Method and device for selecting resistance value of damping resistor of preset arc suppression coil

Abstract

The invention provides a resistance value selection method for a damping resistor of a preset arc suppression coil, and the method comprises the following steps: obtaining the detuning degree v, the capacitance current IC, the neutral point displacement voltage # imgabs0 # of a resonance grounding system through a power monitoring device, and obtaining the resistance value of the damping resistor of the preset arc suppression coil; calculating the damping rate dd of the transition resistor of the resonance grounding system according to the rated phase voltage # imgabs1 # of the system, the capacitance current IC and the target resistance value of the transition resistor Rd, and calculating the asymmetry degree rho of the resonance grounding system according to the rated phase voltage # imgabs2 # of the system and the neutral point displacement voltage # imgabs3 # of the system; determining a resistance value range of parallel damping according to a parallel damping range calculation formula, and determining a resistance value range of series damping according to a series damping range calculation formula; and randomly selecting one resistance value from the resistance value range of the parallel damping as the resistance value of the parallel damping, and randomly selecting one resistance value from the resistance value range of the series damping as the resistance value of the series damping.

Description

Technical Field

[0001] The invention relates to the technical field of power distribution network, and in particular to a method and a device for selecting the resistance value of a pre-adjustable arc suppression coil damping resistor. Background Art

[0002] In order to limit the ground fault current, my country's medium-voltage distribution network often uses resonant grounding to compensate for the system's ground capacitance current. Among them, the pre-adjusted arc suppression coil is one of the commonly used arc suppression coil configuration methods. When the system is operating normally, the arc suppression coil is tuned to the vicinity of the resonance point according to the measured capacitance current, and the damping resistor is used to suppress the series resonance; when a single-phase grounding fault occurs, the damping resistor is quickly removed, the arc suppression coil is put into use to extinguish the arc, and the line selection device is started to identify the fault line. At present, in order to ensure the reliability of power supply, most resonant grounding systems generally set the damping resistor based on the principle of "effectively suppressing series resonance and preventing the line selection device from malfunctioning", and suppress the neutral point displacement voltage at a low level; in some areas where high-resistance grounding faults occur frequently, the existing damping resistor selection strategy is likely to cause the neutral point displacement voltage to be lower than the arc extinguishing and line selection device start threshold during single-phase grounding faults, so that the grounding arc continues to burn the fault point line insulation, reducing the arc extinguishing efficiency. On the other hand, the damping resistor connected to the neutral point branch cannot be removed in time, and it is easy to heat up and burn if it is subjected to the neutral point current for a long time.

[0003] In order to balance the normal operation reliability and high-resistance fault perception sensitivity of the resonant grounding system, many scholars have conducted relevant research, including: using nonlinear resistors whose resistance changes dynamically with the displacement voltage to replace the traditional fixed-resistance damping resistors, the system presents a high-resistance state during normal operation, suppresses series resonance, and automatically transitions to a low-resistance state when single-phase grounding occurs, raising the displacement voltage to facilitate the arc extinguishing device to be put into use, but its volt-ampere characteristic setting relies on multiple field tests, which is relatively cumbersome; re-adjusting the zero-sequence voltage starting value, and reducing the zero-sequence voltage starting value as much as possible on the basis of avoiding the maximum value of the neutral point displacement voltage under various operating modes, which can increase the theoretical transition resistance capability to 12kΩ, but in high-capacitance current systems, it is necessary to add a main transformer and migrate some lines to other busbars to achieve the above goals; in response to the problem of high protection rejection rate during high-resistance grounding faults, parameter identification, time-frequency domain analysis, data-driven and other algorithms are added for high-resistance grounding detection, but such methods require additional hardware equipment to be installed, and the collected transient signals are easily interfered by noise. The identification method relies on training samples or specific distribution network structure parameters, and its versatility and economy are not high.

[0004] In order to solve the above problems, people have been seeking an ideal technical solution. Summary of the invention

[0005] The purpose of the present invention is to address the deficiencies in the prior art and to provide a method and device for selecting the resistance of a pre-adjusted arc suppression coil damping resistor. The method and device only require the use of existing conventional online monitoring data of the arc suppression coil to complete the calculation, without the need to connect to other detection equipment, and has strong feasibility and economy.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: a method for selecting the resistance value of a pre-adjustable arc suppression coil damping resistor, comprising the following steps:

[0007] Use power monitoring devices to obtain the detuning degree v and capacitive current I of the resonant grounding system C , Neutral point displacement voltage According to the system rated phase voltage U Φ , Capacitor current I C And the transition resistance R d The target resistance value is used to calculate the transition resistance damping rate d of the resonant grounding system. d , according to the system rated phase voltage U Φ And the neutral point displacement voltage Calculate the asymmetry ρ of the resonant grounding system;

[0008] Among them, the transition resistance damping rate d d The calculation formula is:

[0009] The calculation formula of asymmetry ρ is:

[0010] The resistance range of parallel damping is determined according to the parallel damping range calculation formula, and the resistance range of series damping is determined according to the series damping range calculation formula;

[0011] Among them, the calculation formula for parallel damping range is:

[0012]

[0013] The series damping range calculation formula is:

[0014]

[0015] Among them, R p is parallel damping, R s is the series damping, k s is the zero-sequence voltage alarm threshold percentage,

[0016] A resistance value is arbitrarily selected from the resistance range of the parallel damping as the resistance value of the parallel damping, and a resistance value is arbitrarily selected from the resistance range of the series damping as the resistance value of the series damping.

[0017] Furthermore, the steps for obtaining the parallel damping range calculation formula are as follows:

[0018] Step 1, calculating the critical resistance value of the parallel damping resistor when the resonant grounding system is in normal operation;

[0019] Step 1.1, obtaining a series resonant equivalent circuit when the resonant grounding system is operating normally;

[0020] Step 1.2, calculate the neutral point displacement voltage when the parallel damping resistor is connected;

[0021] Step 1.3, making the effective value of the neutral point displacement voltage not higher than the zero-sequence voltage alarm threshold, and calculating the upper limit of the parallel damping resistance threshold that meets the neutral point displacement voltage requirement;

[0022] Step 2, calculating the critical resistance value of the damping resistor for improving the high-resistance grounding sensing capability;

[0023] Step 2.1, obtaining a series resonant equivalent circuit when a single-phase grounding fault occurs in the resonant grounding system;

[0024] Step 2.2, calculate the neutral point displacement voltage percentage when the parallel damping resistor is connected;

[0025] Step 2.3, making the neutral point displacement voltage percentage not lower than the neutral point displacement voltage percentage of the zero-sequence voltage alarm, and calculating the lower limit of the parallel damping resistance threshold that meets the neutral point displacement voltage percentage requirement;

[0026] Step 3: Obtain a parallel damping range calculation formula according to the parallel damping resistance threshold lower limit and the parallel damping resistance threshold upper limit.

[0027] Furthermore, the steps for obtaining the series damping range calculation formula are as follows:

[0028] Step 4, calculating the critical resistance value of the series damping resistor when the resonant grounding system is operating normally;

[0029] Step 4.1, let the admittance of the series damping resistor and the parallel damping resistor be equal, and we get:

[0030]

[0031] Step 4.2, respectively set the imaginary part and the real part of the left and right sides of the equation to be equal, and obtain the corresponding relationship between the series resistance and the parallel resistance;

[0032] Step 4.3, substitute the corresponding relationship between the series resistance and the parallel resistance into the calculation formula of the damping rate added by the series damping resistance to obtain the damping rate added by the series damping resistance d s ;

[0033] Step 4.4, add the damping rate d of the series damping resistor s Substitute it into the upper limit of the parallel damping resistance threshold to obtain the lower limit of the series damping resistance value that satisfies the neutral point displacement voltage not exceeding the limit during normal operation;

[0034] Step 5, converting the lower limit of the parallel damping resistance threshold obtained in step 2 into the series damping resistance, and calculating the upper limit of the series damping resistance value;

[0035] Step 6: According to the lower limit of the series damping resistance and the upper limit of the series damping resistance, a calculation formula for the parallel damping range is obtained.

[0036] Further, when a resistance value is arbitrarily selected from the resistance value range of the parallel damping as the resistance value of the parallel damping, the midpoint of the resistance value range of the parallel damping is selected as the resistance value of the parallel damping;

[0037] Specifically, the resistance of parallel damping is:

[0038]

[0039] When any resistance value is selected from the resistance range of the series damping as the resistance value of the series damping, the midpoint of the resistance range of the series damping is selected as the resistance value of the series damping.

