Method and device for determining the direction of an ac line fault

Abstract

The application discloses a kind of determination method and device of alternating current line fault direction, belong to electric power system relay protection field.The determination method includes: obtaining the line voltage or phase voltage of first relay protection device and second relay protection device, judge whether it is less than 10%, if yes, start protection device, and carry out fault direction determination;Acquire the voltage and current signal of the protection device started, obtain post-fault voltage and post-fault current information;According to post-fault voltage information, the phase information of post-fault positive sequence voltage component is obtained by processing, and first power voltage is calculated;According to post-fault voltage, post-fault current and equivalent system impedance information, second power voltage is calculated;Judge whether the change trend of first power voltage and second power voltage is consistent within the preset time, and determine the fault direction according to the change trend.Application in alternating current grid system containing high proportion of new energy or existing complex scene such as DC drop point, the fault direction can be reliably distinguished.

Description

Technical Field

[0001] This invention belongs to the field of power system relay protection, and more specifically, relates to a method and device for determining the direction of AC line faults. Background Technology

[0002] With the widespread application of new energy power generation as a clean energy source in the power system, and the increasing development and application of DC power transmission in the power system, the fault characteristics of these two technologies, which differ from those of traditional synchronous generators, pose a significant challenge to traditional relay protection systems.

[0003] When a short-circuit fault occurs on an AC line containing renewable energy sources or DC transfer points, its fault characteristics are influenced by the power electronic equipment and control systems of the renewable energy or DC converter valves, resulting in complex and diverse fault characteristics. Traditional power directional relays cannot reliably determine the fault direction and are difficult to adapt to changes in the power system. Existing methods for determining the fault direction in new power systems rely on collected and stored memory voltage and current. This requires continuous signal acquisition and storage of electrical quantities near the protection device, resulting in a long operating time for the directional elements. When a line fault occurs, traditional directional elements are highly dependent on historical data, and the stored data can only be maintained for a limited time. If there is a lack of stored data, the fault direction cannot be reliably determined, exhibiting certain limitations. Summary of the Invention

[0004] In view of the shortcomings of related technologies, the present invention aims to provide a method and device for determining the direction of AC line faults, which aims to solve the problems that existing fault determination methods rely on historical data, and that if historical data is missing, the direction element cannot reliably determine the direction of the fault, as well as the problem that the continuous acquisition and storage of historical data leads to excessively long operating time of the direction element.

[0005] To achieve the above objectives, the present invention provides a method for determining the direction of an AC line fault, comprising:

[0006] S1. Obtain the line voltage or phase voltage of the first and second relay protection devices, and determine whether it is less than 10%. If so, activate the corresponding protection device and activate the directional element to determine the fault direction. The first and second relay protection devices are installed at both ends of the protected line. The first relay protection device is a system-side protection device, and the second relay protection device is a new energy-side protection device.

[0007] S2. Collect the voltage and current signals of the activated protection device to obtain the voltage and current information after the fault.

[0008] S3. Based on the voltage information after the fault, process to obtain the phase information of the positive sequence voltage component after the fault, and calculate to obtain the first power supply voltage.

[0009] S4. Calculate the second power supply voltage based on the post-fault voltage, post-fault current and equivalent system impedance information;

[0010] S5. Determine whether the changing trends of the first power supply voltage and the second power supply voltage are consistent within a preset time, and determine the fault direction based on the changing trends.

[0011] If the activated protection device is the first relay protection device and the change trend is consistent, it is a positive fault; if the change trend is inconsistent, it is a reverse fault.

[0012] If the activated protection device is a second relay protection device and the change trend is consistent, it is a reverse fault; if the change trend is inconsistent, it is a forward fault.

[0013] Optionally, the calculation expression for the first power supply voltage is:

[0014]

[0015] u s1ab (t)=u s1a (t)-u s1b (t)

[0016] u s1bc (t)=u s1b (t)-u s1c (t)

[0017] u s1ca (t)=u s1c (t)-u s1a (t)

[0018] in, The positive sequence voltage phase at the installation location of the relay protection device; u s1a (t), u s1b (t), u s1c (t) represents the instantaneous values ​​of each phase voltage of the first power supply voltage; u s1ab (t), u s1bc (t), u s1ca (t) represents the instantaneous values ​​of each line voltage of the first power supply voltage.

