Low-voltage power distribution network single-phase earth fault self-adaptive protection method, single-phase earth fault protection device and computer storage medium

Abstract

The invention relates to the technical field of power distribution network faults, and provides a low-voltage power distribution network single-phase earth fault self-adaptive protection method, a single-phase earth fault protection device and a computer storage medium. Obtaining a three-phase current abrupt change instantaneous value sequence and a three-phase voltage abrupt change instantaneous value sequence after the fault occurs; and then, according to the three-phase current abrupt change instantaneous value sequence and the three-phase voltage abrupt change instantaneous value sequence, positive sequence impedance and zero sequence impedance of a measurement switch system side are calculated, a correction coefficient of a protection current setting value is obtained based on the positive sequence impedance and the zero sequence impedance, and the protection current setting value is corrected by using the correction coefficient. And obtaining a protection current correction value of the single-phase earth fault, and carrying out single-phase earth fault protection according to the protection current correction value. The obtained protection current correction value is smaller than the protection current setting value, and the protection sensitivity during single-phase earth fault is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of distribution network faults, and particularly to a method for adaptive protection against single-phase grounding faults in a low-voltage distribution network, a device for single-phase grounding fault protection, and a computer storage medium. Background Art

[0002] In a low-voltage distribution network, single-phase grounding faults are the most common type of faults. When a single-phase grounding fault occurs, the fault current forms a fault current loop through the phase wire, neutral wire, and / or protective wire and the grounding point. The impedance of the fault loop is significantly greater than that of a three-phase short-circuit fault loop. Therefore, the single-phase grounding fault current is relatively small, generally less than 50% of the three-phase short-circuit fault current. Moreover, the farther the fault point of the single-phase grounding fault is from the distribution transformer, the smaller the ratio of the single-phase grounding fault current to the three-phase short-circuit fault current at that point.

[0003] However, in the prior art, the existing protection for low-voltage distribution networks does not provide targeted protection for different fault types. To maintain the stable operation of the power grid, the current protection setting value is often set to several times the rated current value to avoid multiple triggerings of circuit protection due to small current fluctuations and affect normal operation. Currently, the low-voltage distribution network mainly obtains power grid data through measurement switches and performs two-stage or three-stage current protection on the low-voltage distribution network. Among them, the I-section protection is instantaneous short-circuit protection. Generally, the current protection setting value of this section of protection is 10 times the rated current, and the protection has no delay; the II-section protection is short-time short-circuit protection. Generally, the current protection setting value of this section of protection is 6 times the rated current, with a delay of 400 milliseconds; the III-section protection is over-current protection. Generally, the current protection setting value of this section of protection is 1.3 times the rated current, and the delay is not more than 2 hours. In practical applications, the fault current of a single-phase grounding fault is small and difficult to reach the current protection setting values of the I-section and II-section. Therefore, the existing current protection may have a long-delay action for single-phase grounding faults, which poses a safety hazard to the low-voltage distribution network. When the single-phase grounding fault current flows through the protective wire, since the wire diameter of the protective wire is smaller than that of the phase wire, the protective wire may overheat, burn out, or even cause a fire accident, seriously threatening the safe and stable operation of the low-voltage distribution network. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for adaptive protection against single-phase grounding faults in a low-voltage distribution network, a device for single-phase grounding fault protection, and a computer storage medium, aiming at the problem that the current protection in the prior art has low sensitivity to single-phase grounding faults and cannot start the single-phase grounding fault protection in time, thus affecting the safety of the line.

[0005] The present invention provides a method for adaptive protection against single-phase grounding faults in a low-voltage distribution network to solve the above technical problems. The steps include:

[0006] 1) When it is determined that a single-phase grounding fault has occurred in the low-voltage distribution network, obtain the instantaneous value sequence of the three-phase current mutation and the instantaneous value sequence of the three-phase voltage mutation after the fault occurs;

[0007] 2) Calculate the positive-sequence impedance and zero-sequence impedance on the system side of the measuring switch according to the instantaneous value sequence of the three-phase current mutation and the instantaneous value sequence of the three-phase voltage mutation. Obtain the correction coefficient of the protection current setting value based on the positive-sequence impedance and zero-sequence impedance, and use the correction coefficient to correct the protection current setting value to obtain the corrected value of the protection current for the single-phase grounding fault. Perform single-phase grounding fault protection according to the corrected value of the protection current; the corrected value of the protection current is less than the protection current setting value.

