(19)
(11)EP 2 335 082 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
22.07.2020 Bulletin 2020/30

(21)Application number: 08805187.5

(22)Date of filing:  09.10.2008
(51)International Patent Classification (IPC): 
G01R 19/25(2006.01)
G01R 15/14(2006.01)
H02H 3/05(2006.01)
G01R 15/08(2006.01)
H02H 1/04(2006.01)
(86)International application number:
PCT/EP2008/063547
(87)International publication number:
WO 2010/040409 (15.04.2010 Gazette  2010/15)

(54)

METHOD AND APPARATUS FOR DYNAMIC SIGNAL SWITCHING OF A MERGING UNIT IN AN ELECTRICAL POWER SYSTEM

VERFAHREN UND VORRICHTUNG ZUR DYNAMISCHEN SIGNALUMSCHALTUNG EINER ZUSAMMENFÜHRUNGSEINHEIT IN EINEM ELEKTRISCHEN STROMVERSORGUNGSSYSTEM

PROCÉDÉ ET APPAREIL POUR UNE COMMUTATION DE SIGNAL DYNAMIQUE D UNE UNITÉ DE FUSION DANS UN SYSTÈME D ALIMENTATION ÉLECTRIQUE


(84)Designated Contracting States:
AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MT NL NO PL PT RO SE SI SK TR

(43)Date of publication of application:
22.06.2011 Bulletin 2011/25

(73)Proprietors:
  • General Electric Technology GmbH
    5400 Baden (CH)
  • SCHNEIDER ELECTRIC ENERGY UK Ltd
    Leeds, LS1 5AB (GB)

(72)Inventor:
  • RICHARDS, Simon
    Staffordshire WS15 3DZ (GB)

(74)Representative: Openshaw & Co. 
8 Castle Street
Farnham, Surrey GU9 7HR
Farnham, Surrey GU9 7HR (GB)


(56)References cited: : 
EP-A- 0 300 075
US-A- 4 761 606
FR-A- 2 835 319
US-A1- 2003 234 642
  
  • JIAN ZHANG ET AL: "A new method to realize the relay protection of AOCT following IEC61850" POWER SYSTEM TECHNOLOGY, 2006. POWERCON 2006. INTERNATIONAL CONFERENCE ON, IEEE, PI, 1 October 2006 (2006-10-01), pages 1-5, XP031053473 ISBN: 978-1-4244-0110-9
  • JANSSEN M C ET AL: "IEC 61850 impact on substation design", TRANSMISSION AND DISTRIBUTION CONFERENCE AND EXPOSITION, 2008. T&D. IEEE/PES, IEEE, PISCATAWAY, NJ, USA, 21 April 2008 (2008-04-21), pages 1-7, XP031250242, ISBN: 978-1-4244-1903-6
  
Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


Description

BACKGROUND OF THE INVENTION


1. Field of the invention



[0001] This invention relates to a method and an apparatus for dynamic signal switching of a merging unit in an electrical power system.

2. Description of the related art



[0002] Intelligent electronic devices are installed in electrical power systems to measure the voltage and current flows running through the electrical network. Said intelligent electronic devices may attempt to use these measurements in order to protect the power system against faults or abnormal oscillations, and to allow better control of the power system by human or automatic operators.

[0003] Traditionally, such measurements have been made using current and voltage transformers, transforming the power grid quantities into more manageable, safer, lower magnitude scaled quantities for input to intelligent electronic devices.

[0004] There is presently a growing trend to digitize the output of such current transformers and voltage transformers, for ease of communication and connection to intelligent electronic devices in an electrical substation automation scheme.

[0005] The same existing current transformers and voltage transformers can have their scaled, secondary side analogue signals converted into digital signals by a device termed a "Merging Unit". The field of the present invention relates to the case where multiple current transformer inputs are available at one location, nominally offering redundancy/duplication of the same measured quantity. This is often the case where a current transformer core for protection applications and another core for measurement applications are available.