[0019] Optionally, the calculation expression for the second power supply voltage is:

[0020]

[0021] u s2ab (t)=u s2a(t)-u s2b (t)

[0022] u s2bc (t)=u s2b (t)-u s2c (t)

[0023] u s2ca (t)=u s2c (t)-u s2a (t)

[0024] Among them, u s1a (t), u s1b (t), u s1c (t) represents the instantaneous values ​​of each phase voltage of the second power supply voltage, u s1ab (t), u s1bc (t), u s1ca (t) represents the instantaneous values ​​of each line voltage of the second power supply voltage; t represents each moment within the time window from t0 to t0+T1, where t0 is the moment the fault occurs and T1 is the preset time; u a (t), u b (t), u c (t) represents the fault voltage of each phase of the activated protection device, i a (t), i b (t), i c (t) represents the fault current of each phase of the activated protection device, R is the resistance of the equivalent system impedance, and L is the inductance of the equivalent system impedance.

[0025] Optionally, determining whether the changing trends of the first power supply voltage and the second power supply voltage are consistent within a preset time period includes: determining according to the following formula:

[0026] [u s1 (t+Δt)-u s1 (t)]×[u s2 (t+Δt)-u s2 [t]>0

[0027] Among them, u s1 u represents the instantaneous values ​​of the phase voltages or the line voltages of the first power supply voltage. s2 For each phase voltage of the corresponding second power supply voltage or each line voltage of the second power supply voltage, t is the instantaneous value of each phase voltage or each line voltage of the second power supply voltage, t is the time within the time window from t0 to t0+T1, t0 is the time when the fault occurs, T1 is the preset time, and Δt is the sampling interval.

[0028] If the above formula remains true for a preset period of time after the fault occurs, the trend of change is considered consistent; if the above formula does not remain true for a preset period of time after the fault occurs, the trend of change is considered inconsistent.

[0029] Optionally, if the activated protection device is a first relay protection device and the change trends are consistent, it is a forward fault; if the change trends are inconsistent, it is a reverse fault; including:

[0030] If the activated protection device is the first relay protection device, a positive fault occurs, and the fault is located downstream of the first relay protection device.

[0031] If the activated protection device is the first relay protection device, a reverse fault occurs, and the fault is located upstream of the first relay protection device.

[0032] Optionally, if the activated protection device is a second relay protection device and the change trends are consistent, then it is a reverse fault; if the change trends are inconsistent, then it is a forward fault; including:

[0033] If the activated protection device is the second relay protection device, a reverse fault occurs, and the fault is located downstream of the first relay protection device.

[0034] If the activated protection device is the second relay protection device, a positive fault occurs, and the fault is located upstream of the second relay protection device.

[0035] Secondly, the present invention also provides a device for determining the direction of an AC line fault, comprising:

[0036] The fault identification module is used to obtain the line voltage or phase voltage of the first and second relay protection devices, determine whether it is less than 10%, and if so, activate the corresponding protection device and activate the directional element to determine the fault direction; wherein, the first and second relay protection devices are set at both ends of the protected line; the first relay protection device is the system-side protection device, and the second relay protection device is the new energy-side protection device.

[0037] The voltage and current information acquisition module is used to collect the voltage and current signals of the activated protection device to obtain post-fault voltage and post-fault current information.

[0038] The first power supply voltage calculation module is used to process the phase information of the positive sequence voltage component after the fault based on the voltage information after the fault, and calculate the first power supply voltage.

[0039] The second power supply voltage calculation module is used to calculate the second power supply voltage based on the post-fault voltage, post-fault current and equivalent system impedance information.

[0040] The trend discrimination module is used to determine whether the changing trends of the first power supply voltage and the second power supply voltage are consistent within a preset time, and to determine the fault direction based on the changing trend.

[0041] If the activated protection device is the first relay protection device and the change trend is consistent, it is a positive fault; if the change trend is inconsistent, it is a reverse fault.

[0042] If the activated protection device is a second relay protection device and the change trend is consistent, it is a reverse fault; if the change trend is inconsistent, it is a forward fault.

[0043] Thirdly, the present invention also provides an AC line system, comprising a large equivalent power source, an equivalent system impedance, a first busbar, a first relay protection device, a protected line, a second relay protection device, a second busbar, and a small equivalent power source connected in sequence.

