阅读说明：本技术 一种高精度宽范围的配电网电容电流测试方法 (High-precision wide-range power distribution network capacitance current testing method ) 是由 王鹏 董轩 姚骏 张卓 冯光 张海林 徐铭铭 秦振涛 孙芊 张建宾 陈明 于 2021-07-22 设计创作，主要内容包括：一种高精度宽范围的配电网电容电流测试方法,包括以下步骤：步骤1,构建配电网电容电流测试电路模型；步骤2,依次将三个频率不同但幅值相同的测试电流i-(1)、i-(2)、i-(3)从电压互感器二次侧注入；步骤3,分别采集输入测试电流为i-(1)、i-(2)、i-(3)时,电压互感器二次侧的电流幅值I-(1)、I-(2)、I-(3),电流相位和电流频率ω-(1)、ω-(2)、ω-(3),以及电压互感器二次侧的电压幅值U-(1)、U-(2)、U-(3)和电压相位步骤4,根据阻抗幅值和相位的表达式计算不同测试电流下,测试电路对应的阻抗Z-(1)、Z-(2)、Z-(3)的幅值A-(1)、A-(2)、A-(3)和相位B-(1)、B-(2)、B-(3)；步骤5,根据阻抗幅值和相位获取配电网对地电容C的值。本发明能够实现对配电网电容电流实时在线测量,且测量范围广、精度高。(A high-precision wide-range power distribution network capacitance current testing method comprises the following steps: step 1, constructing a power distribution network capacitance current test circuit model; step 2, sequentially testing three test currents i with different frequencies and same amplitude 1 、i 2 、i 3 Injecting from the secondary side of the voltage transformer; step 3, respectively collecting input test current as i 1 、i 2 、i 3 Current amplitude I of secondary side of voltage transformer 1 、I 2 、I 3 Phase of current Sum current frequency omega 1 、ω 2 、ω 3 And the voltage amplitude U of the secondary side of the voltage transformer 1 、U 2 、U 3 And voltage phase Step 4, calculating the impedance Z corresponding to the test circuit under different test currents according to the expression of the impedance amplitude and the phase 1 、Z 2 、Z 3 Amplitude A of 1 、A 2 、A 3 And phase B 1 、B 2 、B 3 (ii) a And 5, acquiring the value of the capacitance C of the power distribution network to the ground according to the impedance amplitude and the phase. The invention can realize real-time online measurement of the capacitance and current of the power distribution network, and has wide measurement range and high precision.)

1. A high-precision wide-range power distribution network capacitance current testing method is characterized by comprising the following steps:

step 1, constructing a power distribution network capacitance current test circuit model;

step 2, sequentially testing three test currents i with different frequencies and same amplitude₁、i₂、i₃Injecting from a voltage transformer secondary side of the test circuit model;

step 3, respectively collecting input test current as i₁、i₂、i₃Current amplitude I of secondary side of voltage transformer₁、I₂、I₃Phase of currentSum current frequency omega₁、ω₂、ω₃And the voltage amplitude U of the secondary side of the voltage transformer₁、U₂、U₃And voltage phase

Step 4, calculating the impedance Z corresponding to the test circuit under different test currents according to the expression of the impedance amplitude and the phase₁、Z₂、Z₃Amplitude A of₁、A₂、A₃And phase B₁、B₂、B₃；

And 5, acquiring the value of the capacitance C of the power distribution network to the ground according to the impedance amplitude and the phase.

2. The method for testing the capacitance and the current of the power distribution network with high precision and wide range according to claim 1, wherein the amplitude of the test current injected in the step 2 does not exceed one thousandth of the amplitude of the normal working current of the power distribution network, and the frequency is less than 50 Hz.

3. The method for measuring capacitance and current of distribution network with high precision and wide range according to claim 2, wherein the measurement current i is₁、i₂、i₃The frequency combinations of (A) and (B) are 5Hz, 10Hz and 20 Hz.

