CN106093591B - A system and method for measuring capacitive current in a neutral point ungrounded distribution network - Google Patents
A system and method for measuring capacitive current in a neutral point ungrounded distribution network Download PDFInfo
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Abstract
本发明涉及配电网电容电流测量技术,具体涉及一种中性点不接地配电网电容电流测量系统及方法,测量系统包括母线电压互感器、可调电阻、变频电压源和电压测量仪;可调电阻与变频电压源串联后接入母线电压互感器第三绕组两端,电压测量仪也接入母线电压互感器第三绕组两端。利用测量系统进行测量的方法解决母线电压互感器的短路阻抗影响测量精度的问题,并且考虑到由于电网不平衡度而引起的零序电压对信号注入法测量电容电流的影响,提高配电网电容电流测量的准确性,采用精确的戴维南等效电路模型,对系统的对地电容进行求解。测量过程在互感器的第三绕组侧进行,不需要变更一次设备接线,测量方法安全便捷,结果准确可靠。
The invention relates to a capacitive current measurement technology of a distribution network, in particular to a system and method for measuring a capacitive current of a neutral point ungrounded distribution network. The measurement system includes a bus voltage transformer, an adjustable resistor, a variable frequency voltage source and a voltage measuring instrument; The adjustable resistor is connected in series with the variable frequency voltage source and connected to both ends of the third winding of the bus voltage transformer, and the voltage measuring instrument is also connected to both ends of the third winding of the bus voltage transformer. The method of measuring by using the measurement system solves the problem that the short-circuit impedance of the bus voltage transformer affects the measurement accuracy, and considers the influence of the zero-sequence voltage caused by the unbalanced degree of the power grid on the measurement of the capacitance current by the signal injection method, and improves the capacitance of the distribution network. To ensure the accuracy of current measurement, an accurate Thevenin equivalent circuit model is used to solve for the capacitance of the system to ground. The measurement process is carried out on the third winding side of the transformer, without changing the primary equipment wiring, the measurement method is safe and convenient, and the result is accurate and reliable.
Description
技术领域technical field
本发明属于配电网电容电流测量技术领域,特别涉及一种中性点不接地配电网电容电流测量系统及方法。The invention belongs to the technical field of capacitive current measurement of a distribution network, and in particular relates to a system and method for measuring a capacitive current of a neutral point ungrounded distribution network.
背景技术Background technique
我国早期的中低压配电网多采用中性点不接地方式,发生单相接地故障时,在电网电容电流不大的情况下,接地电弧能够自熄,配电网可带故障继续供电1~2小时。随着电力系统配电网络的不断发展,尤其是城市电网中电缆线路的大量投运,线路对地电容电流不断增大,导致配网线路的单相接地故障电流急剧增大,接地弧难以自熄灭,进而引发相间短路故障。为了确保电网中出现的各种接地电弧能可靠熄灭,当系统电容电流大于规程要求的限值时,须安装消弧线圈以补偿接地电容电流。配电网的电容电流的准确测量是消弧线圈合理补偿的前提,消弧线圈安装与否以及安装容量的大小,取决于电容电流测量值的大小。The early medium and low-voltage distribution networks in my country mostly adopted the neutral point ungrounded mode. When a single-phase ground fault occurs, the grounding arc can be self-extinguished under the condition that the grid capacitive current is not large, and the distribution network can continue to supply power with faults for 1~ 2 hours. With the continuous development of the distribution network of the power system, especially the large number of cable lines in the urban power grid, the capacitive current of the line to the ground continues to increase, resulting in a sharp increase in the single-phase ground fault current of the distribution network line, and it is difficult for the grounding arc to be self-sufficient. extinguished, causing a phase-to-phase short circuit fault. In order to ensure that all kinds of grounding arcs in the power grid can be extinguished reliably, when the system capacitive current is greater than the limit value required by regulations, an arc suppression coil must be installed to compensate for the grounding capacitive current. The accurate measurement of the capacitive current of the distribution network is the prerequisite for reasonable compensation of the arc suppression coil. Whether the arc suppression coil is installed or not and the size of the installation capacity depend on the measured value of the capacitive current.
