Small current grounding capacitance current online measurement system

Abstract

The present invention relates to the technical field of small current grounding capacitance current measurement, and in particular to a small current grounding capacitance current online measurement system. The present invention adopts an improved maximum displacement voltage method and a signal injection method to measure and calculate the grounding capacitance current for two states of whether the neutral point of a small current grounding system is grounded, thereby improving the measurement efficiency of the system capacitance current and the full-operation operation capability. Secondly, the system proposes a capacitance current hybrid algorithm method by establishing a displacement voltage method control theory based on an arc extinguishing coil, thereby solving the problem that errors exist in traditional capacitance current calculation methods and affect the compensation effect of the arc extinguishing coil, thereby achieving the technical effect of improving the compensation accuracy of the arc extinguishing coil. Furthermore, in view of the problem that the zero-sequence current and voltage have a large variation range, a displacement voltage 'dual-channel, high-precision' measurement method is proposed, and the high and low ranges are adopted to achieve the technical effect of improving the displacement voltage and capacitance current measurement levels.

Description

Technical Field

[0001] The invention relates to the technical field of small current grounding capacitance current measurement, in particular to a small current grounding capacitance current online measurement system. Background Art

[0002] With the expansion of urban power grids and the increase in cable outlets, the system capacitance current has greatly increased. When a single-phase grounding fault occurs in the system, the grounding arc cannot extinguish itself, and it is very easy to generate intermittent arc grounding overvoltage. If it lasts for a long time, it will develop into a two-phase short circuit accident at the insulation weakness of the line. Therefore, when the network is large enough, it is necessary to use arc suppression coils to compensate for the capacitance current, which is one of the important technical measures to ensure the safe operation of the power system. In order to avoid the threat of inappropriate compensation to the safe operation of the power system, the capacitance current value of the system must be correctly measured first, and the arc suppression coil current value must be reasonably adjusted accordingly to achieve correct tuning, which can not only avoid the arc overcurrent of single-phase grounding well, but also not affect the selectivity and reliability of relay protection.

[0003] At present, arc suppression coil sets are widely used in the distribution network system of the State Grid Corporation and even nationwide. With the continuous improvement of power quality, the three-phase voltage balance of the distribution network is getting higher and higher. When the three-phase voltage of the system is relatively balanced, the zero-sequence voltage and zero-sequence current are small. When the primary value of the neutral point zero-sequence voltage is lower than 10V, the capacitance current value measured by the capacitance current test device of most manufacturers in the industry has a large error, and the corresponding compensation effect is not ideal. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an online measurement system for small current grounding capacitor current in response to the above-mentioned technical deficiencies. The system adopts an improved maximum displacement voltage method and a signal injection method to measure and calculate the grounding capacitor current for the two states of whether the neutral point of the small current grounding system is grounded, thereby improving the measurement efficiency of the system capacitor current; secondly, the system proposes a capacitor current hybrid algorithm method by establishing a displacement voltage method control theory based on the arc suppression coil, thereby solving the problem that the traditional capacitor current calculation method has errors and affects the compensation effect of the arc suppression coil, thereby achieving the technical effect of improving the compensation accuracy of the arc suppression coil; and in response to the problem that the zero-sequence current and voltage have a large range of variation, a displacement voltage 'dual-channel, high-precision' measurement method is proposed, and by adopting a high and low range method, the technical effect of improving the displacement voltage and capacitor current measurement level is achieved; finally, the present invention eliminates the problem that the capacitor current cannot be measured when the neutral point is not grounded by improving the theory and technology of measuring the capacitor current by the signal injection method in a neutral point ungrounded system, thereby achieving the measurement effect of the capacitor current under all working conditions.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: including a power grid line, a capacitor current measuring device and an arc suppression coil; the power grid line is a three-phase circuit, the end of the secondary three-phase circuit of the power grid line is star-connected, one end of the arc suppression coil is connected to the secondary neutral point of the power grid line, and the other end of the arc suppression coil is grounded; one side of the capacitor current measuring device is connected to the monitoring arc suppression coil, and the other side of the capacitor current measuring device is connected to the three-phase line of the power grid line; the arc suppression coil includes a switch S, a resistor R L And adjustable inductor L, switch S, resistor R L and an adjustable inductor L are connected in series;

