Method and system for measuring loop resistance in substations, taking into account the influence of grounding branches.

Abstract

A loop resistance measurement method and system for a substation considering the influence of a grounding branch includes: constructing a loop resistance measurement model for a substation; adding an additional resistor to the grounding branch based on the constructed loop resistance measurement model for a substation; passing current through the circuit based on the preprocessed model to obtain a calculation formula for the contact resistance to be measured; calculating different contact resistances through different additional resistors based on the obtained calculation formula for the contact resistance to be measured, and obtaining the final loop resistance through analysis and judgment; outputting the obtained loop resistance based on the analysis and judgment results. The advantages of this method are that it takes into account the decrease in the difference between the grounding branch and the contact resistance, thereby improving the measurement accuracy of the substation loop resistance; it can adjust the branch state through the ground knife when measuring the loop resistance; and by connecting multiple additional resistors in series in the grounding branch, the test results are enriched and the errors caused by discreteness are reduced.

Description

Technical Field

[0001] The invention relates to the field of substation secondary system operation and inspection, and in particular to a loop resistance measurement method and system for a substation taking into account the influence of a grounding branch. Background Art

[0002] Substations are the heart of the power grid, and it is important to keep the contact resistance of the lap joints of the conductive circuit connectors of the electrical equipment in the substation at a low value. In this context, the contact resistance needs to be measured during equipment maintenance.

[0003] The metal overlap surface on site is generally in the corresponding conductive loop. The grounding branches on both sides of the resistor to be measured are generally less concerned. There is no uniform practice during on-site measurement. It is generally believed that the resistance of the grounding branch is much greater than the contact resistance, and its influence is ignored. In practice, due to the decrease in the resistance of the on-site ground grid or the parallel connection of the grounding branches, the grounding resistance may be comparable to the contact resistance. At this time, the error caused by the grounding branch cannot be ignored. There is currently little discussion on this issue.

[0004] The common method for measuring contact resistance in the prior art is loop resistance measurement. Take the loop resistance measurement of the knife switch as an example. Apply a current of more than 100A, measure the relevant voltage and current, and the contact resistance of the knife switch to be measured is R x .

[0005] It is easy to know that if the grounding branch is not considered or the grounding branch is much larger than Rx, the voltage meter measures U and the current meter measures I, then there is a contact resistance R x for .

[0006] However, the existing methods have the following problems:

[0007] 1) Easily affected by grounding branch.

[0008] It is conventionally considered that the contact resistance at the joint is tens or more than a hundred microohms, while the resistance of the grounding branch in the loop is tens or hundreds of milliohms, a difference of several orders of magnitude, so the existence of the grounding branch is ignored.

[0009] Taking the measurement of knife switch loop resistance as an example, in fact, the above assumptions have at least the following problems: with the increasing attention paid to the substation grounding network, the resistance of the grounding branch in the loop is generally less than 100 milliohms. Taking into account the possible existence of parallel grounding branches, such as adding grounding wires, the grounding branch resistance may further decrease, resulting in a decrease in the gap between the grounding branch resistance and the contact resistance to be measured.

[0010] 2) Uncontrollability of the grounding branch.

[0011] For example, the traditional method is greatly affected by the grounding branch. Another idea is to change the grounding branch state. In fact, it is not feasible in work. Take the knife switch interval under maintenance as an example. Since the ground knife is not closed for measuring the loop resistance, its branch state is difficult to ensure adjustment during the loop resistance measurement.

[0012] 3) The problem of discrete results.

[0013] Due to the discreteness of test data, the test results of loop resistance are often inaccurate in actual work, and the acceptance of a single test result may result in large errors. Summary of the invention

[0014] In order to solve the deficiencies in the prior art, the present invention provides a loop resistance measurement method and system for a substation taking into account the influence of a grounding branch, thereby improving the work quality and efficiency of electrical tests in the substation and improving the measurement accuracy of the loop resistance.

[0015] The present invention adopts the following technical solution. A first aspect of the present invention provides a loop resistance measurement method for a substation considering the influence of a grounding branch, which specifically comprises the following steps:

[0016] Step 1: Construct a loop resistance measurement model for substations;

[0017] Step 2: Based on the substation loop resistance measurement model constructed in step 1, add additional resistance to the grounding branch;

[0018] Step 3: Based on the additional resistance added to the grounding branch in step 2, current is passed through the circuit to obtain a calculation formula for the contact resistance to be measured;

[0019] Step 4: Based on the calculation formula of the contact resistance to be measured obtained in step 3, different contact resistances are calculated by different additional resistances, and the final loop resistance is obtained by analysis and judgment;

[0020] Step 5: Based on the calculation results of step 4, output the loop resistance.

