Analytical method for reducing the error of automatic tracking and compensation of arc suppression coil capacitance current measurement

Abstract

The present invention discloses an analysis method for automatically tracking and compensating the reduction of the capacitance current measurement error of the arc suppression coil, measures the capacitance current by a two-point method, controls the arc suppression coil gear, adjusts the arc suppression coil reactance, measures the neutral point current of the distribution network system, and calculates the network impedance Z including the system capacitance reactance C ; Use the formula to convert Z C The correlation calculation formula is used to analyze the effect of the correlation on Z C The influence of; the relationship between the capacitance measurement error and the measurement gear and the resonance gear distance is obtained by formula conversion and a relationship curve is made; according to the different settings of the formula parameters in the two cases where the measurement gear is greater than the resonance gear and the measurement gear is less than the resonance gear, the analysis result of the measurement error is obtained. The present invention establishes a mathematical model to reveal the relevant factors and trend laws that affect the capacitance and current measurement errors, and on this basis proposes improved methods and measures, which greatly reduce the capacitance and current measurement errors.

Description

Technical Field

[0001] The invention relates to the field of distribution network calculation, in particular to an analysis method for automatically tracking and compensating for reducing the measurement error of arc suppression coil capacitance current. Background Art

[0002] In my country, most 6-35kV distribution networks are non-effectively grounded neutral point systems. When a single-phase grounding fault occurs in the distribution network, it is allowed to continue operating for 1-2 hours [1]. With the rapid development of the national economy, the scale and power supply area of ​​the distribution network have increased rapidly. Secondary accidents caused by single-phase grounding faults in the distribution network (arc grounding overvoltage, personal electric shock accidents and short circuit faults) have attracted more and more attention. Among the many targeted solution designs, the application of arc suppression coils is one of the main candidate solutions. The national power industry standard "Overvoltage Protection and Insulation Coordination of AC Electrical Equipment" [2] stipulates that for systems composed of 3kV~10kV reinforced concrete or metal tower overhead lines and all 35kV and 66kV systems, when the single-phase grounding fault capacitive current exceeds 10A, arc suppression coil grounding should be used; a large number of arc suppression coil automatic tracking compensation devices have been put into operation, which has greatly improved the safe operation level and power supply reliability of the distribution network.

[0003] The core part of the automatic tracking and compensation technology of arc suppression coils is to accurately measure the capacitance current of the capacitor system in real time. According to the measurement results, the arc suppression coil gear is adjusted to provide the corresponding inductive current to compensate the capacitance current of the system. Since the two-point method [3] is simple and easy to implement, it has been reliably and widely used. However, in the operation of the automatic tracking and compensation arc suppression coils, the compensation level is uneven. There are problems such as large capacitance current measurement error, increased residual current error after compensation, poor compensation effect of the arc suppression coil, and weakened ability to reduce secondary accidents caused by single-phase grounding faults in the distribution network.

[0004] Based on the above series of problems, the following technical solutions are proposed. Summary of the invention

[0005] The purpose of the present invention is to address the above-mentioned deficiencies and provide an analytical method for automatically tracking and compensating for the reduction of the capacitance current measurement error of the arc suppression coil. By establishing a mathematical model, the relevant factors and trend laws affecting the capacitance current measurement error are revealed. On this basis, improved methods and measures are proposed, which greatly reduce the capacitance current measurement error.

[0006] The technical solution adopted by the present invention to achieve the above-mentioned purpose is:

[0007] An analysis method for automatically tracking and compensating arc suppression coil capacitance current measurement error reduction, the method comprising:

[0008] S1. Measure the capacitive current by the two-point method, control the arc suppression coil position, adjust the arc suppression coil reactance, measure the neutral point current of the distribution network system, and calculate the network impedance Z including the system capacitive reactance C ;

[0009] S2, based on the calculated Z C , use the formula to convert Z C The correlation calculation formula is used to analyze the effect of the correlation on Z C The impact of

[0010] S3. Calculate the relationship between the capacitive reactance measurement error and the measurement gear and the resonant gear distance through a formula and make a relationship curve;

[0011] S4. According to the different settings of the formula parameters in two cases where the measurement gear is greater than the resonance gear and the measurement gear is less than the resonance gear, the analysis result of the measurement error is obtained.