[0006] The capacitance current measuring device includes an inductance control device, a signal injection device and a central control device. One side of the central control device is connected to control the inductance control device and the signal injection device; the signal injection device is connected to control the adjustable inductance L in the arc suppression coil, and the signal injection device is connected to the three-phase line of the power grid line; the other side of the central control device is connected to the host computer through the GPRS signal;

[0007] To further optimize the technical solution, the inductance control device includes an arc suppression coil measuring unit and an arc suppression coil gear adjustment unit; the signal injection device includes a signal injection unit and an injection device measuring unit;

[0008] To further optimize the technical solution, the central control device includes a single-chip microcomputer system, a motor control circuit, a PWM control circuit, a GPRS module, a power supply module, a latch A and a latch B; latch A and latch B are connected to the data transmission pin of the single-chip microcomputer system, the output end of the arc extinguishing coil measuring unit is connected to the input pin of latch A, and the data output end of the injection device measuring unit is connected to the input pin of latch B; the I / O on one side of the single-chip microcomputer system is connected to a touch screen, and the other side of the single-chip microcomputer system is serially connected to the GPRS module, and the single-chip microcomputer system is wirelessly connected to the host computer through the GPRS module; the controlled end of the PWM control circuit is connected to the output pin of the single-chip microcomputer system, and the control end of the PWM control circuit is connected to the signal injection unit; the controlled end of the motor control circuit is connected to the output pin of the single-chip microcomputer system, and the control end of the motor control circuit is connected to the arc extinguishing coil gear adjustment unit;

[0009] The output end of the power module is connected to a rectifier and voltage regulator circuit, and the power module is connected to the power pin of the single-chip computer system through the rectifier and voltage regulator circuit;

[0010] Further optimizing the technical solution, the single-chip microcomputer system is an ATmega128 single-chip microcomputer chip, a crystal oscillator and a reset circuit;

[0011] To further optimize the technical solution, the online measurement system for small current grounding capacitance current is characterized in that: the arc suppression coil measurement unit includes a high-range voltage sensor, a low-range voltage sensor, a filter amplifier circuit A and an A / D conversion circuit A; the input pin of the A / D conversion circuit A is connected to the filter amplifier circuit A, and the output pin of the A / D conversion circuit A is connected to the central control device; the input pin of the filter amplifier circuit A is connected to a voltage follower, and the filter amplifier circuit A is connected to the high-range voltage sensor and the low-range voltage sensor through the voltage follower; the high-range voltage sensor and the low-range voltage sensor are installed on the arc suppression coil at the same time;

[0012] To further optimize the technical solution, the arc suppression coil gear shifting unit includes a single-phase rectifier circuit, an H-type single-phase inverter circuit and a stepper motor; the stepper motor is mechanically connected to the adjustable inductance L of the arc suppression coil; the power pin of the stepper motor is connected to the power output end of the H-type single-phase inverter circuit; the controlled end of the H-type single-phase inverter circuit is connected to the central control device, the input end of the H-type single-phase inverter circuit is connected to the single-phase rectifier circuit, and the power module is connected to the input end of the single-phase rectifier circuit;

[0013] Further optimizing the technical solution, the injection device measurement unit includes a voltage transformer, a current transformer, a filter amplifier circuit B and an A / D conversion circuit B; the input pin of the A / D conversion circuit B is connected to the filter amplifier circuit B, and the output pin of the A / D conversion circuit B is connected to the central control device; the input pin of the filter amplifier circuit B is connected to an isolation circuit, and the filter amplifier circuit B is connected to the voltage transformer and the current transformer through the isolation circuit; the voltage transformer and the current transformer are installed on the signal injection unit at the same time;

[0014] To further optimize the technical solution, the signal injection unit includes a three-phase rectifier circuit, a three-phase inverter circuit and an active filter circuit; the active filter circuit is connected to a line voltage sensor on the power grid line; the power pin of the active filter circuit is connected to the power output end of the three-phase inverter circuit; the controlled end of the three-phase inverter circuit is connected to the central control device, the input end of the three-phase inverter circuit is connected to the three-phase rectifier circuit, and the power module is connected to the input end of the three-phase rectifier circuit.

