High-resistance grounding fault protection method based on neutral point damping and zero-sequence current phase change relation

Abstract

The invention discloses a high-resistance grounding fault protection method based on a neutral point damping and zero sequence current phase change relation. Firstly, the lower limit of fault zero-sequence current phase difference variation is calculated according to line parameters; then detecting the magnitude of the zero-sequence current of each feeder line, if a starting criterion is met, starting protection, and recording and processing neutral point zero-sequence current and feeder line zero-sequence current signals; when it is detected that the zero-sequence current is larger than the fault feeder current judgment lower limit, it is judged that the line is a fault feeder, and protection action is performed; otherwise, inputting a neutral point parallel small resistor, recording the phase difference between the zero-sequence current of the feeder line and the zero-sequence current of the neutral point at the moment, and disconnecting the parallel small resistor after calculating the variable quantity of the phase difference before and after inputting the small resistor; if the phase difference variable quantity is located in the fault section, the protection action is tripping; if the phase difference variable quantity is in a sound interval, protection does not act; and if not, the protection is re-calculated, researched and judged if the interval does not belong to the fault or sound interval.

Description

Technical Field

[0001] The invention relates to the technical field of relay protection of power systems, and in particular to a high-resistance grounding fault protection method based on the relationship between neutral point damping and zero-sequence current phase change. Background Art

[0002] The increasing reliability of power supply in distribution networks has put forward higher requirements for rapid protection against distribution network faults. However, the large-scale access of distributed power sources has changed the distribution pattern of power flow and fault characteristics in distribution networks, making traditional current protection no longer applicable to active distribution networks. Unlimited zero-sequence current quick-break protection cannot protect the entire length of the line. Zero-sequence overcurrent protection is used in low-resistance grounding systems. According to the principle that false operation of sound outgoing line protection is not allowed under any circumstances, the protection is adjusted to avoid the maximum capacitance current to ground of the line.

[0003] The setting value of zero-sequence overcurrent protection in 10kV low-resistance grounding distribution network is usually between 40A and 60A, and the maximum tolerance is about 85-135Ω transition resistance; due to the high setting value of zero-sequence overcurrent protection, when a high-resistance grounding fault occurs in the system, the fault current is small and protection failure is prone to occur. Although the high-resistance grounding fault current is weak, it may evolve into a more serious short-circuit fault if it is not removed for a long time, and even cause fire and casualties.

[0004] In addition, the access of high-penetration IIDG also changes the single-phase grounding fault characteristics of the low-resistance grounding system. Therefore, in order to address the problem of zero-sequence overcurrent protection failure due to high-resistance grounding faults, a high-resistance grounding protection scheme for low-resistance grounding systems containing new energy sources needs to be proposed urgently. Summary of the invention

[0005] In view of the above problems, the present invention proposes a high-resistance ground fault protection method based on the relationship between neutral point damping and zero-sequence current phase change. The present invention can be applied to the ground fault protection of distribution networks with a high proportion of distributed power sources connected, and has the advantages of simple principle and good flexibility.

[0006] In order to achieve the above technical effects, the present invention is implemented through the following technical solutions:

[0007] A high-resistance ground fault protection method based on the relationship between neutral point damping and zero-sequence current phase change, characterized in that it includes the following steps:

[0008] S1: Calculate the lower limit of the fault zero-sequence current phase difference change according to the line parameters;

[0009] S2: Detect the magnitude of the zero-sequence current of each feeder. If the start criterion is met, the protection is started, and the neutral point zero-sequence current and feeder zero-sequence current signals are recorded and processed;

[0010] S3: When it is detected that the zero-sequence current is greater than the lower limit of the fault feeder current, the line is determined to be a fault feeder and the protection is activated;

[0011] S4: When it is detected that the zero-sequence current is less than the lower limit of the fault feeder current, a small resistor is connected in parallel with the neutral point, and the phase difference between the feeder zero-sequence current and the neutral point zero-sequence current is recorded. After calculating the change in the phase difference before and after the small resistor is connected, the small resistor is disconnected;

[0012] S5: If the phase difference variation is within the fault range, the protection action is tripping;

[0013] S6: If the phase difference variation is within the healthy range, the protection does not operate;

[0014] S7: If the phase difference variation belongs neither to the fault section nor to the sound section, the protection will recalculate and reassess.

[0015] Optionally, the calculation formula for the lower limit of the fault zero-sequence current phase difference variation is:

[0016]

[0017] In the formula, θ set is the lower limit of the fault zero-sequence current phase difference change, K rel is the set margin coefficient, which is 0.9, L is the total length of all feeders after removing the longest feeder in the distribution network, C0 is the zero-sequence capacitance to ground per unit length of the line, ω is the power frequency angular frequency, R n and R' n It is the resistance value of the neutral point small resistor before and after the parallel small resistor is put into operation.