[0021] The substation loop resistance measurement model in step 1 includes: a contact resistance to be measured and two grounding switches.

[0022] The loop resistance measurement model for substations can adjust the branch state through the ground knife during loop resistance measurement and change the resistance value of the additional resistor.

[0023] The step 3 comprises:

[0024] Step 3.1: Based on the substation loop resistance measurement model with additional resistance added to the grounding branch in step 2, analyze the additional branch conditions corresponding to different additional resistances, pass current through the circuit of the model, and solve the simultaneous equations according to Ohm's law;

[0025] Step 3.2: Based on the equations in step 3.1, sort them out to obtain the calculation formula for the contact resistance to be measured.

[0026] The step 4 comprises:

[0027] Step 4.1: Based on the calculation formula obtained in step 3, the numerical ratio of the voltage / current when no additional resistor is connected in series and when a single additional resistor is connected in series is compared with the numerical ratio of the voltage / current when no additional resistor is connected in series. If it is not greater than the set value, the final loop resistance is the numerical ratio of the voltage / current when the additional resistor is connected in series; if it is greater than the set value, further analysis and judgment are performed;

[0028] Step 4.2: Based on the calculation formula obtained in step 3 and the preliminary judgment result obtained in step 4.1, the contact resistance when additional resistors with more resistance values ​​are connected in series is calculated, and a secondary comparison judgment is performed;

[0029] Step 4.3: Based on the comparison results obtained in step 4.1 and step 4.2, the final loop resistance is obtained.

[0030] The step 4.1 comprises:

[0031] Step 4.1.1: Based on the calculation formula obtained in step 3, without inserting additional resistance in series, collect electrical quantity information and calculate the voltage / current ratio when current is flowing;

[0032] Step 4.1.2: Based on the calculation formula obtained in step 3, insert an additional resistor in series through the grounding knife to collect electrical quantity information and calculate the voltage / current ratio when current is flowing;

[0033] Step 4.1.3: Based on the numerical ratio of voltage / current obtained in step 4.1.1 and step 4.1.2, make a preliminary comparison and judgment on the absolute value of the numerical difference between the voltage / current when no additional resistance is connected in series and when the additional resistance is connected in series, and the numerical value of the voltage / current when the additional resistance is not connected in series. If it is not greater than the first set value, the contact resistance is the numerical ratio of the voltage / current when the additional resistance is connected in series, and it is judged as the final loop resistance. If it is greater than the first set value, further analysis and judgment are performed.

[0034] The step 4.2 comprises:

[0035] Step 4.2.1: Based on the preliminary judgment result of step 4.2, if it is greater than the set value, insert additional resistors with more resistance values ​​in series through the grounding knife to collect electrical quantity information, calculate the corresponding voltage / current numerical ratio based on the formula obtained in step 3, and obtain the corresponding contact resistance;

[0036] Step 4.2.2: Based on the contact resistance obtained in step 4.1 and step 4.3.1, make a secondary comparison and judgment on the absolute value of the difference between the contact resistance without the additional resistance and the contact resistance with the additional resistance, and the maximum value of the contact resistance when the additional resistance with more resistance is connected in series; if it is not greater than the second set value, the final loop resistance is the contact resistance when the additional resistance is connected in series; if it is greater than the second set value, the final loop resistance is the maximum value of the contact resistance when the additional resistance with more resistance is connected in series.

[0037] The second aspect of the present invention provides a loop resistance measurement system for a substation considering the influence of a grounding branch, and the loop resistance measurement method for a substation considering the influence of a grounding branch includes: a model building module, a preprocessing module, a contact resistance calculation formula conversion module, a contact resistance calculation result diversification module, and an output module;

[0038] A model building module for building a loop resistance measurement model for a substation;

[0039] A preprocessing module, connected to the model building module, is used to add additional resistance to the grounding branch based on the substation loop resistance measurement model built by the model building module;

[0040] A contact resistance calculation formula conversion module is connected to the preprocessing module and is used to obtain a calculation formula for the contact resistance to be measured by conducting current through the circuit based on a substation loop resistance measurement model with additional resistance obtained by the preprocessing module;

[0041] A contact resistance calculation result diversification module is connected to the contact resistance calculation formula conversion module. Based on the contact resistance calculation formula obtained by the contact resistance calculation formula conversion module, different contact resistances are calculated using different additional resistances on the grounding branch, and the calculation results are diversified to obtain the final loop resistance.

