Active distribution network single-phase fault detection method and system

Abstract

The present invention discloses a method for detecting single-phase faults in an active distribution network, comprising obtaining parameter information of a target active distribution network; obtaining operating data information of the target active distribution network in real time; determining the fault type by obtaining negative-sequence voltage data of each monitoring point; calculating the negative-sequence power of each monitoring point and determining the fault section; calculating the negative-sequence current phase angle difference on both sides of the fault section and determining the single-phase fault type; and completing single-phase fault detection in the active distribution network. The present invention also discloses a system for implementing the method for detecting single-phase faults in an active distribution network. The present invention determines the fault type by using negative-sequence voltage data, determines the fault section by using negative-sequence power, and finally determines the single-phase fault type based on the negative-sequence current phase angle difference. Therefore, the scheme of the present invention can not only complete the detection of single-phase faults in the active distribution network, but also has higher reliability and better accuracy.

Description

Technical Field

[0001] The present invention belongs to the field of electrical automation, and in particular relates to a single-phase fault detection method and system for an active power distribution network. Background Art

[0002] With the development of economy and technology and the improvement of people's living standards, electricity has become an indispensable secondary energy source in people's production and life, bringing endless convenience to people's production and life. Therefore, ensuring a stable and reliable supply of electricity has become one of the most important tasks of the power system.

[0003] Currently, power systems generally use low-current grounding, and single-phase grounding faults are the most common fault in these systems. With the widespread use of overhead insulated conductors, coupled with the effects of lightning strikes, icing, and external forces, single-phase line break faults are a common occurrence. After a single-phase grounding fault occurs, the faulty line current is low and the line voltage remains unchanged, resulting in minimal impact on load power supply. The system is typically allowed to continue operating with the fault for one to two hours. After a single-phase line break fault occurs, the three-phase parameters of the line become severely unbalanced, and continuous discharge occurs at the line break grounding point, posing a significant threat to power equipment and personnel. This requires prompt handling of the line break fault to eliminate potential safety hazards. However, current power systems are generally not equipped with line break protection devices, and line break grounding faults are often treated as single-phase grounding faults, delaying fault resolution.

[0004] The detection of single-phase grounding faults in distribution networks has always been a research hotspot in the field of relay protection. Many scholars at home and abroad have conducted in-depth research on it and proposed a large number of detection methods, which can be roughly divided into two categories: steady-state methods and transient methods. The steady-state method detects faults by calculating the stable power frequency or harmonic signals after the fault, such as the power frequency zero-sequence current amplitude and phase ratio method, the zero-sequence admittance method, the zero-sequence active component method, and the harmonic method. The transient method uses rich transient characteristics and obvious local characteristics to judge faults, such as the inherent modal energy method, the first half-wave polarity method, the active power direction method, the parameter identification method, and the transient characteristic frequency band method. However, due to the significant differences in the characteristics of single-phase line break faults and single-phase grounding faults (such as the negative sequence component), the existing grounding fault detection methods are difficult to apply to single-phase line break faults.

[0005] When a power line disconnection occurs in a distribution network, it is often accompanied by a ground drop, resulting in a complex single-phase disconnection-to-ground fault. This fault is caused by both a power-side ground fault and a load-side ground fault. While existing solutions can identify single-phase disconnection faults, the fault characteristics (such as zero-sequence voltage) are very similar when the power-side ground fault occurs and when the single-phase ground fault occurs. As the fault judgment criteria also apply to single-phase ground faults, single-phase ground faults may be misidentified as disconnection faults.

[0006] Furthermore, distributed generators (DG) have been integrated into the grid on a large scale, and traditional distribution networks are evolving towards active distribution networks. Distribution line topologies are becoming increasingly complex, with an increasing number of lines containing unmeasurable branches. The integration of DGs and unmeasurable branches can impact existing fault detection and protection methods, significantly reducing the reliability and accuracy of existing fault detection solutions. Summary of the Invention

[0007] One of the objectives of the present invention is to provide a method for detecting single-phase faults in an active power distribution network with high reliability and good accuracy.

[0008] A second object of the present invention is to provide a system for implementing the active power distribution network single-phase fault detection method.

[0009] The present invention provides a method for detecting single-phase faults in an active power distribution network, comprising the following steps:

[0010] S1. Obtain parameter information of the target active distribution network;

[0011] S2. Real-time acquisition of target active distribution network operating data information;

[0012] S3. When a fault occurs, the fault type is determined by obtaining the negative sequence voltage data of each monitoring point:

[0013] If the fault is a single-phase fault, proceed to the subsequent steps;

[0014] If the fault is not a single-phase fault, the algorithm ends;

[0015] S4. Calculate the negative sequence power of each monitoring point based on the working data information obtained from each monitoring point;

[0016] S5. According to the negative sequence power of each monitoring point obtained in step S4, the fault section is judged;

[0017] S6. Calculate the negative sequence current phase angle difference on both sides of the fault section based on the acquired working data information of the fault section;

[0018] S7. Determine the type of single-phase fault based on the negative sequence current phase angle difference obtained in step S6;

[0019] S8. Complete single-phase fault detection of the active distribution network.

