Abstract:
A fault point locating device which estimates a fault point in an electric power system, is provided with: a variation range calculating means which obtains a range of variation of sensor values and a range of variation of an impedance of the electric power system, on the basis of the sensor values, which include measured voltage values and measured current values before and after the fault and which are measured using sensors installed in the electric power system, sensor errors representing error ranges of the sensors in relation to the sensor value measurements, said impedance, and an impedance variation parameter for determining the range of variation of the impedance; a combination creating means which creates combinations of values that the sensor values and the impedance value could attain; and a fault point locating means which calculates a fault point range representing distances from the sensors to the fault point.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a fault point locating device and method which estimate a fault point when system fault is generated in an electric power system. In addition, the invention relates to an electric power system monitoring system or a facility planning support system supporting installation planning of system facilities, which communicates with the fault point locating device. 
       BACKGROUND ART 
       [0002]    As a background art of this technical field, there is U.S. Pat. No. 4,313,169 (PTL 1). PTL 1 discloses that “in order to locate a malfunction point of an electric power system without being influenced by resistance of a fault point, a sensor, which is installed in an end of a system, measures current and a voltage of a line at the time of generating a fault, and calculates a distance between the sensor and the fault point from a measured value and an impedance of the system.” (refer to abstract). 
         [0003]    In addition, there is “C37. 114-2004 IEEE Guide for Determining Fault Location on AC Transmission and Distribution Lines” (NTL 1). In this document, a fault point locating scheme disclosed in PTL 1 is described. 
         [0004]    A principle disclosed in NTL 1 will be described with rating of a fault point of a system illustrated in  FIG. 7  as an example. An impedance from a distribution substation  201  of the system to a load  207  is set to ZL. An electric current sensor  210  and a voltage sensor  209  are installed in a busbar  203  of the distribution substation  201 , and a current Ipre before generating the fault is measured. Also, current Ig and a voltage Vg at the time of generating a ground fault or a short fault of a resistance Rf in the fault point  205  are measured. At this time, a distance m from the busbar  203  to the fault point  205  can be obtained using (Equation 1) and (Equation 2). 
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         [0005]    However, ΔIg* represents a conjugate complex number of ΔIg, Im represents an imaginary part of the equation. The voltage Vg, the current Ig, and Ipre which are used vary in accordance with types of the fault. In a case of a one-line ground fault, a phase voltage and phase current of a ground fault phase are used. In a case of a three-line ground fault, a three-line short fault, a two-line short fault, and a two-line ground fault, a line voltage and line current of a line where the fault is generated are used. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         PTL 1: U.S. Pat. No. 4,313,169 
         NTL 1: C37. 114-2004 IEEE Guide for Determining Fault Location on AC Transmission and Distribution Lines 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0008]    An electric power system monitoring system in which a fault point locating scheme disclosed in PTL 1 is implemented obtains a fault point location as a single point, in the form of distances from sensors. However, there are errors in an electric current sensor  210  or a voltage sensor which are used for sensors, and thus there is a problem in that errors arise between the fault point obtained by the electric power system monitoring system and an actual fault point, that is, a locating error arises. In addition, an impedance of the system varies depending on a status of the system. For example, if a temperature of a transmission and distribution line increases, resistance per unit increases, and a span length of the system is also lengthened. This variation is also a problem in that it results in a magnification of the locating error in the fault point locating scheme in the related art. 
         [0009]    In the electric power system monitoring system, if the locating error is great, a person who performs maintenance needs more time for searching a fault point, and thus a blackout time increases. In addition, if a range of the locating error is not found, the person who performs maintenance cannot be allocated to an optimal work, and thus costs of maintenance increase. In addition, if an expensive sensor with high accuracy is installed in order to reduce the locating errors, costs of a facility increase. 
       Solution to Problem 
       [0010]    In order to solve the above-described problems, according to the invention, there is provided a fault point locating device which estimates a fault point in an electric power system, the device includes variation range calculating means for obtaining a range of variation of sensor values and an impedance, based on a sensor value including a measured voltage value and a measured current value before and after fault, which are measured using sensors installed in the electric power system, a sensor error representing an error range of the sensor in relation to measurement of the sensor value, an impedance of the electric power system, and an impedance variation parameter for determining the range of variation of the impedance, combination creating means for creating a combination of values that the sensor value and the impedance are able to attain, based on the range of variation obtained by the variation range calculating means, and fault point locating means for calculating a fault point range representing a distance from the sensor to the fault point based on the combination. 