[0040] Specifically, the resistance of the series damping is:

[0041]

[0042] A second aspect of the present invention provides a resistance value selection device for a pre-adjustable arc suppression coil damping resistor, comprising:

[0043] Power monitoring device, used to obtain the detuning degree v and capacitive current I of the resonant grounding system C , Neutral point displacement voltage

[0044] Parameter calculation module, used to calculate the phase voltage according to the system rated phase voltage U Φ , Capacitor current I C And the transition resistance R d The target resistance value is used to calculate the transition resistance damping rate d of the resonant grounding system. d , according to the system rated phase voltage U Φ And the neutral point displacement voltage Calculate the asymmetry ρ of the resonant grounding system;

[0045] Among them, the transition resistance damping rate d d The calculation formula is:

[0046] The calculation formula of asymmetry ρ is:

[0047] A resistance range calculation module, used to determine the resistance range of parallel damping according to the parallel damping range calculation formula, and to determine the resistance range of series damping according to the series damping range calculation formula;

[0048] Among them, the calculation formula for parallel damping range is:

[0049]

[0050] The series damping range calculation formula is:

[0051]

[0052] Among them, R p is parallel damping, R s is the series damping, k s is the zero-sequence voltage alarm threshold percentage,

[0053] The resistance determination module selects any resistance value from the resistance range of the parallel damping as the resistance value of the parallel damping, and selects any resistance value from the resistance range of the series damping as the resistance value of the series damping.

[0054] Furthermore, the resistance of the parallel damping is:

[0055]

[0056] The resistance of the series damper is:

[0057]

[0058] Compared with the prior art, the present invention has outstanding substantive features and significant progress. Specifically, the damping resistance selection method proposed in the present invention can be realized by only using conventional detection devices to obtain conventional online monitoring data of arc suppression coils such as capacitor current and detuning degree, without the need to connect other equipment additionally, and the transformation cost is low; the optimized and adjusted damping resistance can not only effectively suppress series resonance during normal system operation, but also does not hinder the neutral point displacement voltage from smoothly crossing the limit under high-resistance grounding conditions, and can improve the system's ability to withstand transition resistance, effectively solving problems such as fault handling delays caused by protection refusal; it can improve the high-resistance grounding perception sensitivity and reduce the false alarm and missed alarm rates of grounding signals while ensuring the reliability of normal system operation, and has certain feasibility and engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 It is a flow chart of the resistance value selection method described in Example 1 of the present invention.

[0060] Figure 2It is a schematic diagram of the series resonant equivalent circuit of the normal operation of the resonant grounding system.

[0061] Figure 3 It is a schematic diagram of a simplified circuit when a single-phase grounding fault occurs in a resonant grounding system.

[0062] Figure 4 It is a schematic diagram for verifying the resonant grounding system of 8 outgoing lines in the embodiment.

[0063] Figure 5 It is a simulation waveform diagram for verifying the bus zero-sequence voltage and fault branch current of the embodiment.

[0064] Figure 6 It is a simulation waveform diagram of the neutral point displacement voltage corresponding to the midpoint value of the upper and lower limits of the damping resistance. DETAILED DESCRIPTION

[0065] The existing damping resistor selection principle is generally to increase the damping rate corresponding to the damping resistor as much as possible to suppress the series resonance of normal operation, which can only achieve protection without false operation; but in the case of a high-resistance grounding fault, an excessively high damping rate may limit the neutral point displacement voltage to below the zero-sequence voltage alarm threshold, resulting in the grounding signal cannot be sent in time, which is not conducive to the commissioning of arc extinguishing and line selection devices.

[0066] In order to ensure that the system has a certain ability to withstand transition resistance under the premise of normal operation and protection without false operation, considering the influencing parameters of the reasonable resistance range of the arc suppression coil damping resistance of high-resistance grounding fault, this application proposes a method based on the system asymmetry ρ, system capacitance current I C , detuning degree v, transition resistance damping rate d d A total of 4 system parameters are used to calculate the critical value of the damping resistor under normal operating conditions and the critical resistance value of the damping resistor for improving the high-resistance grounding sensing ability, obtain the critical upper and lower resistance ranges, and then select the damping resistor value within the critical upper and lower resistance ranges.

[0067] The technical solution of the present invention is further described in detail below through specific implementation methods.

[0068] Example 1

[0069] This embodiment provides a method for selecting the resistance value of the pre-adjustable arc suppression coil damping resistor, such as Figure 1 As shown, the following steps are included:

[0070] Use power monitoring devices to obtain the detuning degree v and capacitive current I of the resonant grounding system C , Neutral point displacement voltage According to the system rated phase voltage U Φ , Capacitor current I C And the transition resistance Rd The target resistance value is used to calculate the transition resistance damping rate d of the resonant grounding system. d , according to the system rated phase voltage U Φ And the neutral point displacement voltage Calculate the asymmetry ρ of the resonant grounding system;

[0071] Among them, the transition resistance damping rate d d The calculation formula is:

[0072] For example, the transition resistor R d If the target resistance is 1000Ω, substitute 1000Ω into the above formula for calculation.

