CN114089098A - Power distribution network fault type identification method and device - Google Patents

Abstract

The invention relates to a method and a device for identifying fault types in a distribution network. The effective value of the fundamental wave component of three-phase current is used to judge whether it is a grounding fault, and a small current grounding system or a small resistance grounding system is further utilized, and the effective value of the fundamental wave component is further utilized. The number of phases satisfying the criterion is used to judge the fault type, which improves the effectiveness and efficiency of fault type identification. The technical scheme of the invention is suitable for the phase splitting switch of the distribution network, solves the fault type identification before phase selection and closing, and lays a foundation for the realization of permanent fault identification and self-adaptive reclosing strategy.

Description

A kind of distribution network fault type identification method and device

technical field

The invention relates to the technical field of power system relay protection, in particular to a method and device for identifying fault types in a distribution network, and in particular to a method and device for identifying fault types during phase selection and closing in adaptive reclosing for distribution networks.

Background technique

Since single-phase grounding faults can cause personal injury or death, cable trenches and forest fires, low-current grounding systems are gradually requiring single-phase grounding fault tripping, so the trip rate of the distribution network will increase significantly. According to the actual operation data statistics, most of the faults in the overhead lines of the distribution network are transient faults, and the cables also have a certain proportion of transient faults. When the switch can distinguish between permanent and transient faults before reclosing, it can effectively reduce the impact on the system and the switch after reclosing the fault. In addition, when used in conjunction with feeder automation, it can also effectively reduce the fault handling time, thereby improving the power supply. reliability. The existing distribution network switches are all three-phase integrated switches. When tripping, the three phases are disconnected at the same time. It is impossible to use the single-phase switch in the transmission network to improve the coupled electrical characteristics of the faulty phase to identify the nature of the fault. Therefore, related scholars have studied The permanent fault identification method of injecting the detection signal is proposed, but such methods require additional additional equipment.

SUMMARY OF THE INVENTION

Based on the above-mentioned situation of the prior art, the purpose of the present invention is to provide a method and device for identifying fault types in a distribution network, which are suitable for phase-splitting switches in the distribution network, and solve the fault type identification before phase selection and closing. It lays the foundation for the realization of fault identification and adaptive reclosing strategy.

In order to achieve the above object, according to one aspect of the present invention, a method for identifying fault types in a distribution network is provided, including:

Collect the three-phase current time domain signals iA, iB, iC on the distribution network lines;

其中

分别表示A、B、C三相；Extract the fundamental wave component vector of three-phase current by FFT and calculate the effective value

in

Represents three phases A, B, and C, respectively;

与过负荷电流保护定值I_set进行比较，并根据比较结果判断是否确定发生单相接地故障；the valid value

Compare with the overload current protection fixed value I _set , and judge whether it is determined that a single-phase grounding fault occurs according to the comparison result;

If the judgment result is that the single-phase grounding fault is determined to occur, the faulty phase of the single-phase grounding fault is judged; if the judgment result is that the single-phase grounding fault is uncertain, the fault type and location are continued to be judged.

与过负荷电流保护定值I_set进行比较，并根据比较结果判断是否确定发生单相接地故障，包括：Further, the will be valid value

Compare with the overload current protection setting value I _set , and judge whether it is determined that a single-phase ground fault has occurred according to the comparison result, including:

Judgment based on the following judgments:

If the three phases of A, B, and C do not meet the above criteria, the judgment result is that a single-phase grounding fault has occurred;

If at least one of the three phases A, B, and C satisfies the above criteria, the judgment result is that the single-phase grounding fault is uncertain;

Among them, I _set =k _rel I _Lmax , k _rel is the reliability coefficient, and I _Lmax is the maximum load current.

Further, judging the faulty phase of the single-phase grounding fault includes:

The faulty phase is judged according to whether the distribution network is a low-current grounding system or a low-resistance grounding system.

Further, judging the faulty phase according to whether the distribution network is a low-current grounding system or a low-resistance grounding system includes:

If it is a low-current grounding system, the phase with the largest RMS transient current is the faulty phase;

If it is a small resistance grounding system, the phase with the largest power frequency RMS value is the faulty phase.

Further, the continuing to judge the fault type and location, including:

The fault type and location are judged according to the number of phases satisfying the criterion.

Further, judging the fault type and location according to the number of phases satisfying the criterion, including:

If the three phases of A, B, and C all meet the above criteria, it is judged as a three-phase fault.

Further, judging the fault type and location according to the number of phases satisfying the criterion, including:

If two of the phases meet the above criteria, and the zero sequence current is greater than or equal to the unbalanced current, it is judged as a two-phase grounding fault.