为避免在电网一次侧进行操作,目前广泛采用的测量方法是信号注入法。在测量中性点不接地配电网的电容电流时,通常选择在互感器的开口三角端注入异频信号,通过测量注入信号的电流和开口三角端的电压来计算电网的对地电容。考虑到电压互感器的短路阻抗不能忽略不计,有些方法则通过加一个可调电感来减小误差。但考虑到电网实际运行时会存在一定的零序电压,该零序电压会反映在互感器开口三角端,对电压的测量带来很大的影响,往往使得测量结果误差较大。In order to avoid operation on the primary side of the grid, the widely used measurement method is the signal injection method. When measuring the capacitive current of the neutral point ungrounded distribution network, it is usually chosen to inject different frequency signals at the open triangle end of the transformer, and the ground capacitance of the grid is calculated by measuring the current of the injected signal and the voltage of the open triangle end. Considering that the short-circuit impedance of the voltage transformer cannot be ignored, some methods reduce the error by adding an adjustable inductance. However, considering that there will be a certain zero-sequence voltage in the actual operation of the power grid, the zero-sequence voltage will be reflected in the open delta end of the transformer, which will have a great impact on the voltage measurement and often cause large errors in the measurement results.
发明内容Contents of the invention
本发明的目的是提出了一种测量过程在母线电压互感器的第三绕组侧进行,不需要变更一次设备接线,并考虑采用注入信号法测量电容电流时,电网实际运行时的零序电压对测量结果的影响,能提高配电网电容电流测量准确性的中性点不接地配电网电容电流测量系统及方法。The purpose of the present invention is to propose a measurement process carried out on the third winding side of the bus voltage transformer without changing the wiring of the primary equipment, and considering the influence of the zero-sequence voltage during the actual operation of the power grid when using the injection signal method to measure the capacitive current Influence of measurement results, a neutral point ungrounded distribution network capacitance current measurement system and method that can improve the accuracy of distribution network capacitance current measurement.
为实现上述目的,本发明所采用的技术方案是:一种中性点不接地配电网电容电流测量系统,包括母线电压互感器、可调电阻、变频电压源和电压测量仪;所述可调电阻与变频电压源串联后接入所述母线电压互感器第三绕组两端,所述电压测量仪也接入所述母线电压互感器第三绕组两端。In order to achieve the above object, the technical solution adopted by the present invention is: a neutral point ungrounded distribution network capacitive current measurement system, including a bus voltage transformer, an adjustable resistor, a variable frequency voltage source and a voltage measuring instrument; The adjustable resistor is connected in series with the variable frequency voltage source and connected to both ends of the third winding of the bus voltage transformer, and the voltage measuring instrument is also connected to both ends of the third winding of the bus voltage transformer.
在所述的中性点不接地配电网电容电流测量系统中,所述母线电压互感器第三绕组为开口三角形接法。In the neutral point ungrounded distribution network capacitive current measurement system, the third winding of the bus voltage transformer is connected in an open delta.
在所述的中性点不接地配电网电容电流测量系统中,所述电压测量仪采用电磁式仪表,且连接在所述母线电压互感器的开口三角端。In the neutral point ungrounded distribution network capacitive current measurement system, the voltage measuring instrument is an electromagnetic instrument, and is connected to the open delta end of the bus voltage transformer.
