Distribution network line grounding fault judgment method based on single-phase grounding and voltage transformer disconnection analysis

Abstract

The application provides a distribution network line grounding fault judgment method based on single-phase grounding and voltage transformer disconnection analysis, and belongs to the technical field of distribution network line grounding fault judgment; in order to solve the technical problem that the current distribution network line grounding alarm system cannot detect the abnormality of three-phase voltage values and unbalanced voltage values and cannot timely send a grounding alarm signal, in a neutral point effective grounding system, the symmetrical component method is used to analyze single-phase grounding faults in the distribution network line; the voltage transformer primary side single-phase disconnection is analyzed to obtain corresponding system grounding fault judgment rules; the voltage transformer secondary side single-phase disconnection is analyzed, including two cases of internal disconnection of the protection device and disconnection of the voltage transformer lead-out loop, and based on voltage change characteristics, corresponding system grounding fault judgment rules are obtained; and the application is applied to distribution network line grounding fault judgment.

Description

Technical Field

[0001] This invention provides a method for judging grounding faults in distribution network lines based on single-phase grounding and voltage transformer disconnection analysis, belonging to the technical field of grounding fault judgment in distribution network lines. Background Technology

[0002] There are two operating modes for the neutral point of a power system: direct grounding and indirect grounding. In the indirect grounding mode, the fault current during a single-phase grounding (SLG) fault is relatively small, hence it is also called low-current grounding mode. This includes ungrounded neutral point, grounding via arc suppression coil, and grounding via a large resistor. In the direct grounding mode, the fault current is relatively large, hence it is also called high-current grounding mode. This includes direct grounding and grounding via a small resistor.

[0003] Currently, power grid distribution networks generally operate using low-current grounding. This is because, under this operating mode, when a SLG (Self-Like Power Grid) fault occurs, the line voltage on the load side remains balanced across the three phases, allowing for continuous operation for a period of time. This avoids unnecessary power outages caused by transient faults and effectively improves the reliability of the power supply system. Generally, low-voltage distribution networks of 6kV-10kV typically do not have a grounded neutral point, while medium- and high-voltage distribution networks of 35kV and above usually have arc suppression coils installed. Although some urban distribution networks are gradually adopting low-resistance grounding due to the gradual expansion of distribution network scale and the extensive use of cables, low-current grounding remains the mainstream method overall.

[0004] In the daily operation and maintenance of power distribution networks, ground fault alarm signals are a crucial piece of information, directly reflecting the operating status of 35kV and below systems. If a 35kV or below power system issues a ground fault alarm signal, monitoring personnel need to disconnect circuit breakers to pinpoint the fault location. Under normal circumstances, the ground fault alarm signal is sent from the microcomputer harmonic suppression device installed at the substation site to the public monitoring and control device, displayed on the local back-end computer via the substation network, and simultaneously uploaded to the dispatch master station via the dispatch data network. It is then displayed in the E6000 centralized control master station system, and an alarm sound is emitted to alert monitoring personnel. However, due to malfunctions or power outages of the microcomputer harmonic suppression device, the dispatch master station cannot display fault information when a ground fault occurs in the power system, thus failing to accurately reflect the operating status of the power grid.

[0005] In addition, in actual operation, the dispatch master station can receive not only grounding alarm signals, but also three-phase voltage values ​​and zero sequence values ​​from substations. It can determine whether a grounding fault has occurred by analyzing voltage changes. Since the dispatch master station monitors a large number of substations, monitoring personnel cannot detect abnormalities in three-phase voltage values ​​and unbalanced voltage values ​​U0 in a timely manner. It is necessary to generate photonic signs and alarm signals through logical analysis and calculation in the monitoring master station system, and issue grounding alarm signals in a timely manner. However, the current monitoring master station does not have this function, and the corresponding control analysis strategy is also blank. Summary of the Invention

[0006] To address the technical problems existing in the background art, the present invention provides a method for judging grounding faults in distribution network lines based on single-phase grounding and voltage transformer disconnection analysis, comprising the following steps:

[0007] Step 1: In a neutral-point effectively grounded system, the symmetrical component method is used to analyze single-phase grounding faults in the distribution network lines;

[0008] Step 2: Analyze the single-phase open circuit on the primary side of the voltage transformer to obtain the corresponding system grounding fault judgment rules;

[0009] Step 3: Analyze the single-phase open circuit on the secondary side of the voltage transformer, including two cases: open circuit inside the protection device and open circuit in the voltage transformer lead-out circuit. Based on the voltage change characteristics, obtain the corresponding system grounding fault judgment rules.

[0010] Step 4: Determine the grounding fault of the distribution network lines based on the obtained system grounding fault judgment rules.

[0011] The neutral point effective grounding system used in step one satisfies the following conditions: the ratio of the zero-sequence to the positive-sequence reactance X0 / X1 of the system is positive and not greater than 3, and the ratio of the zero-sequence resistance to the positive-sequence reactance R0 / X1 of the system is not greater than 1.

