Direct current transmission converter valve side ground fault diagnosis method and device and storage medium

Abstract

The application discloses a direct current transmission converter transformer valve side ground fault diagnosis method, device and storage medium, belongs to the technical field of direct current transmission system fault diagnosis, and the direct current transmission converter transformer valve side ground fault diagnosis method provided by the application comprises the following steps: when the converter transformer valve side is grounded, the number of fault current phases of the converter transformer valve side is determined; when the number of fault current phases is two, it can be determined that a single-phase ground fault exists in the connecting line between the converter transformer valve side and the converter valve; and when the number of fault current phases is one, it can be determined that a ground fault exists in the valve side winding of the converter transformer. When the converter transformer valve side is grounded, the number of fault current phases is used to determine the fault position, manual operation is not required, and the fault position can be quickly determined for fault troubleshooting.

Description

Technical Field

[0001] This application belongs to the field of fault diagnosis technology for DC transmission systems, and specifically relates to a method, device and storage medium for diagnosing grounding faults on the valve side of a DC transmission converter transformer. Background Technology

[0002] In DC transmission systems, valve short-circuit protection or valve group differential protection are generally configured to respond to grounding faults on the converter transformer valve side and in the converter valve area. However, for grounding faults on the converter transformer valve side, there is currently no fast and effective fault diagnosis method. Fault investigation and elimination mainly rely on the experience of operation and maintenance personnel, which is inefficient and slow. Summary of the Invention

[0003] Purpose of the invention: This application develops a method, device and storage medium for diagnosing grounding faults on the valve side of a DC transmission converter transformer, aiming to solve the technical problem that existing technologies cannot diagnose grounding faults on the valve side of converter transformers.

[0004] Technical Solution: In a first aspect, embodiments of this application provide a method for diagnosing grounding faults on the converter transformer side of a DC transmission system, used in a DC transmission system. The DC transmission system includes a converter valve group and a converter valve triggering system. The AC side of the converter valve group is connected to a three-phase AC current, and the DC side of the converter valve group is connected to a DC bus. The converter valve triggering system is connected to the control terminal of the converter valve group to output pulse signal words to control the commutation of the converter valve group. The fault diagnosis method includes:

[0005] In response to a ground fault on the converter transformer valve side, determine the number of fault current phases on the converter transformer valve side;

[0006] In response to the fact that the number of fault current phases is two, it is determined that there is a single-phase grounding fault in the connection line between the converter transformer side and the converter valve.

[0007] In response to the fact that the number of fault current phases is one, it is determined that there is a ground fault in the converter valve side winding.

[0008] In some embodiments, the step of determining the number of fault current phases on the converter transformer side includes:

[0009] Obtain the three-phase current on the converter transformer valve side;

[0010] The number of current phases that meet the preset conditions is determined as the number of fault current phases.

[0011] In some embodiments, the formula for representing the preset condition includes:

[0012] ABS(IVY_L1)>k1*IVYNORMMAX;

[0013] ABS(IVY_L2)>k1*IVYNORMMAX;

[0014] ABS(IVY_L3)>k1*IVYNORMMAX;

[0015] ABS(IVD_L1)>k1*IVDNORMMAX;

[0016] ABS(IVD_L2)>k1*IVDNORMMAX;

[0017] ABS(IVD_L3)>k1*IVDNORMMAX;

[0018] IVYNORMMAX=max{IVYNORMA, IVYNORMB, IVYNORMC};

[0019] IVDNORMMAX=max{IVDNORMA, IVDNORMB, IVDNORMC};

[0020] Wherein, ABS is the absolute value operation; MAX is the maximum value operation; IVY_L1 is the valve-side current of phase A of Y bridge; IVY_L2 is the valve-side current of phase B of Y bridge; IVY_L3 is the valve-side current of phase C of Y bridge; IVD_L1 is the valve-side current of phase A of D bridge flowing into the converter valve; IVD_L2 is the valve-side current of phase B of D bridge flowing into the converter valve; IVD_L3 is the valve-side current of phase C of D bridge flowing into the converter valve; k1 is the first proportional coefficient; IVYNORMA, IVYNORMB, and IVYNORMC are the phase A, phase B, and phase C currents of Y bridge before the fault, respectively; IVDNORMA, IVDNORMB, and IVDNORMC are the phase A, phase B, and phase C currents of D bridge before the fault, respectively.

