A method for protecting ungrounded distribution network from electric shock based on current curvature characteristics

Abstract

The present invention discloses a method for anti-electric shock protection of an ungrounded distribution network based on current curvature characteristics, which specifically includes the following steps: S1. Real-time collect the instantaneous values of the three-phase currents of the 10 kV outgoing lines A, B, and C of the substation; S2. Obtain the instantaneous zero-sequence current I0 according to the instantaneous values of the three-phase currents; S3. Calculate the curvatures Q j (j = A, B, C) of the three-phase currents after the grounding fault respectively; S4. Add the curvatures of the three-phase currents of 50 consecutive sampling points respectively; S5. Judge whether R j satisfies: 0.75 ≤ R j ≤ 1.45; The present invention relates to the technical field of power systems. The method for anti-electric shock protection of an ungrounded distribution network based on current curvature characteristics only needs to utilize single-end current information, has a very short data window, and has low requirements for storage space; only the curvatures of the three-phase currents need to be calculated in real time during the calculation, which is very simple and has a short calculation time, and can meet the rapidity. Using the zero-sequence current to judge the grounding fault can eliminate the interference of the increase in line load, and then using the comparison between the curvature characteristic value and the average value ensures the reliability.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to an anti-electric shock protection method for an ungrounded distribution network based on current curvature characteristics. Background Art

[0002] Most of my country's 10kV distribution networks use non-direct neutral point grounding, including neutral point ungrounded and grounded through arc suppression coils. In the neutral point ungrounded mode, a single-phase grounding fault occurs, and the short-circuit current flows into the earth through the fault point. In the event of an electric shock accident, the possibility of single-phase electric shock is the highest (more than 90%). The short-circuit current flows into the earth through the human body, which will cause serious harm to the person who is electrocuted. Studies have shown that the degree of harm of electric shock current to the human body is closely related to the size and duration of the electric shock current. The smaller the electric shock current and the shorter the duration, the less harm to the human body. Therefore, quickly cutting off the electric shock current and reducing the electric shock time are one of the effective protective measures to reduce the degree of harm to the human body.

[0003] Traditional personal electric shock protection devices using fast circuit breakers are as follows Figure 2 As shown, one of the core components of the device is the control system, which analyzes and judges the collected current signals. If a single-phase electric shock accident occurs, the circuit breaker is controlled to close quickly so that the person who is electrocuted is bypassed and the electric shock current is transferred from the circuit breaker branch to the ground, thereby protecting the person who is electrocuted.

[0004] There are many types of faults in ungrounded distribution networks. How to quickly and accurately determine the occurrence of single-phase electric shock accidents and control the closure of circuit breakers is the core problem that the control system needs to solve. At present, the existing distribution network single-phase electric shock fault judgment method is difficult to achieve the expected effect in terms of both speed and accuracy. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides an ungrounded distribution network anti-electric shock protection method based on current curvature characteristics, which solves the problem that the current distribution network single-phase electric shock fault judgment method is difficult to achieve the expected effect in terms of speed and accuracy requirements at the same time.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions: a method for preventing electric shock in an ungrounded distribution network based on current curvature characteristics, specifically comprising the following steps:

[0007] S1, real-time acquisition of the instantaneous current values ​​of the three-phase A, B, and C outgoing lines of the substation 10kV, respectively recorded as I A ,I B ,I C ;

[0008] S2. According to the instantaneous value of the three-phase current, the instantaneous zero-sequence current I0 is obtained, and the formula is as follows:

[0009] I0=I A +I B +I C (1);

[0010] Compare the absolute value of the zero-sequence current with the threshold value. If the zero-sequence current is equal to or greater than the threshold value, it is determined that a ground fault has occurred on the line and the process goes to S3. Otherwise, the process returns to S1.

