Evaluation method for inhibiting stray current from invading along grounding grid through series resistor

Abstract

The invention discloses an evaluation method for inhibiting stray current from invading along a grounding grid by a series resistor, which comprises the following steps of: acquiring a target transformer substation and line information of the target transformer substation, and establishing an intrusion proportionality coefficient model about the stray current; deducing a stray current waveform invading the whole transformer substation based on stray current data of a neutral point of an affected transformer in the target transformer substation and an intrusion proportionality coefficient model; configuring an affected transformer neutral point suppression resistor in the target substation, and analyzing suppression efficiency; the stray current suppression effect is verified; under the conditions that stray current invasion sources are unknown and power grid information is collected as little as possible, an evaluation formula of the series resistance efficiency of the transformer neutral point is obtained; under the condition that stray current intrusion waveforms have randomness and cannot be repeated, the suppression effect after the neutral point suppression resistor is used is quantitatively evaluated through measured data, and the method can be used for verifying the precision of a neutral point resistance suppression efficiency evaluation formula.

Description

Technical Field

[0001] The invention relates to the technical field of transformer substation maintenance, in particular to an evaluation method for suppressing the intrusion of stray current along a grounding grid by using series resistance. Background Art

[0002] Subway stray current is interference generated during the operation of the subway system. It is one of the interference sources of large grounded power transformers in urban power grids. It will cause DC bias magnetic damage to the transformer, resulting in increased vibration of the transformer and reduced power quality of the power grid, inducing mechanical and electrical failures of the transformer itself, and reducing the reliability of power supply of the power grid.

[0003] Urban power grids also have strict control standards for stray current intrusion. Once DC magnetic flux is found in transformers related to subways during operation, resistors or capacitors need to be connected in series at the neutral point of the transformer to suppress stray current intrusion. Field test data show that stray current is a low-frequency bipolar current. There is currently no available evaluation and verification method for selecting the resistance value of the series resistor at the neutral point of the transformer and how to evaluate its suppression effect. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides an evaluation method for suppressing the intrusion of stray current along a grounding grid by a series resistor, which aims to solve the problems in the background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for evaluating the use of series resistors to suppress the intrusion of stray current along a grounding grid, comprising the following steps:

[0006] Step S1: collecting target substation and line information of the target substation, and establishing an intrusion proportional coefficient model for stray current;

[0007] Step S2: based on the stray current data of the neutral point of the affected transformer in the target substation and the intrusion proportional coefficient model of the stray current, deduce the stray current waveform invading the entire substation;

[0008] Step S3: configuring the neutral point suppression resistance of the affected transformer in the target substation and analyzing the suppression efficiency;

[0009] Step S4: verifying the stray current suppression effect;

[0010] The specific process of step S1 is:

[0011] Step S1.1: Collect and organize the stray current information of the target substation;

[0012] Step S1.2: Collect and organize the line information of the target substation;

[0013] Step S1.3: Assume the stray current source I S Unknown, based on the collected stray current information of the target substation and the line information of the target substation, an equivalent model of the target substation with stray current intrusion is established;

[0014] Step S1.4: Calculate the intrusion proportional coefficient Kr of the stray current according to the target substation equivalent model of stray current intrusion.

[0015] Furthermore, the target substation equivalent model of stray current intrusion includes an equivalent grounding resistance R g , Transformer winding resistance R t , Line resistance R L And the system grounding resistance R s ; The equivalent grounding resistance R g One end is grounded, the equivalent grounding resistance R g The other end is connected to the transformer winding resistor R t One end of the transformer winding resistance R t The other end is connected in parallel with multiple line resistors R L Rear connection system grounding resistance R s One end of the system grounding resistance R s The other end is grounded.

[0016] Furthermore, the transformer winding resistance R t Take the parallel value of the DC resistance of the three-phase winding of the transformer; the equivalent grounding resistance R g is the grounding resistance and shunt coefficient K of the target substation f Product; line resistance R L is the relationship between the DC resistance of each line, the system grounding resistance R s =0.1Ω, shunt coefficient K f is the shunt coefficient obtained during the known grounding measurement of the substation. When the shunt coefficient K f If unknown, the typical value is 0.75 for 220kV substation and 0.5 for 500kV substation.