[0012] Furthermore, S1 specifically includes:

[0013] During automatic tuning, the arc suppression coil is adjusted to the T1 and T2 positions respectively, and measurement and calculation are performed. The neutral point current corresponding to the T1 and T2 positions is assumed to be and And think that in the tuning process Keeping it unchanged, we can get

[0014]

[0015] where Z′ T1 =R′ T1 +jX′ T1 , Z′ T2 =R′ T2 +jX′ T2 , Z C =R S -jX C , and then we can get

[0016]

[0017] From (3), we can get

[0018]

[0019] Furthermore, S2 specifically includes:

[0020] Transformation (4) has

[0021]

[0022] The first part of the right side of the formula ZΔ , due to the arc extinguishing coil resistance R' of T1 and T2 gears T1 and R′ T2 The difference is small, so Z′ T1 -Z′ T2 The difference between the arc suppression coil reactances of T1 and T2 is denoted as X T1T2 , X T1T2 It is not affected by measurement errors.

[0023] So we have:

[0024]

[0025] Furthermore, S2 specifically includes:

[0026] According to the actual situation, it is assumed that the phase difference between T1 and T2 is 2, that is, T1-T2=2, the distance between T1 and the resonance is n, the reactance difference between the two adjacent gears of the arc suppression coil is ΔX, T1 and T2 are both on one side of the resonance, the damping resistance is equal to ΔX in value, and the system resistance R is ignored. S , the capacitive reactance of the distribution network system is Z C ,

[0027] Then Z′ T1 =R K +jX′ LT1 =X C +j(X C +n*ΔX) (7)

[0028] Z′ T2 =R K +jX′ LT2 =X C +j(X C +(n+2)*ΔX) (8)

[0029] set up The measurement has an error of m%, which can be substituted into formula (6):

[0030]

[0031] Substituting formulas (1), (2), (7), and (8) into formula (9), we have

[0032]

[0033] Furthermore, S2 specifically includes:

[0034] Due to the existence of m% error, Z Δ The change in the imaginary part is the error in the capacitive reactance (capacitance) measurement.

[0035] Z CΔ, then:

[0036]

[0037] make Then there is

[0038]

[0039] Furthermore, S4 specifically includes:

[0040] Since ΔX and K are related to the arc extinguishing coil gear parameters, assuming ΔX = 10 and K = 5, then Z CΔ The influencing factors are the gear difference n and m% error of the distance resonant gear when shifting.

[0041] When the T1 and T2 gears are both greater than the resonance gear, the error of the measured capacitive reactance increases with the increase of the initial gear difference n, and the error direction is negative;

[0042] If, both T1 and T2 gears are smaller than the resonant gear, assuming that at this time, the m% error of the transformer is a negative value, the error of the measured capacitive reactance at this time increases with the increase of the initial gear difference n, and the error direction is positive;

[0043] When n=0 is substituted into formula (12), we have:

[0044]

[0045] That is, when the T1 gear is the resonant gear, when the current transformer has an m% error, the capacitance measurement error is the smallest, and the capacitive reactance measurement error is the calculation result of formula (13).

[0046] Furthermore, S4 specifically includes:

[0047] If K=10, both T1 and T2 gears are smaller than the resonance gear. When n is smaller, that is, T1 and T2 gears are closer to the resonance gear, the absolute value of the measurement error of the capacitive reactance is smaller. On the contrary, when n is larger, that is, T1 and T2 gears are farther from the resonance gear, the absolute value of the measurement error of the capacitive reactance is larger.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] The method mentioned in the present invention proves the distribution law of the measurement error of the general 2-point capacitance current measurement method through mathematical deduction and graphical display: the closer the two measurement positions of the 2-point capacitance current measurement method are to the resonance position, the smaller the measurement error is, and vice versa. An improved method is also given, which has a positive role in improving the measurement accuracy of the capacitance current of the 2-point method and the accurate compensation of the capacitance current of the arc suppression coil system. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0051] Figure 1 It is a schematic diagram of the process of the present invention;

[0052] Figure 2 It is the zero-sequence equivalent circuit of the arc suppression coil in the i-th gear to compensate the normal state of the power grid;

[0053] Figure 3 It is the equivalent circuit that is converted into series impedance when the arc suppression coil works in the gear position T1;

[0054] Figure 4 It is the equivalent circuit that is converted into series impedance when the arc suppression coil works in the gear position T2;

