Abstract:
Provided are a superconducting rotating machine which improves the cooling efficiency of a rotor by using schemes of passively or actively circulating a coolant and a cooling method thereof. The superconducting rotating machine includes a rotor supported rotatably about a rotation axis and including: at least one superconductive coil; and a central cavity; and a cooling apparatus disposed at an exterior of the rotor and configured to communicate with the cavity, wherein the cooling apparatus includes: a condenser configured to condense a gas coolant supplied through a gas coolant supplying pipe to generate a condensed coolant; a coolant circulating unit configured to supply the condensed coolant into the cavity, configured to recover a vapor coolant evaporated in the cavity into the condenser and configured to circulate the condensed coolant; and a forced circulating unit configured to actively circulate the condensed coolant into the cavity in response to the rotor being tilted.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from Korean Patent Application No. 10-2013-0054315, filed on May 14, 2013, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
       BACKGROUND 
       [0002]    Apparatuses and methods consistent with exemplary embodiments relate to a superconducting rotating machine and a cooling method thereof, and more particularly, to a superconducting rotating machine in which a coolant for cooling a rotor having a superconductive coil is enabled to circulate naturally and compulsively, and a cooling method thereof. 
         [0003]    A superconducting rotating machine includes a superconductive coil which must be cooled during the operation of the superconducting rotating machine. A metallic oxide superconductive material having the transition temperature higher than 77K is generally known in the art. A machine including a superconductive coil containing such a material may be cooled, for example, by liquid nitrogen. 
         [0004]    A technique of cooling a rotor of a superconducting rotating machine is known in the related art. 
         [0005]    The rotor includes a thermal conductive rotor body, and a superconductive coil made of a superconductive material and installed to a coil supporter. 
         [0006]    The rotor body has a central cavity extending in an axial direction and having a cylindrical shape, in which coolant line members drawn out from the coil supporter are connected to a side surface of the central cavity. The line members extends to a condenser chamber of a cooling apparatus geodetically located at a higher position, so that the line members form a closed single-tube line system together with the condenser chamber and the central cavity. 
         [0007]    The coolant is circulated in the line system due to the thermosiphon effect. The coolant condensed in the condenser chamber flows into the central cavity through the coolant line members. The coolant in the central cavity is thermally coupled to the superconductive coil as well as the coil supporter, so that the coolant is evaporated by absorbing heat. Then, the evaporated coolant fluid again arrives at the condenser chamber through the same line members, and then, the coolant is again condensed in the condenser chamber. 
         [0008]    When cooling is performed by the thermosiphon effect, since the conveyance of the liquid coolant is enabled under the gravity, the cooling apparatus or the condenser chamber must be placed at a position higher than that of the coil supporter. 
         [0009]    In addition, when the cooling is performed by the thermosiphon effect, since the rotor is cooled using a natural circulation of the coolant, the initial cooling time is too long. 
       SUMMARY 
       [0010]    One or more exemplary embodiments provide a superconducting rotating machine which can improve the cooling efficiency of a rotor by using schemes of passively or actively circulating a coolant and a cooling method thereof. 
         [0011]    Further, one or more exemplary embodiments provide a superconducting rotating machine which is configured to actively supply an external liquid coolant when a rotor of the superconducting rotating machine is initially cooled, and a cooling method thereof. 
         [0012]    According to an aspect of an exemplary embodiment, there is provided a superconducting rotating machine including a rotor supported rotatably about a rotation axis and including: at least one superconductive coil; and a central cavity; and a cooling apparatus disposed at an exterior of the rotor and configured to communicate with the cavity, wherein the cooling apparatus includes: a condenser configured to condense a gas coolant supplied through a gas coolant supplying pipe to generate a condensed coolant; a coolant circulating unit configured to supply the condensed coolant into the cavity, configured to recover a vapor coolant evaporated in the cavity into the condenser and configured to circulate the condensed coolant; and a forced circulating unit configured to actively circulate the condensed coolant into the cavity in response to the rotor being tilted. 
