Method for measuring off-tuning degree of arc suppression coil grounding system

Abstract

The invention provides an arc suppression coil grounding system off-tuning degree measurement method, which belongs to the technical field of arc suppression coil grounding, and comprises the following steps: a measurement and control board controls a power amplifier to simultaneously inject four signals with different frequencies according to an injection rule, and the signals are injected into a PT secondary coil by an injection transformer; the resonant frequency can be found after three or four times of injection; and calculating the off-tuning degree of the system. The invention improves and expands a method for measuring the off-resonance degree of an arc extinction system by a sweep frequency signal, and particularly provides a method for simultaneously injecting and measuring a plurality of (gt; compared with the prior art, the method has the advantages that the detection accuracy is greatly improved, the measurement time is greatly shortened, the application range of the method is greatly expanded, and the method is suitable for common neutral point PT secondary injection, is also suitable for a specially-made PT attached in an arc suppression coil, and is suitable for online detection and portable detection. Products developed based on the method have been tested and verified in a system.

Description

Technical Field

[0001] The invention relates to the technical field of arc suppression coil grounding, and in particular to a method for measuring the detuning degree of 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 an 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 capacitive current becomes larger and larger, which seriously affects the correct compensation of the arc suppression coil. The signal injection method is becoming more and more necessary to measure the capacitive current, but there have been many studies and published papers in the past decade, but few of them have been promoted and applied in practice. The method of injecting a sweeping frequency signal (20-100Hz) into the neutral point PT twice to measure the detuning degree of the system and calculate the capacitive current of the system has been applied in a certain arc suppression coil product. However, due to its slow sweeping speed and the need to match its specific arc suppression product, it has not been promoted and applied in the system.

[0003] 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

[0004] The purpose of the present invention is to provide a method for measuring the detuning degree of an arc suppression coil grounding system;

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A method for measuring detuning degree of an arc suppression coil grounding system, comprising:

[0007] The measurement and control board controls the power amplifier to inject four signals of different frequencies simultaneously according to the injection rules, and the signals are injected into the PT secondary coil by the injection transformer;

[0008] After three or four injections, the resonant frequency can be found;

[0009] Calculate the detuning of the system.

[0010] Optionally, the injection rule includes:

[0011] First, inject 31Hz, 51Hz, 71Hz, and 91Hz signals. The measurement and control board detects the signals of PT and CT. After Fourier analysis, the amplitudes of the four frequencies are obtained at the same time. After comparison, the frequency Fmax1 with the largest amplitude is found. Then, based on Fmax1=51, the next four frequencies to be injected are determined to be 43Hz, 48Hz, 53Hz, and 58Hz. After detection, it is determined that the frequency with the largest amplitude is Fmax2=48. The next four frequencies to be injected are determined to be 45Hz, 46Hz, 47Hz, and 48Hz. After detection, it is determined that the frequency with the largest amplitude is Fmax3. If Fmax3<>48Hz, the resonant frequency f0=Fmax3. If Fmax3=48, the next four frequencies to be injected are determined to be 48Hz, 49Hz, 50Hz, and 51Hz. After detection, it is determined that the frequency with the largest amplitude is Fmax4, and the resonant frequency f0=Fmax4.

[0012] Optionally, the detuning degree of the computing system is specifically:

[0013] Γ=1-(f0 / 50) 2 ;

[0014] Where Γ is the detuning degree of the system and f0 is the resonant frequency.

[0015] Optionally, also include:

[0016] If the inductive current of the arc suppression coil is known, the capacitive current Ic of the system can be calculated;

[0017] Ic = inductor current / (1-Γ).

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention provides a method for measuring the detuning degree of an arc extinguishing coil grounding system, improves and expands the method for measuring the detuning degree of an arc extinguishing system by using a frequency sweep signal, and in particular, invents a method for simultaneously injecting and measuring multiple (>3) signals of different frequencies, which greatly improves the detection accuracy and also greatly shortens the measurement time, greatly expanding its application scope, and is suitable for both ordinary neutral point PT secondary injection and special PT attached to the arc extinguishing coil, and is suitable for both online detection and portable detection. Products developed based on this method have been tested and verified in the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] 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.

[0021] Figure 1 A circuit diagram of a method for measuring the detuning degree of an arc suppression coil grounding system provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] 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.

[0023] The object of the present invention is to provide a method for measuring the detuning degree of an arc suppression coil grounding system, which can improve accuracy and shorten measurement time.

[0024] 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.

