Quantitative description model and method for the evolution law of grounding fault characteristics with small resistance grounding

Abstract

The present invention relates to the technical field of distribution network fault detection and protection, and discloses a quantitative description model and method for the evolution law of grounding fault characteristics with small resistance grounding. The quantitative description model of the grounding fault characteristics evolution law includes a first evolution characteristic representation model for quantitatively describing the evolution characteristics between the zero-sequence voltage of the system and the fault resistance after the fault, a second evolution characteristic representation model for quantitatively describing the evolution characteristics between the fault-phase voltage and the fault resistance after the fault, a third evolution characteristic representation model for quantitatively describing the evolution characteristics between the fault branch current and the fault resistance after the fault, and a fourth evolution characteristic representation model for quantitatively describing the evolution characteristics between the zero-sequence current of the system and the fault resistance after the fault. Through the present invention, it can serve the grounding line selection device R & D manufacturers to master the evolution characteristics of various electrical faults after the fault, and provide a scientific basis for designing high-quality judgment algorithms.

Description

Technical Field

[0001] The present invention relates to the technical field of distribution network fault detection and protection, and specifically relates to a quantitative description model and method for the evolution law of grounding fault characteristics of small-resistance grounding. Background Art

[0002] There are several typical grounding methods in the distribution network, such as ungrounded method, arc suppression coil grounding method, and small-resistance grounding method. Among them, the small-resistance grounding method is mainly used to generate a large current after a single-phase grounding fault, so as to manifest the grounding fault characteristics, so that the single-phase grounding line selection device can reliably collect the measurement system and enter the judgment function module to realize the accurate identification and rapid disposal of the fault. However, under this kind of grounding system, the fault current is relatively large. Especially in high-risk wildfire areas, the temperature rise energy accumulated by the large current in a short time is relatively high and the time is short. If it cannot be effectively identified and disposed of in time, the probability of triggering a wildfire risk will increase significantly. At present, most grounding line selection devices use the first half-wave and phase asymmetry methods to identify grounding faults. The algorithms mainly focus on analyzing the sampled electrical data and applying relevant methods in signal processing to make judgments and identifications. Obviously, the complexity and variability of the evolution characteristics of grounding faults under this kind of grounding system are ignored.

[0003] Therefore, the present invention will combine the problems encountered in engineering practice and re-examine the characteristic evolution characteristics of grounding faults under this kind of system. Mainly combined with Kirchhoff's law, a mathematical representation model of various electrical characteristics such as zero-sequence voltage, zero-sequence current, fault-phase voltage, and fault-branch current of grounding faults with respect to the fault resistance is constructed. Through this model, the evolution law of various electrical signals is analyzed, providing a scientific basis for the logic design of grounding fault judgment algorithms, strengthening the promotion of the upgrade and transformation of single-phase grounding line selection devices, so as to realize the accurate identification of faults under this kind of grounding system and serve to support the fault operation and maintenance disposal of the production front line. Summary of the Invention

[0004] Aiming at the grounding fault judgment of the neutral point small-resistance grounding system, the current line selection devices mainly focus on data analysis from the perspective of signal processing to realize fault judgment, ignoring the evolution characteristics of fault characteristics, which is not conducive to the accurate identification of faults. The present invention provides a quantitative description model and method for the evolution law of grounding fault characteristics of small-resistance grounding, aiming to provide a judgment logic basis for the algorithm design of grounding line selection devices.

[0005] The present invention is realized through the following technical solutions:

[0006] A quantitative description model for the evolution law of grounding fault characteristics with small resistance grounding. The quantitative description model for the evolution law of grounding fault characteristics includes a first evolution characteristic representation model for quantitatively describing the evolution characteristics between the zero-sequence voltage of the system after a fault and the fault resistance, a second evolution characteristic representation model for quantitatively describing the evolution characteristics between the phase voltage of the fault phase and the fault resistance after a fault, a third evolution characteristic representation model for quantitatively describing the evolution characteristics between the current of the fault branch and the fault resistance after a fault, and a fourth evolution characteristic representation model for quantitatively describing the evolution characteristics between the zero-sequence current of the system and the fault resistance after a fault.

