阅读说明：本技术 10kV母线电容电流监测方法 (10kV bus capacitance current monitoring method ) 是由 田凤兰 景中炤 赵秀娜 刘旭贺 杨铮 迟渊泓 陈嵩 李辉 黄玉洋 于 2020-11-10 设计创作，主要内容包括：本发明公开了一种10kV母线电容电流监测方法,采用开口三角形接法接入电网的电压互感器实现测量信号的输入,将电容的引脚穿过空心线圈,通过空心线圈上串联的采样电阻获取由输入的电流信号产生的电压信号,并形成实时数据库,随机抽取三组数据完成对地电容及系统母线的电容电流,避免了与测试人员与电网的直接接触,从而有效提高了安全性,此外,采用不同于工频电压频率的测量信号,可以避免工频电压对测试结果的影响,使得检测精度高。(The invention discloses a 10kV bus capacitance current monitoring method, which adopts a voltage transformer accessed to a power grid by an open delta connection method to realize the input of a measurement signal, leads pins of a capacitor to penetrate through a hollow coil, obtains a voltage signal generated by the input current signal through a sampling resistor connected in series on the hollow coil, forms a real-time database, randomly extracts three groups of data to complete the capacitance current to ground capacitance and a system bus, avoids the direct contact with a tester and the power grid, thereby effectively improving the safety.)

1. A10 kV bus capacitance current monitoring method comprises the following steps: step one, a voltage transformer is connected into a power grid by adopting an open delta connection method;

inputting a smaller current signal different from the power frequency voltage of the power grid at an open triangular end of the voltage transformer through a signal generator, enabling a pin of a neutral point external capacitor to penetrate through the hollow coil, and acquiring a voltage signal generated by the input current signal through a sampling resistor connected in series on the hollow coil;

changing the frequency of the input current signal until at least five groups of input current signals and voltage signals are obtained, and removing the minimum value and the maximum value and then removing the average value of the remaining three groups to be used as a large group of current and voltage input data;

step four, repeating the step three at least five times, removing the maximum value and the minimum value, forming at least three groups of current signals and voltage signal input signals, and forming a real-time database;

step five, randomly extracting three groups from the database in the step four, and calculating the ground capacitance of the power grid;

and step six, calculating the capacitance current of the power grid ungrounded system bus according to the ground capacitance.

2. The 10kV bus capacitance current monitoring method as claimed in claim 1, wherein: the voltage transformer in the first step comprises a primary winding and a secondary winding, the primary winding is directly connected with a three-phase bus of a power grid, and the secondary winding is connected with a signal generator by adopting an open delta connection method.

3. The 10kV bus capacitance current monitoring method as claimed in claim 1, wherein: in the second step, the hollow coil is connected in series with the sampling resistor, and a voltage detection element for detecting the voltage on the sampling resistor is connected with the sampling resistor.

4. The 10kV bus capacitance current monitoring method as claimed in claim 1, wherein: in the second step, the ampere loop law and the faraday electromagnetic induction law can be known as follows:

∮H·dl＝I

B＝μH

in summary, the voltage across the sampling resistor is:

wherein: n is the number of turns of the air core coil, d is the thickness of the air core coil, u is the magnetic conductivity of the air core coil, R1 and R2 are the center distance (inside and outside diameter) from the inner and outer rings of the air core coil to the capacitive pin, and dI/dt is the change rate of capacitive current.

5. The 10kV bus capacitance current monitoring method as claimed in claim 1, wherein: in the fifth step, the capacitance to ground is calculated according to the following formula:

in the formula, C0 is capacitance to ground, i ═ 1, 2, and 3, and represents three groups of data detected when a current signal is input, Zi is equivalent impedance of a loop in each group of data, n1 is the number of turns of a primary winding, n2 is the number of turns of a secondary winding, uoi is a voltage value of a voltage signal measured in each group of data, io is a current value of the input current signal, ω i ═ 2 pi fi, and fi is a frequency of the current signal input in each group of data.

6. The 10kV bus capacitance current monitoring method as claimed in claim 1, wherein: in the sixth step, the capacitance current I of the bus is calculated according to the following formula:

where ω is 2 π f, f is the frequency of the power frequency voltage in the grid, C0 is the capacitance to ground,the phase voltage of a bus in the power grid.