       Advantageous Effects of Invention 
       [0011]    According to the invention, it has an effect that, even when there is a sensor error or a variation of impedance, a range in which a malfunction point is present is found, and thus a person who performs maintenance accurately estimates time for searching a fault point. Therefore, in order to shorten a searching time and accomplish maintenance within a target blackout time, an optimal number of the persons who perform maintenance can be allocated, and thus costs of maintenance can be reduced. In addition, if the invention is applied to a system or the like which monitors an electric power system and supports a facility planning, the locating error is estimated from a selecting stage of a sensor, and therefore, a low cost sensor which has minimum errors is selected, and costs of a facility can be reduced. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]      FIG. 1  illustrates a software configuration of a fault point locating device  1 . 
           [0013]      FIG. 2  illustrates a software configuration of an electric power system monitoring system. 
           [0014]      FIG. 3  illustrates a software configuration of a facility planning support system. 
           [0015]      FIG. 4  illustrates a hardware configuration of the fault point locating device  1 . 
           [0016]      FIG. 5  illustrates a hardware configuration of the electric power system monitoring system. 
           [0017]      FIG. 6  illustrates the software configuration of the facility planning support system. 
           [0018]      FIG. 7  illustrates an entire view of an electric power system. 
           [0019]      FIG. 8  illustrates an impedance table. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0020]    Hereinafter, examples will be described with reference to drawings. 
       Example 1 
       [0021]      FIG. 1  is an example of a diagram of a software configuration of a fault point locating device  1  in this example. In  FIG. 1 , a sensor value  2 , a sensor error  3 , an impedance  4 , and an impedance variation parameter  5  are input values of a fault point locating system  21 . In addition, a fault point range  11  and a determination not possible flag  12  are output values of the fault point locating device  1 . Sensor value range calculating means  6 , impedance range calculating means  7 , combination creating means  8 , fault point locating means  9 , and determining means  10  are processes of the invention. First, the input values and the output values will be described hereinafter. 
         [0022]    As the sensor value  2 , there are a voltage Vg at the time of the fault, current Ig at the time of the fault, and current Ipre before the fault, which are measured by a voltage sensor  209  in  FIG. 7 . These values are finely stored at a cycle of eight times or more of a system frequency by a controller  212 , and are copied to the fault point locating system  21  through communication or a recording medium such as a USB memory. Also, in the controller  212 , in order to store the current Ig at the time of the fault and the current Ipre before the fault, generation of fault needs to be detected. In this detection, it is detected whether or not current is deviated from a range of normal current which is set in advance. 
         [0023]    The sensor error  3  is a value obtained by normalizing a difference between a measurement value and a true value of the voltage sensor  209  and an electric current sensor  210  in  FIG. 7 , and is a value from zero to 1. The impedance  4  is an impedance  4  of an electric power system from a busbar  203  to a load  207  in  FIG. 7 . The impedance variation parameter  5  is a temperature or time. Any one of the parameters is used by the impedance range calculating means  7 . In a case in which the parameter is a temperature, temperatures of the busbar  203 , a transmission and distribution line, or peripherals thereof which are measured by a temperature sensor  211  in  FIG. 7  are stored. In a case in which the parameter is time, a value of a timer  103  of the fault point locating device  1  illustrated in  FIG. 5  is used. 
         [0024]    Next, processes of the example will be described in order of processing. 
         [0025]    First, the sensor value range calculating means  6  calculates a minimum current value Ipremin before the fault, a maximum current value Ipremax before the fault, a minimum current value Igmin after the fault, a maximum current value Igmax after the fault, a minimum voltage value Vgmin after the fault, and a maximum voltage value Vgmax after the fault, using (Equation 3) to (Equation 8). However, an error E1 of the electric current sensor  210  is set to (0≦E1≦1), and an error E2 of the voltage sensor  209  is set to (0≦E2≦1). 
