A method for analyzing single-phase grounding fault on converter transformer valve side through transition resistance

Abstract

This invention discloses a method for analyzing single-phase grounding faults on the converter transformer valve side via a transition resistor, comprising: fault feature summarization: pre-classifying the conduction type into several on / off categories according to the conduction sequence of the converter valve, and pre-setting the current loop characteristics for each on / off category by referring to the AC system on the inverter side of the distribution network and the wiring circuit diagram of the converter station; fault analysis: determining the on / off status of the corresponding converter valve based on the anode and cathode potentials of the converter valve at the time of the fault, obtaining the on / off category at the time of the fault, and establishing an equivalent circuit and current flow path; combining the current flow path and the pre-set current loop characteristics to analyze and obtain the relevant current magnitude and direction and the transition resistance, and sorting out the relevant fault features to obtain the fault situation. This invention classifies the time of fault occurrence into multiple cases according to the conduction sequence of the converter valve, covering all possibilities of the time of fault occurrence, breaking through the current simplification method, and making the fault features obtained from the analysis more accurate and comprehensive.

Description

Technical Field

[0001] The invention relates to the field of relay protection of power systems, and in particular to a method for analyzing single-phase grounding faults on a converter transformer valve side through a transition resistor. Background Art

[0002] With the increasing application of distributed power sources in power systems, more and more distribution networks have become AC / DC distribution networks. The converter transformer in the distribution network, referred to as the converter transformer, is the core equipment connecting the AC system and the DC system. Its operating reliability is particularly critical to the safe operation of the distribution network. However, existing research statistics show that due to the particularity of the operating environment, the failure rate of the converter transformer is much higher than that of ordinary power transformers, about twice that of ordinary power transformers. In particular, multiple single-phase grounding faults have occurred in the valve-side wall bushing. However, the current literature has failed to classify and analyze all possible moments of the single-phase grounding fault on the valve side of the converter transformer, and then summarize the fault characteristics, and the analysis of the current literature has not considered the influence of transition resistance. Some literature divides the valve-side single-phase grounding fault of the converter transformer into four stages, and analyzes and describes the DC current loop and current characteristics of each stage in combination with the fault recording diagram. Other literature analyzes and describes the current loop of the single-phase grounding fault of the converter transformer bushing on the inverter side, and points out that the fault characteristics are similar to some characteristics of the phase change failure, but the converter transformer has the characteristics of AC two-phase short circuit when the valve-side bushing single-phase grounding fault occurs. Other literatures derive the change function of the converter valve current after the low-voltage bridge, high-voltage bridge and AC busbar of the converter transformer have single-phase grounding, two-phase grounding faults and two-phase short circuits, respectively, and point out that the fault current presents the characteristics of AC multi-phase short circuit when the ground fault occurs. Another literature gives a time division method for the time when the single-phase grounding fault occurs on the valve side of the converter transformer, gives the current flow path when the fault point is located at the low-voltage bridge and the high-voltage bridge, and analyzes the change of the valve side current in combination with the valve commutation law. Another literature considers the control effect of the DC system and the switching of the converter working state, and uses the loop superposition method to construct a fault analysis model when the AC side has symmetrical faults, single-phase grounding and two-phase short circuits, but does not solve the magnitude of the loop current. Another literature combines the simulation of the International Conference on Large Power Systems model, divides the time when the single-phase grounding fault occurs into 4 characteristic time periods according to the different characteristics of the fault evolution process after the single-phase grounding short circuit occurs on the AC side of the converter, and simulates the waveform diagram of the electrical quantity in each characteristic time period, and analyzes the electrical quantity characteristics when the single-phase grounding occurs on the AC side, the DC high-voltage end, the low-voltage end and the midpoint based on the simulation results. Other literature analyzes and points out that a single-phase grounding fault on the inverter side of the converter transformer valve will cause a fault surge current from the perspective of flux change and the current flow path after a converter transformer fault occurs.