[0020] The step S3 specifically includes the following steps:

[0021] When a fault occurs, the negative sequence voltage data of each monitoring point is obtained;

[0022] The following formula is used as the criterion formula for the fault type:

[0023]

[0024] In the formula is the negative sequence voltage measured at each monitoring point after the fault; U set It is the negative sequence voltage value generated by unbalanced load during normal operation; ΔU set is the set negative sequence voltage threshold;

[0025] If the judgment formula is established, the fault type is determined to be a single-phase fault, and the subsequent steps are carried out;

[0026] If the judgment formula is not valid, the fault type is determined not to be a single-phase fault, the algorithm ends, and an alarm is issued.

[0027] Step S5, in accordance with the negative sequence power of each monitoring point obtained in step S4, determines the fault section, specifically comprising the following steps:

[0028] Determine whether the directions of the negative sequence power of any two adjacent monitoring points are the same:

[0029] If the directions of the negative sequence powers of any two adjacent monitoring points are the same, the section between the two adjacent monitoring points is determined to be a normal section;

[0030] If the directions of the negative sequence powers of any two adjacent monitoring points are different, the section between the two adjacent monitoring points is determined to be a fault section, and the subsequent steps are continued.

[0031] The step S7 of determining the single-phase fault type based on the negative sequence current phase angle difference obtained in step S6 specifically includes the following steps:

[0032] The following formula is used as the criterion formula for single-phase fault type:

[0033] -90°<θ<90°

[0034] Where θ is the negative sequence current phase angle difference;

[0035] If the judgment formula is established, the single-phase fault type is determined to be a single-phase disconnection fault;

[0036] If the judgment formula is not valid, the fault type is determined to be a single-phase grounding fault.

[0037] The present invention also provides a system for implementing the active distribution network single-phase fault detection method, comprising a data acquisition module, a real-time monitoring module, a fault judgment module, a negative-sequence power calculation module, a fault section judgment module, a phase angle difference calculation module, a fault type judgment module and a single-phase fault detection module; the data acquisition module, the real-time monitoring module, the fault judgment module, the negative-sequence power calculation module, the fault section judgment module, the phase angle difference calculation module, the fault type judgment module and the single-phase fault detection module are connected in series in sequence; the data acquisition module acquires parameter information of the target active distribution network and uploads the data information to the real-time monitoring module; the real-time monitoring module is used to acquire working data information of the target active distribution network in real time according to the received data information, and upload the data information to the fault judgment module; the fault judgment module is used to determine the fault type according to the received data information by acquiring the negative-sequence voltage data of each monitoring point when a fault occurs: if the fault is a single-phase fault, the data information is uploaded to the negative-sequence power module. rate calculation module; if the fault is not a single-phase fault, the judgment ends; the negative-sequence power calculation module is used to calculate the negative-sequence power of each monitoring point according to the received data information and the obtained working data information of each monitoring point, and upload the data information to the fault section judgment module; the fault section judgment module is used to judge the fault section according to the received data information and the obtained negative-sequence power of each monitoring point, and upload the data information to the phase angle difference calculation module; the phase angle difference calculation module is used to calculate the negative-sequence current phase angle difference on both sides of the fault section according to the received data information and the obtained working data information of the fault section, and upload the data information to the fault type judgment module; the fault type judgment module is used to judge the single-phase fault type according to the received data information and the obtained negative-sequence current phase angle difference, and upload the data information to the single-phase fault detection module; the single-phase fault detection module is used to complete the single-phase fault detection of the active distribution network according to the received data information.

[0038] The present invention provides a method and system for detecting single-phase faults in an active power distribution network. The method and system determine the fault type using negative-sequence voltage data, identify the fault section using negative-sequence power, and finally determine the single-phase fault type based on the negative-sequence current phase angle difference. Therefore, the present invention not only detects single-phase faults in an active power distribution network, but also does so with greater reliability and accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of the process flow of the present invention.

[0040] Figure 2 Schematic diagram of an active distribution network with unmeasurable branches according to the method of the present invention.

[0041] Figure 3 This is a negative sequence network equivalent schematic diagram of single-phase grounding and line break faults according to the method of the present invention.

[0042] Figure 4 Schematic diagram of the phase relationship between the negative sequence voltage and current upstream and downstream of the fault point in the method of the present invention.

[0043] Figure 5 This is a schematic diagram of a negative sequence network for a single-phase disconnected and ungrounded fault according to the method of the present invention.

[0044] Figure 6 This is a schematic diagram of the phase comparison results of the negative sequence current of a single-phase disconnected line and ungrounded fault according to the method of the present invention.

[0045] Figure 7 This is a schematic diagram of a negative sequence network for a ground fault on the single-phase disconnected power supply side of the method of the present invention.

[0046] Figure 8 This is a schematic diagram of the negative sequence decomposition network for a ground fault on the single-phase disconnected power supply side according to the method of the present invention.

[0047] Figure 9 This is a schematic diagram of the phase comparison results of the negative sequence current of the ground fault on the single-phase disconnected power supply side according to the method of the present invention.

[0048] Figure 10 This is a schematic diagram of the negative sequence decomposition network for a single-phase disconnected load-side grounding fault according to the method of the present invention.

[0049] Figure 11 This is a schematic diagram of a negative sequence network for a single-phase grounding fault according to the method of the present invention.