[0008] Further, the calculation formula of the correction coefficient is:

[0009]

[0010] where K is the correction coefficient, Z (1) is the positive-sequence impedance, and Z (0) is the zero-sequence impedance.

[0011] Further, the condition for judging that a single-phase grounding fault has occurred in the circuit is:

[0012] The absolute value of the instantaneous value of the mutation of any one of the three-phase currents at the measuring switch is greater than the set threshold, and the instantaneous value of the mutation of this phase current is greater than an integer multiple of the instantaneous values of the current mutations of the other two phases; the set threshold is calculated based on the rated phase current of the measuring switch, and the set threshold is less than the rated phase current of the measuring switch.

[0013] Further, the set threshold is 0.05I N -0.2I N where I N is the rated phase current of the measuring switch.

[0014] Further, the value range of the integer multiple is 5 to 10.

[0015] Further, the positive-sequence impedance is the ratio of the positive-sequence voltage mutation to the positive-sequence current mutation, and the zero-sequence impedance is the ratio of the zero-sequence voltage mutation to the zero-sequence current mutation; the positive-sequence voltage mutation, the positive-sequence current mutation, the zero-sequence voltage mutation, and the zero-sequence current mutation are calculated through the three-phase current mutation and the three-phase voltage mutation, and the three-phase current mutation and the three-phase voltage mutation are calculated based on the instantaneous value sequence of the three-phase current mutation and the instantaneous value sequence of the three-phase voltage mutation.

[0016] A single-phase grounding fault protection device, which uses the above-mentioned adaptive protection method for single-phase grounding faults in the low-voltage distribution network to perform single-phase grounding fault protection.

[0017] A computer storage medium stores a computer program to implement the single-phase grounding fault adaptive protection method for a low-voltage distribution network as described above.

[0018] The beneficial effects of the present invention are as follows: As an improved invention, after a single-phase grounding fault occurs in a low-voltage distribution network, the present invention calculates the positive-sequence impedance and zero-sequence impedance according to the instantaneous value sequence of the three-phase current mutation and the instantaneous value sequence of the three-phase voltage mutation in the circuit during the fault; subsequently, the correction coefficient of the protection current is calculated using the positive-sequence impedance and zero-sequence impedance, and the protection current setting value is corrected using the correction coefficient of the protection current to obtain a protection current correction value smaller than the protection current setting value, reducing the threshold of the current protection, enabling the protection system to act quickly when detecting a single-phase grounding fault in the low-voltage distribution network, and improving the safety of the line. Description of the Drawings

[0019] Figure 1 is a schematic flowchart of the single-phase grounding fault adaptive protection method for the low-voltage distribution network of the present invention. Detailed Embodiments

[0020] The following further describes the detailed embodiments of the present invention with reference to the drawings.

[0021] The present invention corrects the protection current setting value using the instantaneous value sequence of the three-phase current mutation and the instantaneous value sequence of the three-phase voltage mutation to obtain a protection current correction value smaller than the protection current setting value, realizing timely protection of the line during a single-phase grounding fault.

[0022] Embodiment of the Single-Phase Grounding Fault Adaptive Protection Method for a Low-Voltage Distribution Network

[0023] As Figure 1 shown, the following takes the intelligent measurement switch of the low-voltage metering box for single-phase grounding fault protection as an example to detail the single-phase grounding fault adaptive protection method for the low-voltage distribution network proposed by the present invention. The specific steps are as follows:

[0024] 1. Single-Phase Grounding Fault Judgment

[0025] The single-phase grounding fault is judged according to the instantaneous value of the sudden change in any one of the three-phase currents at the measurement switch. Specifically, first, the three-phase currents at the measurement switch are collected, and the instantaneous value of the three-phase current sudden change Δi φ (n) is calculated based on the three-phase currents at the measurement switch collected this time and the three-phase currents within the previous power frequency axis. For the convenience of subsequent single-phase grounding fault protection, the three-phase voltages at the measurement switch are also collected, and the instantaneous value of the three-phase voltage sudden change Δu φ (n) is calculated based on the three-phase voltages at the measurement switch collected this time and the three-phase voltages within the previous power frequency axis. The specific calculation formula is:

[0026] Δi φ (n) = {i φ (n) - i φ (n - 2N)} φ = a, b, c phases (1)

[0027] Δu φ (n) = {u φ (n) - u φ (n - 2N)} φ = a, b, c phases (2)

[0028] Where N is the number of sampling points within one power frequency cycle of each signal, and in this implementation, N = 32 is set.

