A high-resistance fault line selection method for small resistance grounded systems using inner product matrix

Abstract

The application discloses a small-resistance grounding system high-resistance fault line selection method using an inner product matrix, first, sampling zero sequence currents of each feeder of the small-resistance grounding system, and calculating inner product values between the feeders by using the sampling data; then, accumulating the inner product values between the feeders to obtain comprehensive inner product values, constructing an inner product matrix by the comprehensive inner product values, and improving the matrix to obtain an improved inner product matrix; thirdly, calculating average values of the comprehensive inner product values of each feeder by using the improved inner product matrix; finally, constructing a line selection criterion according to an amplitude difference between a maximum value and a minimum value of the average values of the comprehensive inner product values of each feeder. The high-resistance fault line selection method comprehensively utilizes differences between the feeders of the small-resistance grounding system after a fault, and can detect a fault feeder when a high-resistance fault occurs in the small-resistance grounding system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power system distribution network relay protection, and relates to a high-resistance fault line selection method for a small-resistance grounding system by using an inner product matrix. BACKGROUND

[0002] As the end of the power system, the distribution network directly reflects the requirements of users in terms of power supply reliability, power quality, safety and economy, etc. Statistics show that the distribution network is the part of the power system where faults occur most frequently, and more than 95% of user power outage accidents are caused by faults in the distribution network. The grounding modes mainly used in the neutral point of the distribution network in China include non-grounding, resonance grounding (also known as arc suppression coil grounding), small-resistance grounding and the like. With the development of economy, the structure of the distribution network is becoming increasingly complex. When a high-resistance fault occurs in the distribution network with any grounding mode, the fault characteristics are not obvious, the zero-sequence overcurrent protection at the present stage is prone to refuse to act, and the distribution network with the grounding point is operated for a long time, which may cause phase-to-phase short-circuit faults, cable trench fires, and large-area power outages, and may also cause electric shock and fire, so it is necessary to detect the line with the high-resistance fault in time and shut it down. The operation regulations of the distribution network have been revised by State Grid Corporation of China and Southern Power Grid Corporation, and it is required to quickly isolate the permanent grounding fault as close as possible to eliminate the risk of accident expansion and further improve the safety and reliability of power supply. SUMMARY

[0003] The purpose of the application is to provide a high-resistance fault line selection method for a small-resistance grounding system by using an inner product matrix, which can accurately detect and send a signal to make the relay protection device trip under the condition of a high-resistance fault.

[0004] The technical solution adopted by the application is that the high-resistance fault line selection method for a small-resistance grounding system by using an inner product matrix is implemented according to the following steps:

[0005] Step 1, sampling the zero-sequence currents i l of each feeder of the small-resistance grounding system;

[0006] Step 2, calculating the inner product values between each feeder by using the sampling data;

[0007] Step 3, obtaining a comprehensive inner product value by accumulating the inner product values between each feeder, constructing an inner product matrix by using the comprehensive inner product value, and improving the matrix to obtain an improved inner product matrix;

[0008] Step 4, calculating the average value of the comprehensive inner product values of each feeder by using the improved inner product matrix;

[0009] Step 5, constructing a line selection criterion according to the amplitude difference between the maximum value and the minimum value of the average value of the comprehensive inner product values of each feeder, and determining the fault feeder of the small-resistance grounding system under the condition of a high-resistance fault according to the line selection criterion.

[0010] The application also features that:

[0011] The specific process of step 1 is:

[0012] The time when the fault occurs is set as m, in seconds; the starting time of the sampling sequence is (m+0.04) seconds, and the ending time of the sampling sequence is (m+0.04+0.005) seconds; the zero sequence currents of each feeder of the small-resistance grounding system are sampled l The specific sampling sequence is shown as follows: l (1), i l (2), …, i l (q); wherein, l=1, 2, …, h, e, …, n, l is the feeder number, n is the total number of feeders; q represents the number of sampling points.

[0013] The specific process of step 2 is: calculating the inner product value of the zero sequence current of any feeder h to the zero sequence current of any feeder e, to obtain the inner product value N he of any feeder h on any feeder e. he The calculation formula is as follows:

[0014] N he = <i h , i e > = i h (1) i e (1) cosθ1, i h (2) i e (2) cosθ2, …, i h (q) i e (q) cosθ q

[0015] Wherein, θ1, θ2, …, θ q are the angles between i h (1) and i e (1), i h (2) and i e (2), …, i h (q) and i e (q), respectively.