[0050] Figure 12 This is a schematic diagram of the negative sequence current phase ratio when a distribution network fault occurs according to the method of the present invention.

[0051] Figure 13 Schematic diagram of an active power distribution network line model according to an embodiment of the method of the present invention.

[0052] Figure 14 Schematic diagram of single-phase grounding fault simulation results under different transition resistances according to an embodiment of the method of the present invention.

[0053] Figure 15 Schematic diagram of the grounding simulation results of a single-phase disconnected power supply side under different transition resistances according to an embodiment of the method of the present invention.

[0054] Figure 16 Schematic diagram of the simulation results of single-phase disconnection load side grounding under different transition resistances in an embodiment of the method of the present invention.

[0055] Figure 17 Schematic diagram of negative sequence phase comparison results for a single-phase disconnection and ungrounded fault according to an embodiment of the method of the present invention.

[0056] Figure 18 Schematic diagram of the functional modules of the method system of the present invention. DETAILED DESCRIPTION

[0057] like Figure 1 The figure shows a flow chart of the method of the present invention: The method for detecting single-phase faults in an active power distribution network disclosed in the present invention comprises the following steps:

[0058] S1. Obtain parameter information of the target active distribution network;

[0059] S2. Real-time acquisition of target active distribution network operating data information;

[0060] S3. When a fault occurs, the fault type is determined by obtaining the negative sequence voltage data of each monitoring point:

[0061] If the fault is a single-phase fault, proceed to the subsequent steps;

[0062] If the fault is not a single-phase fault, the algorithm ends;

[0063] The specific implementation includes the following steps:

[0064] When a fault occurs, the negative sequence voltage data of each monitoring point is obtained;

[0065] The following formula is used as the criterion formula for the fault type:

[0066]

[0067] In the formula is the negative sequence voltage measured at each monitoring point after the fault; U set It is the negative sequence voltage value generated by unbalanced load during normal operation; ΔU set is the set negative sequence voltage threshold;

[0068] If the judgment formula is established, the fault type is determined to be a single-phase fault, and the subsequent steps are carried out;

[0069] If the judgment formula is not established, the fault type is determined not to be a single-phase fault, the algorithm ends, and an alarm is issued;

[0070] S4. Calculate the negative sequence power of each monitoring point based on the working data information obtained from each monitoring point;

[0071] S5. According to the negative sequence power of each monitoring point obtained in step S4, the fault section is judged; specifically comprising the following steps:

[0072] Determine whether the directions of the negative sequence power of any two adjacent monitoring points are the same:

[0073] If the directions of the negative sequence powers of any two adjacent monitoring points are the same, the section between the two adjacent monitoring points is determined to be a normal section;

[0074] If the directions of the negative sequence power of any two adjacent monitoring points are different, the section between the two adjacent monitoring points is determined to be a fault section, and the subsequent steps are continued;

[0075] S6. Calculate the negative sequence current phase angle difference on both sides of the fault section based on the acquired working data information of the fault section;

[0076] S7. Determine the type of single-phase fault based on the negative sequence current phase angle difference obtained in step S6; specifically comprising the following steps:

[0077] The following formula is used as the criterion formula for single-phase fault type:

[0078] -90°<θ<90°

[0079] Where θ is the negative sequence current phase angle difference;

[0080] If the judgment formula is established, the single-phase fault type is determined to be a single-phase disconnection fault;

[0081] If the judgment formula is not established, the fault type is determined to be a single-phase grounding fault;

[0082] S8. Complete single-phase fault detection of the active distribution network.

[0083] The method of the present invention is theoretically analyzed and explained below:

[0084] like Figure 2 The figure shows the schematic diagram of the active distribution network with unmeasurable branches; SG is the system power supply, R0 is the neutral point grounding resistance, L g The arc suppression coil. k1 and k2 are the transfer switches for different system grounding methods. When the two switches are disconnected, it is an ungrounded system. When k1 is closed and k2 is disconnected, it indicates an arc suppression coil grounding system. When k1 is disconnected and k2 is closed, it indicates a low resistance grounding system. A, B, C, M, N, P, Q are busbar nodes. L ub1 、L ub2 is an unmeasurable branch line, f1 is the fault point, DG1 and DG2 are distributed power sources connected to the system, and L C1 、L P1 、L N1 、L M1 、L Q1 The load carried by each bus

[0085] DGs in active distribution networks can be broadly categorized as motor-type distributed generators (MTDGs) and inverter-interfaced distributed generators (IIDGs). For MTDGs, the negative-sequence impedance parameter is not strictly equal to the positive-sequence impedance parameter. The negative-sequence impedance is typically equivalent to an inductive impedance, and its capacity is smaller than that of the system power supply. Therefore, the negative-sequence impedance is greater than that of the system power supply, still exhibiting an impedance dominated by reactance, with an impedance angle typically greater than 80°.

