A direct current power distribution line fault location device, method and application

Abstract

The application provides a DC power distribution line fault ranging device and method and application, and relates to the technical field of relay protection of power systems.The application comprises a probe circuit unit;the probe circuit unit comprises two groups of cascaded chopper circuits, wherein the first group of chopper circuits is formed by connecting a first capacitor C1, a first switch tube S1 and a first diode D1 in series;the second group of chopper circuits is formed by connecting a second capacitor C2, a second switch tube S1 and a second diode D2 in series; and the cascaded chopper circuits are grounded at the cascaded midpoint.The application realizes full-automatic measurement, has a smaller volume and a lower cost, requires a lower sampling frequency, is simple and easy to realize, can be integrated in a relay protection device, can be repeatedly detected, is easy to operate, is convenient to use, effectively reduces errors in sampling calculation and improves the positioning accuracy of short-distance DC power distribution line faults.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power system relay protection technology, in particular to a DC distribution line fault distance measuring device, method and application. BACKGROUND

[0002] DC distribution network relay protection technology has been a hot topic in recent years of DC system research. After the fault of DC line, how to quickly and accurately locate the fault point is very important for the rapid repair of DC system fault line and timely recovery of power supply. From the perspective of power system reliability and safety, it is of great significance to study the DC distribution network line fault distance measuring technology.

[0003] At present, the existing fault distance measuring method mainly includes three kinds of traveling wave method, transient method and injection method. The traveling wave method uses the time difference of the traveling wave transmission and reflection in the line to calculate the fault distance of the line. The principle of this method is relatively simple, but it requires a high sampling rate, so it is often used for long distance line fault distance measurement. The transient method calculates the fault distance according to the limited and complex transient signal after the fault. Due to the influence of factors such as mutation and complexity of the fault transient stage, system noise and arc fault, the positioning result may deviate greatly from the actual result, or GPS is needed for data synchronization at both ends. The injection method usually injects a certain specific distance measuring signal on the fault line to locate the fault point, and the distance measuring accuracy is high. The existing technology designs a fault distance measuring probe circuit, which uses the characteristics of RLC or RL series circuit to calculate the fault distance, and achieves certain results, but the volume is large, the cost is high, and the operation process is complicated. SUMMARY

[0004] The purpose of the present application is to provide a DC distribution line fault distance measuring device that meets the requirements, has a low sampling frequency, a simple method, is easy to implement and easy to integrate into a relay protection device, can be repeatedly operated, and can effectively improve the positioning accuracy of short distance DC distribution line faults.

[0005] To achieve the above purpose, the present application realizes the following technical scheme:

[0006] A DC distribution line fault distance measuring device, comprising a probe circuit unit; the probe circuit unit comprises two groups of cascaded chopper circuits, wherein the first group of chopper circuits is composed of a first capacitor C1, a first switch tube S1 and a first diode D1 connected in series, the second group of chopper circuits is composed of a second capacitor C2, a second switch tube S1 and a second diode D2 connected in series, and the cascaded midpoint of the two groups of cascaded chopper circuits is grounded.

[0007] Further, the source electrode of the first switch tube S1 and the cathode of the first diode D1 are connected to the positive electrode of the DC line, and the drain electrode of the second switch tube S2 and the anode of the second diode D2 are connected to the negative electrode of the DC line.

[0008] Further: according to the fault type (positive, negative or bipolar fault), the control switch tube emits square wave voltage signals of specific frequency and duty cycle.

[0009] Further: the value range of the specific frequency f is f>0, and the value range of the duty cycle k is 0

[0010] A DC power distribution line fault distance measurement method, applied to the DC power distribution line fault distance measurement device of any one of the preceding items, comprising: a probe circuit unit, by sampling the voltage and current signals output by the probe circuit unit, sequentially extracting the voltage and current DC components and fundamental wave components, and calculating the fault distance according to the fault distance measurement formula.

[0011] Further: the fault distance measurement method sequentially extracts the voltage and current DC components and fundamental wave components by sampling the voltage and current signals output by the probe circuit unit, and calculates the fault distance according to the fault distance measurement formula.

[0012] Further: the first fault distance measurement formula of the fault distance measurement method is:

[0013]

[0014] In the formula, x1 and x2 are the line fault distances, U1 and I1 are the fundamental wave components of the voltage and current signals output by the probe circuit unit, U0 and I0 are the DC components of the voltage and current signals output by the probe circuit unit, f is the switching frequency of the switch tube S1 or S2, and l0 is the unit kilometer length inductance value of the DC line.