[0012] The symmetric component method used in step one is specifically a decoupling operation process, including:

[0013] A set of three asymmetrical electrical quantities is decomposed into three sets of electrical components: positive sequence, negative sequence, and zero sequence. The angular relationship is expressed in exponential form, and let... , , will 1 ( ), , To form a symmetric system with a modulus of 1 and a phase difference of 120°, Called the operational factors, the methods for calculating the positive, negative, and zero-order components of an asymmetric vector are as follows:

[0014] Suppose that the three voltage or current vectors A, B, and C are asymmetrical, i.e., their magnitudes are unequal and their phases are not 120° apart. According to the method of symmetrical components, vector A is decomposed into three vectors A1, A2, and A0; vector B is decomposed into three vectors B1, B2, and B0; and vector C is decomposed into three vectors C1, C2, and C0. Then, the following conditions are met:

[0015] (1);

[0016] (2);

[0017] Given three vectors A, B, and C, the formulas for calculating their corresponding positive, negative, and zero-order components are as follows:

[0018] (3);

[0019] Analysis revealed that vectors A1, B1, and C1 are equal in magnitude and their phases differ by 120° in sequence. , A1, B1, and C1 are called positive-order components;

[0020] The three vectors A2, B2, and C2 are equal in magnitude and have reversed phase sequence with a phase difference of 120°. , A2, B2, and C2 are called negative-order components;

[0021] Vectors A0, B0, and C0 have equal magnitudes and the same direction; these three vectors are called zero-order components.

[0022] The specific method for analyzing a single-phase ground fault in step one is as follows:

[0023] In a neutral-point effectively grounded system, assuming phase A of the system is metallically grounded, the boundary conditions satisfy:

[0024] (4);

[0025] Among them, the special phase is phase A. In the case of a single-phase ground fault, the special phase is the fault phase.

[0026] Using the symmetric component method, the boundary conditions are expressed in terms of special phase sequence components, as follows:

[0027] (5);

[0028] Draw the composite sequence network diagram when phase A is grounded, identify the zero-sequence component current and voltage at the fault point when a single-phase ground is occurred, and define the parameters in the diagram. Given the electromotive force of phase A before the fault, analyze the voltage at the fault point when a ground fault occurs. Then the following condition is met:

[0029] (6);

[0030] in, , , The combined zero-sequence, positive-sequence, and negative-sequence impedances of the system at the fault point. , , The zero-sequence, positive-sequence, and negative-sequence currents of the fault branch at the fault point. , , The zero-sequence, positive-sequence, and negative-sequence voltages of the fault phase at the fault point;

[0031] Using the symmetrical component method, the voltages of the two non-faulty phases are... and Represented as:

[0032] (7);

[0033] (8);

[0034] In actual operation, it is assumed that the positive-sequence and negative-sequence impedances of stationary components are equal, i.e. Then the above formula simplifies to:

[0035] (9);

[0036] (10);

[0037] In the formula, , , The fault point represents the electromotive force of phases A, B, and C before the fault. , , The voltages of phases A, B, and C at the fault point after a ground fault;

[0038] At that time, the voltage amplitudes of the two non-faulty phases changed from Change to The angle between the two non-faulty phases changes from 180° to 60°;

[0039] when At that time, the voltage values ​​of the two non-faulty phases remain unchanged. The voltage values ​​of the two non-faulty phases increased;

[0040] when At this time, it is equivalent to the neutral point of the system being ungrounded, and the effectively grounded neutral point system becoming an ungrounded system. , Amplitude becomes The included angle becomes 60°, and the zero-sequence voltage becomes ;

[0041] For a single-phase fault in a neutral-point ungrounded system, the voltage of the non-faulty phase rises to 1.732 times the pre-fault voltage, and the zero-sequence voltage rises to 100V. In the dispatch master station system, the amplitudes of the A, B, and C phase voltages and the zero-sequence voltage are judged to determine whether the system is grounded.

[0042] When two phases of the same line are grounded, there is a large fault current at the protection installation point, and the protection device will trip, and the two-phase grounding will change to normal operation;

[0043] In the event of a cross-line phase fault, the protection device will trip, and the two-phase grounding will be converted to a single-phase grounding or normal operation will resume.

[0044] The specific method for step two is as follows:

[0045] Define the open circuit of phase A of the voltage transformer, and obtain the composite sequence network diagram of the open circuit of phase A of the voltage transformer. , , These are the zero-sequence, positive-sequence, and negative-sequence impedances of the voltage transformer's secondary load reflected to the primary side. , , These are the external zero-sequence, positive-sequence, and negative-sequence voltages connected to the primary side of the voltage transformer. , , These are the zero-sequence, positive-sequence, and negative-sequence currents on the primary side of the voltage transformer. Let be the electromotive force of the system, and define a condition that satisfies... , ,in It is the ratio of zero-sequence impedance to positive-sequence impedance. Using the symmetrical component method, we obtain:

[0046] (11);

[0047] in, , , These are the phase A, B, and C voltages on the primary side of the voltage transformer.

[0048] set up , The system nominal voltage is given, and the voltage transformer ratio is given. From the above formula, the calculation formulas for the secondary phase voltage and zero-sequence voltage when the primary side A phase of the voltage transformer is disconnected are as follows:

[0049] (12);

[0050] in, , , These are the voltages of phases A, B, and C on the secondary side of the voltage transformer. The voltage is the zero-sequence voltage connected to the secondary side of the voltage transformer.

[0051] From the above formula, we can see that the secondary voltage of phase A, which is disconnected, decreases, while the secondary voltages of phases B and C remain unchanged; a zero-sequence voltage appears on the open delta side, and this voltage value will not be lower than 14V.