一种中性点不接地配电网电容电流测量方法,包括以下步骤:A method for measuring the capacitive current of a neutral point ungrounded distribution network, comprising the following steps:
S1.将变频电压源和可调电阻支路断开,测量开路电压U0;S1. Disconnect the variable frequency voltage source and the adjustable resistance branch, and measure the open circuit voltage U 0 ;
S2.将变频电压源输出置零,可调电阻阻值调至最大,接上变频电压源和可调电阻支路,调节可调电阻阻值至R1,记录电压测量仪读数U01;S2. Set the output of the variable frequency voltage source to zero, adjust the resistance of the adjustable resistor to the maximum, connect the variable frequency voltage source and the branch of the adjustable resistor, adjust the resistance of the adjustable resistor to R 1 , and record the reading of the voltage measuring instrument U 01 ;
S3.再调节可调电阻阻值至R2,记录电压测量仪读数U02;S3. Adjust the resistance value of the adjustable resistor to R 2 , and record the reading of the voltage measuring instrument U 02 ;
S4.保持可调电阻阻值为R2不变,设置变频电压源输出电压频率为25Hz,输出电压有效值为E1,记录电压测量仪读数U1;S4. Keep the adjustable resistor resistance value R2 unchanged , set the output voltage frequency of the variable frequency voltage source to 25Hz, the effective value of the output voltage is E1, and record the reading of the voltage measuring instrument U1 ;
S5.保持可调电阻阻值为R2不变,设置变频电压源输出电压频率为75Hz,输出电压有效值为E2,记录电压测量仪读数U2;S5. Keep the adjustable resistance value R2 unchanged, set the output voltage frequency of the variable frequency voltage source to 75Hz, the effective value of the output voltage is E2 , and record the reading U2 of the voltage measuring instrument ;
S6.依据步骤S1、S2、S3、S4、S5所测量数据,求解电网对地电容,经计算得到电网的电容电流值。S6. According to the measured data in steps S1, S2, S3, S4, and S5, the capacitance of the grid to ground is calculated, and the capacitance current value of the grid is obtained through calculation.
在所述的中性点不接地配电网电容电流测量方法中,所述步骤S2中的变频电压源为输出电压范围0~5V、频率范围10Hz~100Hz的变频电压源;所述可调电阻为高精确阻值可读,调节范围在0~5Ω的可调电阻。In the neutral point ungrounded distribution network capacitive current measurement method, the variable frequency voltage source in the step S2 is a variable frequency voltage source with an output voltage range of 0 to 5V and a frequency range of 10Hz to 100Hz; the adjustable resistance It is an adjustable resistor with high precision and readable resistance, and the adjustment range is 0~5Ω.
在所述的中性点不接地配电网电容电流测量方法中,所述步骤S2、S3中若开路电压大,则可调电阻阻值相应调大,且可调电阻调节范围1~3Ω。In the method for measuring the capacitive current of the neutral point ungrounded distribution network, if the open circuit voltage is large in the steps S2 and S3, the resistance value of the adjustable resistor is correspondingly increased, and the adjustable resistance range is 1-3Ω.
在所述的中性点不接地配电网电容电流测量方法中,所述步骤S4、S5中变频电压源的输出电压设置在5V左右,原则是不影响电网的正常运行。In the method for measuring the capacitive current of the neutral point ungrounded distribution network, the output voltage of the variable frequency voltage source in the steps S4 and S5 is set at about 5V, and the principle is not to affect the normal operation of the power grid.
