WO2008034400A1

WO2008034400A1 - Method for producing a fault signal, which indicates a fault present in a secondary current transformer circuit, and differential protective device

Info

Publication number: WO2008034400A1
Application number: PCT/DE2006/001707
Authority: WO
Inventors: Andreas Regenbrecht
Original assignee: Siemens Aktiengesellschaft
Priority date: 2006-09-22
Filing date: 2006-09-22
Publication date: 2008-03-27
Also published as: DE112006004145A5; CN101512861A; CN101512861B; EP2064793A1

Abstract

The invention relates to a method for producing a fault signal (F), which indicates a fault in the secondary circuit (for example 32a, 35a) of a current transformer (for example 31a, 34a), which interacts with a local differential protective device (33), which monitors a section end (30) of an electrical energy supply system, wherein in the method, measured current values which are detected by the current transformer (for example 41a, 34a) and indicate a current flowing through the section end (30) are monitored by the local differential protective device (33), and a suspicion signal (V) is produced if the absolute values of successive measured current values drop suddenly, and the fault signal (F) is produced if the suspicion signal (V) is present. In order to be able to identify a fault in a secondary current transformer circuit even more reliably with such a method, the invention proposes that a first reset signal (R1) is produced by the local differential protective device (33) if comparison measured current values, which are detected at the time at which the suspicion signal (V) is produced in at least one remote differential protective device, which monitors a further section end of the electrical energy supply system, likewise drop suddenly in terms of their absolute values, and the fault signal (F) is blocked if the first reset signal (R1) is present. The invention also relates to a correspondingly designed differential protective device.

Description

A method of generating an error signal indicative of an error present in a secondary CT circuit and a differential protection device

The invention relates to a method for generating an error signal indicative of a fault in the secondary circuit of a current transformer cooperating with a local differential protection device monitoring a section end of an electric power network, wherein current measurements detected by the current transformer include a current flowing through the section end be monitored by the local differential protection device and a suspect signal is generated when the amounts of successive current readings fall abruptly; the error signal is generated when the suspicion signal is present.

Moreover, the invention relates to a differential protection device for monitoring a portion end of an electric power supply network, which cooperates with at least one current transformer, by means of which the differential protection device current readings that characterize a current flowing in the section end of the power supply network, are detected. The differential protection device has a computation device which carries out monitoring of the end of the section based on the measured current values and at least one remote differential protection device to the local differential protection device, wherein the computation device has a monitoring unit which monitors a secondary circuit of the current transformer for errors.

Electrical differential protection devices are used in electrical power supply networks to monitor selected cuts to mistakes, such. As short circuits or ground faults used. Typical sections of an electrical power supply network monitored by differential protection devices are, for example, electrical power supply lines or transformers. For monitoring the respective section, a number of differential protection devices are required according to the number of ends of each section. Thus, for example, in the case of a power supply line having three section ends-that is to say, for example, a main line with a branch line leaving therefrom-three differential protection devices are required, one of the differential protection devices being provided at each section end.

The differential protection devices operate according to the following protection principle: Each differential protection device detects, for each phase conductor of the section end monitored by it, current measured values that indicate a current flowing through this phase conductor in each case. The current readings detected at all ends of the monitored section will then be lost

Attention to their respective signs added. The summation can be done either in a selected differential protection device or in all differential protection devices. For this purpose, current measured values simultaneously detected by the remote differential protective devices are transmitted to the local differential protection device via data transmission lines running between the differential protection devices, so that this local differential protection device can form the sum of its own detected current measured values and the transmitted current measured values of the removed differential protection devices.

In the error-free case, the calculated current total should approximately equal zero, that is, the one in the section of the Electric power supply network flowed into it also flows out of this section again. In the faulty case, however, results in a current sum that is significantly different from zero. To carry out the differential protection principle, therefore, the calculated current sum must be compared with a predetermined threshold value. When the threshold value is exceeded, a triggering signal is generated by the respective local differential protection device, with the electric circuit breaker provided at the section ends of the faulty section for opening its

Switching contacts are caused, whereby the faulty portion is separated from the rest of the electrical power grid.

Usually, for the implementation of the explained

Differential protection principle needed current readings initially installed directly at each section end of the electrical energy supply network current transformer - usually inductive current transformer - tapped and transmitted via electrical lines to the respective electric differential protection device. Since the current intensity of the currents detected by these first current transformers for internal processing in the differential protection device is usually too high, the electrical differential protection device again has device-internal current transformers on the input side, with which the transmitted currents are again transformed to a lower current level. Subsequently, the currents thus detected are usually supplied to an analog-to-digital converter, which assigns corresponding digital current measured values to the analog currents. These current measured values are used in a computing device of the respective differential protection device for implementing the differential protection principle. Since the current measurements form the basis for implementing the differential protection for the monitored section of the power supply network, its path from detection to processing in the differential protection device must be continuously monitored. There is the possibility that a current transformer provided for detecting the current measured values of a phase is affected on its secondary side by a fault, for example an interruption in one of the coil windings or one of the lines (a so-called wire breakage), so that the electric differential protection device measures zero apparent current readings even though currents flow through the corresponding phase conductor of the section end. Such erroneously detected current measured values would significantly change the current sum, so that in this case the differential protection devices would respond inadvertently and their respective circuit breakers would open. Since such an overfunction, ie a shutdown of an actually flawless section of the power grid, is associated with the network operator at a high cost, it should be avoided if possible.