         [0000]      [ I   premin   =I   pre ×(1− E   1 )  [Equation 3]
 
         [0000]      [ I   premax   =I   pre ×(1+ E   1 )  [Equation 4]
 
         [0000]        I   gmin   =I   g ×(1− E   1 )  [Equation 5]
 
         [0000]        I   gmax   =I   g ×(1+ E   1 )  [Equation 6]
 
         [0000]        V   gmin   =V   g ×(1− E   2 )  [Equation 7]
 
         [0000]        V   gmax   =V   g ×(1+ E   2 )  [Equation 8]
 
         [0026]    Finally, current ranges [Igmin, Igmax] at the time of the fault, current ranges [Ipremin, Ipremax] before the fault, and voltage ranges [Vgmin, Vgmax] at the time of the fault which are obtained are transmitted to the combination creating means  8 . 
         [0027]    Next, the impedance range calculating means  7  calculates a minimum impedance value ZLmin and a maximum impedance value ZLmax. First, an example of which a temperature is set as the impedance variation parameter  5  is considered. Since the impedance may be considered to be linearly changed due to the temperature, when the temperature is a temperature T, the impedance is obtained using ZL=f(T). In addition, if the temperature sensor  211  has a sensor error E3, ZLmin and ZLmax are respectively obtained using (Equation 9) and (Equation 10). 
         [0000]        Z   Lmin   =f ( t ×(1− E   3 ))  [Equation 9]
 
         [0000]        Z   Lmax   =f ( t ×(1+ E   3 )  [Equation 10]
 
         [0028]    In addition, an example of which an impedance table  109  illustrated in  FIG. 8  is included inside the impedance range calculating means  7  instead of a function f(t) is considered. Since a temperature of a distribution line is changed depending on a temperature of air and the temperature is changed by a time T, the minimum impedance value ZLmin and the maximum impedance value ZLmax in each time are stored in the impedance table  109 . In the example, the each time means every hour; however, the time may be a time (for example, unit of 10 minutes) having a more finely divided width or a time (for example, one month) having a more greatly divided width. Finally, impedance ranges [ZLmin, ZLmax] which are obtained are transmitted to the combination creating means  8 . 
         [0029]    Next, the combination creating means  8  creates a combination {current at the time of the fault, current before the fault, a voltage at the time of the fault, and an impedance} of input parameters of the fault point locating means  9 . The combination creating means  8  selects one each value from the current ranges [Igmin, Igmax] at the time of the fault, the current ranges [Ipremin, Ipremax] before the fault, the voltage ranges [Vgmin, Vgmax] at the time of the fault, and the impedance ranges [ZLmin, ZLmax], and creates a combination of the selected values. In the example, 16 values of a minimum value and a maximum value of each of the values are selected. In order to calculate a malfunction section with higher accuracy, it is possible to divide a closed section into a section of a designated number, and to create each combination of values. Finally, the entire created combination {current at the time of the fault, current before the fault, a voltage at the time of the fault, and an impedance} is transmitted to the fault point locating means  9 . 
         [0030]    Next, the fault point locating means  9  calculates a distance m from the busbar  203  to the fault point according to an algorithm of the fault point. As illustrated in NTL 1, many fault point algorithms are proposed; however, any method can also be applied to the embodiment. The invention adopts a scheme disclosed in NTL 1. In this case, if {current Ig at the time of the fault, current Ipre before the fault, a voltage Vg at the time of the fault, and an impedance ZL} is substituted to (Equation 1), the distances m are obtained. The entire combination obtained by the combination creating means  8  is applied to Equation 1, and all of the obtained distances mare transmitted to the determining means  10 . 
         [0031]    Finally, the determining means  10  calculates a maximum value and a minimum value among the obtained m described above. In the example, since 16 m are obtained, a maximum value and a minimum value of m are obtained using a bubble sort. These values are output as the fault point range  11 . In addition, impedances, currents at the time of the fault, currents before the fault, and voltages at the time of the fault with the maximum value and the minimum value of m may be output. If m of the fault point range  11  is satisfied with m&lt;0 or m&gt;1, a malfunction point is not present on a distribution system, and thus it becomes an abnormal value. At this time, one or more of the impedance, the current at the time of the fault, the current before the fault, and the voltage at the time of the fault are possible to be errors. Therefore, in order to notify this malfunction, a determination not possible flag  12  is output. In addition, the impedance, the current at the time of the fault, the current before the fault, and the voltage at the time of the fault may be output because of debug. 
