Alternating current line fault direction judgment method and device

Abstract

The invention discloses a method and a device for judging a fault direction of an alternating current line, and belongs to the field of relay protection of a power system. The judgment method comprises the following steps: acquiring line voltage or phase voltage of a first relay protection device and a second relay protection device, judging whether the line voltage or the phase voltage is less than 10%, if so, starting the protection device, and judging a fault direction; collecting voltage and current signals of the started protection device, and obtaining voltage and current information after a fault; according to the post-fault voltage information, processing to obtain phase information of a post-fault positive sequence voltage component, and calculating to obtain a first power supply voltage; according to the post-fault voltage, the post-fault current and equivalent system impedance information, calculating to obtain a second power supply voltage; and judging whether the change trends of the first power supply voltage and the second power supply voltage are consistent within a preset time, and judging the fault direction according to the change trends. The method is applied to an alternating-current power grid system with high-proportion new energy or complex scenes with direct-current drop points and the like, and the fault direction is reliably judged.

Description

Technical Field

[0001] The present invention belongs to the field of relay protection of electric power systems, and more specifically, relates to a method and a device for determining the fault direction of an AC line. Background Art

[0002] With the widespread application of renewable energy as a clean energy in the power system, and the increasing development and application of DC transmission in the power system, the fault characteristics of the two are different from those of traditional synchronous generators, which brings huge challenges to the traditional relay protection system.

[0003] When a short circuit fault occurs in an AC line containing new energy or DC drop points, its fault characteristics are affected by the power electronic equipment and control system of the new energy or DC converter valve, resulting in complex and diverse fault characteristics. Traditional power direction relays cannot reliably determine the fault direction and are difficult to adapt to changes in the power system. The existing method of determining the fault direction in the new power system relies on the collected and saved memory voltage and memory current. It is necessary to continuously collect and store signals of electrical quantities near the protection device, and the direction element has a long working time. When a line fault occurs, the traditional direction element has a strong dependence on historical data, and the memory data can only be maintained for a period of time. If there is a lack of memory data, the fault direction cannot be reliably determined, which has certain limitations. Summary of the invention

[0004] In view of the defects of the related art, the purpose of the present invention is to provide a method and device for determining the fault direction of an AC line, aiming to solve the problem that the existing fault determination method needs to rely on historical data. If there is a lack of historical data, the directional element cannot reliably determine the fault direction, and the continuous acquisition and storage of historical data causes the directional element to run for too long.

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

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

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

[0008] S3. According to the post-fault voltage information, obtain the phase information of the post-fault positive sequence voltage component, and calculate and obtain the first power supply voltage;

[0009] S4. Calculate and obtain a second power supply voltage according to the post-fault voltage, post-fault current and equivalent system impedance information;

[0010] S5. Determine whether the change trends of the first power supply voltage and the second power supply voltage are consistent within a preset time, and determine the fault direction according to the change trends;

[0011] If the activated protection device is the 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;

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

[0013] Optionally, the calculation expression of 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, is the positive sequence voltage phase at the installation location of the relay protection device; u s1a (t),u s1b (t),u s1c (t) is the instantaneous value of each phase voltage of the first power supply voltage; u s1ab (t),u s1bc (t),u s1ca (t) is the instantaneous value of each line voltage of the first power supply voltage.

[0019] Optionally, the calculation expression of 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) is the instantaneous value of each phase voltage of the second power supply voltage, u s1ab (t),u s1bc (t),u s1ca (t) is the instantaneous value of each line voltage of the second power supply voltage; t is t 0 ~t 0 +T 1 At each moment in the time window, t 0 is the time when the fault occurs, T 1 is the preset time; a (t),u b (t),u c (t) is the fault voltage of each phase of the activated protection device, i a (t), i b (t), i c (t) is 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, the determining whether the change trends of the first power supply voltage and the second power supply voltage are consistent within a preset time 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 is the instantaneous value of each phase voltage of the first power supply voltage or the instantaneous value of each line voltage of the first power supply voltage, u s2 is the instantaneous value of each phase voltage of the corresponding second power supply voltage or the instantaneous value of each line voltage of the second power supply voltage, and t is t 0 ~t 0 +T 1 At each moment in the time window, t 0 is the time when the fault occurs, T1 is the preset time, Δt is the sampling interval;

[0028] If the above formula continues to hold true within the preset time after the fault occurs, it is judged that the change trends are consistent; if the above formula cannot continue to hold true within the preset time after the fault occurs, it is judged that the change trends are inconsistent.

