Method and device for distinguishing internal fault from external fault

Abstract

The invention discloses a method and device for distinguishing an internal fault from an external fault, and the method comprises the steps: obtaining the real-time voltage of a power transmission line after the fault, carrying out the processing of the real-time voltage of the power transmission line after the fault through a low-pass filter, and obtaining the real-time voltage of the power transmission line which is linearly distributed along the line, the method comprises the following steps: for real-time voltage of a power transmission line which is linearly distributed along the line, converting three-phase voltage from an abc coordinate system to a dq coordinate system by utilizing dq conversion, obtaining d-axis voltage variation of a fault point F and a setting point S after the dq conversion, and judging whether the fault is an internal fault or an external fault based on the d-axis voltage variation of the fault point F and the setting point S. According to the method and the device provided by the embodiment of the invention, the internal and external faults can be distinguished.

Description

Technical Field

[0001] The present invention relates to the technical field of backup protection, and in particular, to a method and device for distinguishing between in-zone faults and out-of-zone faults. Background Art

[0002] Accelerating the promotion of new energy power generation to replace traditional fossil energy power generation and building a new power system with an increasing proportion of new energy has become the main direction of the development of China's power system. Among them, photovoltaic power sources and direct-drive wind turbine generator power sources will account for a large share, and they are connected to the power grid through full-power inverters. After their large-scale access to the power system, the topological structure and fault characteristics of the fault network have changed. Therefore, the unique fault characteristics may seriously threaten the correct operation of distance protection.

[0003] Different from overcurrent protection, the protection range of distance protection is basically not affected by the operation mode of the power grid, so it has been widely used in transmission lines. Compared with traditional synchronous generator power sources, the maximum fault current of new energy can only reach 1.2 to 1.5 p.u. Affected by the amplitude limitation and phase angle control of inverter-type power sources, the boosting effect of the system-side current will be enhanced, and the phase angle difference between the fault currents on the system side and new energy may be very large and difficult to predict in advance, resulting in inaccurate impedance calculation of traditional amplitude-comparison distance protection. In addition, since the positive and negative sequence impedances of new energy vary with factors such as the operation mode and fault conditions, and the new energy power station is a non-linear multi-coupled control system, its system impedance is obviously not constant. Therefore, traditional power-frequency sudden change distance protection also has adaptability problems in the context of new energy access. Summary of the Invention

[0004] In view of this, the present invention proposes a method and device for distinguishing between in-zone faults and out-of-zone faults, aiming to solve one or more of the technical problems mentioned in the above background art section.

[0005] In a first aspect, an embodiment of the present invention provides a method for distinguishing between in-zone faults and out-of-zone faults, the method comprising: acquiring the real-time voltage of a transmission line after a fault; processing the real-time voltage of the transmission line after the fault using a low-pass filter to obtain the real-time voltage of the transmission line linearly distributed along the line; for the real-time voltage of the transmission line linearly distributed along the line, transforming the three-phase voltage from the abc coordinate system to the dq coordinate system using dq transformation; acquiring the change in the d-axis voltage at the fault point F and the setting point S after dq transformation; and determining whether the fault is an in-zone fault or an out-of-zone fault based on the change in the d-axis voltage at the fault point F and the setting point S.

[0006] Further, based on the d-axis voltage change amounts of the fault point F and the setting point S, it is determined whether the fault is an in-zone fault or an out-of-zone fault, including: for the first stage after the fault, comparing the magnitudes of the absolute values of the d-axis voltage change amounts of the fault point F and the setting point S to determine whether the fault is an in-zone fault or an out-of-zone fault; for the second stage after the fault, comparing the magnitudes of the absolute values of the d-axis voltage change amounts of the fault point F and the setting point S under the credibility coefficient to determine whether the fault is an in-zone fault or an out-of-zone fault; where the first stage is the stage when the voltage drop at the fault location on the line after the fault is zero, and the second stage is the stage when the voltage at the fault location on the line remains at a level close to zero after the first stage.

[0007] Further, for the first stage after the fault, comparing the magnitudes of the absolute values of the d-axis voltage change amounts of the fault point F and the setting point S to determine whether the fault is an in-zone fault or an out-of-zone fault, including: for the first stage after the fault, if the absolute value of the d-axis voltage change amount of the fault point F is less than the absolute value of the d-axis voltage change amount of the setting point S, it is determined that the fault is an in-zone fault; if the absolute value of the d-axis voltage change amount of the fault point F is greater than the absolute value of the d-axis voltage change amount of the setting point S, it is determined that the fault is an out-of-zone fault.

