CN113238172B - Current transformer neutral wire abnormity judgment method based on neutral wire resistance - Google Patents
Current transformer neutral wire abnormity judgment method based on neutral wire resistance Download PDFInfo
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- CN113238172B CN113238172B CN202110361366.1A CN202110361366A CN113238172B CN 113238172 B CN113238172 B CN 113238172B CN 202110361366 A CN202110361366 A CN 202110361366A CN 113238172 B CN113238172 B CN 113238172B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/58—Testing of lines, cables or conductors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/54—Testing for continuity
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/50—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to the appearance of abnormal wave forms, e.g. ac in dc installations
- H02H3/52—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to the appearance of abnormal wave forms, e.g. ac in dc installations responsive to the appearance of harmonics
Abstract
The application relates to a current transformer neutral wire abnormity judgment method based on neutral wire resistance. The method comprises the following steps: when the three-phase power supply system fails, acquiring the proportion of second harmonic components in the secondary current of each phase line; when the proportion of second harmonic components in the secondary currents of the at least two phase lines is larger than the first proportion value, acquiring the resistance of a neutral line; the neutral anomaly type is determined based on the resistance of the neutral. And adopting the proportion of the second harmonic component of the secondary current corresponding to each phase line of the three-phase power supply system as a judgment basis for the abnormal condition of the neutral line, further obtaining the resistance of the neutral line and analyzing the abnormal condition of the neutral line based on the resistance of the neutral line. Because the second harmonic component ratio is very small when the system normally operates, but is greatly improved when the neutral line is abnormal, the judgment of the neutral line abnormality based on the second harmonic component ratio is not easy to be interfered, and the judgment accuracy is greatly improved.
Description
Technical Field
The present disclosure relates to the field of three-phase power supply system protection technologies, and in particular, to a method and an apparatus for determining an abnormal neutral line of a current transformer based on a neutral resistance, a computer-readable storage medium, and a relay protection apparatus.
Background
The three-phase power supply system is closely related to the daily life of people and the normal operation of the society, and a relay protection technology is developed in order to ensure that the three-phase power supply system can timely react when a fault occurs. The relay protection technology mainly comprises a differential protection function, a backup protection function, a zero sequence protection function and the like, and the functions have good effects when common faults such as single-phase earth faults and the like in a three-phase power supply system are processed. However, when the neutral line of the secondary circuit of the three-phase power supply system is abnormal, the relay protection device is likely to malfunction or fail to operate. Therefore, accurate judgment of the neutral line abnormality is very important for improving the reliability of the relay protection device. The problem that the abnormality of the neutral line cannot be accurately judged exists in the prior art.
Disclosure of Invention
In view of the above, it is necessary to provide a method and an apparatus for determining a neutral wire abnormality of a current transformer based on neutral resistance, a computer readable storage medium, and a relay protection apparatus, which can accurately determine the neutral wire abnormality.
In one aspect, an embodiment of the present invention provides a method for determining an abnormal neutral line of a current transformer based on a neutral resistance, which is applied to a three-phase power supply system, where the three-phase power supply system includes the current transformer, a primary side of the current transformer is connected to each phase line of the three-phase power supply system, and a secondary side of the current transformer is configured to induce a secondary current corresponding to a current on each phase line, and the method includes: when the three-phase power supply system fails, acquiring the proportion of second harmonic components in the secondary current of each phase line; when the proportion of second harmonic components in the secondary currents of the at least two phase lines is larger than the first proportion value, acquiring the resistance of a neutral line; the neutral anomaly type is determined based on the resistance of the neutral.
In one embodiment, the step of determining the type of neutral anomaly based on the resistance of the neutral line comprises: when the resistance of the neutral line is greater than or equal to a first threshold resistance and less than a second threshold resistance, judging that the resistance of the neutral line is increased and abnormal; wherein the first threshold resistance is less than the second threshold resistance; and when the resistance of the neutral line is greater than or equal to the second threshold resistance, judging that the neutral line is abnormal in disconnection.
In one embodiment, the method further comprises the steps of: when the three-phase power supply system does not have a fault, acquiring the voltage of the neutral line and the current of a shielding layer of the neutral line; obtaining the shielding layer resistance of the neutral line according to the voltage of the neutral line and the shielding layer current of the neutral line; the step of obtaining the resistance of the neutral line comprises: when a three-phase power supply system fails, acquiring voltage of a neutral line, secondary zero-sequence current and shielding layer current of the neutral line; and obtaining the resistance of the neutral line according to the voltage of the neutral line, the secondary zero sequence current, the shielding layer current of the neutral line and the shielding layer resistance of the neutral line.
In one embodiment, the three-phase power supply system further comprises a relay protection device. When the abnormal type of the neutral line is that the resistance of the neutral line is increased and abnormal, the method further comprises the following steps: identifying a non-faulted phase in each phase line; locking a zero-sequence current differential protection function of the relay protection device; locking a phase current differential protection function of the relay protection device corresponding to the non-fault; and the setting value of the backup protection function of the relay protection device corresponding to the non-fault is improved.