[0006] As the measurement core (measurement accuracy class) is more accurate for load currents, said measurement core would normally be considered the truest representation of the real primary current quantity on the power system. As to higher level fault current flows, the measurement current transformer core may saturate, making its output an erroneous representation of the real primary input. In such instances, the protection current transformer core having a larger dynamic range (and better immunity to saturation) would be a better scaled representation of the primary quantity.

[0007] Historically, the secondary wired current transformer circuits would have needed to run cross-site, from the primary power system equipment in the electrical substation yard, to the physical substation building where the intelligent electronic device would have been situated.

[0008] This cross-site run of current transformer circuits is potentially dangerous, as an inadvertent open circuit could yield dangerous voltages and sparking/arcing in the vicinity of the break. Hence, it is desirable to site the merging unit close to the current transformer secondary circuit which the former is digitizing.

[0009] We will then consider prior art documents.

[0010] US 6,954,704 describes a digital protection and control device. Indeed, in conventional protection and control systems, since analog information transmitted through electric cables is used for information transmission between substation main equipments and protection and control devices that protect and control these substation main equipments, contact input circuits and contact output circuits handling a relatively large voltage and current have been required. Further, a space for disposing a large number of electric cables is necessary, and a protection unit and a control unit need to be accommodated in independent cases provided exclusively for the respective units, which has been a cause of the increase in installation space of the devices. US 6,954,704 provides a digital protection and control device configured to realize reduction in installation space thereof by the digitalization of the device, and to realize improvement in protection and control performance by sufficient data exchange in the device. Therefore, US 6,954,704 describes the basic principles of a merging unit.

[0011] EP 1 845 383 describes a method of detecting saturation of a current transformer. Said method involves detecting a fault of a secondary current/voltage waveform of a current transformer. A magnetic flux in the secondary of the transformer is estimated by integration of the secondary current during a time window from the detection of the fault. The estimated magnetic flux is compared with a threshold value, where saturation of the transformer is detected while the threshold value exceeds the magnetic flux.

[0012] "IEC 61850 impact on substation design" in Transmission and Distribution Conference and Exposition, 2008, IEEE, Piscataway NJ USA, 21 April 2008, by Janssen MC et al relates to substation designs, comprising devices, including merging units, switchgear components and high speed communication systems such as GSE.

[0013] There is no existing solution to allow the input from duplicate (or multiple) measurement sources to combine as a single "optimized" one.

[0014] The only way this could be achieved today is to have two separate merging units, each digitizing only one 3-phase set of current transformer signals. The two merging units would then multicast two separate measurements of sampled values, which could be connected to the same Ethernet link. Hypothetically, any intelligent electronic devices could be configured so as to be capable to read the two (or more) separate sources concurrently, and choose between them according to quality bits which are available in the input signals. However, no intelligent electronic device on the market today can offer such capability.

SUMMARY OF THE INVENTION



[0015] Accordingly, it is a general object of the present invention to provide a method and an apparatus for dynamic signal switching of a merging unit, wherein the merging unit chooses the best input signal in terms of accuracy and reliability and generates a digitized output from that quantity.

[0016] In order to achieve the above-mentioned object, there is provided according to one aspect of the present invention, a method for dynamic signal switching with multiple measurement sources as defined in the accompanying claims 1 to 5.

[0017] In an embodiment the input signals are :
  • protection class inputs as three individual phase currents, and
  • measurement class inputs as three individual phase currents.


[0018] Advantageously, the merging unit receives input signals from a protection current transformer and from a measurement current transformer, wherein the output of the merging unit is selected from the measurement current transformer samples, unless saturation for that current transformer is present, or is predicted to occur soon. Advantageously, once switching to the protection current transformer input has been done, this new signal source is held in priority until it can be ensured that the entire instance of the high current flow has reset. Moreover, when there is a switch from one signal source to the other, the transition may be smoothed-in.

[0019] In order to achieve the above-mentioned object, there is provided according to another aspect of the present invention an apparatus as in the accompanying claims 6 to 8.

[0020] Advantageously, the apparatus comprises a protection current transformer and a measurement current transformer. Moreover, it may comprise means for predicting the expected value of next sample, which looks at the present sample value magnitude and at least one previous sample, and means for comparing the real sample with the expected value to detect a possible saturation.