The technical field is as follows:

the invention relates to a power grid detection method, in particular to a 10kV bus capacitance current monitoring method.

Background art:

the capacitance current level is a key indicator of the operation of the power distribution system. However, the accurate detection (monitoring) of the capacitance current is affected by various factors such as grid structure, operation mode, load variation, etc., and it is difficult for the current (monitoring) method to truly reflect the capacitance current value of the system. Firstly, the existing test mode is limited, although the capacitance current direct measurement method can ensure the measurement precision, the method is destructive and has high risk, and the method is mainly applied to type test verification of scientific research and detection instruments, capacitive current examination of special conditions and the like. Common indirect measurement methods comprise a neutral point plus capacitance method and a secondary injection method, the maximum measurement range of the conventional test instrument is 250A, but with the large amount of cables entering the ground, the capacitance current of a 10kV system in a local area exceeds 300A, for the distribution capacitance of a distribution network in a wider range, the conventional device or test platform cannot accurately obtain the distribution capacitance (the error is over 15 percent), and the large-range test instrument is extremely difficult to develop. The secondary injection method is characterized in that a test instrument injects non-power-frequency current at a PT opening triangle, the current respectively generates voltage drop in winding resistance R, leakage reactance XL and lead to ground capacitance of PT three phases, capacitance current of a system is calculated according to the relation between the capacitance and the impedance, and although the risk of the secondary injection method is low, the discreteness of a test result is large. The above measurement methods are limited by the system capacitance current level, operating equipment parameters, harmonic load and the like, and have certain problems in precision or safety.

The invention content is as follows:

the technical problem to be solved by the invention is as follows: the defects in the prior art are overcome, and the 10kV bus capacitance current monitoring method with high detection precision and good safety is provided.

The technical scheme of the invention is as follows: a10 kV bus capacitance current monitoring method comprises the following steps: step one, a voltage transformer is connected into a power grid by adopting an open delta connection method;

inputting a smaller current signal different from the power frequency voltage of the power grid at an open triangular end of the voltage transformer through a signal generator, enabling a pin of a capacitor to penetrate through the hollow coil, and acquiring a voltage signal generated by the input current signal through a sampling resistor connected in series on the hollow coil;

changing the frequency of the input current signal until at least five groups of input current signals and voltage signals are obtained, and removing the minimum value and the maximum value and then removing the average value of the remaining three groups to be used as a large group of current and voltage input data;

step four, repeating the step three at least five times, removing the maximum value and the minimum value, forming at least three groups of current signals and voltage signal input signals, and forming a real-time database;

step five, randomly extracting three groups from the database in the step four, and calculating the ground capacitance of the power grid;

and step six, calculating the capacitance current of the power grid ungrounded system bus according to the ground capacitance.

Further, the voltage transformer in the first step comprises a primary winding and a secondary winding, and the primary winding is directly connected with electricity

The three-phase bus and the secondary winding of the network are connected with a signal generator by adopting an open delta connection method.

Further, in the second step, the hollow coil is connected in series with a sampling resistor, and a voltage detection element for detecting the voltage on the sampling resistor is connected to the sampling resistor.

Further, in the second step, the ampere loop law and the faraday electromagnetic induction law can be used to know that:

∮H·dl＝I

B＝μH

in summary, the voltage across the sampling resistor is:

wherein: n is the number of turns of the air core coil, d is the thickness of the air core coil, u is the magnetic conductivity of the air core coil, R1 and R2 are the center distance (inside and outside diameter) from the inner and outer rings of the air core coil to the capacitive pin, and dI/dt is the change rate of capacitive current.

Further, the capacitance to ground in the fifth step is calculated according to the following formula:

in the formula, C0 is capacitance to ground, i ═ 1, 2, and 3, and represents three groups of data detected when a current signal is input, Zi is equivalent impedance of a loop in each group of data, n1 is the number of turns of a primary winding, n2 is the number of turns of a secondary winding, uoi is a voltage value of a voltage signal measured in each group of data, io is a current value of the input current signal, ω i ═ 2 pi fi, and fi is a frequency of the current signal input in each group of data.

Further, the capacitance current I of the bus in the sixth step is calculated according to the following formula:

where ω is 2 π f, f is the frequency of the power frequency voltage in the grid, C0 is the capacitance to ground,the phase voltage of a bus in the power grid.