Further, judging the fault type and location according to the number of phases satisfying the criterion, including:

If two of the phases meet the above criteria, and the zero sequence current is less than the unbalanced current, it is judged as an interphase fault.

Further, judging the fault type and location according to the number of phases satisfying the criterion, including:

If one of the phases meets the criteria, it is a single-phase ground fault.

According to another aspect of the present invention, a power distribution network fault type identification device is provided, including a signal acquisition module, an effective value extraction module, and a fault judgment module; wherein,

The signal acquisition module is used to acquire the three-phase current time domain signals i _A , i _B , and i _C on the distribution network lines;

其中

分别表示A、B、C三相；The effective value extraction module is used to extract the fundamental wave component vector of the three-phase current by using FFT and calculate the effective value

in

Represents three phases A, B, and C, respectively;

与过负荷电流保护定值I_set进行比较，并根据比较结果判断是否确定发生单相接地故障；若该判断结果为确定发生单相接地故障，则判断单相接地故障的故障相；若该判断结果为不确定发生单相接地故障，则继续对故障类型及位置进行判断。The fault judging module is used to convert the effective value

Compare with the overload current protection fixed value _Iset , and judge whether the single-phase grounding fault has occurred according to the comparison result; The result is that the single-phase grounding fault is uncertain, then continue to judge the fault type and location.

To sum up, the present invention provides a method and device for identifying fault types in a distribution network, which judges whether it is a ground fault through the effective value of the fundamental wave component of the three-phase current, and further utilizes a low-current grounding system or a low-resistance grounding system, And the number of phases whose effective value of the fundamental wave component satisfies the criterion is used to judge the fault type, which improves the effectiveness and efficiency of fault type identification. The technical scheme of the invention is suitable for the phase-separating switch of the distribution network, solves the fault type identification before the phase-selective closing, and lays the foundation for the permanent fault identification and the realization of the self-adaptive reclosing strategy.

Description of drawings

Fig. 1 is a flow chart of the method for identifying fault types in distribution network of the present invention;

Figure 2 is a schematic diagram of the simulation model of the 10kV distribution network.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the specific embodiments and the accompanying drawings. It should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. Also, in the following description, descriptions of well-known structures and techniques are omitted to avoid unnecessarily obscuring the concepts of the present invention.

The technical solutions of the present invention will be described in detail below with reference to the accompanying drawings. According to an embodiment of the present invention, a method for identifying fault types in a distribution network is provided. The flowchart of the method for identifying fault types in a distribution network is shown in FIG. 1 , including the following steps:

S1. Collect the three-phase current time-domain signals i _A , i _B , and i _C on the distribution network line, and set the time-domain waveforms of the three-phase currents of A, B, and C as i _A , i _B , and i _C .

其中

分别表示A、B、C三相。S2. Use FFT to extract the fundamental wave component vector of the three-phase current and calculate the effective value

in

Indicate the three phases of A, B, and C, respectively.

与过负荷电流保护定值I_set进行比较，并根据比较结果判断是否确定发生单相接地故障。可以根据如下判断进行判断：S3. Set the valid value

Compare with the overload current protection fixed value I _set , and judge whether it is determined that a single-phase grounding fault occurs according to the comparison result. It can be judged according to the following judgments:

If none of the three phases A, B, and C meet the above criteria, the judgment result is that a single-phase ground fault has occurred; if at least one of the three phases A, B, and C satisfies the above criteria, the judgment result is that the occurrence of a single-phase ground fault is uncertain. Single-phase ground fault; among them, I _set =k _rel I _Lmax , k _rel is the reliability coefficient, usually 1.1-1.2; I _Lmax is the maximum load current.

S4. If the judgment result is that the single-phase grounding fault is determined to occur, then judge the faulty phase of the single-phase grounding fault; if the judgment result is that the single-phase grounding fault is uncertain, continue to judge the fault type and location. Whether the distribution network is a low-current grounding system or a low-resistance grounding system is used to judge the faulty phase. If it is a small current grounding system, the phase with the largest RMS transient current is the fault phase; if it is a small resistance grounding system, the phase with the largest RMS power frequency is the fault phase. In this step, determine whether the system is a low-current grounding system. If it is a small current grounding system, the phase is selected according to the RMS value of the transient current, and the phase with the largest RMS value is the faulty phase. The RMS value of transient current first filters the current waveform in the time domain, and the filter frequency is 150-600Hz, and then calculates the RMS value of transient current according to the following formula:

Among them, N is the number of sampling points corresponding to the 5ms data window, k=1, 2,...N.

If it is a low-resistance grounding system, the largest phase of the power frequency RMS must be the faulty phase in this case.