[0073] The calculation formula of asymmetry ρ is:

[0074] The resistance range of parallel damping is determined according to the parallel damping range calculation formula, and the resistance range of series damping is determined according to the series damping range calculation formula;

[0075] Among them, the calculation formula for parallel damping range is:

[0076]

[0077] The series damping range calculation formula is:

[0078]

[0079] Among them, R p is parallel damping, R s is the series damping, k s is the zero-sequence voltage alarm threshold percentage,

[0080] A resistance value is arbitrarily selected from the resistance range of the parallel damping as the resistance value of the parallel damping, and a resistance value is arbitrarily selected from the resistance range of the series damping as the resistance value of the series damping.

[0081] In actual selection, too large parallel damping or too small series damping will not suppress resonance enough, and resonance overvoltage is prone to occur during normal operation; too small parallel damping or too large series damping will make it difficult to raise the neutral point displacement voltage to the alarm threshold during a single-phase grounding fault, resulting in the system being unable to sense the grounding fault. When the selected parallel damping and series damping resistance values ​​are both within the aforementioned resistance range, the transition resistance capacity can be improved under the premise that the system normal operation protection does not malfunction.

[0082] Specifically, the steps for obtaining the parallel damping range calculation formula are as follows:

[0083] Step 1, calculating the critical resistance value of the parallel damping resistor for normal operation of the resonant grounding system;

[0084] Step 1.1, obtain the equivalent circuit of the normal operation series resonance of the resonant grounding system, such as Figure 2 As shown;

[0085] In the figure, is the asymmetric voltage of the system, C is the total capacitance of the system to ground; when switch K1 is closed, the system adopts the arc suppression coil parallel damping resistor connection mode, L p With R p are the corresponding arc suppression coil inductance and parallel damping resistor values ​​respectively; when switch K2 is closed, the system adopts the arc suppression coil series damping resistor connection mode, L s With R s are the corresponding arc suppression coil inductance and series damping resistance, is the neutral point displacement voltage.

[0086] Step 1.2, calculate the neutral point displacement voltage when the parallel damping resistor is connected

[0087]

[0088] Where: ω is the angular frequency, its value is 2πf; U 00 is the asymmetric voltage of the system during normal operation, and its value is: U 00 =ρU Φ ;

[0089] v is the detuning degree of the system, and the corresponding formula is:

[0090]

[0091] d is the damping rate added by the parallel damping resistor, and the corresponding formula is:

[0092]

[0093] Where: U Φ is the system rated phase voltage, I C is the capacitive current of the system, and its value is: I C =U Φ ωC.

[0094] Step 1.3: To prevent the system from sending a ground alarm signal by mistake during normal operation, the effective value of the neutral point displacement voltage should be ensured not to be higher than the zero-sequence voltage alarm threshold, that is:

[0095]

[0096] Where: k sIt is the zero-sequence voltage alarm threshold percentage, which is generally set to 15%;

[0097] During normal operation, the parallel damping resistance that meets the neutral point displacement voltage requirement is:

[0098]

[0099]

[0100] Step 2, calculating the critical resistance value of the damping resistor for improving the high-resistance grounding sensing capability;

[0101] Step 2.1, when a single-phase grounding fault occurs in the resonant grounding system, the system asymmetry increases significantly, and the inductance of the arc suppression coil and the capacitance of the line to the ground are converted from series resonance to parallel resonance; when it is detected that the neutral point displacement voltage rises above the zero-sequence voltage setting threshold, the insulation monitoring device sends a grounding fault signal, the damping resistor is quickly cut off, and the pre-tuned arc suppression coil is put into use to compensate for the capacitive current at the fault point.

[0102] The simplified circuit when a single-phase grounding fault occurs in a resonant grounding system is as follows: Figure 3 As shown, is the system phase voltage; O is the system neutral point; C A , C B , C C are the capacitance of each phase to ground, and the total capacitance of the system to ground is C; L is the inductance of the arc suppression coil; R is the parallel damping resistor, R d is the transition resistance of phase A to ground.

[0103] Step 2.2, according to Figure 3 The neutral point displacement voltage is obtained as:

[0104]

[0105]

[0106] Where: d d The damping rate added to the transition resistor.

