Abstract:
A measurement or protective device has an interface for establishing a connection to at least one measurement transducer and a further interface for connecting to a superordinate data bus. In order to allow the measurement or protective device to be used in a particularly universal manner and to make it possible for complex protective systems to be constructed in a particularly cost-effective manner, a communication unit is provided in the measurement or protective device. The communication unit is connected to both interfaces, can be directly connected to the measurement transducer via the interface, can be connected to the superordinate data bus via the further interface, forms messages and transmits them to the superordinate data bus.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a measurement or protective device having an interface which is suitable for establishing a connection to at least one measurement transducer and a further interface which is suitable for connection to a superordinate data bus. 
     Such measurement or protective devices are known in the field of electrical protective technology. These previously known measurement or protective devices are not connected to measurement transducers directly but rather via so-called “merging units” and switches (for example Ethernet switches). The function of the “merging units” is to process phase-conductor-related samples from the measurement transducers and to use them to form data messages which can be processed further by the respective measurement or protective device. As the name already implies, the phase-conductor-related samples relate to current and/or voltage in the phase conductors of an electrical system which are assigned to the respective measurement transducer. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is based on the object of specifying a measurement or protective device which can be used in a particularly universal manner and makes it possible to construct complex protective systems in a particularly cost-effective manner. 
     According to the invention, this object is achieved by means of a measurement or protective device having the features as claimed in claim  1 . Advantageous refinements of the measurement or protective device according to the invention are specified in subclaims. 
     According to this, the invention provides for the measurement or protective device to contain a communication unit which is connected to the two interfaces, can be directly connected to the measurement transducer by means of one interface, can be directly connected to the superordinate data bus by means of the further interface, uses phase-conductor-related samples from the measurement transducer to form sampling-time-related messages and transmits the latter to the superordinate data bus and thus provides them for further consumers. 
     A fundamental advantage of the measurement or protective device according to the invention can be seen in the fact that it enables direct connection both to a superordinate data bus and to one or more measurement transducers. The direct connection of the measurement or protective device is made possible by the communication unit according to the invention which is capable of directly processing the phase-conductor-related samples from the measurement transducer and using them to form sampling-time-related messages. In other words, in the measurement or protective device according to the invention, the function of the physically separate “merging units” and “switches” mentioned in connection with the previously known prior art has been moved to the communication unit, with the result that, in contrast to the prior art, the measurement or protective device according to the invention allows direct connection to measurement transducers. 
     One advantageous refinement of the measurement or protective device provides for the two interfaces to form data bus interfaces; for example, one interface is suitable for connection to a process bus and the further interface is suitable for connection to a station bus. 
     It is considered to be particularly advantageous if the measurement or protective device has two 3-port network connections each having two external ports and one internal port, the two external ports of one 3-port network connection forming one interface and the two external ports of the other 3-port network connection forming the other interface, and the two internal ports of the two 3-port network connections being connected to the communication unit. On account of the two external ports, 3-port network connections enable full-duplex operation of the data bus, thus achieving a particularly high level of fault tolerance. Suitable 3-port network connections are described, for example, in the German laid-open specification DE 102 60 806 A1. The two external ports of one network connection are preferably suitable for direct connection to a process bus and the two external ports of the other network connection are preferably suitable for direct connection to a station bus. 
     The measurement or protective device can be produced in a particularly cost-effective manner if the communication unit and the two network connections are integrated, for example monolithically, in a freely programmable gate array. 
     The communication unit is preferably configured in such a manner that it uses the phase-conductor-related samples applied to the internal port of one network connection to form sampling-time-related messages and outputs the latter to the internal port of the other network connection. 
     The communication unit preferably reduces the sampling rate of the phase-conductor-related samples applied to the internal port of one network connection. For example, it uses the phase-conductor-related samples with their reduced sampling rate to form the sampling-time-related messages; alternatively, data reduction is carried out after the messages have been formed or while the messages are being formed. 
     By way of example, the communication unit is configured in such a manner that it reduces the sampling rate of the phase-conductor-related samples applied to the internal port of one network connection by using only every n-th sample further and leaving all remaining samples out of consideration, n being greater than two. 
     Alternatively, the communication unit may also be configured in such a manner that it uses the phase-conductor-related samples applied to the internal port of one network connection to form pointer values and uses the latter to form the sampling-time-related pointer messages. 
     For the rest, it is considered to be advantageous if the communication unit subjects the phase-conductor-related samples applied to the internal port of one network connection to a renewed sampling operation. 
     Such a “renewed” sampling operation can be carried out, for example, in such a manner that the communication unit uses the phase-conductor-related samples applied to the internal port of one network connection to reconstruct the temporal profile of the electrical signal (current or voltage of the respective phase conductor) sampled, resamples the reconstructed signal at a second sampling rate which differs from the original sampling rate, uses these new samples formed in this manner to form the messages and outputs the messages to the internal port of the other network connection. 
