Abstract:
A method, an arrangement, and a current measurement device with which a signal that characterizes a fault current in an electrical conductor having at least three conductor ends can be produced in a particularly simple fashion. In particular, a current measurement device is provided for measuring a current in a conductor. The current measurement device includes at least one measurement value input and at least one measurement value output, and has an arithmetic unit that adds a current measurement value corresponding to the current to a measurement value present at the at least one measurement value input. A resulting summation current measurement value is output at the at least one measurement value output.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an arrangement, method and device for measuring a current in a conductor. 
     SUMMARY 
     An object of the present invention is to provide a method that is particularly simple to execute for producing a signal that characterizes a fault current in an electrical conductor that has at least three conductor ends. In this context, a fault current is understood to be a current that flows out of the conductor, or that flows into the conductor, at a fault point of the conductor, for example a short-circuit point, and thus not at one of the conductor ends. 
     In order to achieve this object, according to the present invention, a method is provided for producing a fault signal that characterizes a fault current of an electrical conductor that has at least three conductor ends, using current measurement devices that are arranged in such a way that one of the current measurement devices is attached at each conductor end of the conductor and the current measurement devices are connected via data lines. The method the current in the respective conductor ends is measured using the current measurement devices, and current measurement values are formed. A measurement value, formed from the current measurement values of the other current measurement devices using addition that respects the sign, is transmitted to a selected current measurement device, using the selected current measurement device, an overall current value is formed from the current measurement values thereof and the measurement value, using addition that respects the sign, and the fault signal, is produced using the selected current measurement device if the absolute value of the overall current value exceeds a predetermined threshold value. The sign-respecting addition of the current measurement values can take place in the time domain or in the frequency domain. If the method according to the present invention is used in a three-phase alternating current system, the method is executed separately for each phase, i.e. for each phase conductor; in this context, each phase can be switched off individually in the case of a fault current. 
     An advantage of the method according to the present invention is that it is very fast, because in the method, the current measurement values of the other current measurement devices are first combined, by sign-respecting addition, to form one measurement value, and subsequently only this measurement value is transmitted to the selected current measurement device. Since only this single measurement value need be transmitted to the selected current measurement device, the overall quantity of data to be transmitted is very small; this results in the particularly high speed of the method according to the present invention, since the smaller the amount of data to be transmitted, the less is time required for this. In addition, only a single computational step need be executed in the selected current measurement device, consisting in the addition of the transmitted measurement value to the measured current measurement value of the selected current measurement device; the transmission of the previously determined measurement value therefore relieves the selected current measurement device of further computational steps, likewise resulting in an increase in speed. 
     The object is also achieved by a method according to the present invention for producing a fault signal that characterizes a fault current of an electrical conductor having at least three conductor ends, using current measurement devices arranged in such a way that one of the current measurement devices is attached to each conductor end of the conductor and the current measurement devices are connected via data lines. In the method the current in the respective conductor ends is measured using the current measurement devices, with formation of current measurement values, and a measurement value, formed from the current measurement values of a first group of the remaining current measurement devices by sign-respecting addition, is transmitted to a selected current measurement device, and an additional measurement value, formed from the current measurement values of a second group of the remaining current measurement devices by sign-respecting addition, is transmitted to the selected current measurement device. The second group contains all current measurement devices except for the selected ones and the current measurement devices of the first group. Using the selected current measurement device, an overall current value is formed from the current measurement values thereof and the two measurement values through sign-respecting addition, and the fault signal is produced using the selected current measurement device if the absolute value of the overall current value exceeds a predetermined threshold value. The advantages cited in connection with the first method also hold for the second method according to the present invention. A particular advantage of the second method, is that in this method the current measurement devices can be divided into two groups and a separate measurement value can be formed for each of the two groups. This can, for example, be advantageous if the two groups of current measurement devices are separated from one another by a large spatial distance and the formation and transmission of a single measurement value to the selected current measurement device would cause a particularly high expense. 
     Moreover, an arrangement according to the present invention is provided with which a fault signal characterizing a fault current in an electrical conductor having at least three conductor ends can be formed in a particularly simple fashion. 