[0021] Connected intelligent electronic devices can then be configured with a single input from the merging unit which is at the same time accurate enough for measurement purposes, and has the dynamic range for protection applications.

[0022] The invention makes it possible for the merging unit to connect to two separate current transformer secondaries (typically each one is a three phase set of phase current transformer inputs, with a neutral current transformer in some cases), so that the outgoing Ethernet stream of digitized analogue values is a single combined signal, and not two separate signals. The invention is not limited only to two current transformer sets, but may be extended to applications with multiple current transformer sets.

[0023] A significant advantage of the invention is that only one merging unit is used, and that it is able to combine the inputs from two sources in order to select one output as the best for communicating to connected intelligent electronic devices.

[0024] The combination into a single signal according to certain construction rules (implemented as numerical algorithms) reduces the traffic on the Ethernet, and allows connected intelligent electronic devices which support only one signal source to offer both protection and measurement class functionalities. Without the merging unit having the ability to combine the signals before multicasting, the connected intelligent electronic devices would only have been able to offer protection or measurement accuracy, not both together.

[0025] Those connected intelligent electronic devices can then implement measurement and protection functions. Yet, measurement functions would be provided in prior art protection intelligent electronic devices, but these would be low accuracy measurements for indicative purposes only. For revenue purposes (trading and billing) accuracy requirements would therefore have precluded applications within protection intelligent electronic devices.

[0026] In the present invention, the intelligent electronic devices are receiving a single merged signal which is both accurate enough for all measurement applications, and has the full dynamic range for protection applications, the intelligent electronic devices being able to perform both tasks. This reduces device duplication, and costs.

[0027] The accuracy of the merging unit output at low to moderate currents also improves the accuracy of protection functions which are generally "low-set" (i.e. not related to high short-circuit values), such as generator and motor power protection functions, thermal overload, winding interturn protection, and various forms of earth-fault protection functions on systems with fault current limiting (e.g. resistive earthed systems).

BRIEF DESCRIPTION OF THE DRAWINGS



[0028] 

Fig. 1 shows an embodiment of the invention apparatus in a single line diagram application.

Fig. 2 shows the method steps of an embodiment of the invention.

Fig. 3 shows output from a measurement class current transformer at load currents.

Fig. 4 shows output from a measurement class current transformer at fault current exhibiting saturation, with a protection class current transformer output being unaffected.

Fig. 5 shows half a cycle of a current wave with time shown for an example numerical algorithm.

Fig. 6 shows magnification of time period close to the onset of saturation.


DESCRIPTION OF THE PREFERRED EMBODIMENTS



[0029] Fig. 1 shows a typical application, in a single line diagram.

[0030] On said figure are represented :
  • a primary interface and hardwiring 10,
  • a merging unit 11,
  • a process bus 12, for example a IEC 61850-9.2 bus,
  • a protection relay 13,
  • a station bus 14, for example a IEC 61850-9.2 station bus,
  • a control system 15.


[0031] In the invention, the merging unit 11 has two inputs A and B and an output C such that :
  • A is a first current input (e.g. from a protection class current transformer core).
  • B is a second current input, possibly measurement class.
  • C is a combined output of a single stream of measurements, for example IEC 61850-9.2 measurements, based on the real-time best selection from inputs A and B.


[0032] Fig. 2 shows the steps of the invention process in a preferred embodiment, in which the inputs are inputs A (Protection class inputs as three individual, phase currents) and inputs B (measurement class inputs as three individual, phase currents) and the output is an output signal C.

[0033] Said steps are the following ones :
  1. 1) a current transformer (CT) live level detection step 20, in which is determined which current inputs have a level of load or fault current flowing such as to indicate that the CT has a live output and may be considered potentially suitable to be taken as a valid measurement source,
  2. 2) a current transformer supervision step 21, in which is determined which three phase current input(s) is/are healthy (no broken wires, correct phase rotation, balanced when the network voltages indicate they should be balanced),
  3. 3) a current transformer saturation detection step 22, in which is determined whether any current transformer experiences an unexpected decrease in output (or an alternative technique to detect the onset of saturation), said decrease being not accompanied by a similar decrease on the same phase of other inputs,
  4. 4) a current level detection step 23, in which is determined which inputs risk exceeding their accuracy limit factors (the rated measurement range limits before saturation).