4. The method for measuring capacitance and current of distribution network according to claim 3, wherein the impedance Z is₁、Z₂、Z₃Amplitude A of₁、A₂、A₃And phase B₁、B₂、B₃Is calculated as follows:

5. the method for measuring the capacitance and the current of the power distribution network with high precision and wide range according to claim 4, wherein the capacitance to ground C of the power distribution network is calculated by the following formula:

Technical Field

The invention belongs to the technical field of power distribution network measurement, and particularly relates to a high-precision wide-range power distribution network capacitance current testing method.

Background

In recent years, with the enlargement of urban power grid scale and the increase of medium-voltage electrical equipment and cable outgoing lines of a power distribution network in China, the zero sequence capacitance current level has started to influence multiple fields of distribution network system safety, equipment operation and maintenance, system scheduling, development planning and the like. The method for measuring the capacitance and current of the power distribution network is one of important measures for guaranteeing the safe operation of the power distribution network system, however, the existing method for measuring the capacitance and current of the power distribution network has the problems of few measured data, difficulty in reflecting the change process of the capacitance and current of the system, incapability of measuring the capacitance and current of the system in real time on line and the like. In addition, as equipment with own grounding points such as a primary and secondary fusion switch enters large-scale application, grounding parameters of the power distribution network change in real time, and the traditional offline measurement technology cannot meet the requirement of real-time measurement. Therefore, research on a wide-range high-precision ground capacitance and current online test method for the power distribution network is urgently needed, and theoretical support and technical guarantee are provided for safe and stable operation of the power distribution network.

At present, relevant researches have been carried out by scholars at home and abroad aiming at a method for testing capacitance and current of a power distribution network, and the prior art comprises measurement of capacitance and current of the power distribution network based on a three-frequency method. The method comprises the steps of injecting a variable frequency current signal into a power distribution network by using a zero sequence voltage transformer of the power distribution network, measuring a voltage signal returned by the voltage transformer inside an arc suppression coil, establishing a variable frequency equivalent circuit considering a damping resistor, and deducing to obtain the capacitance current of the power distribution network by using the variable frequency equivalent circuit. When the parameters of the arc suppression coil are unknown, the parameters of the ground capacitance of the power distribution network cannot be measured on line.

Disclosure of Invention

In order to solve the defects in the prior art, the invention aims to provide a high-precision wide-range power distribution network capacitance current testing method, which strictly deduces the expression of capacitance current in a current signal injection mode, realizes accurate measurement of the capacitance current of a power distribution network, and remarkably improves the measurement range and accuracy.

The invention adopts the following technical scheme. A high-precision wide-range power distribution network capacitance current testing method comprises the following steps:

step 1, constructing a power distribution network capacitance current test circuit model;

step 2, sequentially testing three test currents i with different frequencies and same amplitude₁、i₂、i₃Injecting from the secondary side of the voltage transformer;

step 3, respectively collecting input test current as i₁、i₂、i₃Current amplitude I of secondary side of voltage transformer₁、I₂、I₃Phase of currentSum current frequency omega₁、ω₂、ω₃And the voltage amplitude U of the secondary side of the voltage transformer₁、U₂、U₃And voltage phase

Step 4, calculating the impedance Z corresponding to the test circuit under different test currents according to the expression of the impedance amplitude and the phase₁、Z₂、Z₃Amplitude A of₁、A₂、A₃And phase B₁、B₂、B₃；

And 5, acquiring the value of the capacitance C of the power distribution network to the ground according to the impedance amplitude and the phase.

Preferably, the amplitude of the test current injected in the step 2 does not exceed one thousandth of the normal working current amplitude of the power distribution network, and the frequency is less than 50 Hz.

Preferably, the current i is tested₁、i₂、i₃The frequency combinations of (A) and (B) are 5Hz, 10Hz and 20 Hz.

Preferably, the impedance Z₁、Z₂、Z₃Amplitude A of₁、A₂、A₃And phase B₁、B₂、B₃Is calculated as follows:

preferably, the calculation formula of the power distribution network ground capacitance C is as follows:

compared with the prior art, the method for testing the capacitance current of the power distribution network has the advantages that the real-time online measurement of the capacitance current of the power distribution network can be realized under the condition that the parameters of the arc suppression coil are unknown, the measurement result is high in accuracy and wide in range, and theoretical support and technical guarantee are provided for safe and stable operation of the power distribution network.