[0044] The directional element in the first and second relay protection devices is used to perform the method for determining the direction of AC line faults as described in any of the first aspects.

[0045] Compared with the prior art, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0046] 1. This invention provides a method for determining the direction of AC line faults. It extracts the positive-sequence voltage phase from the post-fault voltage at the relay protection device installation location to calculate the first power supply voltage. Then, it calculates the second power supply voltage using the post-fault voltage and current at the relay protection device installation location, combined with the system's equivalent impedance parameters. A short time after the fault is taken as the data window, and the direction from the busbar to the line is taken as the positive direction. The change trends of the first and second power supply voltages are compared to determine the fault direction. This method differs significantly from the principle of traditional power direction elements, thus exhibiting excellent adaptability in new power systems. It can be applied to AC power grid systems with a high proportion of renewable energy or complex scenarios such as DC landing points. It solves the problem that traditional direction elements cannot reliably determine the fault direction when a fault occurs. Furthermore, this method has simple criteria and fast operation.

[0047] 2. The AC line fault direction determination method proposed in this invention utilizes the phase information of the positive sequence voltage component after the fault. The positive sequence voltage component can be collected after the fault occurs, avoiding the use of memory information. This eliminates the need for the protection device to constantly store and update memory information, thus solving the problem of the long working time of the direction element in collecting and storing memory information.

[0048] 3. The AC line fault direction determination method proposed in this invention uses the phase information of the positive sequence voltage component after the fault, and does not rely on historical data when a line fault occurs. Memory data can only be maintained for a limited time; if there is a lack of memory data, the fault direction cannot be reliably determined, which has certain limitations. The determination method proposed in this invention significantly extends the working time after a fault and simplifies the workflow of the directional element. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the structure of the AC line system provided in an embodiment of the present invention;

[0050] Figure 2 This is a schematic diagram of the structure of a power system with wind power access provided in an embodiment of the present invention;

[0051] Figure 3 In this embodiment of the invention, when an ab phase-to-phase short-circuit fault f2 occurs at the forward output of the first relay protection device, the first relay protection device calculates the "first type of virtual large equivalent power supply voltage" and the "second type of virtual large equivalent power supply voltage".

[0052] Figure 4 In this embodiment of the invention, when an ab phase-to-phase short-circuit fault f1 occurs at the reverse output of the first relay protection device, the second relay protection device calculates the "first type of virtual large equivalent power supply voltage" and the "second type of virtual large equivalent power supply voltage".

[0053] Figure 5 In this embodiment of the invention, when an ab phase-to-phase short-circuit fault f3 occurs at the forward output of the second relay protection device, the second relay protection device calculates the "first type of virtual large equivalent power supply voltage" and the "second type of virtual large equivalent power supply voltage".

[0054] Figure 6 In this embodiment of the invention, when an ab phase-to-phase short-circuit fault f4 occurs at the reverse output of the second relay protection device, the second relay protection device calculates the "first type of virtual large equivalent power supply voltage" and the "second type of virtual large equivalent power supply voltage".

[0055] Wherein, 1 is the large equivalent power source, 2 is the equivalent system impedance, 3 is the first busbar, 4 is the first relay protection device, 5 is the second relay protection device, 6 is the second busbar, 7 is the wind power system, and 8 is the protected line. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0057] The following description, in conjunction with a preferred embodiment, illustrates the content involved in the above embodiments.

[0058] Example 1

[0059] This invention provides a method for determining the direction of an AC line fault, comprising:

[0060] S1. Obtain the line voltage or phase voltage of the first and second relay protection devices, and determine whether it is less than 10%. If so, activate the corresponding protection device and activate the directional element to determine the fault direction. The first and second relay protection devices are installed at both ends of the protected line. The first relay protection device is a system-side protection device, and the second relay protection device is a new energy-side protection device.

[0061] S2. Collect the voltage and current signals of the activated protection device to obtain the voltage and current information after the fault.

[0062] S3. Based on the voltage information after the fault, process to obtain the phase information of the positive sequence voltage component after the fault, and calculate to obtain the first power supply voltage.

[0063] S4. Calculate the second power supply voltage based on the post-fault voltage, post-fault current and equivalent system impedance information;

[0064] S5. Determine whether the changing trends of the first power supply voltage and the second power supply voltage are consistent within a preset time, and determine the fault direction based on the changing trends.