[0015] Further: one fault distance measurement formula of the fault distance measurement method is:

[0016]

[0017] In the formula, x1 and x2 are the line fault distances, U1 and I1 are the fundamental wave components of the voltage and current signals output by the probe circuit unit, and are the phase angles of the fundamental wave components of the voltage and current signals output by the probe, f is the switching frequency of the switch tubes S1 and S2, and l0 is the unit kilometer length inductance value of the DC line.

[0018] Further: the calculation of the fault distance also includes calculating the relative error of the fault distance, wherein the relative error is equal to the ratio of the absolute value of the difference between the fault distance and the actual fault distance to the actual fault distance.

[0019] The application relates to an application of a DC power distribution line fault distance measuring device in relay protection of a DC power distribution system.

[0020] Compared with the prior art, the application has the following beneficial effects:

[0021] First, the probe circuit unit designed in the application is composed of a capacitor, a diode and a switch tube, is installed at one end of a DC line section, has a smaller volume and a lower cost compared with a module circuit containing an inductor element, and realizes full-automatic measurement without the need of repeatedly opening and closing a switch for charging and discharging operation, and is more convenient to use.

[0022] Second, the fault distance measuring method disclosed by the application is based on DC components and fundamental wave components of voltage and current to calculate the fault distance, requires a lower sampling frequency, is simple and easy to realize.

[0023] Third, the application can be easily integrated in a relay protection device, can be repeatedly detected for multiple times, can be directly measured when a fault occurs, does not need to cut off a circuit to isolate a fault area, is simple to operate and convenient to use, and adopts a repeated sampling and calculation method, effectively reduces errors in sampling and calculation, and improves the positioning precision of a short-distance DC power distribution line fault. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is a schematic diagram of the probe circuit unit of the application;

[0025] Figure 2 It is a schematic diagram of a positive pole grounding fault equivalent circuit of the DC line of the application;

[0026] Figure 3 It is a schematic diagram of a negative pole grounding fault equivalent circuit of the DC line of the application;

[0027] Figure 4 It is a schematic diagram of a bipolar fault equivalent circuit of the DC line of the application;

[0028] Figure 5 It is a voltage waveform diagram and an amplitude-frequency response diagram of the output of the probe circuit unit of the application;

[0029] Figure 6 It is a current waveform diagram and an amplitude-frequency response diagram of the output of the probe circuit unit of the application;

[0030] Figure 7 It is a single-pole grounding fault distance measuring result of the application;

[0031] Figure 8 It is a bipolar short-circuit fault distance measuring result of the application;

[0032] In the drawings:

[0033] C1, first capacitor; C2, second capacitor; D1, first diode; D2, second diode; S1, first switch tube; S2, second switch tube. DETAILED DESCRIPTION

[0034] The technical solutions of the present application will be described clearly and completely below in combination with the drawings.

[0035] As Figure 1 shown, the present application provides a DC power distribution line fault location device, comprising a probe circuit unit; the probe circuit unit comprises two groups of cascaded chopper circuits, wherein the first group of chopper circuits is composed of a first capacitor C1, a first switch tube S1 and a first diode D1 connected in series, the second group of chopper circuits is composed of a second capacitor C2, a second switch tube S1 and a second diode D2 connected in series, and the cascaded midpoint of the two groups of cascaded chopper circuits is grounded.

[0036] According to one specific embodiment of the present application, the source electrode of the first switch tube S1 and the cathode of the first diode D1 are connected to the positive pole of the DC line, and the drain electrode of the second switch tube S2 and the anode of the second diode D2 are connected to the negative pole of the DC line.

[0037] According to one specific embodiment of the present application, according to the fault type (positive pole, negative pole or bipolar fault), the switch tube emits a square wave voltage signal of a specific frequency and duty cycle.

[0038] According to one specific embodiment of the present application, the value range of the specific frequency f is f>0, and the value range of the duty cycle k is 0

[0039] A DC power distribution line fault location method, applied to the DC power distribution line fault location device described in any one of the preceding embodiments, comprising: a probe circuit unit, by sampling the voltage and current signals output by the probe circuit unit, sequentially extracting the voltage and current DC components and fundamental wave components, and calculating the fault distance according to the fault location formula.

[0040] According to one specific embodiment of the present application, the first fault location formula of the fault location method is:

[0041]

[0042] In the formula, x1 and x2 are the line fault distances, U1 and I1 are the fundamental wave components of the voltage and current signals at the output end of the probe circuit unit, U0 and I0 are the DC components of the voltage and current signals at the output end of the probe circuit unit, f is the switching frequency of the switch tube S1 or S2, and l0 is the unit kilometer length inductance value of the DC line.