[0052] When a phase A ground fault occurs in the system and the phase A of the voltage transformer is disconnected, the disconnection sequence network of phase A is approximately the same as the non-disconnection sequence network, which is equivalent to... The voltage of phases B and C without disconnection is about 110V, the voltage of phase A with disconnection is about 0V, and the external zero-sequence voltage is about 110V.

[0053] When a phase A ground fault occurs in the system and the voltage transformer is disconnected on phase B, at this time, The voltage of phase A (non-disconnected) is approximately 0, the voltage of phase C (non-disconnected) is approximately 110V, the voltage of phase B (disconnected) decreases, and the external zero-sequence voltage is not lower than 40V.

[0054] The specific method for analyzing the internal disconnection of the protection device in step three is as follows:

[0055] When the secondary wiring of the voltage transformer is normal, set , , The secondary phase impedance of the voltage transformer. , , This is the secondary phase-to-phase impedance. , , To determine the ground fault caused by an internal open circuit in the protection device based on the voltage change characteristics at the acquisition terminal of the protection device, the following are included:

[0056] When introduced into the internal protection device When the phase is broken, there is , , The self-generated zero-sequence voltage is approximately 19.2V, and the external zero-sequence voltage is approximately 100V.

[0057] When a phase A ground fault occurs in the system, and it is introduced into the protection device... When one phase is disconnected, the other phase is disconnected. , The secondary voltage of the phase is approximately 110V, and the phase is disconnected. The secondary voltage of the phase is approximately 0V, the self-generated zero-sequence voltage is approximately 36.6V, and the external zero-sequence voltage is approximately 110V;

[0058] When a phase A ground fault occurs in the system, and it is introduced into the protection device... When one phase is disconnected, the other phase is disconnected. The secondary voltage of the non-disconnected phase is approximately 0. The secondary voltage of the phase is approximately 110V, and the phase is disconnected. The phase secondary voltage is approximately 0, the self-generated zero-sequence voltage is approximately 36.6V, and the external zero-sequence voltage is approximately 110V.

[0059] The specific method for analyzing the open circuit of the voltage transformer lead-out circuit in step three is as follows:

[0060] When the voltage transformer leads out of the circuit When a phase disconnection occurs, the secondary load is assumed to be symmetrical, satisfying the following conditions: , The secondary phase voltage is calculated based on the superposition principle, and the formula is as follows:

[0061] (13);

[0062] The self-generated zero-sequence voltage is further obtained as follows:

[0063] , ( (14);

[0064] Analysis yielded the following results:

[0065] When the secondary side of a voltage transformer has only phase-to-phase impedance and no phase impedance, that is... The maximum self-generated zero-sequence voltage is 31.76V;

[0066] When the secondary side of a voltage transformer has only phase impedance and no phase-to-phase impedance, i.e. The maximum self-generated zero-sequence voltage is 21.17V;

[0067] The maximum amplitude of the phase voltage during a disconnection is 31.76V, and the minimum amplitude is 0V.

[0068] Then, based on the following voltage change characteristics, the ground fault caused by the disconnection of the system's lead-out circuit is determined, including:

[0069] When a phase A ground fault occurs in the system, and the voltage transformer lead-out circuit... When one phase is disconnected, the other phase is disconnected. , The secondary voltage of the phase is approximately 110V, and the phase is disconnected. The secondary voltage of the phase is approximately 0V, the self-generated zero-sequence voltage is approximately 36.6V, and the external zero-sequence voltage is approximately 110V;

[0070] When a phase A ground fault occurs in the system, and it is introduced into the protection device... When one phase is disconnected, the other phase is disconnected. The secondary voltage of the non-disconnected phase is approximately 0. The secondary voltage of the phase is approximately 110V, and the phase is disconnected. The secondary voltage decreases, ranging from 0 to 55.01V. The self-generated zero-sequence voltage ranges from 55.01V to 36.67V, while the external zero-sequence voltage is approximately 110V.

[0071] The beneficial effects of this invention compared to the prior art are as follows: This invention provides a method for judging grounding faults in distribution network lines based on single-phase grounding and voltage transformer disconnection analysis. By analyzing the voltage change pattern after a distribution network line is grounded, the method performs analysis and calculation at the monitoring master station, actively analyzes the line operating conditions, predicts the grid status in a timely manner, and proposes single-phase grounding fault analysis methods and voltage transformer disconnection fault analysis methods. It controls the generation of grounding alarm signals and solves the problem of issuing grounding signals when the microcomputer harmonic suppression device fails. In addition, this invention also proposes a specific voltage limit setting method by analyzing the voltage change pattern after the system is grounded, including the change pattern after the primary and secondary disconnection of the voltage transformer (PT), combined with the actual grid situation. Attached Figure Description

[0072] The present invention will be further described below with reference to the accompanying drawings:

[0073] Figure 1 This is a schematic diagram of the composite sequence network when phase A is grounded according to the present invention;

[0074] Figure 2 This is a schematic diagram of the non-faulty phase voltage during a single-phase ground fault according to the present invention;

[0075] Figure 3 This is a schematic diagram of the voltage vector when a single-phase grounding occurs in the neutral point ungrounded system of the present invention;

[0076] Figure 4 This is a schematic diagram of the composite sequence network when the A phase of the primary side of the PT is disconnected according to the present invention;

[0077] Figure 5 This is a circuit diagram of the PT secondary wiring of the present invention;