[0029] Compare the absolute value of the instantaneous value of the sudden change in three-phase current |Δi φ (n)| with the set threshold. If the absolute value of the instantaneous value of the sudden change in any phase current is greater than the set threshold, it is determined that a fault may have occurred in the circuit. Where φ is phase a or b or c, and the threshold is 0.05I N -0.2I N , as an example, set the set threshold to 0.1I N , I N is the rated phase current of the measuring switch.

[0030] If the absolute value of the instantaneous value of the sudden change in three-phase current |Δi φ (n)| is less than the set threshold 0.1I N , then no fault has occurred in the circuit, and continue to collect the three-phase current at the measuring switch in real time and make a judgment.

[0031] When it is monitored that a fault may exist in the circuit, it is necessary to further determine whether there is a single-phase grounding fault in the circuit. The specific method is: compare the sudden change in the current of the phase where the absolute value of the instantaneous value of the sudden change in current is greater than the set threshold with the integer multiples of the sudden change in current of the other two phases respectively to determine whether a grounding fault has occurred in this phase.

[0032] If |Δi a (n)| > λ|Δi b (n)| and |Δi a (n)| > λ|Δi c (n)|, then it is determined that a grounding fault has occurred in phase a;

[0033] If |Δi b (n)| > λ|Δi a (n)| and |Δi b (n)| > λ|Δi c (n)|, then it is determined that a grounding fault has occurred in phase b;

[0034] If |Δic (n) | > λ | Δi a (n) | and | Δi c (n) | > λ | Δi b (n), then it is determined that a ground fault has occurred in phase c.

[0035] Among them, the value range of the coefficient λ is 5 to 10, and the coefficient λ can be set according to empirical values.

[0036] 2. Single-phase ground fault protection

[0037] When there is a single-phase ground fault in the low-voltage distribution network, based on the instantaneous value sequence of the three-phase current mutation Δi φ (n) and the instantaneous value sequence of the three-phase voltage mutation Δu φ (n), calculate the three-phase current mutation and the three-phase voltage mutation In this embodiment, the Fourier transform is used to calculate the three-phase current mutation and the three-phase voltage mutation The calculation formula is:

[0038]

[0039] In the formula, in this embodiment, the sequence length is 32, so N = 32; n is the serial number of the sampled value after the fault occurs.

[0040] According to the three-phase current mutation and the three-phase voltage mutation of each phase, calculate the positive-sequence current mutation and the zero-sequence current mutation as well as the positive-sequence voltage mutation and the zero-sequence voltage mutation The calculation formula is:

[0041]

[0042]

[0043] In the formula,

[0044] Subsequently, use the positive-sequence current mutation and the positive-sequence voltage mutation to calculate the positive-sequence impedance Z (1) on the measuring switch system side, and use the zero-sequence current mutation and the zero-sequence voltage mutation to calculate the zero-sequence impedance Z (0) on the measuring switch system side. Among them, the measuring switch system side refers to the power supply side of the low-voltage distribution network.

[0045] Positive sequence impedance Z (1) and zero sequence impedance Z (0) The calculation formula is as follows:

[0046]

[0047] According to the positive sequence impedance Z (1) and zero sequence impedance Z (0) Calculate the correction coefficient K of the setting value of the protection current for single-phase grounding fault:

[0048]

[0049] Among them, the correction coefficient K is the ratio of the short-circuit current of the single-phase grounding fault to the short-circuit current of the three-phase short-circuit fault when a short-circuit fault occurs at the measurement switch. The value range of the correction coefficient K is (0, 1). Generally, the correction coefficient K < 0.5.

[0050] Calculate the corrected setting value I of the protection current for the single-phase grounding fault according to the correction coefficient K of the setting value of the protection current SET :

[0051]

[0052] In the formula, is the original operating current setting value of the current protection, that is, the current protection setting value. Since the zero sequence impedance of the low-voltage distribution line is much greater than the positive sequence impedance, the correction coefficient K is less than 1, and the corrected protection current correction value decreases, and the protection sensitivity is significantly improved.