     This object is achieved by an arrangement for producing a fault signal that characterizes a fault current of an electrical conductor having at least three conductor ends. A current measurement device, attached to each conductor end of the conductor, measures the current in its respective conductor end with formation of a current measurement value. The current measurement devices in the arrangement are connected to one another electrically by means of data lines in a chain-type structure in such a way that each internal current measurement device in the chain is connected, with a measurement value input, to a measurement value output of the current measurement device arranged upstream therefrom, and is connected, with a measurement value output, to a measurement value input of the current measurement device arranged downstream therefrom. A first current measurement device of the two current measurement devices arranged externally in the chain is connected, with its measurement value output, to a measurement value input of the internal current measurement device arranged downstream therefrom. The second of the two external current measurement devices is connected, with a measurement value input, to the measurement value output of the internal current measurement device arranged upstream therefrom. Each internal current measurement device has an arithmetic unit that adds, in sign-respecting fashion, its current measurement value to a measurement value, present at its measurement value input, of the respective upstream current measurement device, so as to form a summation current measurement value, and outputs the summation current measurement value as a measurement value at its measurement value output. The second external current measurement device has a control unit that outputs the fault signal as soon as an overall current value, formed by sign-respecting addition from the measurement value of the upstream internal current measurement device and its current measurement value, exceeds a predetermined threshold value. An advantage of this arrangement is the particularly high speed with which the fault signal is produced, since not all the current measurement values of the other current measurement devices are transmitted individually to the second external current measurement device. Instead, only a single measurement value is transmitted that contains the current sums of the remaining current measurement devices. This results in a particularly rapid production of the fault signal, because the overall quantity of data to be transmitted to the second external current measurement device is relatively small, since only a single measurement value is to be transmitted. An additional advantage of the arrangement according to the present invention is that only relatively few data lines are necessary for connecting the current measurement devices; given a line having N conductor ends, in the chain-type arrangement of the current measurement devices only (N−1) data lines are required, whereas, in contrast, given an arrangement in which all current measurement devices are connected to one another N*(N−1) data lines are required. 
     In order that, in addition to the second external current measurement device, at least one internal current measurement device can also produce the fault signal, within the scope of a development of the arrangement, the internal current measurement devices may be connected to one another in such a way that an additional measurement value input of an internal current measurement device is connected to an additional measurement value output of the internal current measurement device arranged downstream therefrom, and an additional measurement value output of an internal current measurement device is connected to an additional measurement value input of the internal current measurement device arranged upstream therefrom. The first external current measurement device is connected, with a measurement value input, to an additional measurement value output of the internal current measurement device arranged downstream therefrom. The second external current measurement device is connected, with a measurement value output, to an additional measurement value input of the internal current measurement device arranged upstream therefrom. Each internal current measurement device has an additional arithmetic unit that adds, in sign-respecting fashion, the current measurement value of its own current measurement device to an additional measurement value, present at its additional measurement value input, of the downstream current measurement device, so as to form an additional summation current measurement value, and outputs the resulting additional summation current measurement value at its additional measurement value output as an additional measurement value. At least one of the internal current measurement devices has a control unit that produces the fault signal as soon as the overall current value, formed by sign-respecting addition from the measurement values present at its two measurement value inputs and its measured current measurement value, exceeds the predetermined threshold value. The advantage of this arrangement is that a plurality of current measurement devices of the arrangement are able to produce the fault signal, since all the current measurement devices are provided with the required items of current information; in such an arrangement, 2*(N−1) data lines are then required. 
     In order that the fault signal can also be produced using the first external current measurement device, the first external current measurement device may have a control unit that produces the fault signal as soon as the overall current value—formed by sign-respecting addition from the measurement value present at its measurement value input and its measured current measurement value—exceeds the predetermined threshold value. 
     A particularly high degree of reliability can be achieved in the arrangement according to the present invention if the two external current measurement devices are connected with one another by at least one additional data line via which the overall current value is transmitted. This is because in such an arrangement the respectively determined overall current value can be transmitted between the two external current measurement devices for monitoring purposes; for example, the two external current measurement devices can check the readiness for operation of the overall arrangement by comparing their respective overall current values. An additional advantage of the additional data line is that the arrangement according to the present invention can continue to be operated even if one of the data lines is interrupted by a disturbance. 