The invention has the beneficial effects that:

1. the invention realizes the input of the measuring signal by adopting the voltage transformer which is connected into the power grid by adopting an open triangle connection method, leads the pins of the capacitor to pass through the hollow coil, obtains the voltage signal generated by the input current signal through the sampling resistor which is connected in series on the hollow coil, forms a real-time database, randomly extracts three groups of data to complete the capacitance current of the ground capacitor and the system bus, and avoids the direct contact with the power grid by testers, thereby effectively improving the safety.

2. When the invention collects current and voltage data, group data is formed by removing the minimum value and the maximum value and then removing the average value, a plurality of group data are formed by removing the maximum value and the minimum value, at least three groups of current signals and voltage signal input signals are formed, a real-time database is formed, and then three groups of data are randomly extracted from the database to calculate the capacitance current, thereby solving the instability of the capacitance current and ensuring the accuracy of detection.

Description of the drawings:

fig. 1 is a flow chart of a 10kV bus capacitance current monitoring method.

The specific implementation mode is as follows:

example (b): see fig. 1.

A10 kV bus capacitance current monitoring method adopts a voltage transformer which is connected into a power grid by an open delta connection method to realize the input of a measurement signal, a pin of a capacitor penetrates through a hollow coil, a voltage signal generated by the input current signal is obtained through a sampling resistor which is connected in series on the hollow coil, a real-time database is formed, three groups of data are randomly extracted to complete the capacitance current of a ground capacitor and a system bus, the direct contact between a tester and the power grid is avoided, and therefore, the safety is effectively improved.

The present application will be described in detail below with reference to the drawings and examples.

Step one, a voltage transformer is connected into a power grid by adopting an open delta connection method;

the voltage transformer comprises a primary winding and a secondary winding, the primary winding is directly connected with a three-phase bus of a power grid, and the secondary winding is connected with a signal generator by adopting an open delta connection method.

Inputting a smaller current signal different from the power frequency voltage of the power grid at an open triangular end of the voltage transformer through a signal generator, enabling a pin of a capacitor to penetrate through the hollow coil, and acquiring a voltage signal generated by the input current signal through a sampling resistor connected in series on the hollow coil;

the hollow coil is connected with the sampling resistor in series, and a voltage detection element for detecting the voltage on the sampling resistor is connected with the sampling resistor.

From ampere's loop law and faraday's electromagnetic induction law:

∮H·dl＝I

B＝μH

in summary, the voltage across the sampling resistor is:

wherein: n is the number of turns of the air core coil, d is the thickness of the air core coil, u is the magnetic conductivity of the air core coil, R1 and R2 are the center distance (inside and outside diameter) from the inner and outer rings of the air core coil to the capacitive pin, and dI/dt is the change rate of capacitive current.

Changing the frequency of the input current signal until at least five groups of input current signals and voltage signals are obtained, and removing the minimum value and the maximum value and then removing the average value of the remaining three groups to be used as a large group of current and voltage input data;

step four, repeating the step three at least five times, removing the maximum value and the minimum value, forming at least three groups of current signals and voltage signal input signals, and forming a real-time database;

step five, randomly extracting three groups from the database in the step four, and calculating the ground capacitance of the power grid;

the capacitance to ground is calculated according to the following formula:

in the formula, C0 is capacitance to ground, i ═ 1, 2, and 3, and represents three groups of data detected when a current signal is input, Zi is equivalent impedance of a loop in each group of data, n1 is the number of turns of a primary winding, n2 is the number of turns of a secondary winding, uoi is a voltage value of a voltage signal measured in each group of data, io is a current value of the input current signal, ω i ═ 2 pi fi, and fi is a frequency of the current signal input in each group of data.

And step six, calculating the capacitance current of the power grid ungrounded system bus according to the ground capacitance.

The capacitance current I of the bus is calculated according to the following formula:

where ω is 2 π f, f is the frequency of the power frequency voltage in the grid, C0 is the capacitance to ground,the phase voltage of a bus in the power grid.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and all simple modifications, equivalent variations and modifications made to the above embodiment according to the technical spirit of the present invention still fall within the scope of the technical solution of the present invention.