[0021] In some embodiments, the step of determining that there is a single-phase ground fault in the connection line between the converter transformer side and the converter valve includes:

[0022] The sampling time corresponding to the first sampling point that meets the preset conditions is determined as the fault start position.

[0023] Based on the current phases before and after the fault, determine the two phase markings before and after the fault.

[0024] Based on the two-phase markings indicating conduction before and after the fault, the fault phase of a single-phase ground fault is determined.

[0025] In some embodiments, the characterization formula for determining the fault phase of a single-phase ground fault based on the two-phase markings of conduction before and after the fault includes:

[0026] Phasebit=phasebit2^(phasebit1&phasebit2);

[0027] Wherein, Phasebit is the fault phase marker of a single-phase ground fault. When Phasebit=1, it is used to indicate that phase A is grounded; when Phasebit=2, it is used to indicate that phase B is grounded; and when Phasebit=4, it is used to indicate that phase C is grounded. Phasebit1 is the value of the bitwise OR operation of the two phase markers that were conducting before the fault, and phasebit2 is the value of the bitwise OR operation of the two phase markers that were conducting after the fault. Phasebit is the marker of the conducting phase. When phasebit=1, it is used to indicate that phase A is conducting; when phasebit=2, it is used to indicate that phase B is conducting; and when phasebit=4, it is used to indicate that phase C is conducting. ^ is the bitwise XOR operator; & is the bitwise AND operator.

[0028] In some embodiments, the step of determining that there is a ground fault in the converter transformer side winding includes:

[0029] It is determined that there is a current phase with winding difference in the converter transformer side winding;

[0030] In response to the fact that the number of current phases with the winding difference is one, it is determined that there is a single-phase ground fault inside the winding on the converter valve side, and the faulty phase is the current phase with the winding difference.

[0031] In some embodiments, the step of determining that there is a ground fault in the converter transformer valve-side winding further includes:

[0032] It is determined that there is a current phase with winding difference in the converter transformer side winding;

[0033] In response to the fact that the number of current phases with the winding difference is zero, it is determined that there is a grounding fault at the winding end or neutral point on the converter valve side.

[0034] In some embodiments, the step of determining the current phase with winding difference in the converter valve-side winding includes:

[0035] Determine the current difference of the current phase, which is the difference between the current at the beginning of the current phase and the current at the end of the current phase.

[0036] In response to the current difference satisfying a preset threshold condition, it is determined that there is a winding difference in the current phase corresponding to the current difference.

[0037] In some embodiments, the formula for representing the threshold condition includes:

[0038] YYWDI>k2*INORM;

[0039] YDWDI>k2*INORM;

[0040] Wherein, YYWDI is the current difference of the current phase on the converter valve side of the Y-bridge; YDWDI is the current difference of the current phase on the converter valve side of the D-bridge; k2 is the second proportional coefficient; and INORM is the rated current of DC transmission.

[0041] In some embodiments, the first proportionality coefficient satisfies: 1≤k1≤2.

[0042] In some embodiments, the second proportionality coefficient satisfies: 0.1≤k2≤1.

[0043] Secondly, embodiments of this application also provide a DC transmission converter valve-side grounding fault diagnosis device, including a processor and a memory, wherein the memory stores a computer program executable by the processor, and the processor executes the computer program to implement the DC transmission converter valve-side grounding fault diagnosis method as described in any one of the first aspects.

[0044] Thirdly, embodiments of this application also provide a computer-readable storage medium storing a computer program that, when executed by a processor, performs the DC transmission converter valve-side grounding fault diagnosis method as described in any one of the first aspects.

[0045] Beneficial Effects: Compared with the prior art, the present application provides a method for diagnosing ground faults on the valve side of a DC transmission converter transformer. When a ground fault occurs on the valve side of the converter transformer, the number of fault current phases on the valve side is determined. When the number of fault current phases is two, it can be determined that there is a single-phase ground fault in the connection line between the converter transformer valve side and the converter valve. When the number of fault current phases is one, it can be determined that there is a ground fault in the winding on the valve side of the converter transformer. This application determines the fault location by the number of fault current phases when a ground fault occurs on the valve side of the converter transformer, eliminating the need for manual operation and enabling rapid fault location determination and troubleshooting. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 A flowchart illustrating the steps of the DC transmission converter transformer valve-side grounding fault diagnosis method provided in this application embodiment;

[0048] Figure 2 This is a flowchart illustrating step 100 in the DC transmission converter valve-side grounding fault diagnosis method provided in this embodiment of the application.