[0042] The output module is connected to the contact resistance calculation result diversification module and is used for outputting the loop resistance obtained by the contact resistance calculation module.

[0043] The contact resistance calculation result diversification module specifically includes: data collection unit, data calculation unit, analysis and judgment unit;

[0044] A data collection unit is connected to the preprocessing module and is used to measure the voltage and current after the analog circuit is passed through;

[0045] A data calculation unit is connected to the contact resistance calculation formula conversion module and the data collection unit, and calculates different voltage / current value ratios corresponding to different additional resistances based on the general calculation formula obtained by the contact resistance calculation formula conversion module and the voltage and current obtained by the data collection unit;

[0046] The analysis and judgment unit is connected to the data calculation unit, and performs comparison and judgment based on the voltage / current numerical ratio obtained by the data calculation unit to obtain the final contact resistance.

[0047] The analysis and judgment unit includes a first unit and a second unit;

[0048] The first unit is connected to the data calculation unit, and based on the voltage / current numerical ratio obtained by the data calculation unit, the absolute value of the difference between the voltage / current when the additional resistor is not connected in series and when the additional resistor is connected in series, and the value of the voltage / current when the additional resistor is not connected in series, are compared and judged preliminarily. If the difference is not greater than the first set value, the contact resistance is the voltage / current numerical ratio when the additional resistor is connected in series, and is judged as the final loop resistance; if the difference is greater than the first set value, further analysis and judgment are performed;

[0049] The second unit is connected to the data calculation unit and the first unit, and performs a secondary comparison and judgment on the absolute value of the contact resistance difference between when no additional resistance is connected in series and when additional resistance is connected in series, and the maximum value of the contact resistance obtained when additional resistance with more resistance value is connected in series; if it is not greater than the second set value, the final loop resistance is the contact resistance when the additional resistance is connected in series; if it is greater than the second set value, the final loop resistance is the maximum value of the contact resistance when additional resistance with more resistance value is connected in series.

[0050] Compared with the prior art, the beneficial effects of the present invention include at least:

[0051] 1. The present invention takes into account the decreasing degree of the difference between the grounding branch and the contact resistance, and improves the measurement accuracy of the substation loop resistance;

[0052] 2. The present invention can adjust the branch state when measuring the loop resistance through the grounding knife;

[0053] 3. The present invention can enrich the test results and reduce the errors caused by discreteness by serially inserting multiple additional resistors in the grounding branch. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a flowchart of the steps of a method for measuring loop resistance of a substation taking into account the influence of a grounding branch provided by an embodiment of the present invention;

[0055] Figure 2 It is a circuit diagram for measuring resistance of a knife switch loop provided by an embodiment of the present invention;

[0056] Figure 3 A substation loop resistance measurement model provided by an embodiment of the present invention;

[0057] Figure 4This is a model after adding an additional resistor to the ground branch provided by an embodiment of the present invention;

[0058] Figure 5 The present invention is a system module diagram of a loop resistance measurement system for a substation taking into account the influence of a grounding branch circuit provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without creative work are all within the scope of protection of the present invention.

[0060] like Figure 1 As shown, embodiment 1 of the present invention provides a loop resistance measurement method for a substation considering the influence of a grounding branch, comprising the following steps:

[0061] Step 1: Construct a loop resistance measurement model for substations;

[0062] In a further preferred but non-limiting embodiment of the present invention, step 1 specifically comprises:

[0063] based on Figure 2 The circuit diagram of the knife switch circuit resistance measurement is shown in the figure. Figure 3 The measurement model of the loop resistance shown in the figure, the contact resistance to be measured is R x , assuming the resistance of grounding knife 1 is R e1 , the grounding knife 2 resistor is R e2 , the sum of the resistance is recorded as R e .

[0064] Among them, the grounding knife increases the controllability of the grounding branch by adjusting the branch state during loop resistance measurement.