[0003] From the above analysis, it can be seen that the existing technology lacks the ability to judge the impact of transition resistance, and therefore it is urgently needed to be improved. Summary of the invention

[0004] In view of the problem that the analysis process in the prior art does not consider the influence of transition resistance, the present invention provides a method for analyzing single-phase grounding fault on the converter transformer side through transition resistance. By establishing an equivalent circuit of the single-phase grounding fault on the converter transformer side through transition resistance according to the time when the fault occurs and the on-off status of the converter valve, a fault analysis method is proposed and electrical characteristics are obtained, which lays a foundation for the research on relay protection and has important theoretical significance and engineering practical value for ensuring the safe operation of the distribution network.

[0005] The following is the technical solution of the present invention.

[0006] A method for analyzing a single-phase grounding fault on a converter transformer valve side through a transition resistor comprises the following steps:

[0007] Fault feature summary: The conduction type is divided into several on-off categories in advance according to the conduction sequence of the converter valves. The current loop characteristics of each on-off category are preset with reference to the AC system on the inverter side of the distribution network and the converter station wiring circuit diagram;

[0008] Fault analysis: The on / off status of the corresponding converter valve is determined based on the anode potential and cathode potential of the converter valve during the fault, the on / off category of the fault is obtained, and the equivalent circuit and current flow path are established; the current flow path and the preset current loop characteristics are combined to analyze the relevant current size and direction as well as the transition resistance, and the relevant fault characteristics are sorted out to obtain the fault situation.

[0009] The present invention divides the moment of fault occurrence into multiple situations according to the conduction order of the converter valves; corresponding to each situation, the on-off state of the converter valve is judged according to the anode potential and cathode potential of the converter valve after the fault, and an equivalent circuit and a current flow path are established; based on the current flow path analysis, the magnitude and direction of the current in the current transformer are obtained, and then the fault characteristics are summarized.

[0010] Preferably, when the fault occurs during the non-commutation period, one valve of the common anode valve and the common cathode valve is turned on, and there are six on-off categories; when the fault occurs during the commutation period, three valves of the common anode valve and the common cathode valve are turned on, and there are also six on-off categories. Different on-off categories have different current loops, so each situation needs to be considered separately.

[0011] Preferably, the process of analyzing the current flow path and the preset current loop characteristics includes: obtaining the current passing through the conduction valve according to the reading of the current transformer of the branch where the conduction valve is located, calculating the bridge current, the current of each branch and the current passing through the transition resistor in combination with the current flow path and the reading, and sorting out the relevant fault characteristics to obtain the fault situation. Due to the existence of the transition resistor, its resistance value directly affects the reading of the relevant current transformer, so the situation of the transition resistor can be determined based on the reading and the current loop.

[0012] As a preferred method, the method further includes a characteristic analysis step of the post-fault period, including: based on the current on-off category, each off condition of each conduction valve in the post-fault period is subdivided into several categories, and then the equivalent circuit and current flow path after the off condition are obtained, and the current flow path and the preset current loop characteristics are analyzed to obtain the relevant current magnitude and direction and transition resistance, and the relevant fault characteristics are sorted to obtain the situation in the post-fault period. Since the potentials of the two poles of the conduction valve may be different after the fault, and the different potential differences directly affect whether the valve is on or not, and then affect other electrical parameters, the analysis of the post-fault period is also equally important.

[0013] Preferably, the six on-off categories during the non-switching period include: valve V12 and valve V62 are turned on; valve V12 and valve V22 are turned on; valve V22 and valve V32 are turned on; valve V32 and valve V42 are turned on; valve V42 and valve V52 are turned on; valve V52 and valve V62 are turned on.

[0014] Preferably, the six on-off categories during the phase change period include: valve V12, valve V22 and valve V62 are turned on; valve V32, valve V42 and valve V22 are turned on; valve V52, valve V42 and valve V62 are turned on; valve V22, valve V32 and valve V12 are turned on; valve V62, valve V52 and valve V12 are turned on; valve V42, valve V52 and valve V32 are turned on.