[0008] Further, for the second stage after the fault, comparing the magnitudes of the absolute values of the d-axis voltage change amounts of the fault point F and the setting point S under the credibility coefficient to determine whether the fault is an in-zone fault or an out-of-zone fault, including: for the second stage after the fault, if the following protection criterion is satisfied for 15 milliseconds after the fault, it is determined that the fault is an in-zone fault, otherwise it is an out-of-zone fault:

[0009] |Δu Sd (t)|≥K·|Δu Fd (t)|;

[0010] where, |Δu Sd (t)| is the absolute value of the d-axis voltage change amount of the setting point S, |Δu Fd (t)| is the absolute value of the d-axis voltage change amount of the fault point F, and K is the credibility coefficient.

[0011] In a second aspect, an embodiment of the present invention further provides a device for distinguishing between in-zone faults and out-of-zone faults. The device includes: a first acquisition unit configured to acquire the real-time voltage of a power transmission line after a fault; a processing unit configured to process the real-time voltage of the power transmission line after the fault by using a low-pass filter to obtain the real-time voltage of the power transmission line linearly distributed along the line; a transformation unit configured to, for the real-time voltage of the power transmission line linearly distributed along the line, transform the three-phase voltage from the abc coordinate system to the dq coordinate system by using the dq transformation; a second acquisition unit configured to acquire the change in the d-axis voltage at the fault point F and the setting point S after the dq transformation; and a determination unit configured to determine whether the fault is an in-zone fault or an out-of-zone fault based on the change in the d-axis voltage at the fault point F and the setting point S.

[0012] Further, the determination unit is further configured to: for the first stage after the fault, compare the magnitudes of the absolute values of the change in the d-axis voltage at the fault point F and the setting point S to determine whether the fault is an in-zone fault or an out-of-zone fault; for the second stage after the fault, compare the magnitudes of the absolute values of the change in the d-axis voltage at the fault point F and the setting point S under a credibility coefficient to determine whether the fault is an in-zone fault or an out-of-zone fault; where the first stage is the stage where the voltage drop at the fault on the line after the fault is zero, and the second stage is the stage where the voltage at the fault on the line after the first stage remains at a level close to zero.

[0013] Further, for the first stage after the fault, comparing the magnitudes of the absolute values of the change in the d-axis voltage at the fault point F and the setting point S to determine whether the fault is an in-zone fault or an out-of-zone fault includes: for the first stage after the fault, if the absolute value of the change in the d-axis voltage at the fault point F is less than the absolute value of the change in the d-axis voltage at the setting point S, it is determined that the fault is an in-zone fault; if the absolute value of the change in the d-axis voltage at the fault point F is greater than the absolute value of the change in the d-axis voltage at the setting point S, it is determined that the fault is an out-of-zone fault.

[0014] Further, for the second stage after the fault, comparing the magnitudes of the absolute values of the change in the d-axis voltage at the fault point F and the setting point S under a credibility coefficient to determine whether the fault is an in-zone fault or an out-of-zone fault includes: for the second stage after the fault, if the following protection criterion is satisfied for 15 milliseconds after the fault, it is determined that the fault is an in-zone fault, otherwise it is an out-of-zone fault:

[0015] |Δu Sd (t)|≥K·|Δu Fd (t)|;

[0016] where, |Δu Sd (t)| is the absolute value of the change in the d-axis voltage at the setting point S, |Δu Fd(t) | is the absolute value of the change in the d-axis voltage at the fault point F, and K is the credibility coefficient.

[0017] In a third aspect, an embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the methods provided in the above embodiments are implemented.

[0018] In a fourth aspect, an embodiment of the present invention further provides an electronic device, including: a processor; a memory for storing executable instructions executable by the processor; the processor is configured to read the executable instructions from the memory and execute the instructions to implement the methods provided in the above embodiments.

[0019] The method and device for distinguishing between internal faults and external faults provided by the embodiments of the present invention obtain the real-time voltage of the transmission line after a fault, process the real-time voltage of the transmission line after the fault by using a low-pass filter to obtain the real-time voltage of the transmission line that is linearly distributed along the line. For the real-time voltage of the transmission line that is linearly distributed along the line, the three-phase voltage is transformed from the abc coordinate system to the dq coordinate system by using the dq transformation, and the change in the d-axis voltage at the fault point F and the setting point S after the dq transformation is obtained. Based on the change in the d-axis voltage at the fault point F and the setting point S, it is determined whether the fault is an internal fault or an external fault, thereby realizing the distinction between internal and external faults. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Shows an exemplary flowchart of a method for distinguishing between internal faults and external faults according to an embodiment of the present invention;

[0021] Figure 2 Shows a schematic diagram of the response of a low-pass filter to a step input according to an embodiment of the present invention;

