid cooled transformers, which may be readily retrofitted to accommodate the invention. With systems utilizing heat exchangers internally housed within transformer housings, a specially designed transformer must be employed, but the design of such transformers is readily within the scope of a transformer designer skilled in the art.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The aforementioned objects and advantages of the invention will be appreciated from the following description and accompanying drawings wherein:  
         [0014]    [0014]FIG. 1 is a side elevational view of a trailer mounted refrigeration and heat exchanger unit connected to a conventional liquid cooled transformer,  
         [0015]    [0015]FIG. 2 is a schematic view of the embodiment of the invention wherein the heat exchanger is located exteriorly of the transformer,  
         [0016]    [0016]FIG. 3 is a schematic view of an embodiment of the invention wherein the heat exchanger is mounted within the electrical transformer, and  
         [0017]    [0017]FIG. 4 is a schematic illustration wherein two refrigeration units are used to cool four transformers. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    A typical system utilizing concepts of the invention is shown in FIG. 1 wherein a large oil cooled transformer housing is shown at  10  having electrical insulators  12  extending from the upper side thereof for handling the high voltage electrical wires, not shown, connected to the transformer  10 .  
         [0019]    A wheeled trailer  14  is located adjacent the transformer  10  having been towed to this location by a conventional truck. The trailer  14  supports a refrigeration unit  16  of conventional construction including a refrigerant compressor and condenser. The refrigeration unit  16  is normally powered by an electric motor, but an internal combustion engine may be used.  
         [0020]    A heat exchanger  18  is also mounted upon the trailer  14  and is connected by conduits  20  to the refrigeration unit  16 . The heat exchanger  18  may be of a conventional design utilizing an evaporation chamber wherein evaporation of the refrigerant occurs, and the evaporation chamber, which may constitute a finned radiator of conventional construction, is located within the housing for the heat exchanger through which the transformer cooling oil will be circulated.  
         [0021]    The heat exchanger  18  includes an outlet port  22  and an inlet port  24  for the transformer cooling oil. The transformer housing  10  includes an outlet port  26  and an inlet port  28  communicating with the transformer coolant oil. Flexible hose  30  connects outlet  22  to inlet  28 , and flexible hose  32  interconnects inlet  24  with outlet  26 .  
         [0022]    The hoses  30  and  32  are connected to their respective inlets and outlets by easily operable couplings, which may be of the quick-connect type wherein the hoses may be quickly affixed to the respective inlet or outlet fitting. The heat exchanger  18  will include a coolant oil pump having an inlet in communication with the heat exchanger inlet and an outlet communicating with outlet fitting  22 . Accordingly, upon operation of the refrigeration unit  16 , the evaporator coil within the heat exchanger  18  will cool the transformer coolant within the heat exchanger and the cooled coolant is pumped through hose  30  into the lower regions of the transformer  10 . The coolant oil located within the transformer  10  will rise due to convection as it absorbs heat and be removed from the transformer  10  through hose  32  into the heat exchanger  18  wherein the heat of the coolant oil removed from the transformer is absorbed by the refrigeration unit evaporator located within the heat exchanger. A coolant pump, not shown, is located either in the heat exchanger  18  or transformer  10 . In this manner, effective cooling of the transformer  10  is achieved by using conventional refrigeration equipment having readily available components, and transformers cooled in accord with the inventive concepts may be operated on very hot days without a loss of efficiency and the danger of transformer malfunction or explosions is significantly reduced.  
         [0023]    [0023]FIG. 2 is a schematic diagram of a system similar to that previously described wherein the refrigeration unit is illustrated at  34  and is communicating with the heat exchanger  36 . The transformer  38  is connected by a conduit system  40  with the heat exchanger  36 , and the conduit system includes a pump  42  and a valve  44  as well as quick-connect coupling  46 . The conduit  48  constitutes the coolant return system and includes quick-connect coupling  50 . If desired, quick-connect couplings may also be included in the conduit systems adjacent the inlet and outlet ports of the heat exchanger. The direction of coolant movement is indicated by the arrows.  
         [0024]    The pump  42  and valve  44  may be incorporated into the heat exchanger, as may be the case with the embodiment shown in FIG. 1, and it will be appreciated that the operation of the system of FIG. 2 is identical to the operation of the apparatus shown in FIG. 1.  
         [0025]    Another embodiment of the invention is shown schematically in FIG. 3 wherein a conventional refrigeration unit is shown at  52  and the transformer and its housing is represented at  54 . A heat exchanger  56  is located within the transformer housing  54  in direct contact with the cooling oil within the transformer. Conduit system  58  connects the refrigerant outlet of the refrigeration unit  52  to heat exchanger  56  and includes a valve  60  and a quick-connect coupling  62 . The refrigerant return from the heat exchanger is handled by conduit system  64  communicating with the outlet of the heat exchanger and the inlet of the refrigeration unit  52 , and contains the quick-connect coupling  66 .  
         [0026]    In the embodiment of FIG. 3, the transformer  54  must be of a special construction wherein the heat exchanger is incorporated into the transformer housing, which is a relatively simple modification. Because the coolant within the transformer  54  is in direct contact with the heat exchanger  56 , operation of the refrigeration unit  52  will cause the evaporator within the heat exchanger to absorb heat from the transformer coolant oil and cool the transformer while operating without requiring a coolant pump.  
         [0027]    [0027]FIG. 4 is a schematic illustration of how a pair of refrigeration units can be connected to four transformers wherein the refrigeration units and transformers are connected in parallel and operate in a manner similar to that previously disclosed. Referring to FIG. 4, electrical liquid cooled (oil) transformers  68 ,  70 ,  72  and  74  are illustrated. A pair of refrigeration units  76  and  78  may be mounted upon a trailer or truck and the refrigeration units include heat exchangers, not shown, which may be located adjacent the compressors of the refrigeration units and both the refrigeration unit and heat exchanger may be mounted within a common housing. The cooled transformer oil leaving the refrigeration units  76  and  78  is pumped into a manifold  80  through a pair of oil pumps  82 . Conduit systems  84  connect the manifold  80  to the transformers  68 - 74  and conduit systems  86  connect each of the transformers to the refrigeration unit inlet manifold  87 . Valves  88  are located within conduit system  84  and quick-connect couplings  90  are included in both of the conduit systems  84  and  86 . In this manner, a pair of portable refrigeration units/heat exchangers can be quickly set up to provide cooling for a plurality of transformers.  
         [0028]    From the above description, it will be appreciated that effective cooling of high output electrical transformers can be effectively produced by the utilization of conventional industrial grade refrigeration units, and it is to be understood that modifications to the disclosed embodiments may be apparent to those skilled in the art without departing from the spirit and scope of the invention.