Method for identifying parallel resonance of lumped parameters of power transmission line of high-voltage system of transformer substation

Abstract

The invention relates to parallel resonance, in particular to a transformer substation high-voltage system power transmission line lumped parameter parallel resonance identification method, which comprises the following steps of: synchronously monitoring a high-voltage side, a medium-voltage side and a low-voltage side of a main transformer to obtain a harmonic voltage content array, a harmonic current content array and a fundamental wave reactive power array; according to the main transformer low-voltage side fundamental wave reactive power array, selecting a target time period in which reactive power changes frequently; within the target time period, a first correlation coefficient between the main transformer medium-voltage side h-order harmonic voltage content array and the main transformer high-voltage side h-order harmonic current content array is calculated, and a second correlation coefficient between the main transformer medium-voltage side h-order harmonic voltage content array and the main transformer medium-voltage side h-order harmonic current content array is calculated; identifying the resonance state of the high-voltage side of the main transformer based on the first correlation coefficient and the second correlation coefficient; the method can effectively overcome the defect that the lumped parameter parallel resonance of the power transmission line of the high-voltage system of the transformer substation is difficult to accurately identify due to CVT harmonic measurement distortion.

Description

TECHNICAL FIELD

[0001] The present application relates to parallel resonance, in particular to a method for identifying parallel resonance of concentrated parameters of a transmission line of a high-voltage system of a substation. BACKGROUND

[0002] The high-voltage power grid is one of the important means to solve the imbalance between energy production and consumption regions. At present, the high-voltage power grid in China mostly adopts a ring network structure and provincial interconnection. The input harmonic impedance characteristics (resistance-inductance or resistance-capacitance) of long-distance transmission lines are uncertain. When the high-voltage system of a substation contains multiple T-connected lines with different harmonic impedance characteristics, parallel resonance of the concentrated parameters of the transmission line is easily induced. The harmonic impedance at the resonance point has a high resistance characteristic, which causes the harmonic current injected into the high-voltage system to exceed the standard harmonic voltage, threatening the safe and stable operation of the power transmission and transformation equipment (especially the DC converter station).

[0003] At present, CVT is mostly used for voltage signal measurement in China at voltage levels above 35kV. However, CVT has the problem of harmonic voltage amplitude and phase measurement distortion in the low frequency band. In actual engineering applications, the harmonic power flow judgment method based on harmonic impedance angle or harmonic power is sensitive to the harmonic phase. The measurement error of the harmonic phase can easily cause misjudgment of the harmonic power flow and the resonance type. Therefore, how to accurately identify the parallel resonance of the concentrated parameters of the transmission line of the high-voltage system of a substation through technical means is a key technical problem that needs to be solved at present. SUMMARY

[0004] (I) Technical problems solved In view of the above-mentioned shortcomings of the prior art, the present application provides a method for identifying parallel resonance of concentrated parameters of a transmission line of a high-voltage system of a substation, which can effectively overcome the defect that it is difficult to accurately identify the parallel resonance of the concentrated parameters of the transmission line of the high-voltage system of a substation due to the harmonic measurement distortion of CVT.

[0005] (II) Technical solutions In order to achieve the above-mentioned purposes, the present application is realized by the following technical solutions: The method for identifying parallel resonance of concentrated parameters of a transmission line of a high-voltage system of a substation comprises the following steps: S1, synchronously monitoring the high-voltage side, the medium-voltage side and the low-voltage side of the main transformer to obtain a harmonic voltage content rate array, a harmonic current content array and a fundamental reactive power array; S2, selecting a target time period with frequent reactive power changes according to the fundamental reactive power array of the low-voltage side of the main transformer; S3, calculating a first correlation coefficient between the hth harmonic voltage content array of the medium voltage side of the main transformer and the hth harmonic current content array of the high voltage side of the main transformer, and a second correlation coefficient between the hth harmonic voltage content array of the medium voltage side of the main transformer and the hth harmonic current content array of the medium voltage side of the main transformer in the target period; S4, identifying the resonance state of the high voltage side of the main transformer based on the first correlation coefficient and the second correlation coefficient; S5, identifying the harmonic impedance characteristic of the high voltage side of the main transformer based on the hth harmonic voltage content array of the high voltage side and the medium voltage side of the main transformer.

