A method for detecting disconnection faults in FTU

Abstract

The present invention relates to the field of power system automation technology, and discloses a line break fault detection method suitable for FTU, comprising the following steps: low-pass filtering three-phase current and zero-sequence current signals collected by FTU; determining the fault condition by comparing the change in the effective value of the positive sequence current with the size of the threshold a; determining the fault condition by comparing the change in the effective value of each phase current with the size of the threshold b; determining the fault condition by comparing the change in the effective value of the negative sequence current with the size of the threshold c; determining the fault condition by comparing the change in the effective value of the zero sequence current with the size of the threshold f and the change in the effective value of the zero sequence voltage with the size of the threshold d; determining the fault position by comparing the effective value of the line voltage with the relationship between the coefficients k1 and k2. The present invention does not require a distribution automation master station and is not limited to the installation position of the FTU, and can realize accurate detection of line break faults upstream or downstream of the line. The method is simple and easy to implement, and has strong engineering practicality.

Description

Technical Field

[0001] The present invention relates to the technical field of power system automation, and in particular to a line break fault detection method suitable for FTU, which is mainly used for detecting line break faults of distribution lines in power automation systems. Background Art

[0002] With the rapid development of the national economy, the scale of the power system is also growing, the network structure is becoming more and more complex, and users have higher and higher requirements for the stability of power supply. This requires continuous strengthening of the upgrade of the power system to avoid faults during system operation. Even if a fault occurs, the location of the fault must be found quickly and accurately after the fault occurs, and then the fault must be quickly eliminated to ensure the safe operation of the power system and minimize losses.

[0003] In recent years, due to meteorological disasters, line aging and external force damage, line disconnection faults have become more frequent. Line disconnection faults will cause the three-phase voltage and current on the load side to be no longer symmetrical, and the negative sequence and zero sequence components generated will cause serious damage to various loads. In addition, line disconnection faults will also be accompanied by grounding faults to form complex faults, which can easily cause fires and electric shocks to people and animals, and even develop into phase-to-phase short circuit faults, expanding the scope of power outages.

[0004] FTU, feeder automation measurement and control terminal, can detect distribution line break faults.

[0005] At present, the applicable scenario of the disconnection fault detection method applied on FTU is: the disconnection point is located upstream of FTU. When FTU is installed at the head end of the line and a disconnection fault occurs downstream, FTU cannot detect the occurrence of the fault. Therefore, there is an urgent need for a disconnection fault detection method that is not limited to the FTU installation location and can detect both upstream and downstream disconnections. Summary of the invention

[0006] In view of the shortcomings and defects of the prior art, the present invention provides a line break fault detection method applicable to FTU, which is not limited to the installation position of FTU and realizes accurate detection of line breakage upstream or downstream.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A method for detecting a line break fault applicable to a FTU comprises the following steps:

[0009] Step 1: FTU collects three-phase current, zero-sequence current, zero-sequence voltage and line voltage signals, and performs low-pass filtering on the three-phase current and zero-sequence current signals;

[0010] Step 2: According to the three-phase current after filtering in step 1, calculate the positive sequence current effective value once every half power frequency cycle, and calculate the change R_Ip of two adjacent positive sequence current effective values, and compare the change of the positive sequence current effective value with the threshold a. If the above change is not less than a, it is determined that there is no disconnection fault, otherwise go to step 3;

[0011] Step 3: According to the three-phase current filtered in step 1, calculate the effective value of each phase current once every half power frequency cycle, and calculate the change of the effective value of two adjacent currents of each phase R_Ia, R_Ib, R_Ic respectively, and compare the change of the effective value of each phase current with the threshold b respectively. If the change of one phase in the above changes is not less than b, it is determined that there is no disconnection fault, otherwise go to step 4;

[0012] Step 4: According to the three-phase current after filtering in step 1, calculate the negative sequence current effective value once every half power frequency cycle, and calculate the change R_In of two adjacent negative sequence current effective values, and compare the change of the negative sequence current effective value with the threshold c. If the above change is greater than c, go to step 6, otherwise go to step 5;

