A distribution network fault location method and system based on non-contact measurement

Abstract

This application discloses a method and system for fault location in distribution networks based on non-contact measurement. The method includes receiving voltage and current signals sampled by non-contact sensors installed on the line; converting the current amplitude signal into phasor current based on the voltage signal; calculating the operating current and braking current based on the phasor current; and locating the fault based on the operating current and braking current. This invention employs a non-contact sensor and wireless communication with the distribution terminal, without altering the existing line structure, and is suitable for the digital upgrade of existing equipment. Based on differential protection, it utilizes sensor sampling data to achieve rapid and accurate fault location without affecting the setting of upstream protection. The protection mode is independent, enabling local fault isolation and self-healing.

Description

Technical Field

[0001] The present invention belongs to the technical field of distribution network fault processing, and in particular relates to a distribution network fault locating method and system based on non-contact measurement. Background Art

[0002] The introduction of smart devices and new energy sources has led the traditional power grid to develop towards intelligence and low carbonization, and the simple radial distribution network has gradually transformed into a complex multi-power supply distribution network. The low-carbon distribution network adopts power electronics technology on a large scale. The addition of new energy sources has led to differences in the operation mechanism, grid topology and control method of the power grid, resulting in complex and special fault transient characteristics of the distribution network.

[0003] At present, my country mainly adopts four modes for fault handling of distribution network, namely, recloser feeder automation, segmented differential feeder automation, master station centralized feeder automation and intelligent distributed feeder automation. These processing modes all have some defects. The recloser type has slow fault handling and power supply recovery speed, which has a great impact on the system and users. It is only applicable to simple topology lines, and it is very difficult to coordinate parameters when applied to complex networks with multiple power sources and multiple branches; the segmented differential type is very sensitive to the topology structure and operation mode of the power grid. The delay of protection action will cause short-circuit current and voltage sag to exist for a long time, aggravating the harm to distribution station equipment and sensitive loads, and is not conducive to power grid protection setting; the master station centralized fault handling depends on the master station or substation, and the complexity is closely related to the primary network and secondary equipment, and the requirements for control algorithms are high; although intelligent distributed can overcome the defects of the above three methods, it cannot meet the selectivity requirements in the complex network connected to distributed power sources, and the application cost is high and the maintenance efficiency is low.

[0004] A better fault handling method is still needed for the current distribution network fault handling. Summary of the invention

[0005] Based on this, the present invention proposes a distribution network fault location method and system based on non-contact measurement, which adopts non-contact sensors for signal acquisition and combines longitudinal differential protection to realize line fault location, thereby guiding on-site fault isolation and self-healing to overcome the defects of the above-mentioned prior art.

[0006] The present invention provides a distribution network fault location method based on non-contact measurement, comprising:

[0007] The voltage signal and current signal sampled by the non-contact sensor arranged on the receiving line are converted into the current amplitude signal into the phasor current according to the voltage signal;

[0008] Calculate the operating current and braking current based on the phasor current;

[0009] Fault location is performed based on the operating current and braking current.

[0010] Furthermore, when there is a branch line in the line, the above method also includes:

[0011] Receiving a current signal sampled by a non-contact sensor arranged on the branch line;

[0012] Calculate the current mutation value based on the current signal and the normal load current;

[0013] Compare the current mutation value with the current threshold to locate the fault.

[0014] Furthermore, fault location based on the operating current and the braking current includes:

[0015] Calculate the minimum operating current of the longitudinal differential protection based on the operating current and the braking current;

[0016] When the minimum operating current of the longitudinal differential protection meets the following criteria, the fault occurs in the current line.

[0017] I K.act =I CDΦ -I RΦ ≥I set , where I K.act Indicates the minimum operating current of the longitudinal differential protection, I CDΦ Indicates the operating current, I RΦ Indicates the braking current, I set Indicates the current setting value.

[0018] Furthermore, the operating current is calculated according to the following expression:

[0019] Among them, I CDΦ Indicates the operating current, and Represents the phasor current on both sides of the line.

