Abstract:
An embodiment of a system to dissipate heat from electric equipment disposed in an explosive atmosphere comprises at least one electric device disposed in an explosive atmosphere, and a cooling system operable to remove heat from the at least one electric device to cool the at least one electric device to a predetermined temperature.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is entitled to the benefit of, and claims priority to, provisional patent application 61/045,029 filed Apr. 15, 2008, the entire disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. The system and method relate in general to offshore oilfield equipment such as, but not limited to, offshore platforms and oilfield support vessels, such as well stimulation vessels and equipment. 
         [0003]    The system and method is related in general to braking resistors for electrical motors and, in particular, to a system and apparatus to dissipate heat from electric power equipment in an explosive atmosphere. 
         [0004]    It is desirable, therefore, to provide a cooling system and/or apparatus to dissipate heat from electric power equipment in an explosive atmosphere. 
       SUMMARY 
       [0005]    An embodiment of a system to dissipate heat from electric equipment disposed in an explosive atmosphere comprises at least one electric device disposed in an explosive atmosphere, and a cooling system operable to remove heat from the at least one electric device to cool the at least one electric device to a predetermined temperature. Alternatively, the at least one electric device is an electric motor/generator coupled to a braking resistor. The electric motor/generator may be coupled to a braking resistor via a variable speed drive and braking chopper. Alternatively, the cooling system comprises a cooling medium for removing heat from the electric device and a heat exchanger. The cooling medium may comprise a liquid cooling system and the heat exchanger may comprise an air-cooled radiator for cooling the liquid. The cooling medium may comprise a gas cooling system and a refrigeration device for cooling the gas. Alternatively, the predetermined temperature is determined by an ignition point of at least one explosive substance. Alternatively, the predetermined temperature is a surface temperature of the electric device. Alternatively, the predetermined temperature is an ATEX Zone II temperature. 
         [0006]    In an embodiment, a system to dissipate heat from equipment in an explosive atmosphere comprises at least one device generating a source of heat and disposed in an explosive atmosphere, and a cooling system operable to remove heat from the at least one device such that an exterior surface of the at least one device is cooled to a predetermined temperature. Alternatively, the cooling system comprises a cooling medium for removing heat from the electric device and a heat exchanger. The cooling medium may comprise a liquid cooling system and the heat exchanger may comprise an air-cooled radiator for cooling the liquid. The cooling medium may comprise a gas cooling system and a refrigeration device for cooling the gas. Alternatively, the predetermined temperature is determined by an ignition point of at least one explosive substance. 
         [0007]    In an embodiment, a system to dissipate heat from an electric winch drive for wellbore cables, the winch drive disposed in an explosive atmosphere, comprises an electric motor/generator in communication with a source of electrical power and a braking resistor coupled to the electric motor/generator, the motor/generator and the resistor disposed in an explosive atmosphere, and a cooling system operable to remove heat from the braking resistor such that an exterior surface of the resistor is cooled to a predetermined temperature. Alternatively, the electric/motor generator is coupled to and controls a wireline winch having a wireline cable disposed thereon. The system may further comprise a tool attached to the wireline cable for performing at least one wellbore operation. Alternatively, the cooling system comprises a cooling medium for removing heat from the electric device and a heat exchanger. The cooling medium may comprise a liquid cooling system and the heat exchanger may comprise an air-cooled radiator for cooling the liquid. The cooling medium may comprise a gas cooling system and a refrigeration device for cooling the gas. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
           [0009]      FIG. 1  is a schematic block diagram of an electrical motor/generator system. 
           [0010]      FIG. 2  is a schematic block diagram of an embodiment of a heat dissipation system. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    Referring to all of the figures, an embodiment of an electrical system is indicated generally at  10 . The system  10  includes an electrical motor  12 , which supplies energy to a winch or drum  11  to which is attached to or spooled upon, for example, a wireline logging cable  13  (not shown), as will be appreciated by those skilled in the art. The electric motor  12  receives electric power from a power supply  14  (for example, an alternating current (AC) power supply) through a variable speed drive  16 . The cable  13  is spooled on and/or unspooled from the drum # into a wellbore (not shown) due to gravity, drill pipe action, or the like, in accordance with a wellbore operation sequence. The wellbore operation may comprise, for example, a logging operation performed an operation with a wireline tool  15 , or the like. After having unspooled a specific length of cable  13  during the wellbore operation, the electrical motor  12  becomes an electrical generator, as will be appreciated by those skilled in the art. 
