CN104808110B - Distribution line fault section location method based on wide area differential drift rate - Google Patents

Abstract

The invention discloses a method for locating fault sections of distribution network lines based on wide-area differential offset. For ground faults, by analyzing the phase current characteristics of the fault phase current before the fault occurs and before the fault occurs to the action of the arc suppression coil , from which the fault feature is extracted, and the waveform wide-area differential offset of the whole process is used for positioning. The invention only needs to measure the fault phase current of the line, has a simple scheme and strong applicability, and can well solve the problems of weak fault current, poor reliability and low sensitivity in the case of a single-phase ground fault in the current low-current grounding system, and will not Introduce disturbances to the system.

Description

Fault section location method for distribution network based on wide-area differential offset

technical field

The invention relates to a method for diagnosing faults of distribution network lines, in particular to a method for locating fault sections of distribution network lines based on wide-area differential offset.

Background technique

According to statistics, during the operation of the power system, power outages caused by distribution network faults account for more than 95% of the total power outages, of which 70% are caused by single-phase ground faults or busbar faults. The neutral point of domestic and foreign distribution networks widely adopts non-effective grounding (small current grounding) to avoid power supply interruption when a single-phase grounding fault occurs. For single-phase-to-ground faults in distribution networks, due to weak fault characteristics, there has been a lack of reliable fault line selection and location methods. With the improvement of people's requirements for distribution network automation level, it is more urgent to fundamentally solve the fault location problem of distribution network.

At present, the fault location methods proposed by scholars at home and abroad are roughly divided into two categories: one is the injection signal method, and the other is the section location based on the fault characteristic quantity. Injection signal methods include "S" injection method, AC-DC integrated injection method and parallel neutral resistance method. These methods increase the interference to the system and cannot detect instantaneous and intermittent ground faults. Section location based on fault characteristic quantity includes zero-mode current comparison method, section zero-sequence admittance method, zero-sequence reactive power direction method, location based on phase current mutation, residual incremental method, traveling wave method, etc. The electrical automation system mainly uses the master station to realize the time synchronization of the FTU, and the time synchronization error is at least several milliseconds. In this case, methods such as amplitude, polarity, and waveform correlation comparison of transient signals are no longer valid.

The current location methods only use the data after the fault occurs, but ignore the use of the information before the fault. At the same time, most positioning methods only consider zero-sequence current information (requires three-phase information), which requires high transformers and complicated information acquisition, and these methods will fail when the data is missing.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art, and propose a method for locating faulty sections of distribution network lines based on wide-area differential offset.

Principle of the present invention:

Let the fault phase be phase A, and the phase voltage at the detection point before the fault is The phase voltage after the fault is From Figure 1, it is easy to know that the two satisfies

1) Detection points 1 and 2 are located on the opposite side of the fault point

After the fault, the upstream detection point current of the fault point is

In the formula, Respectively, A-phase load current, capacitor current and fault current. in

In the formula, is the capacitor current before the fault. Assuming that the load current in one cycle remains unchanged before and after the fault occurs, that is

Combine the above formulas to get

The arc suppression coil uses the inductance current generated by the neutral point voltage offset to offset the system capacitive current when the fault occurs, and the residual current (fault current) at the grounding point can be expressed as

In the formula, C _Σ is the capacitance of the entire network line to ground. During the period when a fault occurs and the arc suppression coil does not operate, |Z _L | is very large, and the compensation effect of the arc suppression coil is negligible. then there is

Similarly, after a fault, the downstream detection point phase current of the fault point

Variation

It can be seen that the current change characteristics of the detection points on different sides of the fault point are inconsistent, and the specific performance is that the size and phase are not equal.

2) Detection points 1 and 2 are located on the same side of the fault point

If the detection points are located upstream of the fault point, according to the analysis in 1), there is

If the detection points are located downstream of the fault point, there is

Since the difference between the capacitances of adjacent detection points is the section capacitance, its value is very small, so the characteristics of the current changes at the two points are basically the same.