         [0013]    The coolant circulating unit may include: at least one internal coolant supplying line configured to supply the condensed coolant into the cavity; and at least one coolant recovery line configured to recover the vapor coolant into the condenser. 
         [0014]    The forced circulating unit may include a pump connected between the condenser and the internal coolant supplying line, the pump configured to actively supply the condensed coolant of the condenser into the cavity through the internal coolant supplying line. 
         [0015]    The superconducting rotating machine may further include an external liquid coolant supplying unit configured to actively supply an external liquid coolant into the cavity. 
         [0016]    The external liquid coolant supplying unit may include: at least one external coolant supplying line configured to supply the external liquid coolant into the cavity; and a connecting line connecting the pump to the external coolant supplying line. 
         [0017]    The superconducting rotating machine may further include a check valve provided at the connecting line and configured to induce the external liquid coolant to flow in one direction through the external coolant supplying line. 
         [0018]    The internal coolant supplying line, the coolant recovery line and the external coolant supplying line may be concentrically disposed about the rotation axis. 
         [0019]    The superconducting rotating machine may further include: a first connecting line vacuum part configured to enclose the internal coolant supplying line, the coolant recovery line and the external coolant supplying line; a second connecting line vacuum part connected to the rotor to surround the first connecting line vacuum part; and a mechanical seal provided between the first and second connecting line vacuum parts. 
         [0020]    The superconducting rotating machine may further include: a tilt sensor configured to sense a tilt of the rotor; and a control unit configured to output a driving signal configured to drive the pump in response to the control unit receiving a tilt signal from the tilt sensor. 
         [0021]    The superconducting rotating machine may further an initial cooling state sensor configured to determine whether the external liquid coolant is supplied through the external coolant supplying line so that a temperature of the rotor reaches an initial cooling temperature, wherein the control unit may be configured to stop driving the pump and configured to output a signal to supply a gas coolant through the gas coolant supplying line in response to the temperature of the rotor reaching the initial cooling temperature. 
         [0022]    The initial cooling state sensor comprises at least one of a time counter configured to count an initial coolant circulating time, a temperature measuring sensor configured to measure the temperature of the rotor, and a rotation number sensor configured to check a number of rotations of the rotor. 
         [0023]    The superconducting rotating machine may further include a vacuum housing enclosing the condenser and the pump. 
         [0024]    According to an aspect of an exemplary embodiment, there is provided a method of cooling a superconducting rotating machine, the method including: passively circulating a coolant in a thermosiphon scheme to recover a vapor coolant into a condenser through at least one coolant recovery line, wherein the vapor coolant is generated by evaporating a condensed coolant supplied into a cavity of a rotor through at least one internal supplying line by gravity, and the condensed coolant is generated by condensing a gas coolant through the condenser of a cooling apparatus; determining whether the rotor is tilted; and actively circulating the condensed coolant to supply the condensed coolant in response to determining that the rotor is tilted. 
         [0025]    The actively circulating the condensed coolant may be performed through a pumping force of a pump provided between the internal coolant supplying line and the condenser. 
         [0026]    The actively circulating of the condensed coolant may include: determining whether the rotor is tilted while the passively circulating the condensed coolant is performed; and driving the pump in response the rotor being tilted. 
         [0027]    The method may further include initially cooling the rotor by actively supplying an external liquid coolant into the cavity of the rotor before performing the passively circulating the condensed coolant. 
         [0028]    The initial cooling of the rotor may include: actively supplying the external liquid coolant through at least one external coolant supplying line; determining whether a temperature of the rotor reaches at an initial cooling temperature by an initial cooling state sensor; and supplying the gas coolant to a cooling unit after stopping the supplying the external liquid coolant in response to the temperature of the rotor reaching the initial cooling temperature. 
         [0029]    The condensed coolant and the external liquid coolant may be actively supplied by a single pump. 
         [0030]    A check valve may be configured to prevent the external liquid coolant from flowing reversely while the external liquid coolant is being supplied through the external coolant supplying line. 