[0007] As an optimization, the specific expression of the first evolution characteristic representation model is:

[0008]

[0009] Where, is the initial unbalance degree of the distribution network; ω is the angular frequency, ω = 2πf, and f represents the distribution network frequency; C a , C b and C c are the charging capacitances to the ground of the voltages of phase A, phase B, and phase C respectively; g al is the reciprocal of the fault resistance; g r is the reciprocal of the small resistance at the neutral point; is the voltage of phase A of the distribution network before the fault; d al is the fault damping ratio; d r is the damping ratio associated with the small resistance at the neutral point; is the zero-sequence voltage of the system under the fault.

[0010] As an optimization, the specific formula of the fault damping ratio d al is:

[0011]

[0012] Where, X c represents the capacitive reactance; r al represents the fault resistance; U a0 is the voltage of phase A of the system; I C is the capacitive current of the distribution network.

[0013] As an optimization, the specific expression of the second evolution characteristic representation model is:

[0014]

[0015] Where, is the initial unbalance degree of the distribution network; d al is the fault damping ratio; d r is the damping ratio associated with the small resistance at the neutral point; is the voltage of phase A of the distribution network before the fault; It is the voltage of the special phase A for the ground fault.

[0016] As an optimization, the specific expression of the third evolution characteristic representation model is:

[0017]

[0018] where r al represents the fault resistance, represents the fault branch current of phase A.

[0019] As an optimization, the specific expression of the fourth evolution characteristic representation model is:

[0020]

[0021] where represents the zero-sequence current.

[0022] The present invention also discloses a method for quantitatively describing the evolution law of the ground fault characteristics of a small-resistance grounding, constructs the above-mentioned quantitative description model of the evolution law of the ground fault characteristics of a small-resistance grounding, and uses the quantitative description model of the evolution law of the ground fault characteristics to quantitatively describe the evolution law of the ground fault characteristics under the small-resistance grounding method.

[0023] As an optimization, the quantitative description model of the evolution law of the ground fault characteristics includes a first evolution characteristic representation model for quantitatively describing the evolution characteristics between the zero-sequence voltage of the system after the fault and the fault resistance, a second evolution characteristic representation model for quantitatively describing the evolution characteristics between the voltage of the fault phase after the fault and the fault resistance, a third evolution characteristic representation model for quantitatively describing the evolution characteristics between the fault branch current after the fault and the fault resistance, and a fourth evolution characteristic representation model for quantitatively describing the evolution characteristics between the zero-sequence current of the system after the fault and the fault resistance.

[0024] As an optimization, the specific process of constructing the first evolution characteristic representation model is: combining Kirchhoff's law, establishing a ground voltage equation based on the relationship of the inflow and outflow of node currents at the neutral point, so as to construct the first evolution characteristic representation model that can be used to express the evolution of the zero-sequence voltage of the system after the fault with the fault resistance;

[0025] The specific process of constructing the second evolution characteristic representation model is:

[0026] Superposing the voltage of the fault phase as the phasor of the power supply electromotive force and the neutral point voltage, and combining with the first evolution characteristic representation model to obtain the second evolution characteristic representation model that can be used to express the evolution of the voltage of the fault phase after the fault with the fault resistance;

[0027] The specific process of constructing the third evolution characteristic representation model is:

[0028] Based on the reciprocal conversion form of the faulty branch and the correlation relationship among voltage, current, and resistance, and in combination with the second evolution characteristic representation model, a third evolution characteristic representation model that can be used to express the evolution of the current in the faulty branch after a fault with respect to the fault resistance is obtained;

[0029] Based on the relationship between the zero-sequence current and the three-phase currents and in combination with the third evolution characteristic representation model, a fourth evolution characteristic representation model that can be used to express the evolution of the zero-sequence current in the system after a fault with respect to the fault resistance is obtained.

[0030] The present invention also discloses an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the above-mentioned method for quantitatively describing the evolution law of the grounding fault characteristics of a small-resistance grounding is realized.