[0015] Compared with the prior art, the present invention has the following advantages: 1. The capacitance current measuring device for the small current grounding system developed by the project can realize online capacitance current measurement regardless of whether the arc suppression coil is put into operation, thereby improving the capacitance current measurement efficiency of the system. In particular, when the zero-sequence voltage is low, the capacitance current can be accurately measured; 2. The technology of the project can be widely used in 35kV to 220kV substations at all levels. After a small-scale transformation of the substation equipped with a complete set of arc suppression coils, the compensation effect of the arc suppression coil can be significantly improved; for the neutral point ungrounded system, after the installation of this set of equipment, the capacitance current of the system can be monitored in time, providing a scientific basis for the neutral point transformation plan; 3. On the one hand, this system can significantly improve the compensation effect of the arc suppression coil, and prevent various secondary disasters caused by the inadequate compensation of the arc suppression coil when a single-phase grounding fault occurs. On the other hand, the operation and maintenance personnel can be liberated from the annual capacitance current inspection and testing work, saving the operation and maintenance costs; 4. By adopting high and low ranges and customizing high-sensitivity current transformers, the requirements for improving the displacement voltage measurement level are met. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a power grid line connection control diagram of the present invention;

[0017] Figure 2 It is a simplified diagram of control transmission of the present invention;

[0018] Figure 3 It is the structural diagram of the central control device;

[0019] Figure 4 This is the structural diagram of the arc suppression coil measurement unit;

[0020] Figure 5 This is the structural diagram of the arc suppression coil gear adjustment unit;

[0021] Figure 6 is a structural diagram of the signal injection unit;

[0022] Figure 7 It is a structural diagram of the measuring unit of the injection device;

[0023] Figure 8 This is the flow chart of capacitance current measurement when arc suppression coil is grounded;

[0024] Fig. 9 It is the equivalent circuit of the power grid line when the arc suppression coil is grounded;

[0025] Fig.10 This is the maximum displacement voltage measurement principle diagram;

[0026] Fig.11 This is the circuit schematic diagram of the arc suppression coil gear adjustment unit;

[0027] Fig.12This is the flow chart of capacitance current measurement when the arc suppression coil is not grounded;

[0028] Fig.13 It is the circuit schematic diagram of the single-chip microcomputer system.

[0029] In the figure, 1. Power grid line; 2. Neutral point; 3. Arc suppression coil; 4. Capacitor current measuring device; 5. Inductor control device; 6. Signal injection device; 7. Central control device; 8. Host computer; 9. Arc suppression coil measuring unit; 10. Arc suppression coil gear adjustment unit; 11. Signal injection unit; 12. Injection device measuring unit; 101. Touch screen; 102. Motor control circuit; 103. Single chip microcomputer system; 104. Latch A; 105. Rectifier voltage stabilizing circuit; 106. Power module; 107. PWM control circuit; 108. Latch B; 109. GPR S module; 201, high-range voltage sensor; 202, low-range voltage sensor; 203, voltage follower; 204, filter amplifier circuit A; 205, A / D conversion circuit A; 206, single-phase rectifier circuit; 207, H-type single-phase inverter circuit; 208, stepper motor; 301, three-phase rectifier circuit; 302, three-phase inverter circuit; 303, active filter circuit; 304, line voltage sensor; 305, voltage transformer; 306, current transformer; 307, isolation circuit; 308, filter amplifier circuit B; 309, A / D conversion circuit B. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0031] like Figures 1 to 13 The present invention comprises a power grid line 1, a capacitance current measuring device 4 and an arc extinguishing coil 3; the power grid line 1 is a three-phase circuit, the secondary three-phase circuit end of the power grid line 1 is star-connected, one end of the arc extinguishing coil 3 is connected to the secondary neutral point 2 of the power grid line 1, and the other end of the arc extinguishing coil 3 is grounded; one side of the capacitance current measuring device 4 is connected to the monitoring arc extinguishing coil 3, and the other side of the capacitance current measuring device 4 is connected to the three-phase line of the power grid line 1; the arc extinguishing coil 3 comprises a switch S, a resistor R L And adjustable inductor L, switch S, resistor R L and an adjustable inductor L are connected in series;