[0020] Furthermore, the braking current is calculated according to the following expression:

[0021] Among them, I RΦ Indicates the braking current, and It represents the phasor current on both sides of the line, K represents the braking coefficient, and it satisfies 0<K<1.

[0022] Furthermore, the sampling of the voltage signal is performed according to the following expression:

[0023]

[0024] in, represents the voltage signal of the non-contact sensor measurement point, ε0 represents the electric field strength at the measurement point, A eq Represents the equivalent area of ​​the sensor, R m Indicates the measured resistance, R0 indicates the distance between the measuring point and the line, r0 indicates the line conductor radius, Represents the measured potential recorded at the sampling frequency within time t.

[0025] Furthermore, the calculation of the current mutation value includes:

[0026] ΔI=I f -I e , ΔI represents the current mutation value, I f Represents the current signal of the branch line sampled by the non-contact sensor, I e Indicates normal load current.

[0027] Further, comparing the current mutation value and the current threshold to locate the fault includes:

[0028] The current mutation value satisfies ΔI≥I pre When , the fault is located in the current branch line, otherwise the fault is located in the trunk line closest to the branch line;

[0029] Among them I pre Indicates the current threshold.

[0030] Furthermore, the current threshold I pre Set to 150A.

[0031] The present invention also provides a distribution network fault location system based on non-contact measurement, comprising:

[0032] A sampling signal receiving unit is used to receive a voltage signal and a current signal sampled by a non-contact sensor arranged on the line, and convert a current amplitude signal into a phasor current according to the voltage signal;

[0033] A current analysis unit, used for calculating the operating current and the braking current according to the phasor current;

[0034] The line fault locating unit is used to locate the fault according to the operating current and the braking current.

[0035] Furthermore, the above system also includes:

[0036] The sudden change current analysis unit is used to calculate the sudden change current value according to the current signal and the normal load current.

[0037] Furthermore, the current analysis unit is also used to compare the current mutation value with the current threshold value to perform fault location.

[0038] It can be seen from the above technical solutions that the present invention has the following beneficial effects:

[0039] The present invention discloses a distribution network fault location method and system based on non-contact measurement. The method arranges a non-contact sensor on the line, and the sensor collects the voltage and current of the line at the same time. The braking current and the operating current are calculated according to the phasor current, and the fault location is further performed, thereby realizing local fault isolation and self-healing. The present invention adopts a non-contact sensor and a distribution terminal wireless transmission mode to realize the simultaneous acquisition of voltage and current, without changing the original line structure, and is easy to deploy. It is suitable for the digital upgrade and transformation of existing distribution equipment, with low construction cost and high installation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0041] Figure 1 Implementation flow chart of a distribution network fault location method based on non-contact measurement provided by an embodiment of the present invention

[0042] Figure 2 Schematic diagram of longitudinal differential protection principle in one embodiment of the present invention

[0043] Figure 3 Schematic diagram of a braking characteristic curve in an embodiment of the present invention

[0044] Figure 4 Implementation flow chart of a distribution network fault location method based on non-contact measurement provided by another embodiment of the present invention

[0045] Figure 5 A structural block diagram of a distribution network fault location system based on non-contact measurement provided by an embodiment of the present invention

[0046] Figure 6 A structural block diagram of a distribution network fault location system based on non-contact measurement provided by another embodiment of the present invention

[0047] Figure 7 A schematic diagram of a power distribution network line fault provided by another embodiment of the present invention DETAILED DESCRIPTION

[0048] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] In the distribution network connected to distributed power sources, bidirectional fault currents may be generated when a line fails. With the development of intelligent power grids, the traditional fault handling methods are no longer applicable. Figure 1 This embodiment provides a fault location method, in which a non-contact sensor is set on the line, and the sensor and the distribution terminal on the line transmit sampling signals through wireless networking communication, and the longitudinal differential protection is combined to realize the rapid and accurate location and isolation of the distribution network fault.