For this purpose, methods are known which monitor the secondary circuits of current transformers for faults, such as wire breaks, and generate a corresponding fault signal if they have detected a fault in the secondary circuit of a current transformer. This error signal is used to block the differential protection function for the corresponding phase of the section of the electrical power supply network, so that no unwanted shutdown of the section takes place. For example, such a method is known from the Applicant's Equipment Manual "SIPROTEC, Line Differential Protection with Distance Protection 7SD5, V4.3" (Order No. 053000-01100-0169-1), which is described in the section "Monitoring If the current readings of the current measurements drop abruptly to zero, a fault in the secondary current transformer circuit is detected and a fault signal indicating the fault in the secondary circuit of the CT is blocked if at the same time a jump occurs in the course of detected ground-current measured values, since such a jump in the earth-current profile indicates an actual fault in the section of the electrical energy supply network.

The object of the invention is to provide a method and a differential protection device of the type mentioned, with the even more reliable detection of errors in secondary current transformer circuits can be achieved.

In order to achieve this object, it is proposed according to the invention that a first reset signal is generated by the local differential protection device, with respect to their amounts, at the time of generating the suspicion signal in at least one distant differential end of the electrical power supply network monitoring distant differential squirrel also fall abruptly, and the error signal is blocked when the first reset signal is present.

By using the comparative current measurements acquired by the at least one remote differential protection device at another section end, the decision as to whether to make a fault in the secondary circuit of a current transformer can be made even more reliable since the likelihood of the simultaneous occurrence of errors In secondary current transformer circuits distant differential protection devices is very low.

According to an advantageous embodiment of the method according to the invention, it is proposed that, in the case of a multi-phase power supply network, the current measured values detected by current transformers of all phases are monitored for sudden decay with respect to their amounts, the suspect signal is generated, if for at least one phase the amounts are consecutive Current readings of a current transformer of the local differential protection device a sudden drop is detected, and the first reset signal is generated when for each same phase in the amounts of successive comparison current measurements of a current transformer of the at least one remote differential protection device also a sudden drop is detected.

In this way, the method according to the invention reliably detects a fault in a secondary current transformer circuit even in the case of a polyphase power supply network. In addition, simultaneously occurring faults in secondary current transformer circuits are detected in several phases; even in the secondary current transformer circuits of all phases simultaneously occurring errors are reliably detected.

A further advantageous embodiment is seen in that in the local differential protection device, the secondary circuits of the current transformer of all phases are monitored for current flow, a second reset signal is generated, if in at least one current transformer with existing current flow, the amounts of successive current measurement values abruptly len, and the error signal is also blocked when at least the second reset signal is present.

In this way, an overfunction of the differential protection device can be prevented even more reliably, since the error signal is blocked even if there is a current flow in the corresponding secondary current transformer circuit, which indicates an intact secondary current transformer circuit.

According to a further advantageous embodiment of the method according to the invention, it is proposed that in the local differential protection device a sum or ground current in the section end indicating sum or Erdstrommesswerte be detected, a third reset signal is generated if at the time of generating the suspect signal, the course of successive sums - or Erdstrommesswerte has a sudden change, and the error signal is also blocked when at least the third reset signal is present.

By evaluating the sum or ground current, an overfunction of the differential protection device can be prevented even more reliably, since a jump in the sum or ground current indicates an actual fault in the section of the electrical power supply network.

In addition, in order to prevent blocking of the differential protection at very high currents in the phases of the electrical energy supply network, it is also proposed according to the invention that in the local differential protection device the amounts of the current measured values of all phases are monitored for exceeding a predetermined threshold value and a fourth reset signal is generated the magnitude of the current readings of at least one phase exceeds the threshold value. increases, and the error signal is also blocked if at least the fourth reset signal is present.

A further advantageous embodiment of the inventive method also provides that a circuit breaker controllable by the local differential protection device is checked for the position of its switching contacts and a fifth reset signal is generated when the switching contacts of the circuit breaker are open, and also blocks the error signal when at least the fifth reset signal is present.

This prevents the blocking of the differential protection in the event that the section of the electrical energy supply network is in a switched-off state.