[0022] Figures 3a - 3b Shows a schematic diagram of the instantaneous voltage distribution in the first stage of an AC transmission line after a fault according to an embodiment of the present invention, where Figure 3a is an internal fault, Figure 3b is an external fault;

[0023] Figures 4a - 4b Shows a schematic diagram of the instantaneous voltage distribution in the second stage of an AC transmission line after a fault according to an embodiment of the present invention, where Figure 4a is an internal fault, Figure 4b is an external fault;

[0024] Figures 5a - 5b Shows a schematic diagram of the instantaneous d-axis voltage distribution in the first stage of an AC transmission line after a fault according to an embodiment of the present invention, where Figure 5a is an internal fault, Figure 5b is an external fault;

[0025] Figures 6a - 6b A schematic diagram showing the instantaneous d-axis voltage distribution of the second section of an AC transmission line after a fault according to an embodiment of the present invention, wherein, Figure 6a is an in-zone fault, Figure 6b is an out-of-zone fault;

[0026] Figure 7 A schematic diagram showing the system topology of an inverter-type new energy power station sending power through an AC line according to an embodiment of the present invention;

[0027] Figures 8a - 8b A schematic diagram showing the simulation results of four typical short-circuit faults according to an embodiment of the present invention, wherein, Figure 8a is AG, Figure 8b is BC;

[0028] Figures 9a - 9c A schematic diagram showing the simulation results of protection actions for different fault distances according to an embodiment of the present invention, wherein, Figure 9a is 20 km from the measuring point, Figure 9b is 90 km from the measuring point, Figure 9c is a reverse out-of-zone fault;

[0029] Figure 10 A schematic diagram showing the structure of a device for distinguishing in-zone faults and out-of-zone faults according to an embodiment of the present invention. Detailed implementation manners

[0030] Now, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely, and to fully convey the scope of the present invention to those skilled in the art. The terms in the exemplary embodiments shown in the drawings are not limitations on the present invention. In the drawings, the same unit / element is denoted by the same reference numeral.

[0031] Unless otherwise specified, the terms (including scientific and technical terms) used herein have the ordinary meaning understood by those skilled in the art. In addition, it can be understood that the terms defined in the commonly used dictionary should be understood to have a meaning consistent with the context of their related fields, and should not be understood as idealized or overly formal meanings.

[0032] Figure 1 A schematic exemplary flowchart of a method for distinguishing in-zone faults and out-of-zone faults according to an embodiment of the present invention.

[0033] As Figure 1 shown, the method includes:

[0034] Step S101: Obtain the real-time voltage of the power transmission line after a fault;

[0035] Step S102: Process the real-time voltage of the power transmission line after a fault using a low-pass filter to obtain the real-time voltage of the power transmission line that is linearly distributed along the line;

[0036] Step S103: For the real-time voltage of the power transmission line that is linearly distributed along the line, use dq transformation to transform the three-phase voltage from the abc coordinate system to the dq coordinate system.

[0037] Step S104: Obtain the change in the d-axis voltage of the fault point F and the setting point S after dq transformation;

[0038] Step S105: Based on the change in the d-axis voltage of the fault point F and the setting point S, determine whether the fault is an in-zone fault or an out-of-zone fault.

[0039] Further, Step S105 includes:

[0040] For the first stage after a fault, compare the absolute values of the change in the d-axis voltage of the fault point F and the setting point S to determine whether the fault is an in-zone fault or an out-of-zone fault;

[0041] For the second stage after a fault, compare the absolute values of the change in the d-axis voltage of the fault point F and the setting point S under the credibility coefficient to determine whether the fault is an in-zone fault or an out-of-zone fault;

[0042] Among them, the first stage is the stage when the voltage drop at the fault location on the line after the fault is zero, and the second stage is the stage when the voltage at the fault location on the line remains at a level close to zero after the first stage.

[0043] Further, for the first stage after a fault, comparing the absolute values of the change in the d-axis voltage of the fault point F and the setting point S to determine whether the fault is an in-zone fault or an out-of-zone fault includes:

[0044] For the first stage after a fault, if the absolute value of the change in the d-axis voltage of the fault point F is less than the absolute value of the change in the d-axis voltage of the setting point S, it is determined that the fault is an in-zone fault; if the absolute value of the change in the d-axis voltage of the fault point F is greater than the absolute value of the change in the d-axis voltage of the setting point S, it is determined that the fault is an out-of-zone fault.