[0016] The specific process of step 3 is:

[0017] Step 3.1, the inner product value N he is accumulated to obtain the comprehensive inner product value J he , and the expression of J he is as follows:

[0018] J he = N he (1) + N he (2) +, …, + Nhe (q)

[0019] Step 3.2, according to the comprehensive inner product value J he The inner product matrix M is constructed, and M is represented as follows:

[0020]

[0021] Step 3.3, the comprehensive inner product value J on the diagonal of the inner product matrix M is set to 0, and an improved inner product matrix M' is obtained, and M' is represented as follows: 11 , J 22 ,..., J nn All are set to 0, and an improved inner product matrix M' is obtained, and M' is represented as follows:

[0022]

[0023] Step 4 is specifically as follows:

[0024] The absolute value of the sum of all comprehensive inner product values in each row of M' is calculated, and is defined as γ l ; The average value of the comprehensive inner product value of each feeder l in M' is calculated The calculation formula of the average value of the comprehensive inner product value of each feeder l in M' is as follows:

[0025]

[0026] Step 5 is specifically as follows: setting the amplitude threshold The maximum value of the average value of the comprehensive inner product value of each feeder The minimum value of the average value of the comprehensive inner product value of each feeder When , the corresponding feeder is determined as a fault feeder, otherwise, return to step 1 to recalculate.

[0027] The beneficial effects of the present application are:

[0028] The small resistance grounding system high resistance fault line selection method of the present application utilizes the differences between each feeder after the fault of the small resistance grounding system, and can detect the fault feeder when the small resistance grounding system high resistance fault occurs. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is the flow chart of the small resistance grounding system high resistance fault line selection method of the present application;

[0030] Figure 2 is the single-phase grounding fault zero sequence equivalent network diagram of the small resistance grounding system of the present application;

[0031] Figure 3 is the inner product transformation projection schematic diagram in the present application;

[0032] Figure 4 ​This is a simulation model diagram of a 10kV low-resistance grounding system according to an embodiment of the present invention;

[0033] Figure 5 This is the inner product waveform of the zero-sequence current of feeder 1 and other feeders according to the embodiment of the present invention. DETAILED DESCRIPTION

[0034] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] The present invention uses the inner product matrix to select the high-resistance fault line in a low-resistance grounding system. Figure 1 As shown, please follow the steps below:

[0036] Step 1: Set the fault occurrence time to m, in seconds; the sampling sequence start time to (m+0.04) seconds, and the sampling sequence end time to (m+0.04+0.005) seconds; and calculate the zero-sequence current i of each feeder in the low-resistance grounding system. l Sampling is performed, and the specific sampling sequence is expressed as: i l (1), i l (2),…,i l (q); where l = 1, 2, ..., h, e, ..., n, l is the feeder number, n is the total number of feeders, and q represents the number of sampling points.

[0037] Step 2: Calculate the inner product of the zero-sequence current of any feeder h with the zero-sequence current of any feeder e, and obtain the inner product value N of any feeder h on any feeder e. he , N he The calculation formula is as follows:

[0038] N he = h ,i e >=i h (1)i e (1)cosθ1,i h (2)i e (2)cosθ2,…,i h (q)i e (q)cosθ q

[0039] Among them, θ1, θ2, ..., θ q i h (1) with i e (1), i h (2) with i e (2), ..., i h (q) and i e (q) is the angle between them.

[0040] Step 3: Inner product value N​he Accumulate and get the comprehensive inner product value J he , J he The expression is as follows:

[0041] J he =N he (1)+N he (2)+,…,+N he (q)

[0042] According to the comprehensive inner product value J he Construct the inner product matrix M, which is expressed as follows:

[0043]

[0044] The comprehensive inner product value J on the diagonal of the inner product matrix M 11 , J 22 ,...,J nn All are set to 0 to obtain the improved inner product matrix M′, which is expressed as follows:

[0045]

[0046] Step 4: Calculate the absolute value of the sum of all the integrated inner product values ​​of each row in M′, which is defined as γ l ; Calculate the average value of the comprehensive inner product value of each feeder l in M′ The calculation formula is as follows:

[0047]