[0018] Optionally, the start criterion is:

[0019]

[0020] In the formula, is the magnitude of the feeder zero-sequence current detected by the measuring device, I S is the starting current, set to 1.5A.

[0021] Optionally, the fault feeder current determination lower limit I min Set to 30A.

[0022] Optionally, is the neutral point zero sequence current, Δθ is the change in phase difference between the two before and after the small resistor is put into operation, is the feeder zero sequence current The absolute value of the line. The criterion for low-resistance grounding fault is:

[0023]

[0024] If satisfied Greater than I min , the line determines that a fault has occurred and a protection action occurs.

[0025] If satisfied Less than I min , then continue to determine whether a high-resistance grounding fault occurs in the line.

[0026] Optionally, the fault interval is:

[0027] θ set <Δθ<18°

[0028] In the formula, θ set It is the lower limit of the change in the phase difference of the fault zero-sequence current, and Δθ is the change in the phase difference between the feeder zero-sequence current and the neutral point zero-sequence current before and after the small resistor is put into operation.

[0029] Optionally, the sane interval is:

[0030] -1.2°<Δθ<1.2°

[0031] Where Δθ is the change in phase difference between the feeder zero-sequence current and the neutral point zero-sequence current before and after the small resistor is put into operation.

[0032] Optionally, for distribution systems with different importance in power supply areas, the ability to protect against high transition resistance and the economic cost brought by high-precision zero-sequence CT can be traded off, and the starting current I S Make some corrections.

[0033] Optionally, the premise for determining whether a high-resistance grounding fault occurs in the line is that the original small resistance of the neutral point and the subsequently added parallel small resistance are both 20Ω. If the original small resistance of the neutral point is other resistance values, the fault interval needs to be modified accordingly.

[0034] An electronic device includes one or more processors for storing one or more programs. When the one or more programs are executed by the one or more processors, the one or more processors execute the aforementioned high-resistance grounding fault protection method based on the relationship between neutral point damping and zero-sequence current phase change.

[0035] A storage medium stores a computer program, wherein the computer program is configured to execute the aforementioned high-resistance grounding fault protection method based on the relationship between neutral point damping and zero-sequence current phase change when running.

[0036] The high-resistance grounding fault protection method based on the relationship between neutral point damping and zero-sequence current phase change provided by the present invention determines the fault and the sound line according to the difference in the change in the phase difference between the line and the neutral point zero-sequence current before and after the parallel small resistor is put into operation, solves the problem of the traditional zero-sequence overcurrent protection refusing to operate for high-resistance grounding faults, and meets the requirements of relay protection sensitivity and reliability. The advantages of the high-resistance grounding protection scheme adopted by the present invention are as follows: the present invention is not affected by distributed power sources and can be applied to low-resistance grounding distribution networks containing high-proportion inverter-type distributed power sources; the protection criterion is not affected by transition resistance, and the transition resistance tolerance is only related to the accuracy of the zero-sequence current transformer; this scheme only needs to collect the zero-sequence current at the neutral point and each feeder protection installation, and does not need to install a voltage transformer, so the cost is relatively low.

[0037] Compared with the ground fault protection method based on the comparison of zero-sequence current amplitude of the outgoing line, this scheme also has the following advantages. First, there is no need to use a centralized protection device to compare the outgoing lines, which reduces the computational complexity caused by the one-to-one longitudinal comparison when there are many outgoing cables in the distribution network, and has better practicality; second, when there is a feeder in the distribution network that is much longer than other outgoing lines, the zero-sequence current amplitude comparison method may cause the long feeder protection to malfunction when the busbar is grounded, but this scheme does not have this problem. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments in conjunction with the accompanying drawings.

[0039] Figure 1 The present invention is a flow chart of a high-resistance grounding fault protection method based on the relationship between neutral point damping and zero-sequence current phase change.

[0040] Figure 2 This is the simulation topology diagram of the neutral point low resistance grounding distribution network containing IIDG. Specific implementation plan

[0041] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the scope of protection of the present invention.

[0042] Example 1

[0043] The present invention provides a high-resistance ground fault protection method based on the relationship between neutral point damping and zero-sequence current phase change, such as Figure 1 As shown, the following steps are included:

[0044] S1: Calculate the lower limit of the fault zero-sequence current phase difference change according to the line parameters;

[0045] S2: Detect the magnitude of the zero-sequence current of each feeder. If the start criterion is met, the protection is started, and the neutral point zero-sequence current and feeder zero-sequence current signals are recorded and processed;

[0046] S3: When it is detected that the zero-sequence current is greater than the lower limit of the fault feeder current, the line is determined to be a fault feeder and the protection is activated;

[0047] S4: When it is detected that the zero-sequence current is less than the lower limit of the fault feeder current, a small resistor is connected in parallel with the neutral point, and the phase difference between the feeder zero-sequence current and the neutral point zero-sequence current is recorded. After calculating the change in the phase difference before and after the small resistor is connected, the small resistor is disconnected;

[0048] S5: If the phase difference variation is within the fault range, the protection action is tripping;

[0049] S6: If the phase difference variation is within the healthy range, the protection does not operate;

[0050] S7: If the phase difference variation belongs neither to the fault section nor to the sound section, the protection will recalculate and reassess.