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] Regarding the current judgment strategies of single-phase grounding line selection devices, most of them focus on extracting data features and analyzing correlation relationships from the perspective of signal processing to achieve the identification of grounding faults, and do not effectively consider the electrical evolution characteristics of the grounding faults themselves. The present invention focuses on combining a small-resistance grounding system, and according to methods such as Kirchhoff's law and circuit principles, the evolution laws of the zero-sequence voltage in the system after a fault, the zero-sequence current after a fault, the faulty-phase voltage after a fault, and the current in the faulty branch after a fault are derived in detail, and a relatively concise mathematical expression model is formed, which can serve for the grounding line selection device R & D manufacturers to master the evolution characteristics of various electrical faults after a fault, provide a scientific basis for designing high-quality judgment algorithms, realize the iterative update of fault line selection products, and improve the actual effectiveness of the grounding fault line selection device in the application site. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not limit the embodiments of the present invention. In the drawings:

[0034] Figure 1 is a curve graph of the initial zero-sequence voltage change of the system under different small resistances at the neutral point;

[0035] Figure 2 is a curve graph of the change of the zero-sequence voltage of the system (distribution network) with respect to the fault damping ratio;

[0036] Figure 3 is a schematic diagram of the change relationship of the faulty-phase voltage with respect to the fault damping ratio;

[0037] Figure 4 is a schematic diagram of the change relationship of the current in the faulty branch with respect to the fault damping ratio. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] To make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to embodiments and the accompanying drawings. The illustrative embodiments and descriptions thereof of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0039] Embodiment 1 of the present invention provides a quantitative description model for the evolution law of grounding fault characteristics with a small resistance grounded, as Figure 1 shown

[0040] The quantitative description model for the evolution law of grounding fault characteristics includes a first evolution characteristic characterization model for quantitatively describing the evolution characteristics between the zero-sequence voltage of the system after a fault and the fault resistance, a second evolution characteristic characterization model for quantitatively describing the evolution characteristics between the phase voltage of the fault phase and the fault resistance after a fault, a third evolution characteristic characterization model for quantitatively describing the evolution characteristics between the current of the fault branch and the fault resistance after a fault, and a fourth evolution characteristic characterization model for quantitatively describing the evolution characteristics between the zero-sequence current of the system and the fault resistance after a fault.

[0041] In some embodiments, in combination with Kirchhoff's law, a grounding voltage equation is constructed based on the relationship of node current inflow and outflow at the neutral point, so as to construct a first evolution characteristic characterization model that can be used to express the zero-sequence voltage of the system after a fault. The specific expression of the first evolution characteristic characterization model is:

[0042]

[0043] Wherein, is the initial unbalance degree of the distribution network; ω is the angular frequency, ω = 2πf, and f represents the distribution network frequency; C a 、C b and C c are the charging capacitances to the ground of the voltages of phase A, phase B, and phase C respectively; g al is the reciprocal of the fault resistance; g r is the reciprocal of the small resistance at the neutral point; is the voltage of phase A of the distribution network before the fault; d al is the fault damping ratio; d r is the damping ratio associated with the small resistance at the neutral point; is the zero-sequence voltage of the system under the fault.

[0044] It should be noted that in the present invention, phase A is regarded as the fault phase because the three-phase topology is symmetric; if it is a phase B fault, phase B can be renamed as phase A, and the original phase C becomes phase B and phase A becomes phase C; the same applies to a phase C fault. Therefore, from the perspective of analysis, only a phase A fault needs to be considered, which is universal.

[0045] In some embodiments, the fault damping ratio d alThe specific formula is:

[0046]

[0047] Wherein, X c represents capacitive reactance; r al represents the fault resistance; U a0 is the phase A voltage of the system; I C is the capacitive current of the distribution network.

[0048] In some embodiments, when assuming that the special phase is phase A, the fault phase voltage is the phasor superposition of the power supply electromotive force and the neutral point voltage, that is After substituting into the calculation formula of the zero-sequence voltage of the system after the fault, it can be derived that The specific expression of the second evolution characteristic representation model is:

[0049]

[0050] Wherein, is the initial unbalance degree of the distribution network; d al is the fault damping ratio; d r is the damping ratio associated with the small resistance of the neutral point; is the phase A voltage of the distribution network before the fault; is the voltage of the special phase A of the ground fault.