[0065] Step 2: Based on the substation loop resistance measurement model constructed in step 1, add additional resistance to the grounding branch;

[0066] In a further preferred but non-limiting embodiment of the present invention, step 2 specifically includes: adding a resistor R to the grounding branch. d , additional circuit as Figure 4 Similarly, by adding a resistor R di (R d1 , R d2 , ..., R dn ), etc., it is easy to see that there is no additional branch corresponding to R d When it is zero, it is recorded as R d0 .

[0067] Step 3: Based on the additional resistance added to the grounding branch in step 2, current is passed through the circuit to obtain a calculation formula for the contact resistance to be measured;

[0068] In a further preferred but non-limiting embodiment of the present invention, step 3 specifically comprises:

[0069] Step 3.1: Based on the substation loop resistance measurement model with additional resistance added to the grounding branch in step 2, analyze the additional branch conditions corresponding to different additional resistances, conduct current flow n+1 times on the circuit of the model, and establish n+1 equations simultaneously;

[0070] In this embodiment, the circuit is passed through current n+1 times, and the voltages at both ends of the resistor to be measured after the current is passed through are U1, U2, ..., U n+1 , the total current flowing through the circuit is I, then according to Ohm's law,

[0071] (1)

[0072] In the formula,

[0073] U represents the voltage across the contact resistance after current flows;

[0074] I represents the total current flowing through the circuit;

[0075] Represents the additional resistance R dn When , the voltage / current value when the current is passed for the n+1th time;

[0076] R e Represents the sum of the grounding knife resistance;

[0077] R di represents additional resistance;

[0078] R x is the contact resistance to be measured.

[0079] Step 3.2: Based on the equations in step 3.1, sort them out to obtain the calculation formula for the contact resistance to be measured;

[0080] Among them, different additional resistors R are connected in series di (R d0 , R d1 , R d2 , ..., R dn ) The corresponding contact resistance to be measured is R x,i (R x,1 , R x,2 , ..., R x,n ).

[0081] Yizhi, R.e When infinite, ;

[0082] When n=1, the equation has two unknowns (R x , R e ), solvable.

[0083] Arrange equations (1-1) and (1-2) and combine them to obtain

[0084] (2)

[0085] Formula (2) can be rearranged to obtain

[0086] (3)

[0087] By solving equation (3), we can obtain the additional resistance R d1 The corresponding resistance R under the second current flow is x The value of

[0088] (4)

[0089] In the formula, R x,1 The additional resistor is R d1 When , the value of the contact resistance to be measured corresponding to the second current flow;

[0090] Similarly, when n=2, combining (1) with (1-1) and (1-3) yields the additional resistance R d2 The corresponding resistance R under the third current flow is x The value of .

[0091] (5)

[0092] In the formula, R x,2 The additional resistor is R d2 When , the value of the contact resistance to be measured corresponding to the third current flow;

[0093] Finally, the general formula for solving the resistance to be determined is:

[0094] (6)

[0095] In the formula, R x,n The additional resistor is R dn When , the value of the contact resistance to be measured corresponding to the n+1th current flow;

[0096] Step 4: Based on the calculation formula of the contact resistance to be measured obtained in step 3, different contact resistances are calculated by different additional resistances, and the final loop resistance is obtained by analysis and judgment;

[0097] The step 4 comprises:

[0098] Step 4.1: Based on the calculation formula obtained in step 3, the numerical ratio of the voltage / current when no additional resistor is connected in series and when a single additional resistor is connected in series is compared with the numerical ratio of the voltage / current when no additional resistor is connected in series. If it is not greater than the set value, the final loop resistance is the numerical ratio of the voltage / current when the additional resistor is connected in series; if it is greater than the set value, further analysis and judgment are performed;

[0099] Step 4.1 includes:

[0100] Step 4.1.1: Based on the calculation formula obtained in step 3, without inserting additional resistance in series, collect electrical quantity information and calculate the voltage / current ratio when current is flowing;

[0101] Step 4.1.2: Based on the calculation formula obtained in step 3, insert an additional resistor in series through the grounding knife to collect electrical quantity information and calculate the voltage / current ratio when current is flowing;

[0102] Step 4.1.3: Based on the numerical ratio of voltage / current obtained in step 4.1.1 and step 4.1.2, make a preliminary comparison and judgment on the absolute value of the numerical difference between the voltage / current when no additional resistance is connected in series and when the additional resistance is connected in series, and the numerical value of the voltage / current when the additional resistance is not connected in series. If it is not greater than the first set value, the contact resistance is the numerical ratio of the voltage / current when the additional resistance is connected in series, and it is judged as the final loop resistance. If it is greater than the first set value, further analysis and judgment are performed.