In order to be able to make a more reliable statement as to whether there is a fault in a secondary current transformer circuit, it is further proposed according to the invention that voltage readings indicative of voltages present at the end of the range are detected by the local differential protection device for all phases and a sixth reset signal is generated when at the time of generating the suspect signal, the course of successive voltage measurements of at least one phase has a sudden change, and the error signal is also blocked when at least the sixth reset signal is present. A jump in the course of the detected voltages also indicates a fault that has actually occurred on the section of the energy supply network.

In addition, according to a further advantageous embodiment of the method according to the invention, it can be provided that with respect to a phase to which the suspect signal has been generated, the following further current measurement values are monitored for the time at which the suspect signal is generated, and a seventh reset signal is generated if the amounts of these further current measurement values are greater than the magnitude of the current measurement value used to generate the suspicion signal has led, and the error signal is also blocked when at least the seventh reset signal is present. This also makes it possible to further increase the reliability of the detection of a fault in the secondary current transformer circuit.

A further advantageous embodiment of the method according to the invention also provides that, as comparison current measured values of the at least one remote differential protection device, such current measured values are used, which are also transmitted from the at least one remote differential protection device to the local differential protection device for carrying out the differential protection function.

This has the advantage that over the existing between the differential protection communication lines no additional data must be transmitted in order to make a reliable decision on a fault in the secondary current transformer circuit can. Rather, the method according to the invention can be carried out with the data required for carrying out the differential protection and therefore already exchanged between the differential protection devices, for example the current measured values of the individual section ends, intermediate current sums or stabilization current values.

According to a further advantageous embodiment of the method according to the invention, it is also provided that, in the case of the present error signal, the differential protection functions of the local differential protection device and the at least one remote differential protection device are blocked with respect to the phase affected by the fault in the secondary circuit of the corresponding current transformer.

As a result, an overfunction of all the differential protection devices monitoring the corresponding section of the energy supply network can be prevented at the same time.

In order to also inform the operating personnel of the electrical energy supply network of information about a possibly occurring fault in a secondary current transformer circuit, according to a further advantageous embodiment of the method according to the invention, it is provided that the presence of the fault signal from the local differential protection device and / or or the at least one remote differential protection device and / or a control room computer is displayed optically.

With regard to the differential protection device, the above object is achieved by a differential protection device of the type specified, in which the monitoring unit for implementing a method according to one of claims 1 to 11 is set up.

The invention will be explained in more detail below with reference to exemplary embodiments. Show this

FIG. 1 shows a schematic view of a differential protection system for protecting a section of a power supply network having two section ends, FIG. 2 shows a schematic view of a differential protection system for protecting a three-section end section of a power supply network,

FIG. 3 shows a block diagram with a differential protection device arranged at a section end,

Figure 4 is a logic flow diagram for explaining a first embodiment of a method for

Generating an error signal,

FIG. 5 shows a further logical flow diagram for explaining a second exemplary embodiment of a method for generating an error signal and

FIG. 6 shows a further logical flow diagram for explaining a third exemplary embodiment of a method for generating an error signal.

FIG. 1 shows a section 10 of an otherwise not further illustrated electrical energy supply network. Section 10 is shown in FIG. 1 as part of a power transmission line. In the same way, the section 10 of the energy supply network can also be a transformer or another component of an electrical energy supply network to be protected.

To monitor section 10 for faults such as short circuits or ground faults, a differential protection device is provided at each end of section 10. Thus, a first differential protection device 12a is disposed at a first section end IIa and a second differential protection device 12b at a second section end IIb. The differential protection Devices 12a and 12b receive, via current transformers 13a, 13b arranged at the respective section ends IIa, IIb, current measured values which indicate the current flowing through the respective section end IIa, IIb. If the electrical energy supply network is a polyphase, for example a three-phase, electrical energy supply network, appropriate current measured values are recorded at the section ends IIa, IIb for each phase of the section 10 and supplied to the respective differential protection device 12a, 12b.

The differential protection devices 12a, 12b calculate from the own current measured values and simultaneously measured current measured values of the respective remote differential protection device, taking into account the respective signs, a current sum.

For this purpose, the current measured values between the individual differential protection devices 12a, 12b can be exchanged via a communication line 14. In the error-free case of section 10, the calculated current sum should assume a value of approximately zero. However, if there is an error, such as a ground fault on the section 10, at a time at the section ends IIa, IIb in the section 10 into flowed current and out of it leaked current no longer match and the calculated current sum takes a value not equal to zero at. The calculation of the current sum can take place in two differential protection devices 12a, 12b or only one of the two. Therefore, when the calculated current sum exceeds a preset threshold, an error is detected on the section 10 and the differential protection devices 12a, 12b generate a trip signal A which is supplied to power switches 15a and 15b disposed at the respective section ends IIa, IIb these are required for opening their switch contacts. let it be. In this way, the faulty portion 10 is separated from the rest of the power grid.