[0045] Further, for the second stage after a fault, comparing the absolute values of the change in the d-axis voltage of the fault point F and the setting point S under the credibility coefficient to determine whether the fault is an in-zone fault or an out-of-zone fault includes:

[0046] For the second stage after a fault, if the following protection criterion is satisfied for 15 milliseconds after the fault, the fault is determined to be an in-zone fault; otherwise, it is an out-of-zone fault:

[0047] |Δu Sd (t)|≥K·|Δu Fd (t)|;

[0048] Among them, |Δu Sd (t)| is the absolute value of the change in the d-axis voltage at the setting point S, |Δu Fd (t)| is the absolute value of the change in the d-axis voltage at the fault point F, and K is the credibility coefficient.

[0049] Furthermore, K = 1.05.

[0050] Specifically, the implementation of the present invention includes:

[0051] (1) Distance protection analysis based on the change in instantaneous voltage

[0052] In the fault state, the voltage at the fault point can essentially be regarded as a step signal. Using this principle, the voltage at the fault point is filtered by a low-pass filter, and its filtered value gradually decays to zero over time. Figure 2 Shows a schematic diagram of the response of a low-pass filter to a step input according to an embodiment of the present invention. As Figure 2 shown, the change process of the voltage at the fault point after the fault includes two stages: the first stage, which takes approximately 30 milliseconds to reduce the voltage at the fault on the line to zero, that is, the stage where the voltage at the fault on the line drops to zero after the fault; the second stage, after the first stage, the voltage at the fault on the line remains at a level close to zero.

[0053] When the instantaneous voltage passes through the action of the low-pass filter, the real-time voltage can be roughly represented as a linear distribution. Then the real-time voltage on the transmission line can be determined by the following formula:

[0054]

[0055] In the above equation, the total length of the transmission line is represented by L, x represents any position on the transmission line, and p can be represented by a, b, c.

[0056] Figures 3a - 3b Shows a schematic diagram of the instantaneous voltage distribution in the first stage of an AC transmission line after a fault according to an embodiment of the present invention, where Figure 3a is an in-zone fault, Figure 3b is an out-of-zone fault. As Figures 3a - 3bAs shown, after the low-pass filter processes the post-fault transient real-time voltage component, the real-time voltage of the transmission line is linearly distributed along the line. The voltage in the first stage after the fault is shown by the dashed line in the figure, where point F and point S represent the line fault point and the distance protection setting point respectively, point M represents the relay installation point, t0 is the fault occurrence time, and t1, t2, and t3 are the times in the first stage after the fault.

[0057] The change characteristics of the voltages at different points are as follows:

[0058]

[0059] Taking the in-zone fault as an example, in the first stage after the fault, |Δu M (t)| is much smaller than |Δu F (t)|. As mentioned above, the distribution of the post-fault transient voltage along the transmission line can be considered a linear distribution. Therefore, in the Figure 3a shown in-zone fault case, |Δu S (t)| will be greater than |Δu F (t)|.

[0060] Subsequently, for the out-of-zone fault scenario, in the first stage after the fault, the magnitude of |Δu M (t)| is significantly smaller than |Δu F (t)|. According to the linear change of the transient voltage of the AC transmission line, for the Figure 3b described out-of-zone fault, compared with |Δu F (t)|, |Δu S (t)| has a smaller value. Therefore, by using the theory that the voltage of the AC transmission line is approximately linearly distributed, in-zone and out-of-zone faults can be distinguished by comparing the voltage changes at the setting voltage point and the fault occurrence location.

[0061] Figures 4a - 4b shows a schematic diagram of the instantaneous voltage distribution of the second section of the AC transmission line after the fault according to an embodiment of the present invention, where Figure 4a is an in-zone fault, Figure 4b is an out-of-zone fault. A dashed line describes the voltage condition in the second stage after the fault. The time of fault occurrence is denoted as t0. t4, t5, and t6 represent a certain moment in the second stage after the fault.

[0062] As Figure 4a shown, in the case of an in-zone fault, |Δu S (t)| may be greater than or less than |Δu F (t)| in the second stage after the fault. Similarly, in the case of an out-of-zone fault, |Δu S (t)| may be greater than or less than |Δu F (t)|, asFigure 4b As shown. Therefore, comparing |Δu S (t)| and |Δu F (t)| cannot distinguish between internal faults and external faults in the second stage after a fault.

[0063] In summary, by comparing the voltage change between the setting point and the fault point in the second stage after a fault, it is possible to determine whether the fault is internal or external, but it cannot determine whether the fault is internal or external in the second stage. The first stage only lasts for milliseconds, and relying solely on the first stage cannot reliably issue a trip signal.