[0043] According to one specific embodiment of the present application, one fault location formula of the fault location method is:

[0044]

[0045] In the formula, x1 and x2 are the fault location distances respectively, U1 and I1 are the fundamental wave components of the voltage and current signals output from the probe circuit unit respectively, And are the phase angles of the fundamental wave components of the voltage signal and the current signal output from the probe respectively, f is the switching frequency of the switching tubes S1 and S2, and l0 is the inductance value per kilometer of the DC line.

[0046] According to one specific embodiment of the present application, the method further comprises the following steps: by adjusting the duty cycle of the switching tube, the current amplitude output from the probe unit circuit is within the appropriate range of the current transformer, and the repeated sampling and calculation are performed until the error between the calculation results is less than the threshold value or the preset maximum number of repetitions is reached.

[0047] According to one specific embodiment of the present application, the threshold value is in the range of 0.1% to 1%, and the maximum number of repetitions is in the range of 3 to 10 times.

[0048] A DC distribution line fault location device is applied in the relay protection of a DC distribution system, and the fault location device is integrated in the relay protection device.

[0049] The working principle of the present application is as follows:

[0050] As shown in Figure 1 , the probe circuit unit is connected to one end of the DC line section. When the DC line is in normal operation, the DC circuit breaker is in a closed state, the DC distribution network line is in normal power transmission, and the bus voltage charges the capacitors C1 and C2 through the switching tube S1, the switching tube S2, the body diode pair, and the capacitors C1 and C2. The capacitors C1 and C2 store energy to provide energy for fault location. When the DC line fails, the DC circuit breaker trips quickly to terminate power transmission. The length of the DC distribution network line is mostly within 3 km, and the distributed capacitance of the line is particularly small and can be ignored.

[0051] When a single-pole ground fault occurs in the DC line, the probe circuit forms a closed loop with the positive DC line and the fault point, and the equivalent circuit is as shown in Figure 2 . When a negative-pole ground fault occurs in the DC line, the probe circuit forms a closed loop with the negative DC line and the fault point, and the equivalent circuit is as shown in Figure 3 . In the figure, x1 is the distance of the probe unit from the fault point, r0 and l0 are the resistance and inductance per unit length of the DC line respectively, R f is the fault resistance, and U CThe capacitor voltage.

[0052] By Figure 2 and Figure 3 It can be seen that the probe circuit and the single pole ground fault line form a generalized BUCK circuit, by controlling the switch tube S1 or S2, thereby generating a square wave voltage signal with amplitude of 0~U C on the DC line; by collecting the voltage and current signals at the output end of the probe circuit, using time-frequency domain transformation tools, the DC component and the fundamental component of the voltage and current can be obtained, then:

[0053]

[0054] In the formula, u(t) and i(t) are the voltage and current at the output end of the probe circuit, U1 and I1 are the fundamental components of the voltage u(t) and current i(t) signals, U0 and I0 are the DC components of the voltage u(t) and current i(t) signals, and FFT[] is the fast Fourier transform.

[0055] The equivalent circuit voltage and current state equation is:

[0056]

[0057] In the formula, x1 is the line fault distance, f is the switching frequency of the switch tube S1 or S2, r0 and l0 are the resistance and inductance per unit length of the DC line, and R f is the fault resistance.

[0058] According to the state equation (2), the expressions of the line fault distance x1 and the fault resistance R f can be obtained as:

[0059]

[0060] When the DC line has a bipolar short circuit fault, the probe circuit and the positive and negative DC lines and the fault point form a closed loop, and the equivalent circuit is shown in Figure 4 .

[0061] At this time, the state equation (2) of the equivalent circuit can be modified as:

[0062]

[0063] Therefore, according to equation (5), the expression of the DC line bipolar fault is:

[0064]

[0065] Further, according to the equivalent circuit, the phasor form of the voltage and current equation can be written as:

[0066]

[0067] The equation (8) can be calculated as:

[0068]

[0069] In the formula, And The phase angle of the fundamental component of the probe output voltage signal, the phase angle of the fundamental component of the current signal.

[0070] Therefore, the line fault distance x1 and the fault resistance R f The second solving expression is:

[0071]

[0072] Similarly, the expression of the bipolar fault is:

[0073]

[0074] The DC distribution network and the simulation model of the method are established in Matlab / Simulink, and the simulation parameters are set as follows:

[0075] The length of the DC line is L=2km;

[0076] The resistance and inductance parameters of the DC line are r0=121mΩ / km and l0=0.97mH / km, respectively;

[0077] The simulation sampling frequency is set to 100kHz;

[0078] The switching frequency of the switch tubes S1 and S2 is 1kHz, and the duty cycle is 50%.