[0032] The capacitance current measuring device 4 includes an inductance control device 5, a signal injection device 6 and a central control device 7. One side of the central control device 7 is connected to control the inductance control device 5 and the signal injection device; the signal injection device 6 is connected to control the adjustable inductance L in the arc suppression coil 3, and the signal injection device 6 is connected to the three-phase line of the power grid line 1; the other side of the central control device 7 is connected to the host computer 8 through the GPRS signal;

[0033] The inductance control device 5 includes an arc extinguishing coil measuring unit 9 and an arc extinguishing coil gear adjustment unit 10; the signal injection device 6 includes a signal injection unit 11 and an injection device measuring unit 12;

[0034] The central control device 7 includes a single-chip computer system 103, a motor control circuit 102, a PWM control circuit 107, a GPRS module 109, a power module 106, a latch A104 and a latch B108; the latch A104 and the latch B108 are connected to the data transmission pin of the single-chip computer system 103, the output end of the arc extinguishing coil measurement unit is connected to the input pin of the latch A104, and the data output end of the injection device measurement unit 12 is connected to the input pin of the latch B108; the single-chip computer system 103 side I / O is connected with a touch screen 101, the other side of the single-chip system 103 is serially connected to a GPRS module 109, and the single-chip system 103 is wirelessly connected to the host computer 8 through the GPRS module 109; the controlled end of the PWM control circuit 107 is connected to the output pin of the single-chip system 103, and the control end of the PWM control circuit 107 is connected to the signal injection unit 11; the controlled end of the motor control circuit 102 is connected to the output pin of the single-chip system 103, and the control end of the motor control circuit 102 is connected to the arc extinguishing coil gear adjustment unit 10;

[0035] The output end of the power module 106 is connected to the rectifier and voltage regulator circuit 105 , and the power module 106 is connected to the power pin of the single-chip computer system 103 through the rectifier and voltage regulator circuit 105 ;

[0036] The single-chip microcomputer system 103 is an ATmega128 single-chip microcomputer chip, a crystal oscillator and a reset circuit;

[0037] The arc extinguishing coil measuring unit 9 includes a high-range voltage sensor 201, a low-range voltage sensor 202, a filter amplifier circuit A204 and an A / D conversion circuit A205; the input pin of the A / D conversion circuit A205 is connected to the filter amplifier circuit A204, and the output pin of the A / D conversion circuit A205 is connected to the central control device; the input pin of the filter amplifier circuit A204 is connected to a voltage follower 203, and the filter amplifier circuit A204 is connected to the high-range voltage sensor 201 and the low-range voltage sensor 202 through the voltage follower 203; the high-range voltage sensor 201 and the low-range voltage sensor 202 are installed on the arc extinguishing coil 3 at the same time;

[0038] The arc extinguishing coil gear shifting unit 10 comprises a single-phase rectifier circuit 206, an H-type single-phase inverter circuit 207 and a stepper motor 208; the stepper motor 208 is mechanically connected to the adjustable inductance L of the arc extinguishing coil 3; the power pin of the stepper motor 208 is connected to the power output end of the H-type single-phase inverter circuit 207; the controlled end of the H-type single-phase inverter circuit 207 is connected to the central control device, the input end of the H-type single-phase inverter circuit 207 is connected to the single-phase rectifier circuit 206, and the power module 106 is connected to the input end of the single-phase rectifier circuit 206;

[0039] The injection device measurement unit 12 includes a voltage transformer 305, a current transformer 306, a filter amplifier circuit B308 and an A / D conversion circuit B309; the input pin of the A / D conversion circuit B309 is connected to the filter amplifier circuit B308, and the output pin of the A / D conversion circuit B309 is connected to the central control device; the input pin of the filter amplifier circuit B308 is connected to an isolation circuit 307, and the filter amplifier circuit B308 is connected to the voltage transformer 305 and the current transformer 306 through the isolation circuit 307; the voltage transformer 305 and the current transformer 306 are installed on the signal injection unit 11 at the same time;

[0040] The signal injection unit 11 includes a three-phase rectifier circuit 301, a three-phase inverter circuit 302 and an active filter circuit 303; the active filter circuit 303 is connected to a line voltage sensor 304 on the power grid line 1; the power pin of the active filter circuit 303 is connected to the power output end of the three-phase inverter circuit 302; the controlled end of the three-phase inverter circuit 302 is connected to the central control device, the input end of the three-phase inverter circuit 302 is connected to the three-phase rectifier circuit 301, and the power module 106 is connected to the input end of the three-phase rectifier circuit 301.