[0049] Figure 3 A flowchart illustrating step 200 in the DC transmission converter valve-side grounding fault diagnosis method provided in this embodiment of the application.

[0050] Figure 4 A flowchart illustrating step 300 in the DC transmission converter valve-side grounding fault diagnosis method provided in this application embodiment;

[0051] Figure 5 This is a flowchart of step 310 in the DC transmission converter valve side grounding fault diagnosis method provided in the embodiments of this application.

[0052] Figure 6 A schematic diagram of the 12-pulse bridge converter valve structure in the rectifier station;

[0053] Figure 7 A schematic diagram of the structure of the 12-pulse bridge converter valve in the inverter station;

[0054] Figure 8 Diagram of a single-phase grounding fault in the connection line from the converter transformer valve side to the converter valve in the inverter station (showing the three-phase currents IVY_L1, IVY_L2, and IVY_L3 on the valve star side);

[0055] Figure 9 Diagram showing the grounding fault at the end of the converter transformer winding on the rectifier station (showing the three-phase currents IVY_L1, IVY_L2, and IVY_L3 on the valve star side). Detailed Implementation

[0056] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0057] The DC transmission system includes a converter valve group and a converter valve triggering system. The AC side of the converter valve group is connected to three-phase AC current, and the DC side of the converter valve group is connected to the DC bus. The converter valve triggering system is connected to the control terminal of the converter valve group and outputs pulse signal words to control the commutation of the converter valve group.

[0058] This application proposes a method for diagnosing ground faults on the valve side of a DC transmission converter transformer. When a ground fault occurs on the converter transformer valve side, the number of fault current phases on the converter transformer valve side is determined. When the number of fault current phases is two, it can be determined that there is a single-phase ground fault in the connection line between the converter transformer valve side and the converter valve. When the number of fault current phases is one, it can be determined that there is a ground fault in the winding on the converter transformer valve side. This application determines the fault location by the number of fault current phases when a ground fault occurs on the converter transformer valve side, eliminating the need for manual operation and enabling rapid fault location determination and troubleshooting.

[0059] In some embodiments, please refer to Figures 1 to 5 The DC transmission converter transformer valve side grounding fault diagnosis method provided in the embodiments of this application specifically includes the following steps:

[0060] Step 100: In response to a ground fault on the converter transformer valve side, determine the number of fault current phases on the converter transformer valve side.

[0061] In some embodiments, please refer to Figure 2 When a ground fault is detected on the converter transformer valve side, the valve side current is first obtained, and then the instantaneous fault is calculated according to preset conditions, specifically through steps 110 to 120:

[0062] Step 110: Obtain the three-phase current on the converter transformer valve side.

[0063] In some embodiments, when acquiring the three-phase current on the converter transformer valve side, the Y-bridge acquires IVY_L1, IVY_L2, IVY_L3, and the D-bridge acquires IVD_L1, IVD_L2, IVD_L3, where IVY represents the Y-bridge valve side current, IVD represents the D-bridge valve side current, and L1, L2, and L3 represent the three phases A, B, and C, respectively.

[0064] Step 120: Determine the number of current phases that meet the preset conditions, which is the number of fault current phases.

[0065] In some embodiments, the formula for representing the preset conditions includes:

[0066] ABS(IVY_L1)>k1*IVYNORMMAX;

[0067] ABS(IVY_L2)>k1*IVYNORMMAX;

[0068] ABS(IVY_L3)>k1*IVYNORMMAX;

[0069] ABS(IVD_L1)>k1*IVDNORMMAX;

[0070] ABS(IVD_L2)>k1*IVDNORMMAX;

[0071] ABS(IVD_L3)>k1*IVDNORMMAX;

[0072] IVYNORMMAX=max{IVYNORMA, IVYNORMB, IVYNORMC};

[0073] IVDNORMMAX=max{IVDNORMA, IVDNORMB, IVDNORMC};

[0074] Wherein, ABS is the absolute value operation; MAX is the maximum value operation; IVY_L1 is the valve-side current of phase A of Y bridge; IVY_L2 is the valve-side current of phase B of Y bridge; IVY_L3 is the valve-side current of phase C of Y bridge; IVD_L1 is the valve-side current of phase A of D bridge flowing into the converter valve; IVD_L2 is the valve-side current of phase B of D bridge flowing into the converter valve; IVD_L3 is the valve-side current of phase C of D bridge flowing into the converter valve; k1 is the proportional coefficient, and the first proportional coefficient satisfies: 1≤k1≤2; IVYNORMA, IVYNORMB, and IVYNORMC are the phase A, phase B, and phase C currents of Y bridge before the fault, respectively; IVDNORMA, IVDNORMB, and IVDNORMC are the phase A, phase B, and phase C currents of D bridge before the fault, respectively.