[0065] If the activated protection device is the first relay protection device and the change trend is consistent, it is a positive fault; if the change trend is inconsistent, it is a reverse fault.

[0066] If the activated protection device is a second relay protection device and the change trend is consistent, it is a reverse fault; if the change trend is inconsistent, it is a forward fault.

[0067] like Figure 1As shown in the figure, an embodiment of the present invention provides a method for determining the direction of an AC line fault. The system structure on which this method is based includes: a large equivalent power source 1, an equivalent system impedance 2, a first busbar 3, a first relay protection device 4, a protected line 8, a second relay protection device 5, a second busbar 6, and a small equivalent power source 7.

[0068] For the first relay protection device 4, f1 is a reverse fault and f2 is a forward fault. For the second relay protection device 4, f4 is a reverse fault and f3 is a forward fault.

[0069] As an embodiment of the present invention, the following steps are set up sequentially. Figure 2 Faults f1, f2, f3, and f4 were detected, verifying that the first relay protection device 4 could correctly identify f1 and f2, and the second relay protection device 5 could correctly identify f3 and f4.

[0070] Optionally, the calculation expression for the first power supply voltage is:

[0071]

[0072] u s1ab (t)=u s1a (t)-u s1b (t)

[0073] u s1bc (t)=u s1b (t)-u s1c (t)

[0074] u s1ca (t)=u s1c (t)-u s1a (t)

[0075] in, The positive sequence voltage phase at the installation location of the relay protection device; u s1a (t), u s1b (t), u s1c (t) represents the instantaneous values ​​of each phase voltage of the first power supply voltage; u s1ab (t), u s1bc (t), u s1ca (t) represents the instantaneous values ​​of each line voltage of the first power supply voltage.

[0076] Optionally, the calculation expression for the second power supply voltage is:

[0077]

[0078] u s2ab (t)=u s2a (t)-u s2b (t)

[0079] u s2bc (t)=u s2b (t)-u s2c (t)

[0080] u s2ca (t)=u s2c (t)-u s2a (t)

[0081] Among them, u s1a (t), u s1b (t), u s1c (t) represents the instantaneous values ​​of each phase voltage of the second power supply voltage, u s1ab (t), u s1bc (t), u s1ca (t) represents the instantaneous values ​​of each line voltage of the second power supply voltage; t represents each moment within the time window from t0 to t0+T1, where t0 is the moment the fault occurs and T1 is the preset time; u a (t), u b (t), u c (t) represents the fault voltage of each phase of the activated protection device, i a (t), i b (t), i c (t) represents the fault current of each phase of the activated protection device, R is the resistance of the equivalent system impedance, and L is the inductance of the equivalent system impedance.

[0082] Calculate the following formulas based on the calculation expressions for the first and second power supply voltages, respectively, and determine whether the following formula holds true within a preset time period:

[0083] [u s1 (t+Δt)-u s1 (t)]×[u s2 (t+Δt)-u s2 [t]>0

[0084] Among them, u s1 u represents the instantaneous values ​​of the phase voltages or the line voltages of the first power supply voltage. s2 For each phase voltage of the corresponding second power supply voltage or each line voltage of the second power supply voltage, t is the instantaneous value of each phase voltage or each line voltage of the second power supply voltage, t is the time within the time window from t0 to t0+T1, t0 is the time when the fault occurs, T1 is the preset time, and Δt is the sampling interval.

[0085] If this condition continues to hold, then the trends of the first and second power supply voltages are considered to be consistent.

[0086] Furthermore, ground faults or phase-to-phase faults may occur in AC lines. If the corresponding phase selection element of the protection device identifies the fault type as an ab / ac / bc phase-to-phase fault, then only the changing trend of the instantaneous values ​​of the corresponding ab / ac / bc line voltages is judged. If the fault type is not identified, then the changing trend of the instantaneous values ​​of each line voltage is judged in sequence.

[0087] The preset time is a short period of time after the fault occurs, which is set to half a cycle, or 10ms, in this embodiment.

[0088] Optionally, if the activated protection device is a first relay protection device and the change trends are consistent, it is a forward fault; if the change trends are inconsistent, it is a reverse fault; including:

[0089] If the activated protection device is the first relay protection device, a positive fault occurs, and the fault is located downstream of the first relay protection device.

[0090] If the activated protection device is the first relay protection device, a reverse fault occurs, and the fault is located upstream of the first relay protection device.