[0041] The present invention monitors the closed and open states of the switch S in the arc extinguishing coil 3 through the central control unit 7, which can be divided into two real-time modes, as follows:

[0042] Specific implementation method 1: When the switch S in the arc extinguishing coil 3 is closed, that is, the arc extinguishing coil 3 is put into operation, the small current grounding capacitance current is measured and calculated by using the improved maximum displacement voltage method, combined with Figure 8 The measurement flow chart shown in the figure has the following main steps:

[0043] Step 1: The central control device 7 is put into operation through the inductance control device 5 and the signal injection device 6 is turned off; Figure 1 As shown, at this time, the inductance control device 5 controls the arc extinguishing coil 3 to complete the measurement of the capacitive current;

[0044] Step 2: If Figure 5The stepper motor inside the inductance control device 5 is connected to control the adjustable inductance L of the arc extinguishing coil 3. In the process of increasing the arc extinguishing coil L, the voltage U of the neutral point 2 connected to the arc extinguishing coil 3 is measured by the high and low range voltage sensor in the arc extinguishing coil measuring unit 9. N Take measurements;

[0045] Step 3: If the neutral point voltage increases, continue to increase the inductance L of the arc extinguishing coil 3; if the neutral point voltage decreases, decrease the inductance L of the arc extinguishing coil 3;

[0046] Step 4: Whether the inductance is increased or decreased, when the neutral point voltage variable is very small, it is judged as the neutral point voltage U N When the maximum value is reached, record the voltage value and inductance L value at this time;

[0047] Step 5: Calculate the grounding capacitance current by using the improved maximum displacement voltage method. The principle of the improved maximum displacement voltage method is as follows:

[0048] When the arc suppression coil 3 is connected to the power grid, the equivalent circuit diagram of the power grid line is as follows: Fig. 9 As shown, C1 is the line-to-ground reactance, E0 is the asymmetric voltage, and the neutral point displacement voltage U N for:

[0049]

[0050] The traditional maximum displacement method is when Xc = X L When the neutral point voltage reaches the maximum value, Fig.10 As shown, the grounding capacitance value is obtained by finding the inductance value under the maximum displacement voltage, and then the grounding capacitance current value is obtained. In fact, this is not the case. Here is an analysis of it;

[0051] By taking the derivative of formula (1) and setting the derivative formula to zero, it can be known that when the neutral point voltage reaches the maximum value, the system grounding capacitor reactance is:

[0052]

[0053] Therefore, the grounding capacitor current can be obtained as:

[0054]

[0055] in The maximum displacement method is improved by the present invention. The improved maximum displacement voltage method can be used to

[0056] Secondly, if Figure 4As shown, the arc suppression coil measurement unit 9 achieves the requirement of improving the displacement voltage measurement level by adopting high and low range methods. This is because the arc suppression coil grounding is a small current grounding system. Under normal circumstances, the zero-sequence current on the primary side is in the range of 10mA to 300mA, and the zero-sequence voltage on the primary side is around 1V to 200V. When single-phase grounding occurs in the line, the zero-sequence voltage loop rises to several thousand volts. In such a large range, the measuring equipment is required to measure accurately, and there are high requirements for the accuracy of the measuring loop, especially for the measurement of zero-sequence current. Therefore, the present invention adopts high and low range methods, as well as customized high-sensitivity current transformers, to achieve the requirement of improving the displacement voltage measurement level.