[0017] Furthermore, the intrusion proportional coefficient K of the stray current is calculated according to the equivalent model of the target substation with stray current intrusion. r , expressed as:

[0018]

[0019] Furthermore, the specific process of step S2 is as follows:

[0020] Based on the equivalent model of the target substation with stray current intrusion, the stray current data of the affected transformer neutral point is monitored for no less than 24 hours continuously, and the complete data is recorded. m, the measurement accuracy is required to be better than 2% and the data time resolution is 10sps.

[0021] Furthermore, the stray current data of the affected transformer neutral point is monitored for no less than 24 hours continuously. g and transformer winding resistance R t A neutral point stray current measurement point is set between the two terminals for measurement.

[0022] Furthermore, the specific process of step S3 is as follows:

[0023] Step S3.1: Measuring the neutral point stray current and transformer winding resistance R at the target substation equivalent model of stray current intrusion t Set a suppression resistor R between N ;

[0024] Assume the insulation level of the neutral point of the affected transformer is U ins , the maximum single-phase ground fault current is I g , the margin factor is K m , configure the resistance value of the suppression resistor R N for:

[0025]

[0026] Step S3.2: Analyze the suppression resistor R N The inhibition efficiency Y;

[0027] Calculate the suppression resistor R N The intrusion proportional coefficient K of the stray current r2 :

[0028]

[0029] Suppression efficiency Y is the use of suppression resistor R N Ratio of the front and rear stray current intrusion proportional coefficients:

[0030]

[0031] Furthermore, the specific process of step S4 is as follows:

[0032] Step S4.1: Use suppression resistor R N Measure the stray current data of the neutral point of the affected transformer; specifically, use a suppression resistor to monitor the stray current data of the neutral point of the affected transformer for no less than 24 hours, and record the complete data. m2 , the measurement accuracy is required to be better than 2%, and the data time resolution is 10sps;

[0033] Step S4.2: Set the waveform of the stray current source as the waveform I of the stray current invading the entire substation Z , and estimate the suppression efficiency after using the suppression resistor;

[0034] Step S4.3: Construct an evaluation model to evaluate the suppression effect after using the suppression resistor;

[0035] Step S4.4: Verify the accuracy of the evaluation model.

[0036] Furthermore, the suppression efficiency Y2 after using the neutral point suppression resistor is the ratio of the average value of the absolute value of the stray current before and after using the suppression resistor:

[0037]

[0038] In the formula, I xm is the average value of the absolute value of the stray current before using the suppression resistor; I xm2 is the average value of the absolute value of the stray current after using the suppression resistor.

[0039] Furthermore, the specific process of Step S4.3 is as follows:

[0040] When Y2 ≤ 20%, it is determined that the suppression effect on the stray current is "excellent";

[0041] When 20% < Y2 ≤ 40%, it is determined that the suppression effect on the stray current is "good";

[0042] When 40% < Y2 ≤ 60%, it is determined that the suppression effect on the stray current is "medium";

[0043] When Y2 > 60%, it is determined that the suppression effect on the stray current is "poor";

[0044] The specific process of Step S4.4 is as follows:

[0045] The first case: Based on Y2, when the deviation of Y ≤ 25%Y2, it is determined that the accuracy of the evaluation model is "high";

[0046] The second case: When the deviation of Y > 100%Y2, it is determined that the accuracy of the evaluation model is "poor";

[0047] When other cases except the first case and the second case occur, it is determined that the accuracy of the evaluation model is "general".

[0048] Compared with the existing technology, the present invention has the following beneficial effects: the present invention obtains the evaluation formula of the neutral point series resistance efficiency of the transformer under the condition of unknown stray current intrusion source and collecting as little grid information as possible; when the stray current intrusion waveform is random and non-repeatable, the suppression effect after using the neutral point suppression resistor is quantitatively evaluated by the measured data, and can be used to verify the accuracy of the neutral point resistance suppression efficiency evaluation formula. The present invention can control the intrusion stray current level within 20%, and the error of the related evaluation formula can also be controlled within the error range of 25%. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a schematic diagram of the equivalent model structure of the target substation for stray current intrusion of the present invention.

