Model and method for quantitatively describing evolution rule of grounding fault characteristics of small resistance grounding

Abstract

The invention relates to the technical field of power distribution network fault detection and protection, and discloses a model and a method for quantitatively describing a grounding fault characteristic evolution rule of small resistance grounding. Comprising a first evolution characteristic characterization model used for quantitatively describing evolution characteristics between system zero-sequence voltage and fault resistance after a fault, and a second evolution characteristic characterization model used for quantitatively describing evolution characteristics between fault phase voltage and fault resistance after the fault. The third evolution characteristic characterization model is used for quantitatively describing the evolution characteristic between the fault branch current and the fault resistance after the fault; and the fourth evolution characteristic characterization model is used for quantitatively describing the evolution characteristic between the system zero sequence current and the fault resistance after the fault. The method can serve grounding line selection device research and development manufacturers to master the evolution characteristics of various electrical faults after faults, and provides a scientific basis for designing a high-quality research and judgment algorithm.

Description

Technical Field

[0001] The present invention relates to the technical field of distribution network fault detection and protection, and in particular to a quantitative description model and method for the evolution law of grounding fault characteristics of low-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 low resistance grounding method. Among them, the low resistance grounding method is mainly used to generate large current after a single-phase grounding fault, showing the characteristics of the grounding fault, so that the measurement system of the single-phase grounding line selection device can reliably collect and enter the analysis and judgment function module to achieve accurate identification and rapid handling of the fault. However, under this type of grounding system, the fault current is large, especially in areas with high risk of wildfires. The temperature rise energy accumulated by the large current in a short time is high and the time is short. If it cannot be effectively identified and handled in time, the probability of causing wildfire risks will increase significantly. At present, the grounding line selection device mostly adopts the first half-wave and phase asymmetry methods to identify grounding faults. The algorithm focuses on the sampled electrical data and applies the relevant methods in signal processing to conduct analysis and identification. Obviously, the complexity and variability of the evolution characteristics of grounding faults under this type of grounding system are ignored.

[0003] To this end, this invention will combine the problems encountered in engineering practice and re-examine the characteristic evolution characteristics of grounding faults in such systems, mainly combining Kirchhoff's law, to construct a mathematical characterization model of various electrical characteristics such as grounding fault zero-sequence voltage, zero-sequence current, fault phase voltage, fault branch current and fault resistance. Through this model, the evolution law of various electrical signals is analyzed, providing a scientific basis for the logical design of the grounding fault judgment algorithm, strengthening the promotion of the upgrading and transformation of the single-phase grounding line selection device, so as to realize the accurate identification of faults in such grounding systems, and serve to support the fault operation and maintenance disposal of the production line. Summary of the invention

[0004] For the grounding fault analysis of the neutral point low-resistance grounding system, the current line selection device focuses on data analysis from the signal processing perspective to achieve fault analysis, but ignores the evolution characteristics of the fault features, which is not conducive to the accurate identification of the fault. The present invention provides a quantitative description model and method for the evolution law of the grounding fault characteristics of low-resistance grounding, aiming to provide a logical basis for the algorithm design of the grounding line selection device.

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

[0006] A quantitative description model for the evolution law of grounding fault characteristics of low-resistance grounding, the quantitative description model for the evolution law of grounding fault characteristics comprising 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.

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

[0008]

[0009] 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 voltage of phase A before the distribution network fails; 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.

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

[0011]

[0012] 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.

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

[0014]

[0015] 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.

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

[0017]

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

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

[0020]

[0021] in, Indicates zero sequence current.

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

[0023] As an optimization, the quantitative description model of the evolution law of the grounding 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.

[0024] As an optimization, 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;

[0025] The specific process of constructing the second evolution characteristic characterization model is as follows:

[0026] 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;

[0027] The specific process of constructing the third evolution characteristic characterization model is as follows:

[0028] 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;

[0029] Based on the relationship between the zero-sequence current and the three-phase current and the third evolution characteristic characterization model, a fourth evolution characteristic characterization model for expressing the evolution of the system zero-sequence current with the fault resistance after a fault is obtained.