[0025] Embodiment 1:

[0026] This embodiment provides a method for measuring the detuning degree of an arc suppression coil grounding system. The main points of this embodiment are that more than three signals of different frequencies are injected at the same time, and the response of multiple frequencies is detected simultaneously by Fourier transform, thereby avoiding the error caused by the injection of one frequency at a time, improving the accuracy, and shortening the measurement time. The basic principles are as follows:

[0027] like Figure 1 As shown, the measurement and control board is composed of a single-chip microcomputer, etc., which is mainly responsible for collecting analog signals from arc suppression coils PT and CT and 50Hz notch, and generating 4 injection signals of different frequencies. The power amplifier is composed of IGBT, etc., which is responsible for amplifying the signals of 4 different frequencies to drive the injection transformer. The injection transformer is composed of 5 windings of equal voltage, of which the output winding is 2A6V, connected to the PT secondary. The other 4 windings are 0.5A6V, respectively connected to the 4 outputs of the power amplifier.

[0028] The neutral point PT can be a PT attached to the arc suppression coil. The system capacitor and the arc suppression coil form a parallel circuit. The measurement and control board controls the power amplifier to inject 4 signals of different frequencies at the same time according to the injection rule, and the injection transformer injects the PT secondary coil (the current is not more than 1A). When the frequency sweep range is 20-100Hz, the injection rule can be: first inject 31Hz, 51Hz, 71Hz, and 91Hz signals. The measurement and control board detects the signals of PT and CT, and obtains the amplitudes of the 4 frequencies at the same time after Fourier analysis. After comparison, the frequency Fmax1 with the largest amplitude is found. Then according to Fmax1, for example, Fmax1=51, the next 4 frequencies to be injected are determined to be 43Hz, 48Hz, 53Hz, and 58Hz. After detection, the frequency with the largest amplitude is determined to be Fmax2. For example, Fmax2=48, the next 4 frequencies to be injected are determined to be 45Hz, 46Hz, 47Hz, and 48Hz. After detection, the frequency with the largest amplitude is determined to be Fmax3. If Fmax3<>48Hz, the resonant frequency f0=Fmax3. If Fmax3=48, the next four frequencies to be injected are 48Hz, 49Hz, 50Hz, and 51Hz. The frequency with the largest amplitude is Fmax4, and the resonant frequency f0=Fmax4. The same applies to other cases. The resonant frequency f0 can be found by injecting 3 or 4 times at most, and the detuning degree Γ of the system can be calculated. If the compensation current (inductance current) of the arc suppression coil is known, the capacitance current Ic of the system can be calculated.

[0029] Γ=1-(f0 / 50) 2

[0030] Ic=Inductor current / (1-Γ)

[0031] The protection scope of the present invention is not limited to the simultaneous injection and detection of 4 frequencies, but includes the simultaneous injection and detection of 3 or more frequency signals for sweep frequency measurement to find the resonant frequency, especially for arc suppression coil systems.

[0032] 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.

[0033] 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 the detuning degree of an arc suppression coil grounding system, characterized in that: include: The measurement and control board controls the power amplifier to inject four signals of different frequencies simultaneously according to the injection rules, and the signals are injected into the PT secondary coil by the injection transformer; After three or four injections, the resonant frequency can be found; Calculate the detuning of the system.

2. The arc suppression coil grounding system detuning degree measurement method according to claim 1 is characterized in that: The injection rules include: First, inject 31Hz, 51Hz, 71Hz, and 91Hz signals. The measurement and control board detects the signals of PT and CT. After Fourier analysis, the amplitudes of the four frequencies are obtained at the same time. After comparison, the frequency Fmax1 with the largest amplitude is found. Then, based on Fmax1=51, the next four frequencies to be injected are determined to be 43Hz, 48Hz, 53Hz, and 58Hz. After detection, it is determined that the frequency with the largest amplitude is Fmax2=48. The next four frequencies to be injected are determined to be 45Hz, 46Hz, 47Hz, and 48Hz. After detection, it is determined that the frequency with the largest amplitude is Fmax3. If Fmax3<>48Hz, the resonant frequency f0=Fmax3. If Fmax3=48, the next four frequencies to be injected are determined to be 48Hz, 49Hz, 50Hz, and 51Hz. After detection, it is determined that the frequency with the largest amplitude is Fmax4, and the resonant frequency f0=Fmax4.

3. The arc suppression coil grounding system detuning degree measurement method according to claim 1 is characterized in that: The detuning degree of the computing system is specifically: Γ=1-(f0 / 50) 2 ; Where Γ is the detuning degree of the system and f0 is the resonant frequency.

4. The arc suppression coil grounding system detuning degree measurement method according to claim 1 is characterized in that: Also includes: If the inductive current of the arc suppression coil is known, the capacitive current Ic of the system can be calculated; Ic = inductor current / (1-Γ).

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