Drawings

Fig. 1 is a schematic overall flow chart of a method for measuring capacitance and current of a power distribution network with wide precision range according to the present invention;

FIG. 2 is a schematic diagram of the overall structure of a power distribution network capacitance current test circuit according to the present invention;

fig. 3 is a schematic diagram of an equivalent circuit structure of the power distribution network capacitance current test circuit of the invention.

Detailed Description

The present application is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present application is not limited thereby.

Referring to the schematic diagram of fig. 1, which is an overall flow chart of the method for testing the capacitance and current of the power distribution network with high precision and wide range provided by the present invention, the method specifically includes the following steps,

step 1: constructing a power distribution network capacitance current test circuit model;

specifically, referring to the schematic diagram of fig. 2, fig. 2 is a schematic diagram of a structure of a power distribution network capacitance current test circuit in the invention, and the circuit includes a signal injection module 1, a power distribution network ground capacitance module 2, an arc suppression coil module 3 and a power distribution network three-phase power supply E_A、E_B、E_C(ii) a Wherein, the signal injection module 1 comprises a voltage transformer, the test current i passes through the secondary side injection test circuit of the voltage transformer, and the distribution network ground capacitor module 2 comprises a three-phase ground capacitor C_A、C_B、C_CThe arc suppression coil module 3 includes an inductor L₂，。

Wherein, three-phase to ground capacitor C of distribution network to ground capacitor module 2_A、C_B、C_CRespectively connected with a three-phase power supply E of a power distribution network_A、E_B、E_CConnected with each other, and one end of the voltage transformer of the signal injection module 1 and the inductance L of the arc suppression coil module 3₂One end of the transformer is respectively connected with a three-phase power source of the power distribution network, a voltage transformer and an inductor L₂And the other end of the same is grounded.

Further, referring to the schematic diagram of fig. 3, fig. 3 is a schematic diagram of an equivalent circuit structure of the test circuit, where the equivalent circuit includes: voltage transformer excitation resistor R_mAnd excitation reactance X_mWinding resistance R and short-circuit reactance X of voltage transformer_L1Three-phase earth capacitance sum C of distribution network and arc suppression coil reactance X_L2。

The test current i is injected into the power distribution network through the secondary side of the voltage transformer, and because the excitation impedance of the voltage transformer is far greater than the short-circuit impedance, the arc suppression coil impedance and the ground capacitive reactance of the power distribution network, an excitation loop can be ignored and is equivalent to an open circuit, the test current i can eliminate the influence of the internal impedance of the voltage transformer on the capacitive current test of the power distribution network, and the accuracy of a test result is improved.

Further, obtaining the electricity of the secondary side of the voltage transformerAmplitude of current I, phase of currentCurrent frequency omega, and voltage amplitude U and voltage phase of secondary side of voltage transformerAnd calculating the impedance amplitude A and the phase B of the test circuit according to the data.

The impedance amplitude and phase calculation formula of the test circuit is as follows:

step 2, sequentially testing three test currents i with different frequencies and same amplitude₁、i₂、i₃Injecting from the secondary side of the voltage transformer, wherein the amplitude of the injected test current should not exceed one thousandth of the amplitude of the normal working current of the power distribution network, and the frequency is less than 50 Hz;

specifically, the selection of the test current frequency can affect the accuracy of a capacitance current test result, in order to improve the accuracy of calculation of the ground capacitance value, a lower test current frequency should be selected, but if the test current frequency is selected too low, the influence of an excitation loop cannot be ignored, so that the two factors should be considered comprehensively when the frequency of the test current is selected, test currents with different frequencies are selected for simulation analysis, the influence of the different selection of the test current frequency on the accuracy of the final capacitance current test result is compared, and when the selected test current frequency is below 50Hz and does not contain 50Hz, the accurate measurement of the ground capacitance can be realized.