FIG. 2 shows a further differential protection system. The illustration according to FIG. 2 corresponds essentially to that of FIG. Only with the differential protection system according to Figure 2, a portion 20 of an electrical power supply network is monitored, which now has three section ends 21a to 21c. The number of section ends is not limited to three, but a section with any number of section ends can be monitored. The number of differential protection devices used for this corresponds to the number of section ends.

Accordingly, in the example according to FIG. 2, an electrical differential protection device 22a to 22c is provided at each section end 21a to 21c, with which current measured values are detected via correspondingly connected current transformers 23a to 23c. Via all three differential protection devices 22a to 22c connecting communication lines 24, the current measured values are exchanged between the differential protection devices 22a to 22c and can thus be used to form a current sum taking into account all three section ends 21a to 21c. The calculation of the current sum can also take place in each case in all differential protection devices 22a to 22c or in a selected differential protection device.

According to the explanation of FIG. 1, the differential protection devices 22a to 22c generate a respective trigger signal

A is generated when the calculated current sum exceeds a preset threshold. In turn, the trip signals A cause circuit breakers 25a to 25c at the respective section ends 21a to 21c to open their switching circuits. contacts, whereby the faulty portion 20 is separated from the rest of the power grid.

Since the current readings taken at each end of the section provide the basis for calculating the current sum and are thus absolutely fundamental to the decision as to whether there is a fault on the section of the electrical grid, it is necessary to determine the path of the current measurements from their detection to the Use in the respective differential protection device for possibly occurring

To check errors. This will be explained in more detail below by way of example with reference to FIGS. 3 to 6.

For this purpose, FIG. 3 shows a section end 30 of a section of a three-phase energy supply network which is otherwise not shown. Correspondingly, the section end 30 also has three phase conductors L1, L2 and L3. At the individual phase conductors Ll, L2 and L3 first current transformer 31a, 31b, 31c are arranged, which may be, for example, conventional inductive current transformers. The first current transformers 31 a to 31 c emit at their secondary side the currents of lower current intensity which are proportional to the currents flowing in the individual phase conductors L 1, L 2 and L 3, which are transmitted to measuring inputs of a differential protection device 33 via measuring lines of a respective secondary current transformer circuit 32 a, 32 b, 32 c.

The differential protection device 33 has device-internal (second) current transformers 34a, 34b, 34c at its measuring inputs, which again transform the currents transmitted via the secondary current transformer circuits of the first current transformers 31a, 31b, 31c to a lower level so that they can be connected to the sensitive electronic circuits of the Differential protection device 33 can be processed. At the device The current transformers 34a to 34c are also, for example, inductive current transformers. On their secondary side, they in turn deliver the currents proportional to the differential protection device 33 via the secondary current transformer circuits 32a to 32c of the first current transformers 31a to 31c.

Consequently, the device-internal current transformers 34a to 34c also have secondary current transformer circuits 35a, 35b, 35c. The currents flowing in these secondary current transformer circuits 35a to 35c of the device-internal current transformers 34a to 34c are supplied within the differential protection device 33 to analog-to-digital converters 36a, 36b, 36c, which convert the analog currents into digital current measurements. The current measured values generated in each case are supplied to a computing device 37 of the differential protection device 33.

As has already been explained with reference to FIGS. 1 and 2, the arithmetic unit 37 of the differential protection device 33 leads at the same time for the individual phase conductors L1, L2, L3 on the basis of the individual current measured values acquired with respect to the individual phase conductors L1, L2, L3 on the one hand and of at least one remote differential protection device On the other hand, at the other end of the section of detected comparison current measurements, the formation of a current sum. For this purpose, the computing device 37 has a communication unit COM, which is connected to a data transmission line 38. Comparative current measured values from at least one other remote differential protection device can be transmitted to the local differential protection device 33 via the data transmission line 38 and the communication unit COM. Accordingly, the local differential protection device 33 can also be connected to the at least one remote differential protection device via the communication unit COM and the data transmission line 38 transmit its own current readings.

In the case of a fault on the section of the electrical energy supply network - as already explained - the current sum will assume a non-zero value. For this purpose, the differential protection device 33 checks with its computing device 37 whether the calculated current sum exceeds a preset current threshold value, and generates a trigger signal A at a command output if a threshold violation exists. The trigger signal A is used to cause an electrical circuit breaker 39 to open its switch contacts. If the fault on the section of the electrical energy supply network is a single-phase fault, for example a ground fault of the phase conductor L1, then it is sufficient for the power switch 39 to open only those switching contacts which are assigned to the phase conductor L1. In the case of a multi-phase fault, the respective switching contacts of the affected phase conductors L1, L2, L3 of the circuit breaker 39 are opened accordingly. This takes place both at the section end 30 and at the at least one further section end of the section of the electrical power supply network.