[0029] Optionally, if the activated protection device is the 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 forward 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 the second relay protection device and the change trends are consistent, it is a reverse fault; if the change trends are inconsistent, 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 forward fault occurs and the fault is located upstream of the second relay protection device.

[0035] In a second aspect, the present invention further provides a device for determining the fault direction of an AC line, comprising:

[0036] A fault identification module is used to obtain the line voltage or phase voltage of the first relay protection device and the second relay protection device, and determine whether it is less than 10%. If so, the corresponding protection device is started, and the direction element is started to determine the fault direction; wherein the first relay protection device and the second relay protection device are arranged at both ends of the protected line; the first relay protection device is a protection device on the system side, and the second relay protection device is a protection device on the new energy side;

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

[0038] A first power supply voltage calculation module, used to process and obtain phase information of a post-fault positive sequence voltage component according to post-fault voltage information, and calculate and obtain a first power supply voltage;

[0039] A second power supply voltage calculation module, used to calculate and obtain the second power supply voltage according to the post-fault voltage, the post-fault current and the equivalent system impedance information;

[0040] A trend determination module, used to determine whether the change trends of the first power supply voltage and the second power supply voltage are consistent within a preset time, and determine the fault direction according to the change trends;

[0041] If the activated protection device is the 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;

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

[0043] In a third aspect, the present invention further provides an AC line system, comprising a large equivalent power source, an equivalent system impedance, a first bus, a first relay protection device, a protected line, a second relay protection device, a second bus, and a small equivalent power source connected in sequence;

[0044] The directional elements in the first relay protection device and the second relay protection device are used to execute the method for determining the fault direction of an AC line as described in any one of the first aspects.

[0045] Compared with the prior art, the above technical solution conceived by the present invention can achieve the following beneficial effects:

[0046] 1. The present invention provides a method for determining the fault direction of an AC line. The first power supply voltage is calculated by extracting the positive sequence voltage phase using the post-fault voltage at the installation location of the relay protection device; the second power supply voltage is calculated using the post-fault voltage and post-fault current at the installation location of the relay protection device in combination with the system equivalent impedance parameters. The short time after the fault is taken as the data window, and the busbar pointing to the line direction is taken as the positive direction. The first power supply voltage and the second power supply voltage are compared to determine the fault direction. This method is significantly different from the principle of traditional power direction elements, and therefore has good adaptability in new power systems. It can be applied to AC power grid systems with a high proportion of new energy or complex scenarios such as DC drop points. This method solves the problem that traditional direction elements cannot reliably determine the fault direction when a fault occurs, and the method has simple judgment criteria and fast action.

[0047] 2. The method for determining the direction of an AC line fault proposed in the present invention utilizes the phase information of the positive-sequence voltage component of the voltage after the fault. The positive-sequence voltage component can be collected after the fault occurs, thereby avoiding the use of memory information and making it unnecessary for the protection device to store and update the memory information all the time, thus solving the problem of the long time it takes for the directional element to collect and store the memory information.

[0048] 3. The method for determining the direction of an AC line fault proposed in the present invention uses the phase information of the positive sequence voltage component of the voltage after the fault, and has no reliance on historical data when a line fault occurs. The memory data can only be maintained for a period of 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 the present invention greatly prolongs the working time after the fault and simplifies the workflow of the directional element. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0050] Figure 2 It is a schematic diagram of the structure of a power system including wind power access provided by an embodiment of the present invention;

[0051] Figure 3 In the embodiment of the present invention, a phase-to-phase short circuit fault f occurs at the forward output of the first relay protection device. 2 , the "first virtual maximum equivalent power supply voltage" and the "second virtual maximum equivalent power supply voltage" calculated by the first relay protection device;

[0052] Figure 4 In the embodiment of the present invention, a phase-to-phase short circuit fault f occurs at the reverse output of the first relay protection device. 1 , the "first virtual maximum equivalent power supply voltage" and the "second virtual maximum equivalent power supply voltage" calculated by the second relay protection device;

[0053] Figure 5 In the embodiment of the present invention, a phase-to-phase short circuit fault f occurs at the forward output of the second relay protection device. 3 When the second relay protection device calculates the “first virtual maximum equivalent power supply voltage” and the “second virtual maximum equivalent power supply voltage”.