     The communication unit preferably has at least one digital signal processor for the purpose of forming the new samples. 
     In order to transmit the data, the two interfaces of the measurement or protective device preferably operate in accordance with the IEC 61850 standard; the sampling times are synchronized in accordance with the IEEE 1588 standard. With regard to the information relating to the samples, the communication unit preferably forms the messages in accordance with the rules of the IEC 61850 standard. With regard to all other information, that is to say all information apart from the information relating to the samples, the communication unit preferably forms the messages in accordance with the IEC 61850-8-1 standard. 
     The process bus and the station bus preferably operate in accordance with a real-time Ethernet standard (cf. property rights and property right applications CN 1476702, DE 10058524, EP 1388238, JP 2004515122; US 2002064157; WO 200243336; DE 10147422; EP 1430628; US 2004249982; WO 2003028259); accordingly, the two network connections are each preferably suitable for connection to a real-time Ethernet ring. 
     The invention also relates to a protective system having a measurement or protective device, a measurement transducer and a superordinate control system. 
     As regards such a protective system, the invention is based on the object of achieving the possibility of particularly cost-effective implementation. 
     According to the invention, this object is achieved by means of a protective system having a measurement or protective device, a measurement transducer and a superordinate data bus, the two external ports of one 3-port network connection of the measurement or protective device being connected to the measurement transducer by means of a process bus, and the two external ports of another 3-port network connection of the measurement or protective device being connected to the superordinate control system by means of a station bus. 
     As regards the advantages of the protective system according to the invention, reference is made to the above statements in connection with the measurement or protective device according to the invention. 
     The invention is explained below using an exemplary embodiment; in the drawing 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  shows a protective system having two measurement devices according to the prior art, and 
         FIG. 2  shows one exemplary embodiment of a protective system according to the invention with one exemplary embodiment of a measurement and/or protective device according to the invention. 
     
    
    
     DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a protective system according to the prior art. A protective device  10  which is connected to a superordinate data bus  30  can be seen. The protective device  10  is connected, by means of a data line  20 , to an Ethernet switch (Ethernet message distributor)  25  which is also connected to “merging units”  60  and  70  by means of further data lines  40  and  50 . The term “merging unit” is understood below as meaning devices which combine data—in this case current and voltage samples U and I—applied to the input side and forward them as data messages on the output side. 
     Both “merging units”  60  and  70  are each connected to six measurement transducers, to be precise to three respective current transducers and to three respective voltage transducers. The measurement transducers are visualized overall in  FIG. 1  by a block  100 . 
     The protective system according to  FIG. 1  operates as follows: 
     The “merging unit”  60  receives phase-conductor-related samples U 1  and I 1  from the measurement transducers  100  and processes them to form data messages T 1  which it transmits to the Ethernet switch  25  by means of the data line  40 ; the Ethernet switch  25  then forwards the data messages T 1  to the protective device  10 . The task of the “merging unit”  60  is to carry out a type of “data combination” in order to form the data messages T 1 . The data messages T 1  formed in this manner are transmitted to the protective device  10  and are evaluated there. The protective device  10  then transmits the data messages T 1  to the superordinate data bus  30  and thus to further consumers. 
     So that the two “merging units”  60  and  70  generate their data messages T 1  and T 2  in synchronism with one another, the two “merging units”  60  and  70  are each synchronized using synchronization pulses fi, additional devices which are not shown in  FIG. 1  being required for this purpose. 
     In summary, in the protective system according to  FIG. 1 , it is not possible to directly connect the protective device  10  to the measurement transducers  100  since at least one “merging unit” and one Ethernet switch always have to be interposed between the protective device and the measurement transducer. 
       FIG. 2  illustrates one exemplary embodiment of a protective system  200  according to the invention. The protective system  200  has a superordinate control system  210  which is connected to a measurement and/or protective device  230  by means of a superordinate data bus  220  which is referred to below as a station bus. For reasons of clarity, the illustration according to  FIG. 2  illustrates only a single measurement and/or protective device  230  of this type; it goes without saying that a plurality of measurement and/or protective devices  230  which receive and evaluate the messages on the station bus  220  can also be connected to the station bus  220 . 
     The measurement and/or protective device  230  is also connected to a further data bus  240  which is referred to below as a process bus and makes it possible to connect the measurement and/or protective device  230  to one or more measurement transducers  250 . The measurement transducers  250  are connected to phase conductors (not shown in  FIG. 2 ) of an electrical system with a system frequency of 50 Hz or 60 Hz. 