[0055] Figure 5 When the T1 and T2 gears are both greater than the resonant gear and K is 5, the relationship curve between the capacitive reactance measurement error and the distance n between the measurement gear and the resonant gear is shown;

[0056] Figure 6 When the T1 and T2 gears are both smaller than the resonant gear and K is 5, the relationship curve between the capacitive reactance measurement error and the distance n between the measurement gear and the resonant gear is shown;

[0057] Figure 7 When the T1 and T2 gears are both greater than the resonant gear and K is 10, the relationship curve between the capacitive reactance measurement error and the distance n between the measurement gear and the resonant gear is shown;

[0058] Figure 8 When the T1 and T2 gears are both smaller than the resonant gear and K is 10, the relationship curve between the capacitive reactance measurement error and the distance n between the measurement gear and the resonant gear is shown in the figure. DETAILED DESCRIPTION

[0059] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0060] The present invention provides an analysis method for automatically tracking and compensating the arc suppression coil capacitance current measurement error reduction. Figures 1 to 8 The technical solution provided by the present invention is described in more detail.

[0061] The present invention is based on practice and theory, and adopts the two-point method (three-point method) to measure the capacitance current. That is, under the same operation mode, by controlling the arc suppression coil gear and adjusting the arc suppression coil reactance, two sets of equations can be obtained to calculate the capacitance current of the distribution network system, such as Figure 2 As shown, Figure 2 It is the zero-sequence equivalent circuit of the arc suppression coil in the i-th gear to compensate the normal state of the power grid. bd is the asymmetric voltage of the power grid, R s is the system damping, R k is the series damping resistor, X Li is the inductive reactance of the arc extinguishing coil at the i-th gear, X c is the capacitive reactance of the power grid to ground.

[0062] like Figure 3-4 As shown, Figure 3 and Figure 4 They are the equivalent circuits of the arc suppression coil converted into series impedance when it works in T1 and T2 positions. T1 and X T2 are the inductive reactances corresponding to the arc suppression coil working at T1 and T2 positions, X′ T1 , R′ T1 , X′ T2 , R′ T2 They are series circuits, corresponding equivalent reactance and equivalent resistance respectively.

[0063] During automatic tuning, the arc suppression coil is adjusted to the T1 and T2 positions respectively, and the measurement and calculation are performed. Assume that the neutral point current corresponding to the T1 and T2 positions is and And think that in the tuning process remains unchanged, then Figure 3-4 The following equation can be obtained

[0064]

[0065] where Z′ T1 =R′ T1 +jX′ T1 , Z′ T2 =R′ T2 +jX′ T2 , Z C =R S -jX C

[0066]

[0067] From (3), we can obtain:

[0068]

[0069] According to the obtained Z C , and further calculate the system capacitance and capacitance current. The arc suppression coil controller with automatic tracking compensation will adjust the arc suppression coil to the appropriate gear to compensate for the system capacitance current when a single-phase grounding fault occurs.

[0070] Next is the error analysis:

[0071] Formula (4) is a theoretical calculation value. In field operation, the quantity measured in the formula is and The accuracy of its measurement will deviate. Now we discuss the impact of measurement error on the calculation of capacitor reactance and capacitor current measurement.

[0072] The transformation formula (4) is:

[0073]

[0074] The second part on the right side of the equation is -Z′ T2 The first part on the right is the reactance and resistance of the arc extinguishing coil in the T2 gear, which is fixed. Z Δ , which is affected by measurement error, thus affecting Z C measurement accuracy.

[0075] (Z′ T1 -Z′ T2 )=(R′ T1 +jX' T1 )-(R′ T2 +jX' T2 )

[0076] =(R′ T1 -R′ T2 )+(jX′ T1 -jX′ T2 )

[0077] Due to the arc extinguishing coil resistance R' of T1 and T2 gears T1 and R′ T2 The difference is small, so Z′ T1 -Z′ T2 The difference between the arc suppression coil reactances of T1 and T2 is denoted as X T1T2 , X T1T2 It is not affected by measurement errors.

