Abstract:
In one embodiment a fault current limiter comprises a current splitting reactor having interleaved windings to reduce an insertion impedance of the fault current limiter during non-fault conditions. The current splitting reactor having interleaved windings may include a first winding, the first winding including a plurality of sub-windings and a second winding, the second winding including a plurality of sub-windings, the sub-windings of the first winding and the sub-windings of the second winding wounds about the core and interleaved.

Description:
FIELD 
       [0001]    The present embodiments relate to current control devices, and more particularly, to fault current limiting devices and systems. 
       BACKGROUND 
       [0002]    Fault current limiters (FCLs) are used to provide protection against current surges, for example in a power transmission network. Various types of FCLs have been developed over the last several decades, including superconducting fault current limiters (SCFCLs), solid-state fault current limiters, inductive fault current limiters, as well as other varieties that are well known in the art. A power system in which an FCL is implemented may include generation, transmission, and distribution networks that generate and deliver power to various industrial, commercial, and/or residential electrical loads. 
         [0003]    A fault current is an abnormal current in an electrical system that may result from a fault in the system, such as a short circuit. A fault current may arise in a system due to any number of events or failures, such as power lines or other system components being damaged by severe weather (e.g. lightning strikes). When such a fault occurs, the fault current limiter acts to protect the system from the fault current. During normal operation, however, it is desired that the fault current limiter will have as little affect on the system being protected as possible. 
         [0004]    Thus there is a need for a fault current limiter that has low insertion impedance and causes negligible voltages drop and power loss in the circuit being protected during normal operation but which is still able to protect against fault currents. 
       SUMMARY 
       [0005]    This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended as an aid in determining the scope of the claimed subject matter. 
         [0006]    In one embodiment, a fault current limiter is provided. The fault current limiter includes a current splitting reactor having interleaved windings, the current splitting reactor comprising a core, a first winding wound about the core, and a second winding wound about the core and interleaved with the first winding to reduce an insertion impedance of the fault current limiter. 
         [0007]    In one embodiment, a fault current limiter is provided. The fault current limiter includes a current splitting reactor having interleaved windings, the current splitting reactor comprising a core, a first winding, the first winding including a plurality of sub-windings, and a second winding, the second winding including a plurality of sub-windings, the sub-windings of the first winding and the sub-windings of the second winding wounds about the core and interleaved to reduce an insertion impedance of the fault current limiter. 
         [0008]    In one embodiment, a power system is provided. The power system includes a power source, a load electrically connected to the power source, and a fault current limiter electrically coupled to the power source and the load to limit the amount of current in the power system during a fault condition, the fault current limiter comprising a current splitting reactor having interleaved windings, the current splitting reactor comprising a core, a first winding, the first winding including a plurality of sub-windings, and a second winding, the second winding including a plurality of sub-windings, the sub-windings of the first winding and the sub-windings of the second winding wounds about the core and interleaved to reduce an insertion impedance of the fault current limiter during normal operating conditions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  depicts a one embodiment of an system incorporating an FCL device including a current splitting reactor having interleaved windings; 
           [0010]      FIG. 2  depicts a one embodiment of an FCL device including a current splitting reactor having interleaved windings; 
           [0011]      FIG. 3  depicts a one embodiment of a current splitting reactor having interleaved windings; 
           [0012]      FIG. 4  depicts a schematic diagram of the current splitting reactor having interleaved windings of  FIG. 3 ; 
           [0013]      FIG. 5  depicts a one embodiment of a current splitting reactor having interleaved windings; and 
           [0014]      FIG. 6  depicts a schematic diagram of the current splitting reactor having interleaved windings of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    The present embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which some embodiments are shown. The subject matter of the present disclosure, however, may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the subject matter to those skilled in the art. In the drawings, like numbers refer to like elements throughout. 
         [0016]    Various embodiments described herein provide FCLs that include a current splitting reactor (CSR) having interleaved windings. Additionally, the current splitting reactor may have an open core design. The FCLs including a CSR having interleaved windings advantageously provides low insertion impedance. As an example, the FCLs described herein may have insertion impedance during normal operating conditions of less than 1% of the total system impedance. 
         [0017]    Additionally, the example FCLs described herein may be implemented to limit fault currents in any electrical system, such as, for example, transmission, distribution, and generation systems. Furthermore, with some examples the CSR with interleaved windings may be implemented in a superconducting FCL, a solid state FCL, a fast switch FCL, or in general, any fault current limiting circuit configured to protect a system from fault currents where low insertion impedance is desired during normal operation. In some examples, the FCLs described herein may incorporate saturated iron cores or shielded cores. In a particularly illustrative example, an FCL device with a CSR having interleaved windings as described herein may be provided to lower the insertion impedance of a saturated iron core FCL, which as will be appreciated, typically has high insertion impedance. 