[0006] Preferably, the main transformer high voltage side, medium voltage side and low voltage side are synchronously monitored in S1 to obtain the harmonic voltage content array, the harmonic current content array and the fundamental wave reactive power array, including: synchronously monitoring the main transformer high voltage side, medium voltage side and low voltage side to obtain the main transformer high voltage side hth harmonic voltage content array U 1h [1,M], the main transformer high voltage side hth harmonic current content array I 1h [1,M], the main transformer medium voltage side hth harmonic voltage content array U 2h [1,M], the main transformer medium voltage side hth harmonic current content array I 2h [1,M], and the main transformer low voltage side fundamental wave reactive power array Q3[1,M]; Wherein, M is the initial array length, and the data analysis interval is less than 3s.

[0007] Preferably, the target period with frequent reactive power changes is selected according to the main transformer low voltage side fundamental wave reactive power array in S2, including: According to the main transformer low voltage side fundamental wave reactive power array, combined with the operation state of the reactive power compensation device, the target period with frequent reactive power changes is selected to obtain each group of data in the target period: the main transformer high voltage side hth harmonic voltage content array U 1h [1,N], the main transformer high voltage side hth harmonic current content array I 1h [1,N], the main transformer medium voltage side hth harmonic voltage content array U 2h [1,N], the main transformer medium voltage side hth harmonic current content array I 2h [1,N], and the main transformer low voltage side fundamental wave reactive power array Q3[1,N]; Wherein, N is the array length after screening, the span length of the target period is in the range of 2-24h, when the span length of the target period is too long, the resonance state of the power transmission line will change, and when the span length of the target period is too short, it will affect the subsequent correlation calculation result.

[0008] Preferably, in S3, a first correlation coefficient between the hth harmonic voltage content array of the medium voltage side of the main transformer and the hth harmonic current content array of the high voltage side of the main transformer, and a second correlation coefficient between the hth harmonic voltage content array of the medium voltage side of the main transformer and the hth harmonic current content array of the medium voltage side of the main transformer are calculated in the target period, comprising: In the target period, the first correlation coefficient r 2h between the hth harmonic voltage content array U 1h [1,N] of the medium voltage side of the main transformer and the hth harmonic current content array I 21 [1,N] of the high voltage side of the main transformer is calculated. ; In the target period, the second correlation coefficient r 2h between the hth harmonic voltage content array U 2h [1,N] of the medium voltage side of the main transformer and the hth harmonic current content array I 22 [1,N] of the medium voltage side of the main transformer is calculated. ; Wherein, U 2h [1,n] is the nth data in the hth harmonic voltage content array U 2h [1,N] of the medium voltage side of the main transformer, is the average value of the hth harmonic voltage content array U 2h [1,N] of the medium voltage side of the main transformer; I 1h [1,n] is the nth data in the hth harmonic current content array I 1h [1,N] of the high voltage side of the main transformer, is the average value of the hth harmonic current content array I 1h [1,N] of the high voltage side of the main transformer; I 2h [1,n] is the nth data in the hth harmonic current content array I 2h [1,N] of the medium voltage side of the main transformer, is the average value of the hth harmonic current content array I 2h [1,N] of the medium voltage side of the main transformer.

[0009] Preferably, in S4, the resonance state of the high voltage side of the main transformer is identified based on the first correlation coefficient and the second correlation coefficient, comprising: If the first correlation coefficient r 21 is greater than a preset threshold value, and the first correlation coefficient r 21 is greater than a preset multiple of the second correlation coefficient r 22 , it is determined that there is a lumped parameter parallel resonance problem in the power transmission line of the high voltage system of the substation main transformer.

[0010] Preferably, the S5 is based on the main transformer high-voltage side and the h harmonic voltage content array, the harmonic impedance characteristic of the main transformer high-voltage side is identified, including: If the main transformer high-voltage side h harmonic voltage content array U 1h The average value of [1, N] The main transformer high-voltage side h harmonic voltage content array U 2h The average value of [1, N] The harmonic impedance of the parallel resonance of the power transmission line of the high-voltage system of the transformer substation presents a resistance-capacitance characteristic; If the main transformer high-voltage side h harmonic voltage content array U 1h The average value of [1, N] The main transformer high-voltage side h harmonic voltage content array U 2h The average value of [1, N] The harmonic impedance of the parallel resonance of the power transmission line of the high-voltage system of the transformer substation presents a resistance-inductance characteristic.