         [0031]    The determining the temperature of the rotor may include at least one of counting an initial coolant circulating time, sensing the rotor temperature and checking a number of rotations of the rotor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    The above and/or other aspects of the disclosure will become apparent and more readily appreciated from the following description of exemplary embodiments, taken in conjunction with the accompanying drawings in which: 
           [0033]      FIG. 1  is a view showing an entire configuration of a superconducting rotating machine according to an exemplary embodiment. 
           [0034]      FIG. 2  is a view of the superconducting rotating machine when seen in the direction of arrow Π of  FIG. 1  according to an exemplary embodiment. 
           [0035]      FIG. 3  is a flowchart illustrating a method of cooling a superconducting rotating machine according to an exemplary embodiment. 
           [0036]      FIG. 4  is a flowchart illustrating an initial coolant circulating step of  FIG. 3  according to an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0037]    Hereinafter, exemplary embodiments will be described in more detail with reference to accompanying drawings. The present inventive concept is not limited to the following the exemplary embodiments but includes various applications and modifications. The exemplary embodiments will allow those skilled in the art to completely comprehend the scope of the present inventive concept. 
         [0038]      FIG. 1  is a view showing a configuration of a superconducting rotating machine according to an exemplary embodiment. 
         [0039]    Referring to  FIG. 1 , the superconducting rotating machine  1  includes an outer housing  3 , a stator coil  5  installed in the outer housing  3 , and a rotor  10  placed in the outer housing  3  and surrounded with the stator coil  5 . 
         [0040]    The rotor  10  includes a vacuum housing  11  rotatably supported based on a rotation axis A by a bearing  7  in the outer housing  3 , and a coil supporter  15  having a superconductive coil  12  and supported in the vacuum housing  11 , for example, by a hollow cylindrical torque transferring supporting member  13 . 
         [0041]    The coil supporter  15  includes a central cavity  17  disposed concentrically with the rotation axis A and extending along the rotation axis A. The cavity  17  may have a cylindrical shape. The cavity  17  is maintained in a vacuum state by the coil supporter  15 . One side of the rotor  10  is supported in the outer housing  3  by a rotational shaft  19 . 
         [0042]    For example, a cooling apparatus  30  may be provided at an outside of the rotor  10  while being spaced apart from the rotor  10  by several meters. 
         [0043]    The cooling apparatus  30  includes a cooler  31  for indirectly cooling the superconductive coil  12  through a thermal conductive member. A cold head  31   a  of the cooler  31  is only depicted in the drawings. The cooler  31  may be formed in a Gifford-McMahon type, a Stirling type or a pulse-tube type. 
         [0044]    The cooling apparatus  30  may include a condenser  35  which is thermally coupled to the thermal conductive member (not shown) coupled to the cold head  31   a  to condense a gas coolant G supplied through a gas coolant supplying line  33 , and a coolant circulating unit  37  which connects the cavity and the condenser  35  to each other. 
         [0045]    The coolant circulating unit  37  allows the coolant L 1  condensed in the condenser  35  to flow into the cavity  17 . The condensed coolant L 1  is thermally coupled to the superconductive coil  12  as well as the coil supporter  15  in the cavity  17 , so that the condensed coolant absorbs heat to evaporate, and then, the evaporated coolant V returns to the condenser  35 . 
         [0046]    The coolant circulating unit  37  includes at least one internal coolant supplying line  37   a  for supplying the condensed coolant L 1  from the condenser  35  into the cavity  17  and at least one coolant recovery line  37   b  for drawing back the evaporated coolant V evaporated in the cavity  17  into the condenser  35 , so that the coolant may be circulated by thermosiphon effect. 
         [0047]    A connecting line  37   c  may be further provided between the coolant recovery line  37   b  and the condenser  35 . 
         [0048]    In this case, the internal coolant supplying line  37   a  and the coolant recovering line  37   b  may be prepared as the same line, such that the condensed coolant L 1  and the evaporated coolant V may be circulated through the same line. 
         [0049]    The cooling apparatus  30  may include a forced circulating unit  38  for actively supplying the condensed coolant L 1  into the cavity  17  when the rotor  10  is tilted. 