[0057] Specific implementation method 2: When the switch S in the arc suppression coil 3 is disconnected, that is, the arc suppression coil 3 is not put into operation, it is impossible to use the improved maximum displacement voltage method to measure and calculate the small current grounding capacitance current, so the signal injection method can be used to measure the capacitance current, combined with Fig.12 The measurement flow chart shown, the main steps are as follows:.

[0058] Step 1: The central control device 7 is put into operation through the signal injection device 6, and the inductance control device 5 is turned off; Figure 1 As shown, at this time, the signal injection device 6 injects a signal into the power grid line 1 to complete the measurement of the capacitive current;

[0059] Step 2: If Figure 7 The voltage transformer 305 in the injection device measurement unit 12 measures the system frequency and displacement voltage U N ;

[0060] Step 3: Determine U N Whether it exceeds the limit value, if it exceeds the limit value, it determines whether the line has a ground fault; if a fault occurs, a fault alarm is issued;

[0061] Step 4: If the displacement voltage does not exceed the limit value, Figure 6 , the three-phase inverter circuit 302 inside the signal injection device 6 injects a harmonic signal into the power grid line 1 through the line voltage sensor 304 by inverting the DC power supply signal into a small current harmonic of a specific frequency and a specific amplitude;

[0062] Step 5: Measure and calculate the injected current, injected voltage and grid detuning degree through the voltage transformer 305 and the current transformer 306 in the injection device measurement unit 12;

[0063] Step 6: If the grid detuning degree exceeds the limit, a fault alarm is issued;

[0064] Step 7: Calculate the line grounding capacitance current through the calculated injection current, injection voltage and grid detuning degree. The principle is similar to the displacement method and will not be described in detail.

[0065] It can be seen that the present invention establishes an improved maximum displacement voltage control theory based on arc suppression coils according to the research results of online capacitance current measurement technology of small current grounding systems, adopts a capacitance current hybrid algorithm method, proposes a "dual-channel, high-precision" displacement voltage measurement scheme, establishes theories and technologies for measuring capacitance current using a signal injection method in a neutral point ungrounded system, proposes a capacitance current measurement scheme under full working conditions, and calculates the capacitance current using an improved maximum displacement voltage method when the arc suppression coil is put into operation, and calculates using a signal injection method when the arc suppression coil is not put into operation, that is, develops a device that can accurately measure capacitance current online (the measurement error does not exceed 2%), improves capacitance current testing efficiency and accuracy, and provides accurate online capacitance current values ​​for power grid dispatchers, facilitating them to formulate appropriate compensation control strategies.

[0066] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, and do not constitute a limitation of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modifications that fall within the scope and boundaries of the appended claims, or the equivalent forms of such scope and boundaries.

Claims

1. Small current grounding capacitance current online measurement system, characterized by: The invention comprises a power grid line (1), a capacitor current measuring device (4) and an arc extinguishing coil (3); the power grid line (1) is a three-phase circuit, the secondary three-phase circuit end of the power grid line (1) is star-connected, one end of the arc extinguishing coil (3) is connected to the secondary neutral point (2) of the power grid line (1), and the other end of the arc extinguishing coil (3) is grounded; one side of the capacitor current measuring device (4) is connected to the monitoring arc extinguishing coil (3), and the other side of the capacitor current measuring device (4) is connected in parallel to the three-phase line of the power grid line (1); the arc extinguishing coil (3) comprises a switch S, a resistor R L and adjustable inductance L , switch S, resistor R L and adjustable inductance L Serial connection; the capacitance current measuring device (4) includes an inductance control device (5), a signal injection device (6) and a central control device (7); one side of the central control device (7) is connected to control the inductance control device (5) and the signal injection device (6); the signal injection device (6) is connected to control the adjustable inductance in the arc extinguishing coil (3) L The signal injection device (6) is connected to the three-phase line of the power grid line (1); the other side of the central control device (7) is connected to the host computer (8) through the GPRS signal; the inductance control device (5) includes an arc extinguishing coil measuring unit (9) and an arc extinguishing coil gear adjustment unit (10); the signal injection device (6) includes a signal injection unit (11) and an injection device measuring unit (12); the arc extinguishing coil measuring unit (9) includes a high-range voltage sensor (201), a low-range voltage sensor (202), a filter amplifier circuit A (204) and an A / D conversion circuit A (205); the input pin of the A / D conversion circuit A (205) is connected to the filter amplifier circuit A (204), The output pin of the A / D conversion circuit A (205) is connected to the central control unit; the input pin of the filter amplifier circuit A (204) is connected to a voltage follower (203), and the filter amplifier circuit A (204) is connected to a high-range voltage sensor (201) and a low-range voltage sensor (202) through the voltage follower (203); the high-range voltage sensor (201) and the low-range voltage sensor (202) are simultaneously installed on the arc extinguishing coil (3); the arc extinguishing coil gear adjustment unit (10) includes a single-phase rectifier circuit (206), an H-type single-phase inverter circuit (207) and a stepper motor (208); the stepper motor (208) is mechanically connected to the adjustable inductance of the arc extinguishing coil (3) L The power supply pin of the stepper motor (208) is connected to the power supply output end of the H-type single-phase inverter circuit (207); the controlled end of the H-type single-phase inverter circuit (207) is connected to the central control unit, the input end of the H-type single-phase inverter circuit (207) is connected to the single-phase rectifier circuit (206), and the power module (106) is connected to the input end of the single-phase rectifier circuit (206).