[0064] (2) Distance protection based on voltage dq transformation

[0065] This section introduces the dq transformation. After completing the rotation from the abc coordinate system to the dq axes, the AC instantaneous voltage is transformed into its equivalent DC voltage components. The transformation equations that control this dq transformation process are as follows:

[0066]

[0067] At a specific moment, the voltage existing in the transmission line follows this equation:

[0068]

[0069] L MF represents the length of the line connecting point M to point F, and L FS represents the length of the line connecting point F to point S. u Mp is the voltage at the measurement point on this side; u Fp represents the voltage at the fault point; u Sp represents the voltage at the setting point; p is represented by a, b, and c respectively.

[0070] Substituting formula (5) into formula (3), we derive

[0071]

[0072] u Mq is the q-axis voltage at the measurement point on this side; u Fq represents the q-axis voltage at the fault point; u Sq represents the q-axis voltage at the setting point; u Md is the d-axis voltage at the measurement point on this side; u Fd represents the d-axis voltage at the fault point; u Sd represents the d-axis voltage at the setting point; Equation (6) has a linear distribution in the dq coordinate system. Next, use the voltage change between the protection setting point S and the fault point F in this coordinate system to determine whether the fault is an internal fault or an external fault.

[0073] At the fault point F and the distance protection setting point S, it is crucial that the phase angle θ(t) between the d- and q-axis voltage components remains consistent. The digital phase-locked loop method is used to accurately measure the three-phase voltages at point M, thus providing accurate phase information.

[0074] Figures 5a - 5b The schematic diagram shows the instantaneous d-axis voltage distribution of the first section of the AC transmission line after a fault according to an embodiment of the present invention, where Figure 5a is an in-zone fault, Figure 5b is an out-of-zone fault. The dashed line represents the voltage state in the first stage after the fault.

[0075] The occurrence of the fault is recorded as time t0, and t1, t2, and t3 represent different periods in the early stage after the fault. At positions M, F, and S, the d-axis voltage components exhibit stable DC values before the fault. The voltage on the d-axis indicates that the proposed method remains effective immediately after the fault occurs.

[0076] Figures 6a - 6b The schematic diagram shows the instantaneous d-axis voltage distribution of the second section of the AC transmission line after a fault according to an embodiment of the present invention, where Figure 6a is an in-zone fault, Figure 6b is an out-of-zone fault. The voltage distribution in the second stage after the fault is described by the dotted line. In the second stage after the fault, t4, t5, and t6 represent different times. Among them, the calculated d-axis voltage components at the instantaneous moments of points M, F, and S remain unchanged in terms of the DC component in this stage. This method solves the difficulty of distinguishing in-zone and out-of-zone faults by comparing the transient change values of the abc three-phase voltages at the setting point and the fault location.

[0077] The embodiment of the present invention uses the difference in the d-axis voltage change values at the fault point F and the setting point S to distinguish in-zone and out-of-zone faults. The protection criterion is as follows:

[0078] |Δu Sd (t)|≥K·|Δu Fd (t)| (7)

[0079] The credibility coefficient is represented by K. Preferably, the credibility coefficient K is fixed at 1.05. After the fault, the protection device starts to calculate. When the criterion of Equation (7) is satisfied for 15 milliseconds, it is judged as an in-zone fault.

[0080] In the above embodiments, aiming at the problem that traditional distance protection has a risk of refusal to operate in a system where new energy is transmitted through an AC transmission line, a new backup protection method based on low-frequency filtering and voltage instantaneous value rotation coordinate transformation is proposed. By acquiring the real-time voltage of the transmission line after a fault, a low-pass filter is used to process the real-time voltage of the transmission line after the fault to obtain the real-time voltage of the transmission line that is linearly distributed along the line. For the real-time voltage of the transmission line that is linearly distributed along the line, the dq transformation is used to transform the three-phase voltage from the abc coordinate system to the dq coordinate system, and the change in the d-axis voltage of the fault point F and the setting point S after the dq transformation is obtained. Based on the change in the d-axis voltage of the fault point F and the setting point S, it is determined whether the fault is an in-zone fault or an out-of-zone fault, thereby realizing the distinction between in-zone and out-of-zone faults.

[0081] Embodiment 1

[0082] Figure 7 Fig. shows a schematic topology diagram of a system for an inverter-type new energy power station to be transmitted through an AC line according to an embodiment of the present invention. To verify the proposed distance protection scheme for the transmission line, a simulation model of the new energy power station transmission line as shown in Figure 7 is built in PSCAD. The type of generator is a direct-drive wind turbine, and the power supply type is an inverter-type power supply. All new energy power sources based on full-power inverters are boosted by a step-up transformer through a collection line and then transmit the generated power to the power grid through the transmission line. The capacity of this wind farm is 200 MW, the voltage level of the transmission line is 220 kV, and the length is 100 km. The system uses a second-order Butterworth low-pass filter with a cut-off frequency of 150 Hz for filtering, and the sampling frequency of the line is 5 kHz.