[0015] The substantial effects of the present invention include: covering all possibilities of the time when the fault occurs, breaking through the current simplified method of analyzing the single-phase grounding fault through the transition resistance on the valve side of the converter transformer in the distribution network, dividing the time when the fault occurs into 12 situations during the phase change period and the non-phase change period, and analyzing them in turn, and introducing the analysis of the post-fault period, so that the fault characteristics obtained by analysis are more accurate and comprehensive. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The AC system and converter station wiring diagram on the inverter side of the AC / DC distribution network of this embodiment;

[0017] Figure 2 The diagram is a diagram of the phase voltage and line voltage on the converter transformer valve side and the conduction interval of the valve under normal conditions in this embodiment;

[0018] Figure 3 It is a partial circuit diagram of the embodiment when a single-phase grounding fault occurs through a transition resistor during the non-commutation period. DETAILED DESCRIPTION

[0019] The technical scheme of the present application will be described below in conjunction with the embodiments. In addition, in order to better illustrate the present invention, numerous specific details are provided below. It should be understood by those skilled in the art that the present invention can be implemented without certain specific details. In some instances, methods, means, components and circuits well known to those skilled in the art are not described in detail in order to highlight the gist of the present invention.

[0020] Example:

[0021] A method for analyzing a single-phase grounding fault on a converter transformer valve side through a transition resistor comprises the following steps:

[0022] Fault feature summary: The conduction type is divided into several on-off categories in advance according to the conduction sequence of the converter valves. The current loop characteristics of each on-off category are preset with reference to the AC system on the inverter side of the distribution network and the converter station wiring circuit diagram;

[0023] Fault analysis: The on / off status of the corresponding converter valve is determined based on the anode potential and cathode potential of the converter valve during the fault, the on / off category of the fault is obtained, and the equivalent circuit and current flow path are established; the current flow path and the preset current loop characteristics are combined to analyze the relevant current size and direction as well as the transition resistance, and the relevant fault characteristics are sorted out to obtain the fault situation.

[0024] This embodiment divides the moment of fault occurrence into multiple situations according to the conduction order of the converter valves; corresponding to each situation, the on-off state of the converter valve is judged according to the anode potential and cathode potential of the converter valve after the fault, and an equivalent circuit and a current flow path are established; based on the current flow path analysis, the magnitude and direction of the current in the current transformer are obtained, and then the fault characteristics are summarized.

[0025] When the fault occurs during non-commutation, one valve of the common anode valve and the common cathode valve is turned on, with six on-off categories; when the fault occurs during commutation, three valves of the common anode valve and the common cathode valve are turned on, also with six on-off categories. Different on-off categories have different current loops, so each case needs to be considered separately.

[0026] The process of analyzing the current flow path and the preset current loop characteristics includes: obtaining the current passing through the conduction valve according to the reading of the current transformer of the branch where the conduction valve is located, calculating the bridge current, the current of each branch and the current passing through the transition resistor in combination with the current flow path and the reading, and sorting out the relevant fault characteristics to obtain the fault situation. Due to the existence of the transition resistor, its resistance value directly affects the reading of the relevant current transformer, so the situation of the transition resistor can be judged based on the reading and the current loop.

[0027] This embodiment also includes a characteristic analysis step of the post-fault period, including: based on the current on-off category, each off condition of each conduction valve in the post-fault period is subdivided into several categories, and then the equivalent circuit and current flow path after the off condition are obtained, and the current flow path and the preset current loop characteristics are combined to analyze the relevant current magnitude and direction and transition resistance, and the relevant fault characteristics are sorted to obtain the situation of the post-fault period. Since the potentials of the two poles of the conduction valve may be different after the fault, and the different potential differences directly affect whether the valve is on or not, and then affect other electrical parameters, the analysis of the post-fault period is also equally important.