The fault type and location are judged according to the number of phases satisfying the criterion, including the following situations:

If all three phases of A, B and C meet the above criteria, it is judged as a three-phase fault; if two of the three phases meet the above criteria, and the zero sequence current is greater than or equal to the unbalanced current, it is judged that the two phases are grounded If two of the phases meet the criteria and the zero-sequence current is less than the unbalanced current, it is judged as an interphase fault; if one of the phases meets the criteria, it is a single-phase ground fault.

According to a second embodiment of the present invention, there is provided a distribution network fault type identification device, including a signal acquisition module, an effective value extraction module, and a fault judgment module.

其中

分别表示A、B、C三相；所述故障判断模块，用于将所述有效值

与过负荷电流保护定值I_set进行比较，并根据比较结果判断是否确定发生单相接地故障；若该判断结果为确定发生单相接地故障，则判断单相接地故障的故障相；若该判断结果为不确定发生单相接地故障，则继续对故障类型及位置进行判断。The signal acquisition module is used to collect the three-phase current time domain signals i _A , i _B , i _C on the distribution network line; the effective value extraction module is used to extract the fundamental wave component vector of the three-phase current by using FFT and calculate the effective value

in

respectively represent three phases of A, B and C; the fault judging module is used to convert the effective value

Compare with the overload current protection fixed value _Iset , and judge whether the single-phase grounding fault has occurred according to the comparison result; The result is that the single-phase grounding fault is uncertain, then continue to judge the fault type and location.

The specific steps for each module in the apparatus provided in the second embodiment to implement corresponding functions are the same as those in the method provided in the first embodiment of the present invention, and are not repeated here.

In order to verify the correctness of the technical solutions provided by the embodiments of the present invention, a distribution network as shown in Figure 2 is established based on PSCAD for simulation verification. Figure 2 shows a schematic diagram of a 10kV distribution network simulation model. The neutral point can be changed by the switch position, the detailed parameters of the model are as follows.

The 35kV substation has two incoming lines, and the 10kV system distributed through two main transformers is in the form of a single bus; the bus has four main feeders, and the number of each section on the outgoing line is shown in Figure 2. Wherein, sections 1, 3, 5, and 10 are cables, sections 2, 9, 11, 12, and 13 are overhead insulated wires, and sections 4, 6, 7, 8, and 14 are overhead bare wires. The arc suppression coil is installed on the neutral point used. When switch K is open, the system is a neutral point ungrounded system; when switch K is closed at 1, it is an arc suppression coil grounding system, and the overcompensation degree is taken as 10%. When switch K is closed at 2, it is a resistance-resistance grounding system. Take it as 10Ω. The impedance of each equivalent power supply of 35kV is (0.3+j3.2)Ω.

The lengths of each section are: L1=5.1km, L2=4km, L3=3.8km, L4=7.5km, L5=4km, L6=10km, L7=0.1km, L8=3km, L9=4km, L10=3.2 km, L11=10km, L12=5km, L13=3km, L14=7.5km.

Cable parameters are: r1=0.157Ω/km, x1=0.076Ω/km, b1=132×10-6S/km; r0=0.307Ω/km, x0=0.304Ω/km, b0=110×10-6S/ km.

The parameters of the overhead insulated wire are: r1=0.27Ω/km, x1=0.352Ω/km, b1=3.178×10-6S/km; r0=0.42Ω/km, x0=3.618Ω/km, b0=0.676×10- 6S/km.

The parameters of the bare wires in sections 7 and 8 are: r1=0.91Ω/km, x1=0.403Ω/km, b1=2.729×10-6S/km; r0=1.06Ω/km, x0=3.618Ω/km, b0= 0.672×10-6S/km.

The bare conductor parameters of other sections are: r1=0.63Ω/km, x1=0.392Ω/km; r0=0.78Ω/km, x0=3.593Ω/km, b0=0.683×10-6S/km.

The parameters of the two main transformers are: SN=2MVA, Pk=20.586kW, Uk%=6.37%, P0=2.88kW, I0%=0.61%; SN=2MVA, Pk=20.591kW, Uk%=6.35%, P0 =2.83kW, I0%=0.62%.

Let each distribution transformer be the same as the connected section number, then their capacities are: S5N=50kVA, S7N=500kVA, S8N=200kVA, S9N=1MVA, S10N=100kVA, S12N=1MVA, S13N=400kVA, S14N= 630kVA. For the sake of simplicity, the load carried by each distribution transformer is unified to 80% of the transformer capacity, and the power factor is adjustable.

When the neutral point is not grounded, set BG fault, AC fault, ACG fault and ABCG fault at the end of section 11 respectively. The results of fault type discrimination are shown in Table 1. Change the neutral point grounding method to arc suppression coil grounding and small resistance grounding, and repeat the simulation of various faults in Table 1. The same results can be obtained. Therefore, it can be proved that the method I invented can reliably identify the fault type and achieve accurate fault phase selection. .