[0083] (1) Verification of protection operation for different fault types

[0084] For the operation of different fault types, the following figure shows the simulation results of the proposed method for a fault occurring 10 km from the measurement point on the new energy side, where the fault occurs at 2 s. Figures 8a - 8b Fig. shows a schematic diagram of the simulation results of four typical short-circuit faults according to an embodiment of the present invention, where, Figure 8a is AG, Figure 8b is BC. It can be seen from Figure 8a that after the fault occurs, the value of |Δu Sd (t)| is significantly greater than the value of |Δu Fd (t)|, verifying the correctness of the proposed protection principle. It can be seen from Figure 8b that in the case of an in-zone fault, |Δu Sd (t)| is greater than |Δu Fd (t)|, and the protection can operate correctly, proving that the protection operation performance is consistent with the theoretical analysis results, and this method has good quick-acting performance for different fault types.

[0085] (2) Verification of protection operation for different fault distances

[0086] To verify the performance of the proposed method under different fault distances, the simulation results of the proposed method for single-phase grounding faults occurring at different positions from the measuring point are given. The fault occurs at 2 seconds, and the protection range is set to 80% of the transmission line length. Figures 9a - 9c The schematic diagram showing the protection operation simulation results for different fault distances according to an embodiment of the present invention is shown, wherein, Figure 9a is 20 km from the measuring point, Figure 9b is 90 km from the measuring point, Figure 9c is an out-of-zone fault in the reverse direction.

[0087] As Figures 9a - 9c shown, the dashed line represents the change in the d-axis voltage |Δu Sd (t)| at the setting point, and the solid line represents the change in the d-axis voltage |Δu Fd (t)| at the virtual fault position. Figure 9a The simulation scenario for in-zone faults is given. It can be seen that the absolute value of |Δu Sd (t)| quickly exceeds that of |Δu Fd (t)| after the fault. These simulation data confirm the fast response characteristic of the designed protection scheme, which is also a major advantage of this distance protection scheme.

[0088] Figure 9b The simulation results for forward out-of-zone faults are shown. It should be noted that Figure 9c the simulation results for reverse faults are shown. As can be seen from the figure, |Δu Sd (t)| is less than |Δu Fd (t)|, and the distance protection does not operate. The simulation results show that the proposed distance protection can ensure that the relay protection does not operate when the fault is not within the forward protection range.

[0089] Figure 10 The schematic structural diagram of the device for distinguishing in-zone faults and out-of-zone faults according to an embodiment of the present invention is shown.

[0090] As Figure 10 shown, the device includes:

[0091] The first acquisition unit 1001 is used to acquire the real-time voltage of the transmission line after the fault;

[0092] The processing unit 1002 is used to process the real-time voltage of the transmission line after the fault by using a low-pass filter to obtain the real-time voltage of the transmission line linearly distributed along the line;

[0093] The transformation unit 1003 is configured to transform the three-phase voltage from the abc coordinate system to the dq coordinate system by using the dq transformation for the real-time voltage of the transmission line linearly distributed along the line.

[0094] The second acquisition unit 1004 is configured to acquire the change in the d-axis voltage of the fault point F and the setting point S after the dq transformation.

[0095] The determination unit 1005 is configured to determine whether the fault is an in-zone fault or an out-of-zone fault based on the change in the d-axis voltage of the fault point F and the setting point S.

[0096] Furthermore, the determination unit 1005 is further configured to:

[0097] For the first stage after the fault, compare the absolute values of the change in the d-axis voltage of the fault point F and the setting point S to determine whether the fault is an in-zone fault or an out-of-zone fault;

[0098] For the second stage after the fault, compare the absolute values of the change in the d-axis voltage of the fault point F and the setting point S under the credibility coefficient to determine whether the fault is an in-zone fault or an out-of-zone fault;

[0099] Wherein, the first stage is the stage when the voltage drop at the fault location on the line after the fault is zero, and the second stage is the stage when the voltage at the fault location on the line after the first stage remains at a level close to zero.

[0100] Furthermore, for the first stage after the fault, comparing the absolute values of the change in the d-axis voltage of the fault point F and the setting point S to determine whether the fault is an in-zone fault or an out-of-zone fault includes:

[0101] For the first stage after the fault, if the absolute value of the change in the d-axis voltage of the fault point F is less than the absolute value of the change in the d-axis voltage of the setting point S, it is determined that the fault is an in-zone fault; if the absolute value of the change in the d-axis voltage of the fault point F is greater than the absolute value of the change in the d-axis voltage of the setting point S, it is determined that the fault is an out-of-zone fault.