[0028] The principle of this embodiment is described below with reference to the accompanying drawings.

[0029] Attached Figure 1 It is the AC system and converter station wiring diagram on the inverter side of the AC / DC distribution network, including the AC three-phase equivalent system, AC bus, converter transformer and grid commutation converter. T is the leakage reactance of the converter transformer, L s is the impedance of the AC equivalent system, R is the DC neutral line grounding resistance; U dc is the DC voltage; I dH ,I dN and I m They are the DC side current, neutral line current and bridge current respectively. During normal operation, the three currents satisfy the following relationship

[0030] I dH =I dN =I m (1)

[0031] Attached Figure 1 Where I is the three-phase current on the valve side, I' is the three-phase current on the grid side, CT is the current transformer, R g is the transition resistance, f1 is the high voltage bridge fault, f2 is the low voltage bridge fault. The subscript of each quantity of the high voltage bridge is 1, and the subscript of each quantity of the low voltage bridge is 2.

[0032] The waveforms of the phase voltage and line voltage on the converter transformer side and the conduction interval of the converter valve during normal operation are shown in the attached figure. Figure 2 As shown, the voltage of each phase on the valve side of the high-voltage bridge lags behind the low-voltage bridge by 30°, and the corresponding valve conduction interval also lags by 30°. In the figure, β is the Echizen trigger angle, γ=7°:19° is the shutdown angle, μ=20°:30° is the commutation overlap angle, and β=γ+μ.

[0033] Next, f2 is passed through the transition resistor R g Taking single-phase grounding as an example, an analysis method for single-phase grounding fault on the valve side of converter transformer through transition resistance in distribution network is given.

[0034] When the fault occurs during the non-commutation period, one valve of the common anode valve and the common cathode valve is turned on. The fault occurrence time is divided into 6 categories according to the valve conduction status, as shown in the attached figure. Figure 3 As shown, six types of situations are analyzed respectively and equivalent circuits and current flow paths are drawn to obtain the fault characteristics.

[0035] (1) The fault occurs during the conduction period between valves V12 and V62. The equivalent circuit and current flow path are as shown in the following figure. Figure 3 (a). Due to the transition resistance R g The anode potential of valve V12 is higher than the cathode potential, so valve V12 continues to conduct after the fault. m Flows through valve V62 and phase B current transformer CT in sequence B2 , the B-phase and A-phase windings of the transformer are divided into two branches: the first branch is the ground branch at the fault point, and the current I g Through the transition resistor R g Then it is injected into the earth; the second branch flows through the A phase current transformer CT A2 After that, it passes through valve V12. If the transition resistance is large enough, the loop impedance after the fault is not much different from that before the fault, and the current I m It is basically the same as before the fault. Figure 3 (a) It can be seen that CT B2 The measured current i B2 =I m , direction is positive; CT A2 The measured current i A2 =I m -I g , the direction is negative. If the transition resistance is larger, the current I g The smaller the CT A2 and CT B2 The closer the measured current is, the A2 ≈I m ; If the transition resistance is smaller, CT A2 and CT B2 The greater the difference in the measured current values.

[0036] (2) The fault occurs during the conduction period between valves V12 and V22. The equivalent circuit and current flow path are as shown in the following figure. Figure 3 (b) Valve V12 continues to conduct after the fault, and the current I m Flows through valve V22 and C phase current transformer CT in sequence C2 , after the C-phase and A-phase windings are commutated, they are divided into two branches: the first branch current I g Through the transition resistor R g Then the ground fault point is injected; the second branch flows through the A phase current transformer CT A2 After the valve V12. When the transition resistance is large enough, after the fault Im ≈1.0pu. It can be seen that CT C2 The measured current is i C2 =I m , direction is positive; CT A2 The measured current is i A2 =I m -I g , the direction is negative. And the larger the transition resistance, the greater the current I g The smaller the CT A2 and CT B2 The closer the measured current values ​​are.