[0103] Step 4.2: Based on the calculation formula obtained in step 3 and the preliminary judgment result obtained in step 4.1, the contact resistance when additional resistors with more resistance values ​​are connected in series is calculated, and a secondary comparison judgment is performed;

[0104] Step 4.2 includes:

[0105] Step 4.2.1: Based on the preliminary judgment result of step 4.2, if it is greater than the set value, insert additional resistors with more resistance values ​​in series through the grounding knife to collect electrical quantity information, calculate the corresponding voltage / current numerical ratio based on the formula obtained in step 3, and obtain the corresponding contact resistance;

[0106] Step 4.2.2: Based on the contact resistance obtained in step 4.1 and step 4.3.1, make a secondary comparison and judgment on the absolute value of the difference between the contact resistance without the additional resistance and the contact resistance with the additional resistance, and the maximum value of the contact resistance when the additional resistance with more resistance is connected in series; if it is not greater than the second set value, the final loop resistance is the contact resistance when the additional resistance is connected in series; if it is greater than the second set value, the final loop resistance is the maximum value of the contact resistance when the additional resistance with more resistance is connected in series.

[0107] Step 4.3: Based on the comparison results obtained in step 4.1 and step 4.2, the final loop resistance is obtained.

[0108] In a further preferred but non-limiting embodiment of the present invention, step 4 specifically comprises:

[0109] Using the general formula obtained in step 3, Calculate different , through analysis and judgment, the final loop resistance is obtained;

[0110] if , the final loop resistance is ;

[0111] if , then more resistance R is connected in series in the grounding branch d Like the three R d , at this time, if each All of them satisfy the resistance solution formula.

[0112] , the final loop resistance is ;

[0113] if ,and , the final loop resistance is ;

[0114] This resistance is the loop resistance obtained by this method.

[0115] Among them, a larger resistance R is connected in series in the grounding branch. d , can reduce the impact of discreteness, increasing the number of measurement groups can avoid errors in one or two measurements, enrich the test results, and reduce errors caused by discreteness.

[0116] Step 5: Based on the calculation results of step 4, output the loop resistance.

[0117] like Figure 5 As shown, embodiment 2 of the present invention provides a loop resistance measurement system for a substation taking into account the influence of a grounding branch, and runs a loop resistance measurement method for a substation taking into account the influence of a grounding branch. The system includes: a model building module, a preprocessing module, a contact resistance calculation formula conversion module, a contact resistance calculation result diversification module, and an output module.

[0118] In a preferred but non-limiting embodiment of the present invention,

[0119] The model building module is used to build a loop resistance measurement model for a substation;

[0120] The preprocessing module is connected to the model building module and is used to add additional resistance to the grounding branch based on the substation loop resistance measurement model built by the model building module;

[0121] The contact resistance calculation formula conversion module is connected to the preprocessing module and is used to obtain a calculation formula for the contact resistance to be measured by conducting current through the circuit based on the substation loop resistance measurement model with additional resistance obtained by the preprocessing module;

[0122] The contact resistance calculation result diversification module is connected to the contact resistance calculation formula conversion module, and based on the contact resistance calculation formula obtained by the contact resistance calculation formula conversion module, different contact resistances are calculated using different additional resistances on the grounding branch, and the calculation results are diversified to obtain the final loop resistance;

[0123] The contact resistance calculation result diversification module specifically includes: data collection unit, data calculation unit, analysis and judgment unit;

[0124] A data collection unit is connected to the preprocessing module and is used to measure the voltage and current after the analog circuit is passed through;

[0125] A data calculation unit is connected to the contact resistance calculation formula conversion module and the data collection unit, and calculates different voltage / current value ratios corresponding to different additional resistances based on the general calculation formula obtained by the contact resistance calculation formula conversion module and the voltage and current obtained by the data collection unit;

[0126] The analysis and judgment unit is connected to the data calculation unit, and performs comparison and judgment based on the voltage / current numerical ratio obtained by the data calculation unit to obtain the final contact resistance.