         [0012]    During this phase, the electrical motor/generator  12  needs to be controlled. Indeed, in order to have a counter torque on the drum to maintain the load (which may include the weight of the cable  13 , the weight of the tool  15  to tool string, and extra tension on the cable  13  induced by tough logging conditions (TLC)) an electrical load needs to be connected to the electric motor/generator  12 . This electrical load may be a resistor  18 , which receives power from the motor/generator  12  through a braking chopper  17  that modulates the voltage and thus the current sent from the variable speed drive  16  into the braking resistor  18 . The system  10  (including the motor/generator  12  and the braking resistor  18 ) may be disposed in an enclosure  19  or the like that contains an explosive atmosphere. 
         [0013]    The braking resistor  18  dissipates the electrical power received from the variable speed drive  16  and braking chopper  17  in the form of heat. To comply with the explosive atmosphere standards such as ATEX Zone II or the like, the braking resistor  18  needs to be cooled in order maintain a predetermined temperature such as, but not limited to, a maximum surface temperature. A cooling or heat dissipation system  20 , best seen in  FIG. 2 , is therefore provided to remove heat from the resistor  18  and thereby from the explosive atmosphere in the enclosure  19 . The system  20  comprises a cooling medium  22  that is in fluid communication with both the resistor  18  and a heat exchanger  24 . The cooling medium  22  may be circulated between the resistor  18  and the heat exchanger  24  by a pump  26  or the like, as will be appreciated by those skilled in the art. 
         [0014]    In an embodiment, the cooling medium  22  is a liquid, such as water, a glycol mixture, or the like, and the heat exchanger  24  is an air-cooled radiator including an electrically driven fan or the like, which exchanges the heat from the heat exchanger  24  into the atmosphere, allowing the system  10  to be compliant with explosive atmosphere standards. Alternatively, the cooling medium  22  may be a gas and the heat exchanger  24  may be a refrigeration unit or the like that cools the gas  22  prior to being routed by a cooling fan  26  to the resistor  18  and enclosure  19 , as will be appreciated by those skilled in the art. The cooling system  20 , including the cooling medium  22 , the heat exchanger  24 , and the pump/fan  26  may also be disposed in the enclosure  19  that contains the explosive atmosphere, with the exhaust air, for example, from the heat exchanger  24  being routed out of the enclosure  19 . Those skilled in the art will appreciate that numerous types of cooling and/or refrigeration systems and devices may be utilized to remove heat from an electrical component, such as the resistor  18 , while remaining within the scope of the present invention. 
         [0015]    The system  20  preferably includes a control system (not shown) that controls the function of the pump  26  and the heat exchanger  24  to maintain the resistor  18  at a predetermined temperature. The control system may also be to shut down the system  10  in the event the predetermined temperature is exceeded. The resistor  18  may be provided with a suitable sensor or sensors (not shown) and the like to provide a signal or signals to the control system for acquisition and control purposes, as will be appreciated by those skilled in the art. In an embodiment, the predetermined temperature and/or installed sensor on the resistor  18  corresponds to maintain a surface temperature of the braking resistor  18  below the ignition point of any potential explosive substances. The predetermined temperature may, but it not limited to, correspond to standards such as ATEX standards or the like, such as ATEX Zone II. The system  20  may comprise other suitable sensors such as, but not limited to, a temperature sensor or atmospheric sensor for the enclosure  19 , and temperature sensors for the motor generator  12 , the variable speed drive  16 , and the like. 
         [0016]    An embodiment of the system  10  and/or apparatus may be advantageously utilized with an offshore wireline logging unit that is deployed in an enclosure comprising an explosive atmosphere (ATEX Zone II), which specify a maximum surface temperature of equipment, such as equipment in an enclosed area, such as the enclosure  19 . Those skilled in the art will appreciate that embodiments of the system  10  or  20  may be utilized to meet many types of temperature controls in various configurations and/or industries. 
         [0017]    The removal of heat from a braking resistor in electric/electronic fields is known such as, for example, systems comprising braking resistors that utilize the dissipated heat from the braking resistor to heat other elements of the system. Embodiments of the system  10  and  20 , however, advantageously are utilized to remove heat from components disposed in explosive atmospheres. 
         [0018]    The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood as referring to the power set (the set of all subsets) of the respective range of values. Accordingly, the protection sought herein is as set forth in the claims below. 
         [0019]    The preceding description has been presented with reference to presently preferred embodiments of the invention. Persons skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structures and methods of operation can be practiced without meaningfully departing from the principle, and scope of this invention. Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and shown in the accompanying drawings, but rather should be read as consistent with and as support for the following claims, which are to have their fullest and fairest scope.