[0107] Then the neutral point displacement voltage percentage λ is:

[0108]

[0109] From the above formula, we can know that the neutral point displacement voltage percentage during a single-phase grounding fault is given by For It consists of two parts, It is caused by the original asymmetry of the line and is expressed in exponential form as:

[0110]

[0111] tanα=-(d+d d ) / v (13)

[0112] and Caused by the transition resistance of the grounding branch, it is expressed in exponential form as:

[0113]

[0114] tanβ=v / (d+d d ) (15)

[0115] Since tanαtanβ=-1, and The two parts are perpendicular to each other, so we get:

[0116]

[0117] Step 2.3: Make sure the neutral point displacement voltage percentage is not lower than the zero-sequence voltage alarm threshold percentage k s ,get:

[0118]

[0119] Substituting equation (4) and equation (5) into equation (16), the reasonable resistance range of the parallel damping resistor is calculated as:

[0120]

[0121] To simplify the formula, let

[0122] That is, we get: R p ≥U Φ / QI C ;

[0123] Step 3, according to the lower limit of the parallel damping resistance threshold and the upper limit of the parallel damping resistance threshold, obtain the parallel damping range calculation formula:

[0124]

[0125] Furthermore, the steps for obtaining the series damping range calculation formula are as follows:

[0126] Step 4, calculating the critical resistance value of the series damping resistor when the resonant grounding system is operating normally;

[0127] Step 4.1, when using a series damping resistor, its impedance can be converted to that of a parallel damping resistor, such as Figure 2 As shown; let the admittance of the series damping resistor and the parallel damping resistor be equal, we can get:

[0128]

[0129] Step 4.2, let the imaginary parts of both sides of the equation be equal, and solve:

[0130]

[0131] Taking the system with capacitor current of 200A, overcompensation of 5%, and series damping of 10Ω as an example, the second term of the above formula is 3.46, which is much smaller than the first term of 30.31. To simplify the calculation, the second term of the above formula can be ignored, and it is assumed that the inductance value of the arc suppression coil converted to the series damping circuit is approximately the same as that of the parallel damping, that is:

[0132] L p ≈L s =L (21)

[0133] Let the real parts of both sides of the equation be equal, and solve for the corresponding relationship between series resistance and parallel resistance:

[0134]

[0135] Step 4.3, substitute the corresponding relationship between the series resistance and the parallel resistance into formula (8) to obtain the damping rate d added by the series damping resistance s for:

[0136]

[0137] Substituting formula (23) into formula (8), we can obtain:

[0138]

[0139] The lower limit of the series damping resistance value to ensure that the neutral point displacement voltage does not exceed the limit during normal operation is obtained:

[0140]

[0141] Step 5: convert the obtained critical resistance of the parallel damping resistor for improving the high-resistance grounding sensing capability into a series damping resistor, and solve the upper limit of the series damping resistance value to be:

[0142]

[0143] Step 6: According to the lower limit of the series damping resistance and the upper limit of the series damping resistance, the parallel damping range calculation formula is obtained:

[0144]

[0145] Further, when a resistance value is arbitrarily selected from the resistance value range of the parallel damping as the resistance value of the parallel damping, the midpoint of the resistance value range of the parallel damping is selected as the resistance value of the parallel damping;

[0146] Right now

[0147] When any resistance value is selected from the resistance range of the series damping as the resistance value of the series damping, the midpoint of the resistance range of the series damping is selected as the resistance value of the series damping.

[0148] Right now

[0149] It can be understood that when the selected resistance of the parallel damping is at the midpoint of its resistance range and the resistance of the series damping is at the midpoint of its resistance range, a certain margin can be left for changes in detuning caused by arc suppression coil gear adjustment, changes in capacitive current caused by line inversion, etc.

[0150] The excessively high damping rate corresponding to the arc suppression coil damping resistance is the main reason for the insufficient transition resistance resistance of the resonant grounding system. Taking the neutral point displacement voltage not exceeding the limit during normal operation and the over-limit alarm during high-resistance grounding as boundary conditions, the critical resistance value of the damping resistor is calculated, and the damping resistor can be adjusted to the midpoint of the upper and lower limits of the critical resistance value to improve the system's transition resistance resistance.

[0151] It should be noted that the capacitive current of the distribution network in large and medium-sized cities with cable lines as the main structure is relatively high, resulting in a narrow range of damping resistance values, and as the transition resistance increases, the range will be further tightened. At this time, a parallel damping resistor with a relatively wide resistance range can be used to reduce the probability of protection misoperation and refusal caused by changes in system parameters such as line inversion and detuning.