在所述的中性点不接地配电网电容电流测量方法中,所述步骤S6中求解电网对地电容以及电网的电容电流值包括以下步骤:In the described neutral point ungrounded distribution network capacitive current measurement method, solving the grid-to-ground capacitance and the capacitor current value of the grid in the step S6 includes the following steps:
S61.求出R和|X50|;S61. Obtain R and |X 50 |;
根据所述步骤S1、S2、S3,得以下方程组:According to the steps S1, S2, S3, the following equations are obtained:
其中,U0为开路电压;C0为折算到母线电压互感器第三绕组的电网对地电容;R和L为母线电压互感器折算到第三绕组的漏阻和漏感;X50为电容C0和电感L在工频50Hz下的电抗;Among them, U 0 is the open circuit voltage; C 0 is the grid-to-ground capacitance converted to the third winding of the bus voltage transformer; R and L are the leakage resistance and leakage inductance converted to the third winding of the bus voltage transformer; X 50 is the capacitance The reactance of C 0 and inductance L at power frequency 50Hz;
解(1)得到R和|X50|;Solve (1) to get R and |X 50 |;
S62.求出UE1和UE2;S62. Calculate U E1 and U E2 ;
根据所述步骤S4、S5得:Obtain according to described step S4, S5:
其中,U02为电压源U0单独作用时测量点电压有效值,UE1为变频电压源输出频率为25Hz时输出电压有效值,UE2为变频电压源输出频率为75Hz时输出电压有效值;Among them, U 02 is the effective value of the voltage at the measurement point when the voltage source U 0 acts alone, U E1 is the effective value of the output voltage when the output frequency of the variable frequency voltage source is 25Hz, and U E2 is the effective value of the output voltage when the output frequency of the variable frequency voltage source is 75Hz;
解(2)得到UE1和UE2;Solution (2) to get U E1 and U E2 ;
S63.求出|X25|和|X75|;S63. Calculate |X 25 | and |X 75 |;
由分压原理,可得:According to the principle of partial pressure, we can get:
其中,X25为电容C0和电感L在25Hz下的电抗,X75为电容C0和电感L在75Hz下的电抗;Among them, X 25 is the reactance of capacitor C 0 and inductance L at 25Hz, and X 75 is the reactance of capacitor C 0 and inductance L at 75Hz;
解(3)得到|X25|和|X75|;Solution (3) gets |X 25 | and |X 75 |;
S64.计算电容C0;S64. Calculate the capacitance C 0 ;
比较所述步骤S61、S63所得|X50|、|X25|和|X75|的大小;Comparing the sizes of |X 50 |, |X 25 | and |X 75 | obtained in steps S61 and S63;
a.若|X75|为最小,则有a. If |X 75 | is the smallest, then there is
b.若|X50|为最小,则有b. If |X 50 | is the smallest, then there is
c.若|X25|为最小,则有c. If |X 25 | is the smallest, then there is
其中,ω75、ω50和ω25分别为与频率75Hz、50Hz和25Hz相对应的角频率;Wherein, ω 75 , ω 50 and ω 25 are angular frequencies corresponding to frequencies 75Hz, 50Hz and 25Hz, respectively;
解(4)、(5)、(6)得到电容C0;Solve (4), (5), (6) to obtain capacitance C 0 ;
S65.将步骤S64得到的电容C0换算成电网的对地电容C0′;S65. Convert the capacitance C 0 obtained in step S64 into the ground capacitance C 0 ′ of the power grid;
换算公式为:The conversion formula is:
其中,k13为电压互感器第一绕组到第三绕组的变比;Wherein, k 13 is the transformation ratio from the first winding to the third winding of the voltage transformer;
S66.最后求出电网的电容电流:S66. Find the capacitive current of the grid at last:
其中,IC为电网的电容电流,为电网额定相电压。Among them, I C is the capacitive current of the grid, is the rated phase voltage of the grid.
为了解决母线电压互感器的短路阻抗影响测量精度的问题,并且考虑到由于电网不平衡度而引起的零序电压对信号注入法测量电容电流的影响,提高配电网电容电流测量的准确性,提出的中性点不接地配电网电容电流测量系统,包括母线电压互感器、可调电阻、变频电压源和电压测量仪;当母线电压互感器处于正常工作状态,其第三绕组为开口三角形接法,变频电压源与可调电阻串联后接入电压互感器的开口三角端,电压测量仪为电磁式仪表,将其接入互感器开口三角端,用于测量电压有效值。In order to solve the problem that the short-circuit impedance of the bus voltage transformer affects the measurement accuracy, and consider the influence of the zero-sequence voltage caused by the unbalanced degree of the power grid on the signal injection method to measure the capacitive current, improve the accuracy of the capacitive current measurement of the distribution network, The proposed neutral point ungrounded distribution network capacitive current measurement system includes a bus voltage transformer, an adjustable resistor, a variable frequency voltage source and a voltage measuring instrument; when the bus voltage transformer is in a normal working state, its third winding is an open triangle Connection method, the variable frequency voltage source and the adjustable resistor are connected in series to the open triangle end of the voltage transformer, and the voltage measuring instrument is an electromagnetic instrument, which is connected to the open triangle end of the transformer for measuring the effective value of the voltage.