Frequently, an earth current or a total current is detected for the individual phase conductors Ll, L2, L3 of the section 30 of the electrical energy supply network. An earth current can be tapped at a grounded three-phase section of an electrical energy supply network, for example, at the connection between neutral point and earth. By contrast, a total current can, for example, as indicated in FIG. 3, be detected via a summation current transformer, which is designed as conversion converter 31c and encompasses all phase conductors L1 to L3 of section 30 of the electrical energy supply network become. The detected summation current is in turn fed via a secondary current transformer circuit 32d of the conversion converter 31c, a device-internal current transformer 34d and a device-internal secondary current transformer circuit 35d to another analog / digital converter 36d, which converts the analog sum current into digital summation current measurements and to the computing device 37 of the Differential protection device 33 outputs.

If an error should now occur on one of the secondary current transformer circuits (ie either one of the secondary current transformer circuits 32a to 32c of the first current transformers 31a to 31c or one of the device-internal current transformer circuits 35a to 35c of the device-internal current transformers 34a to 34c), the arithmetic means 37 of the differential - Protective device 33 transmitted faulty current measured values. In most cases, faults in secondary CT circuits are so-called wire breaks, i. E. H. an interruption, for example, of the secondary winding of the respective current transformer or the measuring lines of the secondary current transformer circuit. These are e.g. interruptions of the power converter circuits 32a to 32c of the first power converters 31a to 31c, which may be unintentionally caused by construction machinery due to building activities near the end of the section. In the event of such an interruption of one (or more) secondary current transformer circuit, the arithmetic unit 37 of the differential protection device 33 will not be supplied with correct current transformer measured values, which will result in erroneous calculation of the total current and thus in unwanted tripping of the electrical circuit breaker 39.

In order to prevent such an overfunction of the differential protection device 33, which is usually associated with high costs for the operator of the electrical power supply network. In addition, the computing device 37 of the differential protection device 33 has a monitoring unit 40 which monitors the secondary current transformer circuits 32a, 32b, 32c of the first current transformers 31a, 31b, 31c and / or the device-internal secondary current transformer circuits 35a to 35c for interruptions and in the event of a detected interruption emits an error signal. In the case of the present error signal, the arithmetic unit 37 is caused to block the differential protection functions for the phase conductors L1, L2, L3 correspondingly affected by the fault in the secondary current transformer circuit. In this way, the delivery of a trigger signal A based on a current sum calculated with erroneous current measurements is avoided and the circuit breaker contacts remain closed.

The method performed by the monitoring unit 40 will be explained in more detail below with reference to FIGS. 4 to 6.

First, for the sake of simplicity, in FIG. 4, the case of one

Section of a single-phase electrical power grid adopted. The monitoring unit 40a of this exemplary embodiment is supplied at a first input 41a to the current measured value IL recorded by a phase conductor. The monitoring unit 40a monitors - as per

Block 42a indicated - these current readings to determine whether the time course of their amounts has a sudden drop. Such an abrupt drop in the amounts of the current measured values can be due to an interruption of a secondary current-carrying circuit, but also to an actual current

Indicates faults in the monitored section of the electrical energy supply network. For this reason, first of all, no error signal indicating an error in a secondary current transformer circuit is rejected by the monitoring unit 40a. but only generates a suspect signal V, as indicated by block 43a. If the suspect signal V is present, it is at an input of a block 44 for generating the error signal F on. To verify the presence of a fault in a secondary CT circuit, the control unit 40a uses compare current measurements IaL, IbL which have been acquired for the phase conductor with differential protection devices removed at other section ends of the monitored section. As mentioned, these comparison current measurements are communicated to the local differential protection device by the remote differential protection devices via data transmission lines. The comparative current measurements are applied to the monitor at second inputs 41b, 41c, which are highlighted in Figure 4 by a dashed frame 41b.

In correspondence with the monitoring of the own current measured values, the monitoring unit 40a also examines the amounts of the comparison current measured value for sudden dropping, as indicated by blocks 42b and 42c. If the amounts of the comparative current measurements fall abruptly at the same time as their own current measurement values, this indicates an actual error in the monitored section of the electrical energy supply network, since the probability of a simultaneous occurring error in the secondary current transformer circuits at different section ends is highly unlikely , If, however, no abrupt drop in the amounts can be detected in the comparison current measured values, this indicates an error in the secondary current transformer circuit of a current transformer cooperating with the local differential protection device.

Accordingly, in a block 43b, a first reset signal R1 is generated when coincident with the sudden drop in the amounts of the own current measured values also with respect to the amounts of the comparative current measured values an occurring abrupt drop is recognized. This first reset signal R1 is applied to a blocking input of the block 44 for generating the error signal F and blocks the output of the error signal F.