[0102] Furthermore, for the second stage after the fault, comparing the absolute values of the change in the d-axis voltage of the fault point F and the setting point S under the credibility coefficient to determine whether the fault is an in-zone fault or an out-of-zone fault includes:

[0103] For the second stage after the fault, if the following protection criterion is satisfied for 15 milliseconds after the fault, it is determined that the fault is an in-zone fault, otherwise it is an out-of-zone fault:

[0104] |Δu Sd (t)|≥K·|Δu Fd (t)|;

[0105] Wherein, |ΔuSd (t) | is the absolute value of the change in the d-axis voltage of the fixed point S, Δu Fd (t) | is the absolute value of the change in the d-axis voltage of the fault point F, and K is the credibility coefficient.

[0106] In the above embodiments, for the problem that traditional distance protection has a risk of refusal to operate in a system where new energy is transmitted through an AC transmission line, a new backup protection method based on low-frequency filtering and voltage instantaneous value rotation coordinate transformation is proposed. By obtaining the real-time voltage of the transmission line after a fault, a low-pass filter is used to process the real-time voltage of the transmission line after the fault to obtain the real-time voltage of the transmission line that is linearly distributed along the line. For the real-time voltage of the transmission line that is linearly distributed along the line, the dq transformation is used to transform the three-phase voltage from the abc coordinate system to the dq coordinate system, and the change in the d-axis voltage of the fault point F and the fixed point S after the dq transformation is obtained. Based on the change in the d-axis voltage of the fault point F and the fixed point S, it is determined whether the fault is an in-zone fault or an out-of-zone fault, so as to distinguish in-zone and out-of-zone faults.

[0107] It should be noted that when the device provided in the above embodiments realizes its functions, only the above-mentioned division of each functional module is used as an example. In practical applications, the above functions can be allocated to different functional modules according to needs, that is, the internal structure of the device is divided into different functional modules to complete all or part of the functions described above. In addition, the device provided in the above embodiments and the method embodiments belong to the same concept, and the specific implementation process is detailed in the method embodiments, which will not be repeated here.

[0108] The embodiments of the present invention also provide a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the method for distinguishing in-zone faults and out-of-zone faults provided in the above embodiments is realized.

[0109] The embodiments of the present invention also provide an electronic device, including: a processor; a memory for storing processor-executable instructions; the processor is used to read the executable instructions from the memory and execute the instructions to realize the method for distinguishing in-zone faults and out-of-zone faults provided in the above embodiments.

[0110] The present invention has been described by referring to a few embodiments. However, as is well known to those skilled in the art, other embodiments equivalent to those disclosed above of the present invention equally fall within the scope of the present invention as defined by the appended patent claims.

[0111] Generally, all terms used in the claims are construed according to their ordinary meaning in the technical field, unless otherwise expressly defined therein. All references to "a / the [device, component, etc.]" are to be construed openly as at least one instance of the device, component, etc., unless otherwise expressly stated. The steps of any method disclosed herein need not be performed in the exact order disclosed, unless expressly stated.

[0112] Those skilled in the art will appreciate that embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) having computer-usable program code therein.

[0113] The present invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and / or block of the flowchart illustrations and / or block diagrams, and combinations of flows and / or blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to the processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing device to produce a machine, such that the instructions executed by the processor of the computer or other programmable data processing device create means for implementing the functions specified in Figure 1 one or more of the flows Figure 1 or blocks or combinations of blocks.

[0114] These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means that implement the functions specified in Figure 1 one or more of the flows Figure 1 or blocks or combinations of blocks.

[0115] These computer program instructions may also be loaded onto a computer or other programmable data processing device, such that a series of operational steps are performed on the computer or other programmable device to produce a computer-implemented process, whereby the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in Figure 1 one or more of the flows Figure 1 or blocks or combinations of blocks.

[0116] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent replacements can still be made to the specific implementation manners of the present invention, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for distinguishing internal faults and external faults, characterized in that, The method includes: Obtaining the real-time voltage of the power transmission line after a fault; Processing the real-time voltage of the power transmission line after a fault using a low-pass filter to obtain the real-time voltage of the power transmission line that is linearly distributed along the line; For the real-time voltage of the power transmission line that is linearly distributed along the line, using dq transformation to transform the three-phase voltage from the abc coordinate system to the dq coordinate system; Obtaining the change in the d-axis voltage of the fault point F and the setting point S after dq transformation; Based on the change in the d-axis voltage of the fault point F and the setting point S, determining whether the fault is an internal fault or an external fault.