[0011] (Three) beneficial effects Compared with the prior art, the identification method for the concentrated parameter parallel resonance of the power transmission line of the high-voltage system of the transformer substation provided by the present application has the following beneficial effects: 1) The data of the period when the operation state of the low-voltage side reactive power compensation device of the main transformer frequently changes is selected, the change of the operation state of the reactive power compensation device is utilized, the change range of the grid harmonic and its impedance is increased, and the robustness of the identification result of the concentrated parameter parallel resonance state of the power transmission line of the high-voltage system of the transformer substation can be effectively improved; 2) The first correlation coefficient between the h harmonic voltage content array of the main transformer medium-voltage side and the h harmonic current content array of the main transformer high-voltage side, and the second correlation coefficient between the h harmonic voltage content array of the main transformer medium-voltage side and the h harmonic current content array of the main transformer medium-voltage side are used for comprehensive judgment, the harmonic current misjudgment problem caused by harmonic phase measurement distortion is avoided, and the accuracy of the identification of the concentrated parameter parallel resonance state of the power transmission line of the high-voltage system of the transformer substation can be effectively improved; 3) The method is simple to implement and accurate to judge, does not need to monitor the power transmission line of the high-voltage system of the transformer substation, only needs to monitor the voltage signals and current signals of the three nodes of the main transformer high-voltage side, medium-voltage side and low-voltage side, and can realize effective identification of the resonance state of each power transmission line of the high-voltage system of the transformer substation, and can be used for identification and early warning of the resonance state of the grid in the power quality online monitoring system. BRIEF DESCRIPTION OF DRAWINGS

[0012] In order to make the technical solutions in the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only show some of the embodiments of the present application, and all other embodiments obtained by a person of ordinary skill in the art without any creative effort based on these drawings also belong to the protection scope of the present application.

[0013] Figure 1 A flowchart of the present application; Figure 2 A power grid topology diagram of a certain substation; Figure 3 A flowchart of the present application Figure 2 A change trend diagram of the fundamental reactive power of the main transformer on the low-voltage side during the test period; Figure 4 A flowchart of the present application Figure 3 A local amplification change trend diagram of the 13h~15h period; Figure 5 A flowchart of the present application Figure 2 A change trend diagram of the 5th harmonic voltage content on the high-voltage side of the main transformer during the 13h~15h period; Figure 6 A flowchart of the present application Figure 2 A change trend diagram of the 5th harmonic current content on the high-voltage side of the main transformer during the 13h~15h period; Figure 7 A flowchart of the present application Figure 2 A change trend diagram of the 5th harmonic voltage content on the medium-voltage side of the main transformer during the 13h~15h period; Figure 8 A flowchart of the present application Figure 2 A change trend diagram of the 5th harmonic current content on the medium-voltage side of the main transformer during the 13h~15h period. DETAILED DESCRIPTION

[0014] In order to make the technical solutions in the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only show some of the embodiments of the present application, and all other embodiments obtained by a person of ordinary skill in the art without any creative effort based on these drawings also belong to the protection scope of the present application.

[0015] The specific flow of the identification method of the concentrated parameter parallel resonance of the power transmission line of the high-voltage system of the substation provided by the present application (as shown in Figure 1 ) and the technical effects will be introduced below in combination with specific examples.

[0016] I. Synchronous monitoring of the high-voltage side, the medium-voltage side and the low-voltage side of the main transformer is performed to obtain a harmonic voltage content array, a harmonic current content array and a fundamental reactive power array.

[0017] I. Synchronous monitoring of the high-voltage side, the medium-voltage side and the low-voltage side of the main transformer is performed to obtain a harmonic voltage content array, a harmonic current content array and a fundamental reactive power array. 1h [1,M], the hth harmonic current content array I of the high-voltage side of the main transformer 1h [1,M], the hth harmonic voltage content array U of the medium-voltage side of the main transformer 2h [1,M], the hth harmonic current content array I of the medium-voltage side of the main transformer 2h [1,M], and the fundamental reactive power array Q3[1,M] of the low-voltage side of the main transformer; Wherein, M is the initial array length, and the data analysis interval is less than 3s.