[0091] Optionally, if the activated protection device is a second relay protection device and the change trends are consistent, then it is a reverse fault; if the change trends are inconsistent, then it is a forward fault; including:

[0092] If the activated protection device is the second relay protection device, a reverse fault occurs, and the fault is located downstream of the first relay protection device.

[0093] If the activated protection device is the second relay protection device, a positive fault occurs, and the fault is located upstream of the second relay protection device.

[0094] Specifically, in this embodiment, a phase-to-phase short circuit fault occurs at the positive output of the first relay protection device 4. Figure 2 (at point f2), the first power supply voltage and the second power supply voltage calculated by the first relay protection device 4 are as follows: Figure 3 As shown, the formula at this time is:

[0095] [u s1 (t+Δt)-u s1 (t)]×[u s2 (t+Δt)-u s2 [t]>0

[0096] The condition persists for a short period after the fault occurs, therefore it is determined to be a positive fault.

[0097] In this embodiment, a phase-to-phase short circuit fault occurs at the reverse output of the first relay protection device 4. Figure 2(at point f1), the first power supply voltage and the second power supply voltage calculated by the first relay protection device 4 are as follows: Figure 4 As shown, the formula at this time is:

[0098] [u s1ab (t+Δt)-u s1ab (t)]×[u s2ab (t+Δt)-u s2ab [t]>0

[0099] The fault does not persist for a short period after the failure, therefore it is determined to be a reverse fault.

[0100] In this embodiment, a phase-to-phase short circuit fault occurs at the positive output of the second relay protection device 5. Figure 2 (at point f3), the first power supply voltage and the second power supply voltage calculated by the second relay protection device 5 are as follows: Figure 5 As shown, at this time the formula

[0101] [u s1ab (t+Δt)-u s1ab (t)]×[u s2ab (t+Δt)-u s2ab [t]>0

[0102] The fault did not persist for a short period after it occurred, therefore it was determined to be a positive fault.

[0103] In this embodiment, a phase-to-phase short circuit fault occurs at the reverse output of the second relay protection device 5. Figure 2 (at point f4), the first power supply voltage and the second power supply voltage calculated by the second relay protection device 5 are as follows: Figure 6 As shown, at this time the formula

[0104] [u s1 (t+Δt)-u s1 (t)]×[u s2 (t+Δt)-u s2 [t]>0

[0105] The condition persists for a short period after the fault occurs, therefore it is determined to be a reverse fault.

[0106] Reference Figure 3 , Figure 4 , Figure 5 and Figure 6 In this embodiment, the system of the present invention is a power system with wind power access. In this embodiment, the "first power supply voltage" corresponds to the "first type of virtual large power supply voltage" in the figure, and the "second power supply voltage" in this embodiment corresponds to the "second type of virtual large power supply voltage" in the figure.

[0107] Figure 3When an ab phase-to-phase short circuit fault (f2) occurs at the positive output of the first relay protection device 4, the first relay protection device 4 calculates the first power supply voltage and the second power supply voltage.

[0108] Figure 4 When an ab phase-to-phase short circuit fault (f1) occurs at the reverse output of the first relay protection device 4, the first power supply voltage and the second power supply voltage are calculated by the first relay protection device 4.

[0109] Figure 5 When an ab phase-to-phase short circuit fault (f3) occurs at the positive output of the second relay protection device 5, the second relay protection device 5 calculates the first power supply voltage and the second power supply voltage.

[0110] Figure 6 When an ab phase-to-phase short circuit fault (f4) occurs at the reverse output of the second relay protection device 5, the second relay protection device 5 calculates the first power supply voltage and the second power supply voltage.

[0111] from Figures 3-6 As can be seen from the embodiments of the present invention, the method provided can effectively determine the direction of line faults.

[0112] In this embodiment of the invention, the positive-sequence voltage phase is extracted using the post-fault voltage at the installation location of the relay protection device to calculate the first power supply voltage; the post-fault voltage and current at the installation location of the relay protection device, combined with the system's equivalent impedance parameters, are used to calculate the second power supply voltage; a short period after the fault is taken as a data window, with the direction from the busbar to the line as the positive direction, and the changing trends of the first and second power supply voltages are compared to determine the fault direction. This solves the problem that existing fault judgment methods rely on historical data, and if historical data is missing, the directional element cannot reliably determine the fault direction. It simplifies the workflow of the directional element, eliminating the need for constant collection and recording of electrical quantity data, achieving real-time acquisition of electrical quantities for real-time fault judgment, improving the reliability of fault direction judgment, and expanding the system's applicability.