[0034] The output signal C is derived from B if : (1) B is Live, (2) B is Healthy, (3) B has No Saturation, and (4) B has No Current Excess, and, derived from A if : (1) A is Live, (2) A is Healthy, and B fails any healthiness, saturation, or dynamic range excess test as per 1-4 above

[0035] In the invention, the merging unit 10 receives wired signals from two current transformers CTi, or two output cores from the same physical current transformer, and then provides a single combined signal as digitized output. We may have more than two input signals, two signals being a typical application. Said input signals are essentially measuring the same physical primary quantity on the power system itself, and are provided to give redundancy in measurement, or more typically for different measuring ranges and accuracy classes.

[0036] The merging unit 10 is able to perform an intelligent merging of the two signals into one, which is expected to give the best representation of the real primary power system quantity on a real time basis. As the digital output data stream is in sampled values format, in a fast real-time mode the merging unit selects on a per sample basis the most accurate output it is able to achieve, based on the two (or more) available inputs.

[0037] In an embodiment, a phase current signal on the power system is measurable by a protection current transformer core, and a measurement current transformer core. The two current transformers have different characteristics of core design, and hence a different magnetizing curve from each other. The measurement current transformer may belong for example to Class 0.2, meaning that current measurement is very accurate, with generally no greater than 0.2% error rate. The protection current transformer may belong for example to Class 5P, meaning that the error rate could now be as great as 5%. The output of the measurement current transformer is thus better (more accurate), except at high currents where its output may saturate. A measurement current transformer is only designed for accuracy in the range of 0-120% of rated current, and typically above 200% rated current (400% in some cases) its output will become unreliable. A measurement current transformer can thus measure load current reliably, but is not dimensioned to cover the full dynamic range of power network short-circuit currents. The protection current transformer will typically cover 20 to 50 times rated current before appreciable core saturation, and therefore provides a more reliable measurement of current high values.

[0038] The merging unit is able to make an intelligent selection from which of the two signals appears to include no saturation, biasing towards the measurement current transformer output if the latter shows no saturation.

[0039] Fig. 3 shows a theoretical sinusoidal AC load current, with the dots showing the idealized sampled value outputs (just 20 samples within the AC cycle are shown in this example, although 80 or 256 samples per cycle would be more common according to a standard IEC 61850-9.2 application). It can be seen that as the current is a load example, no current transformer will saturate, and the sampled value data stream output is a true representation of the real power system quantity. This can be assumed to be the output of both the protection and the measurement class current transformers, in which case the merging unit will select the measurement class input as the basis of its output, thanks to the greater accuracy.

[0040] Fig. 4 shows an example of two current transformers measuring the same signal. It is assumed that both are being viewed on the same basis (given that, in some instances, the primary to secondary current transformation ratios of the two may differ). The example shown is a fault current value, with the dotted line I showing the output of the measurement class current transformer, and line II showing the output of the protection current transformer. It can be seen that for a portion of each half cycle, the measurement current transformer core saturates, and the output is unrealistically low compared to the real fault current. The error in the first sample of saturation is indicated by arrow III. The protection current transformer represents the full cycle of current, unsaturated and accurate, as shown by line II.

[0041] A preferred technique for the invention is for each measurement source to have a numerical algorithm which makes it possible to obtain the present sampled value magnitude, and compares with one or more of the previous samples to estimate the general trend of the sinusoidal curve. On this basis, the expected value of the next sample can be predicted. If the next incoming sample unexpectedly falls lower in magnitude than the prediction, the onset of saturation is detectable, as per the arrow III, in the diagram of Fig. 4. Conversely, if the waveshape of the sampled values indicates a rate of rise so steep that it will inevitably lead to saturation, this can be used to switch the signals in advance.