[0054] Figure 6 In the embodiment of the present invention, a phase-to-phase short circuit fault f occurs at the reverse output of the second relay protection device. 4 When the second relay protection device calculates the “first virtual maximum equivalent power supply voltage” and the “second virtual maximum equivalent power supply voltage”.

[0055] Among them, 1 is the large equivalent power source, 2 is the equivalent system impedance, 3 is the first bus, 4 is the first relay protection device, 5 is the second relay protection device, 6 is the second bus, 7 is the wind power system, and 8 is the protected line. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solutions 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 are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0057] The contents involved in the above embodiment are described below in conjunction with a preferred embodiment.

[0058] Embodiment 1

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

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

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

[0062] S3. According to the post-fault voltage information, obtain the phase information of the post-fault positive sequence voltage component, and calculate and obtain the first power supply voltage;

[0063] S4. Calculate and obtain a second power supply voltage according to the post-fault voltage, post-fault current and equivalent system impedance information;

[0064] S5. Determine whether the change trends of the first power supply voltage and the second power supply voltage are consistent within a preset time, and determine the fault direction according to the change trends;

[0065] If the activated protection device is the 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;

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

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

[0068] For the first relay protection device 4, f 1 For reverse fault, f 2 For a positive fault, for the second relay protection device 4, f 4 For reverse fault, f 3 It is a positive fault.

[0069] As an embodiment of the present invention, set Figure 2 Medium 1 、f 2 、f 3 、f 4 Fault, verify that the first relay protection device 4 can correctly judge f 1 With f 2 , the second relay protection device 5 can correctly judge f 3 With f 4 .

[0070] Optionally, the calculation expression of 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, is the positive sequence voltage phase at the installation location of the relay protection device; u s1a (t),u s1b (t),u s1c (t) is the instantaneous value of each phase voltage of the first power supply voltage; u s1ab (t),u s1bc (t),u s1ca (t) is the instantaneous value of each line voltage of the first power supply voltage.

[0076] Optionally, the calculation expression of 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) is the instantaneous value of each phase voltage of the second power supply voltage, u s1ab (t),u s1bc (t),u s1ca (t) is the instantaneous value of each line voltage of the second power supply voltage; t is t 0 ~t 0 +T 1 At each moment in the time window, t 0 is the time when the fault occurs, T 1 is the preset time; a (t),u b (t),u c (t) is the fault voltage of each phase of the activated protection device, i a (t), i b (t), i c (t) is 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] Calculations are performed according to the calculation expression of the first power supply voltage and the calculation expression of the second power supply voltage to determine whether the following expression holds true within a preset time:

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

[0084] Among them, u s1 is the instantaneous value of each phase voltage of the first power supply voltage or the instantaneous value of each line voltage of the first power supply voltage, u s2is the instantaneous value of each phase voltage of the corresponding second power supply voltage or the instantaneous value of each line voltage of the second power supply voltage, and t is t 0 ~t 0 +T 1 At each moment in the time window, t 0 is the time when the fault occurs, T 1 is the preset time, Δt is the sampling interval;

[0085] If this continues to hold true, it is considered that the change trends of the first power supply voltage and the second power supply voltage are consistent.

[0086] Furthermore, a ground fault or a phase-to-phase fault may occur in the AC line; if the corresponding phase selection element of the protection device identifies the fault type as an ab / ac / bc phase-to-phase fault, only the change trend of the corresponding ab / ac / bc line voltage instantaneous value is judged; if the fault type is not identified, the change trend of the instantaneous value of each line voltage is judged in turn.

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

[0088] Optionally, if the activated protection device is the 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 forward 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 the second relay protection device and the change trends are consistent, it is a reverse fault; if the change trends are inconsistent, 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 forward fault occurs and the fault is located upstream of the second relay protection device.