[0053] Implementation method of single-phase grounding fault protection device

[0054] The single-phase grounding fault protection device proposed by the present invention is used to implement the adaptive protection method for single-phase grounding faults in low-voltage distribution networks; in this embodiment, the single-phase grounding fault protection device can be set in the intelligent measurement switch. The intelligent measurement switch is a low-voltage switch electrical appliance with high-precision current sensors and measurement units, used to realize the normal connection and disconnection of the power distribution and use lines, as well as functions such as overload and short-circuit protection, and can realize local or remote interaction of measurement data. It is applicable to power distribution and use lines with an alternating current of 50 Hz, a working voltage not exceeding 440 V, and a rated current not greater than 800 A, and can be installed in low-voltage metering boxes, etc.

[0055] In this implementation scheme, the intelligent measurement switch collects the three-phase current and three-phase voltage in the circuit in real time, calculates and monitors the line state according to the data in the circuit. When a single-phase grounding fault occurs in the circuit, the intelligent measurement switch calculates the corrected value of the protection current for the single-phase grounding fault according to the data in the circuit during the fault, and transmits the corrected value of the protection current to the circuit protection system to realize the protection of the line.

[0056] The specific implementation process has been described in detail in the method embodiments and will not be elaborated here.

[0057] Computer storage medium

[0058] The present invention provides a computer storage medium, in which a computer program is stored to implement the above-mentioned adaptive protection method for single-phase grounding faults in low-voltage distribution networks.

[0059] The specific implementation process has been described in detail in the method embodiments and will not be elaborated here.

Claims

1. An adaptive protection method for single-phase grounding faults in a low-voltage distribution network, characterized in that the steps Including: 1) When it is determined that a single-phase grounding fault has occurred in the low-voltage distribution network, obtain the instantaneous value sequence of the three-phase current mutation and the instantaneous value sequence of the three-phase voltage mutation after the fault occurs; 2) Calculate the positive-sequence impedance and zero-sequence impedance on the system side of the measurement switch according to the instantaneous value sequence of the three-phase current mutation and the instantaneous value sequence of the three-phase voltage mutation, obtain the correction coefficient of the protection current setting value based on the positive-sequence impedance and zero-sequence impedance, use the correction coefficient to correct the protection current setting value, obtain the corrected value of the protection current for the single-phase grounding fault, and perform single-phase grounding fault protection according to the corrected value of the protection current; The corrected value of the protection current is less than the protection current setting value.

2. The adaptive protection method for single-phase grounding faults in a low-voltage distribution network according to claim 1, wherein, The formula for calculating the correction coefficient is: Among them, K is the correction coefficient, and Z (1) is the positive-sequence impedance, and Z (0) is the zero-sequence impedance.

3. The single-phase grounding fault adaptive protection method for a low-voltage distribution network according to claim 1, wherein The condition for determining a single-phase grounding fault in the low-voltage distribution network is: The absolute value of the instantaneous value of the mutation of any one of the three-phase currents at the measurement switch is greater than the set threshold, and the instantaneous value of the mutation of this phase current is greater than an integer multiple of the instantaneous values of the current mutations of the other two phases; the set threshold is calculated based on the rated phase current of the measurement switch, and the set threshold is less than the rated phase current of the measurement switch.

4. The single-phase grounding fault adaptive protection method for a low-voltage distribution network according to claim 3, wherein The set threshold is 0.05I N -0.2I N , I N is the rated phase current of the measurement switch.

5. The single-phase grounding fault adaptive protection method for a low-voltage distribution network according to claim 3, characterized in that, The value range of the integer multiple is 5 to 10.

6. The single-phase grounding fault adaptive protection method for a low-voltage distribution network according to claim 2, characterized in that, The positive-sequence impedance is the ratio of the positive-sequence voltage mutation to the positive-sequence current mutation, and the zero-sequence impedance is the ratio of the zero-sequence voltage mutation to the zero-sequence current mutation; the positive-sequence voltage mutation, positive-sequence current mutation, zero-sequence voltage mutation, and zero-sequence current mutation are calculated from the three-phase current mutation and the three-phase voltage mutation, and the three-phase current mutation and the three-phase voltage mutation are calculated based on the instantaneous value sequence of the three-phase current mutation and the instantaneous value sequence of the three-phase voltage mutation.

7. A single-phase grounding fault protection device, characterized in that, This device performs single-phase grounding fault protection by using the single-phase grounding fault adaptive protection method for the low-voltage distribution network described in any one of claims 1-6.

8. A computer storage medium, characterized in that, The computer storage medium stores a computer program to implement the single-phase grounding fault adaptive protection method for the low-voltage distribution network described in any one of claims 1-6 above.

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