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

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

[0032] In view of the fact that the current analysis and judgment strategies of single-phase grounding line selection devices mostly focus on extracting data features and analyzing correlation relationships from the perspective of signal processing to realize the identification of grounding faults, but do not effectively consider the electrical evolution characteristics of the grounding fault itself, the present invention focuses on combining the low-resistance grounding system, and according to Kirchhoff's law and circuit principles and other methods, it derives in detail the evolution laws of the system zero-sequence voltage after the fault, the zero-sequence current after the fault, the fault phase voltage after the fault, and the fault branch current after the fault, and organizes them to form a relatively simple mathematical expression model, which can serve the research and development manufacturers of grounding line selection devices to master the evolution characteristics of various electrical faults after the fault, provide a scientific basis for designing high-quality analysis and judgment algorithms, realize the iterative update of fault line selection products, and enhance the effectiveness of grounding fault line selection devices in the field. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0034] Figure 1 It is the curve diagram of the system initial zero-sequence voltage change under different neutral point small resistance;

[0035] Figure 2 It is a curve diagram of the change between the zero-sequence voltage of the system (distribution network) and the fault damping rate;

[0036] Figure 3 It is a schematic diagram of the relationship between the fault phase voltage and the fault damping rate;

[0037] Figure 4 Schematic diagram of the relationship between the fault branch current and the fault damping rate. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0039] This embodiment 1 provides a quantitative description model of the evolution law of the ground fault characteristics of a small resistance grounding, such as Figure 1 As shown,

[0040] 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.

[0041] In some embodiments, in combination with Kirchhoff's law, a grounding voltage equation is constructed at the neutral point based on the inflow and outflow relationship of the node current, thereby constructing 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] 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 voltage of phase A before the distribution network fails; 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.

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

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

[0046]

[0047] 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.

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

[0049]

[0050] 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.

[0051] In some embodiments, considering that the faulty special phase is phase A, and the inverse conversion form of the faulty branch, i.e., r al =1 / g al , considering the relationship between voltage, current and resistance, we can know or Through a series of derivations, it can be learned that the specific expression of the third evolution characteristic characterization model corresponding to the fault branch current of the special phase A is:

[0052]

[0053] Among them, r al represents the fault resistance, Indicates 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 electromotive force of the three-phase power supply is still completely symmetrical, the corresponding load current parts are basically the same in magnitude, and the phases differ by 120°. The difference is that the fault phase is also superimposed with the fault current of the fault branch. According to the conversion rule of the complex sequence network, the zero-sequence current is equal to one-third of the sum of the three-phase current phase quantities, that is, On this basis, through a series of derivations, the final form of the zero-sequence current of the system after the fault (the specific expression of the fourth evolution characteristic characterization model) is:

[0055]

[0056] in, Indicates zero sequence current. Respectively represents the load current of phase A, phase B, and phase C

[0057] Example 2 also discloses a method for quantitatively describing the evolution law of grounding fault characteristics of low-resistance grounding, constructs a quantitative description model for the evolution law of grounding fault characteristics of low-resistance grounding of Example 1, and uses the quantitative description model for the evolution law of grounding fault characteristics to quantitatively describe the evolution law of grounding fault characteristics under low-resistance grounding.

[0058] In some embodiments, the quantitative description model of the evolution law of the 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.

[0059] In some embodiments, the specific process of constructing the first evolution characteristic characterization model is: combining Kirchhoff's law, constructing a ground voltage equation at the neutral point based on the relationship between the inflow and outflow of node current, 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;

[0060] The specific process of constructing the second evolution characteristic characterization model is as follows:

[0061] 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;

[0062] The specific process of constructing the third evolution characteristic characterization model is as follows:

[0063] 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;

[0064] Based on the relationship between the zero-sequence current and the three-phase current and the third evolution characteristic characterization model, a fourth evolution characteristic characterization 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 in the memory and executable on the processor. When the processor executes the computer program, a quantitative description method for the evolution law of the grounding fault characteristics of a low-resistance grounding of embodiment 2 is implemented.