[0075] In some embodiments, the first scaling factor can be any value from 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or any two arbitrary values ​​forming the value within the interval.

[0076] Step 200: In response to the fact that the number of fault current phases is two, it is determined that there is a single-phase grounding fault in the connection line between the converter transformer side and the converter valve.

[0077] In some embodiments, please refer to Figure 3 After determining that there are two fault current phases on the converter transformer valve side, the fault type can be identified as a single-phase ground fault in the connection line between the converter transformer valve side and the converter valve. Simultaneously, the fault phase must be identified, specifically through steps 210 to 220:

[0078] Step 210: Determine the sampling time corresponding to the first sampling point that meets the preset conditions as the fault start position.

[0079] Step 220: Based on the current phases before and after the fault, determine the two phase markers that were conducting before and after the fault.

[0080] In some embodiments, the fault initiation location is used as the dividing point to determine the current phases that were conducting before the fault and those that were conducting after the fault. Specifically, phasebit is a marker for the conducting phases. When phase A has conducting current, its conduction marker phasebit = 1; when phase B has conducting current, its conduction marker phasebit = 2; and when phase C has conducting current, its conduction marker phasebit = 4. For two conducting current phases, the conduction markers are converted into binary numbers and bitwise ORed or summed in decimal. For example, if the phases conducting before the fault are phase B (positive current) and phase C (negative current), then the binary numbers phasebit = 2 and phasebit = 4 are used for bitwise ORing or summing in decimal to obtain phasebit1 = 6. If the currents conducting after the fault are phase A (negative current) and phase B (positive current), then the binary numbers phasebit = 1 and phasebit = 2 are used for bitwise ORing or summing in decimal to obtain phasebit2 = 3.

[0081] Step 230: Based on the two-phase markings indicating conduction before and after the fault, determine the faulty phase of the single-phase ground fault.

[0082] In some embodiments, the characterization formula for determining the fault phase of a single-phase ground fault includes:

[0083] Phasebit=phasebit2^(phasebit1&phasebit2);

[0084] Wherein, Phasebit is the fault phase marker for a single-phase ground fault. Phasebit=1 is used to indicate phase A grounding, Phasebit=2 is used to indicate phase B grounding, and Phasebit=4 is used to indicate phase C grounding; phasebit1 is the marker for the two phases that were conducting before the fault; phasebit2 is the marker for the two phases that were conducting after the fault; ^ is the bitwise XOR operator; & is the bitwise AND operator.

[0085] For example, before the fault, the phases conducting were phase B with positive current and phase C with negative current, and the current-conducting phases before the fault were marked as phasebit1 = 6; after the fault, the currents conducting were phase A with negative current and phase B with positive current, and the current-conducting phases were marked as phasebit2 = 3; then Phasebit = phasebit2^(phasebit1&phasebit2) = 3^(6&3) = 3^2 = 1, that is, the fault is a ground fault of phase A of the converter transformer valve side connection line.

[0086] Step 300: In response to the fact that the number of fault current phases is one, it is determined that there is a ground fault in the winding on the converter valve side.

[0087] In some embodiments, please refer to Figure 4 The winding grounding fault on the converter transformer valve side includes single-phase grounding faults inside the winding as well as grounding faults at the winding end or neutral point. To further determine the fault type, it is also necessary to analyze the winding difference in the three-phase current, which is specifically achieved through steps 310 to 330:

[0088] Step 310: Determine the current phase with winding difference in the converter valve side winding.

[0089] In some embodiments, please refer to Figure 5 Step 310 is specifically implemented through steps 311 to 312:

[0090] Step 311: Determine the current difference of the current phase, which is the difference between the current at the beginning of the current phase and the current at the end of the current phase winding.

[0091] Step 312: In response to the current difference meeting the preset threshold condition, determine that there is a winding difference in the current phase corresponding to the current difference.