     Within the scope of the present invention, a current measurement device is also proposed that can be used in the method or in the arrangement according to the present invention. This is a current measurement device for measuring a current in a conductor having at least one measurement value input and at least one measurement value output, as well as an arithmetic unit that adds a current measurement value corresponding to the current to a current measurement value present at the at least one measurement value input, and outputs the resulting summation current measurement value at the at least one measurement value output. The advantage of the current measurement device according to the present invention is that it has an arithmetic unit with which, for example, summation current measurement values can be formed, as was explained above in connection with the method or the arrangement according to the present invention. The advantages described above in connection with the method and with the arrangement thus hold in corresponding fashion for the current measurement device according to the present invention. 
     In order to facilitate the installation of the current measurement device according to the present invention, it is proposed, within the scope of a development of the current measurement device, that the arithmetic unit have a device with which the sign of the current measurement value can be changed. Such a current measurement device has the advantage that when connecting the current measurement device to a conductor or to a conductor end no attention need be paid to the direction of the current in the conductor or conductor end, because the sign of the current measurement value determined by the current measurement device can be changed if necessary, so to speak retroactively. This may be for example, important with respect to the sign-respecting addition of the current measurement values in the inventive method for producing a fault signal, since in the formation of a summation current measurement value the signs are of course to be taken into account. 
     If in addition a fault signal is also to be formed using the inventive current measurement device, may be as advantageous if the current measurement device has a control unit that outputs a signal for a fault current as soon as the summation current measurement value exceeds a predetermined threshold value. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an exemplary embodiment for an arrangement for the execution of the method according to the present invention. 
     FIG. 2 shows an exemplary embodiment for an arrangement according to the present invention. 
     FIG. 3 shows an exemplary embodiment for a current measurement device according to the present invention having an arithmetic unit and a control unit. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows an arrangement  3  for monitoring an electrical conductor  6  for a fault current. Electrical conductor  6  has a total of five conductor ends, including a first conductor end  9 , a second conductor end  12 , a third conductor end  15 , a fourth conductor end  18 , and a fifth conductor end  21 . A current measurement device is attached to each of conductor ends  9 ,  12 ,  15 ,  18 , and  21 , the current measurement devices being connected with one another via data lines, for example optical glass fibers. In this context, a selected first current measurement device  30  is connected to first conductor end  9  and additional current measurement devices  33 ,  36 ,  39 , and  42  are connected respectively to the remaining conductor ends  12 ,  15 ,  18 , and  21 . 
     Specifically, first current measurement device  30  is connected with its measurement value input E 30   a  to a measurement value output A 33   a  of first additional current measurement device  33  (referred to in the following as second current measurement device  33  for short). Upstream from this current measurement device, the second of the additional current measurement devices  36  (referred to in the following as third current measurement device  36  for short) is connected, with its measurement value output A 36   a , at a measurement value input E 33   a.    
     Moreover, first current measurement device  30  is connected, with an additional measurement value input E 30   b , to a measurement value output A 39   a  of the third of the additional current measurement devices  39  (referred to below as fourth current measurement device  39  for short). Upstream from this current measurement device, the fourth of the additional current measurement devices  42  (referred to in the following as fifth current measurement device  42  for short) is connected, with its measurement value output A 42   a , at a measurement value input E 39   a.    
     Five current measurement devices  30 ,  33 ,  36 ,  39 , and  42  are thus connected to one another in a chain-type structure, third current measurement device  26  and fifth current measurement device  42  forming external current measurement devices in the chain, and first current measurement device  30 , second current measurement device  33 , and fourth current measurement device  39  forming internal current measurement devices in the chain. 
     Arrangement  3  is used to monitor electrical conductor  6  for a fault current in the manner described below. 
     Using a clock (pulse) generator (not shown), a clock signal is transmitted to all current measurement devices. This clock signal ensures that all current measurement devices determine the respective current in their conductor end at respectively identical points in time. 