[0050] The distribution network fault location method based on non-contact measurement provided in this embodiment includes:

[0051] The voltage signal and current signal sampled by the non-contact sensor arranged on the receiving line are converted into the phasor current according to the voltage signal.

[0052] This embodiment requires the installation of non-contact sensors at the distribution automation terminals of each trunk line and branch line. At present, various micro current sensors have been widely used on site, such as current sensors based on magnetoresistance, etc., which obtain current amplitude by measuring the magnetic field. They have good performance in measurement accuracy, sensitivity, measurement range, linearity, anti-interference, installation convenience, size, power consumption and cost. However, non-contact sensors can only measure current amplitude, and longitudinal differential protection requires current phasor for judgment, so voltage measurement values ​​need to be collected.

[0053] The non-contact sensor can indirectly measure the conductor potential by measuring the electric field strength around the conductor. There is no direct energy transfer in this process. The electrode of the sensor near the conductor to be measured will induce charge through electric field coupling. When the changing induced charge flows through the measuring resistor connected to the electrode, a voltage drop will be generated. The resistance voltage drop is proportional to the rate of change of the electric field at the measuring point where the sensor is located. For a conductor, the output of a single electrode is proportional to the measured voltage phase. The relationship can be expressed as:

[0054]

[0055] in, represents the voltage signal of the non-contact sensor measurement point, ε0 represents the electric field strength at the measurement point, A eq Represents the equivalent area of ​​the sensor, R mIndicates the measured resistance, R0 indicates the distance between the measuring point and the line, r0 indicates the line conductor radius, Represents the measured potential recorded at the sampling frequency within time t.

[0056] Get the line voltage phasor After that, the line current amplitude collected by the sensor can be taken in the voltage direction to obtain the phasor current.

[0057] The operating current and braking current are calculated based on the phasor current.

[0058] The longitudinal differential protection based on non-contact measurement adopts the phase-splitting current phasor differential method. Its protection principle is based on Kirchhoff's current law, that is, the current flowing into a node (or closed space) is equal to the current flowing out of the node (or closed space). The only condition for the fault judgment to be established is that there is additional branch current flowing out, which is independent of the nature of the external power supply providing current. That is, the external power supply can be a three-phase symmetrical synchronous motor or asynchronous motor, or a distributed power supply using a power electronic converter interface.

[0059] The longitudinal differential protection based on non-contact measurement mainly handles trunk line faults between ring network cabinets. The terminal collects the measurement information of the non-contact sensor, and then completes the protection control decision and action through wireless communication interaction and longitudinal differential calculation between terminals.

[0060] When the line is operating normally or a fault occurs outside the line, the current flowing through both sides of the line is equal. When a fault occurs inside the line, the components connected to the power supply all provide current to the fault point, such as Figure 2 shown.

[0061] The action current represents the current that triggers the protection action, and its calculation can be expressed as Among them, I CDΦ Indicates the operating current, and Represents the phasor current on both sides of the line.

[0062] The braking current is the current that prevents the protection action, and its calculation can be expressed as Among them, I RΦ Indicates the braking current, and It represents the phasor current on both sides of the line, K represents the braking coefficient, and it satisfies 0<K<1.

[0063] Fault location is performed based on the operating current and braking current.

[0064] In this embodiment, fault location needs to calculate the minimum operating current of the longitudinal differential protection based on the operating current and the braking current. When the minimum operating current of the longitudinal differential protection meets the following criteria, it is determined that the fault occurs in the current line:

[0065] I K.act =I CDΦ -I RΦ ≥I set , where I K.act Indicates the minimum operating current of the longitudinal differential protection, I CDΦ Indicates the operating current, I RΦ Indicates the braking current, I set Indicates the current setting value.

[0066] Minimum operating current of longitudinal differential protection I K.act and braking current I RΦ The relationship satisfies the braking characteristics of the longitudinal differential protection, such as Figure 3 As shown, I K.act With I RΦ increases with the increase of .