[0018] II. According to the fundamental reactive power array of the low-voltage side of the main transformer, a target period with frequent reactive power changes is selected.

[0019] According to the fundamental reactive power array of the low-voltage side of the main transformer, in combination with the operating state of the reactive power compensation device, a target period with frequent reactive power changes is selected, and each group of data in the target period is obtained: the hth harmonic voltage content array U of the high-voltage side of the main transformer 1h [1,N], the hth harmonic current content array I of the high-voltage side of the main transformer 1h [1,N], the hth harmonic voltage content array U of the medium-voltage side of the main transformer 2h [1,N], the hth harmonic current content array I of the medium-voltage side of the main transformer 2h [1,N], and the fundamental reactive power array Q3[1,N] of the low-voltage side of the main transformer; Wherein, N is the array length after screening, the span length of the target period is in the range of 2-24h, when the span length of the target period is too long, the resonance state of the power transmission line will change, and when the span length of the target period is too short, the correlation calculation result will be affected.

[0020] III. In the target period, the first correlation coefficient between the hth harmonic voltage content array of the medium-voltage side of the main transformer and the hth harmonic current content array of the high-voltage side of the main transformer is calculated, and the second correlation coefficient between the hth harmonic voltage content array of the medium-voltage side of the main transformer and the hth harmonic current content array of the medium-voltage side of the main transformer is calculated.

[0021] In the target period, the first correlation coefficient r between the hth harmonic voltage content array U 2h [1,N] of the medium-voltage side of the main transformer and the hth harmonic current content array I 1h [1,N] of the high-voltage side of the main transformer is calculated. 21 ​; Within the target time period, calculate the h-th harmonic voltage content array U on the medium-voltage side of the main transformer. 2h [1,N] and the array I of h-th harmonic current content on the medium voltage side of the main transformer 2h The second correlation coefficient r between [1,N] 22 : ; Among them, U 2h [1,n] represents the array U of the h-th harmonic voltage content rate on the medium voltage side of the main transformer. 2h The nth data in [1,N] The array U of the h-th harmonic voltage content of the main transformer medium voltage side 2h The average value of [1,N]; I 1h [1,n] represents the array of h-th harmonic current content on the high-voltage side of the main transformer. 1h The nth data in [1,N] Main transformer high voltage side h-th harmonic current content array I 1h The average value of [1,N]; I 2h [1,n] represents the array of h-th harmonic current content on the medium voltage side of the main transformer. 2h The nth data in [1,N] Main transformer medium voltage side h-th harmonic current content array I 2h The average value of [1,N].

[0022] IV. Identify the resonance state of the high-voltage side of the main transformer based on the first and second correlation coefficients.

[0023] If the first correlation coefficient r 21 Greater than the preset threshold (the preset threshold is 0.9), and the first correlation coefficient r 21 The second correlation coefficient r is greater than the preset multiple (the preset multiple is 1.2 times). 22 If so, the high-voltage transmission line of the substation's main transformer will have a problem of lumped parameter parallel resonance.

[0024] V. Based on the h-th harmonic voltage content array of the high-voltage and medium-voltage sides of the main transformer, identify the harmonic impedance characteristics of the high-voltage side of the main transformer.

[0025] If the h-th harmonic voltage content array U on the high-voltage side of the main transformer 1h The average value of [1,N] The voltage content of the h-th harmonic on the medium-voltage side of the main transformer is greater than the array U. 2h The average value of [1,N] Then the harmonic impedance of the high-voltage transmission line of the main transformer of the substation after parallel resonance exhibits RC characteristics. If the h-th harmonic voltage content array U on the high-voltage side of the main transformer1h average of [1, N] smaller than the main transformer in the pressure side h harmonic voltage content array U 2h average of [1, N] , the substation main transformer high voltage system transmission line parallel resonance after the harmonic impedance shows the inductive characteristic.

[0026] In order to better illustrate the technical effect of the technical scheme of the present application, a specific example is introduced below.