[0050] Figure 2 This is a schematic diagram of the equivalent model structure of the target substation after adding suppression resistance according to the present invention. DETAILED DESCRIPTION

[0051] The present invention provides a technical solution: a method for evaluating the use of series resistors to suppress the intrusion of stray currents along a grounding grid, comprising the following steps:

[0052] Step S1: Collect the target substation and the line information of the target substation, and establish an intrusion proportional coefficient model for stray current.

[0053] Step S1.1: Collect and organize the stray current information of the target substation.

[0054] The stray current modeling information includes the transformer type of the target substation (single-phase transformer, autotransformer, three-winding transformer), the DC resistance of the windings of the transformer at a voltage level of 110kV and above in the target substation, the busbar connection method of the target substation at a voltage level of 110kV and above, and the neutral point connection method of the transformer at a voltage level of 110kV and above in the target substation.

[0055] The busbar and neutral point in the target substation are attributed to node information, the transformer windings and lines in the target substation are attributed to branch information, and the topological connection relationship between the branches of the lines and the nodes of the lines in the target substation is attributed to topological information. The node, branch and topological element models of the target substation are constructed, as shown in Table 1.

[0056] Table 1 Node, branch and topology element models of target substation

[0057]

[0058]

[0059] Step S1.2: Collect and organize the line information of the target substation.

[0060] The line information in the target substation includes the topological relationship between the lines and busbars of the target substation with a voltage level of 110 kV and above, as well as the number of line loops, line length, conductor and lightning protection line cross-sectional areas. The node, branch and topological model of the line in the target substation are constructed, as shown in Table 2.

[0061] Table 2 Nodes, branches and topology models of the lines in the target substation

[0062]

[0063] Step S1.3: Assume the stray current source I S Unknown, an equivalent model of the target substation with stray current intrusion is established based on the collected stray current information of the target substation and the line information of the target substation.

[0064] like Figure 1 As shown in the figure, the target substation equivalent model of stray current intrusion includes the equivalent grounding resistance R g , Transformer winding resistance R t , Line resistance R L And the system grounding resistance R s ; The equivalent grounding resistance R g One end is grounded, the equivalent grounding resistance R g The other end is connected to the transformer winding resistor R t One end of the transformer winding resistance R t The other end is connected in parallel with multiple line resistors R L Rear connection system grounding resistance R s One end of the system grounding resistance R s The other end is grounded.

[0065] Among them, the transformer winding resistance R t Take the parallel value of the DC resistance of the three-phase winding of the transformer; the equivalent grounding resistance R g is the grounding resistance and shunt coefficient K of the target substation f Product; line resistance R L is the relationship between the DC resistance of each line, the system grounding resistance R s =0.1Ω. Shunt coefficient K f is the shunt coefficient obtained during the known grounding measurement of the substation. If the shunt coefficient K f If unknown, the typical value is 0.75 for 220kV substation and 0.5 for 500kV substation.

[0066] Step S1.4: Calculate the intrusion proportional coefficient K of stray current according to the target substation equivalent model of stray current intrusion r :

[0067]

[0068] Step S2: Based on the stray current data of the neutral point of the affected transformer in the target substation and the intrusion proportional coefficient model of the stray current, the stray current waveform invading the entire substation is deduced.

[0069] based on Figure 1 , monitor the stray current data of the affected transformer neutral point for no less than 24 hours continuously, and record the complete data. m The measurement accuracy is required to be better than 2% and the data time resolution is 10sps.

[0070] Among them, the stray current data monitoring of the neutral point of the affected transformer is carried out for no less than 24 hours continuously. g and transformer winding resistance R t A neutral point stray current measurement point is set between the two terminals for measurement.

[0071] Step S3: configure the neutral point suppression resistance of the affected transformer in the target substation and analyze the suppression efficiency.

[0072] Step S3.1: Measuring the neutral point stray current and transformer winding resistance R at the target substation equivalent model of stray current intrusion t Set a suppression resistor R between N ,like Figure 2 shown.

[0073] Configure suppression resistor R N The resistance value;

[0074] Assume the insulation level of the neutral point of the affected transformer is U ins , the maximum single-phase ground fault current is I g , the margin factor is K m , configure the resistance value of the suppression resistor R N for:

[0075]

[0076] Step S3.2: Analyze the suppression resistor R N The inhibition efficiency Y.