[0094] Specifically, in this embodiment, the first relay protection device 4 is set to have an ab phase short circuit fault at the forward outlet ( Figure 2 Medium 2 Point), 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, this time:

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

[0096] This condition continues to hold for a short time after the fault, so it is determined to be a forward fault.

[0097] In this embodiment, the first relay protection device 4 is set to have an ab phase short circuit fault at the reverse output ( Figure 2 Medium 1 Point), 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, this time:

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

[0099] It is not continuously established within a short period of time after the fault, so it is judged as a reverse fault.

[0100] In this embodiment, the second relay protection device 5 is set to have an ab phase short circuit fault at the forward outlet ( Figure 2 Medium 3 point), 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

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

[0102] It does not continue to hold for a short period of time after the fault, so it is determined to be a forward fault.

[0103] In this embodiment, the second relay protection device 5 is set to have an ab phase short circuit fault at the reverse output ( Figure 2 Medium 4 point), 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

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

[0105] This condition persists for a short time after the fault, so 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 including wind power access. The "first power supply voltage" in this embodiment corresponds to the "first virtual large power supply voltage" in the figure, and the "second power supply voltage" in this embodiment corresponds to the "second virtual large power supply voltage" in the figure.

[0107] Figure 3 The ab phase short circuit fault occurs at the forward output of the first relay protection device 4 (f 2 ), the first relay protection device 4 calculates the first power supply voltage and the second power supply voltage.

[0108] Figure 4 The ab phase short circuit fault occurs at the reverse output of the first relay protection device 4 (f 1 ), the first relay protection device 4 calculates the first power supply voltage and the second power supply voltage.

[0109] Figure 5 The ab phase short circuit fault occurs at the forward output of the second relay protection device 5 (f 3 ), the second relay protection device 5 calculates the first power supply voltage and the second power supply voltage.

[0110] Figure 6 The ab phase short circuit fault occurs at the reverse output of the second relay protection device 5 (f 4 ), the second relay protection device 5 calculates the first power supply voltage and the second power supply voltage.

[0111] from Figure 3-Figure 6 It can be seen from the figure that the method provided in the embodiment of the present invention can effectively determine the direction of the line fault.

[0112] In the embodiment of the present invention, the positive sequence voltage phase is extracted by using the post-fault voltage at the installation location of the relay protection device to calculate the first power supply voltage; the second power supply voltage is calculated by using the post-fault voltage and the post-fault current at the installation location of the relay protection device in combination with the system equivalent impedance parameters; the short time after the fault is taken as the data window, and the busbar pointing to the line direction is taken as the positive direction, and the first power supply voltage and the second power supply voltage change trend are compared to determine the fault direction. This solves the problem that the existing fault judgment method needs to rely on historical data, and if there is a lack of historical data, the direction element cannot reliably determine the fault direction. This realizes the simplification of the workflow of the direction element, and no longer needs to collect and record electrical quantity data at all times, and achieves the effect of real-time acquisition of electrical quantities for real-time fault judgment, improves the reliability of fault direction judgment, and improves the scope of application of the system.

[0113] Embodiment 2

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

[0115] A fault identification module is used to obtain the line voltage or phase voltage of the first relay protection device and the second relay protection device, and determine whether it is less than 10%. If so, the corresponding protection device is started, and the direction element is started to determine the fault direction; wherein the first relay protection device and the second relay protection device are arranged at both ends of the protected line; the first relay protection device is a protection device on the system side, and the second relay protection device is a protection device on the new energy side;

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

[0117] A first power supply voltage calculation module, used to process and obtain phase information of a post-fault positive sequence voltage component according to post-fault voltage information, and calculate and obtain a first power supply voltage;

[0118] A second power supply voltage calculation module, used to calculate and obtain the second power supply voltage according to the post-fault voltage, the post-fault current and the equivalent system impedance information;

[0119] A fault direction determination module, used to determine whether the change trends of the first power supply voltage and the second power supply voltage are consistent within a preset time, and determine the fault direction according to the change trends;

[0120] If the activated protection device is the 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;

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

[0122] An AC line fault direction determination device provided by an embodiment of the present invention is used to execute an AC line fault direction determination method provided by any embodiment of the present invention, and has corresponding beneficial effects.