In other words, an error signal F is consequently generated by the block 44 if a sudden drop in the amounts of the own current measured values has been recognized, but in the comparison current measured values of the remote differential protection devices no abrupt drop has been recognized. If, on the other hand, an abrupt drop also occurs at the same time in the comparison current measurement values, this indicates an actual fault on the section of the electrical power supply network and correspondingly no error signal F is output by the monitoring unit 40a, which blocks the differential protection functions of the differential protection device.

The relative according to Figure 4 illustrated a single-phase power supply network method for producing a an error in a secondary power converter circuit indicating error signal F is extended as shown in FIG 5 ^{'gieversorgungsnetz} on a three-phase energy. For this purpose, FIG. 5 shows a monitoring unit 40b, to which the measured current values IL1, IL2, IL3 of the three phase conductors detected at the local differential protection device are supplied at a first input 51a. These are then checked to determine whether the course of their amounts shows a sudden drop. If such an abrupt drop is detected in at least one phase of the current measured values, the first suspect signal V is generated at block 53a. If the suspicion signal is present in block 53a, this becomes active passed a block 54 to generate an error signal.

In addition, the monitoring unit 40b is also supplied with the comparison current measured values IaL1 to IaL3 and IbL1 to IbL3 of all three phases of the remote differential protection devices at inputs 51b and 51c. In blocks 52b and 52c, it is checked in accordance with the procedure in the single-phase system according to FIG. 4 whether the amounts of the comparison current measured values of the removed differential protection devices have a sudden, sudden drop.

At a block 53b, a first reset signal R1 is generated correspondingly precisely when a sudden drop in at least one course of the other comparison current measured values is detected based on the same phase conductor in which the jump has occurred at its own current measured values. Block 53b requires the information about which phase conductor the sudden drop in its own current measured values has occurred. The transmission of this information is indicated by a dashed line 56 in FIG.

If the first reset signal R 1 is also present with respect to the same phase in which the suspicion signal V was generated, this is transmitted to the blocking input of the block 54 for generating the error signal F and blocks the output of the error signal F, because in this case the signal F 1 is blocked actual error is detected in the section of the power grid.

The particular advantage of the described method is that hereby also interruptions in all three secondary Current transformer circuits can be detected, as for example, by an external effect, eg. B. by construction machines, on the test leads between the first current transformers and the differential protection device (see Figure 3) may arise. In this case, it is with respect to all three

In the own current measured values, a sudden drop occurs, while the comparison current measured values transmitted by the remote differential protection devices are unaffected. In this way, a reliable decision for generating the error signal F can be made in a simple manner, even with an interruption of the secondary current transformer circuits of all three phases.

Finally, FIG. 6 shows a further exemplary embodiment of a monitoring unit. The monitoring unit 40c according to FIG. 6 carries out some additional checks, by means of which a decision can more reliably be made as to whether a fault has occurred in a secondary current transformer circuit or whether there is an actual fault on the section of the electrical power supply network.

First of all, according to the function of the monitoring unit 40b according to FIG. 5, the individual current measured values are detected at the input 61a with respect to all phase conductors and tested for sudden decay at blocks 62a. A suspect signal V is generated at block 62a when such a jump has been detected in the current readings of at least one phase. The suspected signal V is forwarded to block 64 for generating the error signal F.

5, the comparison current measured values which are present at inputs 61b and 61c in blocks 62b and 62c are recorded simultaneously at the same time. supervised by a sudden drop in their amounts. If, in the comparison current measured values of at least one remote differential protection device with respect to the same phase, a sudden drop can be detected, the first reset signal R1 is generated in block 63b. The first reset signal Rl is supplied to an input of an OR module 65, whose output side is connected to the blocking input of the block 64 for error signal generation.

To further increase the reliability of the fault signal generation decision, the secondary current transformer circuits are also monitored for current flow. A current flow can be detected, for example, by current sensors used in accordance with the secondary current transformer circuits, for example Hall sensors. This information is fed to input 61d of the monitoring unit 40c. In blocks 62d it is checked whether there is a corresponding current flow and a second reset signal R2 is generated if there is a current flow in a secondary current transformer circuit with respect to the phase to which the suspect signal V has been generated, since a current flow indicates that the secondary current transformer circuit is not interrupted. The second reset signal is also supplied to the OR block 65 on the input side.

The monitoring unit 40c additionally detects at a further input 6Ie the sum current or ground current which has been detected at the respective section end with a corresponding converter (see FIG. According to FIG. 6, the sum current Isum is to be detected by way of example. In a block 62e it is checked whether at the same time as the sudden drop in the amounts of the own current measured values, a jump occurs in the course of the cumulative or ground current. is If so, a third reset signal is generated because a jump in the course of the sum or earth current measurements indicates an actual fault on the portion of the electrical power grid. The third reset signal R3 is also supplied to the OR block 65.