[0092] In some embodiments, the formula for representing the threshold condition includes:

[0093] YYWDI>k2*INORM;

[0094] YDWDI>k2*INORM;

[0095] Where YYWDI is the current difference between the current phases on the valve side of the Y-bridge converter transformer; YDWDI is the current difference between the current phases on the valve side of the D-bridge converter transformer; k2 is the second proportional coefficient, 0.1≤k2≤1; INORM is the rated current of DC transmission.

[0096] Specifically, the formula for representing the above threshold condition is specifically represented in the three-phase currents A, B, and C as follows:

[0097] YYWDIA>k2*INORM;

[0098] YYWDIB>k2*INORM;

[0099] YYWDIC>k2*INORM;

[0100] YDWDIA>k2*INORM;

[0101] YDWDIB>k2*INORM;

[0102] YDWDIC>k2*INORM;

[0103] Wherein, YYWDIA is the current difference of phase A on the Y-bridge converter valve side; YYWDIB is the current difference of phase B on the Y-bridge converter valve side; YYWDIC is the current difference of phase C on the Y-bridge converter valve side; YDWDIA is the current difference of phase A on the D-bridge converter valve side; YDWDIB is the current difference of phase B on the D-bridge converter valve side; and YDWDIC is the current difference of phase C on the D-bridge converter valve side.

[0104] In some embodiments, the second scaling factor may be selected from any one or any two of the following: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.

[0105] Step 320: In response to the fact that the number of current phases with winding difference is one, it is determined that there is a single-phase ground fault inside the winding on the converter valve side, and the faulty phase is the current phase with winding difference.

[0106] Step 330: In response to the fact that the number of current phases with winding differential is zero, it is determined that there is a grounding fault at the winding end or neutral point on the converter valve side.

[0107] Understandably, the DC transmission converter transformer valve-side grounding fault diagnosis method provided in this application determines the number of fault current phases on the converter transformer valve side when a grounding fault occurs. When the number of fault current phases is two, it can be determined that there is a single-phase grounding fault in the connection line between the converter transformer valve side and the converter valve; when the number of fault current phases is one, it can be determined that there is a grounding fault in the winding on the converter transformer valve side. This application determines the fault location by the number of fault current phases when a grounding fault occurs on the converter transformer valve side, eliminating the need for manual operation and enabling rapid fault location determination and troubleshooting.

[0108] For example, please refer to Figure 6 , Figure 7 and Figure 8 , Figure 6 and Figure 7 A YY converter transformer refers to a converter transformer (converter) where both the primary and secondary sides are connected in a star (Y-type) configuration. A YD converter transformer refers to a converter transformer (converter) where the primary and secondary sides are connected in a star (Y-type) configuration and a delta (D-type) configuration, respectively. This application provides a case study of a single-phase grounding fault diagnosis for the connection line from the converter transformer valve side to the converter valve in an actual inverter station. Before diagnosis, it was unknown whether the fault occurred at pole one or pole two, the high-voltage valve or the low-voltage valve, the Y-bridge or the D-bridge, or the type of fault. Therefore, the grounding fault diagnosis method for the DC transmission converter transformer valve side provided in this application was used to diagnose the high-voltage valve and the low-voltage valve Y-bridge and D-bridge of pole one and pole two, respectively.

[0109] Taking the faulty Y-bridge valve as an example, the valve-side current is first obtained, and then the instantaneous fault on the converter transformer valve side is determined based on the characterization formula under preset conditions, such as... Figure 8 As indicated by the label.

[0110] Then, based on the characterization formula of the preset conditions, it is calculated that the fault current has two phases, so it can be determined that a single-phase ground fault has occurred in the connection line from the converter transformer side to the converter valve.

[0111] Then, by analyzing the conduction currents before and after the fault, it was calculated that before the fault, phases B and C were conducting (phasebit1 = 6), and after the fault, phases A and B were conducting (phasebit2 = 3). The specific phase that experienced the fault was calculated using the characteristic formula for the faulty phase.

[0112] Phasebit=phasebit2^(phasebit1&phasebit2)=3^(6&3)=3^2=1;

[0113] The fault is a grounding fault in phase A of the converter transformer valve side connection line.

[0114] The fault process is as follows: Before the fault, the current flows into phase B and then out of phase C. At this time, a ground fault occurs in phase A of the connecting line on the converter valve side. The current then changes from flowing into phase B to flowing out of phase A and into the grounding point of phase A. Therefore, the fault currents of phases A and B are measured, and the current increases, causing the protection to trip.