         [0018]    Furthermore, various examples provided herein may be implemented in FCL devices for both high and low frequency systems. 
         [0019]      FIG. 1  illustrates an FCL circuit  200 , implemented in an exemplary system  1000 . The FCL  200  includes a current splitting reactor having interleaved windings (IWCSR)  210  (described in greater detail with reference to  FIGS. 3-6 .) A power source  101  supplies power through interface circuit  103  and circuit breaker  105 . Power transmission line  106  leads to an interface  107  with a substation having a transformer  109 , which is configured to step the transmission line voltage to a voltage compatible with loads  121 ,  123 . Output of transformer  109  may be coupled to circuit breaker  111  and a FCL  200 . FCL  200  may be coupled through circuit breaker  115  and matching circuits  117 ,  119  to loads  121 ,  123 . Additional loads and matching circuits may be provided. A short circuit fault  125  may exist and, if present, may be isolated by operation of various embodiments described herein. 
         [0020]      FIG. 2  illustrates an exemplary FCL  200  arranged according to at least some embodiments of the present disclosure. The FCL  200  includes the IWCSR  210  having a first winding  212  and a second winding  214 , which are counter wound and interleaved about a core  216  (described in greater detail with reference to  FIGS. 3-6 ). The FCL  200  includes an input  202  and an output  204  for connecting the FCL  200  to a circuit to be protected (e.g., the loads  121 ,  123  shown in  FIG. 1 .) Additionally, the FCL  200  includes a parallel connected voltage controlled reactor (VCR)  220  and fault trigger circuit (FTC)  230 . The second winding  214  is connected in series between the input  202  and the parallel connected VCR  220  and FTC  230 . Furthermore, various other transient overvoltage control circuits (not shown) may be connected to the VCR  220  for suppressing, shunting, or otherwise protecting the circuits from transient overvoltages caused by fault currents. An FCL including a CSR and its operation may be more fully described in commonly owned U.S. Patent Application Publication No. 2012/0264613, which is incorporated herein by reference in its entirety. It is important to note, that although  FIG. 2  illustrates the FCL  200  implemented with the VCR  220 , various embodiments of the present disclosure may be implemented without a VCR. For example, a FCL may be implemented according to the present disclosure without a VCR, in which case, the FCL controls its own voltage and in the case of fault, current flows through the high impedance circuitry of the FCL. 
         [0021]    During normal operation (e.g., no fault current, such as, the short circuit fault  125 , detected), the FTC  230  will be closed and present very little impedance. Accordingly, total current (“I T ”) will flow into the FCL  200  through the input  202  and pass through the first winding  212  and the second winding  214 . As the FTC  230  is closed, the VCR  220  will have negligible current flowing through it. Accordingly, the first winding  212  and the second winding  214  will have portions of the total current I T  proportional to the turns ratio of their winding flowing through them. As the first winding  212  and the second winding  214  are counter wound, their magnetic fields cancel inside the core  216 . As a result, the FCL  200  may exhibit very low insertion impedance during normal operation. In some examples, the FCL  200  may insert less than 1% of the system impedance or have less than a 1% voltage drop during normal operation. In some examples, (e.g., where the CSR  210  has a 3:1 current ratio between the first winding  212  and the second winding  214 ,) the VCR  220  and FTC  230  will merely see 25% of the total current I T . Other ratios can be achieved by changing the winding turns ratio between windings  212  and  214 . 
         [0022]    During a fault current condition, a fault current higher than the normal current flows into both the first winding  212  and the second winding  214  through the input  202 . When the fault current exceeds a predefined trigger current, the FTC  230  opens or inserts very high impedance and fault current transfers to the VCR  220  and any other connected transient overvoltage control circuits (TOCCs). Furthermore, when the FTC opens or becomes high impedance, the impedance of the VCR  220  and any other connected TOCCs becomes high enough to reduce the current flowing through winding  214 , which causes the CSR  210  to lose its magnetic field cancellation and introduces a high current limiting reactance. Said differently, during a fault condition, current begins to flow through the VCR  220 , which causes the amount of current flowing through the second winding  214  to be reduced. As such, the amount of amper-turns flowing through the first winding  212  and the second winding  214  is no longer equal and the magnetic fields within the core  216  will no longer cancel out, thereby increasing the reactance of the IWCSR  210 . This causes the insertion impedance of the FCL  200  to increase, which in turn assists in limiting the fault current. 
         [0023]    Accordingly, the FCL  200  provides low insertion impedance during normal operation but high insertion impedance during fault conditions, which operates to limit the fault current. As will be appreciated, when the system voltage increases, the impedance required to limit fault currents also increases. Increasing the current limiting impedance requires the self-reactance of the first winding  212  and the second winding  214  to be increased. The equivalent reactance (“Xeq”) of the FCL  200  during normal operation can be described by the following equation, where Xw1 is the self reactance of the first winding  212 , Xw2 is the self reactance of the second winding  214 , and k is the magnetic coupling between the first winding  212  and the second winding  214 . Furthermore, the impedance of the FTC  230  (“Z FTC ”) is zero as the FTC  230  is closed during normal operating conditions. 
         [0000]    
       