In a further block 62f, the locally detected current measured values are also checked as to whether they exceed a predefined threshold. If this is the case, then a fourth reset signal R4 is generated, which is supplied to the OR block 65. This is to prevent blocking of the differential protection functions in the case of very high currents on the section of the power supply network. In such a case, it may in fact be, for example, short-circuit currents flowing in the section of the electrical energy supply network, so that the differential protection functions must not be blocked for safety reasons in any case.

At a further input 61g, the monitoring unit 40c receives information about the state (open / closed) of the switching contacts of the circuit breaker associated with the local differential protection device. In block 62g, it is checked whether the switching contacts are in the open position, ie whether the monitored section is already disconnected from the power supply network. A fifth reset signal R5 is generated when the switch contacts of the circuit breaker are in the open state. This fifth reset signal R5 is also supplied to the OR block 65. This is to ensure that the differential protection functions are not interrupted when the section of the power supply network is switched off. This could in fact lead to an unwanted blocking of the differential protection when restarting the section of the power supply network. At a further input 61h, the monitoring unit 40c receives voltage measured values with respect to all phases of the section of the energy supply network. For the sake of simplicity, however, only one voltage value input is shown in FIG. this is representative of voltage value fairings of all three phases. The course of the voltage measurement values is checked in block 62h as to whether it has a sudden change and a sixth reset signal R6 is generated in block 63h if a sudden change in the course of the voltage measurement values occurs simultaneously with the generation of the suspicion signal V. Indeed, such an erratic course of the voltage readings would also indicate an error on the section of the electrical power grid, rather than a fault in the secondary CT circuit.

Finally, in block 62i, the locally measured current measured values are checked to see whether the course of their amounts continues to decrease even after the generation of the suspicion signal V.

Usually, in the presence of an interruption in a secondary current transformer circuit, the magnitude of the current measured values will approach zero after a first abrupt drop over time, ie decrease monotonically. However, should this monotone decrease in the amounts of the current measurement values not be present, this indicates that there is no fault in a secondary current transformer circuit. Consequently, a seventh reset signal R7 is generated in block 63i if the monotony condition is not met, ie if the current measurement values following the generation of the suspect signal V do not approach zero. Also, the seventh reset signal R7 is supplied to the OR block 65. The OR module outputs at its output a signal to the blocking input of the block 64 for generating the error signal F, if at least one of the reset signals Rl to R7 is present. In such a case, the generation of the error signal F should be blocked, so that the differential protection functions of the differential protection device are not impaired.

It should be noted that not necessarily in a monitoring unit in the context of the invention, all checks discussed in Figure 6 for the generation of the reset signals Rl to R7 must be performed. An appropriate selection can also be made. All that is essential is that according to the representation of FIG. 5, the comparison current measured values of the other differential protection devices are included in the check in addition to their own current measured values. The further checks, which have been addressed according to Figure 6, serve to verify the decision on a fault in the secondary current transformer circuit and can optionally be added individually or together.

Upon generation of a fault signal F indicative of a fault in the secondary CT circuit, the differential contactor functions for the affected phase of the electrical power grid in the local differential protection device and the remote differential protection devices are blocked. The blocking is canceled as soon as the error signal F is no longer generated, i. H. if the fault in the secondary CT circuit is eliminated.

At the same time, the local and / or the remote differential protection devices can visually be used to indicate that a fault has occurred in a secondary current transformer. Circuit has been detected. This error can be specified by specifying the appropriate phase and location of the CT. Such a display may alternatively or additionally also be displayed to the operating personnel of the electrical energy supply network in a control room via a host computer. In this way, operators can promptly initiate actions to correct the fault in the secondary CT circuit.

In the exemplary embodiments discussed here, in each case the comparison current measured values measured at the respective remote differential protection devices were checked for abrupt changes. Likewise, for example, the course of the current sum or a current subtotal or the course of so-called stabilization current values that can be used to stabilize the differential protection system can be used. The type of information used about the current measured values recorded at the remote differential protection devices should advantageously be selected such that values exchanged between the differential protection devices in any case are used in the course of the differential protection procedure for the function of the monitoring unit. As a result, no additional transmission bandwidth on the data transmission line between the differential protection is required for the transmission of additional information.

Claims

claims

A method of generating an error signal (F) indicative of a fault in the secondary circuit (eg, 32a, 35a) of a power converter (eg, 31a, 34a) that is connected to one of

Section end (30) of a electrical power grid monitoring local differential protection device (33) cooperates, wherein in the method

current measurement values detected by the current transformer (eg 41a, 34a), which flow through the section end (30)

Specify current, be monitored by the local differential protection device (33) and a suspected signal (V) is generated when the amounts of successive current readings abruptly drop, and - the error signal (F) is generated when the suspect signal (V) is present, characterized that

- A first reset signal (Rl) is generated by the local differential protection device (33), when at the time of Er- generating the suspicion signal (V) in at least one another section end of the electrical power supply network monitoring remote differential protection device detected comparison current measurements in terms of their amounts also leaps and bounds fall off, and - the error signal (F) is blocked when the first reset signal (Rl) is present.