[0115] For example, please refer to Figure 6 , Figure 7 and Figure 9 , Figure 6 and Figure 7 YY converter transformers refer to converter transformers (converters) whose primary and secondary sides are both star (Y-type) connected, while YD converter transformers refer to converter transformers (converters) whose primary and secondary sides are respectively star (Y-type) and delta (D-type) connected. This application provides a case study of a grounding fault diagnosis at the end of the converter transformer valve side winding in a rectifier station. Before the diagnosis, it was unknown whether the fault occurred at pole one or pole two, whether it was in the Y-bridge or D-bridge, and what type of fault it was. Therefore, the Y-bridge and D-bridge of pole one and pole two were diagnosed using the method of this application respectively.

[0116] Taking the faulty two-pole Y-bridge as an example, firstly, the valve-side current is obtained, and then the instantaneous fault on the converter transformer valve side is determined based on the characterization formula under preset conditions, such as... Figure 9 As indicated by the label.

[0117] Then, based on the characterization formula of the preset conditions, it is determined that the fault current is only in phase B, so it can be judged that there is a grounding fault in the winding on the converter valve side.

[0118] Further calculation of the winding difference of the three-phase current on the converter transformer valve side revealed that none of the three-phase winding differences met the characteristic formula of the threshold condition. Therefore, the fault was determined to be a ground fault at the end of the winding or the neutral point on the converter transformer valve side.

[0119] The short circuit process is as follows: Before the fault, the current flows into the converter transformer from phase B and then flows out from phase C. At this time, a grounding fault occurs at the end of the phase B winding or the neutral point grounding fault on the valve side of the converter transformer. After the current flows into phase B, it flows into the grounding point instead. Therefore, only the fault current of phase B is measured, and the current increases, causing the protection to trip.

[0120] Accordingly, embodiments of this application also provide a DC transmission converter valve-side grounding fault diagnosis device, including a processor and a memory. The memory stores a computer program executable by the processor, and when the processor executes the computer program, it implements the DC transmission converter valve-side grounding fault diagnosis method provided in the embodiments of this application.

[0121] Accordingly, embodiments of this application also provide a computer-readable storage medium storing a computer program, which, when executed by a processor, performs the DC transmission converter valve-side grounding fault diagnosis method provided in the embodiments of this application.

[0122] This application has provided a detailed description of a method, apparatus, and storage medium for diagnosing grounding faults on the valve side of a DC transmission converter transformer, as provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and its core ideas. At the same time, those skilled in the art will recognize that there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for diagnosing grounding faults on the valve side of a DC transmission converter transformer, characterized in that, For use in a DC transmission system, the DC transmission system includes a converter valve group and a converter valve triggering system. The AC side of the converter valve group is connected to a three-phase AC current, and the DC side of the converter valve group is connected to a DC bus. The converter valve triggering system is connected to the control terminal of the converter valve group to output pulse signal words to control the commutation of the converter valve group. The fault diagnosis method includes: In response to a ground fault on the converter transformer valve side, determine the number of fault current phases on the converter transformer valve side; In response to the fact that the number of fault current phases is two, it is determined that there is a single-phase grounding fault in the connection line between the converter transformer side and the converter valve. In response to the fact that the number of fault current phases is one, it is determined that a ground fault exists in the valve-side winding of the converter transformer valve; wherein, the step of determining that a ground fault exists in the valve-side winding of the converter transformer valve includes: Determine the number of current phases with winding differences in the converter transformer side winding; In response to the fact that the number of current phases with the winding difference is one, it is determined that there is a single-phase ground fault inside the winding on the converter valve side, and the faulty phase is the current phase with the winding difference. In response to the fact that the number of current phases with the winding difference is zero, it is determined that there is a grounding fault at the winding end or neutral point on the converter valve side.

2. The method for diagnosing grounding faults on the valve side of a DC transmission converter transformer according to claim 1, characterized in that, The step of determining the number of fault current phases on the converter transformer side includes: Obtain the three-phase current on the converter transformer valve side; The number of current phases that meet the preset conditions is determined as the number of fault current phases.