2. The low current grounding capacitance current online measurement system according to claim 1 is characterized in that: The central control device (7) comprises a single-chip computer system (103), a motor control circuit (102), a PWM control circuit (107), a GPRS module (109), a power module (106), a latch A (104) and a latch B (108); the latch A (104) and the latch B (108) are connected to the data transmission pin of the single-chip computer system (103); the output end of the arc extinguishing coil measuring unit (9) is connected to the input pin of the latch A (104); the data output end of the injection device measuring unit (12) is connected to the input pin of the latch B (108); the I / O on one side of the single-chip computer system (103) is connected to the touch screen (101); the other side of the single-chip computer system (103) is serially connected to the touch screen (101). A GPRS module (109), the single-chip computer system (103) is wirelessly connected to a host computer (8) via the GPRS module (109); a controlled end of a PWM control circuit (107) is connected to an output pin of the single-chip computer system (103), and a control end of the PWM control circuit (107) is connected to a signal injection unit (11); a controlled end of a motor control circuit (102) is connected to an output pin of the single-chip computer system (103), and a control end of the motor control circuit (102) is connected to an arc extinguishing coil gear adjustment unit (10); an output end of a power module (106) is connected to a rectifier and voltage stabilizing circuit (105), and the power module (106) is connected to a power pin of the single-chip computer system (103) via the rectifier and voltage stabilizing circuit (105).

3. The low current grounding capacitance current online measurement system according to claim 2 is characterized in that: The single-chip microcomputer system (103) is an ATmega (128) single-chip microcomputer chip, a crystal oscillator and a reset circuit.

4. The low current grounding capacitance current online measurement system according to claim 2 is characterized in that: The injection device measurement unit (12) comprises a voltage transformer (305), a current transformer (306), a filter amplifier circuit B (308) and an A / D conversion circuit B (309); an input pin of the A / D conversion circuit B (309) is connected to the filter amplifier circuit B (308), and an output pin of the A / D conversion circuit B (309) is connected to a central control device (7); an input pin of the filter amplifier circuit B (308) is connected to an isolation circuit (307), and the filter amplifier circuit B (308) is connected to the voltage transformer (305) and the current transformer (306) via the isolation circuit (307); the voltage transformer (305) and the current transformer (306) are simultaneously mounted on the signal injection unit (11).

5. The low current grounding capacitance current online measurement system according to claim 2 is characterized in that: The signal injection unit (11) comprises a three-phase rectifier circuit (301), a three-phase inverter circuit (302) and an active filter circuit (303); the active filter circuit (303) is connected to a line voltage sensor (304) on a power grid line (1); a power supply pin of the active filter circuit (303) is connected to a power supply output end of the three-phase inverter circuit (302); a controlled end of the three-phase inverter circuit (302) is connected to a central control unit, an input end of the three-phase inverter circuit (302) is connected to the three-phase rectifier circuit (301), and a power module (106) is connected to the input end of the three-phase rectifier circuit (301).

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