[0067] In the distribution network, when the current I K.act Satisfy the above criteria I K.act =I CDΦ -I RΦ ≥I set When the fault occurs, it means that the fault occurs in the current line. The distribution terminals on both sides of the fault point can control the switches on both sides of the line to disconnect to complete the fault isolation. Since the sampling frequency of the non-contact sensor is above 4KHz, the fault self-healing of the distribution network can be quickly realized.

[0068] In a further embodiment, the braking coefficient K can be obtained through on-site debugging. Add balancing current on both sides of the line to make the protection inoperative; then use a tester such as a relay to gradually increase the current on one side with a fixed step length until the longitudinal differential protection is activated, record the longitudinal differential action current at this time, add another set of balancing currents of different sizes, use the same steps to make the longitudinal differential protection act, record another longitudinal differential action current, and calculate the braking current according to the above braking current calculation formula and criterion I K.act =I CDΦ -I RΦ ≥I set The braking coefficient K can be calculated and verified.

[0069] See also Figure 4 , another embodiment of the present invention is introduced below, which is used to realize fault location of branch lines.

[0070] In the overhead lines of the distribution network, some faults are eliminated by manual line inspection. Due to the low reliability of fault indicators, it is difficult to locate faults on branch lines by simply installing fault indicators on the lines. Especially in mountainous areas, manual search for fault points is extremely difficult, inefficient, time-consuming and labor-intensive, and may even pose a threat to personal safety.

[0071] When a fault occurs in the overhead line of the distribution network, if there is a branch line on the main line, the fault may occur on the main line or the branch line. The fault location method provided in the above embodiment can only locate the location of the fault in a certain line section, and cannot accurately determine the location of the fault point. It is necessary to use a non-contact sensor installed on the branch line terminal to further determine the location of the fault point.

[0072] For a distribution network with branch lines, it is necessary to first calculate the minimum operating current I of the longitudinal differential protection of the trunk line according to the above embodiment. K.act , I K.act Satisfy Criterion I K.act =I CDΦ -I RΦ ≥I set When the current in the branch line is analyzed,

[0073] The normal load current of the branch line is I e When a fault occurs, the load current of the branch line suddenly increases by ΔI and jumps to I f , that is, ΔI=I f -I e , the sensor sampling current I on the branch line f , when the current mutation value satisfies ΔI ≥ I pre When the fault is located in the current branch line, if ΔI<I pre , the fault is located on the trunk line closest to the branch line, I pre Indicates the current threshold.

[0074] Current threshold I pre You can refer to the recommended test data for overhead indicators in clause 6.5.1.1.3 of the national standard DLT 1157-2019 "General Technical Conditions for Distribution Line Fault Indicators", that is, the minimum action value of the indicator alarm is set to 150A.

[0075] See also Figure 5 This embodiment provides a distribution network fault location system based on non-contact measurement, which is used to implement the fault location method provided in the above embodiment, including:

[0076] The sampling signal receiving unit 201 is used to receive the voltage signal and the current signal sampled by the non-contact sensor arranged on the line, and convert the current amplitude signal into the phasor current according to the voltage signal;

[0077] A current analysis unit 202, used for calculating the operating current and the braking current according to the phasor current;

[0078] The line fault locating unit 203 is used to locate the fault according to the operating current and the braking current.

[0079] like Figure 6 As shown, in a further embodiment, in order to realize fault location of a branch line, Figure 5 The fault location system shown also includes:

[0080] The sudden change current analysis unit 204 is used to calculate the sudden change current value according to the current signal and the normal load current.

[0081] To further illustrate the fault location method provided by the present invention, Figure 7 As shown, in the following embodiment, a specific distribution network environment is described.

[0082] In the case of a trunk line failure, such as Figure 7 As shown, a fault occurs in the trunk line between terminals FS2 and FS3, and the contactless sensors on each terminal sample the voltage and current on the line and send the sampled information to the terminal respectively. The terminal then transmits the instantaneous phasor current at the moment of the fault to the adjacent terminal through wireless communication. Terminals FS2 and FS3 determine that the fault location is inside their lines through the collected phasor current calculations, and quickly trip the switches of FS2 and FS3 to complete the fault isolation.