         [0032]      FIG. 4  is an example of a hardware configuration of the fault point locating device  1  in the example. In  FIG. 4 , a computer, in which a CPU  101 , a RAM  102 , the timer  103 , a communicating device  104 , a program file  107 , and a data file  106  are connected by a system bus  105 , constitutes the fault point locating system  21 . The CPU  101  of the computer executes the fault point locating system  21  of the program file  107 . The RAM  102  is a memory temporally storing result data during calculation of the fault point locating system  21 . 
         [0033]    The program file  107  and the data file  106  are constituted by a non-volatile memory such as flash memory or a magnetic disk. In the program file  107 , the fault point locating system  21  which is executed by the CPU  101  is stored. The fault point locating system  21  is constituted by the sensor value range calculating means  6 , the impedance range calculating means  7 , the combination creating means  8 , the fault point locating means  9 , and the determining means  10 . In the data file  106 , the sensor value  2 , the sensor error  3 , the impedance  4 , and the impedance variation parameter  5  which are input by the fault point locating system  21  are stored. In addition, the fault point range  11  and the determination not possible flag  12  which are output by the fault point locating system  21  are stored. The communicating device  104  may be a wired network such as Ethernet (registered trademark), CAN, or LIN, or may be a wireless communication such as IEEE 802. 11a or Zigbee (registered trademark). One of them is selected depending on maintenance statuses or costs of a public communication network. 
       Example 2 
       [0034]    In this example, an example when the fault point locating system  21  of Example 1 is mounted on the electric power system monitoring system  13  is described. As illustrated in  FIG. 7 , the electric power system monitoring system  13  is a system for displaying a voltage and current on the monitor  108  in real time using online information such as the voltage sensor  209  or the electric current sensor  210  of the electric power system, and rating a fault point. 
         [0035]      FIG. 2  is an example of a diagram of the software configuration of the electric power system monitoring system  13  in the example. In  FIG. 2 , the voltage sensor  209 , the electric current sensor  210 , and the temperature sensor  211  are input devices of the electric power system monitoring system  13 . As the impedance variation parameter  5 , in a case in which a temperature is not used as the parameter, the temperature sensor  211  can be omitted. The monitor  108  is an output device. Communicating means  14 , fault determining means  15 , the fault point locating system  21 , and displaying means  16  are processes of the invention. The fault point locating system  21  performs the same processes as those of Example 1. First, the input device will be described as follows. 
         [0036]    The voltage sensor  209  measures the voltage Vg at the time of the fault. The electric current sensor  210  measures the current Ig at the time of the fault, and the current Ipre before the fault. In addition, the temperature sensor  211  measures any one of temperatures of the busbar  203 , transmission and distribution lines, and peripherals thereof. These values are finely stored at a cycle of eight times or more of a system frequency by the controller  212 , and are transmitted to the electric power system monitoring system  13  through communication. 
         [0037]    Next, processes of the example will be described in order of processing. 
         [0038]    The communicating means  14  collects pieces of information relating to the voltage Vg at the time of the fault, the current Ig at the time of the fault, the current Ipre before the fault, and the temperatures T by communicating with the controller  212 . The controller  212  determines that there is a fault in the voltage sensor  209 , the electric current sensor  210 , the temperature sensor  211  when the current is deviated from a designated range by polling the electric current sensor  210  at the cycle of eight times or more of the system frequency, and updates Ig and Vg. If the fault is removed, Ig and Vg are cleared to be zero. The communicating means  14  always performs polling at a predetermined cycle using the timer  103 . 
         [0039]    Next, the fault determining means  15  determines whether or not new fault is generated. In the controller  212 , as illustrated in Example 1, since generation of the fault is detected in order to store the current Ig at the time of the fault and the current Ipre before the fault, this result may be used. That is, if the current Ig at the time of the fault and the voltage Vg at the time of the fault are not cleared to be zero, it is possible to determine that the fault is generated. When the fault is generated, Vg, Ig, and Ipre are written as the sensor value  2 . In addition, the temperature T or the current timer  103  are written as the impedance variation parameter  5 . After that, the fault point locating system  21  is driven. 
         [0040]    Next, the fault point locating system  21  outputs the fault point range  11  and the determination not possible flag  12  in the same manner as that of the processes of Example 1. 
         [0041]    Finally, the displaying means  16  displays the fault point range  11  and the determination not possible flag  12  on the monitor  108 . The fault point range  11  may represent a range of percentages of m, and may be shown in a system diagram illustrated in  FIG. 7 , or on a map. 