         
           
             Xeq 
             = 
             
               
                 
                   X 
                    
                   
                       
                   
                    
                   w 
                    
                   
                       
                   
                    
                   1 
                   * 
                   Xw 
                    
                   
                       
                   
                    
                   2 
                 
                 - 
                 
                   
                     k 
                     2 
                   
                   * 
                   Xw 
                    
                   
                       
                   
                    
                   1 
                   * 
                   Xw 
                    
                   
                       
                   
                    
                   2 
                 
               
               
                 
                   Xw 
                    
                   
                       
                   
                    
                   1 
                 
                 + 
                 
                   Xw 
                    
                   
                       
                   
                    
                   2 
                 
                 + 
                 
                   2 
                   * 
                   k 
                   * 
                   
                     
                       Xw 
                        
                       
                           
                       
                        
                       1 
                       * 
                       Xw 
                        
                       
                           
                       
                        
                       2 
                     
                   
                 
               
             
           
         
       
     
         [0024]    The equivalent reactance Xeq of the FCL  200  during fault current operation can be described by the following equation, wherein X VCR  is the reactance of the VCR  220 . 
         [0000]    
       
         
           
             Xeq 
             = 
             
               
                 
                   Xw 
                    
                   
                       
                   
                    
                   1 
                   * 
                   
                     ( 
                     
                       
                         X 
                          
                         
                             
                         
                          
                         w 
                          
                         
                             
                         
                          
                         2 
                       
                       + 
                       
                         X 
                         VCR 
                       
                     
                     ) 
                   
                 
                 - 
                 
                   
                     k 
                     2 
                   
                   * 
                   Xw 
                    
                   
                       
                   
                    
                   1 
                   * 
                   X 
                    
                   
                       
                   
                    
                   w 
                    
                   
                       
                   
                    
                   2 
                 
               
               
                 
                   Xw 
                    
                   
                       
                   
                    
                   1 
                 
                 + 
                 
                   X 
                    
                   
                       
                   
                    
                   w 
                    
                   
                       
                   
                    
                   2 
                 
                 + 
                 
                   2 
                   * 
                   k 
                   * 
                   
                     
                       Xw 
                        
                       
                           
                       
                        
                       1 
                       * 
                       X 
                        
                       
                           
                       
                        
                       w 
                        
                       
                           
                       
                        
                       2 
                     
                   
                 
               
             
           
         
       
     
         [0000]    With some embodiments, it is desirable to design the FCL  200  such that the magnetic coupling k is approximately equal to 1. Accordingly, the equivalent reactance Xeq of the FCL  200  during fault current operation can be expressed by the following equation, which assumes that k=1. 
         [0000]    
       
         
           
             Xeq 
             = 
             
               
                 Xw 
                  
                 
                     
                 
                  
                 1 
                 * 
                 
                   X 
                   VCR 
                 
               
               
                 
                   Xw 
                    
                   
                       
                   
                    
                   1 
                 
                 + 
                 
                   Xw 
                    
                   
                       
                   
                    
                   2 
                 
                 + 
                 
                   X 
                   VCR 
                 
                 + 
                 
                   2 
                   * 
                   
                     
                       Xw 
                        
                       
                           
                       
                        
                       1 
                       * 
                       Xw 
                        
                       
                           
                       
                        
                       2 
                     
                   
                 
               
             
           
         
       
     
         [0000]    Furthermore, given a turns ratio n=N2/N1, where N2 is the number of turns in the second winding  214  and N1 is the number of turns in the first winding  212  and where Xw2=n 2 *Xw1, the equivalent reactance of the FCL  200  may be expressed by the following equation. 
         [0000]    
       
         
           
             Xeq 
             = 
             
               
                 Xw 
                  
                 
                     