同时还提出了中性点不接地配电网电容电流测量方法,包括以下步骤:At the same time, a method for measuring the capacitive current of the neutral point ungrounded distribution network is proposed, including the following steps:
1)把变频电压源和可调电阻支路断开,测量开路电压;1) Disconnect the variable frequency voltage source and the adjustable resistance branch, and measure the open circuit voltage;
2)把变频电压源输出置零,可调电阻阻值调到最大,接上变频电压源和可调电阻支路,调节可调电阻阻值,记录电压测量仪读数;2) Set the output of the variable frequency voltage source to zero, adjust the resistance value of the adjustable resistor to the maximum, connect the variable frequency voltage source and the branch circuit of the adjustable resistor, adjust the resistance value of the adjustable resistor, and record the reading of the voltage measuring instrument;
3)改变可调电阻阻值,记录电压测量仪读数;3) Change the resistance value of the adjustable resistor and record the reading of the voltage measuring instrument;
4)保持可调电阻阻值不变,设置变频电压源,使其输出25Hz的电压,记录电压测量仪读数;4) Keep the resistance value of the adjustable resistor unchanged, set the variable frequency voltage source to output a voltage of 25Hz, and record the readings of the voltage measuring instrument;
5)保持可调电阻阻值不变,设置变频电压源,使其输出75Hz的电压,记录电压测量仪读数;5) Keep the resistance value of the adjustable resistor unchanged, set the variable frequency voltage source to output a voltage of 75Hz, and record the readings of the voltage measuring instrument;
上述步骤1)中,所选变频电压源输出电压范围0-5V、频率范围10Hz-100Hz即可,所选可调电阻调节范围0-5Ω,阻值可读并且精度高。In the above step 1), the output voltage range of the selected variable frequency voltage source is 0-5V, and the frequency range is 10Hz-100Hz. The selected adjustable resistor has an adjustment range of 0-5Ω, and the resistance value is readable and has high precision.
上述步骤2)、3)中,可调电阻阻值在1-3Ω范围内调节较为合适,不能太小,也不宜过大,为了提高测量精度,如果开路电压较大,阻值可以相应的调大些。In the above steps 2) and 3), it is more appropriate to adjust the resistance value of the adjustable resistor within the range of 1-3Ω, which should not be too small or too large. In order to improve the measurement accuracy, if the open circuit voltage is large, the resistance value can be adjusted accordingly. bigger.
上述步骤4)、5)中,变频电压源的输出电压可以设置在5V左右,不会影响电网的正常运行。In the above steps 4) and 5), the output voltage of the variable frequency voltage source can be set at about 5V, which will not affect the normal operation of the power grid.
本发明有益效果:在考虑系统零序电压和互感器短路阻抗的情况下,采用精确的戴维南等效电路模型,对系统的对地电容进行求解。在原理上不仅避免了电压互感器短路阻抗对测量结果的影响,而且解决了一般信号注入法测量电容电流时无法避免的工频电压干扰的问题。测量过程在互感器的第三绕组侧进行,不需要变更一次设备接线,测量方法安全便捷。解决了采用注入信号法测量电容电流时,电网实际运行时的零序电压对测量结果的影响问题,测量结果准确可靠。The beneficial effect of the present invention is that under the condition of considering the zero-sequence voltage of the system and the short-circuit impedance of the transformer, an accurate Thevenin equivalent circuit model is used to solve the ground capacitance of the system. In principle, it not only avoids the influence of the short-circuit impedance of the voltage transformer on the measurement results, but also solves the problem of unavoidable power frequency voltage interference when the general signal injection method measures the capacitive current. The measurement process is carried out on the third winding side of the transformer, without changing the primary equipment wiring, and the measurement method is safe and convenient. When using the injection signal method to measure the capacitive current, the problem of the influence of the zero-sequence voltage in the actual operation of the power grid on the measurement results is solved, and the measurement results are accurate and reliable.