Let i _1A (n) and i _2A (n) be the phase current sampling sequences of adjacent detection points. Let the subscript of the data point at the time of the fault occur is zero, in order to ensure that the length of the data is sufficient, thereby increasing the fault characteristic value, the present invention selects the difference of the three-cycle time difference, that is, defines the phase current variation of the two detection points

In the formula, N=0.02f _s , which is a cycle sampling point. Define wide-area differential offset

As a measure of the difference in phase current variation. According to the analysis in the previous section, it is easy to know that the wdiff of the non-faulty section is close to 0, and the wdiff of the faulty section is a positive number greater than 0.

Technical solution of the present invention is as follows:

A method for locating a faulty section of a distribution network line is characterized in that the method includes the following steps:

Step S1, determine the fault phase and fault time t _f : After the system detects the occurrence of a ground fault, select the fault phase according to the phase voltage change law, and determine the fault time t _f according to the sudden change time of the phase voltage or the sudden change time of the power of the arc suppression device;

Step S2, select the fault phase current waveform data of a total of 6N points in the interval [t _f -0.06s, t _f +0.06s] of the detection device, set the subscript of the data point at the time of fault occurrence to zero, and calculate the wide-area differential deviation Shift wdiff, the formula is as follows:

In the formula, Δi _1A (n) and Δi _2A (n) are the phase current changes at the two detection points respectively, and the formulas are as follows:

In the formula, i _1A (n) and i _2A (n) are the phase current sampling sequences of adjacent detection points;

Step S3, judge whether each section is a faulty section according to the magnitude of the wide-area differential offset, that is, when wdiff>wdiff _set , it is judged as a faulty section, otherwise it is a non-faulty section, where wdiff _set is an artificially set action threshold , take 0.1～1;

Step S4, according to the network topology and the distribution position of the detection points on the line, traverse in turn until the faulty section is found, so as to realize the location of the faulty section.

Compared with the prior art, the beneficial effect of the present invention is: for the grounding fault, by analyzing the phase current characteristics of the fault phase current before the fault occurs and before the fault occurs to the action of the arc suppressing coil, the fault characteristic quantity is extracted from it, and the full The waveform Euclidean distance of the process is used for positioning. Therefore, it is only necessary to measure the fault phase current of the line, breaking the previous tradition of only considering zero sequence (requires three-phase information), the data acquisition is simple, and the applicability is strong; from the perspective of signal synchronization, the whole system adopts GPS-synchronized monitoring data, making the difference between different detection points more sensitive. It can well solve the problems of weak fault current, poor reliability and low sensitivity in the case of single-phase ground faults in small current grounding systems, and will not introduce interference to the system at the same time.

Description of drawings

Figure 1 is a schematic diagram of single-phase grounding in a small current grounding system

Figure 2 is the architecture diagram of the distributed fault section location system

Figure 3 is a 10kV system simulation diagram

Figure 4 is the waveform of the current variation along the ground fault

detailed description

The fault waveform required by the present invention comes from a distributed fault section location system, and the system architecture is shown in FIG. 2 . The distribution network fault section location system consists of a monitoring master station, a substation (busbar) measurement device, and node fault location devices distributed throughout the distribution line. The fault location node divides the line into several sections topologically, and each node installs three sets of measuring devices to collect the three-phase current and voltage of the line synchronously in real time.

According to the fault location method invented, different types of faults are set in the 10kV distribution network simulation system. The system structure diagram is shown in Figure 3, ①, ②, ③ are section numbers, and faults are set on section ②. The sampling frequency is 20kHz (N = 400 data points per cycle), the fault occurrence time is 0.7s, the action time of the arc suppression device is set to 0.04s when the ground fault occurs, and the threshold value of the wide-area differential offset is set to 1.

An example of the implementation of fault section judgment:

Step S1, after the system detects the occurrence of a ground fault based on the zero-sequence voltage, it measures that phase A of the three-phase voltage of the busbar drops, and phases B and C rise, which is determined to be a phase A fault; 0.71s;

Step S2, select the fault phase current waveform data of a total of 2400 points in the interval [0, 65, 0.77] of each detection device (set the subscript of the data point at the time of fault occurrence to be zero), according to the definition of wide-area differential offset degree , calculate wdiff, the results are shown in Table 1, where the waveform of the current variation along the fault phase is shown in Figure 4 when the grounding resistance is 500Ω;

Table 1 Simulation results of single-phase ground fault

In step S3, the wide-area differential offset degree of section ② satisfies wdiff>1, and it is judged to be a faulty section; otherwise, sections ① and ③ are non-faulty sections.