In one embodiment, when the abnormality type of the neutral line is a neutral line disconnection abnormality, the method further includes the steps of: identifying a fault phase and a non-fault phase in each phase line; locking a zero sequence current differential protection function of the relay protection device; locking a phase current differential protection function of the relay protection device corresponding to the non-fault; the setting value of the backup protection function of the relay protection device corresponding to the non-fault is improved; and reducing the setting value of the phase current differential protection function of the relay protection device corresponding to the fault.
In one embodiment, identifying the faulty and non-faulty phases in the phase lines comprises the steps of: obtaining phase voltage and phase current of each phase line; if the phase voltage of the phase line is smaller than the first threshold phase voltage and the sudden change of the phase current of the phase line is larger than the threshold phase current sudden change, the phase line is judged to be a fault phase; if the phase voltage of the phase line is larger than the second threshold phase voltage, the phase line is judged to be a non-fault phase; wherein the second threshold phase voltage is greater than or equal to the first threshold phase voltage.
On the other hand, an embodiment of the present invention further provides a neutral line abnormality determination apparatus, including: the second harmonic component proportion obtaining module is used for obtaining the second harmonic component proportion in the second current of each phase line when the three-phase power supply system fails; the neutral line resistance obtaining module is used for obtaining the resistance of the neutral line when the proportion of second harmonic components in the secondary currents of the at least two phase lines is larger than the first proportion value; and the neutral line abnormity judging module determines the type of the neutral line abnormity according to the resistance of the neutral line.
In still another aspect, an embodiment of the present invention further provides a neutral wire abnormality determination computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the steps of the neutral wire abnormality determination method for a neutral wire resistance-based current transformer according to any of the embodiments described above.
In another aspect, an embodiment of the present invention further provides a relay protection device, including: the current acquisition unit is connected with the secondary side of the current transformer and is used for acquiring the secondary current of each phase line; the controller comprises a memory and a processor, the memory stores a computer program, and the processor realizes the following steps when executing the computer program: acquiring the proportion of second harmonic components in the secondary current of each phase line; when the proportion of second harmonic components in the secondary currents of the at least two phase lines is larger than the first proportion value, acquiring the resistance of a neutral line; the neutral anomaly type is determined based on the resistance of the neutral.
In one embodiment, the relay protection device further includes: the neutral line voltage acquisition unit is connected with the neutral line and used for acquiring the voltage of the neutral line; the controller is connected with the neutral line voltage acquisition unit, and the processor executes the computer program to realize the following steps: acquiring secondary zero sequence current and voltage of a neutral line; and obtaining the resistance of the neutral line according to the secondary zero sequence current and the voltage of the neutral line.
According to the embodiment of the method for judging the neutral line abnormity of the current transformer based on the neutral line resistance, the proportion of the second harmonic component of the secondary current corresponding to each phase line of the three-phase power supply system is used as a judgment basis for the abnormity of the neutral line, the resistance of the neutral line is further obtained, and the abnormity type of the neutral line is analyzed based on the resistance of the neutral line. Because the second harmonic component ratio is very small when the system normally operates, but is greatly improved when the neutral line is abnormal, the judgment of the neutral line abnormality based on the second harmonic component ratio is not easy to be interfered, and the judgment accuracy is greatly improved.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments or the conventional technologies of the present application, the drawings used in the descriptions of the embodiments or the conventional technologies will be briefly introduced below, it is obvious that the drawings in the following descriptions are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic view of a usage environment of a method for determining an abnormal neutral line of a current transformer based on neutral line resistance according to an embodiment;
FIG. 2 is a schematic flow chart illustrating a method for determining an abnormal neutral line of a current transformer based on neutral resistance according to an embodiment;
FIG. 3 is a schematic flowchart illustrating a method for determining an abnormal neutral line of a current transformer based on neutral resistance according to another embodiment;
FIG. 4 is a schematic flowchart illustrating a method for determining an abnormal neutral line of a current transformer based on neutral resistance according to another embodiment;
FIG. 5 is a schematic diagram of a process for handling an abnormal increase in neutral resistance according to an embodiment;
FIG. 6 is a schematic diagram of a process for handling a neutral line disconnect exception in one embodiment;
FIG. 7 is a schematic flow chart illustrating the identification of a failed phase and a non-failed phase in the phase lines in one embodiment;
fig. 8 is a schematic flow chart illustrating the process of identifying a failed phase and a non-failed phase in each phase line in another embodiment;
FIG. 9 is a functional block diagram of a neutral wire abnormality determining apparatus according to an embodiment;
fig. 10 is a schematic structural diagram of a relay protection device in one embodiment;
fig. 11 is a schematic structural diagram of a relay protection device in another embodiment.
Detailed Description
To facilitate an understanding of the present application, the present application will now be described more fully with reference to the accompanying drawings. Embodiments of the present application are set forth in the accompanying drawings. This application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.
It will be understood that, as used herein, the terms "first," "second," and the like may be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another.