[0152] Verification Example

[0153] The measured capacitive current of a 110kV / 10.5kV system is 150A, the line asymmetry is 1.45%, and a pre-adjusted arc suppression coil with an overcompensation degree of 4% is used, with a 15Ω series damping resistor. During normal operation, the system zero-sequence voltage is 234V, which is lower than the single-phase grounding alarm threshold of 15% phase voltage; but after calculation, its transition resistance limit is only 665.98Ω. In order to improve the high-resistance grounding perception sensitivity of the system and take into account the normal operation reliability, the damping resistance calculation method proposed in this paper is used to optimize it.

[0154] In the MATLAB / Simulink simulation software, an 8-line resonant grounding system is constructed, such as Figure 4 As shown:

[0155] In the model, 110kV AC power source is used to replace the upstream 110kV power supply line; considering the line voltage loss, the main transformer is set as a 110kV / 10.5kV Y-△ type transformer, and the rated phase voltage effective value of the secondary side is 6062V. If the grounding alarm threshold is set to 15% of the phase voltage, the corresponding neutral point displacement voltage should be 909V; to lead out the neutral point, a Z-type grounding transformer is connected to the secondary side of the main transformer, and the arc suppression coil and the damping resistor are connected, where K1 is closed to represent the parallel damping resistor, and K2 is closed to represent the series damping resistor; to simulate the high capacitance current characteristics of urban distribution lines, L1~L6 are set as cable lines, L7~L8 are set as overhead lines, and the specific parameters of the lines are shown in the following table:

[0156] Table 1 Overhead line and cable impedance parameters

[0157] Line Type Line resistance (Ω / km) Line inductance (mH / km) Line to ground capacitance (μF / km) Overhead lines 0.25 5.58 0.008 Cable lines 2.7 1.055 0.29

[0158] To facilitate the adjustment of the asymmetry of the system, line 3 is set as a three-phase unbalanced capacitance line, where the capacitance of phases A and B to ground is 0.29μF / km, and the capacitance of phase C to ground is 0.35μF / km. Calculation shows that the system capacitance current to ground is 151.4A, and the asymmetry is 1.5%.

[0159] To verify the validity of the model, the neutral point branch is removed to construct an ungrounded system. During normal operation, the busbar zero-sequence voltage is the asymmetric voltage of the system, and its effective value is 87.4V, corresponding to an asymmetry of 1.45%, with an error of only 3.3% from the calculated value. Then, a metallic grounding fault is set in the line, and the current flowing through the fault branch is the system capacitive current, with an effective value of 150.33A, which is consistent with the calculated result. At this time, the effective value of the zero-sequence voltage of the system is 6055V, which is only 0.1% different from the effective value of the phase voltage, which is consistent with the characteristics of a single-phase grounding fault. Finally, the arc suppression coil branch is connected to the system, and the residual current is compensated to less than 5A after a short oscillation process. The corresponding simulation waveform is shown in the figure below. Figure 5 As shown:

[0160] Substitute the system's asymmetry, ground capacitance and other parameters into the damping resistance calculation formula, calculate the critical resistance of the damping resistance that just makes the neutral point displacement voltage reach the alarm value during normal operation, and substitute this resistance into the simulation model to verify whether the neutral point displacement voltage reaches the alarm value. The results are shown in the following table:

[0161] Table 2 Critical resistance of damping resistor and simulation results during normal operation

[0162] Critical resistance / Ω Neutral point displacement voltage simulation effective value / V Error from neutral point displacement voltage alarm value / % String Damping 3.31 895.20 1.52 and damping 459.23 889.54 2.14

[0163] In case of high-resistance grounding, the transition resistance is set to 500Ω, 1000Ω, and 1500Ω respectively, and the critical resistance of the damping resistance that just makes the neutral point displacement voltage cross the starting threshold of the line selection device is calculated. The results are shown in the following table:

[0164] Table 3 Critical resistance of damping resistor and simulation results under different transition resistances

[0165]

[0166] By comparing the calculation results with the simulation results, it can be seen that the method proposed in this paper can calculate the critical damping resistance under different operating conditions more accurately, and the corresponding neutral point displacement voltage simulation value is less than 10% of the alarm threshold value of 15% phase voltage; and with the increase of transition resistance, the maximum value of series damping gradually decreases and the minimum value of damping gradually increases, and both gradually approach the critical value under normal operation, and the corresponding resistance range shows a shrinking trend, which is consistent with the above analysis conclusions.