[0042] In Fig. 3 and Fig. 4, the used units are "multiples of rated current" (rated current is the nominal load current, so the scale is a effectively a per unit scalar value of "overload").

[0043] Fig. 5 illustrates a numerical algorithm, in an example half cycle of a current wave with time shown. References 30 corresponds to actual current samples. References 31 corresponds to predicted samples if no saturation occurs (it assumes a sinusoidal profile) . It can even be a straight line assumption at typical merging unit sample rates of 80 or 256 samples per cycle.

[0044] The merging unit will normally select its output from the measurement current transformer samples, unless it detects that saturation is present, or is predicted to occur soon.

[0045] Although switching from one current transformer source to another could be done on a per sample basis, it is preferred that the switching is not happening at multiple times within each 50 or 60 Hz AC power cycle. Thus, once switching to the protection current transformer input has been done, this new signal source can be held in priority until it can be ensured that the entire instance of the high current flow has reset (which can last up to 3 seconds in an electrical distribution system or 1 second in a transmission grid). This temporary reversal of the signal priority selection is acceptable as the duration on the power system stays small, and the window of time during which the measurement accuracy is impaired is small too.

[0046] When the switch from one signal source to the other occurs, the merging unit may take steps to smooth-in the transition. For example, if the protection current transformer and measurement current transformer are both measuring the same rising signal and the protection class current transformer measures said signal 5% higher than the actual one, and the measurement current transformer at 0.2% less than the actual one, there is over 5% difference between the two. On switching from one source to another, the merging unit may take steps to smooth the transition over a period of a few successive samples, based on its prior knowledge that the two readings were not identical.

[0047] Fig. 6 shows the sample method to detect the non-linearity as an error figure ε. The CT live, CT supervision and CT level detection steps, referenced as 20, 21 and 23, would normally use the output of a traditional one cycle or half-cycle Fourier transform of the sampled values. Such transformation techniques are commonplace in the industry today.

[0048] On said figure 6, in which there is a magnification of time period close to the onset of saturation :
  • References 40 correspond to actual current samples.
  • Reference 41 corresponds to a predicted sample, if no saturation were to occur (simple straight line assumption shown in this example). As sample time interval remains constant :





[0049] If the error ε is greater than an allowable tolerance, a significant non-linearity is detected.


Claims

1. A method for dynamic signal switching with multiple measurement sources, for a merging unit in an electrical power system, said power system comprising at least one current transformer and at least one intelligent electronic device, said method comprising the following steps performed by the merging unit:
an input receiving step of receiving at the merging unit at least two input signals (A,B) from at least one current transformer measuring the same physical primary quantity to give redundancy in measurement or for different measuring ranges and accuracy classes, wherein the at least one current transformer is two current transformers, or two output cores from the same current transformer wherein the input signals are each a three phase set of phase current transformer inputs:

- a current transformer live level detection step (20), in which is determined which current input signals have a level of load or fault current flowing such as to indicate that the current transformer may be considered potentially suitable to be taken as a valid measurement source,

- a current transformer supervision step (21), in which is determined which three phase current input signals of the current input signals is/are healthy,

- a current transformer saturation detection step (22) in which is determined whether saturation for any current transformer is present or the onset of said saturation is detected,

- a current level detection step (23), in which is determined which inputs risk exceeding accuracy limits,

- a step of real-time selection from the input signals (A,B), as a function of the results of the previous steps, wherein the selection is derived from

(a) input signal B if (1) B is live, (2) B is healthy, (3) B has no saturation, and (4) B has no current excess

(b) input signal A if (1) A is live, (2) A is healthy, and B fails any healthiness, saturation or dynamic range excess test as set out in the previous steps; and

- said method further comprising a step of outputting from the merging unit a single combined signal as digitized output to at least one intelligent electronic device.


 
2. The method pursuant claim 1, in which the input signals are :

- protection class inputs as three individual phase currents, and

- measurement class inputs as three individual phase currents.