[0027] The power grid topology of a certain substation is shown in Figure 2 , and there is a problem of 5th harmonic voltage exceeding the standard in the low voltage side of the main transformer.

[0028] The main transformer high voltage side, medium voltage side and low voltage side are synchronously monitored, and the total test time is 20h. The change trend of the fundamental reactive power of the main transformer low voltage side during the test period is shown in Figure 3 , it can be seen that the reactive power compensation device of the main transformer low voltage side frequently switches in the period of 13h~15h, as shown in Figure 4 .

[0029] In the period of 13h~15h, the change trend of the 5th harmonic voltage content and the 5th harmonic current content synchronously monitored in the main transformer high voltage side and medium voltage side is shown in Figures 5 to 8 . According to the correlation analysis, the first correlation coefficient between the 5th harmonic voltage content of the main transformer medium voltage side and the 5th harmonic current content of the high voltage side is r 21 =0.98, and the second correlation coefficient between the 5th harmonic voltage content of the main transformer medium voltage side and the 5th harmonic current content of the main transformer medium voltage side is r 22 =0.25. At this time, r 21 >0.9 and r 21 >1.2*r 22 (the first correlation coefficient r 21 is obviously greater than the second correlation coefficient r 22 of the preset multiple), that is, the substation main transformer high voltage system transmission line exists the problem of concentrated parameter parallel resonance.

[0030] According to the statistical results of the average values of the 5th harmonic voltage content of the main transformer high voltage side and medium voltage side in the period of 13h~15h, the 5th harmonic voltage content of the main transformer high voltage side is 1.02%, the 5th harmonic voltage content of the main transformer medium voltage side is 1.52%, and the 5th harmonic voltage content of the main transformer medium voltage side is greater than that of the main transformer high voltage side. Therefore, the harmonic impedance of the substation main transformer high voltage system transmission line after parallel resonance shows the inductive characteristic.

[0031] The above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can be modified, or some technical features can be replaced by equivalent features; and these modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for identifying parallel resonance of lumped parameters in transmission lines of high-voltage substation systems, characterized in that: Includes the following steps: S1. Simultaneously monitor the high-voltage side, medium-voltage side and low-voltage side of the main transformer to obtain the harmonic voltage content array, harmonic current content array and fundamental reactive power array; S2. Select the target time period with frequent changes in reactive power based on the fundamental reactive power array of the low-voltage side of the main transformer; S3. Within the target time period, calculate the first correlation coefficient between the array of the h-th harmonic voltage content rate on the medium-voltage side of the main transformer and the array of the h-th harmonic current content on the high-voltage side of the main transformer, and the second correlation coefficient between the array of the h-th harmonic voltage content rate on the medium-voltage side of the main transformer and the array of the h-th harmonic current content on the medium-voltage side of the main transformer. S4. Based on the first and second correlation coefficients, identify the resonance state of the high-voltage side of the main transformer; S5. Based on the h-th harmonic voltage content array of the high-voltage side and medium-voltage side of the main transformer, identify the harmonic impedance characteristics of the high-voltage side of the main transformer.

2. The method for identifying parallel resonance of lumped parameters in transmission lines of substation high-voltage systems according to claim 1, characterized in that: S1 performs synchronous monitoring of the high-voltage, medium-voltage, and low-voltage sides of the main transformer to obtain harmonic voltage content arrays, harmonic current content arrays, and fundamental reactive power arrays, including: Synchronous monitoring is performed on the high-voltage, medium-voltage, and low-voltage sides of the main transformer to obtain the h-th harmonic voltage content array U on the high-voltage side of the main transformer. 1h [1,M], Array I of h-th harmonic current content on the high-voltage side of the main transformer 1h [1,M], Array U of h-th harmonic voltage content of the medium voltage side of the main transformer 2h [1,M], Array of h-th harmonic current content on the medium voltage side of the main transformer I 2h [1,M], and the fundamental reactive power array Q3[1,M] on the low-voltage side of the main transformer; Where M is the initial array length, and the data analysis interval is less than 3 seconds.

