A distribution network fault recording method based on zero-sequence component of electric field

Abstract

The present invention relates to the field of electric power technology, and discloses a distribution network fault recording method based on the zero-sequence component of the electric field, comprising the following steps: an acquisition unit collects three-phase electric field data in real time; a three-phase electric field current cycle signal phasor is subtracted from a three-phase electric field previous cycle signal phasor to obtain the zero-sequence component of the three-phase electric field; a discrete Fourier transform is performed on the three-phase electric field zero-sequence component to obtain characteristic data of the three-phase electric field zero-sequence component, and the characteristic data is uploaded to a collection unit; the collection unit determines whether the characteristic data meets a preset condition, and if so, starts the fault recording; otherwise, does not start the fault recording and jumps to the first step. The present invention solves the problem of frequent recording startup in situations where the electromagnetic environment changes frequently, such as rainy days, and is more accurate in determining single-phase grounding faults, with strong engineering practicality.

Description

Technical Field

[0001] The present invention relates to the field of electric power technology, and in particular to a distribution network fault recording method based on electric field zero-sequence component, which is mainly used for analyzing the start timing of recording single-phase grounding faults in medium-voltage distribution networks in power systems. Background Art

[0002] To achieve the dual goals of carbon peak and carbon neutrality, more and more new energy equipment such as wind and solar energy are being connected to the power grid system, making the distribution network increasingly complex and the accurate and rapid identification of faults increasingly difficult. In the 2017 edition of the "Technical Guidelines for Distribution Networks," the State Grid Corporation of China explicitly requires that permanent short-circuit faults be quickly isolated nearby. Therefore, the demand for real-time monitoring of the distribution network and the rapid identification and handling of faults and abnormal conditions is becoming increasingly urgent. The existing fault recording startup method is based on the rise and fall of electric field amplitude data, but the electric field is easily affected by factors such as environmental changes, weather changes, and electromagnetic interference. This can easily lead to frequent false startup of the recording algorithm, thereby affecting the recording of the actual fault waveform. Summary of the Invention

[0003] In view of the shortcomings and defects of the existing technology, the present invention provides a distribution network single-phase grounding fault recording method based on the zero-sequence component of the electric field. The electric field changes of the distribution network are monitored by a fault indicator acquisition unit, and the grounding fault recording is started when the change meets the preset conditions.

[0004] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0005] A distribution network fault recording method based on electric field zero-sequence component, characterized by comprising the following steps:

[0006] S1: The acquisition unit acquires three-phase electric field data in real time; the acquisition unit is a fault indicator acquisition unit, which acquires the electric field data of the three-phase line in real time through an internal electric field measurement module.

[0007] S2: Subtract the phasor of the previous cycle signal from the current cycle signal phasor of the three-phase electric field to obtain the zero-sequence component of the three-phase electric field;

[0008] Note that the method for obtaining the zero-sequence component is not limited to the phasor subtraction of two adjacent frequency signals. The phasors of the two frequency signals to be subtracted may be separated by m power frequency cycles, where the value of m ranges from 1 to 5.

[0009] S3: Perform discrete Fourier transform on the zero-sequence components of the three-phase electric field respectively to obtain characteristic data of the zero-sequence components of the three-phase electric field, and upload the characteristic data to the collection unit;

[0010] The characteristic data are the phase and amplitude of the power frequency zero-sequence component of the three-phase electric field; the phase and amplitude of the Nth harmonic zero-sequence component of the three-phase electric field, where N is 2, 3, 4, or 5.

[0011] The aggregation unit, namely the fault indicator aggregation unit, is used to receive the fault information of the fault indicator, analyze and compile the fault information, and then send it to the power distribution master station.

[0012] S4: The collection unit determines whether the characteristic data meets the preset conditions. If so, the fault recording is started; otherwise, the fault recording is not started and the process jumps to S1.