 
3. The method pursuant claim 1, wherein the merging unit receives input signals from the at least one current transformer that is from a protection current transformer and from a measurement current transformer, wherein the output of the merging unit is selected from measurement current transformer samples, unless saturation for that current transformer is present, or is predicted to occur soon.
 
4. The method pursuant claim 3, wherein once switching to the protection current transformer input has been done, this new signal source is held in priority for the entire duration at the high current flow.
 
5. The method pursuant claim 4, wherein when there is a switch from one signal source to the other, the transition is smoothed-in.
 
6. An apparatus for dynamic signal switching with multiple measurement sources, the apparatus configured to implement the method for dynamic switching pursuant claim 1, said apparatus, comprising:

- at least one multiple input current transformer (CTi), wherein the at least one multiple input current transformer is two current transformers, or two output cores from the same current transformer wherein the input signals are each a three phase set of phase current transformer inputs,

- a primary interface (10),

- a merging unit (11) whose two inputs (A, B), receiving input signals, are connected to said at least one input current transformer measuring the same physical primary quantity and digitizing said input signals,
a process bus (12),
a protection relay (13),
a station bus (14),
a control system,
wherein said merging unit (11) comprises means for real-time selection of the input signals.


 
7. The apparatus pursuant claim 6, wherein the at least one multiple input current transformer (CTi) comprises a protection current transformer and a measurement current transformer.
 
8. The apparatus pursuant claim 6, further comprising means for predicting the expected value of an input signal, and means for comparing the real value of said input signal with the expected value to detect a possible saturation of the measurement current transformer core.
 


Ansprüche

1. Verfahren zur dynamischen Signalumschaltung mit mehreren Messquellen für eine Zusammenführungseinheit in einem elektrischen Stromversorgungssystem, wobei das Stromversorgungssystem mindestens einen Stromwandler und mindestens ein intelligentes elektronisches Bauteil umfasst, wobei das Verfahren die folgenden von der Zusammenführungseinheit durchgeführten Schritte umfasst:
einen Eingangsempfangsschritt zum Empfangen an der Zusammenführungseinheit von mindestens zwei Eingangssignalen (A, B) von mindestens einem Stromwandler, der die gleiche physikalische Primärgröße misst, um Redundanz bei der Messung oder für verschiedene Messbereiche und Genauigkeitsklassen zu erhalten, wobei der mindestens eine Stromwandler zwei Stromwandler oder zwei Ausgangskerne desselben Stromwandlers sind, wobei die Eingangssignale jeweils ein Dreiphasensatz von Phasenstromwandlereingängen sind:

- einen Stromwandler-Stromführungspegel-Erfassungsschritt (20), in dem bestimmt wird, welche Stromeingangssignale einen solchen Last- oder Fehlerstrompegel aufweisen, dass angezeigt wird, dass der Stromwandler als potenziell geeignet angesehen werden kann, um als gültige Messquelle genommen zu werden,

- einen Stromwandler-Überwachungsschritt (21), in dem bestimmt wird, welche dreiphasigen Stromeingangssignale der Stromeingangssignale gut funktionierend ist/sind,

- einen Stromwandler-Sättigungserfassungsschritt (22), in dem bestimmt wird, ob eine Sättigung für irgendeinen Stromwandler vorhanden ist oder der Beginn der Sättigung erfasst wird,

- einen Strompegel-Erfassungsschritt (23), in dem bestimmt wird, bei welchen Eingängen das Risiko besteht, dass die Genauigkeitsgrenzen überschritten werden,

- einen Schritt der Echtzeit-Auswahl aus den Eingangssignalen (A, B) in Abhängigkeit von den Ergebnissen der vorhergehenden Schritte, wobei die Auswahl abgeleitet wird von

(a) Eingangssignal B, wenn (1) B stromführend ist, (2) B gut funktionierend ist, (3) B keine Sättigung hat und (4) B keinen Stromüberschuss aufweist

(b) Eingangssignal A, wenn (1) A stromführend ist, (2) A gut funktionierend ist und B einen Funktions-, Sättigungs- oder Dynamikbereich-Überschreitungstest, wie in den vorstehenden Schritten dargelegt, nicht besteht; und

- wobei das Verfahren weiter einen Schritt des Ausgebens eines einzelnen kombinierten Signals von der Zusammenführungseinheit als digitalisierte Ausgabe an mindestens ein intelligentes elektronisches Bauteil umfasst.