[0127] The analysis and judgment unit includes a first unit and a second unit;

[0128] The first unit is connected to the data calculation unit, and based on the voltage / current numerical ratio obtained by the data calculation unit, the absolute value of the difference between the voltage / current when the additional resistor is not connected in series and when the additional resistor is connected in series, and the value of the voltage / current when the additional resistor is not connected in series, are compared and judged preliminarily. If the difference is not greater than the first set value, the contact resistance is the voltage / current numerical ratio when the additional resistor is connected in series, and is judged as the final loop resistance; if the difference is greater than the first set value, further analysis and judgment are performed;

[0129] The second unit is connected to the data calculation unit and the first unit, and performs a secondary comparison and judgment on the absolute value of the contact resistance difference between when no additional resistance is connected in series and when additional resistance is connected in series, and the maximum value of the contact resistance obtained when additional resistance with more resistance value is connected in series; if it is not greater than the second set value, the final loop resistance is the contact resistance when the additional resistance is connected in series; if it is greater than the second set value, the final loop resistance is the maximum value of the contact resistance when additional resistance with more resistance value is connected in series.

[0130] The output module is connected to the contact resistance calculation result diversification module and is used to output the loop resistance obtained by the contact resistance calculation module.

[0131] Compared with the prior art, the beneficial effects of the present invention include at least:

[0132] 1. The present invention takes into account the decreasing degree of the difference between the grounding branch and the contact resistance, and improves the measurement accuracy of the substation loop resistance;

[0133] 2. The present invention can adjust the branch state when measuring the loop resistance through the grounding knife;

[0134] 3. The present invention can enrich the test results and reduce the errors caused by discreteness by serially inserting multiple additional resistors in the grounding branch.

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A loop resistance measurement method for a substation considering the influence of a grounding branch circuit, characterized in that: The following steps are involved: Step 1: Construct a loop resistance measurement model for substations; Step 2: Based on the substation loop resistance measurement model constructed in step 1, add additional resistance to the grounding branch; Step 3: Based on the additional resistance added to the grounding branch in step 2, current is passed through the circuit to obtain a calculation formula for the contact resistance to be measured; Step 4: Based on the calculation formula of the contact resistance to be measured obtained in step 3, different contact resistances are calculated by different additional resistances, and the final loop resistance is obtained by analysis and judgment; Step 4.1: Based on the calculation formula obtained in step 3, the numerical ratio of the voltage to the current when no additional resistor is connected in series and when a single additional resistor is connected in series is compared with the numerical ratio of the voltage to the current when no additional resistor is connected in series. If it is not greater than the first set value, the final loop resistance is the numerical ratio of the voltage to the current when no additional resistor is connected in series; if it is greater than the first set value, further analysis and judgment are performed; Step 4.2: Based on the calculation formula obtained in step 3 and the preliminary judgment result obtained in step 4.1, the contact resistance when additional resistors with more resistance values ​​are connected in series is calculated, and a secondary comparison judgment is performed; Step 4.3: Based on the comparison results obtained in step 4.1 and step 4.2, the final loop resistance is obtained; The step 4.1 comprises: Step 4.1.1: Based on the calculation formula obtained in step 3, without inserting additional resistance in series, collect electrical quantity information and calculate the numerical ratio of voltage to current when current is flowing; Step 4.1.2: Based on the calculation formula obtained in step 3, insert an additional resistor in series through the grounding knife to collect electrical quantity information and calculate the numerical ratio of voltage to current when current is flowing; Step 4.1.3: Based on the numerical ratio of voltage to current obtained in step 4.1.1 and step 4.1.2, the absolute value of the difference between the numerical ratio of voltage to current when no additional resistance is connected in series and when the additional resistance is connected in series and the numerical ratio of voltage to current when the additional resistance is not connected in series are compared and judged preliminarily. If it is not greater than the first set value, the contact resistance is the numerical ratio of voltage to current when the additional resistance is not connected in series and is judged as the final loop resistance; if it is greater than the first set value, further analysis and judgment are performed; The step 4.2 comprises: Step 4.2.1: Based on the preliminary judgment result of step 4.1, if it is greater than the first set value, insert additional resistors with more resistance values ​​in series through the grounding knife to collect electrical quantity information, and calculate the corresponding voltage and current numerical ratio based on the formula obtained in step 3 to obtain the corresponding contact resistance; Step 4.2.2: Based on the contact resistance obtained in step 4.1 and step 4.2.1, the absolute value of the difference between the contact resistance without the additional resistor and the contact resistance with the additional resistor is compared with the maximum value of the contact resistance when the additional resistor with more resistance is connected in series. If it is not greater than the second set value, the final loop resistance is the contact resistance when the additional resistor is not connected in series; if it is greater than the second set value, the final loop resistance is the maximum value of the contact resistance when the additional resistor with more resistance is connected in series. Step 5: Based on the calculation results of step 4, output the loop resistance.