[0048] Step 5: Set the amplitude threshold The maximum value of the average value of the comprehensive inner product value of each feeder The minimum value of the average value of the comprehensive inner product value of each feeder when When The corresponding feeder is determined to be a faulty feeder. Otherwise, return to step 1 and recalculate, where: The threshold is determined by the actual line parameters of the low-resistance grounding system and the detected grounding resistance. The present invention uses the method for selecting high-resistance fault lines in a low-resistance grounding system using the inner product matrix. The working principle is as follows:

[0049] 1. Direction and amplitude characteristics of zero-sequence current in each feeder and neutral point during high-resistance fault in low-resistance grounding system

[0050] The zero-sequence equivalent network of a single-phase grounding fault on a single feeder in a low-resistance grounding system is as follows: Figure 2 As shown in the figure (in the case of high-resistance grounding, the feeder impedance has little effect on the zero-sequence current distribution of each feeder, so the feeder impedance is ignored), where is the virtual voltage source at the fault location, where Vf0is the phase voltage before the fault occurs, R g Rf0is the transition resistance at the fault, Z Rn0is the neutral grounding resistance of the transformer, If0is the zero-sequence current of the faulty feeder, In0is the zero-sequence current of the neutral point, Vb0is the zero-sequence voltage of the busbar, Cf0is the zero-sequence capacitance of the healthy feeder to ground, s is the number of the healthy feeder, and C 0s Cf0is the zero-sequence capacitance of the healthy feeder to ground, s is the number of the healthy feeder, and C 0v Cf0is the zero-sequence capacitance of the healthy feeder to ground, s is the number of the healthy feeder, and C

[0051] The zero-sequence impedance Z0is as follows:

[0052]

[0053] The zero-sequence voltage of the busbar is as follows:

[0054]

[0055] The zero-sequence current of the healthy feeder is as follows:

[0056]

[0057] The zero-sequence current of the neutral point is as follows:

[0058]

[0059] The zero-sequence current of the faulty feeder is as follows:

[0060]

[0061] The zero-sequence current of the healthy feeder The zero-sequence current of the neutral point The zero-sequence current of the faulty feeder The phase amplitudes and the phase differences of the zero-sequence currents of the healthy feeder, the neutral point, and the faulty feeder can be obtained according to the formulas.

[0062] The ratio of the zero-sequence current of the healthy feeder to the zero-sequence current of the neutral point is as follows:

[0063]

[0064] According to The phase of the zero-sequence current of the healthy feeder leads the phase of the zero-sequence current of the neutral point by 90°, and ωR Z C 0sThe ratio of the fault feeder zero-sequence current amplitude to the neutral point zero-sequence current amplitude is as follows:

[0065] The ratio of the fault feeder zero-sequence current amplitude to the neutral point zero-sequence current amplitude is as follows:

[0066]

[0067] According to The formula shows that, since The fault feeder zero-sequence current amplitude is slightly greater than the neutral point zero-sequence current amplitude, and the phase difference between the fault feeder zero-sequence current and the neutral point zero-sequence current is about 180°.

[0068] 2 Inner product transform basic principle

[0069] For the vector The distribution characteristics in space illustrate the principle of inner product transform (IPT), as shown in Figure 3 The inner product transform between the vector and the vector is to calculate the projection of on The modulus product of depends on the value of the included angle θ3, where Figure 3 The specific inner product transform in has the following several cases:

[0070] Case 1:

[0071] Case 2:

[0072] Case 3:

[0073] Case 4:

[0074] Case 5:

[0075] According to the above cases, the value of the included angle θ between the two vectors can directly affect the value of the inner product of the two vectors.

[0076] 3 Inner product selection principle of small resistance grounding system

[0077] When the high resistance fault occurs, the zero-sequence current of the healthy feeder to the inner product expression of the zero-sequence current of the healthy feeder is as follows:

[0078]

[0079] wherein

[0080] In the case of a high-resistance fault, the inner product of the zero-sequence current of the faulty feeder and the zero-sequence current of the sound feeder is expressed as follows:

[0081]

[0082] The inner product expression of the sound feeder zero-sequence current and the fault feeder zero-sequence current is the same as the inner product expression of the fault feeder zero-sequence current and the sound feeder zero-sequence current.