[0077] Calculate the suppression resistor R N The intrusion proportional coefficient K of the stray current r2 :

[0078]

[0079] Suppression efficiency Y is the use of suppression resistor R NRatio of the proportion coefficients of the forward and backward stray current intrusion:

[0080]

[0081] Step S4: Verify the suppression effect of the stray current.

[0082] Step S4.1: Use the suppression resistor R N Measure the stray current data of the neutral point of the affected transformer; specifically, use the suppression resistor to conduct continuous stray current data monitoring for no less than 24 hours on the neutral point of the affected transformer, and record the complete data I m2 . It is required that the measurement accuracy is better than 2%, and the data time resolution is 10 sps.

[0083] Step S4.2: Assume that the waveform of the stray current source is the stray current waveform I invading the entire substation Z , and estimate the suppression efficiency after using the suppression resistor.

[0084] Among them, the suppression efficiency Y2 after using the neutral point suppression resistor is the ratio of the average value of the absolute values of the stray current before and after using the suppression resistor:

[0085]

[0086] In the formula, I xm is the average value of the absolute value of the stray current before using the suppression resistor; I xm2 is the average value of the absolute value of the stray current after using the suppression resistor.

[0087] Step S4.3: Construct an evaluation model to evaluate the suppression effect after using the suppression resistor.

[0088] If Y2 ≤ 20%, it is determined that the suppression effect on the stray current is "excellent".

[0089] If 20% < Y2 ≤ 40%, it is determined that the suppression effect on the stray current is "good".

[0090] If 40% < Y2 ≤ 60%, it is determined that the suppression effect on the stray current is "medium".

[0091] If Y2 > 60%, it is determined that the suppression effect on the stray current is "poor".

[0092] Step S4.4: Verify the accuracy of the evaluation model.

[0093] The first case: Based on Y2, if the deviation of Y ≤ 25%Y2, it is determined that the accuracy of the evaluation model is "high".

[0094] The second case: If the deviation of Y > 100%Y2, it is determined that the accuracy of the evaluation model is "poor".

[0095] When situations other than the first and second situations occur, the accuracy of the evaluation model is judged to be "average".

[0096] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for evaluating the use of series resistors to suppress the intrusion of stray current along a grounding grid, characterized in that: It includes the following steps: Step S1: Collect the information of the target substation and the lines of the target substation, and establish an invasion ratio coefficient model for stray current; Step S2: Based on the measured stray current data of the neutral point of the affected transformer in the target substation and the invasion ratio coefficient model of stray current, deduce the waveform of the stray current invading the entire substation; Step S3: Configure the suppression resistance of the neutral point of the affected transformer in the target substation and analyze the suppression efficiency; Step S4: Verify the suppression effect of the stray current; The specific process of Step S1 is as follows: Step S1.1: Collect and sort out the stray current information of the target substation; Step S1.2: Collect and sort out the line information of the target substation; Step S1.3: Assume the stray current source I S Unknown, based on the collected stray current information of the target substation and the line information of the target substation, an equivalent model of the target substation with stray current intrusion is established; Step S1.4: Calculate the invasion ratio coefficient Kr of the stray current according to the equivalent model of the target substation invaded by the stray current.

2. The method for evaluating the use of series resistors to suppress the intrusion of stray current along the grounding grid according to claim 1, characterized in that: The target substation equivalent model of stray current intrusion includes an equivalent grounding resistance R g , Transformer winding resistance R t , Line resistance R L And the system grounding resistance R s ; The equivalent grounding resistance R g One end is grounded, the equivalent grounding resistance R g The other end is connected to the transformer winding resistor R t One end of the transformer winding resistance R t The other end is connected in parallel with multiple line resistors R L Rear connection system grounding resistance R s One end of the system grounding resistance R s The other end is grounded.