[0078] Figure 6 This is a schematic diagram illustrating the use of a formula editor in an embodiment of the present invention;

[0079] Figure 7 This is a schematic diagram illustrating the creation of photon card information in an embodiment of the present invention. Detailed Implementation

[0080] like Figures 1 to 5 As shown, this invention provides a method for judging grounding faults in distribution network lines based on single-phase grounding and voltage transformer disconnection analysis. It relates to a method for judging grounding faults by the dual occurrence of grounding fault signals at a monitoring station, specifically including:

[0081] Step 1: Analyze single-phase ground faults, which involve:

[0082] Neutral grounding method:

[0083] The electrical connection between the neutral point and the ground in a three-phase AC power system is called the neutral point grounding method, which can be divided into effective grounding and ineffective grounding. In 110kV-750kV systems, the neutral point should adopt an effective grounding method. Under various conditions, the ratio of the zero-sequence to the positive-sequence reactance (X0 / X1) should be positive and not greater than 3, while the ratio of the zero-sequence resistance to the positive-sequence reactance (R0 / X1) should not be greater than 1. Ineffective grounding methods can be divided into ungrounded neutral point, low-resistance neutral point grounding, high-resistance neutral point grounding, and resonant neutral point grounding.

[0084] Symmetric component method:

[0085] The essence of the symmetrical component method is decoupling operation. A set of three asymmetrical electrical quantities can be decomposed into three sets of electrical components: positive sequence, negative sequence, and zero sequence. This invention uses exponential form to represent the angular relationship, letting... , , then 1 ( ), , They form a symmetrical system with a modulus of 1 and a phase difference of 120°. These are called operational factors. The solutions for the positive, negative, and zero-sequence components of an asymmetric vector are as follows: Assume that the three vectors A, B, and C (voltage or current) are asymmetric, i.e., their magnitudes are unequal and their phases are not 120° apart. According to the symmetric component method, we can decompose vector A into three vectors A1, A2, and A0, vector B into three vectors B1, B2, and B0, and vector C into three vectors C1, C2, and C0, as shown in equations (1) and (2); Assume that the three vectors A, B, and C are known, and the solutions for their corresponding positive, negative, and zero-sequence components are as shown in equation (3).

[0086] (1);

[0087] (2);

[0088] (3);

[0089] From the previous analysis, we can see that the three vectors A1, B1, and C1 are equal in magnitude and their phases differ by 120° in sequence. , Among them, A1, B1, and C1 are called positive sequence components; the three vectors A2, B2, and C2 are equal in magnitude and have opposite phases, differing by 120° from each other. , A2, B2, and C2 are called negative-order components;

[0090] Vectors A0, B0, and C0 have equal magnitudes and the same direction; these three vectors are called zero-order components.

[0091] When performing single-phase grounding fault analysis, it is required that in a neutral point effectively grounded system, the system phase A is metallically grounded, and the boundary conditions are as shown in equation (4), where the special phase is phase A, and the special phase is the fault phase in the case of a single-phase grounding fault.

[0092] (4);

[0093] When the boundary conditions of equation (4) are expressed by special phase sequence components using the symmetric component method, equation (5) is obtained.

[0094] (5);

[0095] Constructing the composite sequence network when phase A is grounded, as follows: Figure 1 As shown, Figure 1 It can be seen that zero-sequence current and voltage will appear at the fault point during a single-phase ground fault. Note that the composite sequence network refers to the sequence network of a special phase; the sequence network of non-special phases cannot be represented in this way.

[0096] exist Figure 1 middle, The electromotive force of phase A before the fault point is given. Now, when analyzing a ground fault, the voltage at the fault point is given. ,Depend on Figure 1 It can be known that the following conditions are met:

[0097] (6);

[0098] In the above formula, , , The combined zero-sequence, positive-sequence, and negative-sequence impedances of the system at the fault point. , , The zero-sequence, positive-sequence, and negative-sequence currents of the fault branch at the fault point. , , These represent the zero-sequence, positive-sequence, and negative-sequence voltages of the faulty phase at the fault point. According to the symmetrical component method, the voltages of the two non-faulty phases are... and It can be expressed as the following formula:

[0099] (7);

[0100] (8);

[0101] In actual operation, it is assumed that the positive-sequence and negative-sequence impedances of stationary components are equal, i.e. Equations (7) and (8) can be simplified to the following equations:

[0102] (9);

[0103] (10);

[0104] In the above formula, , , The fault point represents the electromotive force of phases A, B, and C before the fault. , , The voltages of phases A, B, and C at the fault point after a ground fault. hour, , The trajectory of the endpoint change is as follows Figure 2 As shown, the voltage amplitudes of the two non-faulty phases are from Change to The angle between the two non-faulty phases changes from 180° to 60°. At that time, the voltage values ​​of the two non-faulty phases remain unchanged. The voltage values ​​of the two non-faulty phases increased.

[0105] when At this time, it is equivalent to the neutral point of the system being ungrounded, and the effectively grounded neutral point system becoming an ungrounded system. Figure 2 It can be seen that, , Amplitude becomes The included angle becomes 60°, and the zero-sequence voltage becomes ;from Figure 1 It can be seen that the ground fault current is 0, such as Figure 3 As shown, the situation of B-phase or C-phase ground faults will not be analyzed further.