[0086] IIDGs can be divided into negative-sequence suppression IIDGs and non-negative-sequence suppression IIDGs based on their control strategies. Negative-sequence suppression IIDGs often employ a PQ control method, and IIDGs directly connected to a 10kV distribution network are required to possess low-voltage ride-through capability. When connected upstream of the fault point, they are clamped by the system power supply voltage, and the positive-sequence voltage at their grid connection point approaches the system power supply voltage, thus eliminating the need for low-voltage ride-through. However, when located downstream of the fault point, the positive-sequence voltage at their grid connection point is affected by their rated capacity and load impedance, resulting in complex variations. This can be seen as a voltage-controlled positive-sequence current source. Therefore, in a negative-sequence network, a negative-sequence suppression IIDG can be considered an open circuit with extremely high impedance.

[0087] For the IIDG that is not subject to negative sequence suppression, it can be equivalent to a passive resistive-inductive impedance. The negative sequence impedance is larger than that of the MTDG and has no obvious fluctuations. Taking into account the characteristics of the IIDG and factors such as the downstream load, in the negative sequence network, the IIDG that is not subject to negative sequence suppression can be equivalent to a passive impedance. If there is only a negative sequence suppression IIDG in the system on this side, after an asymmetric short circuit occurs, it is equivalent to an open circuit state for the negative sequence network, and the negative sequence current cannot be detected. However, since the DG access point is usually connected to the load, this side still provides a negative sequence path, and the negative sequence current can still be detected.

[0088] Negative sequence component analysis of single-phase grounding and disconnection faults:

[0089] Figure 3 This is the negative sequence impedance network equivalent diagram for line MN when a single-phase grounding and line break fault occurs. m is the system equivalent negative sequence impedance upstream of line MN, Z n is the system equivalent negative sequence impedance downstream of line MN, Z L is the equivalent negative sequence impedance of line MN, α is the ratio of the length from the fault point to the line head end M to the total length of line MN, α∈(0,1), Add a negative sequence voltage source for the fault, is the equivalent current source of a single-phase line-break fault, are the negative sequence currents flowing through measuring points M and N respectively.

[0090] When a single-phase grounding fault occurs on line MN, it is equivalent to connecting an additional negative sequence voltage source at the fault point. Figure 3 (a) The negative sequence current distribution characteristics can be obtained: upstream of the fault point, the negative sequence current flows from the fault point through the upstream line and busbar to the power supply side, and finally flows back to the equivalent voltage source through the earth; downstream of the fault point, the negative sequence current flows from the fault point through the downstream line to the load, and finally returns to the equivalent voltage source.

[0091] When a single-phase disconnection fault occurs on line MN, it is equivalent to connecting an additional negative sequence current source at the fault point. Figure 3 (b) The negative-sequence current distribution characteristic is obtained: the negative-sequence current flows from the fault point through the upstream fault point and the busbar to the power source, then flows through the ground to the load, and finally returns to the equivalent current source downstream of the fault point. The analysis results for a single-phase disconnected ungrounded fault and a disconnected and grounded complex fault are the same.

[0092] The literature points out that the equivalent negative-sequence impedance of the load is much larger than the equivalent negative-sequence impedance of the high-voltage system, so the negative-sequence current basically flows into the high-voltage system, while the negative-sequence current downstream of the fault point is relatively small.

[0093] From the above analysis, it can be concluded that, assuming that the current flows from the busbar to the line in a positive direction, the upstream and downstream negative sequence currents of a single-phase grounding fault have opposite directions, while the upstream and downstream negative sequence currents of a single-phase line break fault have the same direction. Since the negative sequence voltages on both sides of the break of a single-phase line break fault are opposite, the negative sequence voltages on both sides of the fault point of a single-phase grounding fault are continuous. Regardless of whether the system has a single-phase grounding fault or a single-phase line break fault, for the line upstream of the fault point, the negative sequence voltage at measuring point M is the voltage drop generated by the negative sequence impedance before the negative sequence current flows through the measuring point. The relationship between the negative sequence voltage and negative sequence current at measuring point M is: in is the negative sequence voltage at the measuring point M, Z M is the equivalent negative sequence impedance viewed from the measuring point M toward the system side.

[0094] For the line downstream of the fault point, the relationship between the negative sequence voltage and negative sequence current at the measuring point N satisfies in is the negative sequence voltage at the measuring point N, Z N is the equivalent negative sequence impedance viewed from the measuring point N toward the system side;

[0095] According to the above two equations, the phase difference of the negative sequence voltage and current at the upstream measuring point of the fault point depends on the equivalent negative sequence impedance of the line and system in front of the measuring point, and is related to the power factor. When the reactive power on the system side is under-compensated or over-compensated, the phase difference of the negative sequence voltage and current at the upstream measuring point of the fault point falls in the second and third quadrants, such as Figure 4As shown in Figure 2, the phase difference between the negative-sequence voltage and current at the measurement point downstream of the fault depends on the line and load behind the measurement point. During normal operation, the load power factor must be at least 0.95, and the phase difference between the negative-sequence voltage and current at the measurement point downstream of the fault must be greater than 0°. However, if the load is light and the reactive power compensation equipment is out of control, the system may be overcompensated, resulting in a capacitive equivalent impedance. Therefore, the phase difference between the negative-sequence voltage and current downstream of the fault point is in the 1st and 4th quadrants.