3. The evaluation method for suppressing stray current intrusion along the grounding grid by series resistance according to claim 2 is characterized in that: the transformer Winding resistance R t Take the parallel value of the DC resistance of the three-phase winding of the transformer; the equivalent grounding resistance R g is the grounding resistance and shunt coefficient K of the target substation f Product; line resistance R L is the relationship between the DC resistance of each line, the system grounding resistance R s =0.1Ω, shunt coefficient K f is the shunt coefficient obtained during the known grounding measurement of the substation. When the shunt coefficient K f If unknown, the typical value is 0.75 for 220kV substation and 0.5 for 500kV substation.

4. The method for evaluating the use of series resistors to suppress the intrusion of stray current along the grounding grid according to claim 3, characterized in that: Calculate the intrusion proportional coefficient K of stray current according to the equivalent model of the target substation where stray current is intruded r , expressed as:

5. The method for evaluating the use of series resistors to suppress the intrusion of stray current along the grounding grid according to claim 4, characterized in that: The specific process of Step S2 is as follows: Based on the equivalent model of the target substation with stray current intrusion, the stray current data of the affected transformer neutral point is monitored for no less than 24 hours continuously, and the complete data is recorded. m , the measurement accuracy is required to be better than 2% and the data time resolution is 10sps.

6. The method for evaluating the use of series resistors to suppress the intrusion of stray current along the grounding grid according to claim 5, characterized in that: Conduct stray current data monitoring on the neutral point of the affected transformer for no less than 24 hours continuously. g and transformer winding resistance R t A neutral point stray current measurement point is set between the two terminals for measurement.

7. The method for evaluating the use of series resistors to suppress the intrusion of stray current along the grounding grid according to claim 6, characterized in that: The specific process of Step S3 is as follows: Step S3.1: Measuring the neutral point stray current and transformer winding resistance R at the target substation equivalent model of stray current intrusion t Set a suppression resistor R between N ; Suppose The neutral point insulation level of the affected transformer is U ins , the maximum single-phase ground fault current is I g , the margin factor is K m , configure the suppression resistor value R N for: Step S3.2: Analyze the suppression resistor R N The inhibition efficiency Y; Calculate the suppression resistor R N The intrusion proportional coefficient K of the stray current r2 : Suppression efficiency Y is the use of suppression resistor R N Ratio of the front and rear stray current intrusion proportional coefficients:

8. The method for evaluating the use of series resistors to suppress the intrusion of stray current along the grounding grid according to claim 7, characterized in that: The specific process of Step S4 is as follows: Step S4.1: Use suppression resistor R N Measure the stray current data of the neutral point of the affected transformer; specifically, use a suppression resistor to monitor the stray current data of the neutral point of the affected transformer for no less than 24 hours, and record the complete data. m2 , the measurement accuracy is required to be better than 2%, and the data time resolution is 10sps; Step S4.2: Assume that the stray current source waveform is the stray current waveform I that invades the entire substation Z , estimate the suppression efficiency after using suppression resistor; Step S4.3: Build an evaluation model to evaluate the suppression effect after using the suppression resistance; Step S4.4: Verify the accuracy of the evaluation model.

9. The method for evaluating the use of series resistors to suppress the intrusion of stray current along the grounding grid according to claim 8, characterized in that: The suppression efficiency Y2 after using the neutral point suppression resistance is the ratio of the average value of the absolute values of the stray current before and after using the suppression resistance: In the formula, I xm is the average absolute value of the stray current before using the suppression resistor; I xm2 It is the absolute average value of stray current after using suppression resistor.

10. The method for evaluating the use of series resistors to suppress the intrusion of stray current along the grounding grid according to claim 9, characterized in that: The specific process of Step S4.3 is as follows: When Y2 ≤ 20%, it is determined that the suppression effect on the stray current is "excellent"; When 20% < Y2 ≤ 40%, it is determined that the suppression effect on the stray current is "good"; When 40% < Y2 ≤ 60%, it is determined that the suppression effect on the stray current is "medium"; When Y2 > 60%, it is determined that the suppression effect on the stray current is "poor"; The specific process of Step S4.4 is as follows: The first case: Taking Y2 as the reference, when the deviation of Y ≤ 25%Y2, it is determined that the accuracy of the evaluation model is "high"; The second case: When the deviation of Y > 100%Y2, it is determined that the accuracy of the evaluation model is "poor"; When other cases except the first case and the second case occur, it is determined that the accuracy of the evaluation model is "general".

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