[0106] As analyzed above, in a neutral-point ungrounded system, during a single-phase fault, the voltage of the non-faulty phase rises to 1.732 times the pre-fault voltage, and the zero-sequence voltage rises to 100V. In the OPEN3000 system at the dispatch master station, this characteristic can be used as one of the criteria for grounding faults, i.e., judging the amplitude of the A, B, and C phase voltages and the zero-sequence voltage to determine whether the system is grounded. When two phases of the same line are grounded, there is a large fault current at the protection installation point, and the protection device will trip, changing the two-phase grounding to normal operation. When there is a cross-line phase fault, the protection device will trip, changing the two-phase grounding to single-phase grounding or normal operation, as analyzed above. The neutral-point low-resistance grounding, neutral-point high-resistance grounding, and neutral-point resonant grounding methods can be analyzed similarly. Note that in a composite sequence network, the grounding impedance is 3 times the actual value, which will not be discussed further here.

[0107] Analysis of open circuit in voltage transformers (PTs):

[0108] Due to aging, dirt, mechanical damage, and other reasons, voltage transformers may experience secondary circuit disconnections and primary circuit disconnections, posing certain hidden dangers to the safe and stable operation of the system and increasing the difficulty of analyzing and handling grounding faults. These issues will be explained in detail below.

[0109] Step 2: Single-phase open circuit analysis on the primary side of the voltage transformer (PT):

[0110] In the following analysis, it is assumed that phase A of the voltage transformer is disconnected. Since the capacity of the voltage transformer is much smaller than the system capacity, the system can be considered as an infinitely large power grid. The composite sequence network of phase A disconnected from the voltage transformer is as follows: Figure 4 As shown in the figure , , These are the zero-sequence, positive-sequence, and negative-sequence impedances of the voltage transformer's secondary load response to the primary side, respectively. , , These are the external zero-sequence, positive-sequence, and negative-sequence voltages connected to the primary side of the voltage transformer. , , These are the zero-sequence, positive-sequence, and negative-sequence currents on the primary side of the voltage transformer. Let be the system electromotive force.

[0111] Generally speaking, there are , ,in It is the ratio of zero-sequence impedance to positive-sequence impedance. According to the method of symmetrical components, from... Figure 4 Equation (11) can be obtained.

[0112] (11);

[0113] in, , , These are the A, B, and C phase voltages on the primary side of the voltage transformer.

[0114] set up ( (The voltage is the system nominal voltage, such as 35kV, 10kV, etc.), and the voltage transformer ratio is... From equation (11), the secondary phase voltage and zero sequence voltage when phase A of the primary side of the voltage transformer is disconnected are shown in equation (12).

[0115] (12);

[0116] in, , , These are the voltages of phases A, B, and C on the secondary side of the voltage transformer. This is the zero-sequence voltage connected externally to the secondary side of the voltage transformer.

[0117] From equation (12), it can be seen that the secondary voltage of phase A, which is disconnected, decreases, while the secondary voltages of phases B and C remain unchanged; a zero-sequence voltage appears on the open delta side, and this voltage value will not be lower than 14V. When a phase A ground fault occurs in the system and the voltage transformer is disconnected in phase A, as can be seen from the above analysis, at this time, the phase A disconnected sequence network and the unconnected sequence network are approximately the same, equivalent to The voltage of phases B and C (non-disconnected) is approximately 110V, the voltage of phase A (disconnected) is approximately 0V, and the external zero-sequence voltage is approximately 110V. When a ground fault occurs in phase A of the system and the voltage transformer is disconnected in phase B, equations (11), (12), and... Figure 4 It can be seen that at this time, The voltage of phase A (non-disconnected) is approximately 0, the voltage of phase C (non-disconnected) is approximately 110V, the voltage of phase B (disconnected) decreases, and the external zero-sequence voltage is not lower than 40V.

[0118] This characteristic of voltage change can be used as one of the criteria for judging system grounding faults; the judgment methods for other cases are similar.

[0119] Step 3: Single-phase open circuit analysis on the secondary side of the voltage transformer (PT):

[0120] There are two types of open circuits in the secondary circuit of a voltage transformer: one is an open circuit inside the protection device, and the other is an open circuit in the lead-out circuit of the voltage transformer. These will be explained separately below.

[0121] Internal breakage analysis:

[0122] When the secondary wiring of the voltage transformer is normal, the circuit diagram is as follows: Figure 5 As shown in the figure. , , The secondary phase impedance of the voltage transformer. , , This is the secondary phase-to-phase impedance. , , This is the output voltage of the secondary side of the voltage transformer (voltage acquired by the protection and control device).

[0123] When introduced into the internal protection device When the phase is broken, there is , , The self-generated zero-sequence voltage is approximately 19.2V, and the external zero-sequence voltage is approximately 100V. When a phase A ground fault occurs in the system, and it is introduced into the protection device... When one phase is disconnected, the other phase is disconnected. , The secondary voltage of the phase is approximately 110V, and the phase is disconnected. The phase secondary voltage is approximately 0V, the self-generated zero-sequence voltage is approximately 36.6V, and the external zero-sequence voltage is approximately 110V. When a phase A ground fault occurs in the system, and it is introduced into the protection device... When one phase is disconnected, the other phase is disconnected. The secondary voltage of the non-disconnected phase is approximately 0. The secondary voltage of the phase is approximately 110V, and the phase is disconnected. The phase secondary voltage is approximately 0, the self-generated zero-sequence voltage is approximately 36.6V, and the external zero-sequence voltage is approximately 110V.