[0123] Embodiment 3

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

[0125] The directional elements in the first relay protection device and the second relay protection device are used to execute the method for determining the fault direction of an AC line as described in any one 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 relay protection device or the second relay protection device is started, and the direction element in the first relay protection device or the second relay protection device determines the fault direction, and the circuit breaker trips after combining the results of each element.

[0127] It will be easily understood by those skilled in the art that the above description is only 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 in the protection scope of the present invention.

Claims

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

2. The determination method according to claim 1, characterized in that: The calculation expression of 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, is the positive sequence voltage phase at the installation location of the relay protection device; u s1a (t),u s1b (t),u s1c (t) is the instantaneous value of each phase voltage of the first power supply voltage; u s1ab (t),u s1bc (t),u s1ca (t) is the instantaneous value of each line voltage of the first power supply voltage.

3. The determination method according to claim 2, characterized in that: The calculation expression of 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) is the instantaneous value of each phase voltage of the second power supply voltage, u s1ab (t),u s1bc (t),u s1ca (t) is the instantaneous value of each line voltage of the second power supply voltage; t is each moment in the time window of t0 to t0+T1, t0 is the moment of fault occurrence, and T1 is the preset time; u a (t),u b (t),u c (t) is the fault voltage of each phase of the activated protection device, i a (t), i b (t), i c (t) is 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 according to claim 3, characterized in that: The determining whether the change trends of the first power supply voltage and the second power supply voltage are consistent within a preset time includes: Judge according to the following formula: [u s1 (t+Δt)-u s1 (t)]×[u s2 (t+Δt)-u s2 (t)]>0 Among them, u s1 is the instantaneous value of each phase voltage of the first power supply voltage or the instantaneous value of each line voltage of the first power supply voltage, u s2 is the instantaneous value of each phase voltage of the corresponding second power supply voltage or the instantaneous value of each line voltage of the second power supply voltage, t is each moment in the time window of t0 to t0+T1, t0 is the moment of fault occurrence, T1 is the preset time, and Δt is the sampling interval; If the above formula continues to hold true within the preset time after the fault occurs, it is judged that the change trends are consistent; if the above formula cannot continue to hold true within the preset time after the fault occurs, it is judged that the change trends are inconsistent.

5. The determination method according to claim 1, characterized in that: If the activated protection device is the 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: If the activated protection device is the first relay protection device, a forward 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 according to claim 1, characterized in that: If the activated protection device is the second relay protection device and the change trends are consistent, it is a reverse fault; If the change trends 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 forward fault occurs and the fault is located upstream of the second relay protection device.

7. A device for determining the fault direction of an AC line, characterized in that: include: A fault identification module is used to obtain the line voltage or phase voltage of the first relay protection device and the second relay protection device, and determine whether it is less than 10%. If so, the corresponding protection device is started, and the direction element is started to determine the fault direction; wherein the first relay protection device and the second relay protection device are arranged at both ends of the protected line; the first relay protection device is a protection device on the system side, and the second relay protection device is a protection device on the new energy side; The voltage and current information acquisition module is used to collect the voltage and current signals of the activated protection device to obtain the post-fault voltage and post-fault current information; A first power supply voltage calculation module, used to process and obtain phase information of a post-fault positive sequence voltage component according to post-fault voltage information, and calculate and obtain a first power supply voltage; A second power supply voltage calculation module, used to calculate and obtain the second power supply voltage according to the post-fault voltage, the post-fault current and the equivalent system impedance information; A trend determination module, used to determine whether the change trends of the first power supply voltage and the second power supply voltage are consistent within a preset time, and determine the fault direction according to the change trends; If the activated protection device is the 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; If the activated protection device is the second relay protection device and the change trends are consistent, it is a reverse fault; if the change trends are 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 bus, a first relay protection device, a protected line, a second relay protection device, a second bus and a small equivalent power source connected in sequence; The directional elements in the first relay protection device and the second relay protection device are used to execute the method for determining the fault direction of an AC line as described in any one of claims 1 to 6.

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