         [0042]      FIG. 5  is an example of a diagram of a hardware configuration of the electric power system monitoring system  13  in the example.  FIG. 5  is almost the same as that of  FIG. 4  of Example 1, but is different from  FIG. 4  in that the monitor  108  is connected to the system bus  105  and the communicating means  14 , the fault determining means  15 , and the displaying means  16  are stored in the program file  107 . The communicating means  14  is capable of communicating with the controller  212  which is connected to a network through the communicating device  104 . In addition, the displaying means  16  is capable of displaying characters and images on the monitor  108 . 
       Example 3 
       [0043]    In this example, an example when the fault point locating system of Example 1 is mounted in the facility planning support system  17  is illustrated. 
         [0044]    The facility planning support system  17  is a system for obtaining accuracy of locating a fault point at the time of generating power flow or fault of future by a simulation, and for supporting facility investment plan, using offline information such as a log of the voltage sensor  209  or the electric current sensor  210 . 
         [0045]      FIG. 3  is an example of a diagram of a software configuration of a facility planning system in the example. In  FIG. 3 , a sensor record data  18  and a user creating data  19  are input of the facility planning support system  17 . The monitor  108  is an output device. Parameter generating means  20 , the fault point locating system  21 , and the displaying means  16  are processes of the invention. The fault point locating system  21  performs the same processes as those of Example 1. First, the input device will be described as follows. 
         [0046]    The sensor record data  18  is a log of the voltage sensor  209 , the electric current sensor  210 , and the temperature sensor  211 . A log at the time of generating the fault is used in order to evaluate accuracy of locating a fault point. Specifically, a voltage and current of each phase at the time of one-line ground fault, two-line ground fault, two-line short fault, three-line ground fault, and three-line short fault, are provided in chronological order. A divided width of the time is equal to or more than eight times of the system frequency. The user creating data  19  is also a chronological data of a voltage, a current, a temperature of each phase at the time of the fault, as with the sensor record data  18 . The user creating data  19  is data created by a user, in order to evaluate accuracy of locating the fault point relating to voltage variation or current variation which is not logged. 
         [0047]    Next, processes of the example will be described in order of processing. 
         [0048]    The parameter generating means  20  determines whether or not current deviates from a designated range by scanning the sensor record data  18 . If there is a deviated current, it is determined that the fault is generated, and the data is extracted as the voltage Vg at the time of the fault, the current Ig at the time of the fault, and the temperature T. In addition, the current immediately before the data is extracted as the current Ipre before the fault. Also, Vg, Ig, and Ipre are written as the sensor value  2 . In addition, the temperature T or the time is written as the impedance variation parameter  5 . After that, the fault point locating system  21  is driven. 
         [0049]    Processes of the fault point locating system  21 , and the displaying means  16  are the same as those of Example 2. 
         [0050]      FIG. 6  is an example of a diagram of a hardware configuration of the facility planning support system  17  in the example.  FIG. 6  is almost the same as that of  FIG. 4  of Example 1, but is different from  FIG. 4  in that the monitor  108  is connected to the system bus  105 , and sensor value generating means and the displaying means  16  are stored in the program file  107 . The displaying means  16  is capable of displaying characters and images on the monitor  108 . 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               1  fault point locating device 
               2  sensor value 
               3  sensor error 
               4  impedance 
               5  impedance variation parameter 
               6  sensor value range calculating means 
               7  impedance range calculating means 
               8  combination creating means 
               9  fault point locating means 
               10  determining means 
               11  fault point range 
               12  determination not possible flag 
               13  electric power system monitoring system 
               14  communicating means 
               15  fault determining means 
               16  displaying means 
               17  facility planning support system 
               18  sensor record data 
               19  user creating data 
               20  parameter generating means 
               21  fault point locating system 
               101  CPU 
               102  RAM 
               103  timer 
               104  communicating device 
               105  system bus 
               106  data file 
               107  program file 
               108  monitor 
               109  impedance table 
               201  distribution substation 
               202  behind impedance 
               203  busbar 
               204  impedance from busbar to fault point 
               205  fault point 
               206  impedance from fault point to load 
               207  load 
               208  resistance of fault point 
               209  voltage sensor 
               210  electric current sensor 
               211  temperature sensor 
               212  controller 
               213  communication network