It will be understood that when an element is referred to as being "connected" to another element, it can be directly connected to the other element or be connected to the other element through intervening elements. Further, "connection" in the following embodiments is understood to mean "electrical connection", "communication connection", or the like, if there is a transfer of electrical signals or data between the connected objects.
As used herein, the singular forms "a", "an" and "the" may include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises/comprising," "includes" or "including," etc., specify the presence of stated features, integers, steps, operations, components, parts, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, components, parts, or combinations thereof.
Referring to fig. 1, the three-phase power supply system includes three phase lines for supplying power and a current transformer. The three phase lines are respectively phase A, phase B and phase C. The primary side of the current transformer 10 is connected to each phase line, and the secondary side of the current transformer 10 is used for inducing a secondary current corresponding to the current on each phase line. It can be understood that the currents in the three phase lines are generally high-current signals, and it is difficult to directly obtain the currents, so the current transformer 10 is adopted to reduce the currents of the high-current signals. The current flowing through each phase line on the primary side of the current transformer 10 will obtain the secondary current corresponding to these large current signals on the secondary side of the current transformer 10. When a three-phase power supply system fails, the current measured at one time is abnormal, and the secondary current changes accordingly, so that the relay protection device 50 in the three-phase power supply system can perform corresponding protection actions on the system failure according to the secondary current.
As described in the background art, the conventional relay protection device 50 has a problem that it is easy to misjudge or malfunction, and this problem is caused by that the secondary zero-sequence current flows through the neutral line 30, and if the neutral line 30 is abnormal, and the zero-sequence current in the secondary zero-sequence circuit is affected, the zero-sequence current differential protection function in the relay protection device 50 may malfunction. It can be understood that the secondary zero sequence current is the zero sequence current of the secondary side of the current transformer 10. Furthermore, the abnormality of the neutral wire 30 may cause malfunction of the phase current differential protection function of each phase line in the relay protection device 50. Further, in order to solve the above problems, some technical solutions determine whether the neutral line 30 is abnormal based on a ratio of a third harmonic component in the second zero-sequence voltage or the zero-sequence current, where the third harmonic component refers to a signal component with a signal frequency three times a fundamental frequency of the three-phase power supply system. However, the inventor researches and discovers that with the addition of more and more power conversion devices such as a rectifier, an inverter and the like, a three-phase power supply system still contains third harmonic waves with a large specific gravity in normal operation, so that the accuracy of the method for judging the neutral line abnormality in the prior art is not high.
The inventors have also found that the cause of the malfunction of the differential protection is that the secondary current of each phase line in the three-phase system is abnormal due to the abnormality of the neutral line 30, so that a differential current occurs, and the relay protection device 50 malfunctions after detecting the differential current. Specifically, the neutral line 30 abnormality includes an abnormality of an increase in neutral resistance and an abnormality of a disconnection of the neutral line. If the neutral line 30 is normal, when a short-circuit fault occurs in the three-phase power supply system, taking a single-phase ground fault as an example, because the impedance of the resistance of the neutral line 30 is negligible compared with that of a non-fault phase, a large secondary short-circuit current generated in the secondary side of the current transformer 10 corresponding to the fault can completely flow through the neutral line 30 and finally be guided to the grounding grid, and the non-fault phase can not be influenced, so that the secondary current and the secondary voltage of the non-fault phase are not influenced, and the relay protection device corresponding to the non-fault cannot malfunction. If the neutral line 30 is abnormal, a single-phase earth fault also occurs, the resistance of the neutral line 30 is increased due to the abnormality and cannot be ignored, part of the secondary short-circuit current flows back to the secondary side of the current transformer 10 corresponding to the non-fault, and a differential current occurs on the secondary side of the current transformer 10 corresponding to the non-fault, so that the relay protection device malfunctions. When the secondary short-circuit current flows backward, the neutral point voltage is increased due to the shunt of the secondary short-circuit current and the large resistance of the neutral line 30, and at the moment, the large voltage of the neutral point acts on the secondary side of the current transformer 10, so that the coil on the secondary side of the current transformer 10 is saturated, and a large amount of secondary harmonic components appear between a fault phase and a non-fault phase. The second harmonic component refers to a signal component with a signal frequency twice the fundamental frequency of the three-phase power supply system.
Based on the above reasons, the present invention provides a method for determining an abnormal neutral line of a current transformer based on a neutral resistance, as shown in fig. 2, an embodiment of the present invention is applied to a three-phase power supply system, please refer to fig. 1, where the three-phase power supply system includes a current transformer 10, a primary side of the current transformer 10 is connected to each phase line of the three-phase power supply system, and a secondary side of the current transformer 10 is used for inducing a secondary current corresponding to a current on each phase line, and the method in this embodiment includes:
and S100, when the three-phase power supply system has a fault, acquiring the proportion of second harmonic components in the secondary current of each phase line.