[0011] S3. Calculate the curvature Q of the three-phase current after the ground fault j (j=A,B,C), the formula is as follows:

[0012]

[0013] S4. Add the curvatures of the three-phase currents at 50 consecutive sampling points to obtain the three-phase current curvature characteristic value T j (j=A,B,C), the formula is as follows:

[0014]

[0015] Calculate the average value T0 of the three-phase current curvature characteristic value, the formula is as follows:

[0016]

[0017] Calculate the ratio R of the three-phase current curvature characteristic value to the average value j (j=A,B,C), the formula is as follows:

[0018]

[0019] S5. Judge R j Whether it meets: 0.75≤R j ≤1.45. If all of them are satisfied, it is judged that a single-phase human electric shock accident has occurred on the line, and the controller issues a circuit breaker closing command. As long as one of the values ​​is not satisfied, it is judged that no human electric shock accident has occurred, and the controller returns to S1.

[0020] Preferably, in S2, the threshold value is 0.5 ampere.

[0021] Preferably, in S3, in formula (2), I j i It represents the current value of the i-th sampling point of the j-phase, and l represents the current sampling interval.

[0022] Beneficial Effects

[0023] The present invention provides an ungrounded distribution network anti-electric shock protection method based on current curvature characteristics. Compared with the prior art, it has the following beneficial effects:

[0024] This method of protecting against electric shock in ungrounded distribution network based on current curvature characteristics is specifically designed for the detection of single-phase personal electric shock accidents in ungrounded distribution network. It has a strong purpose and only needs to use single-end current information (only the 10kV outgoing line three-phase current needs to be collected). The data window is very short and the storage space requirement is low. In the calculation, only the three-phase current curvature needs to be calculated in real time, which is very simple and has a short calculation time, and can meet the requirements of rapidity. Using zero-sequence current to judge grounding faults can eliminate the interference caused by increased line load, and then the curvature characteristic value is compared with the average value to ensure reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of the method for protecting against electric shock in a power distribution network of the present invention;

[0026] Figure 2 This is a structural diagram of a traditional device for preventing electric shock using a fast circuit breaker;

[0027] Figure 3 This is a simulation model diagram of an ungrounded power distribution network of the present invention;

[0028] Figure 4 When a large load is added to the line of the present invention at 0.3s, a zero-sequence current waveform diagram when a non-grounding fault occurs at 0.5s;

[0029] Figure 5 This is a zero-sequence current waveform diagram when a single-phase grounding fault occurs at 0.5s in the present invention;

[0030] Figure 6 It is a three-phase current curvature waveform diagram when a single-phase grounding non-electric shock fault occurs in the 0.5s circuit of the present invention;

[0031] Figure 7 It is a three-phase current curvature waveform diagram when a two-phase grounding non-electric shock fault occurs in the 0.5s circuit of the present invention;

[0032] Figure 8 It is a three-phase current curvature waveform diagram when a three-phase grounding non-electric shock fault occurs in the 0.5s circuit of the present invention;

[0033] Fig. 9 This is a three-phase current curvature waveform diagram when a personal electric shock accident occurs in the 0.5s circuit of the present invention. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] See also Figure 1-9 The present invention provides a technical solution: a method for protecting an ungrounded distribution network from electric shock based on current curvature characteristics, which specifically includes the following steps:

[0036] S1, real-time acquisition of the instantaneous current values ​​of the three-phase A, B, and C outgoing lines of the substation 10kV, respectively recorded as I A ,I B ,I C ;

[0037] S2. According to the instantaneous value of the three-phase current, the instantaneous zero-sequence current I0 is obtained, and the formula is as follows:

[0038] I0=I A +I B +I C (1);

[0039] The absolute value of the zero-sequence current is compared with the threshold value, which is 0.5 amperes. If the zero-sequence current is equal to or greater than the threshold value, it is determined that a ground fault has occurred on the line and the process goes to S3, otherwise it returns to S1.