[0167] If the resonant grounding system is to be able to operate reliably under the premise of normal operation without false protection under the condition of 1500Ω single-phase grounding fault, the midpoint value of the upper and lower limits of the damping resistance can be selected, that is, parallel damping 346.37Ω or series damping 5.05Ω. The corresponding simulation waveform of the neutral point displacement voltage is as follows: Figure 6 As shown:

[0168] Depend on Figure 6 It can be seen that the parallel and series damping resistors adopted according to the calculation method in this paper can reliably suppress the neutral point displacement voltage below 15% of the phase voltage when the system is operating normally; under a 1500Ω grounding fault, the neutral point displacement voltage can also smoothly cross the starting threshold value after a short transition process, indicating that the calculation method in this paper can meet the established target requirements.

[0169] After selecting the damping resistance value, calculate the transition resistance value corresponding to when the neutral point displacement voltage is about to fall below the alarm value in the single-phase grounding state. This value is the maximum value of the system's transition resistance. The theoretical calculation and simulation results are shown in the following table:

[0170] Table 4 System transition resistance limit value and simulation results

[0171]

[0172] It can be seen from the above table that the operating structure of the arc suppression coil and the damping resistor in parallel can further improve the system's ability to withstand transition resistance, which is about 600Ω higher than the series damping; and the corresponding neutral point displacement voltage simulation values ​​are close to the alarm value, with an error of no more than 5%, indicating that the calculation method in this paper can better solve the problem of single-phase grounding fault perception below 3000Ω in the resonant grounding system, which is conducive to the timely investment of subsequent arc extinguishing and line selection devices, and improves the efficiency of grounding fault handling.

[0173] The optimized and adjusted damping resistor can not only effectively suppress series resonance during normal system operation, but also does not hinder the neutral point displacement voltage from crossing the limit smoothly under high-resistance grounding conditions. It can increase the system's transition resistance capability from 665Ω to 2.78kΩ, effectively solving problems such as fault handling delays caused by protection refusal to operate.

[0174] Example 2

[0175] This embodiment provides a resistance value selection device for a pre-adjustable arc suppression coil damping resistor, comprising:

[0176] Power monitoring device, used to obtain the detuning degree v and capacitive current I of the resonant grounding system C , Neutral point displacement voltage

[0177] Parameter calculation module, used to calculate the phase voltage according to the system rated phase voltage U Φ , Capacitor current I C And the transition resistance R d The target resistance value is used to calculate the transition resistance damping rate d of the resonant grounding system. d , according to the system rated phase voltage U Φ And the neutral point displacement voltage Calculate the asymmetry ρ of the resonant grounding system;

[0178] Among them, the transition resistance damping rate d d The calculation formula is:

[0179] The calculation formula of asymmetry ρ is:

[0180] A resistance range calculation module, used to determine the resistance range of parallel damping according to the parallel damping range calculation formula, and to determine the resistance range of series damping according to the series damping range calculation formula;

[0181]

[0182]

[0183] Among them, R p is parallel damping, Rs is the series damping, k s is the zero-sequence voltage alarm threshold percentage,

[0184] The resistance determination module selects any resistance value from the resistance range of the parallel damping as the resistance value of the parallel damping, and selects any resistance value from the resistance range of the series damping as the resistance value of the series damping.

[0185] In one embodiment, the resistance of the parallel damping is:

[0186]

[0187] The resistance of the series damper is:

[0188]

[0189] That is, the resistance of the parallel damping is at the midpoint of its resistance range, and the resistance of the series damping is at the midpoint of its resistance range, leaving a certain margin for changes in detuning caused by the gear adjustment of the arc suppression coil and changes in capacitive current caused by line inversion.

[0190] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solution of the present invention, which should be included in the scope of the technical solution for protection of the present invention.

Claims

1. A method for selecting the resistance value of a pre-adjustable arc suppression coil damping resistor, characterized in that: The following steps are involved: Use power monitoring devices to obtain the detuning degree v and capacitive current I of the resonant grounding system C , Neutral point displacement voltage According to the system rated phase voltage U Φ , Capacitor current I C And the transition resistance R d The target resistance value is used to calculate the transition resistance damping rate d of the resonant grounding system. d , according to the system rated phase voltage U Φ And the neutral point displacement voltage Calculate the asymmetry ρ of the resonant grounding system; Among them, the transition resistance damping rate d d The calculation formula is: The calculation formula of asymmetry ρ is: The resistance range of parallel damping is determined according to the parallel damping range calculation formula, and the resistance range of series damping is determined according to the series damping range calculation formula; The calculation formula for parallel damping range is: The series damping range calculation formula is: Among them, R p is parallel damping, R s is the series damping, k s is the zero-sequence voltage alarm threshold percentage, A resistance value is arbitrarily selected from the resistance range of the parallel damping as the resistance value of the parallel damping, and a resistance value is arbitrarily selected from the resistance range of the series damping as the resistance value of the series damping.