[0124] The aforementioned voltage variation characteristic can be used as one of the criteria for judging system grounding faults; the judgment methods for other cases are similar.

[0125] Analysis of broken wires in the lead-out circuit:

[0126] When the voltage transformer leads out of the circuit When a phase is disconnected, to simplify the analysis, we assume the secondary load is symmetrical, i.e. Figure 5 middle , According to the superposition principle, the secondary phase voltage is:

[0127] (13);

[0128] From the above formula, the self-generated zero-sequence voltage can be obtained as:

[0129] , ( (14);

[0130] From the above analysis, we can conclude that:

[0131] When the secondary side of a voltage transformer has only phase-to-phase impedance and no phase impedance, that is... The maximum self-generated zero-sequence voltage is 31.76V;

[0132] When the secondary side of a voltage transformer has only phase impedance and no phase-to-phase impedance, i.e. The maximum self-generated zero-sequence voltage is 21.17V; the maximum amplitude of the disconnected phase voltage is no more than 31.76V, and the minimum amplitude is 0V.

[0133] When a phase A ground fault occurs in the system, and the voltage transformer lead-out circuit... When one phase is disconnected, the other phase is disconnected. , The secondary voltage of the phase is approximately 110V, and the phase is disconnected. The secondary voltage of the phase is approximately 0V, the self-generated zero-sequence voltage is approximately 36.6V, and the external zero-sequence voltage is approximately 110V;

[0134] When a phase A ground fault occurs in the system, and it is introduced into the protection device... When one phase is disconnected, the other phase is disconnected. The secondary voltage of the non-disconnected phase is approximately 0. The secondary voltage of the phase is approximately 110V, and the phase is disconnected. The secondary voltage decreases, ranging from 0 to 55.01V. The self-generated zero-sequence voltage ranges from 55.01V to 36.67V, while the external zero-sequence voltage is approximately 110V.

[0135] The aforementioned voltage variation characteristic can be used as one of the criteria for judging system grounding faults; the judgment methods for other cases are similar.

[0136] In an embodiment of the present invention, after the conventional grounding signal is issued by the microcomputer harmonic elimination device, it is sent to the main station via the scheduling data network, and the operators are alerted through sound and messages. The specific process is as follows:

[0137] The main station actively generates a mechanism (after the microcomputer harmonic elimination device fails). Taking the E6000 system as an example, database configuration and diagram drawing are generally performed in the E6000 system.

[0138] The voltage changes under different types of faults during a phase A ground fault on the 10kV busbar of a certain substation are shown in Table 1 below (voltage values ​​are quadratic).

[0139] Table 1 Voltage changes during phase A ground fault (secondary values)

[0140]

[0141] Analysis of the table above reveals the following characteristics of different types of A-phase grounding faults: A-phase voltage is approximately 0V, B-phase or C-phase voltage is approximately 100V, and zero-sequence voltage is greater than 40V. Considering practical engineering scenarios and converting these values ​​to primary values, the fault voltages are determined to be: A-phase voltage less than 3kV, B-phase or C-phase voltage greater than 7kV, and zero-sequence voltage greater than 40V (secondary value). When a phase PT fuse blows, the phase voltage of that phase is between 3.5kV and 5.5kV, and the voltages of the other two phases are between 5.7kV and 6.5kV (in the E6000 system, phase voltage is a primary value, and zero-sequence voltage is a secondary value). First, set an upper limit for the unbalanced voltage value 3U0 in the telemetry limit library. If this value is exceeded, the monitoring system will sound an alarm to alert the monitoring personnel. Next, define the remote signaling value for a specific voltage and phase grounding alarm in the protection information table, and define the alarm method for the above information as an accident alarm in the secondary remote signaling definition table. Finally, set the logical operations in the E6000 system using the formula editor, taking into account the voltage value range, as follows:

[0142] {if(@1<3&(@2>7|@3>7)&5>40)

[0143] @4=1;

[0144] Else

[0145] @4=0

[0146] ;}

[0147] like Figure 6 As shown, @1 is the voltage of phase A, @2 is the voltage of phase B, @3 is the voltage of phase C, @5 is the zero-sequence voltage, and @4 is the predefined grounding alarm signal.

[0148] After the photon tag associated with phase A ground fault is set to @4, an alarm message can be issued during a ground fault, further improving the safety of the power system operation. Then, the photon tag information is created, such as... Figure 7 As shown, when phase A experiences a ground fault, the photon sign lights up; similar results can be obtained for phases B and C.

[0149] Similarly, define the remote signaling value for a PT fuse blowout alarm for a certain phase at a certain voltage in the protection information table, and enter the following logical judgment relationship in the formula editor:

[0150] {if ((3.5<@1<5.5)&(5.7<@2<6.5)&(5.7<@3<6.5))

[0151] @4=1;

[0152] Else

[0153] @4=0

[0154] ;}

[0155] Where @1 is the voltage of phase A, @2 is the voltage of phase B, @3 is the voltage of phase C, @5 is the zero-sequence voltage, and @4 is the predefined PT fuse blown alarm signal. When the PT fuse in phase A blows, an alarm message will be issued.