2. The loop resistance measurement method for substation considering the influence of grounding branch according to claim 1 is characterized in that: The substation loop resistance measurement model in step 1 includes: a contact resistance to be measured and two grounding switches.

3. The loop resistance measurement method for substation considering the influence of grounding branch according to claim 2 is characterized in that: The loop resistance measurement model for substations can adjust the branch state through the ground knife during loop resistance measurement and change the resistance value of the additional resistor.

4. The loop resistance measurement method for substation considering the influence of grounding branch according to claim 1, characterized in that: The step 3 comprises: Step 3.1: Based on the substation loop resistance measurement model with additional resistance added to the grounding branch in step 2, analyze the additional branch conditions corresponding to different additional resistances, conduct current flow through the circuit of the model, and solve the simultaneous equations; Step 3.2: Based on the equations in step 3.1, sort them out to obtain the calculation formula for the contact resistance to be measured.

5. A loop resistance measurement system for a substation considering the influence of a grounding branch, running a loop resistance measurement method for a substation considering the influence of a grounding branch as claimed in any one of claims 1 to 4, comprising: Model building module, preprocessing module, contact resistance calculation formula conversion module, contact resistance calculation result diversification module, output module; A model building module for building a loop resistance measurement model for a substation; A preprocessing module, connected to the model building module, is used to add additional resistance to the grounding branch based on the substation loop resistance measurement model built by the model building module; A contact resistance calculation formula conversion module is connected to the preprocessing module and is used to obtain a calculation formula for the contact resistance to be measured by passing current through the circuit based on a substation loop resistance measurement model with additional resistance obtained by the preprocessing module; A contact resistance calculation result diversification module is connected to the contact resistance calculation formula conversion module. Based on the contact resistance calculation formula obtained by the contact resistance calculation formula conversion module, different contact resistances are calculated using different additional resistances on the grounding branch, and the calculation results are diversified to obtain the final loop resistance. The output module is connected to the contact resistance calculation result diversification module and is used for outputting the loop resistance obtained by the contact resistance calculation module.

6. The loop resistance measurement system for substation considering the influence of grounding branch according to claim 5, characterized in that: The contact resistance calculation result diversification module specifically includes: data collection unit, data calculation unit, analysis and judgment unit; A data collection unit is connected to the preprocessing module and is used to measure the voltage and current after the analog circuit is passed through; A data calculation unit is connected to the contact resistance calculation formula conversion module and the data collection unit, and calculates different voltage and current value ratios corresponding to different additional resistances based on the general calculation formula obtained by the contact resistance calculation formula conversion module and the voltage and current obtained by the data collection unit; The analysis and judgment unit is connected to the data calculation unit, and performs comparison and judgment based on the voltage and current numerical ratio obtained by the data calculation unit to obtain the final contact resistance.

7. The loop resistance measurement system for substation considering the influence of grounding branch according to claim 6, characterized in that: The analysis and judgment unit includes a first unit and a second unit; The first unit is connected to the data calculation unit, and based on the voltage-to-current numerical ratio obtained by the data calculation unit, the absolute value of the difference between the numerical ratio of the voltage and the current when the additional resistor is not connected in series and when the additional resistor is connected in series, and the numerical ratio of the voltage and the current when the additional resistor is not connected in series, are compared and judged preliminarily. If the difference is not greater than the first set value, the contact resistance is the numerical ratio of the voltage and the current when the additional resistor is not connected in series, and is judged as the final loop resistance; if the difference is greater than the first set value, further analysis and judgment are performed; The second unit is connected to the data calculation unit and the first unit, and performs secondary comparison and judgment on the absolute value of the contact resistance difference between when no additional resistor is connected in series and when the additional resistor is connected in series, and the maximum value of the contact resistance obtained when the additional resistor with more resistance value is connected in series; If it is not greater than the second set value, the final loop resistance is the contact resistance when no additional resistor is connected in series; if it is greater than the second set value, the final loop resistance is the maximum value of the contact resistance when additional resistors with greater resistance values ​​are connected in series.

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