3. The method for diagnosing grounding faults on the valve side of a DC transmission converter transformer according to claim 2, characterized in that, The formulas representing the preset conditions include: ABS(IVY_L1)>k1*IVYNORMMAX; ABS(IVY_L2)>k1*IVYNORMMAX; ABS(IVY_L3)>k1*IVYNORMMAX; ABS(IVD_L1)>k1*IVDNORMMAX; ABS(IVD_L2)>k1*IVDNORMMAX; ABS(IVD_L3)>k1*IVDNORMMAX; IVYNORMMAX=max{IVYNORMA, IVYNORMB, IVYNORMC}; IVDNORMMAX=max{IVDNORMA, IVDNORMB, IVDNORMC}; Wherein, ABS is the absolute value operation; MAX is the maximum value operation; IVY_L1 is the valve-side current of phase A of Y bridge; IVY_L2 is the valve-side current of phase B of Y bridge; IVY_L3 is the valve-side current of phase C of Y bridge; IVD_L1 is the valve-side current of phase A of D bridge flowing into the converter valve; IVD_L2 is the valve-side current of phase B of D bridge flowing into the converter valve; IVD_L3 is the valve-side current of phase C of D bridge flowing into the converter valve; k1 is the first proportional coefficient; IVYNORMA, IVYNORMB, and IVYNORMC are the phase A, phase B, and phase C currents of Y bridge before the fault, respectively; IVDNORMA, IVDNORMB, and IVDNORMC are the phase A, phase B, and phase C currents of D bridge before the fault, respectively.

4. The method for diagnosing grounding faults on the valve side of a DC transmission converter transformer according to claim 3, characterized in that, The steps for determining the faulty phase with a single-phase ground fault in the connection line between the converter transformer valve side and the converter valve include: The sampling time corresponding to the first sampling point that meets the preset conditions is determined as the fault start position. Based on the current phases before and after the fault, determine the two phase markings before and after the fault. Based on the two-phase markings indicating conduction before and after the fault, the fault phase of a single-phase ground fault is determined.

5. The method for diagnosing grounding faults on the valve side of a DC transmission converter transformer according to claim 4, characterized in that, The characterization formula for determining the fault phase of a single-phase ground fault based on the two-phase markings of conduction before and after the fault includes: Phasebit=phasebit2^(phasebit1&phasebit2); Wherein, Phasebit is the fault phase marker of a single-phase ground fault. When Phasebit=1, it is used to indicate that phase A is grounded; when Phasebit=2, it is used to indicate that phase B is grounded; and when Phasebit=4, it is used to indicate that phase C is grounded. Phasebit1 is the value of the bitwise OR operation of the two phase markers that were conducting before the fault, and phasebit2 is the value of the bitwise OR operation of the two phase markers that were conducting after the fault. Phasebit is the marker of the conducting phase. When phasebit=1, it is used to indicate that phase A is conducting; when phasebit=2, it is used to indicate that phase B is conducting; and when phasebit=4, it is used to indicate that phase C is conducting. ^ is the bitwise XOR operator; & is the bitwise AND operator.

6. The method for diagnosing grounding faults on the valve side of a DC transmission converter transformer according to claim 1, characterized in that, The step of determining that there is a current phase with winding difference in the converter transformer side winding includes: Determine the current difference of the current phase, which is the difference between the current at the beginning of the current phase and the current at the end of the current phase. In response to the current difference satisfying a preset threshold condition, it is determined that there is a winding difference in the current phase corresponding to the current difference.

7. The method for diagnosing grounding faults on the valve side of a DC transmission converter transformer according to claim 6, characterized in that, The formula for characterizing the threshold condition includes: YYWDI>k2*INORM; YDWDI>k2*INORM; Wherein, YYWDI is the current difference of the current phase on the converter valve side of the Y-bridge; YDWDI is the current difference of the current phase on the converter valve side of the D-bridge; k2 is the second proportional coefficient; and INORM is the rated current of DC transmission.

8. The method for diagnosing grounding faults on the valve side of a DC transmission converter transformer according to claim 3, characterized in that, The first proportionality coefficient k1 satisfies: 1≤k1≤2.

9. The method for diagnosing grounding faults on the valve side of a DC transmission converter transformer according to claim 7, characterized in that, The second proportionality coefficient k2 satisfies: 0.1≤k2≤1.

10. A DC transmission converter transformer valve-side grounding fault diagnosis device, characterized in that, It includes a processor and a memory, the memory storing a computer program executable by the processor, wherein when the processor executes the computer program, it implements the DC transmission converter valve side grounding fault diagnosis method according to any one of claims 1-9.

11. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, performs the DC transmission converter valve-side grounding fault diagnosis method as described in any one of claims 1-9.

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