     After all the current measurement devices have measured, at one point in time, currents IA′, . . . , IE′ in respective conductor ends  9 ,  12 ,  15 ,  18 ,  21 , the following is carried out: 
     Current measurement value IC of third current measurement device  36 , corresponding to current IC′ in conductor end  15 , is outputted at measurement value output A 36   a  of third current measurement device  36 , and is transmitted to measurement value input E 33   a  of second current measurement device  33 . Using an arithmetic unit (not shown in FIG.  1 ), this second current measurement device  33  adds current measurement value IC, transmitted from third current measurement device  36 , to current measurement value IB, which corresponds to current IB′ flowing through conductor end  12  of second current measurement device  33 , forming a summation current measurement value IC+IB. This summation current measurement value IC+IB is transmitted to first current measurement device  30  from second current measurement device  33 . 
     Fifth current measurement device  42  at fifth conductor end  21 , as well as fourth current measurement device  39  at fourth conductor end  18 , operate in exactly the same manner as the second and the third current measurement device, i.e., each adds, in sign-respecting fashion, the current measurement value of its own respective current measurement device to a current measurement value—present at its measurement value input—of the current measurement device that may respectively be arranged upstream, taking into account the respective direction of current, and outputs the resulting summation current measurement value at its measurement value output as a measurement value. 
     A measurement value composed of current measurement values IB and IC thus arrives at the one measurement value input E 30   a  of first current measurement device  30 , and an additional measurement value, composed of current measurement values IE and ID, arrives at additional measurement value input E 30   b  of first current measurement device  30 . 
     An overall current value is thereupon formed in first current measurement device  30  by addition of the one measurement value and the additional measurement value, as well as the current measurement value IA that indicates the current IA′ in conductor end  9 ; this overall current value is equal to IA+IB+IC+ID+IE. 
     In accordance with the Kirchhoff laws, overall current value IA+IB+. . . +IE must be equal to 0 if no fault current has occurred; if the overall current value is not equal to 0, or if it exceeds a predetermined threshold value, a fault current has occurred. Here a fault current is understood to be a current flowing from conductor  6 , or into conductor  6 , at a fault point, for example a short-circuit point, and thus not at one of conductor ends  9 ,  12 ,  15 ,  18 , or  21 . Both types of fault current are reflected in the overall current value of current measurement device  30 , which can be determined by comparison of the overall current value with the threshold value, which is approximately equal to 0. 
     To sum up, on the basis of the overall current value in selected first current measurement device  30  it is determined, by comparison with the threshold value, whether a fault current has occurred. In this context, for example in a direct-current system, it is possible not only to determine whether a fault has occurred at all, but in addition it is of course also possible to determine the type of the fault, if after the comparison of the overall current value with the predetermined threshold value with respect to absolute value the sign of the overall current value is also evaluated. This is because, according to its allocation to a direction of current, the sign indicates whether the fault current flowed into conductor  6  or out of conductor  6 . 
     FIG. 2 shows an exemplary embodiment of an example arrangement according to the present invention. Current measurement devices  100 ,  103 ,  106 , and  109  are connected to one another electrically by means of data lines  112  to form a chain-type structure. Here two current measurement devices— 100  and  109 —are located at the outer end of the chain, and two current measurement devices— 103  and  106 —are located in the interior of the chain. 
     First internal current measurement device  103  is connected, with its measurement value input E 103   a , to a measurement value output A 100   a  of current measurement device  100 , which is arranged upstream from device  103 . A measurement value input E 106   a  of second internal current measurement device  106  is arranged downstream from first internal current measurement device  103 , at its measurement value output A 103   a , and a measurement value input E 109   a  of second external current measurement device  109  is in turn connected downstream from second current measurement device  106 , at its measurement value output A 106   a . Moreover, second external current measurement device  109  has a measurement value output A 109   b  that is connected with an additional measurement value input E 106   b  of second internal current measurement device  106 ; this second internal current measurement device  106  is moreover connected, with an additional measurement value output A 106   b , to an additional measurement value input E 103   b  of first internal current measurement device  103 . With an additional measurement value output A 103   b , this first internal current measurement device  103  is also connected with a measurement value input E 100   b  of first external current measurement device  100 . 
     Moreover, there is another data line  115 —a duplex line between—first external current measurement device  100  and second external current measurement device  109 . 