[0037] (3) The fault occurs during the conduction period between valves V22 and V32. The equivalent circuit and current flow path are as shown in the following figure. Figure 3 (c) According to the attached Figure 2 and attached Figure 3 (c) It can be seen that the anode potential of valve V32 after a ground fault occurs is

[0038]

[0039] By the attached Figure 2 It can be seen that the line voltage u B2A2 It is positive in the γ+μ angle range before the valve V32 is turned on, and negative after the γ+μ angle. Due to the existence of the grounding resistor R, the cathode potential of the common cathode valve is

[0040] u - =u R (3)

[0041] Then the anode potential of valve V32 after the fault is u 32 With cathode potential u - =u R The magnitude relationship depends on the voltage u g and u B2A2 size.

[0042] If the failure 32 >u - , then valve V32 continues to conduct, and the current loop is as shown in the attached Figure 3 (c) shows the current I m Flows through valve V22 and C phase current transformer CT in sequence C2 After the C-phase winding is commutated, it is divided into two branches: the first branch is the ground branch at the fault point, and the current I g After commutation, the A phase winding and transition resistor R g Then it is injected into the earth; the second branch current passes through the B phase current transformer CT B2 The second branch is the circuit for normal operation. After the fault, the first branch is connected in parallel to it, causing the circuit impedance after the fault to be smaller than that before the fault. Therefore, CTC2 The measured current i C2 =I m >1.0pu., direction is positive; CT B2 The measured current i B2 =I m -I g , the direction is negative. And the smaller the transition resistance, the current I g The larger the CT C2 and CT B2 The greater the difference in the measured current values. A2 No current flows, i A2 =0.

[0043] If the failure 32 <u - , the valve V32 is closed due to the reverse pressure, and the current I m Flows through valve V22 and C phase current transformer CT in sequence C2 After the C-phase winding of the commutation transformer, all the current flows through the A-phase winding of the commutation transformer and the transition resistor R g The loop impedance after the fault has changed compared to the loop impedance during normal operation, resulting in the current I m The size of CT is different from that in normal operation. C2 The measured current i C2 =I′ m , direction is positive; CT A2 and CT B2 No current flows, i A2 =i B2 =0.

[0044] (4) The fault occurs during the conduction period between valves V32 and V42. The equivalent circuit and current flow path are as shown in the following figure. Figure 3 (d). Similarly, according to formula (2), the anode potential u of valve V32 after the fault 32 and cathode potential u - The size of the valve V32 is divided into two situations: the valve V32 continues to be turned on and the valve V32 is turned off.

[0045] If valve V32 continues to conduct after a fault, the current circuit after the fault is as shown in the attached figure. Figure 3 (d) shows the current I m Flows through valve V42 and phase A current transformer CT in sequence A2 After that, it is divided into two branches: the first branch current I g Through the transition resistor R g Then the ground fault point is injected; the second branch current passes through the A-phase and B-phase windings of the converter, and the B-phase current transformer CT B2The first branch is the same as the normal operation circuit, and the parallel connection of the second branch makes the circuit impedance after the fault smaller than the value during normal operation. A2 The measured current i A2 =I m >1.0pu., direction is positive; CT B2 The measured current i B2 =I m -I g , the direction is negative. And the larger the transition resistance, the A2 and CT B2 The closer the measured current is. C2 No current flows, i C2 =0.

[0046] If the valve V32 is closed after a fault, the current I m Flows through valve V42 and phase A current transformer CT in sequence A2 After that, all the transition resistors R g Then injected into the earth. In this case, only CT A2 The measured current i A2 =I′ m If the current after the fault is greater than the current during normal operation, then I′ m >I m .

[0047] (5) The fault occurs during the conduction period between valves V42 and V52. The equivalent circuit and current flow path are as shown in the following figure. Figure 3 (e) According to the attached Figure 2 and attached Figure 3 (e) It can be seen that the anode potential of valve V52 after the failure is

[0048]

[0049] So after the failure, the anode potential of valve V52 is u 52 With cathode potential u - =u R The magnitude relationship depends on the voltage u g and u C2A2 size.