                 
                  
                 1 
                 * 
                 
                   X 
                   VCR 
                 
               
               
                 
                   Xw 
                    
                   
                       
                   
                    
                   1 
                 
                 + 
                 
                   
                     ( 
                     
                       1 
                       + 
                       n 
                     
                     ) 
                   
                   2 
                 
                 + 
                 
                   X 
                   VCR 
                 
               
             
           
         
       
     
         [0000]    Where X VCR &gt;&gt;Xw1*(1+n) 2 , the equivalent reactance Xeq of the FCL  200  is approximately equal to the reactance of the first winding  212 . Said differently, Xeq is approximately equal to Xw1. 
         [0025]    As will be appreciated from the above equations, realizing low insertion impedance (e.g., below 1% of the system impedance) can be difficult, particularly for large FCL devices. Said differently, as the magnetic coupling of the first winding  212  and the second winding  214  tends to increase with increases in the size of the first winding  212  and the second winding  214 , getting the magnetic fields to substantially cancel out during normal operation may be difficult. 
         [0026]    The present disclosure, however, provides the IWCSR  210  where the first winding  212  and the second winding  214  are interleaved to reduce the insertion impedance during normal operation. In general, the IWCSR  210  increases the coupling of the first winding  212  and the second winding  214  by splitting the first winding  212  and the second winding  214  into sub-windings and interleaving the sub-windings about the core  216 .  FIGS. 3-6  illustrate examples of an IWCSR, which may be implemented as the IWCSR  210 . In particular,  FIGS. 3-4  illustrate an example IWCSR where the sub-windings are connected in series while  FIGS. 5-6  illustrate an example IWCSR where the sub-windings are connected in parallel. 
         [0027]    Turning more particularly to  FIG. 3 , an IWCSR  310  having a first winding  312  and a second winding  314  wound about a core  316  is illustrated. As can be seen, the first winding  312  includes sub-windings  312 - 1  to  312 - 4  and the second winding  314  includes sub-windings  314 - 1  to  314 - 4 . It is noted that  FIG. 3  illustrates a cut-away side view of the IWCSR  310 . It is to be appreciated that the first winding  312  and the second winding  314  are wound about the core  316 . Accordingly, each of the sub-windings (e.g., the sub-windings  312 - 1  to  312 - 4  and  314 - 1  to  314 - 4 ) is shown twice, on either side of the core  316 , corresponding to the portions that would be visible in a cut-away representation. Furthermore, the sub-windings are counter wounds. More particularly, the sub-windings  312 - 1  to  312 - 4  of the first winding  312  are wound in a first direction while the sub-windings  314 - 1  to  314 - 4  of the second winding  314  are wound in the opposite direction. This is indicated by the notation of the plus sign within a circle in  FIG. 3 . 
         [0028]    In some examples, the sub-windings  312 - 1  to  312 - 4  of the first winding  312  are electrically connected in series and the sub-windings  314 - 1  to  314 - 4  of the second winding  314  are electrically connected in series. Additionally, the sub-windings (e.g.,  312  and  314 ) are separated by gaps  340 . More specifically, gaps  340 - 1  to  340 - 7  separate the sub-windings  312 - 1  to  312 - 4  and  314 - 1  to  314 - 4 . In some examples, the gaps  340 - 1  to  340 - 7  may be between 2 mm and 3 cm, and may be provided to facilitate cooling and high voltage insulation. 
         [0029]      FIG. 4  illustrates a schematic diagram of the IWCSR  310  shown in  FIG. 3 . As can be seen from this figure, the sub-windings  312 - 1  to  312 - 4  are electrically connected in series to form the first winding  312  and the sub-windings  314 - 1  to  314 - 4  are also electrically connected in series to form the second winding  314 . Additionally, the core  316  is shown. In some examples, an FCL device may be implemented with the IWCSR  310  to provide increased voltage carrying capacity as a result of the series connected sub-windings. 
         [0030]    Turning more particularly to  FIG. 5 , an IWCSR  510  having a first winding  512  and a second winding  514  wound about a core  516  is illustrated. As can be seen, the first winding  512  includes sub-windings  512 - 1  to  512 - 4  and the second winding  514  includes sub-windings  514 - 1  to  514 - 4 . It is noted that  FIG. 5  illustrates a cut-away side view of the IWCSR  510 . It is to be appreciated, that the first winding  512  and the second winding  514  are wound about the core  516 . Accordingly, each of the sub-windings (e.g., the sub-windings  512 - 1  to  512 - 4  and  514 - 1  to  514 - 4 ) is shown twice, on either side of the core  516 , corresponding to the portions that would be visible in a cut-away representation. Furthermore, the sub-windings are counter wounds. More particularly, the sub-windings  512 - 1  to  512 - 4  of the first winding  512  are wound in a first direction while the sub-windings  514 - 1  to  514 - 4  of the second winding  514  are wound in the opposite direction. This is indicated by the notation of the plus sign within a circle in  FIG. 5   
         [0031]    In some examples, the sub-windings  512 - 1  to  512 - 4  of the first winding  512  are electrically connected in parallel and the sub-windings  514 - 1  to  514 - 4  of the second winding  514  are electrically connected in parallel. Additionally, the sub-windings (e.g.,  512  and  514 ) are separated by gaps  540 . More specifically, gaps  540 - 1  to  540 - 7  separate the sub-windings  512 - 1  to  512 - 4  and  514 - 1  to  514 - 4 . In some examples, the gaps  340 - 1  to  340 - 7  may be between 2 mm and 3 cm, and may be provided to facilitate cooling and high voltage insulation. 
         [0032]      FIG. 6  illustrates a schematic diagram of the IWCSR  510  shown in  FIG. 5 . As can be seen from this figure, the sub-windings  512 - 1  to  512 - 4  are electrically connected in parallel to form the first winding  512  and the sub-windings  514 - 1  to  514 - 4  are also electrically connected in parallel to form the second winding  514 . Additionally, the core  516  is shown. In some examples, an FCL device may be implemented with the IWCSR  510  to provide increased current carrying capacity as a result of the parallel connected sub-windings. 
         [0033]    As described, the sub-windings are separated by a number of gaps (e.g., the gaps  340  in the case of the IWCSR  310  or the gaps  540  in the case of the IWCSR  510 ). The equivalent reactance of the IWCSR  310  or  510 , can be represented based on the number of gaps separating the sub-windings. For example, the following equation may be used to represent the equivalent reactance, where p equals the number of gaps between sub-windings and X FULL  equals the full reactance of the first winding and the second winding. 
         [0000]    
       