附图说明Description of drawings
图1为本发明一个具体实施方式的系统示意图;Fig. 1 is a system schematic diagram of a specific embodiment of the present invention;
图2为本发明一个具体实施方式的测量原理图;Fig. 2 is the measurement schematic diagram of a specific embodiment of the present invention;
其中,1-母线电压互感器、2-可调电阻、3-变频电压源、4-电压测量仪、A-第三绕组开口端标记、B-第三绕组开口端标记。Among them, 1-bus voltage transformer, 2-adjustable resistor, 3-variable frequency voltage source, 4-voltage measuring instrument, A-mark of the opening end of the third winding, B-mark of the opening end of the third winding.
具体实施方式Detailed ways
下面结合附图对本发明的实施方式进行详细描述。Embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.
图1是本发明的实施方式中性点不接地配电网电容电流测量系统示意图,包括母线电压互感器1、可调电阻2、变频电压源3和电压测量仪4;所述可调电阻2与变频电压源3串联后接入所述母线电压互感器1第三绕组两端,所述电压测量仪4也接入所述母线电压互感器1第三绕组两端。Fig. 1 is the schematic diagram of the capacitive current measuring system of neutral point ungrounded distribution network of the embodiment of the present invention, comprises bus voltage transformer 1, adjustable resistance 2, variable frequency voltage source 3 and voltage measuring instrument 4; Said adjustable resistance 2 After being connected in series with the variable frequency voltage source 3, it is connected to both ends of the third winding of the bus voltage transformer 1, and the voltage measuring instrument 4 is also connected to both ends of the third winding of the bus voltage transformer 1.
在上述的的中性点不接地配电网电容电流测量系统中,所述母线电压互感器1第三绕组为开口三角形接法。所述电压测量仪4采用电磁式仪表,且连接在所述母线电压互感器1的开口三角端。In the above-mentioned capacitive current measurement system of the neutral point ungrounded distribution network, the third winding of the bus voltage transformer 1 is connected in an open delta. The voltage measuring instrument 4 is an electromagnetic instrument, and is connected to the open triangle end of the bus voltage transformer 1 .
具体实施时,中性点不接地配电网电容电流测量系统,包括母线电压互感器1、可调电阻2、变频电压源3和电压测量仪4。母线电压互感器1处于正常工作状态,其第三绕组为开口三角形接法,开口端标记为A、B,可调电阻2与变频电压源3串联后,接入到电压互感器的A、B两端,电压测量仪4为电磁式仪表,将其接入到A、B两端,用于测量开口三角端电压有效值。During specific implementation, the neutral point ungrounded distribution network capacitive current measurement system includes a bus voltage transformer 1 , an adjustable resistor 2 , a variable frequency voltage source 3 and a voltage measuring instrument 4 . The busbar voltage transformer 1 is in normal working condition, its third winding is open delta connection, the opening ends are marked as A, B, after the adjustable resistor 2 is connected in series with the variable frequency voltage source 3, it is connected to A, B of the voltage transformer At both ends, the voltage measuring instrument 4 is an electromagnetic instrument, which is connected to both ends of A and B to measure the effective value of the voltage at the open triangle end.
图2所示,是利用上述测量系统的中性点不接地配电网电容电流测量方法,由于电网的不平衡度的影响,会在电压互感器的开口三角端产生一个零序电压,U0即为电压互感器开口三角端的开口电压。从A、B两端往电网侧看进去,其戴维南等效电路如图2中部分Ⅰ所示,其开路电压为U0;C0为折算到电压互感器第三绕组的电网对地电容;R和L为电压互感器折算到第三绕组的漏阻和漏感。另外,R’为可调电阻;E为变频电压源。As shown in Fig. 2, it is the method of measuring the capacitive current of the neutral point ungrounded distribution network using the above-mentioned measurement system. Due to the influence of the unbalanced degree of the power grid, a zero-sequence voltage will be generated at the open triangle end of the voltage transformer, U 0 That is, the opening voltage at the open triangle end of the voltage transformer. Looking from both ends of A and B to the grid side, its Thevenin equivalent circuit is shown in part I of Figure 2, and its open circuit voltage is U 0 ; C 0 is the grid-to-ground capacitance converted to the third winding of the voltage transformer; R and L are the leakage resistance and leakage inductance converted from the voltage transformer to the third winding. In addition, R' is an adjustable resistor; E is a variable frequency voltage source.