[0013] Step 5: According to the zero-sequence current after filtering in step 1, the zero-sequence current effective value and the zero-sequence voltage effective value are calculated once every half power frequency cycle, and the change amount R_Izero of two adjacent zero-sequence current effective values ​​and the change amount R_Uzero of two adjacent zero-sequence voltage effective values ​​are calculated respectively, and the change amount of the zero-sequence current effective value is compared with the threshold value f, and the change amount of the zero-sequence voltage effective value is compared with the threshold value d. If the change amount of the zero-sequence current effective value is not less than f or the change amount of the zero-sequence voltage effective value is not less than d, then go to step 6, otherwise it is determined that there is no disconnection fault;

[0014] Step 6: Calculate the effective value of the line voltage every half power frequency cycle, given the coefficients k1 and k2:

[0015] If this step is entered from step 4, it is determined whether there is any effective value of the line voltage within [k1*U n ,k2*U n ] range, where U n is the standard line voltage. If it exists, it is determined that the upstream of FTU is disconnected. Otherwise, it is determined that the downstream of FTU is disconnected.

[0016] If this step is entered from step 5, it is determined whether there are at least two line voltages whose effective values ​​are less than or equal to k1*U at the same time. n If it exists, it is determined that the upstream of FTU is disconnected, otherwise it is determined that the downstream of FTU is disconnected.

[0017] Preferably, the cut-off frequency of the low-pass filter in step 1 is greater than 50 Hz and less than 100 Hz.

[0018] Preferably, the value of the threshold a in step 2 is greater than -30A and less than or equal to 0A.

[0019] Preferably, the value of the threshold b in step 3 is greater than -45A and less than or equal to 0A.

[0020] Preferably, the value of the threshold c in step 4 is greater than or equal to 0A and less than 30A.

[0021] Preferably, in step 5, the value of the threshold f is greater than or equal to 0A and less than 10A, and the value of the threshold d is greater than or equal to 50V.

[0022] Preferably, in step 6, the value of coefficient k1 is greater than or equal to 0.1 and less than or equal to 0.4, and the value of coefficient k2 is greater than or equal to 0.65 and less than or equal to 0.85.

[0023] Preferably, the calculation method of the change amount appearing in steps 2 to 5 is to subtract the first half of the power frequency cycle from the second half of the power frequency cycle.

[0024] The beneficial technical effect of the present invention is that it can accurately detect upstream or downstream line break faults without the need for a distribution automation master station and is not limited by the FTU installation location. The method is simple and easy to implement and has strong engineering practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the overall flow chart of the present invention.

[0026] Figure 2 Schematic diagram of topological circuits in an embodiment of the present invention.

[0027] Figure 3 : is the three-phase current waveform after filtering in the embodiment of the present invention.

[0028] Figure 4 : is the positive sequence current waveform in the embodiment of the present invention.

[0029] Figure 5 : is the negative sequence current waveform in the embodiment of the present invention.

[0030] Figure 6 : is the line voltage waveform in the embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not limit the present invention.

[0032] Example

[0033] like Figure 2 The figure shows the on-site topology of a medium voltage (1kV~35kV) distribution line, where a line break occurs upstream of the FTU.

[0034] Combined with Figure 1 , a disconnection fault detection method applicable to FTU, comprising the following steps:

[0035] Step 1: FTU collects three-phase current, zero-sequence current, zero-sequence voltage and line voltage signals, and performs low-pass filtering on the three-phase current and zero-sequence current signals with a cut-off frequency of 80 Hz.

[0036] Step 2: If Figure 3 The three-phase current after filtering in step 1 is shown as follows: Figure 4 The positive sequence current effective value is calculated once every half power frequency cycle, and the change of two adjacent positive sequence current effective values ​​is calculated, and the change of the positive sequence current effective value is compared with the threshold value 0A. If the above change is not less than 0A, it is determined that there is no disconnection fault, otherwise it goes to step 3. In the embodiment, its value at the time of the fault is -1.44A, and step 3 is entered.