         
           
             Xeq 
             = 
             
               
                 X 
                 FULL 
               
               
                 
                   p 
                   2 
                 
                  
                 
                     
                 
               
             
           
         
       
     
         [0034]    Using the example IWCSR shown in either  FIG. 3  or  FIG. 5 , the equivalent reactance Xeq can be determined as follows: the number of gaps p equals 7, therefor the equivalent reactance Xeq is reduced to Xeq=X Full /(7 2 )=X Full /49=0.02X Full . Said differently, the insertion impedance of an FCL device incorporating the IWCSR  310  or the IWCSR  510  may be approximately 2% of the full reactance of the FCL device. 
         [0035]    It is to be appreciated that the number of sub-windings can be more or less than depicted in the examples presented herein. For example, the first winding and the second winding may include as few as 2 sub-windings each. As another example, the first winding and the second winding may include more than 4 sub-windings. In some examples, the first winding and the second winding may each include between 2 and 7 sub-windings. Furthermore, as described, the turn ratio between the first winding and the second winding may vary. For example, higher current applications require higher turns ratio. 
         [0036]    In addition to having first windings and second windings that are interleaved, an IWCSR (e.g., the IWCSR  210 ,  310 , or  510 ) described above may have either an open core or a closed core. Furthermore, the core may be formed from air, plastic, iron materials. In some examples, an iron core may be used to provide higher current limiting impedance with smaller IWCSR designs. In the case where the core is closed, the core (e.g., the core  216 ,  316 , or  516 ) may completely enclose the first winding and the second winding. Said differently, the closed core may provide a return path for the magnetic field. For example, for an iron core, an iron return path would be provided. In the case where the core is open, the core (e.g., the core  216 ,  316 , or  516 ) may not completely enclose the first winding and the second winding (e.g., refer to  FIG. 3  and  FIG. 5 .) Said differently, the open core may not provide a return path for the magnetic field. In some examples, an open core may be used to provide for a soft saturation and a reduction in the loss of current limiting impedance during a fault condition. Furthermore, in some examples, an open core using iron materials may provide a reactance between 3 and 5 times that of an air core. 
         [0037]    Thus, FCLs having low insertion impedance during normal operating conditions but high insertion impedance during fault current conditions are provided. In particular, the FCLs include a CSR having interleaved windings, which provides a significant reduction in the insertion impedance of the FCL device. 
         [0038]    The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are in the tended to fall within the scope of the present disclosure. Furthermore, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Thus, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.