[0013] Furthermore, the specific content of whether the preset conditions are met in step S4 is:

[0014] 1) The amplitude difference between the power frequency zero-sequence components of the electric field of any two phases in the three phases is less than the preset threshold value t1, and the phase difference between the power frequency zero-sequence components of the electric field of any two phases in the three phases is less than the preset threshold value t2;

[0015] 2) The amplitude difference of the zero-sequence component of the Nth harmonic of the electric field of any two phases in the three-phase is less than the preset threshold value t1, and the phase difference of the zero-sequence component of the Nth harmonic of the electric field of any two phases in the three-phase is less than the preset threshold value t2;

[0016] If the characteristic data meets any of the above two conditions, it is deemed to meet the preset conditions.

[0017] Furthermore, the electric field data in step S1 is voltage data.

[0018] Furthermore, the fault in step S4 is a single-phase grounding fault, that is, the fault type applicable to the solution of the present invention is a single-phase grounding fault.

[0019] Furthermore, the method is applicable to a distribution network voltage level of a medium voltage level, i.e., 1 kV to 35 kV.

[0020] The beneficial effects of the present invention are as follows: the three-phase electric field changes of the distribution network are monitored by the fault indicator acquisition unit, and whether a single-phase grounding fault has occurred in the distribution network is determined based on the phase and amplitude of the zero-sequence component of the three-phase electric field. The electric field changes caused by rainy days are disordered. After the adjacent cycles of the measured electric field are subtracted, the changes in the zero-sequence components of the three-phase electric field are inconsistent, and do not meet the zero-sequence component change characteristics of a grounding fault. That is, if the amplitude difference and phase difference of the zero-sequence components of any two items of the three-phase electric field do not meet the set conditions, the fault recording will not be started. Therefore, this method solves the problem of frequently starting the recording when the electromagnetic environment changes frequently, such as on rainy days, and makes the fault judgment more accurate, with strong engineering practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the overall flow chart of the present invention.

[0022] Figure 2 Schematic diagram of the installation of a transient waveform recording fault indicator in an embodiment of the present invention.

[0023] Figure 3 1 is the three-phase electric field waveform before and after a single-phase grounding fault in an embodiment of the present invention.

[0024] Figure 4 is the three-phase zero-sequence electric field waveform in the embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0026] The embodiment occurs in a medium voltage (1kV to 35kV) distribution line. The installation diagram of the transient waveform fault indicator is as follows: Figure 2 shown.

[0027] Combined with attachment Figure 1 A distribution network fault recording method based on electric field zero-sequence component comprises the following steps:

[0028] S1: The three-phase electric field waveforms before and after a single-phase grounding fault are as follows Figure 3 As shown, the acquisition unit collects three-phase electric field data in real time. The voltage is the product of the distance from the detection point to the zero potential (i.e., infinity) and the electric field strength. The two are proportional. Changes in the electric field can represent changes in voltage. The electric field data here is also voltage data.

[0029] S2: Subtract the phasor of the previous cycle signal from the current cycle signal phasor of the three-phase electric field to obtain the zero-sequence component of the three-phase electric field;

[0030] Note that the method for obtaining the zero-sequence component is not limited to the phasor subtraction of two adjacent frequency signals. The phasors of the two subtracted frequency signals can be separated by m power frequency cycles, and the value range of m is 1 to 5.

[0031] S3: Perform discrete Fourier transform on the zero-sequence components of the three-phase electric field phasors respectively to obtain characteristic data of the zero-sequence components of the three-phase electric field, and upload the characteristic data to the aggregation unit; the characteristic data include: the phase and amplitude of the power frequency zero-sequence component of the three-phase electric field; the phase and amplitude of the Nth harmonic zero-sequence component of the three-phase electric field, where N is 2, 3, 4, or 5.

[0032] The discrete Fourier transform formula is as follows:

[0033]

[0034] Wherein, X(k) represents the data of the zero-sequence component of the three-phase electric field after discrete Fourier transform, k is the extracted harmonic order, x(l) is the data point to be discrete Fourier transformed, l = 0, 1, 2…M-1, and M is the maximum harmonic order that can be obtained by discrete Fourier transform.