[0037] Step 3: According to the three-phase current after filtering in step 1, the effective value of each phase current is calculated once every half power frequency cycle, and the change in the effective value of two adjacent currents of each phase is calculated respectively, and the change in the effective value of each phase current is compared with the threshold value 0A respectively. If the change in one phase among the above changes is not less than 0A, it is determined that there is no disconnection fault, otherwise, it goes to step 4. In the embodiment, when the fault occurs, the change in phase A is -2.23A, the change in phase B is -0.80A, and the change in phase C is -0.15A, and step 4 is entered.

[0038] Step 4: According to the three-phase current filtered in step 1, the negative sequence current waveform is as follows: Figure 5 The negative sequence current effective value is calculated once for every half power frequency cycle, and the change of two adjacent negative sequence current effective values ​​is calculated, and the change of the negative sequence current effective value is compared with the threshold value of 0.5A. If the above change is greater than 0.5A, then go to step 6, otherwise go to step 5. In the embodiment, when the fault occurs, its value is 7.84A, and then go to step 6.

[0039] Step 5: Based on the zero-sequence current after filtering in step 1, calculate the effective value of the zero-sequence current and the effective value of the zero-sequence voltage once every half power frequency cycle, and calculate the change of two adjacent zero-sequence current effective values ​​and the change of two adjacent zero-sequence voltage effective values ​​respectively, compare the change of the zero-sequence current effective value with the threshold value f, and compare the change of the zero-sequence voltage effective value with the threshold value d. If the change of the zero-sequence current effective value is not less than f or the change of the zero-sequence voltage effective value is not less than d, go to step 6, otherwise it is determined that there is no disconnection fault.

[0040] Step 6: Figure 6 The figure shows the line voltage waveform collected by FTU. The effective value of the line voltage is calculated once every half power frequency cycle, with given coefficients k1 and k2:

[0041] If this step is entered from step 4, it is determined whether there is any effective value of the line voltage within [k1*U n ,k2*U n ] range, where U n is the standard line voltage. If it exists, it is determined that the upstream of FTU is disconnected. Otherwise, it is determined that the downstream of FTU is disconnected.

[0042] If this step is entered from step 5, it is determined whether there are at least two line voltages whose effective values ​​are less than or equal to k1*U at the same time. n If it exists, it is determined that the upstream of FTU is disconnected, otherwise it is determined that the downstream of FTU is disconnected.

[0043] In the embodiment, k1*U n 3000V, k2*U n is 8000V, line voltage U AB It is 6785.40V, which is within [3000V, 8000V]. Its value is within [3000V, 8000V], so it is determined that there is a line break upstream of FTU.

[0044] It has been verified that, in the embodiment, the recognition result of the method is consistent with the actual situation.

[0045] The above embodiments are descriptions of specific implementation methods of the present invention rather than limitations of the present invention. Technical personnel in the relevant technical field may make various changes and modifications to obtain corresponding equivalent technical solutions without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions should be included in the patent protection scope of the present invention.