[0079] Assuming that the fault distance of the single-pole grounding of the DC line is 1km and the fault resistance is 1Ω, the voltage waveform and its amplitude-frequency response output by the probe circuit unit are as shown in Figure 5 , and U0=48.6558V and U1=62.448V can be obtained; the voltage waveform and its amplitude-frequency response output by the probe circuit unit are as shown in Figure 6 , and I0=43.4102A and I1=10.0639A can be obtained, and the fault distance D1 is calculated to be 1.0019km according to the first distance measuring formula (3), and the relative error of the distance measuring result is 0.19%, as shown in formula (14):

[0080]

[0081] The voltage and current phase angles are According to the second ranging formula (10), the fault distance D2 is calculated as 1.0013 km, and the relative error of the ranging result is 0.16%, as shown in formula (15):

[0082]

[0083] Similarly, when the bipolar fault occurs, U0=48.807 V, I0=39.3077 A, U1=62.604 V, I1=5.1025 A, according to the first ranging formula (6), the fault distance D2 is calculated as 1.0014 km, and the relative error is 0.14%; at this time, the voltage and current phase angles are respectively According to the second ranging formula (12), the fault distance D2 is calculated as 1.0013 km, and the relative error is 0.14%.

[0084] The above embodiments are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. Any equivalent transformation or modification according to the spirit and essence of the present application should be covered within the protection scope of the present application.

Claims

1. A method for fault location in DC power distribution lines, characterized in that, The DC power distribution line fault location device includes a probe circuit unit; the probe circuit unit includes two cascaded chopper circuits, wherein the first chopper circuit is composed of a first capacitor C1, a first switch S1 and a first diode D1 connected in series, and the second chopper circuit is composed of a second capacitor C2, a second switch S2 and a second diode D2 connected in series, and the cascaded midpoint of the two cascaded chopper circuits is grounded. In the DC power distribution line fault location device, the source of the first switch S1 and the cathode of the first diode D1 are connected to the positive terminal of the DC line, and the drain of the second switch S2 and the anode of the second diode D2 are connected to the negative terminal of the DC line. The DC distribution line fault location method is applied to a DC distribution line fault location device, including: a probe circuit unit, which samples the voltage and current signals output by the probe circuit unit, extracts the DC component and fundamental component of the voltage and current in sequence, and calculates the fault distance according to the fault location formula; One fault location formula of the fault location method is: In the formula, x 1 represents the fault distance of a single-pole line. x 2 represents the fault distance of a bipolar line. U 1 and I 1 represents the fundamental components of the voltage and current signals at the output terminals of the probe circuit unit, respectively. U 0 and I 0 represents the DC component of the voltage and current signal output from the probe circuit unit, respectively. f For switching transistors S 1 or S 2 switching frequency, l 0 represents the inductance value per kilometer of DC line.

2. The method for fault location in DC power distribution lines according to claim 1, characterized in that: One fault location formula of the fault location method is: In the formula, x 1 represents the fault distance of a single-pole line. x 2 represents the fault distance of a bipolar line. U 1 and I 1 represents the fundamental components of the voltage and current signals at the output terminals of the probe circuit unit, respectively. and These are the phase angles of the fundamental components of the voltage and current signals at the probe output terminals, respectively. f For switching transistors S 1 or S 2 switching frequency, l 0 represents the inductance value per kilometer of DC line.

3. The method for fault location of DC distribution lines according to any one of claims 1-2, characterized in that: It also includes the following steps: By adjusting the duty cycle of the switching transistor, the current amplitude output by the probe unit circuit is repeatedly sampled and calculated within the range of the current transformer until the error between the calculation results is less than a preset threshold or the preset maximum number of repetitions is reached.

4. The DC power distribution line fault location method according to claim 3, characterized in that: The threshold value ranges from 0.1% to 1%, and the maximum number of repetitions ranges from 3 to 10 times.

5. The method for fault location in DC power distribution lines according to claim 1, characterized in that: In a DC power distribution line fault location device, the switching transistor is controlled to emit a square wave voltage signal with a specific frequency and duty cycle based on whether the fault is positive, negative, or bipolar.

6. The DC power distribution line fault location method according to claim 5, characterized in that: In the DC power distribution line fault location device, the specific frequency f has a range of values ​​of: f > 0, and the duty cycle k has a range of values ​​of: 0 < k < 1.

7. The application of the DC distribution line fault location method according to any one of claims 5-6 in the relay protection of DC distribution systems, characterized in that: The fault location device is integrated into the relay protection device.

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