[0113] Example 2

[0114] The present invention also provides a device for determining the direction of an AC line fault, comprising:

[0115] The fault identification module is used to obtain the line voltage or phase voltage of the first and second relay protection devices, determine whether it is less than 10%, and if so, activate the corresponding protection device and activate the directional element to determine the fault direction; wherein, the first and second relay protection devices are set at both ends of the protected line; the first relay protection device is the system-side protection device, and the second relay protection device is the new energy-side protection device.

[0116] The voltage and current information acquisition module is used to collect the voltage and current signals of the activated protection device to obtain post-fault voltage and post-fault current information.

[0117] The first power supply voltage calculation module is used to process the phase information of the positive sequence voltage component after the fault based on the voltage information after the fault, and calculate the first power supply voltage.

[0118] The second power supply voltage calculation module is used to calculate the second power supply voltage based on the post-fault voltage, post-fault current and equivalent system impedance information.

[0119] The fault direction determination module is used to determine whether the changing trends of the first power supply voltage and the second power supply voltage are consistent within a preset time, and to determine the fault direction based on the changing trends.

[0120] If the activated protection device is the first relay protection device and the change trend is consistent, it is a positive fault; if the change trend is inconsistent, it is a reverse fault.

[0121] If the activated protection device is a second relay protection device and the change trend is consistent, it is a reverse fault; if the change trend is inconsistent, it is a forward fault.

[0122] The AC line fault direction determination device provided in this embodiment of the invention is used to execute the AC line fault direction determination method provided in any embodiment of the invention, and has corresponding beneficial effects.

[0123] Example 3

[0124] The present invention also provides an AC line system, comprising a large equivalent power source, an equivalent system impedance, a first busbar, a first relay protection device, a protected line, a second relay protection device, a second busbar, and a small equivalent power source connected in sequence.

[0125] The directional element in the first and second relay protection devices is used to perform the method for determining the direction of AC line faults as described in any of the first aspects.

[0126] like Figure 1 As shown, the AC line system includes: a large equivalent power source 1, an equivalent system impedance 2, a first busbar 3, a first relay protection device 4, a protected line 8, a second relay protection device 5, a second busbar 6, and a small equivalent power source 7. When a fault occurs in the protected line 8, the corresponding first or second relay protection device is activated. The directional element in the first or second relay protection device determines the direction of the fault. Based on the combined results of all elements, the circuit breaker trips.

[0127] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for determining the direction of an AC line fault, characterized in that, include: S1. Obtain the line voltage or phase voltage of the first and second relay protection devices, and determine whether it is less than 10%. If so, activate the corresponding protection device and activate the directional element to determine the fault direction. The first and second relay protection devices are installed at both ends of the protected line. The first relay protection device is a system-side protection device, and the second relay protection device is a new energy-side protection device. S2. Collect the voltage and current signals of the activated protection device to obtain the voltage and current information after the fault. S3. Based on the voltage information after the fault, process to obtain the phase information of the positive sequence voltage component after the fault, and calculate to obtain the first power supply voltage. S4. Calculate the second power supply voltage based on the post-fault voltage, post-fault current and equivalent system impedance information; S5. Determine whether the changing trends of the first power supply voltage and the second power supply voltage are consistent within a preset time, and determine the fault direction based on the changing trends. If the activated protection device is the first relay protection device and the change trend is consistent, it is a positive fault; if the change trend is inconsistent, it is a reverse fault. If the activated protection device is a second relay protection device and the change trend is consistent, it is a reverse fault; if the change trend is inconsistent, it is a forward fault.

2. The determination method as described in claim 1, characterized in that, The expression for calculating the first power supply voltage is: u s1ab (t)=u s1a (t)-u s1b (t) u s1bc (t)=u s1b (t)-u s1c (t) u s1ca (t)=u s1c (t)-u s1a (t) in, The positive sequence voltage phase at the installation location of the relay protection device; u s1a (t), u s1b (t), u s1c (t) represents the instantaneous values ​​of each phase voltage of the first power supply voltage; u s1ab (t), u s1bc (t), u s1ca (t) represents the instantaneous values ​​of each line voltage of the first power supply voltage.