[0078] So we have:

[0079]

[0080] According to the actual situation, it is assumed that the phase difference between T1 and T2 is 2, that is, T1-T2=2, the distance between T1 and the resonance is n, the reactance difference between the two adjacent gears of the arc suppression coil is ΔX, T1 and T2 are both on one side of the resonance, the damping resistance is equal to ΔX in value, and the system resistance R is ignored. S , the capacitive reactance of the distribution network system is X C ,

[0081] Then we have: Z′ T1 =R K +jX′ LT1

[0082] =X C +j(X C +n*ΔX) (7)

[0083] Z′ T2 =R K +jX LT2

[0084] =X C +j(X C +(n+2)*ΔX) (8)

[0085] set up The measurement has an error of m%, which can be substituted into formula (6):

[0086]

[0087] Substituting equations (1), (2), (7), and (8) into equation (9), we have:

[0088]

[0089] Due to the existence of m% error, Z Δ The change in the imaginary part is the error in the capacitive reactance (capacitance) measurement, recorded as Z CΔ , then:

[0090]

[0091] make,

[0092] but:

[0093]

[0094] like Figure 5-8 As shown in the figure, since ΔX and K are related to the gear parameters of the arc extinguishing coil, assuming ΔX = 10 and K = 5, then Z CΔ The main influencing factors are the gear difference n and m% error of the distance resonant gear during gear adjustment. The relationship curve is as follows: Figure 5As shown in the figure, the T1 and T2 gears are both greater than the resonance gear. At this time, the error of the measured capacitive reactance increases with the increase of the initial gear difference n, and the error direction is negative.

[0095] If the T1 and T2 positions are both less than the resonant position, and it is assumed that the m% error of the transformer is a negative value, then Figure 5 As shown in the relationship curve, the error of the measured capacitive reactance at this time increases with the increase of the initial measurement gear difference n, and the error direction is positive.

[0096] When K takes different values, there are similar graphs. For example, when K=10, it is as follows Figure 7 , Figure 8 shown.

[0097] Therefore, by Figure 5-Figure 8 It can be seen that when n is smaller, that is, the closer the T1 and T2 gears are to the resonance gear, the smaller the absolute value of the measurement error of the capacitive reactance is. On the contrary, when n is larger, that is, the farther the T1 and T2 gears are from the resonance gear, the greater the absolute value of the measurement error of the capacitive reactance is.

[0098] Since the m% error of the current transformer is random within a certain range and can be positive or negative, the above conclusion is still applicable.

[0099] The following are the improvement measures made to the current situation:

[0100] Substituting n=0 into equation (12), we have:

[0101]

[0102] That is, when the T1 gear is the resonant gear, when the current transformer has an m% error, the capacitance measurement error is the smallest, and the capacitive reactance measurement error is the calculation result of formula (13).

[0103] According to the above analysis, the working point of the two-point method for measuring capacitor current should be near the resonant position. To this end, the following steps are adopted to ensure that the error of capacitor reactance and capacitor current measurement is minimized:

[0104] 1. Determine the resonant gear. When the equipment is put into operation for the first time, adjust the gear once in the full range and determine the resonant gear based on the appearance of the maximum value of the neutral point voltage.

[0105] 2. Measure the system capacitance and current: near the resonance position, use the two-point method to measure the system capacitance and reactance, capacitance and current

[0106] 3. Follow the system mode: When the system operation mode changes, track the change in operation mode in real time, measure the system capacitance, reactance and current twice in succession, and if the error of the two measurements is less than 5%, it is determined to be a valid measurement.

[0107] 4. When the system operation mode changes dramatically: If the error between two measurements is greater than 5%, it is determined to be an invalid measurement, indicating that the system operation mode changes dramatically. Repeat steps 1-2 to measure the system capacitance and current.

[0108] The present invention proves the distribution law of the measurement error of the universal 2-point capacitance current measurement method through mathematical deduction and graphical display: the closer the two measurement positions of the 2-point capacitance current measurement method are to the resonance position, the smaller the measurement error is, and vice versa. An improved method is given, which has a positive role in improving the measurement accuracy of the capacitance current of the 2-point method and the accurate compensation of the capacitance current of the arc suppression coil system.