     In addition, each of current measurement devices  100 ,  103 ,  106 , and  109  is respectively connected to a conductor end of electrical conductor  130  (shown only schematically in FIG.  2 ), which has four conductor ends  120 ,  123 ,  126 , and  129 , and measures current IA′, IB′, IC′, or ID′ flowing at its conductor end, with formation of current measurement values IA, IB, IC, or ID. In this context, first external current measurement device  100  measures current measurement value or values IA at first conductor end  120 , first internal current measurement device  103  measures current measurement value or values IB at second conductor end  123 , second internal current measurement device  106  measures current measurement value or values IC at third conductor end  126 , and second external current measurement device  109  measures current measurement value or values ID at fourth conductor end  129 . 
     The arrangement according to FIG. 2 is operated as follows: current measurement value IA, measured using first external current measurement device  100 , is transmitted to the one measurement value input E 103   a  of first internal current measurement device  103  via data line  112 . In this data line, from its own current measurement value IB and from measurement value IA of first external current measurement device  100 , a summation current measurement value IA+IB is formed that is transmitted, as measurement value IA+IB, to the one measurement value input E 106   a  of second internal current measurement device  106 . In second internal current measurement device  106 , from measurement value IA+IB and its own current measurement value IC, a new summation current measurement value IA+IB+IC is formed that is transmitted as a measurement value to the one measurement value input E 109   a  of second external current measurement device  109 . In this current measurement device  109 , from measurement value IA+IB+IC and from its own current measurement value ID, an overall current value IA+IB+IC+ID is formed; current measurement device  109  produces, at a control output that is not depicted, a fault signal S for a fault current if overall current value IA+IB+IC+ID is not equal to 0, or if it exceeds a predetermined threshold value. 
     Simultaneously, current measurement value ID of second external current measurement device  109  is transmitted, as an additional measurement value, to additional measurement value input E 106   b  of second internal current measurement device  106 . In second internal current measurement  106 , the one measurement value IA+IB of first internal current measurement device  103  is now present at the one measurement value input E 106   a , and additional measurement value ID is now present at additional measurement value input E 106   b . From the two measurement values and from its own measured current measurement value IC, overall current value IA+IB+IC+ID is formed in current measurement device  106 , and the fault signal is formed as soon as overall current value IA+IB+IC+ID is not equal to 0 or exceeds the predetermined threshold value; fault signal S is then outputted at a control output (not shown). Moreover, in current measurement device  106 , an additional summation current measurement value IC+ID is formed from additional measurement value ID—present at additional measurement value input E 106   b —and its own current measurement value IC; the additional summation current measurement value IC+ID is outputted at additional measurement value output A 106   b  and is transmitted to first internal current measurement device  103 . 
     In first internal current measurement device  103 , the one measurement value IA of first external current measurement device  100  is now present at the one measurement value input E 103   a , and additional measurement value IC+ID is now present at additional measurement value input E 103   b . From the two measurement values IA and IC+ID, and from its own measured current measurement value IB, overall current value IA+IB+IC+ID is formed in current measurement device  103 , and the fault signal is formed as soon as overall current value IA+IB+IC+ID is not equal to 0 or exceeds the predetermined threshold value. Fault signal S is then outputted at a control output (not shown). Moreover, in current measurement device  103  an additional summation current measurement value IB+IC+ID is formed from additional measurement value IC+ID—present at additional measurement value input E 103   b —and its own current measurement value IB, and this additional summation current measurement value IB+IC+ID is outputted, at additional measurement value output A 103   b , to first external current measurement device  100 . 
     In first external current measurement device  100 , measurement value IB+IC+ID of first internal current measurement device  103  is now present at measurement value input E 100   b . In first external current measurement device  100 , overall current value IA+IB+IC+ID is formed from measurement value IB+IC+ID and from its own measured current measurement value IA, and the fault signal is formed as soon as overall current value IA+IB+IC+ID is not equal to 0 or exceeds the predetermined threshold value; fault signal S is then outputted at a control output (not shown). 
     To sum up, one measurement value or two measurement values are thus transmitted to each of the current measurement devices, and with these values each of the current measurement devices is able, using its own current measurement value, to determine the overall current value and to produce the fault signal. 