[0083] in,

[0084] According to the above analysis, it can be concluded that the inner product of the healthy feeder zero-sequence current and the healthy feeder zero-sequence current has an amplitude difference with the inner product of the faulty feeder zero-sequence current and the healthy feeder zero-sequence current. The amplitude difference of the inner product results can be used to effectively identify the faulty feeder and implement protection.

[0085] Example

[0086] Establish as Figure 4 The 10kV low-resistance grounding system simulation model has a total of 5 feeders and a sampling frequency of 200kHz. In this simulation model, the threshold Set to 70, where the parameters of the cable and overhead line are shown in Table 1:

[0087] Table 1

[0088]

[0089] When l 21 When the fault occurs at the end at 0.2s with an initial angle of 90° and a grounding resistance of 3000Ω, the waveform of the product of the zero-sequence current of feeder 1 with the inner current of other feeders is as follows: Figure 5 As shown, from Figure 5 It can be concluded that the inner product amplitude of the zero-sequence current of healthy feeder 1 with the zero-sequence currents of other healthy feeders 3, 4, and 5 is small, and the inner product amplitude of the zero-sequence current of healthy feeder 1 with the zero-sequence current of faulty feeder 2 is large. Therefore, it can be concluded that the inner product amplitude of the zero-sequence current of healthy feeder with the zero-sequence current of healthy feeder is smaller than the inner product amplitude of the zero-sequence current of healthy feeder with the zero-sequence current of faulty feeder.

[0090] Taking the fault initial phase angle of 0°, fault location l4, and grounding resistance of 1200Ω as an example, the average values ​​of the comprehensive inner product values ​​of feeders 1 to 5 are 358.92, 251.74, 132.88, 702.71, and 7.43, respectively. but Therefore, the general The corresponding feeder 4 is determined to be the fault feeder. For different ground fault conditions, the average value of the comprehensive inner product value of each feeder is The simulation results under different working conditions are shown in Table 2, and the faulty feeder can be identified in all of them.

[0091] Table 2

[0092]

[0093]

[0094] By the above manner, the small-resistance grounding system high-resistance fault line selection method using inner product matrix comprehensively utilizes the differences between each feeder after the small-resistance grounding system fault, and can detect the fault feeder when the small-resistance grounding system high-resistance fault.

Claims

1. A method for selecting high-resistance fault lines in a low-resistance grounding system using an inner product matrix, characterized in that: Please follow the steps below to implement it: Step 1: Set the fault occurrence time to m, in seconds; the sampling sequence start time to (m+0.04) seconds, and the sampling sequence end time to (m+0.04+0.005) seconds; and calculate the zero-sequence current i of each feeder in the low-resistance grounding system. l Sampling is performed, and the specific sampling sequence is expressed as: ;in, , l is the feeder number, n is the total number of feeders; q represents the number of sampling points; Step 2: Calculate the inner product of the zero-sequence current of any feeder h and the zero-sequence current of any feeder e, and obtain the inner product of any feeder h on any feeder e. , The calculation formula is as follows: Among them, θ1, θ2, ..., θ q i h (1) with i e (1), i h (2) with i e (2),…,i h (q) and i e (q) the angle between them; Step 3.1: Inner product value Accumulate and get the comprehensive inner product value , The expression is as follows: ； Step 3.2: Based on the comprehensive inner product value Construct the inner product matrix M, which is expressed as follows: ； Step 3.3: Take the comprehensive inner product value J on the diagonal of the inner product matrix M 11 , J 22 ,…,J nn Set all to 0 to get the improved inner product matrix , It is expressed as follows: ； Step 4. Calculation The absolute value of the sum of all the integrated inner product values ​​in each row is defined as ;calculate The average value of the comprehensive inner product value of each feeder l , The calculation formula is as follows: ； Step 5: Construct a line selection criterion based on the amplitude difference between the maximum and minimum average values ​​of the comprehensive inner product values ​​of each feeder, and determine the faulty feeder in the case of a high-resistance fault in a low-resistance grounding system according to the line selection criterion.

2. The method for selecting high-resistance fault lines in a low-resistance grounding system using an inner product matrix according to claim 1, characterized in that: The specific process of step 5 is: setting the amplitude threshold , the maximum value of the average value of the comprehensive inner product value of each feeder , the minimum value of the average value of the comprehensive inner product value of each feeder ;when When The corresponding feeder is determined to be a faulty feeder. Otherwise, return to step 1 and recalculate.

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