[0096] From the above, we can see that the phase difference of negative sequence voltage and current at each measuring point on the downstream line of the fault point satisfies Where arg represents the phase difference of negative sequence voltage and current, is the negative sequence voltage measured at each measuring point, is the negative sequence current flowing through each measuring point;

[0097] The phase difference of negative sequence voltage and current at each measuring point on the upstream line of the fault point satisfies

[0098] The negative sequence power flowing through each measuring point is Among them, P i (i=1,2,…n-1) is the active power flowing through each measuring point, U i (i=1,2,…n-1),I i (i=1,2,…n-1) are the amplitudes of negative sequence voltage and negative sequence current flowing through each measuring point, is the phase difference between the negative sequence voltage and current, It is the sensitive angle of the negative-sequence power direction element, which can be taken as the impedance angle of the equivalent negative-sequence impedance behind the measuring point.

[0099] Combining the above three equations, we can get that for each measuring point upstream of the fault point, P i <0, the power direction is negative, indicating that a fault has occurred in the positive direction of the measuring point i; for each measuring point downstream of the fault point, P i >0, the power direction is positive, indicating that a fault has occurred in the opposite direction of measuring point i.

[0100] Single-phase fault identification method for active distribution network

[0101] The fault section location criterion based on the negative sequence power direction can only locate the fault section, but cannot complete the fault type identification. Therefore, a negative sequence current phase ratio criterion is constructed for single-phase grounding fault and single-phase disconnection fault to further identify the fault type.

[0102] Figure 5 It is the negative sequence impedance network equivalent diagram of the single-phase disconnection and ungrounded fault on line MN. uLis the negative sequence impedance of the unmeasurable branch Lub1; β is the ratio of the length from the unmeasurable branch point to the line head end M to the total length of the line MN, β∈(0,1); They are the negative sequence currents flowing through the line M terminal, line N terminal and unmeasurable branch respectively.

[0103] According to Kirchhoff's voltage law, the negative sequence current can be obtained and The relationship is Comparing the two currents, we get

[0104] When the line does not contain unmeasurable branches, that is, Z uL =∞, there is

[0105] When the line contains unmeasurable branches, there are in

[0106] And the coefficient A1 has an inequality relationship k1 is the maximum value of A1;

[0107] In the power distribution system, the distribution line impedance, system equivalent impedance and load impedance are generally inductive. For the phase angle α1, Thus we get

[0108] In order to more intuitively show the negative sequence current in the case of unmeasurable branch faults and The phase comparison result of the two negative sequence currents can be obtained by combining the above formulas. Figure 6 As shown, it can be seen

[0109] In summary, the negative sequence ratio phase angle of the disconnected and ungrounded fault with unmeasurable branches is

[0110] The faults in the above analysis are all set to be downstream of the unmeasurable branch. If a fault occurs upstream of the unmeasurable branch, the theoretical derivation process is the same as the above analysis, and the location of the unmeasurable branch has no effect on the phase comparison results. The same is true for subsequent analyses.

[0111] Figure 7 The negative sequence impedance network isovalue diagram of the ground fault on the power supply side of the line MN when a single-phase line is disconnected. f is the transition resistance at the fault point. By decomposing the negative sequence network equivalent diagram of the ground fault on the single-phase disconnected power supply side, we can obtain the equivalent circuit of the additional current source acting alone and the equivalent circuit of the additional voltage source acting alone, as shown in the following example: Figure 8 shown.

[0112] When the additional current source acts alone, the relationship between the negative sequence currents at both ends is:

[0113]

[0114] When the additional voltage source acts alone, the negative sequence current Negative sequence current It can be expressed as

[0115]

[0116] According to Kirchhoff's voltage law,

[0117]

[0118] The negative sequence current ratio at both ends is obtained

[0119]

[0120] When the line does not contain unmeasurable branches, that is, Z uL =∞, the above formula is expressed as

[0121]

[0122] in

[0123] Thus we get When the line does not contain unmeasurable branches, the negative sequence phase comparison result is: When the line contains unmeasurable branches, there is in

[0124]

[0125] Then get

[0126] Considering the actual distribution network |Z uL |>>|Z L |+|Z m |, then there is That is, α5∈[-θ2,θ2], where θ2 is a very small positive angle;

[0127] When the line contains unmeasurable branches, the negative sequence phase comparison result is

[0128] The phase comparison results of the ground fault on the power supply side of a single-phase disconnected line with an unmeasurable branch are as follows: Figure 9 As shown;

[0129] In summary, the phase comparison result of the ground fault on the single-phase disconnected power supply side is:

[0130] For a single-phase disconnected load side ground fault, the negative sequence network can also be decomposed into additional networks with current source and voltage source acting independently, such as Figure 10 The negative sequence current phase ratio result of the load side fault at both ends of the single-phase disconnection is the same as that of the single-phase disconnection and ungrounded fault.