Specifically, the second harmonic component fraction is used to characterize the content of the second harmonic in the second current. The ratio of the amplitude of the second harmonic component in the second current to the amplitude of the second current may be used as the second harmonic component proportion, or the ratio of the square of the amplitude of the second harmonic component in the second current to the square of the amplitude of the second current may be used as the second harmonic component proportion. Wherein, the secondary current can be collected by arranging a sensor at the secondary side of the current transformer 10. The amplitude of the second harmonic component can be processed according to Fourier analysis methods such as a fast Fourier algorithm, a discrete Fourier algorithm and the like, and the amplitude of the second harmonic component is extracted from a processing result.
And S300, when the proportion of second harmonic components in the secondary currents of the at least two phase lines is larger than the first proportion value, acquiring the resistance of the neutral line.
It can be understood that when the neutral line 30 is abnormal and the three-phase power supply system fails, the three phase lines will have more second harmonics, and when a large amount of second harmonics of at least two phase lines are detected, it can be determined that the neutral line 30 is abnormal. The first duty ratio value may be set by combining the simulation analysis result with a related file when the neutral line 30 of the three-phase power supply system is abnormal. For example, a three-phase power supply system simulation model is established in simulation software, various common faults occurring when the neutral line 30 is abnormal are simulated, and the proportion of second harmonic components when various faults occur is counted. And (3) calling a related file in a fault recorder when the neutral line 30 of the three-phase power supply system is abnormal, analyzing a fault waveform, and extracting a second harmonic component ratio in an actual fault. And setting the first ratio value by combining the data obtained by simulation and the related data in the actual fault.
And S500, determining the neutral line abnormal type according to the resistance of the neutral line.
It will be appreciated that the abnormality of the neutral line 30 is directly reflected in the neutral line resistance value, so the type of neutral line abnormality can be determined based on the neutral line resistance.
According to the embodiment of the method for judging the neutral line abnormity of the current transformer based on the neutral line resistance, the proportion of the second harmonic component of the secondary current corresponding to each phase line of the three-phase power supply system is used as a judgment basis for the abnormity of the neutral line, the resistance of the neutral line is further obtained, and the abnormity type of the neutral line is analyzed based on the resistance of the neutral line. Because the second harmonic component ratio is very small when the system normally operates, but is greatly improved when the neutral line is abnormal, the judgment of the neutral line abnormality based on the second harmonic component ratio is not easy to be interfered, and the judgment accuracy is greatly improved.
In one embodiment, as shown in fig. 3, the step S500 can be implemented by the following steps:
s510, when the resistance of the neutral line is larger than or equal to a first threshold value resistance and smaller than a second threshold value resistance, judging that the resistance of the neutral line is increased and abnormal; wherein the first threshold resistance is less than the second threshold resistance.
And S530, when the resistance of the neutral line is greater than or equal to the second threshold resistance, judging that the neutral line is abnormal in disconnection.
It is understood that the neutral anomaly types include an increase in neutral resistance anomaly and a neutral disconnection anomaly. When the resistance of the neutral line 30 is in a section where the section end points are the first threshold resistance and the second threshold resistance, respectively, it is determined that the resistance of the neutral line 30 is too large, that is, an abnormality occurs in that the neutral resistance becomes large. In reality, there is a possibility that an abnormality of increasing the neutral resistance occurs due to, for example, a virtual connection of the neutral line 30, and when it is found that the type of the neutral line abnormality is an abnormality of increasing the neutral resistance, the cause of the neutral line 30 abnormality can be found by checking whether or not the neutral line 30 connection point is stable. When the neutral line 30 is disconnected, the resistance of the neutral line 30 becomes extremely large, so when the resistance of the neutral line 30 is greater than or equal to the second threshold resistance, it is determined that the neutral line 30 has a neutral disconnection abnormality. The first threshold resistance and the second threshold resistance may be set according to a rated resistance value of the neutral line, or the like. For example, the first threshold resistance is set to 1.5 times the rated resistance value, and the second threshold resistance is set to 20 times the rated resistance value.
In one embodiment, the step of obtaining the neutral resistance may be achieved by:
and acquiring the voltage and the secondary zero sequence current of the neutral line, and acquiring the resistance of the neutral line according to the voltage and the secondary zero sequence current of the neutral line.
The step of obtaining the neutral resistance described above uses ohm's law, and specifically, the resistance of the neutral line 30 can be obtained from the ratio of the voltage of the neutral line 30 to the current of the neutral line 30. The secondary zero-sequence current is equal to the current of the neutral line 30, so the resistance of the neutral line can be obtained according to the voltage of the neutral line 30 and the secondary zero-sequence current.
Further, in a specific embodiment, as shown in fig. 4, the method further includes the steps of:
s306, when the three-phase power supply system does not have faults, acquiring the voltage of a neutral line and the current of a shielding layer of the neutral line; and obtaining the shield layer resistance of the neutral line according to the voltage of the neutral line and the shield layer current of the neutral line.