       FIG. 2  also shows the internal structure of the measurement and/or protective device  230 . A communication unit  300  which is connected to two 3-port network connections  310  and  320  which are physically contained in the measurement and/or protective device and are capable of full duplex operation can be seen. The 3-port network connections  310  and  320  may be, for example, those described in the German laid-open specification DE 102 60 806 A1. 
     One of the two 3-port network connections  310  has two external ports  330  and  340  which allow an interface  350  for connecting the measurement and/or protective device  230  to the process bus  240 . The term “port” is thus to be understood as meaning an electrical bus connection or a bus interface. An internal port  360  of one 3-port network connection  310  is connected to a process-bus-side connection A 300   a  of the communication unit  300 . 
     The further 3-port network connection  320  likewise has two external ports  400  and  410 ; these external ports  400  and  410  form an interface  420  for connecting the measurement and/or protective device  230  to the station bus  220 . An internal port  430  of the further 3-port network connection  320  is connected to a station-bus-side connection A 300   b  of the communication unit  300 . 
     The two 3-port network connections  310  and  320  and the communication unit  300  are shown in  FIG. 2  as separate elements which are contained in the measurement and/or protective device  230 . The two 3-port network connections  310  and  320  and the communication unit  300  are preferably formed by a single physical unit, preferably by a freely programmable gate array, for example a monolithically integrated array. 
     The protective system  200  according to  FIG. 2  operates as follows: 
     The measurement transducers  250  generate phase-conductor-related samples U and I which are transmitted to the measurement and/or protective device  230  via the process bus  240 . The phase-conductor-related samples U and I are transmitted on the process bus  240  in accordance with a real-time Ethernet method (cf. property rights and property right applications CN 1476702, DE 10058524, EP 1388238, JP 2004515122; US 2002064157; WO 200243336; DE 10147422; EP 1430628; US 2004249982; WO 2003028259) and in accordance with the IEC 61850 standard. Specifically, the samples U and I are transmitted in the form of messages Tp which are formed in accordance with the rules of the IEC 61850 standard. For the rest, that is to say with regard to data other than the samples, the messages are formed in accordance with the IEC 61850-8-1 standard. 
     The station bus  220  operates just like the process bus  240 , that is to say likewise in accordance with a real-time Ethernet method and in accordance with the IEC 61850 standard. The two data buses  220  and  240  are each operated in the full duplex mode; this is possible since each of the two 3-port network connections  310  and  320  respectively has two output-side ports for connection to the respective data bus. 
     The messages containing the samples Tp are formed on the basis of a time clock which has a temporal accuracy of one microsecond. 
     When transmitting the samples U and I via the process bus  240 , a time stamp (for example “sample counter” value) is respectively added to each sample. The “sample counter value” indicates the time slot for the seconds jump of the synchronization clock in which the respective phase-conductor-related sample has been formed. Since the bus clock is set precisely to one microsecond, the respective sampling time can be determined for each transmitted sample with an accuracy of one microsecond. 
     A multiplicity of phase-conductor-related samples U and I which have been determined at different points in time and accordingly contain different “sample counter values” arrive at the measurement and/or protective device  230 . The measurement and/or protective device  230  sorts the phase-conductor-related samples U and I in accordance with their respective time slot or their respective “sample counter value” and uses these samples to generate data messages Ts which respectively relate to the same sampling time or to the same “sample counter value”. The correspondingly formed messages Ts are transmitted in the direction of the station bus  220  using the further 3-port network connection  320 . 
     When processing the phase-conductor-related samples U and I from the measurement transducers  250 , the measurement and/or protective device  230  preferably carries out “downsampling”. This means that the number of samples provided by the measurement transducers  250  is reduced, before they are forwarded to the station bus  220 , by discarding nine out of ten samples from the measurement transducers  250 , for example, and keeping only one respective single sample. If the sampling rate in the measurement transducers  250  is 10 kHz or 20 kHz, for example, only a sampling rate of 1 or 2 kHz is forwarded on the station bus in the form of the messages Ts. Despite the reduction in the sampling rate, “transparency” of the measured values—when seen from the superordinate control system  210 —is nevertheless retained because, despite only every tenth sample being transmitted by the station bus  220 , sufficient measured values which characterize the respective measured value situation in each of the measurement transducers  250  to a sufficient extent are still provided. The resultant transparency is diagrammatically indicated by the reference symbol V in  FIG. 2 . 
     Instead of the described reduction in the number of samples, in which only every n-th (for example n=10) sample is used further, data reduction may also take place by converting the samples into complex measured value pointers. In this variant, the measurement and/or protective device  230  uses the phase-conductor-related samples U and I received from the measurement transducers  250  to determine complex measured value pointers which indicate the magnitude and the phase of the current or voltage on the associated phase conductors. 