Claims

1. A line break fault detection method applicable to FTU, characterized in that: The following steps are involved: Step 1: FTU collects three-phase current, zero-sequence current, zero-sequence voltage and line voltage signals, and performs low-pass filtering on the three-phase current and zero-sequence current signals; Step 2: Based on the three-phase current after filtering in step 1, calculate the positive sequence current effective value once every half power frequency cycle, and calculate the change of two adjacent positive sequence current effective values, and compare the change of two adjacent positive sequence current effective values ​​with the threshold a. If the above change is not less than a, it is determined that there is no disconnection fault, otherwise go to step 3; Step 3: According to the three-phase current after filtering in step 1, the effective value of each phase current is calculated once every half power frequency cycle, and the change of the effective value of two adjacent currents of each phase is calculated respectively, and the change of the effective value of two adjacent currents of each phase is compared with the threshold value b respectively. If the change of one phase in the above changes is not less than b, it is determined that there is no disconnection fault, otherwise, go to step 4; Step 4: According to the three-phase current after filtering in step 1, the negative sequence current effective value is calculated once every half power frequency cycle, and the change of two adjacent negative sequence current effective values ​​is calculated, and the change of two adjacent negative sequence current effective values ​​is compared with the threshold value c. If the above change is greater than c, go to step 6, otherwise go to step 5; Step 5: According to the zero-sequence current after filtering in step 1, calculate the effective value of the zero-sequence current and the effective value of the zero-sequence voltage once every half power frequency cycle, and respectively calculate the change of the effective values ​​of two adjacent zero-sequence currents and the change of the effective values ​​of two adjacent zero-sequence voltages, compare the change of the effective values ​​of two adjacent zero-sequence currents with the threshold value f, and compare the change of the effective values ​​of two adjacent zero-sequence voltages with the threshold value d. If the change of the effective value of the zero-sequence current is not less than f or the change of the effective value of the zero-sequence voltage is not less than d, proceed to step 6, otherwise it is determined that there is no disconnection fault; Step 6: Calculate the effective value of the line voltage every half power frequency cycle, given the coefficients k1 and k2: If this step is entered from step 4, it is determined whether there is any line voltage whose effective value is greater than or equal to k1*U n and less than or equal to k2*U n , where U n is the standard line voltage. If it exists, it is determined that the upstream of FTU is disconnected. Otherwise, it is determined that the downstream of FTU is disconnected. If this step is entered from step 5, it is determined whether there are at least two line voltages whose effective values ​​are less than or equal to k1*U at the same time. n If it exists, it is determined that the upstream of FTU is disconnected, otherwise it is determined that the downstream of FTU is disconnected.

2. A line break fault detection method applicable to FTU according to claim 1, characterized in that: The cut-off frequency of the low-pass filter in step 1 is greater than 50 Hz and less than 100 Hz, and the voltage level applicable to the value range is the medium voltage level, that is, the distribution network voltage level should be greater than 1 kV and less than 35 kV.

3. A line break fault detection method applicable to FTU according to claim 1, characterized in that: The value of the threshold a in step 2 is greater than -30A and less than or equal to 0A, and the voltage level applicable to the value range is the medium voltage level, that is, the distribution network voltage level should be greater than 1kV and less than 35kV.

4. A line break fault detection method applicable to FTU according to claim 1, characterized in that: The value of the threshold b in step 3 is greater than -45A and less than or equal to 0A, and the voltage level applicable to the value range is the medium voltage level, that is, the distribution network voltage level should be greater than 1kV and less than 35kV.

5. A line break fault detection method applicable to FTU according to claim 1, characterized in that: The value of the threshold c in step 4 is greater than or equal to 0A and less than 30A, and the voltage level applicable to the value range is the medium voltage level, that is, the distribution network voltage level should be greater than 1kV and less than 35kV.

6. A line break fault detection method applicable to FTU according to claim 1, characterized in that: In step 5, the value of the threshold value f is greater than or equal to 0A and less than 10A, and the value of the threshold value d is greater than or equal to 50V. The voltage level applicable to the above f and d value ranges is the medium voltage level, that is, the distribution network voltage level should be greater than 1kV and less than 35kV.

7. A line break fault detection method applicable to FTU according to claim 1, characterized in that: In step 6, the value of coefficient k1 is greater than or equal to 0.1 and less than or equal to 0.4, and the value of coefficient k2 is greater than or equal to 0.65 and less than or equal to 0.

85. The voltage level applicable to the above k1 and k2 value ranges is the medium voltage level, that is, the distribution network voltage level should be greater than 1kV and less than 35kV.

8. A line break fault detection method applicable to FTU according to claim 1, characterized in that: The calculation method of the change amount appearing in the steps 2 to 5 is to subtract the first half of the power frequency cycle from the second half of the power frequency cycle.

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