         [0050]    The tilting of the rotor  10  corresponds to an unbalance state of the superconducting rotating machine  1 , that is, the tilting of the rotor  10  occurs when the superconducting rotating machine  1  is inclined from a horizontal state H at a predetermined angle (α°) or more when the superconducting rotating machine  1  is employed in a ship or coastal equipment. In other words, the tilting of the rotor corresponds to a state where the condenser  35  is placed at a position lower than that of the cavity  17  in the gravity direction. 
         [0051]    Further, the tilting of the rotor  10  means that there may be a problem in the flow of the condensed coolant from the condenser  35  to the cavity  17 . 
         [0052]    The forced circulating unit  38  may include a pump  38   a  connected between the condenser  35  and the internal coolant supplying line  37   a  to actively supply the condensed coolant L 1  supplied from the condenser  35  into the cavity  17  through the internal coolant supplying line  37   a . In other words, the pump  38   a  moves the condensed coolant L 1  supplied from the condenser  35  into the cavity  17  through pumping action. 
         [0053]    The superconducting rotating machine  1  may further include a tilt sensor  21  in order to determine whether the rotor  10  is tilted. For example, the tilt sensor  21  may adhere to an upper portion of the outer housing  3 . However, the exemplary embodiment is not limited thereto. 
         [0054]    The superconducting rotating machine  1  may include a control unit  23  which outputs a driving signal to drive the pump  38   a  when the superconducting rotating machine  1  receives a tilt signal indicating that the superconducting rotating machine  1  is tilted from the tilt sensor  21 . 
         [0055]    The cooling apparatus  30  may further include an external liquid supplying unit  39  for actively supplying or moving an external liquid coolant when the rotor  10  is initially cooled. 
         [0056]    The external liquid supplying unit  39  may include at least one external coolant supplying line  39   a  and a pump to supply an external liquid coolant L 2  into the cavity  17 . The pump the same as the pump  38   a  employed in the forced circulating unit  38  may be used. That is, the pump  38   a  may supply the condensed coolant L 1  from the condenser  35  and the external liquid coolant L 2  supplied through the external coolant supplying line  39   a  into the cavity  17  via pumping the condensed coolant L 1  and the external liquid coolant L 2 . 
         [0057]    A connecting line  39   c  may be provided between the external coolant supplying line  39   a  and the pump  38   a . The connecting line  39   c  may be connected to a main supplying pipe  39   e  for supplying the external liquid coolant L 2 . 
         [0058]    A control valve  45  may be provided to the main supplying pipe  39   e  to be enabled to be opened or closed, such that the control valve  45  may control the supplying or blocking of the external liquid coolant L 2 . 
         [0059]    The external liquid coolant L 2  may include an extremely low temperature liquid coolant such as liquid nitrogen. 
         [0060]    A check valve  32  may be provided to the connecting line  39   c , such that, when the external liquid coolant L 2  is supplied by the pump  38   a  through the external supplying line  39   a , the external liquid coolant L 2  is induced to flow through the connecting line  39   c  along the external supplying line  39   a  in a single direction and is prevented from flowing in the reverse direction. 
         [0061]    The external liquid supplying unit  39  may further include an initial cooling state sensor  25  for sensing whether the external liquid coolant L 2  is supplied through the external coolant supplying line  39   a  so that the rotor  10  is cooled at the initial cooling temperature. 
         [0062]    The initial cooling state sensor  25  may include a counter for counting an initial coolant circulating time taken for the external liquid coolant L 2  to be circulated, a temperature sensor for sensing the temperature of the rotor  10 , and a rotation sensor for checking the rotation number of the rotor  10 . 
         [0063]    When the control unit  23  determines that the temperature of the rotor  10  reaches the initial cooling temperature based on the signal transferred from the initial cooling state sensor  25 , the control unit  23  may stop driving the pump  38   a  and may output a signal by which the gas coolant G is enabled to be supplied through the gas supplying line  33 . 
         [0064]    The gas coolant may include at least one of neon, hydrogen and helium. 
         [0065]    The condenser  35  and the pump  38   a  are surrounded by the vacuum housing  36  of the cooling apparatus to be heat-insulated from an outside. 