[0035] X(k) is a set of complex numbers, the real part of

[0036]

[0037] Imaginary part

[0038]

[0039] The amplitude and phase of the kth harmonic can be calculated based on the real and imaginary parts. k ranges from 1 to N, that is, the amplitude and phase of the zero-sequence component of the three-phase electric field are:

[0040]

[0041]

[0042] Where A represents the amplitude of the kth harmonic, represents the phase of the kth harmonic;

[0043] The steps of discrete Fourier transform of the zero-sequence component of the three-phase electric field are as follows:

[0044] First, calculate the real part U of the discrete Fourier transform of the zero-sequence component of the three-phase electric field r (k) and the imaginary part U i (k), respectively:

[0045]

[0046]

[0047] Among them, u(i) is the three-phase zero-sequence electric field data point, i=0, 1, 2…p-1, p is the three-phase zero-sequence electric field data length (i.e., the number of data points), and k is the harmonic order of the three-phase zero-sequence electric field, which ranges from 1 to N.

[0048] The amplitude and initial phase of the kth harmonic can be calculated based on the real and imaginary parts, where k ranges from 1 to N, respectively:

[0049]

[0050]

[0051] Δu(k), is the amplitude and phase of the kth harmonic of the zero-sequence component of the three-phase electric field, that is, the characteristic data of the zero-sequence component of the three-phase electric field.

[0052] In the embodiment, the three zero-sequence electric field waveforms are as follows: Figure 4 shown.

[0053] S4: The collection unit determines whether the characteristic data meets the preset conditions. If so, the fault recording is started; otherwise, the fault recording is not started and the process goes to S1. The specific content of whether the preset conditions are met is:

[0054] 1) The amplitude difference between the power frequency zero-sequence components of the electric field of any two phases in the three phases is less than the preset threshold value t1, and the phase difference between the power frequency zero-sequence components of the electric field of any two phases in the three phases is less than the preset threshold value t2;

[0055] 2) The amplitude difference of the zero-sequence component of the Nth harmonic of the electric field of any two phases in the three-phase is less than the preset threshold value t1, and the phase difference of the zero-sequence component of the Nth harmonic of the electric field of any two phases in the three-phase is less than the preset threshold value t2;

[0056] If the characteristic data meets any of the above two conditions, it is deemed to meet the preset conditions.

[0057] In the embodiment, t1 is 5 V / m, and t2 is 30°.

[0058] In this embodiment, the zero-sequence component of the three-phase electric field is first obtained by subtracting the phasor of the previous cycle signal of the three-phase electric field from the current cycle signal phasor of the three-phase electric field. Then, the zero-sequence component is subjected to discrete Fourier transform processing to obtain the phase and amplitude of the power frequency zero-sequence component of the three-phase electric field and the 2nd, 3rd, 4th, and 5th harmonic zero-sequence components of the three-phase electric field:

[0059] The amplitude of the zero-sequence component of the electric field of phase a is ΔUa(P), P = 1, 2, 3, 4, 5

[0060] The amplitude of the zero-sequence component of the electric field of phase b is ΔUb(P), P = 1, 2, 3, 4, 5

[0061] The amplitude of the zero-sequence component of the electric field of phase c is ΔUc(P), P=1, 2, 3, 4, 5

[0062] The phase of the zero-sequence component of the electric field of phase a is

[0063] The phase of the zero-sequence component of the electric field of phase b is

[0064] The phase of the zero-sequence component of the electric field of phase c is

[0065] The above features are uploaded to the aggregation unit, which calculates the amplitude difference and phase difference of the power frequency zero-sequence component of the electric field of any two phases in the three-phase, as well as the amplitude difference and phase difference of the 2nd, 3rd, 4th, and 5th harmonic zero-sequence component of the electric field of any two phases in the three-phase:

[0066] The amplitude difference of the zero-sequence component of the electric field between phases ab is ΔUab(P), where P = 1, 2, 3, 4, 5

[0067] The amplitude difference of the zero-sequence component of the electric field between phases bc is ΔUbc(P), P = 1, 2, 3, 4, 5

[0068] The amplitude difference of the zero-sequence component of the electric field of the two phases ca is ΔUca(P), P = 1, 2, 3, 4, 5

[0069] The phase difference between the zero-sequence components of the electric field of phases ab is

[0070] The phase difference between the zero-sequence components of the electric field of the two phases bc is

[0071] The phase difference between the zero-sequence components of the electric field of the two phases ca is

[0072] Then the fault diagnosis was carried out based on the calculation results of the aggregation unit.