It can be understood that the neutral wire 30 is wrapped by a shielding layer, the shielding layer is used for reducing interference of a space electromagnetic field to the secondary cable, and two ends of the shielding layer are respectively connected with the grounding grid. When the interference is large or the ground screen is not good enough, a large current flows through the shielding layer, and a voltage difference is generated between two ends of the shielding layer due to the resistance of the shielding layer. The voltage difference affects the accuracy of detecting the neutral line voltage, and the voltage generated by the resistance of the shielding layer can be calculated according to the resistance of the shielding layer and the real-time current flowing through the resistance of the shielding layer. In order to remove the influence of the voltage on the accuracy of detecting the neutral line voltage, the resistance of the shielding layer needs to be acquired first. Specifically, when the three-phase power supply system is not in fault, the secondary zero-sequence current is zero, so the voltage generated by the neutral resistance is zero. The measured neutral line voltage is the voltage due to the resistance of the shield layer, and at this time, the neutral line voltage is divided by the shield layer current to obtain the resistance of the shield layer.
On the basis, the step of obtaining the neutral resistance can be further realized by the following steps:
and S310, when the three-phase power supply system has a fault, acquiring the voltage of the neutral line, the secondary zero sequence current and the shielding layer current of the neutral line.
And S330, obtaining the resistance of the neutral line according to the voltage of the neutral line, the secondary zero sequence current, the shielding layer current of the neutral line and the shielding layer resistance of the neutral line.
Specifically, in the event of a fault in the three-phase power supply system, the measured neutral line voltage includes the voltage produced by the neutral resistance and also includes the voltage produced by the shield resistance. And obtaining the voltage generated by the resistance of the shielding layer according to the current of the shielding layer of the neutral wire and the resistance of the shielding layer of the neutral wire. The difference between the voltage of the neutral line 30 and the voltage produced by the shield resistance is calculated. The difference between the voltage of the neutral line 30 and the voltage generated by the resistance of the shielding layer is divided by the second zero sequence current to obtain the accurate resistance of the neutral line 30.
In one embodiment, the configured functions of the relay protection device 50 include a differential protection function. The differential protection function is to use kirchhoff's current law, regard the protected device as a node, when the device is normal, the current flowing into the device and the current flowing out of the device should be equal, when the two currents have a difference current, it can be judged that a certain fault occurs, and the differential protection function is started. Further, the differential protection function comprises a zero-sequence current differential protection function, which is activated based on a difference current of the zero-sequence current. Specifically, according to the symmetrical component method, the sum of three-phase currents is three times of zero-sequence current, when the three-phase power supply system is normal, the zero-sequence currents flowing into the protected device and flowing out of the protected device are both 0, and when the protected device fails, the three phases are asymmetrical, so that the zero-sequence currents are in different flows, and the zero-sequence current differential protection function is started. Further, the differential protection function includes a phase current differential protection function that is activated based on a difference current of the phase currents. Specifically, when a phase line has a fault, a differential current will appear at two ends of the phase line, and the phase current differential protection function is started. Further, the relay protection device 50 is provided with a backup protection function, which is a protection function that is activated by a backup protection when the main protection is not activated for various reasons when the device to be protected is in a failure.
In order to cope with the influence of the abnormality of the neutral line 30, it is necessary to adjust the protection function of the relay protection device 50 to prevent the relay protection device 50 from malfunctioning. In the present embodiment, as shown in fig. 5, when the abnormality type of the neutral line 30 is an abnormality in which the neutral line resistance becomes large, the method further includes the steps of:
and S700, identifying non-fault phases in the phase lines.
And S730, locking the zero-sequence current differential protection function of the relay protection device.
It is understood that latching refers to opening a control loop of a protection function in the relay protection device 50 so that the protection function does not operate when the condition is satisfied. When the resistance of the neutral line 30 becomes large, the impedance of the secondary zero sequence loop is changed, and the secondary zero sequence current is also greatly influenced. Therefore, the zero-sequence current differential protection function in the relay protection device 50 based on the secondary zero-sequence current is not reliable, and the zero-sequence current differential protection function is locked to prevent the occurrence of false operation.
And S750, locking the phase current differential protection function corresponding to the non-fault of the relay protection device.
It can be understood that, because the resistance of the neutral line 30 becomes large, the current flowing backward occurs on the secondary side of the current transformer 10 corresponding to the non-fault, the current on the secondary side of the current transformer 10 corresponding to the non-fault cannot accurately reflect the fault current on the primary side, the current on the current side and the current on the opposite side must have a difference current, but the non-fault phase does not have a fault at this time, and the relay protection device 50 should not act, so that the phase current differential protection function corresponding to the non-fault of the relay protection device 50 is locked, and the occurrence of false operation is prevented.
And S770, improving the setting value of the backup protection function of the relay protection device corresponding to the non-fault.
In one embodiment, as shown in fig. 6, when the abnormal type of the neutral line 30 is a neutral line breakage, the method further includes the following steps:
and S900, identifying a fault phase and a non-fault phase in each phase line.
And S930, locking the zero-sequence current differential protection function of the relay protection device.
And S950, locking the phase current differential protection function corresponding to the non-fault of the relay protection device.
And S970, improving the setting value of the backup protection function of the relay protection device corresponding to the non-fault.
And S990, reducing the setting value of the phase current differential protection function corresponding to the fault of the relay protection device.