[0131] Figure 11 The negative sequence impedance network isovalue diagram of line MN when a single-phase grounding fault occurs. The negative sequence current expression at both ends is:

[0132] Comparing the two currents, we get

[0133]

[0134] When the line does not contain unmeasurable branches, the above formula is expressed as

[0135] Taking into account the characteristics of each equivalent impedance, there is

[0136] Comprehensively obtain

[0137] When the line contains unmeasurable branches, it can be simplified to in

[0138] Finally got

[0139] Combining the above formula, we know that α5∈[-θ2,θ2], so the phase comparison result of the line containing unmeasurable branches is

[0140] When a single-phase ground fault or single-phase disconnection fault occurs in the distribution network, negative sequence voltage appears at each monitoring point in the system, and load imbalance will also produce negative sequence voltage. Therefore, the setting value of the fault detection start criterion should avoid the negative sequence voltage generated by the unbalanced load, that is, in is the negative sequence voltage measured at each monitoring point after the fault; U set It is the negative sequence voltage value generated by unbalanced load during normal operation; ΔU set It can be 5% of the system rated voltage;

[0141] The present invention locates the fault by comparing the negative sequence power directions on both sides of the line. Figure 2 In the distribution line shown, monitoring devices are installed on both sides of each section and exchange information to determine the fault section;

[0142] When a fault occurs at f1, the negative sequence power measured at the monitoring points at both ends of the faulty line MN has opposite directions, thus confirming that the line is a faulty section. For the healthy line NP, the negative sequence power measured at the monitoring points at both ends has the same direction, thus confirming that the line is a healthy section.

[0143] Fault location methods based on negative-sequence power direction are also applicable to single-phase grounding faults and single-phase disconnection faults, but they cannot distinguish the fault type and often require different fault handling methods for different fault types. Therefore, further identification of the fault type is required.

[0144] Considering unmeasurable branches, the phase comparison results for the negative sequence currents at both ends of the fault section for single-phase line failure with no grounding, single-phase line failure with load-side grounding, and most single-phase line failures with power-side grounding are all on the right side of the vertical axis. In extreme cases, the phase comparison results for single-phase line failure with power-side grounding may fall on the left side of the vertical axis. The phase comparison results for single-phase line failure can be expressed as:

[0145] For a single-phase grounding fault, considering the unmeasurable branch, the phase comparison result of the negative sequence current at both ends is:

[0146] The distribution of the negative sequence current phase difference on both sides of the fault line for single-phase grounding fault and single-phase disconnection fault can be obtained as follows: Figure 12 shown

[0147] In the figure, in extreme cases, the single-phase ground fault area and the single-phase disconnected power supply side ground fault area may theoretically overlap. As discussed above, θ2 is generally a very small angle. When the equivalent negative-sequence impedance angle of the branch load and its angle with the line and system impedance are large, the accuracy of the judgment criteria is affected. However, in actual distribution networks, the angles α3, α4, and α6 derived above do not reach their theoretical maximum values, and the likelihood of the phase comparison results overlapping is minimal. Furthermore, extensive simulation analysis has not demonstrated this phenomenon. This provides the fault type identification criterion: when the negative-sequence current phase comparison result is to the right of the vertical axis, a single-phase disconnected fault has occurred in the system; when the phase comparison result is to the left of the vertical axis, a single-phase disconnected fault has occurred in the system.

[0148] The following simulation experiments are conducted to verify the effect of the method of the present invention:

[0149] In order to verify the effectiveness of the method proposed in the present invention, the following Figure 13The 10kV active distribution network model shown in the figure has a transformer capacity of 50MVA and a transformer ratio of 110kV / 10kV. The lengths of lines AB, BC, and CD are 3km, 8km, and 3km, respectively. Considering that the unmeasured branch load is generally less than 10% of the total load, its load is set to 0.5MV·A. The positive sequence parameters of the line are r1 = 0.031Ω / km, l1 = 0.096mH / km, and c1 = 0.338μF / km; the zero sequence parameters are r0 = 0.234Ω / km, l0 = 0.355mH / km, and c0 = 0.265μF / km. Fault point f1 is located at the midpoint of section AB; fault points f2, f3, and f4 are located at the beginning, midpoint, and end of section BC, respectively; and f5 is located at the midpoint of section CD. DG1 is an IIDG and DG2 is an MTDG, both with a rated capacity of 1.2MV·A. Monitoring points 1, 2, 3, 4, 5, and 6 are located at the beginning and end of lines AB, BC, and CD, respectively.

[0150] Different fault types are set at the six fault locations f1 to f5 (since the single-phase disconnection and ungrounded fault is not affected by the transition resistance, only the influence of the fault location is considered). The fault resistance is 100Ω. The negative sequence power of each monitoring point is shown in Tables 1 to 4:

[0151] Table 1 Schematic diagram of the simulation results of negative sequence power of single-phase ground fault

[0152]

[0153] Table 2 Schematic diagram of negative sequence power simulation results for single-phase disconnection and ungrounded fault

[0154]

[0155] Table 3 Schematic diagram of the simulation results of negative sequence power of ground fault on the single-phase disconnected power supply side

[0156]

[0157] Table 4 Schematic diagram of the simulation results of negative sequence power for single-phase disconnection load side grounding fault

[0158]

[0159] Tables 1-4 show that when a fault occurs at f1, the negative-sequence power at monitoring point 1 is negative, while the negative-sequence power at monitoring points 2-6 is positive. Therefore, the fault section can be determined to be line AB. Similarly, when faults occur at f2, f3, and f4, the fault section can be determined to be line BC.

[0160] Similarly, different fault types are set at the fault location at f3. When the transition resistance values ​​are 10Ω, 50Ω, 100Ω and 300Ω respectively, the negative sequence power of each monitoring point is as follows: Figures 14-16 shown.