上述测量方法具体包括以下步骤:The above measurement method specifically includes the following steps:
①把变频电压源和可调电阻支路断开,测量开路电压U0;① Disconnect the variable frequency voltage source and the adjustable resistance branch, and measure the open circuit voltage U 0 ;
②把变频电压源输出置零,可调电阻阻值调到最大,接上变频电压源和可调电阻支路,将可调电阻阻值调到R1,记录电压测量仪读数U01;②Set the output of the variable frequency voltage source to zero, adjust the resistance value of the adjustable resistor to the maximum, connect the variable frequency voltage source and the branch circuit of the adjustable resistor, adjust the resistance value of the adjustable resistor to R 1 , and record the reading U 01 of the voltage measuring instrument;
③将可调电阻阻值调到R2,记录电压测量仪读数U02;③ Adjust the resistance value of the adjustable resistor to R 2 , and record the reading of the voltage measuring instrument U 02 ;
④保持可调电阻阻值为R2不变,设置变频电压源输出电压频率为25Hz,输出电压有效值大小为E1,记录电压测量仪读数U1;④Keep the resistance value of the adjustable resistor R 2 unchanged, set the output voltage frequency of the variable frequency voltage source to 25Hz, the effective value of the output voltage is E 1 , and record the reading of the voltage measuring instrument U 1 ;
⑤保持可调电阻阻值为R2不变,设置变频电压源输出电压频率为75Hz,输出电压有效值大小为E2,记录电压测量仪读数U2; ⑤Keep the resistance value of the adjustable resistor R2 unchanged, set the output voltage frequency of the variable frequency voltage source to 75Hz, the effective value of the output voltage is E2 , and record the reading U2 of the voltage measuring instrument ;
根据上述步骤①、②、③,可得以下方程组:According to the above steps ①, ②, ③, the following equations can be obtained:
其中X50为电容C0和电感L在工频50Hz下的电抗,由此方程组可以求出R和|X50|。Among them, X 50 is the reactance of capacitor C 0 and inductance L at the power frequency of 50Hz, and R and |X 50 | can be obtained from this equation group.
上述步骤④、⑤的原理如下:The principles of the above steps ④ and ⑤ are as follows:
在两个不同频率的电压源U0和E1或E2的共同作用下,电压测量仪的读数U1或U2与两电源分别单独作用时测量点电压有效值有如下关系:Under the combined action of two voltage sources U 0 and E 1 or E 2 with different frequencies, the reading U 1 or U 2 of the voltage measuring instrument has the following relationship with the effective value of the voltage at the measuring point when the two power sources act separately:
其中,U02为电压源U0单独作用时测量点电压有效值,UE1为变频电压源输出频率为25Hz时输出电压有效值,UE2为变频电压源输出频率为75Hz时输出电压有效值。根据上式可以求得UE1和UE2。Among them, U 02 is the effective value of the voltage at the measurement point when the voltage source U 0 acts alone, U E1 is the effective value of the output voltage when the output frequency of the variable frequency voltage source is 25Hz, and U E2 is the effective value of the output voltage when the output frequency of the variable frequency voltage source is 75Hz. U E1 and U E2 can be obtained according to the above formula.
由分压原理,可得以下方程组:According to the principle of partial pressure, the following equations can be obtained:
上式中,X25为电容C0和电感L在25Hz下的电抗,X75为电容C0和电感L在75Hz下的电抗。代入数据解方程组可求得|X25|和|X75|。In the above formula, X 25 is the reactance of capacitor C 0 and inductance L at 25Hz, and X 75 is the reactance of capacitor C 0 and inductance L at 75Hz. By substituting data into the equations, |X 25 | and |X 75 | can be obtained.