[0050] If the failure 52 >u - , then valve V52 continues to conduct, and the current loop is as shown in the attached Figure 3 (e) shows the current I m Flows through valve V42 and phase A current transformer CT in sequence A2 After that, it is divided into two branches: the first branch current I g Through the transition resistor R gThen the ground fault point is injected; the second branch current passes through the A-phase and C-phase windings of the converter, and the C-phase current transformer CT C2 After the valve V52. Similarly CT A2 The measured current i A2 =I m >1.0pu., direction is positive; CT C2 The measured current i C2 =I m -I g , the direction is negative. And the larger the transition resistance, the greater the current I g The smaller the CT A2 and CT C2 The smaller the difference in the measured current values ​​is. B2 No current flows, i B2 =0.

[0051] If the failure 52 <u - , the valve V52 is closed due to the reverse pressure, and the current I m Flows through valve V42 and phase A current transformer CT in sequence A2 After that, all flows through the transition resistor R g Then injected into the earth. A2 The measured current i A2 =I′ m >I m , direction is positive; CT B2 and CT C2 No current flows, i B2 =i C2 =0.

[0052] (6) The fault occurs during the conduction period between valves V52 and V62. The equivalent circuit and current flow path are as shown in the following figure. Figure 3 (f). Similarly, the anode potential u of valve V52 after the fault in equation (4) can be 52 and cathode potential u - =u R The level of divides the current loop into two situations: valve V52 continues to be turned on and valve V52 is turned off.

[0053] If valve V52 continues to conduct after a fault, the current circuit is as shown in the attached Figure 3 (f) shows the current I m Flows through valve V62 and phase B current transformer CT in sequence B2 After the B-phase winding is commutated, it is divided into two branches: the first branch current I g After commutation, the A phase winding and transition resistor R g Then the short-circuit point is injected; the second branch flows through the C-phase winding of the converter transformer and the C-phase current transformer CT C2 After the valve V52. CTB2 The measured current i B2 =I m >1.0pu., direction is positive; CT C2 The measured current i C2 =I m -I g , the direction is negative. And the larger the transition resistance, the greater the current I g The smaller the CT B2 and CT C2 The closer the measured current value is. A2 No current flows, i A2 =0.

[0054] If the valve V52 is closed due to the reverse pressure after the fault, the current I m Flows through valve V62 and phase B current transformer CT in sequence B2 After that, all the current flows through the A phase winding of the commutation transformer and the transition resistor R g Then inject the short-circuit point. B2 The measured current i B2 =I′ m >I m , direction is positive; CT A2 and CT C2 No current flows, i A2 =i C2 =0.

[0055] In summary, by establishing an equivalent circuit after the fault and analyzing the six situations when the single-phase grounding fault occurs through the transition resistance on the converter transformer valve side, the following fault characteristics can be obtained.

[0056] (1) After a single-phase grounding fault occurs on the valve side of the converter transformer in the distribution network, the transition resistor R g The supporting effect makes the common cathode valve V12 of the faulty phase continue to be turned on, and the on-off status of the common cathode valves V32 and V52 of the non-faulty phase depends on the transition resistance R g The voltage drop u g and line voltage u B2A2 、u C2A2 size.

[0057] (2) After the fault, at most two phase current transformers can measure the current, and the current values ​​are I m and I m -I g When the transition resistance R g The smaller the value, the greater the difference between the two values; when the transition resistance R g The larger the value, the smaller the difference between the two. g = 0, it is a metallic ground fault, at this time I g =I m, the current values ​​measured by the two-phase current transformers are I m and 0, the difference is the largest.

[0058] (3) If a fault occurs and the common cathode valve of the non-fault phase is closed, only one current transformer in the non-fault phase can measure the current, and its value is I′ m , I′ m is the fault current, which is greater than the current I during normal operation m .