[0051] In a specific implementation of the embodiment of the present invention, the calculation formula for the lower limit of the change in the fault zero-sequence current phase difference is:

[0052]

[0053] In the formula, θ set is the lower limit of the fault zero-sequence current phase difference change, K rel is the set margin coefficient, which is 0.9, L is the total length of all feeders after removing the longest feeder in the distribution network, C0 is the zero-sequence capacitance to ground per unit length of the line, ω is the power frequency angular frequency, R n and R' n It is the resistance value of the neutral point small resistor before and after the parallel small resistor is put into operation.

[0054] In a specific implementation of the embodiment of the present invention, the start criterion is:

[0055]

[0056] In the formula, is the magnitude of the feeder zero-sequence current detected by the measuring device, I S is the starting current, set to 1.5A.

[0057] In a specific implementation of the embodiment of the present invention, the fault feeder current determination lower limit I min Set to 30A.

[0058] In a specific implementation of the embodiment of the present invention, is the feeder zero sequence current, is the neutral point zero sequence current, Δθ is the change in phase difference between the two before and after the small resistor is put into operation. The criterion for the occurrence of a low resistance grounding fault in the line is:

[0059]

[0060] If satisfied Greater than I min , the line determines that a fault has occurred and a protection action occurs.

[0061] If satisfied Less than I min , then continue to determine whether a high-resistance grounding fault occurs in the line.

[0062] In a specific implementation of the embodiment of the present invention, the fault interval is:

[0063] θ set <Δθ<18°

[0064] In the formula, θ set It is the lower limit of the change in the phase difference of the fault zero-sequence current, and Δθ is the change in the phase difference between the feeder zero-sequence current and the neutral point zero-sequence current before and after the small resistor is put into operation.

[0065] In a specific implementation of the embodiment of the present invention, the healthy interval is:

[0066] -1.2°<Δθ<1.2°

[0067] Where Δθ is the change in phase difference between the feeder zero-sequence current and the neutral point zero-sequence current before and after the small resistor is put into operation.

[0068] In a specific implementation of an embodiment of the present invention, the premise for determining whether a high-resistance grounding fault occurs in the line is that the original small resistance of the neutral point and the subsequently added parallel small resistance are both 20Ω. For the case where the original neutral point small resistance has other resistance values, the fault interval needs to be modified accordingly.

[0069] An electronic device includes one or more processors for storing one or more programs. When the one or more programs are executed by the one or more processors, the one or more processors execute the aforementioned high-resistance grounding fault protection method based on the relationship between neutral point damping and zero-sequence current phase change.

[0070] A storage medium stores a computer program, wherein the computer program is configured to execute the aforementioned high-resistance grounding fault protection method based on the relationship between neutral point damping and zero-sequence current phase change when running.

[0071] Simulation verification:

[0072] In order to verify the effectiveness and reliability of the present invention, the following Figure 2 The simulation model shown in the figure shows that the distribution network has an original small neutral point resistor and a small parallel resistor R n All are 20Ω, and the line head is equipped with protection 1 to 6. The lines all use cable lines of model YJV22-6 / 10kV-3*70mm2, and the unit zero-sequence capacitance parameter to ground is C0=124.28×10-9F / km. The photovoltaic model of PQ control is packaged as IIDG module T connected to the line, and each outgoing line end is connected to a constant impedance load model of 1MW+0.1MVar per phase.

[0073]

[0074] Table 1

[0075] Table 1 is the simulation data of zero-sequence current of each line when a single-phase grounding fault occurs in line l2. The fault time is set to 0.1s, and the time for the small resistor in parallel with the neutral point is 0.2s. 01 ~3I 06 They are the triple zero-sequence current at protection points 1 to 6, 3I 01B ~3I 06B Indicates the neutral point current I 0R As the corresponding zero-sequence current after the reference, its phase angle is the angle between the line zero-sequence current and the neutral point current, and Δθ is the change of θ before and after the neutral point small resistor value changes. As shown in Table 1, the Δθ of lines l3 and l4~l6 are -0.31° and -0.32° respectively, which are in the interval (-1.2°, 1.2°), and are judged as sound feeders; the Δθ of lines l1 and l2 are 3° and 3.34° respectively, which are in the interval (2.4°, 18°), and are judged as faulty lines. Since the action time limit of protection 1 is Δt more than that of protection 2, protection 2 will act on tripping and selectively cut off the high-resistance grounding fault, verifying the effectiveness of the proposed protection scheme.