[0051] In some embodiments, considering that the special fault phase is phase A and the reciprocal conversion form of the fault branch, that is r al = 1 / g al , considering the correlation relationship between voltage, current and resistance, it can be known that Or Through a series of derivations, it can be known that the specific expression of the third evolution characteristic representation model corresponding to the fault branch current of the special phase A is:

[0052]

[0053] Wherein, r al represents the fault resistance, represents the fault branch current of phase A.

[0054] In some embodiments, when considering the relationship between the zero-sequence current and the three-phase current, considering that the three-phase power supply electromotive force is still completely symmetric, the corresponding load current part is basically the same in magnitude and the phases differ by 120° in sequence. The difference is that the fault phase also superimposes the fault current of the fault branch. According to the conversion rule of the complex sequence network, that is, the zero-sequence current is equal to one-third of the phasor sum of the three-phase currents, that is On this basis, through a series of derivations, the final form of the zero-sequence current of the system after a fault (the specific expression of the fourth evolution characteristic representation model) is:

[0055]

[0056] Among them, represents the zero-sequence current. respectively represent the load currents of phase A, phase B, and phase C

[0057] Embodiment 2 also discloses a method for quantitatively describing the evolution law of the grounding fault characteristics of a small-resistance grounding. A quantitative description model of the evolution law of the grounding fault characteristics of a small-resistance grounding in Embodiment 1 is constructed, and the quantitative description model of the evolution law of the grounding fault characteristics is used to quantitatively describe the evolution law of the grounding fault characteristics under the small-resistance grounding method.

[0058] In some embodiments, the quantitative description model of the evolution law of the grounding fault characteristics includes a first evolution characteristic representation model for quantitatively describing the evolution characteristics between the zero-sequence voltage of the system after a fault and the fault resistance, a second evolution characteristic representation model for quantitatively describing the evolution characteristics between the fault-phase voltage and the fault resistance after a fault, a third evolution characteristic representation model for quantitatively describing the evolution characteristics between the fault-branch current and the fault resistance after a fault, and a fourth evolution characteristic representation model for quantitatively describing the evolution characteristics between the zero-sequence current of the system and the fault resistance after a fault.

[0059] In some embodiments, the specific process of constructing the first evolution characteristic representation model is: combining Kirchhoff's law, establishing a grounding voltage equation based on the inflow and outflow relationship of node currents at the neutral point, so as to construct a first evolution characteristic representation model that can be used to express the evolution of the zero-sequence voltage of the system after a fault with respect to the fault resistance;

[0060] The specific process of constructing the second evolution characteristic representation model is:

[0061] Superpose the fault-phase voltage as the phasor of the power supply electromotive force and the neutral-point voltage, and combine the first evolution characteristic representation model to obtain a second evolution characteristic representation model that can be used to express the evolution of the fault-phase voltage after a fault with respect to the fault resistance;

[0062] The specific process of constructing the third evolution characteristic representation model is:

[0063] Based on the reciprocal conversion form of the fault branch and the correlation relationship between voltage, current, and resistance, combine the second evolution characteristic representation model to obtain a third evolution characteristic representation model that can be used to express the evolution of the fault-branch current after a fault with respect to the fault resistance;

[0064] Based on the relationship between zero-sequence current and three-phase current and in combination with the third evolution characteristic representation model, a fourth evolution characteristic representation model for expressing the evolution of the system zero-sequence current with the fault resistance after a fault is obtained.

[0065] Embodiment 3 also discloses an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, a method for quantitatively describing the evolution law of the grounding fault characteristics of a small-resistance grounding in Embodiment 2 is implemented.

[0066] Next, the present invention will be described through specific cases.