3. The judgment method as described in claim 2, characterized in that, The expression for calculating the second power supply voltage is: u s2ab (t)=u s2a (t)-u s2b (t) u s2bc (t)=u s2b (t)-u s2c (t) u s2ca (t)=u s2c (t)-u s2a (t) Among them, u s1a (t), u s1b (t), u s1c (t) represents the instantaneous values ​​of each phase voltage of the second power supply voltage, u s1ab (t), u s1bc (t), u s1ca (t) represents the instantaneous values ​​of each line voltage of the second power supply voltage; t represents each moment within the time window from t0 to t0+T1, where t0 is the moment the fault occurs and T1 is the preset time; u a (t), u b (t), u c (t) represents the fault voltage of each phase of the activated protection device, i a (t), i b (t), i c (t) represents the fault current of each phase of the activated protection device, R is the resistance of the equivalent system impedance, and L is the inductance of the equivalent system impedance.

4. The determination method as described in claim 3, characterized in that, The determination of whether the changing trends of the first power supply voltage and the second power supply voltage are consistent within a preset time period includes: The following formula is used to determine the result: [u s1 (t+Δt)-u s1 (t)]×[u s2 (t+Δt)-u s2 (t)]>0 Among them, u s1 u represents the instantaneous values ​​of the phase voltages or the line voltages of the first power supply voltage. s2 For each phase voltage of the corresponding second power supply voltage or each line voltage of the second power supply voltage, t is the instantaneous value of each phase voltage or each line voltage of the second power supply voltage, t is the time within the time window from t0 to t0+T1, t0 is the time when the fault occurs, T1 is the preset time, and Δt is the sampling interval. If the above formula remains true for a preset period of time after the fault occurs, the trend of change is considered consistent; if the above formula does not remain true for a preset period of time after the fault occurs, the trend of change is considered inconsistent.

5. The determination method as described in claim 1, characterized in that, If the activated protection device is a first relay protection device, and the change trends are consistent, then it is a forward fault; if the change trends are inconsistent, then it is a reverse fault; including: If the activated protection device is the first relay protection device, a positive fault occurs, and the fault is located downstream of the first relay protection device. If the activated protection device is the first relay protection device, a reverse fault occurs, and the fault is located upstream of the first relay protection device.

6. The determination method as described in claim 1, characterized in that, If the activated protection device is a second relay protection device and the trend of change is consistent, then it is a reverse fault. If the trends of change are inconsistent, it is a positive fault; including: If the activated protection device is the second relay protection device, a reverse fault occurs, and the fault is located downstream of the first relay protection device. If the activated protection device is the second relay protection device, a positive fault occurs, and the fault is located upstream of the second relay protection device.

7. A device for determining the direction of an AC line fault, characterized in that, include: The fault identification module is used to obtain the line voltage or phase voltage of the first and second relay protection devices, determine whether it is less than 10%, and if so, activate the corresponding protection device and activate the directional element to determine the fault direction; wherein, the first and second relay protection devices are set at both ends of the protected line; the first relay protection device is the system-side protection device, and the second relay protection device is the new energy-side protection device. The voltage and current information acquisition module is used to collect the voltage and current signals of the activated protection device to obtain post-fault voltage and post-fault current information. The first power supply voltage calculation module is used to process the phase information of the positive sequence voltage component after the fault based on the voltage information after the fault, and calculate the first power supply voltage. The second power supply voltage calculation module is used to calculate the second power supply voltage based on the post-fault voltage, post-fault current and equivalent system impedance information. The trend discrimination module is used to determine whether the changing trends of the first power supply voltage and the second power supply voltage are consistent within a preset time, and to determine the fault direction based on the changing trend. If the activated protection device is the first relay protection device and the change trend is consistent, it is a positive fault; if the change trend is inconsistent, it is a reverse fault. If the activated protection device is a second relay protection device and the change trend is consistent, it is a reverse fault; if the change trend is inconsistent, it is a forward fault.

8. An AC line system, characterized in that, It includes a large equivalent power source, an equivalent system impedance, a first busbar, a first relay protection device, a protected line, a second relay protection device, a second busbar, and a small equivalent power source connected in sequence. The directional element in the first and second relay protection devices is used to perform the method for determining the direction of AC line faults as described in any one of claims 1-6.

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