2. The method according to claim 1, characterized in that Based on the change in the d-axis voltage of the fault point F and the setting point S, determining whether the fault is an internal fault or an external fault, including: For the first stage after a fault, comparing the absolute values of the change in the d-axis voltage of the fault point F and the setting point S to determine whether the fault is an internal fault or an external fault; For the second stage after a fault, comparing the absolute values of the change in the d-axis voltage of the fault point F and the setting point S under the credibility coefficient to determine whether the fault is an internal fault or an external fault; Wherein, the first stage is the stage when the voltage drop at the fault on the line after the fault is zero, and the second stage is the stage when the voltage at the fault on the line after the first stage remains at a level close to zero.

3. The method according to claim 2, characterized in that, For the first stage after a fault, comparing the absolute values of the change in the d-axis voltage of the fault point F and the setting point S to determine whether the fault is an internal fault or an external fault, including: For the first stage after a fault, if the absolute value of the change in the d-axis voltage of the fault point F is less than the absolute value of the change in the d-axis voltage of the setting point S, it is determined that the fault is an internal fault; if the absolute value of the change in the d-axis voltage of the fault point F is greater than the absolute value of the change in the d-axis voltage of the setting point S, it is determined that the fault is an external fault.

4. The method according to claim 2, wherein For the second stage after a fault, comparing the absolute values of the change in the d-axis voltage of the fault point F and the setting point S under the credibility coefficient to determine whether the fault is an internal fault or an external fault, including: For the second stage after a fault, if the following protection criterion is satisfied for 15 milliseconds after the fault, it is determined that the fault is an internal fault, otherwise it is an external fault: |Δu Sd (t)|≥K·|Δu Fd (t)|; Among them, |Δu Sd (t)| is the absolute value of the change in the d-axis voltage at the fixed point S, and |Δu Fd (t)| is the absolute value of the change in the d-axis voltage at the fault point F. K is the credibility coefficient.

5. A device for distinguishing between internal faults and external faults, characterized in that, The device includes: A first acquisition unit for obtaining the real-time voltage of the power transmission line after a fault; A processing unit for processing the real-time voltage of the power transmission line after a fault using a low-pass filter to obtain the real-time voltage of the power transmission line that is linearly distributed along the line; A transformation unit for, for the real-time voltage of the power transmission line that is linearly distributed along the line, using dq transformation to transform the three-phase voltage from the abc coordinate system to the dq coordinate system; A second acquisition unit for obtaining the change in the d-axis voltage of the fault point F and the setting point S after dq transformation; A determination unit for determining whether the fault is an internal fault or an external fault based on the change in the d-axis voltage of the fault point F and the setting point S.

6. The device according to claim 5, characterized in that The determination unit is further configured to: For the first stage after a fault, compare the absolute values of the change in the d-axis voltage of the fault point F and the setting point S to determine whether the fault is an internal fault or an external fault; For the second stage after a fault, compare the absolute values of the d-axis voltage change amounts at the fault point F and the setting point S under the credibility coefficient to determine whether the fault is an internal fault or an external fault. Among them, the first stage is the stage where the voltage drop at the fault location on the line after the fault is zero, and the second stage is the stage where the voltage at the fault location on the line remains at a level close to zero after the first stage.

7. The device according to claim 6, characterized in that, For the first stage after a fault, compare the absolute values of the d-axis voltage change amounts at the fault point F and the setting point S to determine whether the fault is an internal fault or an external fault, including: For the first stage after a fault, if the absolute value of the d-axis voltage change amount at the fault point F is less than the absolute value of the d-axis voltage change amount at the setting point S, it is determined that the fault is an internal fault; if the absolute value of the d-axis voltage change amount at the fault point F is greater than the absolute value of the d-axis voltage change amount at the setting point S, it is determined that the fault is an external fault.

8. The device according to claim 6, characterized in that, For the second stage after a fault, compare the absolute values of the d-axis voltage change amounts at the fault point F and the setting point S under the credibility coefficient to determine whether the fault is an internal fault or an external fault, including: For the second stage after a fault, if the following protection criterion is satisfied for 15 milliseconds after the fault, it is determined that the fault is an internal fault; otherwise, it is an external fault: |Δu Sd (t)| ≥ K·|Δu Fd (t)|; where |Δu Sd (t)| is the absolute value of the change in the d-axis voltage at the fixed point S, and |Δu Fd (t)| is the absolute value of the change in the d-axis voltage at the fault point F, and K is the credibility coefficient.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, the method described in any one of claims 1-4 is implemented.

10. An electronic device, comprising: A processor; A memory for storing executable instructions that can be executed by the processor; The processor is configured to read the executable instructions from the memory and execute the instructions to implement the method described in any one of claims 1-4.

Images