[0083] For branch line faults, such as Figure 7 As shown, a fault occurs on the branch line of the overhead line where the terminal FZ1 is located. The longitudinal differential protection can only locate the fault location in the line section between FS1 and FS2, but cannot determine whether the fault is located on the main line or the branch line. The non-contact sensor on FZ1 samples the current of the branch line, and the branch line sensor sends the current to FZ1. At this time, FZ1 detects a sudden change in the collected current value, which means that the fault point is located on the branch line where FZ1 is located.

[0084] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A distribution network fault location method based on non-contact measurement, characterized in that: include: The voltage signal and current signal sampled by the non-contact sensor arranged on the receiving line are converted into the current amplitude signal into the phasor current according to the voltage signal; Calculating the operating current and the braking current according to the phasor current; The fault location is performed according to the action current and the braking current, specifically including calculating the minimum action current of the longitudinal differential protection according to the action current and the braking current. When the minimum action current of the longitudinal differential protection meets the following criteria, the fault occurs in the current line. I K.act =I CDΦ -I RΦ ≥I set , where I K.act Indicates the minimum operating current of the longitudinal differential protection, I CDΦ Indicates the operating current, I RΦ Indicates the braking current, I set Indicates the current setting value; The operating current is expressed as The braking current is expressed as in, and It represents the phasor current on both sides of the line, K represents the braking coefficient, and it satisfies 0<K<1.

2. The distribution network fault location method based on non-contact measurement according to claim 1 is characterized in that: When there is a branch line on the line, the method further includes: Receiving a current signal sampled by a non-contact sensor arranged on the branch line; Calculate the current mutation value based on the current signal on the branch line and the normal load current; The current mutation value is compared with a current threshold to perform fault location.

3. The distribution network fault location method based on non-contact measurement according to claim 1, characterized in that: The sampling of the voltage signal is performed according to the following expression: in, represents the voltage signal of the non-contact sensor measurement point, ε0 represents the electric field strength at the measurement point, A eq Represents the equivalent area of ​​the sensor, R m Indicates the measured resistance, R0 indicates the distance between the measuring point and the line, r0 indicates the line conductor radius, Represents the measured potential recorded at the sampling frequency within time t.

4. The distribution network fault location method based on non-contact measurement according to claim 2, characterized in that: The calculation of the current mutation value includes: ΔI=I f -I e , ΔI represents the current mutation value, I f Represents the current signal of the branch line sampled by the non-contact sensor, I e Indicates normal load current.

5. The distribution network fault location method based on non-contact measurement according to claim 4 is characterized in that: Comparing the current mutation value with the current threshold to locate the fault includes: The current mutation value satisfies ΔI≥I pre When , the fault is located in the current branch line, otherwise the fault is located in the trunk line closest to the branch line; Among them I pre Indicates the current threshold.

6. A distribution network fault location system based on non-contact measurement, characterized in that: include: A sampling signal receiving unit is used to receive a voltage signal and a current signal sampled by a non-contact sensor arranged on the line, and convert a current amplitude signal into a phasor current according to the voltage signal; A current analysis unit, used for calculating the operating current and the braking current according to the phasor current; The line fault locating unit is used to locate the fault according to the action current and the braking current, specifically including calculating the minimum action current of the longitudinal differential protection according to the action current and the braking current. When the minimum action current of the longitudinal differential protection meets the following criteria, the fault occurs in the current line. I K.act =I CDφ -I Rφ ≥I set , where I K.act Indicates the minimum operating current of the longitudinal differential protection, I CDφ Indicates the operating current, I RΦ Indicates the braking current, I set Indicates the current setting value; The operating current is expressed as The braking current is expressed as in, and It represents the phasor current on both sides of the line, K represents the braking coefficient, and it satisfies 0<K<1.

7. The distribution network fault location system based on non-contact measurement according to claim 6, characterized in that: The system further comprises: The sudden change current analysis unit is used to calculate the sudden change current value according to the current signal and the normal load current.

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