Claims (3)

1. A distribution network line fault section location method based on wide-area differential offset degree, it is characterized in that, described method comprises the following steps: Step S1, determine the fault phase and fault time t _f ; Step S2, select the fault phase current waveform data of a total of 6N points in the interval [t _f -0.06s, t _f +0.06s] of the detection device, set the subscript of the data point at the time of fault occurrence to zero, and calculate the wide-area differential deviation Shift wdiff, the formula is as follows: <mrow> <mi>w</mi> <mi>d</mi> <mi>i</mi> <mi>f</mi> <mi>f</mi> <mo>=</mo> <mfrac> <mrow> <munderover> <mo>&amp;Sigma;</mo> <mrow> <mi>n</mi> <mo>=</mo> <mn>0</mn> </mrow> <mrow> <mn>3</mn> <mi>N</mi> <mo>-</mo> <mn>1</mn> </mrow> </munderover> <msup> <mrow> <mo>&amp;lsqb;</mo> <msub> <mi>&amp;Delta;i</mi> <mrow> <mn>1</mn> <mi>A</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>-</mo> <msub> <mi>&amp;Delta;i</mi> <mrow> <mn>2</mn> <mi>A</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>&amp;rsqb;</mo> </mrow> <mn>2</mn> </msup> </mrow> <mrow> <munderover> <mo>&amp;Sigma;</mo> <mrow> <mi>n</mi> <mo>=</mo> <mn>0</mn> </mrow> <mrow> <mn>3</mn> <mi>N</mi> <mo>-</mo> <mn>1</mn> </mrow> </munderover> <msup> <mrow> <mo>&amp;lsqb;</mo> <msub> <mi>&amp;Delta;i</mi> <mrow> <mn>1</mn> <mi>A</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>+</mo> <msub> <mi>&amp;Delta;i</mi> <mrow> <mn>2</mn> <mi>A</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>&amp;rsqb;</mo> </mrow> <mn>2</mn> </msup> </mrow> </mfrac> </mrow> In the formula, Δi _1A (n) and Δi _2A (n) are the phase current changes at the two detection points respectively, and the formulas are as follows: <mrow> <mfenced open='' close=''> <mtable> <mtr> <mtd> <msub> <mi>&amp;Delta;i</mi> <mrow> <mn>1</mn> <mi>A</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>i</mi> <mrow> <mn>1</mn> <mi>A</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>-</mo> <msub> <mi>i</mi> <mrow> <mn>1</mn> <mi>A</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>-</mo> <mn>3</mn> <mi>N</mi> <mo>)</mo> </mrow> </mtd> </mtr> <mtr> <mtd> <msub> <mi>&amp;Delta;i</mi> <mrow> <mn>2</mn> <mi>A</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>i</mi> <mrow> <mn>2</mn> <mi>A</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>-</mo> <msub> <mi>i</mi> <mrow> <mn>2</mn> <mi>A</mi> </mrow> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>-</mo> <mn>3</mn> <mi>N</mi> <mo>)</mo> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>,</mo> <mi>n</mi> <mo>&amp;Element;</mo> <mo>[</mo> <mn>0,3</mn> <mi>N</mi> <mo>-</mo> <mn>1</mn> <mo>]</mo> </mrow> In the formula, i _1A (n) and i _2A (n) are the phase current sampling sequences of adjacent detection points; Step S3, judging whether each section is a faulty section according to the magnitude of the wide-area differential offset, that is, when wdiff>wdiff _set , it is judged as a faulty section, otherwise it is a non-faulty section; Step S4, according to the network topology and the distribution position of the detection points on the line, traverse in sequence until the faulty section is found. 2. The distribution network line fault section location method according to claim 1, wherein said step S1 comprises: After the system detects the occurrence of the ground fault, it selects the fault phase according to the phase voltage change rule, and determines the fault time _tf according to the sudden change time of the phase voltage or the sudden change time of the power of the arc suppression device. 3. The method for locating a faulty section of a distribution network line according to claim 1, characterized in that in the step S3, wdiff _set is an artificially set action threshold, which is 0.1-1.