[0067] I. To analyze the relationship between the initial zero-sequence voltage of the system under different small-resistance values, the initial system unbalance degree is set System capacitive current I c = 60 A, and the curve of the relationship between the initial zero-sequence voltage of the system and the small-resistance value can be plotted, as Figure 1 shown. It can be observed Figure 1 that the introduction of a small resistance can effectively improve the asymmetry of the system. When approaching 0 Ω, it is basically equivalent to direct grounding, and the system asymmetry degree tends to zero. As the resistance value further increases and tends to be above 200 Ω, it is basically an ungrounded mode, and the asymmetry degree is the same as the initial unbalance degree. In addition, according to Guo Xinhui's "Research and Application of the Method for Grounding the Neutral Point of the 10 kV Industrial Power Grid with a Small Resistance", it is mentioned that the neutral point grounding device is divided into 4 models, and the corresponding small-resistance values are 10 Ω, 15 Ω, 30 Ω, and 60 Ω respectively.

[0068] II. To analyze the relationship between the zero-sequence voltage of the system and the fault resistance (fault damping ratio), the initial system unbalance degree is set System capacitive current I c = 60 A. When the small resistance of the neutral point R = 10 Ω, the curve of the relationship between the zero-sequence voltage of the system and the fault damping ratio can be plotted, as Figure 2 shown. After adopting the small-resistance grounding method, the system asymmetry degree will change and will be weakened to 0.0015. It can be observed Figure 2, it can be known that when the fault resistances are 10Ω, 100Ω, 200Ω, 500Ω, 1000Ω and 3000Ω respectively, the corresponding fault damping ratios are 10, 1, 0.5, 0.2, 0.1 and 0.03 respectively, and the unit ratios of the zero-sequence voltage of the system after the fault to the rated phase voltage are 0.498, 0.089, 0.046, 0.018, 0.008 and 0.0018 respectively. The detection criterion constructed by using the zero-sequence voltage still has better detection performance basically below 3000Ω. This shows that for such systems adopting the small-resistance grounding method, using the same detection criterion, the detection upper limit is obviously inferior to that of the non-grounding method and the arc suppression coil grounding method. The latter two can at least reach the detection upper limit within 5000Ω.

[0069] III. To analyze the variation relationship between the fault phase voltage and the fault point current with the fault resistance, the initial system unbalance degree is set System capacitive current I c = 60A. When the neutral small resistance R = 10Ω, the variation relationship between the fault phase voltage and the fault point current with the fault resistance can be plotted, as shown respectively in Figures 3 - 4 shown. Observing Figures 3 - 4 it can be known that: 1) Adopting the small-resistance grounding method, the fault point current shows the characteristic of large current, and the highest can reach 300.67A, which is obviously easy to be collected by the measurement system and further start detection to achieve the rapid disposal of the grounding fault; 2) When the fault resistance is 3000Ω, the zero-sequence voltage after the fault accounts for about 0.001818 of the rated phase voltage, slightly higher than the initial zero-sequence voltage ratio 0.001493 of the system after the small resistance acts, and at this time the fault phase voltage is 5971.38V and the fault point current is 1.99A. Obviously, constructing the detection criterion by using the phase voltage is no longer as advantageous as using the phase current (zero-sequence current).

[0070] The specific implementation manners described above further elaborate on the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above is only the specific implementation manners of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A quantitative description model for the evolution law of ground fault characteristics of low resistance grounding, characterized in that: The quantitative description model of the evolution law of ground fault characteristics includes a first evolution characteristic characterization model for quantitatively describing the evolution characteristics between the system zero-sequence voltage and the fault resistance after the fault, a second evolution characteristic characterization model for quantitatively describing the evolution characteristics between the fault phase voltage and the fault resistance after the fault, a third evolution characteristic characterization model for quantitatively describing the evolution characteristics between the fault branch current and the fault resistance after the fault, and a fourth evolution characteristic characterization model for quantitatively describing the evolution characteristics between the system zero-sequence current and the fault resistance after the fault; The specific expression of the first evolution characteristic characterization model is: in, is the initial unbalance of the distribution network; ω is the angular frequency, ω=2πf, f represents the distribution network frequency; C a , C b and C c are the charging capacitance to ground of phase A, phase B, and phase C voltages respectively; g al is the reciprocal of the fault resistance; g r It is the reciprocal of the small resistance of the neutral point; is the phase A voltage before the distribution network fault; d al is the fault damping rate; d r is the damping rate associated with the small resistance at the neutral point; is the system zero-sequence voltage under fault.