[0161] Depend on Figures 14-16 It can be seen that the negative-sequence power upstream of a single-phase grounding fault is much greater than the negative-sequence power downstream, and the negative-sequence power downstream of a single-phase line break fault is much greater than the negative-sequence power upstream. The magnitude of the negative-sequence power in a single-phase line break fault is much greater than that in a single-phase grounding fault because the negative-sequence voltage and current values ​​in a single-phase line break fault are larger and less affected by the magnitude of the transition resistance. Therefore, the present invention can still accurately locate the fault section under different transition resistances.

[0162] When the fault section is determined to be line BC, four fault types with different transition resistances are set at the three fault points f2, f3, and f4, and the negative sequence current phase ratio results of the single-phase disconnection and ungrounded fault are obtained as follows: Figure 17 The negative sequence current phase ratio results of the other three faults are shown in Tables 5 to 7.

[0163] Table 5 Schematic diagram of negative sequence current phase comparison results for ground fault on the power supply side of single-phase disconnection

[0164]

[0165] Table 6 Schematic diagram of negative sequence current phase comparison results for single-phase disconnection load side grounding fault

[0166]

[0167] Table 7 Schematic diagram of negative sequence current phase comparison results for single-phase grounding fault

[0168]

[0169] according to Figure 17 It can be seen that the single-phase disconnection and ungrounded fault occurs at 0.1s. Limited by the time window of the Fourier algorithm, the negative sequence phase comparison result changes one cycle after the fault, and the phase comparison result is consistent with the negative sequence phase comparison method. According to the phase comparison results in Tables 5 to 7, the proposed negative sequence phase comparison fault identification method can effectively distinguish the faults in the other three fault conditions. The phase comparison results of the three disconnection faults are all on the right side of the coordinate axis, the phase comparison results of the single-phase grounding fault are all on the left side of the coordinate axis, and the negative sequence current phase comparison results do not fall into Figure 12 The overlapping area in .

[0170] In actual distribution networks, the nature of branch connections in different areas may vary, and the magnitude of unmeasurable branch loads may also change. Therefore, further verification of the impact of load variations on the proposed method is necessary. Taking line BC in the figure as an example, four faults with a transition resistance of 100Ω were set at fault f3. The simulation results for varying the nature and magnitude of the unmeasurable branch loads are shown in Table 8.

[0171] Table 8 Schematic diagram of phase comparison results for different branch properties and capacities

[0172]

[0173] As shown in Table 8, when the load level of the unmeasurable branch changes, the negative sequence current phase ratio result does not change much, which shows that the proposed fault identification method is universal for distribution lines with branch structures.

[0174] In order to verify the adaptability of different types of DGs and their criteria at different penetration rates, a simulation analysis was conducted to analyze the impact of the control strategy on the detection performance after a line fault when the DG is at the weak sending end. Figure 13 In this example, DG1 is a doubly-fed wind turbine generator and DG2 is a synchronous generator. Considering different penetration rates below 30%, four faults with a transition resistance of 50Ω were set at f3 in the BC section to verify the results of the proposed method. Table 9 shows the simulation results of the negative-sequence power direction measured at monitoring points 3 and 4, where "+" indicates a positive negative-sequence power direction and "-" indicates a negative negative-sequence power direction. Table 10 shows the phase comparison results for the fault section BC.

[0175] Table 9 Schematic diagram of negative sequence power direction results at monitoring points 3 and 4 under different DG penetration rates

[0176]

[0177] Table 10 Schematic diagram of phase comparison results of fault section BC under different DG penetration rates

[0178]

[0179] Tables 9 and 10 show that when using the negative-sequence power direction for fault location, different DG penetration rates have no effect on this method, and the fault section can still be accurately located. When using the negative-sequence current phase ratio results to identify fault types, the boundaries between single-phase grounding faults and single-phase line break faults are very clear. The negative-sequence current phase ratio results for single-phase line break faults are stable near 0°, while those for single-phase grounding faults are around 180°, showing little impact from the DG penetration rate.

[0180] like Figure 18The figure shows a functional module diagram of the system of the present invention: the system for realizing the single-phase fault detection method of the active distribution network disclosed in the present invention comprises a data acquisition module, a real-time monitoring module, a fault judgment module, a negative-sequence power calculation module, a fault section judgment module, a phase angle difference calculation module, a fault type judgment module and a single-phase fault detection module; the data acquisition module, the real-time monitoring module, the fault judgment module, the negative-sequence power calculation module, the fault section judgment module, the phase angle difference calculation module, the fault type judgment module and the single-phase fault detection module are connected in series in sequence; the data acquisition module acquires the parameter information of the target active distribution network and uploads the data information to the real-time monitoring module; the real-time monitoring module is used to acquire the working data information of the target active distribution network in real time according to the received data information, and upload the data information to the fault judgment module; the fault judgment module is used to determine the fault type according to the received data information by acquiring the negative-sequence voltage data of each monitoring point when a fault occurs: if the fault is a single-phase fault, the data is uploaded to the fault judgment module. The negative-sequence power calculation module is uploaded according to the information; if the fault is not a single-phase fault, the judgment ends; the negative-sequence power calculation module is used to calculate the negative-sequence power of each monitoring point according to the received data information and the obtained working data information of each monitoring point, and upload the data information to the fault section judgment module; the fault section judgment module is used to judge the fault section according to the received data information and the obtained negative-sequence power of each monitoring point, and upload the data information to the phase angle difference calculation module; the phase angle difference calculation module is used to calculate the negative-sequence current phase angle difference on both sides of the fault section according to the received data information and the obtained working data information of the fault section, and upload the data information to the fault type judgment module; the fault type judgment module is used to judge the single-phase fault type according to the received data information and the obtained negative-sequence current phase angle difference, and upload the data information to the single-phase fault detection module; the single-phase fault detection module is used to complete the single-phase fault detection of the active distribution network according to the received data information.