[0066] Next, the present invention will be described using specific examples.

[0067] 1. To analyze the relationship between the initial zero-sequence voltage change of the system under different small resistance values, set the initial unbalance of the system System Capacity I c =60A, we can draw a curve showing the relationship between the initial zero-sequence voltage of the system and the resistance value of the small resistor, such as Figure 1 Observation Figure 1 It can be seen that the introduction of small resistors can effectively improve the asymmetry of the system. When it is close to 0Ω, it is basically equivalent to direct grounding, and the system asymmetry tends to zero. As the resistance value increases further, when it tends to be above 200Ω, it is basically ungrounded, and the asymmetry is the same as the initial imbalance. In addition, according to Guo Xinhui's "Research and Application of Small Resistance Grounding Methods for Neutral Points of Industrial 10kV Power Grids", it is mentioned that the neutral point grounding device is divided into 4 models, and the corresponding small resistor values ​​are 10Ω, 15Ω, 30Ω and 60Ω respectively.

[0068] 2. To analyze the relationship between the system zero-sequence voltage and the fault resistance (fault damping rate), set the system initial unbalance System Capacity I c =60A, neutral point resistance R = 10Ω, the relationship between the system zero-sequence voltage and the fault damping rate can be drawn, such as Figure 2 After adopting the low resistance grounding method, the system asymmetry will change and will be weakened to 0.0015. Figure 2It can be seen that when the fault resistance is 10Ω, 100Ω, 200Ω, 500Ω, 1000Ω and 3000Ω, the corresponding fault damping rates are 10, 1, 0.5, 0.2, 0.1 and 0.03, respectively. The unit proportion of the system zero-sequence voltage to the rated phase voltage after the fault is 0.498, 0.089, 0.046, 0.018, 0.008 and 0.0018, respectively. Basically, the detection criterion constructed using zero-sequence voltage below 3000Ω still has better detection performance. This shows that for such systems using a small resistance grounding method, using the same detection criterion, the detection upper line is obviously not as good as the ungrounded method and the arc suppression coil grounding method. The latter two can at least reach the detection upper limit within 5000Ω.

[0069] 3. To analyze the relationship between the fault phase voltage and the fault point current and the fault resistance, set the initial system imbalance System Capacity I c =60A, when the neutral point resistance R = 10Ω, the relationship between the fault phase voltage and the fault point current and the fault resistance can be drawn as follows: Figure 3-Figure 4 Observation Figure 3-Figure 4 It can be learned that: 1) When a small resistance grounding method is used, the current at the fault point presents a large current characteristic, which can be as high as 300.67A. It is obviously easy to be collected by the measurement system and further start detection, so as to achieve rapid handling 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, which is slightly higher than the initial zero-sequence zero voltage of the system after the small resistance is used. The proportion is 0.001493, and the fault phase voltage at this time is 5971.38V, and the fault point current is 1.99A. Obviously, using phase voltage to construct detection criteria is obviously not as advantageous as using phase current (zero-sequence current).

[0070] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection 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.

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 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.

3. The quantitative description model for the evolution law of ground fault characteristics of a low-resistance grounding according to claim 2 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.

4. 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.

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 third evolution characteristic characterization model is: Among them, r al represents the fault resistance, Indicates the fault branch current of phase A.

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

7. 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 1-6 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.

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 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.

9. The method for quantitatively describing the evolution law of ground fault characteristics of low-resistance grounding according to claim 8 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 the third evolution characteristic characterization model, a fourth evolution characteristic characterization model for expressing the evolution of the system zero-sequence current with the fault resistance after a fault is obtained.

10. 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 7 to 9 is implemented.

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