         [0066]    A first connecting line vacuum part  36   a , which surrounds the internal coolant supplying line  37   a , the coolant recovery line  37   b  and the external coolant supplying line  39   a  to be heat-insulated from an outside, may be provided to a portion of the vacuum housing  36 . 
         [0067]    A second connecting line vacuum part  11   a , which surrounds the first connecting line vacuum part  36   a  to be heat-insulated, may be provided to a portion of the vacuum housing  11 . 
         [0068]    A magnetic liquid seal  41  may be provided near the vacuum housing  36  of the cooling apparatus between the first and second connecting line vacuum parts  36   a  and  11   a  and a mechanical seal  43  may be further provided opposite to the magnetic liquid seal  41  between the first and second connecting line vacuum parts  36   a  and  11   a.    
         [0069]    The magnetic liquid seal  41  and the mechanical seal are spaced apart from each other by a predetermined interval, so that the coolant is doubly prevented from being leaked. Specifically, the mechanical seal  43  may primarily prevent the coolant from being leaked, so that the magnetic liquid seal  41  may be prevented from being corroded by the coolant. 
         [0070]      FIG. 2  is a view of the superconducting rotating machine when seen in the direction of arrow Π of  FIG. 1  according to an exemplary embodiment. 
         [0071]    Referring to  FIG. 2 , the internal coolant supply line  37   a , the coolant recovery line  37   b  and the external coolant supplying line  39   a  are concentrically disposed about the rotation axis A. 
         [0072]    At least one internal coolant supplying line  37   a  may be provided and may be disposed to allow the center to be on the rotation axis A. 
         [0073]    At least one coolant recovery line  37   b  may be provided at a predetermined interval in a circumferential direction about the inner coolant supplying line  37   a.    
         [0074]    The external coolant supplying line  39   a  may be disposed between the coolant supplying line  37   a  and the coolant recovery line  37   b  and aligned in a circumferential direction at a predetermined interval. 
         [0075]    Hereinafter, a method of cooling a superconducting rotating machine according to an exemplary embodiment will be described. 
         [0076]      FIG. 3  is a flowchart illustrating a method of cooling a superconducting rotating machine according to an exemplary embodiment. 
         [0077]    Referring to  FIGS. 1 and 3 , the method of cooling a superconducting rotating machine may include a passive coolant circulating step S 30 , a rotor tilt determining step S 50 , and an active condensed coolant circulating step S 70 . 
         [0078]    In the passive coolant circulating step S 30 , the gas coolant G supplied through the gas coolant supplying line  33  is condensed by the condenser  35 . The condensed coolant L 1  by the condenser  35  is supplied into the cavity  17  of the rotor  10  through the internal coolant supplying line  37   a  by gravity. 
         [0079]    The condensed coolant L 1  supplied into the cavity  17  is evaporated. The coolant V evaporated in a vapor type by absorbing heat flows into the condenser  35  through the coolant recovery line  37   b . The coolant circulation is achieved under the condition of using so-called “thermosiphon effect.” 
         [0080]    In the rotor tilt determining step S 50 , the tilt sensor  23  senses a tilt of the rotor  10 . 
         [0081]    Based on the signal received through the tilt sensor  23 , the control unit  23  determines whether the rotor  10  is tilted and then, determines whether the rotor  10  is tilted at a predetermined angle (α°) or more, so that it is impossible to supply the liquid coolant L 1  into the cavity  17  by gravity. 
         [0082]    As described above, when it is determined in the rotor tilt determining step S 50  that the rotor is tilted, the control unit  23  outputs the pump driving signal to drive the pump  38   a.    
         [0083]    Thus, the liquid coolant L 1  received in the condenser  35  is actively supplied into the cavity  17  by the driving force of the pump  38   a . The liquid coolant L 1  supplied into the cavity  17  is evaporated by absorbing heat and the vapor coolant V flows into the condenser  35  through the coolant recovery line  37   b.    
         [0084]    In addition, an initial coolant circulating step S 10  for actively circulating the external liquid coolant L 2  before performing the natural coolant circulating step S 30  may be further included. 