[0109] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. An analysis method for automatically tracking and compensating arc suppression coil capacitance current measurement error reduction, characterized in that: The method comprises: S1. Measure the capacitive current by the two-point method, control the arc suppression coil position, adjust the arc suppression coil reactance, measure the neutral point current of the distribution network system, and calculate the network impedance Z including the system capacitive reactance C ; S1 specifically includes: During automatic tuning, the arc suppression coil is adjusted to the T1 and T2 positions respectively, and measurement and calculation are performed. The neutral point current corresponding to the T1 and T2 positions is assumed to be and And think that in the tuning process Keeping it unchanged, we can get where Z' T1 =R' T1 +jX′ T1 , Z′ T2 =R′ T2 +jX′ T2 , Z C =R S -jX C , and then we can get From (3), we can get Above is the asymmetric voltage of the power grid; X′ T1 is the equivalent reactance corresponding to the arc suppression coil working at T1 position; R′ T1 is the equivalent resistance corresponding to the arc suppression coil working at T1 position; X′ T2 is the equivalent reactance corresponding to the arc suppression coil working at T2 position; R′ T2 is the equivalent resistance corresponding to the arc suppression coil working in T2 position; R S is the system damping; X C is the ground capacitive reactance of the power grid; S2, based on the calculated Z C , use the formula to convert Z C The correlation calculation formula is used to analyze the effect of the correlation on Z C The impact of S2 specifically includes: Transformation (4) has The first part of the right side of the formula Z Δ , due to the arc extinguishing coil resistance R' of T1 and T2 gears T1 and R′ T2 The difference is small, so Z′ T1 -Z′ T2 The difference between the arc suppression coil reactances of T1 and T2 is denoted as X T1T2 , X T1T2 It is not affected by measurement errors. So we have: Above is the neutral point current corresponding to T1 gear; is the neutral point current corresponding to T2 gear; Z′ T1 is the reactance of the arc suppression coil in T1 position; Z′ T2 is the reactance of the arc suppression coil in T2 gear; According to the actual situation, it is assumed that the difference between T1 and T2 is 2 levels, that is, T1-T2=2, the distance between T1 and the resonance level is n levels, the reactance difference between the two adjacent levels of the arc suppression coil is ΔX, T1 and T2 are both on one side of the resonance level, the damping resistance is equal to ΔX in value, and the system resistance R is ignored. S , the capacitive reactance of the distribution network system is X C , Then Z′ T1 =R K +jX′ LT1 =X C +j(X C +n*ΔX) (7) Z′ T2 =R K +jX′ LT2 =X C +j(X C +(n+2)*ΔX) (8) set up The measurement has an error of m%, which can be substituted into formula (6): The above X′ LT1 is the inductive reactance of the arc extinguishing coil at the T1 position, X′ LT2 R is the inductive reactance of the arc suppression coil at the T2 position. K is the series damping resistor; Substituting formulas (1), (2), (7), and (8) into formula (9), we have Due to the existence of m% error, Z Δ The change in the imaginary part is the error in the capacitive reactance (capacitance) measurement. Z CΔ , then: make Then there is S3. Calculate the relationship between the capacitive reactance measurement error and the measurement gear and the resonant gear distance through a formula and make a relationship curve; S4. Obtaining analysis results of the measurement error according to different formula parameter settings in two cases where the measurement gear is greater than the resonance gear and the measurement gear is less than the resonance gear; S4 specifically includes: Since ΔX and K are related to the arc extinguishing coil gear parameters, assuming ΔX = 10 and K = 5, then Z CΔ The influencing factors are the gear difference n and m% error of the distance resonant gear when shifting. When the T1 and T2 gears are both greater than the resonance gear, the error of the measured capacitive reactance increases with the increase of the initial gear difference n, and the error direction is negative; If, both T1 and T2 gears are smaller than the resonant gear, assuming that at this time, the m% error of the transformer is a negative value, the error of the measured capacitive reactance at this time increases with the increase of the initial gear difference n, and the error direction is positive; When n=0 is substituted into formula (12), we have: That is, when the T1 gear is the resonant gear, when the current transformer has an m% error, the capacitance measurement error is the smallest, and the capacitive reactance measurement error is the calculation result of formula (13).

2. The analysis method for automatically tracking and compensating arc suppression coil capacitance current measurement error reduction as claimed in claim 1, characterized in that: S4 specifically includes: If K=10, both T1 and T2 gears are smaller than the resonance gear. When n is smaller, that is, T1 and T2 gears are closer to the resonance gear, the absolute value of the measurement error of the capacitive reactance is smaller. On the contrary, when n is larger, that is, T1 and T2 gears are farther from the resonance gear, the absolute value of the measurement error of the capacitive reactance is larger. The above K is That is, the ground capacitance of the power grid is X C The ratio of the reactance difference ΔX between the two adjacent gears of the arc suppression coil; n is the gear difference between the T1 or T2 gear and the resonant gear.

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