Further comparing the measurement accuracy under different test current frequency combinations to obtain three test currents i₁、i₂、i₃Has a preferred combination of frequencies of 5Hz, 10Hz and 20Hz。

Step 3, respectively collecting input test current as i₁、i₂、i₃Current amplitude I of secondary side of voltage transformer₁、I₂、I₃Phase of currentSum current frequency omega₁、ω₂、ω₃And the voltage amplitude U of the secondary side of the voltage transformer₁、U₂、U₃And voltage phase

Step 4, calculating the impedance Z corresponding to the test circuit under different test currents according to the expression of the impedance amplitude and the phase₁、Z₂、Z₃Amplitude A of₁、A₂、A₃And phase B₁、B₂、B₃；

Specifically, according to the input test current, the calculation formula of the impedance and the amplitude of the measuring circuit is as follows:

and 5, acquiring the value of the capacitance C of the power distribution network to the ground according to the impedance amplitude and the phase.

Specifically, the calculation formula of the power distribution network ground capacitance C is as follows:

compared with the prior art, the method has the advantages that the expression of the capacitance current is strictly deduced by injecting the current signal, and the specific values of the impedance amplitude and the phase are substituted, so that the online accurate measurement of the capacitance current of the power distribution network is realized, and the measurement range and the accuracy are remarkably improved.

The measuring method provided by the invention can realize real-time online measurement of the capacitance and current of the power distribution network when the parameters of the arc suppression coil of the test circuit are unknown, has high accuracy of the measurement result and wide range, and provides theoretical support and technical guarantee for safe and stable operation of the power distribution network.

In order to verify the beneficial effect of the power distribution network capacitance current testing method provided by the invention in practical application, the testing method provided by the invention is used for measuring the capacitances with different sizes, the difference between the testing value and the actual value is compared, and the comparison result is shown in the following table 1; further, for capacitors with the same size, the test method provided by the invention and the test method of the prior art for solving the capacitance current by injecting three constant currents with different frequencies into the secondary side of the voltage transformer and solving the capacitance current by injecting a variable frequency current signal into the power distribution network by using the zero sequence voltage transformer of the power distribution network are respectively adopted, the test is carried out under the same measurement background, and the measurement result and the measurement accuracy of the capacitance to ground are obtained under the comparison of the three methods, and the results are shown in the following table 2:

table 1: capacitance test value and actual value comparison table based on test method provided by the invention

3	3.03	0.110000
			9	9.07	0.070000
30	29.973	0.090000
			60	59.94	0.010000
80	79.896	0.030000
			100	99.99	0.010000
120	119.97	0.025000
			160	160.013	0.008125

Table 2: capacitance test value and actual value comparison table based on traditional three-frequency test method

Actual value of capacitance (μ F)	Test value (μ F)	Measurement error (%)
			10	7.7088	-29.21
20	15.032	-24.84
			30	22.927	-23.58
100	123.51	23.51
			150	208.89	40.52
180	253.47	39.26

As can be seen from tables 1 and 2, the measurement errors obtained by the online test method provided by the invention are all below 0.11%, while the measurement errors of the traditional measurement method exceed 20%, and when the size of the ground capacitance of the power distribution network is 150 muF, the test error is as high as 40%, and when the size of the ground capacitance of the power distribution network is 10 muF, the test error is close to 30%. Therefore, the error of the ground capacitance test value of the power distribution network under the traditional test method is large, the test range is small, when the ground capacitance of the power distribution network is large or small, the test error can be further enlarged, and the online accurate measurement of the ground capacitance of the power distribution network cannot be realized, but the test method provided by the invention can realize the high-precision online measurement of the capacitance of the power distribution network in a wide range of 3-160 mu F.

In summary, it can be seen that the measurement method provided by the invention can accurately measure the capacitance and current of the power distribution network in a wide range on line, and can effectively ensure the safe and stable operation of the power distribution network.

The present applicant has described and illustrated embodiments of the present invention in detail with reference to the accompanying drawings, but it should be understood by those skilled in the art that the above embodiments are merely preferred embodiments of the present invention, and the detailed description is only for the purpose of helping the reader to better understand the spirit of the present invention, and not for limiting the scope of the present invention, and on the contrary, any improvement or modification made based on the spirit of the present invention should fall within the scope of the present invention.