Capacitive current measuring method for arc suppression coil grounding system

Abstract

The invention provides a capacitance current measuring method for an arc suppression coil grounding system, which belongs to the technical field of arc suppression coil grounding, and comprises the following steps: injecting a power frequency signal into a neutral point of the system, and calculating the capacitance current of the system according to the change of the voltage and current of the neutral point. Due to small neutral point current and nonlinearity of a current transformer, the measurement error is large. And a certain current is biased, so that the mutual inductor works in a linear section, and the measurement precision is greatly improved. A controllable micro-circuit breaker is further arranged for protection. When single-phase grounding occurs, instantaneous high voltage may occur at the two ends of the damping resistor, so that the injection transformer can be damaged. And the micro circuit breaker is added, so that the injection loop can be disconnected within 0.1 S, and the injection transformer is protected. The miniature circuit breaker is additionally provided with the opening and closing coil, after protection action, closing can be controlled by the control device during measurement, and normal measurement is not affected. A prototype manufactured on the basis of the method passes a simulation field test and completely reaches a design index.

Description

Technical Field

[0001] The invention relates to the technical field of arc suppression coil grounding, and in particular to a capacitance current measurement method for an arc suppression coil grounding system. Background Art

[0002] In the system where the neutral point of the power transmission and distribution network is grounded through the arc suppression coil, as the proportion of the cable network increases, the three-phase symmetry becomes better and better, and the neutral point voltage becomes lower and lower, the error of the conventional tuning method and the two-speed calculation method in calculating the capacitor current becomes larger and larger, which seriously affects the correct compensation of the arc suppression coil. The signal injection method is increasingly necessary to measure the capacitor current, but there have been many studies and many papers published in the past decade, but few of them have been promoted and applied in practice. The reason is that it has low accuracy and high failure rate, and has not been promoted and applied in the system.

[0003] Therefore, there is an urgent need in the art for a capacitive current measurement method for an arc suppression coil grounding system with high accuracy and low failure rate.

[0004] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention

[0005] The purpose of the present invention is to provide a method for measuring capacitance current of an arc suppression coil grounding system with high accuracy and low failure rate.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] A method for measuring capacitance current of an arc suppression coil grounding system, comprising:

[0008] Injecting a power frequency signal into the neutral point of the system, and calculating the capacitance current of the system according to the change of the neutral point voltage and current. Injecting a power frequency signal into the neutral point of the system, and calculating the capacitance current of the system according to the change of the neutral point voltage and current comprises: connecting an injection transformer in parallel to the damping resistor, and during measurement, injecting 36V and 24V voltages respectively by the control device, measuring the neutral point voltage and current, and obtaining the capacitance current of the system through calculation.

[0009] Optionally, an injection transformer is connected in parallel to the damping resistor. During measurement, the control device injects 36V and 24V voltages respectively, measures the neutral point voltage and current, and calculates the system capacitance current including:

[0010] When 36V is injected: U 01 =U bd +I 01 *Zc

[0011] When 24V is injected: U 02 =U bd +I 02 *Zc

[0012] Subtracting: U 01 -U 02 =(I 01 -I 02 )*Zc

[0013] Zc=(U 01 -U 02 ) / (I 01 -I 02 )

[0014] Therefore: Ic=Ux / Zc

[0015] Among them: U 01、 U 02、 I 01、 I 02 Both are vectors, which are the neutral point voltage and current measured twice. The measuring device must measure their amplitude and phase based on the same reference. bd is the system asymmetric voltage, Zc is the system capacitor equivalent impedance, Ux is the system phase voltage, and Ic is the system capacitor current.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention is provided with a neutral point current bias circuit. Since the neutral point current is small, the nonlinearity of the current transformer causes a large measurement error. By biasing a certain current, the transformer works in a linear section, which greatly improves the measurement accuracy. The present invention is also provided with a controllable micro-break protection. Since when single-phase grounding occurs, there may be instantaneous high voltage at both ends of the damping resistor, which may damage the injection transformer. By adding a micro-break, the injection circuit can be disconnected within 0.1S, protecting the injection transformer. The micro-break is equipped with a separation coil. After the protection is actuated, the control device can control the closing of the switch during measurement without affecting the normal measurement. The prototype manufactured based on the present invention has passed the simulated field test and fully met the design indicators. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0019] Figure 1 A schematic diagram of the system circuit structure provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] The purpose of the present invention is to provide a method for measuring capacitance current of an arc suppression coil grounding system with high accuracy and low failure rate.