[0073] ΔUab(2)=0.106V / m

[0074] ΔUab(3)=0.018V / m

[0075] ΔUab(4)=0.06V / m

[0076] ΔUab(5)=0.026V / m

[0077] ΔUbc(2)=0.107V / m

[0078] ΔUbc(3)=0.154V / m

[0079] ΔUbc(4)=0.19V / m

[0080] ΔUbc(5)=0.046V / m

[0081] ΔUca(2)=0.032V / m

[0082] ΔUca(3)=0.0173V / m

[0083] ΔUca(4)=0.0125V / m

[0084] ΔUca(3)=0.0103V / m

[0085] are all less than the preset threshold of 5V / m, and

[0086]

[0087]

[0088]

[0089]

[0090]

[0091]

[0092]

[0093]

[0094]

[0095]

[0096]

[0097]

[0098] If both are less than the preset threshold of 30 degrees, it is considered that a single-phase grounding fault has occurred and the fault recording is started.

[0099] The above embodiments are illustrations of specific implementation methods of the present invention, rather than limitations of the present invention. Technicians in the relevant technical fields can make various changes and modifications to obtain corresponding equivalent technical solutions without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions should be included in the patent protection scope of the present invention.

Claims

1. A distribution network fault recording method based on electric field zero sequence component, characterized in that: The following steps are involved: S1: The acquisition unit collects three-phase electric field data in real time; The electric field data is voltage data; S2: Subtract the phasor of the previous cycle signal of the three-phase electric field from the phasor of the current cycle signal of the electric field to obtain the zero-sequence component of the three-phase electric field; S3: Perform discrete Fourier transform on the zero-sequence components of the three-phase electric field respectively to obtain characteristic data of the zero-sequence components of the three-phase electric field, and upload the characteristic data to the collection unit; The characteristic data include: the phase and amplitude of the power frequency zero-sequence component of the three-phase electric field; the phase and amplitude of the Nth harmonic zero-sequence component of the three-phase electric field, where N is 2, 3, 4, or 5; S4: The collection unit determines whether the characteristic data meets the preset conditions. If so, the single-phase grounding fault recording is started; otherwise, the single-phase grounding fault recording is not started and the process jumps to S1.

2. A distribution network fault recording method based on electric field zero sequence component according to claim 1, characterized in that: The method for obtaining the zero-sequence component in step S2 is to subtract the phases of two adjacent frequency signals, and the phases of the two subtracted frequency signals are separated by m power frequency cycles, and the value range of m is 1-5.

3. A distribution network fault recording method based on electric field zero sequence component according to claim 1, characterized in that: The specific content of whether the preset conditions are met in step S4 is: 1) The amplitude difference between the power frequency zero-sequence components of the electric field of any two phases in the three phases is less than the preset threshold value t1, and the phase difference between the power frequency zero-sequence components of the electric field of any two phases in the three phases is less than the preset threshold value t2; 2) The amplitude difference of the zero-sequence component of the Nth harmonic of the electric field of any two phases in the three-phase is less than the preset threshold value t1, and the phase difference of the zero-sequence component of the Nth harmonic of the electric field of any two phases in the three-phase is less than the preset threshold value t2; If the characteristic data meets any of the above two conditions, it is deemed to meet the preset conditions.

4. A distribution network fault recording method based on electric field zero sequence component according to claim 1, characterized in that: The method is applicable to a distribution network voltage level of a medium voltage level, i.e., 1 kV to 35 kV.

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