It can be understood that when the neutral line 30 is completely disconnected, the secondary zero sequence current also flows into the secondary side of the current transformer 10 corresponding to the non-fault, the current impedance of the fault phase is greatly increased, and the amplitude of the fault phase current is greatly reduced. In order to ensure the sensitivity of the phase current differential protection function, the setting value of the phase current differential protection function corresponding to the fault should be correspondingly reduced.
In addition, the descriptions of steps S930, S950, and S970 may refer to the descriptions of steps S730, S750, and S770 in the above embodiments, and are not repeated herein.
In one embodiment, as shown in fig. 7, the above method step S900 can be implemented by the following steps:
s910, phase voltage and phase current of each phase line are obtained.
It can be understood that, when each phase line of the three-phase power supply system has a fault, the phase voltage and the phase current corresponding to each phase line are affected. And judging the phase lines to be fault phases or non-fault phases based on the conditions of the phase voltages and the phase currents corresponding to the phase lines.
And S930, if the phase voltage of the phase line is smaller than the first threshold phase voltage and the sudden change of the phase current of the phase line is larger than the threshold phase current sudden change, judging that the phase line is a fault phase.
It is understood that the abrupt change amount of the phase current refers to an abrupt change amount of the phase current. Specifically, the phase current abrupt change amount can be obtained by comparing the obtained amplitude values of the phase currents at the continuous time, and the comparison and judgment of the phase current abrupt change and the threshold phase current abrupt change amount are realized through the controller. The most common fault in a three-phase power supply system is a short-circuit fault, when a phase line has a short-circuit fault, phase voltage can be reduced, and phase current can suddenly change due to short circuit. And therefore, the sudden change of the phase voltage and the phase current is combined to judge whether the phase line is a fault phase. The values of the first threshold phase voltage and the threshold phase current abrupt change may be set according to an actual operating state of the three-phase power supply system, a relevant regulation of the three-phase power supply system, and the like.
S950, if the phase voltage of the phase line is larger than the second threshold phase voltage, judging that the phase line is a non-fault phase; wherein the second threshold phase voltage is greater than or equal to the first threshold phase voltage.
It can be understood that improper values of the first threshold phase voltage and the second threshold phase voltage may cause a fault phase and a non-fault phase to occur, for example, when the first threshold phase voltage is selected to be 0.8 times of the rated phase voltage, and the second threshold phase voltage is selected to be 0.7 times of the rated phase voltage, if the phase voltage of the phase line is 0.75 times of the rated phase voltage, and the abrupt change of the phase current is also greater than the abrupt change of the threshold phase current, the phase line may be determined as the fault phase and the non-fault phase at the same time. Therefore, the second threshold phase voltage should be greater than or equal to the first threshold phase voltage to avoid the situation in the above example.
In one embodiment, as shown in fig. 8, the above method step S900 can be further implemented by:
and S911, acquiring the phase voltage and the phase current of the current side of each phase line, and the phase voltage and the phase current of the opposite side of each phase line.
It is understood that one side close to the main body of the embodiment of the present invention, such as the relay protection device, is the home side, and the side far away from the main body of the embodiment of the present invention is the opposite side. When the opposite side has a fault, the voltage and phase current of the local side may fluctuate very little, and whether the local phase line has the fault or not can be further judged by combining the voltage and phase current of the opposite side.
And S931, if the phase voltage of the local side is smaller than the first threshold phase voltage and the abrupt change of the phase current of the local side is larger than the abrupt change of the phase current of the first threshold, judging that the phase current is a fault phase.
The description of step S931 may refer to the description of step S930.
S951, if the phase voltage of the current side is greater than a second threshold phase voltage, the phase voltage of the opposite side is greater than the second threshold phase voltage, and the abrupt change of the phase current of the opposite side is less than a second threshold phase current abrupt change, judging that the phase current is a non-fault phase; the second threshold phase voltage is greater than or equal to the first threshold phase voltage, and the second threshold phase current mutation is less than or equal to the first threshold phase current mutation.
It is understood that when the phase voltage of the present side is greater than the second threshold phase voltage, it may be determined that the present side is not malfunctioning. When the phase voltage on the opposite side also meets the condition that the phase voltage is larger than the second threshold phase voltage and the condition that the phase current changes suddenly does not occur, the opposite side can be judged not to have faults. And judging that the side and the opposite side have no fault by combining the conditions, wherein the corresponding phase line is a non-fault phase.
It should be understood that although the various steps in the flowcharts of fig. 1-8 are shown in order as indicated by the arrows, the steps are not necessarily performed in order as indicated by the arrows. The steps are not performed in the exact order shown and described, and may be performed in other orders, unless explicitly stated otherwise. Moreover, at least some of the steps in fig. 1-8 may include multiple steps or multiple stages, which are not necessarily performed at the same time, but may be performed at different times, which are not necessarily performed in sequence, but may be performed in turn or alternately with other steps or at least some of the other steps or stages.