[0059] When the fault occurs during the commutation period, the fault characteristics analysis method is the same as the fault analysis method during the non-commutation period. The difference between the two is that three converter valves are turned on during the commutation period. According to the conduction status of the converter valves and the on-off change law after the fault, the fault occurrence time is divided into 6 situations. The 6 types of situations are analyzed and the equivalent circuits and current flow paths are drawn, and then the fault characteristics are obtained, which will not be repeated here.

[0060] Similarly, for F1 fault, a current loop can be established based on the fault occurrence time and the on-off status of the valve after the fault to conduct fault analysis, and obtain the fault characteristics during the commutation period and the non-commutation period. The same applies to the rectifier side.

[0061] Through the description of the above implementation mode, the technicians in the relevant field can understand that all or part of the present embodiment can also be embodied in the form of a software product and stored in a storage medium, including a number of instructions to enable a device (which can be a single-chip microcomputer, chip, etc.) or a processor to execute all or part of the steps of the methods of each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read only memory (ROM), random access memory (RAM), disk or optical disk and other media that can store program codes.

[0062] The above contents are only specific implementation methods of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for analyzing single-phase grounding fault on the converter transformer valve side through transition resistance. It is characterized in that The following steps are involved: Fault feature summary: The conduction type is divided into several on-off categories in advance according to the conduction sequence of the converter valves. The current loop characteristics of each on-off category are preset with reference to the AC system on the inverter side of the distribution network and the converter station wiring circuit diagram; Fault analysis: The on-off status of the corresponding converter valve is determined according to the anode potential and cathode potential of the converter valve at the time of the fault, the on-off category when the fault occurs is obtained, and the equivalent circuit and current flow path are established; the current flow path and the preset current loop characteristics are combined to analyze the relevant current size and direction and transition resistance, and the relevant fault characteristics are sorted out to obtain the fault situation; When the fault occurs during the non-commutation period, one valve of the common anode valve and the common cathode valve is turned on, with six on-off categories; when the fault occurs during the commutation period, three valves of the common anode valve and the common cathode valve are turned on, also with six on-off categories; The process of analyzing by combining the current flow path and the preset current loop characteristics includes: obtaining the current passing through the conduction valve based on the reading of the current transformer of the branch where the conduction valve is located, calculating the bridge current, the current of each branch and the current passing through the transition resistor by combining the current flow path and the reading, and sorting out the relevant fault characteristics to obtain the fault situation.

2. A method for analyzing a single-phase grounding fault on the converter transformer valve side through a transition resistor according to claim 1, It is characterized in that It also includes a characteristic analysis step for the post-fault period, including: based on the current on-off category, each shutdown situation of each conduction valve in the post-fault period is subdivided into several categories, so as to obtain the equivalent circuit and current flow path after the shutdown, and analyze the current flow path and the preset current loop characteristics to obtain the relevant current size and direction and transition resistance, and sort out the relevant fault characteristics to obtain the situation in the post-fault period.

3. A method for analyzing a single-phase grounding fault on the converter transformer valve side through a transition resistor according to claim 1, It is characterized in that The six on-off categories during the non-switching period include: valve V12 and valve V62 are turned on; valve V12 and valve V22 are turned on; valve V22 and valve V32 are turned on; valve V32 and valve V42 are turned on; valve V42 and valve V52 are turned on; valve V52 and valve V62 are turned on.

4. A method for analyzing a single-phase grounding fault on the converter transformer valve side through a transition resistor according to claim 1, It is characterized in that The six on-off categories during the commutation period include: valve V12, valve V22 and valve V62 are turned on; valve V32, valve V42 and valve V22 are turned on; valve V52, valve V42 and valve V62 are turned on; valve V22, valve V32 and valve V12 are turned on; valve V62, valve V52 and valve V12 are turned on; valve V42, valve V52 and valve V32 are turned on.

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