Table 1 Discrimination results of fault types

To sum up, the present invention relates to a method and device for identifying fault types in a distribution network, which judges whether it is a ground fault through the effective value of the fundamental wave component of the three-phase current, and further utilizes a low-current grounding system or a small-resistance grounding system, and The effective value of the fundamental wave component satisfies the number of phases of the criterion to judge the fault type, which improves the effectiveness and efficiency of fault type identification. The technical scheme of the invention is suitable for the phase-separating switch of the distribution network, solves the fault type identification before the phase-selective closing, and lays the foundation for the permanent fault identification and the realization of the self-adaptive reclosing strategy.

It should be understood that the above-mentioned specific embodiments of the present invention are only used to illustrate or explain the principle of the present invention, but not to limit the present invention. Therefore, any modifications, equivalent replacements, improvements, etc. made without departing from the spirit and scope of the present invention should be included within the protection scope of the present invention. Furthermore, the appended claims of this invention are intended to cover all changes and modifications that fall within the scope and boundaries of the appended claims, or the equivalents of such scope and boundaries.

Claims (10)

1. A method for identifying fault types of a power distribution network is characterized by comprising the following steps:

collecting three-phase current time domain signal i on power distribution network line_A、i_B、i_C；

Extracting fundamental component vectors of three-phase current by FFT and calculating effective value

Wherein

A. B, C represent A, B, C three phases respectively;

the effective value is added

And overload current protection constant value I_setComparing, and judging whether the single-phase earth fault is determined to occur according to the comparison result;

if the judgment result is that the single-phase earth fault is determined to occur, judging the fault phase of the single-phase earth fault; if the judging result is that the single-phase earth fault is not determined to occur, the fault type and the fault position are continuously judged.

2. The method of claim 1, wherein the validating value is based on a predetermined threshold value

And overload current protection constant value I_setComparing, and judging whether the single-phase earth fault is determined to occur according to the comparison result, comprising:

the judgment is made according to the following judgment:

if the A, B, C three phases do not meet the criterion, the judgment result is that the single-phase earth fault is determined to occur;

if at least one of the A, B, C three phases meets the criterion, the judgment result is that the single-phase earth fault is not determined to occur;

wherein, I_set＝k_relI_Lmax，k_relTo a reliability factor, I_LmaxIs the maximum load current.

3. The method of claim 2, wherein determining the faulted phase of the single-phase ground fault comprises:

and judging the fault phase according to whether the power distribution network is a low-current grounding system or a low-resistance grounding system.

4. The method of claim 3, wherein determining the failed phase based on whether the power distribution network is a low current grounding system or a low resistance grounding system comprises:

if the current is a low-current grounding system, the phase with the maximum effective value of the transient current is a fault phase;

and if the power frequency is the minimum resistance grounding system, the phase with the maximum power frequency effective value is the fault phase.

5. The method of claim 2, wherein said continuing to determine the type and location of the fault comprises:

and judging the fault type and the fault position according to the number of the phases meeting the criterion.

6. The method of claim 5, wherein said determining the fault type and location based on the number of phases that satisfy the criteria comprises:

and if the A, B, C three phases all meet the criterion, judging that the three phases are in fault.

7. The method of claim 5, wherein said determining the fault type and location based on the number of phases that satisfy the criteria comprises:

and if two phases of the two phases meet the criterion and the zero sequence current is greater than or equal to the unbalanced current, judging that the two phases are in ground fault.

8. The method of claim 5, wherein said determining the fault type and location based on the number of phases that satisfy the criteria comprises:

and if the two phases meet the criterion and the zero-sequence current is less than the unbalanced current, judging that the phase-to-phase fault occurs.

9. The method of claim 5, wherein said determining the fault type and location based on the number of phases that satisfy the criteria comprises:

and if one phase meets the criterion, the fault is a single-phase earth fault.

10. A distribution network fault type recognition device is characterized by comprising a signal acquisition module, an effective value extraction module and a fault judgment module; wherein,

the signal acquisition module is used for acquiring a three-phase current time domain signal i on a power distribution network line_A、i_B、i_C；

The effective value extraction module is used for extracting fundamental component vectors of three-phase current by using FFT and calculating effective values

Wherein

A. B, C represent A, B, C three phases respectively;

the fault judgment module is used for judging the effective value

And overload current protection constant value I_setComparing, and judging whether the single-phase earth fault is determined to occur according to the comparison result; if the judgment result is that the single-phase earth fault is determined to occur, judging the fault phase of the single-phase earth fault; if the judging result is that the single-phase earth fault is not determined to occur, the fault type and the fault position are continuously judged.

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