 
2. Verfahren nach Anspruch 1, wobei die Eingangssignale sind:

- Schutzklasse-Eingänge als drei einzelne Phasenströme, und

- Messklassen-Eingänge als drei einzelne Phasenströme.


 
3. Verfahren nach Anspruch 1, wobei die Zusammenführungseinheit Eingangssignale von dem mindestens einen Stromwandler empfängt, die von einem Schutzstromwandler und von einem Messstromwandler stammen, wobei der Ausgang der Zusammenführungseinheit aus Messstromwandlerproben ausgewählt wird, es sei denn, die Sättigung für diesen Stromwandler ist vorhanden oder es wird vorhergesagt, dass sie bald eintritt.
 
4. Verfahren nach Anspruch 3, wobei nachdem Umschalten auf den Schutzstromwandlereingang erfolgt ist, diese neue Signalquelle für die gesamte Dauer des hohen Stromflusses in Priorität gehalten wird.
 
5. Verfahren nach Anspruch 4, wobei bei einem Wechsel von einer Signalquelle zur anderen der Übergang geglättet wird.
 
6. Vorrichtung zur dynamischen Signalumschaltung mit mehreren Messquellen, wobei die Vorrichtung so konfiguriert ist, dass sie das Verfahren zur dynamischen Umschaltung nach Anspruch 1 implementiert, wobei die Vorrichtung umfasst:

- mindestens einen Mehrfach-Eingangs-Stromwandler (CTi), wobei der mindestens eine Mehrfach-Eingangs-Stromwandler zwei Stromwandler oder zwei Ausgangskerne desselben Stromwandlers sind, wobei die Eingangssignale jeweils ein Dreiphasensatz von Phasen-Stromwandlereingängen sind,

- eine primäre Schnittstelle (10),

- eine Zusammenführungseinheit (11), deren zwei Eingänge (A, B), die Eingangssignale empfangen, mit dem mindestens einen Eingangsstromwandler verbunden sind, der die gleiche physikalische Primärgröße misst und die Eingangssignale digitalisiert,
einen Prozessbus (12),
ein Schutzrelais (13),
einen Stationsbus (14),
ein Steuerungssystem,
wobei die Zusammenführungseinheit (11) Mittel zur Echtzeitauswahl der Eingangssignale umfasst.


 
7. Vorrichtung nach Anspruch 6, wobei der mindestens eine Mehrfach-Eingangs-Stromwandler (CTi) einen Schutzstromwandler und einen Messstromwandler umfasst.
 
8. Vorrichtung nach Anspruch 6, weiter umfassend Mittel zur Vorhersage des erwarteten Wertes eines Eingangssignals und Mittel zum Vergleichen des tatsächlichen Wertes des Eingangssignals mit dem erwarteten Wert, um eine mögliche Sättigung des Messstromwandlerkerns zu erfassen.
 


Revendications

1. Procédé de commutation dynamique de signal avec de multiples sources de mesure, pour une unité de fusion dans un système d'alimentation électrique, ledit système d'alimentation comprenant au moins un transformateur de courant et au moins un dispositif électronique intelligent, ledit procédé comprenant les étapes suivantes effectuées par l'unité de fusion :
une étape de réception d'entrée consistant à recevoir au niveau de l'unité de fusion au moins deux signaux d'entrée (A, B) provenant d'au moins un transformateur de courant mesurant la même quantité physique primaire pour donner une redondance dans la mesure ou pour différentes plages de mesure et classes de précision, dans lequel le au moins un transformateur de courant est deux transformateurs de courant, ou deux noyaux de sortie du même transformateur de courant dans lequel les signaux d'entrée sont chacun un ensemble triphasé d'entrées de transformateur de courant de phase :