2. The quantitative description model for the evolution law of ground fault characteristics of a low-resistance grounding according to claim 1 is characterized in that: The fault damping rate d al The specific formula is: Among them, X c represents capacitive reactance; r al Indicates fault resistance; U a0 System A phase voltage; I C is the capacity of the distribution network.

3. The quantitative description model for the evolution law of ground fault characteristics of a low-resistance grounding according to claim 1 is characterized in that: The specific expression of the second evolution characteristic characterization model is: in, is the initial imbalance of the distribution network; d al is the fault damping rate; d r is the damping rate associated with the small resistance at the neutral point; is the phase A voltage before the distribution network fault; It is the voltage of the special phase A of the ground fault.

4. The quantitative description model for the evolution law of ground fault characteristics of a low-resistance grounding according to claim 3 is characterized in that: The specific expression of the third evolution characteristic characterization model is: Among them, r al represents the fault resistance, Indicates the fault branch current of phase A.

5. The quantitative description model for the evolution law of ground fault characteristics of a low-resistance grounding according to claim 4 is characterized in that: The specific expression of the fourth evolution characteristic characterization model is: in, Indicates zero sequence current.

6. A quantitative description method for the evolution law of ground fault characteristics of low resistance grounding, characterized in that: A quantitative description model for the evolution law of grounding fault characteristics of a low-resistance grounding as described in any one of claims 1-5 is constructed, and the quantitative description model for the evolution law of grounding fault characteristics is used to quantitatively describe the evolution law of grounding fault characteristics under the low-resistance grounding mode.

7. The method for quantitatively describing the evolution law of ground fault characteristics of low-resistance grounding according to claim 6 is characterized in that: The quantitative description model of the evolution law of ground fault characteristics includes a first evolution characteristic characterization model for quantitatively describing the evolution characteristics between the system zero-sequence voltage and the fault resistance after the fault, a second evolution characteristic characterization model for quantitatively describing the evolution characteristics between the fault phase voltage and the fault resistance after the fault, a third evolution characteristic characterization model for quantitatively describing the evolution characteristics between the fault branch current and the fault resistance after the fault, and a fourth evolution characteristic characterization model for quantitatively describing the evolution characteristics between the system zero-sequence current and the fault resistance after the fault.

8. The method for quantitatively describing the evolution law of ground fault characteristics of low-resistance grounding according to claim 7 is characterized in that: The specific process of constructing the first evolution characteristic characterization model is as follows: combining Kirchhoff's law, constructing a grounding voltage equation at the neutral point based on the relationship between the inflow and outflow of node currents, thereby constructing a first evolution characteristic characterization model that can be used to express the evolution of the system zero-sequence voltage with the fault resistance after the fault; The specific process of constructing the second evolution characteristic characterization model is as follows: The fault phase voltage is the phase sum of the power source electromotive force and the neutral point voltage, and combined with the first evolution characteristic characterization model, a second evolution characteristic characterization model that can be used to express the evolution of the fault phase voltage with the fault resistance after the fault is obtained; The specific process of constructing the third evolution characteristic characterization model is as follows: Based on the inverse conversion form of the fault branch and the correlation between voltage, current and resistance, combined with the second evolution characteristic characterization model, a third evolution characteristic characterization model that can be used to express the evolution of the fault branch current with the fault resistance after the fault is obtained; Based on the relationship between the zero-sequence current and the three-phase current and in combination with the third evolution characteristic characterization model, a fourth evolution characteristic characterization model that can be used to express the evolution of the system zero-sequence current with the fault resistance after a fault is obtained.

9. An electronic device, characterized in that: The invention comprises a memory, a processor and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, a method for quantitatively describing the evolution law of the grounding fault characteristics of a low-resistance grounding as described in any one of claims 6 to 8 is implemented.

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