         [0085]      FIG. 4  is a flowchart illustrating details of the initial coolant circulating step S 10  of  FIG. 3  according to an exemplary embodiment. 
         [0086]    Referring to  FIGS. 1 and 4 , the initial coolant circulating step S 10  includes an external liquid coolant supplying step S 11 , an initial cooling state determining step S 13  and a gas coolant supplying step S 15 . 
         [0087]    In the external liquid coolant supplying step S 11 , the pump  38   a  is driven and the control valve  45  is opened so that the external liquid coolant L 2 , which is liquid nitrogen, is supplied through the main supplying pipe  39   e . In this case, the control valve  45  is opened according to the signal output from the control unit  23 . 
         [0088]    The external liquid coolant L 2  is supplied into the cavity  17  through the connecting line  39   c  and the external liquid coolant supplying line  39   a.    
         [0089]    The external liquid coolant L 2  supplied into the cavity  17  absorbs heat to evaporate into a vapor state and then, the evaporated coolant flows into the condenser  35  through the coolant recovery line  37   b , so that the evaporated coolant is re-condensed. The re-condensed coolant L 1  is supplied into the cavity  17  through the internal coolant supplying line  37   a.    
         [0090]    While the external liquid coolant L 2  is actively pumped by the pumping force of the pump  38   a , the external liquid coolant L 2  is induced to flow in one direction by the check valve  32  provided in the connecting line  39   c , so that the external liquid coolant L 2  flows along the external liquid coolant supplying line  39   a  through the connecting line  39   c  and is prevented from flowing in the reverse direction. 
         [0091]    Thus, as the external liquid coolant L 2  is compulsively supplied into the cavity  17  by the driving force of the pump  38   a , the initial cooling time of the rotor  10  may be reduced. 
         [0092]    It is described above that the driving force for circulating the external liquid coolant L 2  is provided by the pump  38   a  which actively pumps the condensed coolant L 1 , but it is understood that another pump may be used instead of the pump  38   a.    
         [0093]    In the initial cooling state determining step S 13 , the external liquid coolant L 2  is supplied into the cavity  17  to evaporate and then, the initial cooling state of the rotor  10  is sensed through the initial cooling state sensor  25  while an initial coolant circulation operation, in which the vapor coolant is recovered into the condenser  35  to be re-condensed and the re-condensed coolant L 1  is supplied into the cavity  17 , is performed. 
         [0094]    The sensing of the initial cooling state may be performed by counting an initial coolant circulating time, sensing the temperature of the rotor  10  or checking the rotation number of the rotor  10 . 
         [0095]    In the gas coolant supplying step S 15 , the control unit  23  determines whether the temperature of the rotor  10  reaches the desired initial cooling temperature based on the date received through the initial coolant state sensor  25 . 
         [0096]    When it is determined that the temperature of the rotor  10  reaches the desired initial cooling temperature, the control unit  23  outputs the driving signal to stop driving the pump  38   a  and then, allows the gas coolant G including at least one of neon, hydrogen and helium to be supplied through the gas coolant supplying line  33 . 
         [0097]    Thus, when the rotor  10  is initially cooled through liquid nitrogen, after the gas coolant G is supplied through the gas coolant supplying line  33  and condensed through the condenser  35 , the coolant is supplied into the cavity  17  by gravity so that the rotor  10  is cooled at the target temperature. 
         [0098]    According to the exemplary embodiment of the present invention, it is configured in a natural circulation scheme or a compulsive circulation scheme to enable the coolant to be circulated, so that the coolant can be smoothly circulated even in state that the rotor is in a non-level state (i.e. not in a horizontal state). 
         [0099]    According to the exemplary embodiment, the superconducting rotating machine is configured to actively circulate liquid nitrogen in the initial cooling of the rotating machine, so that the initial cooling time of the superconducting rotating machine can be reduced. 
         [0100]    While exemplary embodiments have been particularly described above, it will be understood by those skilled in the art that various modifications, additions and substitutions in form and details may be made therein without departing from the scope and spirit of the inventive concept as defined by the following claims.