- une étape (20) de détection de niveau sous tension de transformateur de courant, dans laquelle il est déterminé quels sont les signaux d'entrée de courant qui présentent un niveau de charge ou de courant de défaut qui passe pour indiquer que le transformateur de courant peut être considéré potentiellement approprié pour être pris comme une source de mesure valide,

- une étape (21) de supervision de transformateur de courant, dans laquelle il est déterminé quels est/sont les signaux d'entrée de courant triphasé des signaux d'entrée de courant sains,

- une étape (22) de détection de saturation de transformateur de courant dans laquelle il est déterminé si une saturation pour un quelconque transformateur de courant est présente ou le début de ladite saturation est détectée,

- une étape (23) de détection de niveau de courant, dans laquelle il est déterminé quelles sont les entrées risquant de dépasser les limites de précision,

- une étape de sélection en temps réel parmi les signaux d'entrée (A, B), en fonction des résultats des étapes précédentes, dans lequel la sélection est dérivée à partir

(a) d'un signal d'entrée B si (1) B est sous tension, (2) B est sain, (3) B ne présente pas de saturation, et (4) B ne présente pas un courant en excès

(b) d'un signal d'entrée A si (1) A est sous tension, (2) A est sain, et B échoue à un quelconque test de santé, de saturation ou d'excès de plage dynamique comme indiqué dans les étapes précédentes ; et

- ledit procédé comprenant en outre une étape de sortie à partir de l'unité de fusion d'un unique signal combiné sous la forme d'une sortie numérisée vers au moins un dispositif électronique intelligent.


 
2. Procédé selon la revendication 1, dans lequel les signaux d'entrée sont :

- des entrées de classe de protection sous forme de trois courants de phase individuels, et

- des entrées de classe de mesure sous forme de trois courants de phase individuels.


 
3. Procédé selon la revendication 1, dans lequel l'unité de fusion reçoit des signaux d'entrée provenant du au moins un transformateur de courant qui provient d'un transformateur de courant de protection et d'un transformateur de courant de mesure, dans lequel la sortie de l'unité de fusion est sélectionnée parmi des échantillons de transformateur de courant de mesure, sauf si la saturation de ce transformateur de courant est présente, ou est prédite pour se produire bientôt.
 
4. Procédé selon la revendication 3, dans lequel dès que la commutation vers l'entrée du transformateur de courant de protection a été effectuée, cette nouvelle source de signal est conservée en priorité pendant le durée entière au débit de courant élevé.
 
5. Procédé selon la revendication 4, dans lequel lorsqu'il y a commutation d'une source de signal à l'autre, la transition est lissée.
 
6. Appareil de commutation dynamique de signal avec de multiples sources de mesure, l'appareil étant configuré pour mettre en œuvre le procédé de commutation dynamique selon la revendication 1, ledit appareil comprenant :

- au moins un transformateur de courant à multiples entrées (CTi), dans lequel le au moins un transformateur de courant à multiples entrées est deux transformateurs de courant, ou deux noyaux de sortie du même transformateur de courant dans lequel les signaux d'entrée sont chacun un ensemble triphasé d'entrées de transformateur de courant de phase,

- une interface principale (10),

- une unité de fusion (11) dont deux entrées (A, B), recevant des signaux d'entrée, sont connectées audit au moins un transformateur de courant d'entrée mesurant la même quantité physique primaire et numérisant lesdits signaux d'entrée,
un bus de processus (12),
un relais de protection (13),
un bus de station (14),
un système de commande,
dans lequel ladite unité de fusion (11) comprend un moyen de sélection en temps réel des signaux d'entrée.


 
7. Appareil selon la revendication 6, dans lequel le au moins un transformateur de courant à multiples entrées (CTi) comprend un transformateur de courant de protection et un transformateur de courant de mesure.
 
8. Appareil selon la revendication 6, comprenant en outre un moyen de prédiction de la valeur attendue d'un signal d'entrée, et un moyen de comparaison de la valeur réelle dudit signal d'entrée à la valeur attendue pour détecter une saturation possible du noyau de transformateur de courant de mesure.
 




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Cited references

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