[0156] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for judging grounding faults in distribution network lines based on single-phase grounding and voltage transformer disconnection analysis, characterized in that: Includes the following steps: Step 1: In a neutral-point effectively grounded system, the symmetrical component method is used to analyze single-phase grounding faults in the distribution network lines; Step 2: Analyze the single-phase open circuit on the primary side of the voltage transformer to obtain the corresponding system grounding fault judgment rules; Step 3: Analyze the single-phase open circuit on the secondary side of the voltage transformer, including two cases: open circuit inside the protection device and open circuit in the voltage transformer lead-out circuit. Based on the voltage change characteristics, obtain the corresponding system grounding fault judgment rules. Step 4: Determine the grounding fault of the distribution network lines based on the obtained system grounding fault judgment rules.

2. The method for judging grounding faults in distribution network lines based on single-phase grounding and voltage transformer disconnection analysis according to claim 1, characterized in that: The neutral point effective grounding system used in step one satisfies the following conditions: the ratio of the zero-sequence to the positive-sequence reactance X0 / X1 of the system is positive and not greater than 3, and the ratio of the zero-sequence resistance to the positive-sequence reactance R0 / X1 of the system is not greater than 1.

3. The method for judging grounding faults in distribution network lines based on single-phase grounding and voltage transformer disconnection analysis according to claim 2, characterized in that: The symmetric component method used in step one is specifically a decoupling operation process, including: A set of three asymmetrical electrical quantities is decomposed into three sets of electrical components: positive sequence, negative sequence, and zero sequence. The angular relationship is expressed in exponential form, and let... , , will 1 ( ), , To form a symmetric system with a modulus of 1 and a phase difference of 120°, Called the operational factors, the methods for calculating the positive, negative, and zero-order components of an asymmetric vector are as follows: Suppose that the three voltage or current vectors A, B, and C are asymmetrical, i.e., their magnitudes are unequal and their phases are not 120° apart. According to the method of symmetrical components, vector A is decomposed into three vectors A1, A2, and A0; vector B is decomposed into three vectors B1, B2, and B0; and vector C is decomposed into three vectors C1, C2, and C0. Then, the following conditions are met: （1）； （2）； Given three vectors A, B, and C, the formulas for calculating their corresponding positive, negative, and zero-order components are as follows: （3）； Analysis revealed that vectors A1, B1, and C1 are equal in magnitude and their phases differ by 120° in sequence. , A1, B1, and C1 are called positive-order components; The three vectors A2, B2, and C2 are equal in magnitude and have reversed phase sequence with a phase difference of 120°. , A2, B2, and C2 are called negative-order components; Vectors A0, B0, and C0 have equal magnitudes and the same direction; these three vectors are called zero-order components.

4. The method for judging grounding faults in distribution network lines based on single-phase grounding and voltage transformer disconnection analysis according to claim 3, characterized in that: The specific method for analyzing a single-phase ground fault in step one is as follows: In a neutral-point effectively grounded system, assuming phase A of the system is metallically grounded, the boundary conditions satisfy: （4）； Among them, the special phase is phase A. In the case of a single-phase ground fault, the special phase is the fault phase. Using the symmetric component method, the boundary conditions are expressed in terms of special phase sequence components, as follows: （5）； Draw the composite sequence network diagram when phase A is grounded, identify the zero-sequence component current and voltage at the fault point when a single-phase ground is occurred, and define the parameters in the diagram. Given the electromotive force of phase A before the fault, analyze the voltage at the fault point when a ground fault occurs. Then the following condition is met: （6）； in, , , The combined zero-sequence, positive-sequence, and negative-sequence impedances of the system at the fault point. , , The zero-sequence, positive-sequence, and negative-sequence currents of the fault branch at the fault point. , , The zero-sequence, positive-sequence, and negative-sequence voltages of the fault phase at the fault point; Using the symmetrical component method, the voltages of the two non-faulty phases are... and Represented as: （7）； （8）； In actual operation, it is assumed that the positive-sequence and negative-sequence impedances of stationary components are equal, i.e. Then the above formula simplifies to: （9）； （10）； In the formula, , , The fault point represents the electromotive force of phases A, B, and C before the fault. , , The voltages of phases A, B, and C at the fault point after a ground fault; At that time, the voltage amplitudes of the two non-faulty phases changed from Change to The angle between the two non-faulty phases changes from 180° to 60°; when At that time, the voltage values ​​of the two non-faulty phases remain unchanged. The voltage values ​​of the two non-faulty phases increased; when At this time, it is equivalent to the neutral point of the system being ungrounded, and the effectively grounded neutral point system becoming an ungrounded system. , Amplitude becomes The included angle becomes 60°, and the zero-sequence voltage becomes ; For a single-phase fault in a neutral-point ungrounded system, the voltage of the non-faulty phase rises to 1.732 times the pre-fault voltage, and the zero-sequence voltage rises to 100V. In the dispatch master station system, the amplitudes of the A, B, and C phase voltages and the zero-sequence voltage are judged to determine whether the system is grounded. When two phases of the same line are grounded, there is a large fault current at the protection installation point, and the protection device will trip, and the two-phase grounding will change to normal operation; In the event of a cross-line phase fault, the protection device will trip, and the two-phase grounding will be converted to a single-phase grounding or normal operation will resume.