Claims

1. A method for detecting single-phase faults in an active power distribution network, comprising the following steps: S1. Obtain parameter information of the target active distribution network; S2. Real-time acquisition of target active distribution network operating data information; S3. When a fault occurs, the fault type is determined by obtaining the negative sequence voltage data of each monitoring point: If the fault is a single-phase fault, proceed to the subsequent steps; If the fault is not a single-phase fault, the algorithm ends; S4. Calculate the negative sequence power of each monitoring point based on the working data information obtained from each monitoring point; S5. According to the negative sequence power of each monitoring point obtained in step S4, the fault section is judged; S6. Calculate the negative sequence current phase angle difference on both sides of the fault section based on the acquired working data information of the fault section; S7. Determine the type of single-phase fault based on the negative sequence current phase angle difference obtained in step S6; S8. Complete single-phase fault detection of the active distribution network.

2. The method for detecting single-phase faults in an active power distribution network according to claim 1, characterized in that The step S3 specifically includes the following steps: When a fault occurs, the negative sequence voltage data of each monitoring point is obtained; The following formula is used as the criterion formula for the fault type: In the formula is the negative sequence voltage measured at each monitoring point after the fault; U set It is the negative sequence voltage value generated by unbalanced load during normal operation; ΔU set is the set negative sequence voltage threshold; If the judgment formula is established, the fault type is determined to be a single-phase fault, and the subsequent steps are carried out; If the judgment formula is not valid, the fault type is determined not to be a single-phase fault, the algorithm ends, and an alarm is issued.

3. The method for detecting single-phase faults in an active power distribution network according to claim 2, characterized in that Step S5, in accordance with the negative sequence power of each monitoring point obtained in step S4, determines the fault section, specifically comprising the following steps: Determine whether the directions of the negative sequence power of any two adjacent monitoring points are the same: If the directions of the negative sequence powers of any two adjacent monitoring points are the same, the section between the two adjacent monitoring points is determined to be a normal section; If the directions of the negative sequence powers of any two adjacent monitoring points are different, the section between the two adjacent monitoring points is determined to be a fault section, and the subsequent steps are continued.

4. The method for detecting single-phase faults in an active power distribution network according to claim 3, characterized in that The step S7 of determining the single-phase fault type based on the negative sequence current phase angle difference obtained in step S6 specifically includes the following steps: The following formula is used as the criterion formula for single-phase fault type: -90°<θ<90° Where θ is the negative sequence current phase angle difference; If the judgment formula is established, the single-phase fault type is determined to be a single-phase disconnection fault; If the judgment formula is not valid, the fault type is determined to be a single-phase grounding fault.

5. A system for implementing the method for detecting single-phase faults in an active power distribution network according to any one of claims 1 to 4, characterized in that It includes a data acquisition module, a real-time monitoring module, a fault judgment module, a negative-sequence power calculation module, a fault section judgment module, a phase angle difference calculation module, a fault type judgment module and a single-phase fault detection module; the data acquisition module, the real-time monitoring module, the fault judgment module, the negative-sequence power calculation module, the fault section judgment module, the phase angle difference calculation module, the fault type judgment module and the single-phase fault detection module are connected in series in sequence; the data acquisition module obtains parameter information of the target active distribution network and uploads the data information to the real-time monitoring module; The real-time monitoring module is used to obtain the working data information of the target active distribution network in real time based on the received data information, and upload the data information to the fault judgment module; The fault determination module is used to determine the fault type based on the received data information when a fault occurs by obtaining the negative sequence voltage data of each monitoring point: if the fault is a single-phase fault, the data information is uploaded to the negative sequence power calculation module; If the fault is not a single-phase fault, the judgment ends; the negative sequence power calculation module is used to calculate the negative sequence power of each monitoring point according to the received data information and the working data information of each monitoring point, and upload the data information to the fault section judgment module; The fault section judgment module is used to judge the fault section according to the received data information and the negative sequence power of each monitoring point, and upload the data information to the phase angle difference calculation module; The phase angle difference calculation module is used to calculate the negative sequence current phase angle difference on both sides of the fault section according to the received data information and the obtained working data information of the fault section, and upload the data information to the fault type judgment module; The fault type judgment module is used to judge the single-phase fault type according to the received data information and the obtained negative sequence current phase angle difference, and upload the data information to the single-phase fault detection module; The single-phase fault detection module is used to complete the single-phase fault detection of the active power distribution network according to the received data information.

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