2. The method according to claim 1, characterized in that - in the case of a multi-phase energy supply network, the current measured values detected by current transformers (eg 31a, 31b, 31c) of all phases (L1, L2, L3) are monitored for sudden decay with respect to their amounts . the suspected signal (V) is generated when, for at least one phase (eg L1), the values of successive current measured values of a current transformer (eg 31a) of the local differential protection device (33) cause a sudden drop

5 is known, and

the first reset signal (R1) is generated when, for the same phase in each case (eg L1), the amounts of successive comparison current measured values of a current transformer of the at least one remote differential protection device are also identical.

10 if a sudden drop is detected.

3. Method according to claim 2, characterized in that

in the local differential protection device (33) the secondary circuits (eg 32a, 32b, 32c) of the current transformers (eg 31a,

31b, 31c) of all phases (L1, L2, L3) are monitored for current flow,

a second reset signal (R2) is generated when at least one current transformer (eg 31a) is present in the presence of a current

20 flow amounts of successive current readings fall sharply, and

- The error signal (P) is also blocked when at least the second reset signal (R2) is present.

4. The method according to claim 2 or 3, wherein a

in the local differential protection device (33) a sum or ground current is detected in the section end (30) indicating sums or earth current measured values,

30 - a third reset signal (R3) is generated when the

Time of generating the suspect signal (V), the course of successive sum or Erdstrommesswerte has a sudden change, and - The error signal (F) is also blocked when at least the third reset signal (R3) is present.

5. The method of claim 2, wherein:

in the local differential protection device (33), the amounts of the current measured values of all phases (L1, L2, L3) are monitored for exceeding a predetermined threshold value and a fourth reset signal (R4) is generated if the magnitude of the current measured values of at least one phase (e.g. Ll) exceeds the threshold, and

- The error signal (F) is also blocked when at least the fourth reset signal (R4) is present.

6. Method according to one of claims 2 to 5, characterized in that a

a circuit breaker (39) controllable by the local differential protection device (33) is checked for the position of its switching contacts and a fifth reset signal (R5) is generated when the switching contacts of the circuit breaker (39) are open, and

- The error signal (F) is also blocked when at least the fifth reset signal (R5) is present.

7. Method according to one of claims 2 to 6, characterized in that

- the local differential protection device (33) for all phases (Ll, L2, L3) voltage readings indicating voltage applied to the section end (30) are detected and a sixth reset signal (R6) is generated, if at the time of generating the course of successive voltage measurement values of at least one phase (eg L1) has a sudden change in the suspect signal (V), and - The error signal (F) is also blocked when at least the sixth reset signal (R6) is present.

8. The method of claim 2, wherein:

in respect of a phase (eg L1) at which the suspect signal (V) has been generated, the following further current measured values are monitored at the time of generation of the suspect signal (V) and a seventh reset signal (R7) is generated when the Amounts of these other current readings are greater than the amount of that current measurement that has led to generating the suspicion signal (V), and

- The error signal (F) is also blocked when at least the seventh reset signal (R7) is present.

9. The method according to any one of the preceding claims, d a d u r c h e c e n e c e in that e

- be used as comparison current measurements of at least one remote differential protection device such current readings that are also transmitted to perform the differential protection function of the at least one remote differential protection device to the local differential protection device (33).

10. The method according to any one of the preceding claims, d a d u r c h e c e n e c e in that e

in the case of the present error signal (F), the differential protection functions of the local differential protection device (33) and of the at least one remote differential protection device relative to the fault in the secondary circuit (eg 32a, 35a) of the corresponding current transformer (eg 31a, 34a) are blocked (eg Ll).

11. The method according to any one of the preceding claims, characterized in that - the presence of the error signal (F) from the local differential protection device (33) and / or the at least one remote differential protection device and / or a control room computer is displayed optically.

12. Differential protection device (33) for monitoring a section end (30) of an electrical power supply network, which - cooperates with at least one current transformer (eg 31a, 34a), by means of the current from the differential protection device (33) current readings in the Characterize the current flowing portion (30) end of the power supply network, and the - comprising a computing device (37), the monitoring of the end of section on the basis of the current measurements and by at least one remote differential protection device to the local differential protection device (33) transmitted comparison current measurements (30), wherein the computing device (37) has a monitoring unit (40) which monitors a secondary circuit (eg 32a, 35a) of the current transformer (eg 31a, 34a) for faults, characterized in that the monitoring unit (40) for carrying out a method according to one of claims 1 to 11 is built.