5. The method for judging grounding faults in distribution network lines based on single-phase grounding and voltage transformer disconnection analysis according to claim 4, characterized in that: The specific method for step two is as follows: Define the open circuit of phase A of the voltage transformer, and obtain the composite sequence network diagram of the open circuit of phase A of the voltage transformer. , , These are the zero-sequence, positive-sequence, and negative-sequence impedances of the voltage transformer's secondary load reflected to the primary side. , , These are the external zero-sequence, positive-sequence, and negative-sequence voltages connected to the primary side of the voltage transformer. , , These are the zero-sequence, positive-sequence, and negative-sequence currents on the primary side of the voltage transformer. Let be the electromotive force of the system, and define a condition that satisfies... , ,in It is the ratio of zero-sequence impedance to positive-sequence impedance. Using the symmetrical component method, we obtain: （11）； in, , , These are the phase A, B, and C voltages on the primary side of the voltage transformer. set up , The system nominal voltage is given, and the voltage transformer ratio is given. From the above formula, the calculation formulas for the secondary phase voltage and zero-sequence voltage when the primary side A phase of the voltage transformer is disconnected are as follows: （12）； in, , , These are the voltages of phases A, B, and C on the secondary side of the voltage transformer. The voltage is the zero-sequence voltage connected to the secondary side of the voltage transformer. From the above formula, we can see that the secondary voltage of phase A, which is disconnected, decreases, while the secondary voltages of phases B and C remain unchanged; a zero-sequence voltage appears on the open delta side, and this voltage value will not be lower than 14V. When a phase A ground fault occurs in the system and the phase A of the voltage transformer is disconnected, the disconnection sequence network of phase A is approximately the same as the non-disconnection sequence network, which is equivalent to... The voltage of phases B and C without disconnection is about 110V, the voltage of phase A with disconnection is about 0V, and the external zero-sequence voltage is about 110V. When a phase A ground fault occurs in the system and the voltage transformer is disconnected on phase B, at this time, The voltage of phase A (non-disconnected) is approximately 0, the voltage of phase C (non-disconnected) is approximately 110V, the voltage of phase B (disconnected) decreases, and the external zero-sequence voltage is not lower than 40V.

6. The method for judging grounding faults in distribution network lines based on single-phase grounding and voltage transformer disconnection analysis according to claim 5, characterized in that: The specific method for analyzing the internal disconnection of the protection device in step three is as follows: When the secondary wiring of the voltage transformer is normal, set , , The secondary phase impedance of the voltage transformer. , , This is the secondary phase-to-phase impedance. , , To determine the ground fault caused by an internal open circuit in the protection device based on the voltage change characteristics at the acquisition terminal of the protection device, the following are included: When introduced into the internal protection device When the phase is broken, there is , , The self-generated zero-sequence voltage is approximately 19.2V, and the external zero-sequence voltage is approximately 100V. When a phase A ground fault occurs in the system, and it is introduced into the protection device... When one phase is disconnected, the other phase is disconnected. , The secondary voltage of the phase is approximately 110V, and the phase is disconnected. The secondary voltage of the phase is approximately 0V, the self-generated zero-sequence voltage is approximately 36.6V, and the external zero-sequence voltage is approximately 110V; When a phase A ground fault occurs in the system, and it is introduced into the protection device... When one phase is disconnected, the other phase is disconnected. The secondary voltage of the non-disconnected phase is approximately 0. The secondary voltage of the phase is approximately 110V, and the phase is disconnected. The phase secondary voltage is approximately 0, the self-generated zero-sequence voltage is approximately 36.6V, and the external zero-sequence voltage is approximately 110V.

7. The method for judging grounding faults in distribution network lines based on single-phase grounding and voltage transformer disconnection analysis according to claim 6, characterized in that: The specific method for analyzing the open circuit of the voltage transformer lead-out circuit in step three is as follows: When the voltage transformer leads out of the circuit When a phase disconnection occurs, the secondary load is assumed to be symmetrical, satisfying the following conditions: , The secondary phase voltage is calculated based on the superposition principle, and the formula is as follows: （13）； The self-generated zero-sequence voltage is further obtained as follows: ，（ ）（14）； Analysis yielded the following results: When the secondary side of a voltage transformer has only phase-to-phase impedance and no phase impedance, that is... The maximum self-generated zero-sequence voltage is 31.76V; When the secondary side of a voltage transformer has only phase impedance and no phase-to-phase impedance, i.e. The maximum self-generated zero-sequence voltage is 21.17V; The maximum amplitude of the phase voltage during a disconnection is 31.76V, and the minimum amplitude is 0V. Then, based on the following voltage change characteristics, the ground fault caused by the disconnection of the system's lead-out circuit is determined, including: When a phase A ground fault occurs in the system, and the voltage transformer lead-out circuit... When one phase is disconnected, the other phase is disconnected. , The secondary voltage of the phase is approximately 110V, and the phase is disconnected. The secondary voltage of the phase is approximately 0V, the self-generated zero-sequence voltage is approximately 36.6V, and the external zero-sequence voltage is approximately 110V; When a phase A ground fault occurs in the system, and it is introduced into the protection device... When one phase is disconnected, the other phase is disconnected. The secondary voltage of the non-disconnected phase is approximately 0. The secondary voltage of the phase is approximately 110V, and the phase is disconnected. The secondary voltage decreases, ranging from 0 to 55.01V. The self-generated zero-sequence voltage ranges from 55.01V to 36.67V, while the external zero-sequence voltage is approximately 110V.

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