The embodiment of the present invention further provides a neutral line abnormality determining apparatus 100, which is applied to a three-phase power supply system, where the three-phase power supply system includes a current transformer 10, a primary side of the current transformer 10 is respectively connected to each phase line of the three-phase power supply system, and a secondary side of the current transformer 10 is used for inducing a secondary current corresponding to a current on each phase line. As shown in fig. 9, the neutral line abnormality determination device includes: and the second harmonic component proportion obtaining module 103 is configured to obtain a second harmonic component proportion in a second current of each phase line when the three-phase power supply system fails. The neutral resistance acquiring module 105 is configured to acquire a neutral resistance when a ratio of second harmonic components in the secondary currents of the at least two phase lines is greater than a first ratio. And a neutral line abnormality judgment module 107, which determines the type of the neutral line abnormality according to the secondary zero sequence current.
For the specific definition of the neutral line abnormality determining device, reference may be made to the above definition of the neutral line abnormality determining method of the current transformer based on the neutral line resistance, and details are not repeated here. All or part of the modules in the neutral line abnormality judgment device can be realized by software, hardware and a combination thereof. The modules can be embedded in a hardware form or independent from a processor in the computer device, and can also be stored in a memory in the computer device in a software form, so that the processor can call and execute operations corresponding to the modules. It should be noted that, in the embodiment of the present application, the division of the module is schematic, and is only one logic function division, and there may be another division manner in actual implementation.
In an embodiment, referring to fig. 10, the present invention further provides a relay protection device 50, which is applied to a three-phase power supply system, where the three-phase power supply system includes a current transformer 10, a primary side of the current transformer 10 is connected to each phase line of the three-phase power supply system, and a secondary side of the current transformer 10 is used for inducing a secondary current corresponding to a current on each phase line. The relay protection device 50 includes a current collection unit 53 and a controller 55. The current collecting unit 53 is connected to the secondary side of the current transformer 10, and is configured to collect the secondary current of each phase line. The controller 55 comprises a memory and a processor, the memory stores computer programs, and the processor implements the following steps when executing the computer programs: when the three-phase power supply system fails, acquiring the proportion of second harmonic components in the secondary current of each phase line; when the proportion of second harmonic components in the secondary currents of the at least two phase lines is larger than the first proportion value, acquiring the resistance of a neutral line; the neutral anomaly type is determined based on the resistance of the neutral.
In one embodiment, as shown in fig. 11, the relay protection device 50 further includes a neutral line voltage collecting unit 57, and the neutral line voltage collecting unit 57 is connected to the neutral line 30 for collecting a voltage of the neutral line 30. The controller 55 is connected to the neutral line voltage pick-up unit 57, and the computer program when executed further performs the steps of: acquiring secondary zero sequence current and voltage of a neutral line; and obtaining the resistance of the neutral line according to the secondary zero sequence current and the voltage of the neutral line.
In some embodiments, the controller 55 of the relay protection device 50, when executing the computer program, further implements the steps of the above-described neutral wire abnormality determination method embodiment of the neutral wire resistance-based current transformer.
The steps implemented when the computer program in the relay protection device provided in the embodiment of the present invention is executed may refer to the descriptions of the steps in the above method for determining an abnormal neutral line of a current transformer based on a neutral resistance, and are not described herein again.
In one embodiment, the present invention further provides a computer-readable storage medium, on which a computer program is stored, and the computer program, when executed by a processor, implements the steps of the method for determining an abnormality of a neutral wire of a neutral resistance-based current transformer in the above embodiments.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by hardware instructions of a computer program, which can be stored in a non-volatile computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. Any reference to memory, storage, database or other medium used in the embodiments provided herein can include at least one of non-volatile and volatile memory. Non-volatile Memory may include Read-Only Memory (ROM), magnetic tape, floppy disk, flash Memory, optical storage, or the like. Volatile Memory can include Random Access Memory (RAM) or external cache Memory. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM), among others.
In the description herein, references to the description of "some embodiments," "other embodiments," "desired embodiments," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, a schematic description of the above terminology may not necessarily refer to the same embodiment or example.
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, and these are all within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (8)
1. A neutral line abnormity judgment method of a current transformer based on neutral line resistance is applied to a three-phase power supply system, the three-phase power supply system comprises the current transformer, the primary side of the current transformer is respectively connected with each phase line of the three-phase power supply system, and the secondary side of the current transformer is used for inducing secondary current corresponding to the current on each phase line, and the method is characterized by comprising the following steps:
when the three-phase power supply system fails, acquiring the proportion of second harmonic components in the secondary current of each phase line;
when the proportion of second harmonic components in the secondary currents of the at least two phases of the phase lines is larger than the first proportion value, acquiring the resistance of a neutral line;
when the resistance of the neutral line is greater than or equal to a first threshold resistance and less than a second threshold resistance, determining that the neutral line abnormity type is a neutral line resistance increase abnormity; wherein the first threshold resistance is less than the second threshold resistance;
determining that the type of neutral anomaly is a neutral disconnection anomaly when the resistance of the neutral is greater than or equal to the second threshold resistance;
the three-phase power supply system also comprises a relay protection device; when the abnormality type of the neutral line is the neutral line disconnection abnormality, the method further comprises the following steps:
identifying a failed phase and a non-failed phase in each of the phase lines;
locking the zero sequence current differential protection function of the relay protection device;
locking the phase current differential protection function of the relay protection device corresponding to the non-fault;
improving the setting value of the backup protection function of the relay protection device corresponding to the non-fault;
and reducing the setting value of the phase current differential protection function of the relay protection device corresponding to the fault.