     Via additional data line  115 , the overall current value is transmitted between the two external current measurement devices  100  to and  109  for monitoring purposes; for this purpose, in the two current measurement devices it is checked whether the overall current value transmitted by the respective other external current measurement device corresponds to its own overall current value. If this is not the case, an alarm signal is produced indicating a fault in the measurement arrangement. A further advantage of additional data line  115  is that the arrangement according to FIG. 2 can also continue to be operated when data line  112  between two adjacent current measurement devices has been interrupted, since in such a case additional data line  115  can be used as a replacement for interrupted data line  112 . 
     The one arithmetic unit and the additional arithmetic unit can for example be formed by a data processing installation or by a microprocessor arrangement. 
     FIG. 3 shows an exemplary embodiment of a current measurement device that can be used in the arrangements according to FIGS. 1 and 2. Here, for purposes of explanation the current measurement device  103  according to FIG. 2 is used as a basis, and, in order to facilitate understanding of FIG. 3, reference characters identical to those used in FIG. 2 are used for components in FIG. 3 that have already been explained in connection with FIG.  2 . 
     Current measurement device  103  has a current input I 103   a  and an additional current input I 103   b , with which current measurement device  103  is connected to conductor end  123  of conductor  130  according to FIG. 2. A measurement unit  73  is connected with the two current inputs I 103   a  and I 103   b , and downstream from this measurement unit  73  there are arranged a summation element  76  as an arithmetic unit with an input E 76   a , an additional summation element  77  as an additional arithmetic unit with an input E 77   a , and a control unit  78  with an input E 78   a . Summation element  76  is connected, with an additional input E 76   b , with the one measurement value input E 103   a  of current measurement device  103 , and is connected, with an output A 76 , with the one measurement value output A 103   a  of current measurement device  103 . Additional summation element  77  is connected, with an additional input E 77   b , to additional measurement value input E 103   b  of current measurement device  103 , and is connected, with an output A 77 , to additional measurement value output A 103   b  of current measurement device  103 . 
     An additional input E 78   b  of control unit  78  is connected to the one measurement value input E 103   a  of current measurement device  103 ; an additional measurement value input E 78   c  of control unit  78  is connected with additional measurement value input E 103   b  of current measurement device  103 . 
     Using measurement unit  73 , current IB′ in conductor end  123  is measured, and a current measurement value IB corresponding to current IB′ is formed. This value arrives at arithmetic unit  76 , in which a summation current measurement value IA+IB is formed from this value and from the one measurement value IA at the one measurement value input E 103   a , and this summation current measurement value is transmitted as a measurement value to the one measurement value output A 103   a  of current measurement device  103 . 
     Current measurement value IB also arrives at additional summation element  77 , in which an additional summation current measurement value IB+IC+ID is formed from additional measurement value IC+ID at additional measurement value input E 103   b  of current measurement device  103  and from current measurement value IB, and this additional summation current measurement value IB+IC+ID is outputted as a measurement value at the additional measurement value output A 103   b  of current measurement device  103 . 
     Moreover, current measurement value IB is transmitted to control unit  78 , in which an overall current value IA+IB+IC+ID is formed from its own current measurement value IB, the one measurement value IA, and additional measurement value IC+ID. 
     In control unit  78 , this overall current value IA+. . . +ID is compared with a predetermined threshold value that is approximately equal to 0. If the overall current value exceeds the predetermined threshold value, a signal S is outputted at a control signal output S 103  of current measurement device  103 , indicating a fault current in conductor  130 . 
     Moreover, current measurement device  103  has a terminal Q 1  that is connected with control unit  78 . If current measurement device  103  is to be operated as an external current measurement device  100  or  109  according to FIG. 2, the current measurement device can be connected via this terminal Q 1  with the respective other external current measurement device via additional data line  115 , for the transmission of overall current value IA+. . . +ID. In control unit  78 , it is then compared whether its own overall current value is equal to the transmitted overall current value of the other external current measurement device. If this is not the case, an alarm signal A is outputted at an additional terminal Q 2 , indicating that a fault has occurred in the measurement arrangement. 
     The one and the other arithmetic unit  76  and  77 , as well as control unit  78 , can be formed by a data processing installation, for example a microprocessor arrangement.