[0076] The above description is only a specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Any person familiar with the technology can understand and think of any changes or substitutions within the technical scope disclosed by the present invention, which should be included in the scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A high-resistance ground fault protection method based on the relationship between neutral point damping and zero-sequence current phase change, characterized in that: The following steps are involved: S1: Calculate the lower limit of the fault zero-sequence current phase difference change according to the line parameters; S2: Detect the magnitude of the zero-sequence current of each feeder. If the start criterion is met, the protection is started, and the neutral point zero-sequence current and feeder zero-sequence current signals are recorded and processed; S3: When it is detected that the zero-sequence current is greater than the lower limit of the fault feeder current, the line is determined to be a fault feeder and the protection is activated; S4: When it is detected that the zero-sequence current is less than the lower limit of the fault feeder current, a small resistor is connected in parallel with the neutral point, and the phase difference between the feeder zero-sequence current and the neutral point zero-sequence current is recorded. After calculating the change in the phase difference before and after the small resistor is connected, the small resistor is disconnected; S5: If the phase difference variation is within the fault range, the protection action is tripping; S6: If the phase difference variation is within the healthy range, the protection does not operate; S7: If the phase difference variation belongs neither to the fault section nor to the sound section, the protection will recalculate and reassess.

2. A high-resistance ground fault protection method based on the relationship between neutral point damping and zero-sequence current phase change according to claim 1, characterized in that: In step S1, the calculation formula for the lower limit of the fault zero-sequence current phase difference change is: In the formula, θ set is the lower limit of the fault zero-sequence current phase difference change, K rel is the set margin coefficient, which is 0.9, L is the total length of all feeders after removing the longest feeder in the distribution network, C0 is the zero-sequence capacitance to ground per unit length of the line, ω is the power frequency angular frequency, R n and R' n It is the resistance value of the neutral point small resistor before and after the parallel small resistor is put into operation.

3. A high-resistance grounding fault protection method based on the relationship between neutral point damping and zero-sequence current phase change according to claim 1, characterized in that: In step S2, the start criterion is: In the formula, is the feeder zero-sequence current detected by the measuring device, I S is the starting current, set to 1.5A.

4. A high-resistance grounding fault protection method based on the relationship between neutral point damping and zero-sequence current phase change according to claim 1, characterized in that: In step S3, the fault feeder current lower limit I min Set to 30A.

5. A high-resistance grounding fault protection method based on the relationship between neutral point damping and zero-sequence current phase change according to claim 1, characterized in that: In step S4, is the neutral point zero sequence current, Δθ is the change in phase difference between the two before and after the small resistor is put into operation, is the feeder zero sequence current The absolute value of the line low resistance grounding fault criterion is: If satisfied Greater than I min , the line determines that a fault has occurred on the line and a protection action occurs; If satisfied Less than I min , then continue to determine whether a high-resistance grounding fault occurs in the line.

6. A high-resistance grounding fault protection method based on the relationship between neutral point damping and zero-sequence current phase change according to claim 1, characterized in that: In step S5, the fault interval is: i set <Δθ<18° In the formula, θ set It is the lower limit of the change in the phase difference of the fault zero-sequence current, and Δθ is the change in the phase difference between the feeder zero-sequence current and the neutral point zero-sequence current before and after the small resistor is put into operation.

7. A high-resistance grounding fault protection method based on the relationship between neutral point damping and zero-sequence current phase change according to claim 1, characterized in that: In step S6, the healthy interval is: -1.2°<Δθ<1.2° Where Δθ is the change in phase difference between the feeder zero-sequence current and the neutral point zero-sequence current before and after the small resistor is put into operation.

8. A high-resistance grounding fault protection method based on the relationship between neutral point damping and zero-sequence current phase change according to claim 1, characterized in that: The premise for judging whether a high-resistance grounding fault occurs in the line is that the original small resistance of the neutral point and the small parallel resistance added later are both 20Ω. If the original small resistance of the neutral point is of other resistance values, the fault range needs to be modified accordingly.

9. An electronic device, characterized in that: It includes one or more processors for storing one or more programs. When the one or more programs are executed by the one or more processors, the one or more processors execute the high-resistance grounding fault protection method based on the relationship between neutral point damping and zero-sequence current phase change as described in any one of claims 1 to 8.

10. A storage medium storing a computer program, wherein: in, The computer program is configured to execute, when running, the high-resistance grounding fault protection method based on the relationship between neutral point damping and zero-sequence current phase change as claimed in any one of claims 1 to 8.

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