     In the case of such data reduction by means of “pointer conversion”, the data rate can be reduced to a very significant extent, with the result that a transmission rate of 50 Hz, for example, suffices to characterize the measured values from the current transducers  250 . 
     Frequency tracking can also be carried out in the measurement and/or protective device  230  or in the communication unit  300  of the measurement and/or protective device  230  by using the time-related and phase-conductor-related samples U and I from the measurement transducers  250  to first of all reconstruct the temporal profile of the respective electrical “system” signal sampled. The temporal profile reconstructed in this manner is then “resampled”. Such “resampling”—that is to say repeated sampling—makes it possible to introduce another time standard, with the result that the samples relate to a new sampling clock, namely the sampling clock of the resampling operation. 
     Such a new time standard makes it possible to track frequencies and is expedient, for example, if transmission of the samples by the station bus  220  is intended to depend on the respective system frequency: if, for example, the system frequency of the system changes from 50 Hz to 51 Hz, the samples will be shifted relative to the temporal profile of the measurement signal in the case of a fixed sampling clock. If distribution of the samples which is matched to the respective system frequency of the measurement signal is then intended to be achieved, the communication unit  300  distributes the predefined number of samples per period over the respective period duration of the measurement signal measured and thus matches distribution of the samples to the respective system frequency. Frequency tracking may be necessary, for example, if the station bus  220  requires samples whose frequency has been tracked and if the process bus provides only samples with a fixed time. 
     As already mentioned, the two data buses  220  and  240  are preferably operated with a bus clock which is a great deal higher than the fundamental frequency of the measurement signals to be characterized and the system frequency of the electrical system. For example, samples can be formed in a very effective manner with a bus clock whose timing is set precisely to one microsecond. 
     In order to avoid the possibility of data being lost in the event of the ring structure of the two data buses  220  and  240  being interrupted, the two data buses  220  and  240  preferably operate in a full duplex mode, as already mentioned. 
     In summary, it can be stated that, on account of the described configuration of the measurement and/or protective device  230 , the protective system  200  according to  FIG. 2  makes it possible to pass through data between the process bus  240  and the station bus  220  in a virtually transparent manner, decoupling of the samples between the two data buses nevertheless being ensured by the communication unit  300 ; the communication unit  300  carries out—as explained—a “merging function” in this case by further processing the phase-conductor-related and time-related samples U and I provided by the measurement transducers  250  and using them to produce the sampling-time-related messages Ts for forwarding to the station bus  220 . For the “merging process”, the communication unit  300  is preferably equipped with one or more digital signal processors; such a signal processor is labeled, by way of example, with the reference symbol  500  in  FIG. 2 . 
     In summary, the protective system  200  according to  FIG. 2  thus satisfies the following criteria:
         The phase-conductor-related and time-related samples from the measurement transducers  250  are synchronized in the microsecond range an account of the use of the IEEE 1588 standard;   a deterministic response is achieved by using the described real-time Ethernet transmission method with time synchronization in accordance with IEEE 1588;   there is ring redundancy on account of the full duplex operation of the two data buses  220  and  240 , thus increasing the fault tolerance;   there is decoupling between the two communication ring structures  220  and  240 , to be precise with regard to decoupled transmission of the digital transducer data from the measurement transducers  250  to the superordinate control system  210 ;   both data buses  220  and  240  have integrated switch functionality, for example Ethernet switch functionality.       

     On account of the features mentioned, the protective system  200  makes it possible to transmit the samples from the measurement transducers  250 , both at the process bus level and at the station bus level, in a manner that is synchronized for each sampling time. The samples are synchronized at the station bus level across all fields and are synchronized at the process bus level inside a field using all respective measurement points or measurement transducers. In this case, synchronization between the station bus  220  and the respective process bus  240  is ensured by the communication unit  300  of the measurement and/or protective device  230  which connects the two data buses  220  and  240 . 
     LIST OF REFERENCE SYMBOLS 
     
         
           10  Measurement and/or protective device 
           20  Data line 
           25  Ethernet switch 
           30  Superordinate data bus 
           40  Data line 
           50  Data line 
           60  Merging unit 
           70  Merging unit 
           100  Measurement transducer 
           200  Protective system 
           210  Superordinate control system 
           220  Station bus 
           230  Measurement and/or protective device 
           240  Process bus 
           250  Measurement transducer 
           300  Communication unit 
           310  3-port network connection 
           320  Further 3-port network connection 
           330 ,  340  External ports of one 3-port network connection 
           350  Δn interface 
           360  Internal port of one 3-port network connection 
           400 ,  410  External ports of the further 3-port network connection 
           420  Further interface 
           430  Internal port of the further 3-port network connection 
           500  Signal processor 
         U, I Current and voltage samples 
         fi Synchronization pulse 
         Ts, Tp Messages