2. The method for selecting the resistance value of a pre-adjustable arc suppression coil damping resistor according to claim 1 is characterized in that: When any resistance value is selected from the resistance range of the parallel damping as the resistance value of the parallel damping, the midpoint of the resistance range of the parallel damping is selected as the resistance value of the parallel damping: When any resistance value is selected from the resistance range of the series damping as the resistance value of the series damping, the midpoint of the resistance range of the series damping is selected as the resistance value of the series damping.

3. The method for selecting the resistance value of a pre-adjustable arc suppression coil damping resistor according to claim 1 is characterized in that: The steps to obtain the parallel damping range calculation formula are: Step 1, calculating the critical resistance value of the parallel damping resistor when the resonant grounding system is in normal operation; Step 1.1, obtaining a series resonant equivalent circuit when the resonant grounding system is operating normally; Step 1.2, calculate the neutral point displacement voltage when the parallel damping resistor is connected; Step 1.3, making the effective value of the neutral point displacement voltage not higher than the zero-sequence voltage alarm threshold, and calculating the upper limit of the parallel damping resistance threshold that meets the neutral point displacement voltage requirement; Step 2, calculating the critical resistance value of the damping resistor for improving the high-resistance grounding sensing capability; Step 2.1, obtaining a series resonant equivalent circuit when a single-phase grounding fault occurs in the resonant grounding system; Step 2.2, calculate the neutral point displacement voltage percentage when the parallel damping resistor is connected; Step 2.3: Make sure the neutral point displacement voltage percentage is not lower than the zero-sequence voltage alarm threshold percentage k s , calculate the lower limit of the parallel damping resistance threshold that meets the neutral point displacement voltage percentage requirement; Step 3: Obtain a parallel damping range calculation formula according to the parallel damping resistance threshold lower limit and the parallel damping resistance threshold upper limit.

4. The method for selecting the resistance value of the pre-adjustable arc suppression coil damping resistor according to claim 3 is characterized in that: The steps to obtain the series damping range calculation formula are: Step 4, calculating the critical resistance value of the series damping resistor when the resonant grounding system is operating normally; Step 4.1, let the admittance of the series damping resistor and the parallel damping resistor be equal, and we get: Step 4.2, respectively set the imaginary part and the real part of the left and right sides of the equation to be equal, and obtain the corresponding relationship between the series resistance and the parallel resistance; Step 4.3, substitute the corresponding relationship between the series resistance and the parallel resistance into the calculation formula of the damping rate added by the series damping resistance to obtain the damping rate added by the series damping resistance d s ; Step 4.4, add the damping rate d of the series damping resistor s Substitute it into the upper limit of the parallel damping resistance threshold to obtain the lower limit of the series damping resistance value that satisfies the neutral point displacement voltage not exceeding the limit during normal operation; Step 5, converting the lower limit of the parallel damping resistance threshold obtained in step 2 into the series damping resistance, and calculating the upper limit of the series damping resistance value; Step 6: According to the lower limit of the series damping resistance and the upper limit of the series damping resistance, a calculation formula for the parallel damping range is obtained.

5. A resistance value selection device for a pre-adjustable arc suppression coil damping resistor, characterized in that: Power monitoring device, used to obtain the detuning degree v and capacitive current I of the resonant grounding system C , Neutral point displacement voltage Parameter calculation module, used to calculate the phase voltage according to the system rated phase voltage U Φ , Capacitor current I C And the transition resistance R d The target resistance value is used to calculate the transition resistance damping rate d of the resonant grounding system. d , according to the system rated phase voltage U Φ And the neutral point displacement voltage Calculate the asymmetry ρ of the resonant grounding system; Among them, the transition resistance damping rate d d The calculation formula is: The calculation formula of asymmetry ρ is: A resistance range calculation module, used to determine the resistance range of parallel damping according to the parallel damping range calculation formula, and to determine the resistance range of series damping according to the series damping range calculation formula; The calculation formula for parallel damping range is: The series damping range calculation formula is: Among them, R p is parallel damping, R s is the series damping, k s is the zero-sequence voltage alarm threshold percentage, The resistance determination module selects any resistance value from the resistance range of the parallel damping as the resistance value of the parallel damping, and selects any resistance value from the resistance range of the series damping as the resistance value of the series damping.

6. The resistance value selection device of the pre-adjustable arc suppression coil damping resistor according to claim 5 is characterized in that: The resistance of parallel damping is: The resistance of the series damper is:

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