[0040] S3. Calculate the curvature Q of the three-phase current after the ground fault j (j=A,B,C), the formula is as follows:

[0041]

[0042] In formula (2), I j i represents the current value of the i-th sampling point of phase j, and l represents the current sampling interval;

[0043] S4. Add the curvatures of the three-phase currents at 50 consecutive sampling points to obtain the three-phase current curvature characteristic value T j (j=A,B,C), the formula is as follows:

[0044]

[0045] Calculate the average value T0 of the three-phase current curvature characteristic value, the formula is as follows:

[0046]

[0047] Calculate the ratio R of the three-phase current curvature characteristic value to the average value j (j=A,B,C), the formula is as follows:

[0048]

[0049] S5. Judge R j Whether it meets: 0.75≤R j≤1.45. If all of them are satisfied, it is judged that a single-phase human electric shock accident has occurred on the line, and the controller issues a circuit breaker closing command. As long as one of the values ​​is not satisfied, it is judged that no human electric shock accident has occurred, and the controller returns to S1.

[0050] See also Figure 3 In the simulation model of the neutral point ungrounded distribution network, the protection device against electric shock is installed at the 10kV bus outlet. The original load of line 1 with a length of 5km is (0.6+j0.3)MVA, and the (0.1)MW large load is connected to the line at 0.3s.

[0051] At 0.5s, a fault occurs at point f, 3km away from the 10kV busbar (there are four possible faults: single-phase grounding, two-phase grounding, three-phase grounding, and non-grounding faults), and the fault is removed at 0.6s. When a single-phase human body electric shock fault occurs, the human body electric shock resistance is 800Ω, and the sampling period is 0.1ms, that is, 50 current values ​​are sampled in 5ms. When a non-metallic short circuit fault occurs, the transition resistance of the fault point is assumed to be 1Ω.

[0052] By calculating the zero-sequence current to see whether it reaches the threshold value, it is determined whether it is a ground fault, thereby eliminating the impact of load increase at 0.3s and non-ground fault at 0.5s on the current curvature.

[0053] See also Figure 2 , the neutral point ungrounded distribution network protection device for personal electric shock is installed at the 10kV outgoing line, and the control system is the core component of the device.

[0054] The ratio of the three-phase curvature characteristic value to the average value when non-electric shock faults and electric shock faults occur at 0.5s is shown in Table 1 below:

[0055] Table 1

[0056]

[0057]

[0058] It can be seen from the results in Table 1 that when an electric shock accident occurs, the ratio of the characteristic value of the three-phase current curvature to the average value is in the range of 0.75-1.45. It can be seen that the method proposed in the present invention can realize the identification of electric shock accidents, thereby controlling the closing of the circuit breaker and realizing personal protection against electric shock accidents.

[0059] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0060] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for protecting an ungrounded distribution network from electric shock based on current curvature characteristics, characterized in that: The specific steps include: S1, real-time acquisition of the instantaneous values ​​of the three-phase currents of the 10kV outgoing lines A, B, and C of the substation, recorded as , , ; S2. According to the instantaneous value of the three-phase current, the instantaneous zero-sequence current is obtained , the formula is as follows: （1）； Compare the absolute value of the zero-sequence current with the threshold value. If the zero-sequence current is equal to or greater than the threshold value, it is determined that a ground fault has occurred on the line and the process goes to S3. Otherwise, the process returns to S1. S3. Calculate the curvature of the three-phase current after the ground fault ,in , the formula is as follows: （2）； S4. Add the curvatures of the three-phase currents at 50 consecutive sampling points to obtain the curvature characteristic value of the three-phase current. ,in , the formula is as follows: （3）； Calculate the average value of the three-phase current curvature characteristic value , the formula is as follows: （4）； Calculate the ratio of the characteristic value to the average value of the three-phase current curvature ,in , the formula is as follows: （5）； S5. Judgment Whether it meets: If all the above conditions are met, it is determined that a single-phase electric shock accident has occurred on the line, and the controller issues a circuit breaker closing command. As long as one of the values ​​is not met, it is determined that no electric shock accident has occurred, and the controller returns to S1.

2. The method for protecting against electric shock in an ungrounded distribution network based on current curvature characteristics according to claim 1, characterized in that: In S2, the threshold value is set to 0.5 ampere.

3. The method for protecting against electric shock in an ungrounded distribution network based on current curvature characteristics according to claim 1, characterized in that: In S3, in formula (2), express Xiangdi The current value of the sampling point, Indicates the current sampling interval.

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