⑥根据求出的|X50|、|X25|和|X75|,计算电网的对地电容C0,方法如下:⑥ According to the obtained |X 50 |, |X 25 | and |X 75 |, calculate the ground capacitance C 0 of the power grid, the method is as follows:
判断|X50|、|X25|和|X75|的大小,Judging the size of |X 50 |, |X 25 | and |X 75 |,
a.若|X75|最小,则有a. If |X 75 | is the smallest, then there is
b.若|X50|最小,则有b. If |X 50 | is the smallest, then there is
c.若|X25|最小,则有c. If |X 25 | is the smallest, then there is
上式中ω75、ω50和ω25分别为与频率75Hz、50Hz和25Hz相对应的角频率,求解方程组即可得C0。In the above formula, ω 75 , ω 50 and ω 25 are the angular frequencies corresponding to the frequencies 75Hz, 50Hz and 25Hz respectively, and C 0 can be obtained by solving the equations.
⑦最后将求得的C0换算成电网的对地电容C0′,换算公式为其中k13为电压互感器第一绕组到第三绕组的变比。⑦Finally, convert the obtained C 0 into the ground capacitance C 0 ′ of the power grid, and the conversion formula is Where k 13 is the transformation ratio from the first winding to the third winding of the voltage transformer.
电网的电容电流其中,为电网额定相电压。grid capacitive current in, is the rated phase voltage of the grid.
为了验证本发明具体实施方式的有效性,在Matlab/Simulink中设置三组不同的电容值分别进行仿真分析,第一组为3μF、3.05μF、3.1μF;第二组为10μF、10.3μF、10.5μF;第三组为30.1μF、30.5μF、30.8μF。In order to verify the effectiveness of the specific implementation of the present invention, three groups of different capacitance values are set in Matlab/Simulink to carry out simulation analysis respectively, the first group is 3 μ F, 3.05 μ F, 3.1 μ F; the second group is 10 μ F, 10.3 μ F, 10.5 μF; the third group is 30.1μF, 30.5μF, 30.8μF.
对于不同组合的系统对地电容,分别进行了仿真,得到数据如表1所示。For different combinations of system capacitances to ground, simulations were carried out, and the data obtained are shown in Table 1.
表1、不同对地电容组合下的仿真测量数据及计算结果Table 1. Simulation measurement data and calculation results under different ground capacitance combinations
上述仿真结果中,不同对地电容组合下的测量误差均在2%以内,验证了本具体实施方式的方法不仅有效,而且具有较高的精确性。In the above simulation results, the measurement errors under different ground capacitance combinations are all within 2%, which verifies that the method in this embodiment is not only effective, but also has high accuracy.
本具体实施方式采用精确的戴维南等效电路模型,对系统的对地电容进行求解。在原理上不仅避免了电压互感器短路阻抗对测量结果的影响,而且解决了一般信号注入法测量电容电流时无法避免的工频电压干扰的问题。In this specific implementation manner, an accurate Thevenin equivalent circuit model is used to solve the ground capacitance of the system. In principle, it not only avoids the influence of the short-circuit impedance of the voltage transformer on the measurement results, but also solves the problem of unavoidable power frequency voltage interference when the general signal injection method measures the capacitive current.
应当理解的是,本说明书未详细阐述的部分均属于现有技术。It should be understood that the parts not described in detail in this specification belong to the prior art.
虽然以上结合附图描述了本发明的具体实施方式,但是本领域普通技术人员应当理解,这些仅是举例说明,可以对这些实施方式做出多种变形或修改,而不背离本发明的原理和实质。本发明的范围仅由所附权利要求书限定。Although the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, those of ordinary skill in the art should understand that these are only examples, and various variations or modifications can be made to these embodiments without departing from the principles and principles of the present invention. substance. The scope of the invention is limited only by the appended claims.
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