3. The method for identifying parallel resonance of lumped parameters in transmission lines of substation high-voltage systems according to claim 2, characterized in that: S2 selects target time periods with frequent reactive power changes based on the fundamental reactive power array on the low-voltage side of the main transformer, including: Based on the fundamental reactive power array of the low-voltage side of the main transformer and the operating status of the reactive power compensation device, a target time period with frequent reactive power changes is selected, and data sets are obtained for each target time period: The array U of the h-th harmonic voltage content of the high-voltage side of the main transformer 1h [1,N], Array I of h-th harmonic current content on the high-voltage side of the main transformer 1h [1,N], array U of h-th harmonic voltage content of the medium voltage side of the main transformer 2h [1,N], Array I of h-th harmonic current content on the medium voltage side of the main transformer 2h [1,N], and the fundamental reactive power array Q3[1,N] on the low-voltage side of the main transformer; Where N is the length of the filtered array, the span of the target time period is in the range of 2 to 24 hours. If the span of the target time period is too long, the resonance state of the transmission line will change, and if the span of the target time period is too short, it will affect the subsequent correlation calculation results.

4. The method for identifying parallel resonance of lumped parameters in transmission lines of substation high-voltage systems according to claim 3, characterized in that: In S3, within the target time period, the first correlation coefficient between the array of h-th harmonic voltage content on the medium-voltage side of the main transformer and the array of h-th harmonic current content on the high-voltage side of the main transformer, and the second correlation coefficient between the array of h-th harmonic voltage content on the medium-voltage side of the main transformer and the array of h-th harmonic current content on the medium-voltage side of the main transformer are calculated, including: Within the target time period, calculate the h-th harmonic voltage content array U on the medium-voltage side of the main transformer. 2h [1,N] and the array I of h-th harmonic current content on the high voltage side of the main transformer 1h The first correlation coefficient r between [1,N] 21 : ； Within the target time period, calculate the h-th harmonic voltage content array U on the medium-voltage side of the main transformer. 2h [1,N] and the array I of h-th harmonic current content on the medium voltage side of the main transformer 2h The second correlation coefficient r between [1,N] 22 : ； Among them, U 2h [1,n] represents the array U of the h-th harmonic voltage content rate on the medium voltage side of the main transformer. 2h The nth data in [1,N] The array U of the h-th harmonic voltage content of the main transformer medium voltage side 2h The average value of [1,N]; I 1h [1,n] represents the array of h-th harmonic current content on the high-voltage side of the main transformer. 1h The nth data in [1,N] Main transformer high voltage side h-th harmonic current content array I 1h The average value of [1,N]; I 2h [1,n] represents the array of h-th harmonic current content on the medium voltage side of the main transformer. 2h The nth data in [1,N] Main transformer medium voltage side h-th harmonic current content array I 2h The average value of [1,N].

5. The method for identifying parallel resonance of lumped parameters in the transmission lines of a substation high-voltage system according to claim 4, characterized in that: Based on the first and second correlation coefficients, S4 identifies the resonance state of the high-voltage side of the main transformer, including: If the first correlation coefficient r 21 The first correlation coefficient r is greater than the preset threshold. 21 The second correlation coefficient r is greater than the preset multiple. 22 If so, the high-voltage transmission line of the substation's main transformer will have a problem of lumped parameter parallel resonance.

6. The method for identifying parallel resonance of lumped parameters in transmission lines of substation high-voltage systems according to claim 5, characterized in that: Based on the h-th harmonic voltage content rate arrays of the high-voltage and medium-voltage sides of the main transformer, S5 identifies the harmonic impedance characteristics of the high-voltage side of the main transformer, including: If the h-th harmonic voltage content array U on the high-voltage side of the main transformer 1h The average value of [1,N] The voltage content of the h-th harmonic on the medium-voltage side of the main transformer is greater than the array U. 2h The average value of [1,N] Then the harmonic impedance of the high-voltage transmission line of the main transformer of the substation after parallel resonance exhibits RC characteristics. If the h-th harmonic voltage content array U on the high-voltage side of the main transformer 1h The average value of [1,N] The voltage content of the h-th harmonic on the medium-voltage side of the main transformer is less than the array U. 2h The average value of [1,N] The harmonic impedance of the high-voltage transmission line of the main transformer in the substation exhibits resistive-inductive characteristics after parallel resonance.

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