2. The neutral wire abnormality judgment method of a neutral wire resistance-based current transformer according to claim 1, characterized by further comprising the steps of:
when the three-phase power supply system does not have a fault, acquiring the voltage of the neutral line and the current of a shielding layer of the neutral line;
obtaining the shielding layer resistance of the neutral line according to the voltage of the neutral line and the shielding layer current of the neutral line;
the step of obtaining the resistance of the neutral line includes:
when a three-phase power supply system breaks down, acquiring the voltage of the neutral line, the secondary zero sequence current and the shielding layer current of the neutral line;
and obtaining the resistance of the neutral line according to the voltage of the neutral line, the secondary zero sequence current, the shielding layer current of the neutral line and the shielding layer resistance of the neutral line.
3. The neutral wire abnormality judgment method of a neutral wire resistance-based current transformer according to claim 1, characterized by further comprising, when the abnormality type of the neutral wire is a neutral wire resistance increase abnormality, the steps of:
identifying a non-faulted phase in each of the phase lines;
locking the zero sequence current differential protection function of the relay protection device;
locking the phase current differential protection function of the relay protection device corresponding to the non-fault;
and improving the setting value of the backup protection function of the relay protection device corresponding to the non-fault.
4. The neutral wire abnormality judgment method of a neutral wire resistance-based current transformer according to claim 3, wherein said identifying a faulty phase and a non-faulty phase in each of said phase wires comprises the steps of:
obtaining phase voltage and phase current of each phase line;
if the phase voltage of the phase line is smaller than a first threshold phase voltage and the sudden change of the phase current of the phase line is larger than a threshold phase current sudden change, judging that the phase line is a fault phase;
if the phase voltage of the phase line is larger than a second threshold phase voltage, judging that the phase line is a non-fault phase; wherein the second threshold phase voltage is greater than or equal to the first threshold phase voltage.
5. A neutral wire abnormity judgment device is applied to a three-phase power supply system, the three-phase power supply system comprises a current transformer, the primary side of the current transformer is respectively connected with each phase wire of the three-phase power supply system, and the secondary side of the current transformer is used for inducing secondary current corresponding to the current on each phase wire, and the neutral wire abnormity judgment device is characterized by comprising:
the second harmonic component proportion obtaining module is used for obtaining the second harmonic component proportion in the second current of each phase line when the three-phase power supply system fails;
the neutral line resistance obtaining module is used for obtaining the resistance of the neutral line when the proportion of second harmonic components in the secondary currents of the at least two phase lines is larger than a first proportion value;
the neutral line abnormity judging module is used for determining that the neutral line abnormity type is the neutral line resistance increase abnormity when the resistance of the neutral line is greater than or equal to a first threshold resistance and less than a second threshold resistance; wherein the first threshold resistance is less than the second threshold resistance; when the resistance of the neutral line is greater than or equal to the second threshold resistance, determining that the type of neutral line abnormality is a neutral line disconnection abnormality.
6. A computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out the steps of the method of any one of claims 1 to 4.
7. The utility model provides a relay protection device, is applied to three-phase power supply system, three-phase power supply system includes current transformer, current transformer's primary side respectively with each phase line of three-phase power supply system is connected, current transformer's secondary side is used for inducting out with each secondary current that the electric current on the phase line corresponds, its characterized in that, relay protection device still includes:
the current acquisition unit is connected with the secondary side of the current transformer and is used for acquiring the secondary current of each phase line;
a controller comprising a memory and a processor, the memory storing a computer program, the processor implementing the following steps when executing the computer program:
when the three-phase power supply system fails, acquiring the proportion of second harmonic components in the secondary current of each phase line;
when the proportion of second harmonic components in the secondary currents of the at least two phase lines is larger than the first proportion value, acquiring the resistance of a neutral line;
when the resistance of the neutral line is greater than or equal to a first threshold resistance and less than a second threshold resistance, determining that the neutral line abnormity type is a neutral line resistance increase abnormity; wherein the first threshold resistance is less than the second threshold resistance;
when the resistance of the neutral line is greater than or equal to the second threshold resistance, determining that the type of the neutral line abnormality is a neutral line disconnection abnormality.
8. The relay protection device according to claim 7, further comprising a neutral line voltage collecting unit connected to the neutral line for collecting a voltage of the neutral line; the controller is connected with the neutral line voltage acquisition unit, and the processor executes the computer program to realize the following steps:
acquiring secondary zero sequence current and voltage of the neutral line;
and obtaining the resistance of the neutral line according to the secondary zero sequence current and the voltage of the neutral line.
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