[0022] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] Embodiment 1:

[0024] This embodiment provides a method for measuring capacitance current of an arc suppression coil grounding system. The circuit structure diagram is shown in FIG. Figure 1 As shown, including:

[0025] The power frequency signal is injected into the neutral point of the system, and the capacitive current of the system is calculated based on the changes in the neutral point voltage and current.

[0026] Furthermore, the method of injecting an industrial frequency signal into the neutral point of the system and calculating the capacitive current of the system according to the changes in the neutral point voltage and current includes: connecting an injection transformer in parallel to the damping resistor, and during measurement, injecting 36V and 24V voltages respectively by the control device, measuring the neutral point voltage and current, and obtaining the system capacitive current through calculation.

[0027] Furthermore, an injection transformer is connected in parallel to the damping resistor. During measurement, the control device injects 36V and 24V voltages respectively, measures the neutral point voltage and current, and calculates the system capacitance current including:

[0028] When 36V is injected: U 01 =U bd +I 01 *Zc

[0029] When 24V is injected: U 02 =U bd +I 02 *Zc

[0030] Subtracting: U 01 -U 02 =(I 01 -I 02 )*Zc

[0031] Zc=(U 01 -U02 ) / (I 01 -I 02 )

[0032] Therefore: Ic=Ux / Zc

[0033] Among them: U 01、 U 02、 I 01、 I 02 Both are vectors, which are the neutral point voltage and current measured twice. The measuring device must measure their amplitude and phase based on the same reference. bd is the system asymmetric voltage, Zc is the system capacitor equivalent impedance, Ux is the system phase voltage, and Ic is the system capacitor current.

[0034] The advantage of the measurement based on power frequency injection is that the power frequency signal injected is the same frequency as the system, which has little interference to the system, avoids the problem of filtering out the power frequency when injecting other frequency signals, and improves the measurement accuracy. The device developed based on the present invention is suitable for online measurement of systems with neutral point voltage lower than 100V, and its accuracy is better than other measurement methods.

[0035] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0036] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for measuring capacitance current of arc suppression coil grounding system, characterized in that: include: The power frequency signal is injected into the neutral point of the system, and the capacitive current of the system is calculated based on the changes in the neutral point voltage and current.

2. The arc suppression coil grounding system capacitance current measurement method according to claim 1 is characterized in that: The method of injecting a power frequency signal into the neutral point of the system and calculating the capacitance current of the system according to the change of the neutral point voltage and current comprises: connecting an injection transformer in parallel with the damping resistor, injecting 36V and 24V voltages respectively by a control device during measurement, measuring the neutral point voltage and current, and obtaining the capacitance current of the system by calculation.

3. The arc suppression coil grounding system capacitance current measurement method according to claim 2 is characterized in that: The damping resistor is connected in parallel with an injection transformer. During measurement, the control device injects 36V and 24V voltages respectively, measures the neutral point voltage and current, and calculates the system capacitance current including: When 36V is injected: U 01 =U bd +I 01 *Zc When 24V is injected: U 02 =U bd +I 02 *Zc Mutual benefit: U 01 -U 02 = (I 01 -I 02 )*Zc Zc=(U 01 -IN 02 ) / (AND 01 -AND 02 ) Ic=Ux / Zc Among them: U 01、 U 02、 I 01、 I 02 Both are vectors, which are the neutral point voltage and current measured twice. The measuring device must measure their amplitude and phase based on the same reference. bd is the system asymmetric voltage, Zc is the system capacitor equivalent impedance, Ux is the system phase voltage, and Ic is the system capacitor current.

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