CN111521904A

CN111521904A - Direct-current distribution line double-end fault location method based on current harmonic quantity

Info

Publication number: CN111521904A
Application number: CN201911118304.7A
Authority: CN
Inventors: 范春菊; 徐峰; 孙秋
Original assignee: Shanghai Jiaotong University
Current assignee: Shanghai Jiaotong University
Priority date: 2019-11-15
Filing date: 2019-11-15
Publication date: 2020-08-11

Abstract

A fault location method for double-end faults of a direct current distribution line based on current harmonic quantity is characterized in that fault location is carried out on the basis of fault characteristic analysis of a direct current distribution network containing a power electronic transformer, fault stages are divided firstly, and elimination of attenuation direct current components and extraction of high-frequency components of faults are carried out on fault transient currents recorded from a wave recording device in the first stage of the faults, namely an RLC resonance stage; and then, by utilizing the characteristic that the voltages on the transition resistors from the two ends of the outlet of the converter to the line fault point are the same, the functional relation among the fault distance, the system parameters and the harmonic current is deduced, so that the fault distance measurement is realized. The invention has the advantages that the ranging precision is not influenced by the system operation mode, the fault type and the fault point transition resistance, the fault ranging can be realized more accurately under various fault conditions, and the ranging precision is still higher under the asymmetric system parameters.

Description

Direct-current distribution line double-end fault location method based on current harmonic quantity

Technical Field

The invention relates to a technology in the field of relay protection and fault location of a power system, in particular to a direct-current distribution line double-end fault location method based on current harmonic quantity.

Background

The existing direct current distribution network fault location technology usually utilizes the frequency spectrum of fault transient wave to realize fault location and protection scheme. The research on the direct-current power distribution network containing the power electronic transformer is still in a starting stage, and the research on the fault characteristics of the power electronic transformer, which is an important basis for fault location of the direct-current power distribution network containing the power electronic transformer, is less.

Disclosure of Invention

The invention provides a direct current distribution line double-end fault location method based on current harmonic quantity, which aims at the defects in the prior art, and obtains the functional relation between the fault distance and system parameters and harmonic current by utilizing the characteristic that the voltages on transition resistors from outlets of converters at two ends are respectively calculated to the fault point are the same, thereby realizing fault location, having the location precision not influenced by the system operation mode, the fault type and the fault point transition resistor, being capable of realizing fault location more accurately under various fault conditions and still having higher location precision under asymmetric system parameters.

The invention is realized by the following technical scheme:

the method comprises the steps of carrying out fault location on the basis of fault characteristic analysis of a direct-current power distribution network containing a power electronic transformer, dividing fault stages, and eliminating attenuation direct-current components and extracting high-frequency components of faults of fault transient currents recorded from a wave recording device in the first stage of the faults, namely an RLC resonance stage; and then, by utilizing the characteristic that the voltages on the transition resistors from the two ends of the outlet of the converter to the line fault point are the same, the functional relation among the fault distance, the system parameters and the harmonic current is deduced, so that the fault distance measurement is realized.

The failure stage is as follows: when a fault of a direct-current power distribution network occurs, an RLC resonance stage of a power electronic transformer is automatically locked, a wave recording device records transient current data of fault pole current, positive fault current is recorded as Ip, negative fault current is recorded as In, and the length of a data window is selected to be 4 ms; and comparing and judging the measured two-pole current by calculation to obtain the fault type.

The judgment means that: and KI is Ip/In, when KI is approximately equal to 1, the fault is an interelectrode short-circuit fault, otherwise, the fault is a unipolar grounding fault.

The RLC resonance stage, namely, the transient discharge stage of the RLC resonance stage exists when a single-pole ground fault and an inter-electrode short-circuit fault occur in the dc line, and the transient current of the RLC resonance stage contains a plurality of harmonic quantities.

The fault transient current refers to: the current of the fault electrode during the monopolar earth fault and the current of the fault electrode during the interelectrode short circuit are taken as the current of the anode: 1 terminal fault pole current is marked as I₁And the 2-terminal fault pole current is marked as I₂。

The attenuated dc component is filtered out by, but not limited to, differential filtering.

The fault high-frequency component adopts a full-period Fourier algorithm to decompose the transient current into a 250Hz component and a frequency multiplication component thereof, and the maximum decomposition is 3 frequency multiplication.

The functional relation among the fault distance, the system parameters and the harmonic current refers to that: applying the Kth (K is 1, 2 and 3) harmonic in the fault high-frequency component to an RL line model during the monopolar earth fault or the interelectrode fault, calculating the ranging result under the subharmonic, and finally calculating the average value of the ranging results under all the harmonics as the final ranging result, wherein:

the RL line model includes:

ranging formula in case of single-pole ground fault:

distance measurement formula when interelectrode trouble:

wherein: c_DAB1And C_DAB2Is a DAB direct current outlet bipolar voltage stabilizing capacitor r of a power electronic transformer at two ends of a direct current distribution line₀And l₀Respectively unit resistance and inductance of DC distribution line, F as fault point, R_fSetting current for transition resistance of fault point, S is total length of line, S is distance from fault point to DAB outlet at 1 end

There is some subharmonic component with frequency f and angular frequency ω.

The final ranging result is as follows: and sequentially calculating the ranging result under three current harmonic quantities of 250Hz, 500Hz and 750Hz respectively, and obtaining the final ranging result after arithmetic averaging.

Technical effects

Compared with the prior art, the method only utilizes the transient current magnitude, has simple principle and better robustness, is less influenced by transition resistance, operation parameters and fault types, can eliminate the influence caused by the transition resistance possibly occurring in single-ended distance measurement by adopting double-end fault distance measurement, has a unique and accurate solution because a fault distance function is a linear function, avoids the problem of false roots possibly existing in the traditional distance measurement method, and has higher distance measurement precision.

Drawings

Fig. 1 is a schematic diagram of a medium voltage dc distribution line fault according to the present invention;

FIG. 2 is an equivalent circuit diagram of two types of faults of the DC distribution line;

in the figure: a is an equivalent circuit diagram of a single-pole grounding fault, and b is an equivalent circuit diagram of an inter-pole short-circuit fault;

fig. 3 is a schematic flow chart of a double-ended fault location method based on the harmonic amount of the fault pole current.

Detailed Description

As shown in fig. 1, the 10kV dc distribution line model according to this embodiment is a 10Km full-length line.

The specific detection process of the embodiment is as follows:

step 1) considering that the outlet of the converter has large capacitance, the distributed capacitance of the distribution line is small, and the capacitive reactance under high-frequency components is also small, so that the distributed capacitance of the line is ignored. And (4) building an RL line model by using PSCAD, and simulating the RL line model.

And 2) taking the outlet of the 1-end DAB module as a reference point, and respectively setting fault distances of 0.5Km, 3Km and 5Km to perform fault distance measurement simulation verification under the same transition resistance in monopole ground fault simulation. In consideration of the fact that the maximum transition resistance of the inter-electrode short-circuit fault does not generally exceed 50 Ω in actual operation, the maximum transition resistance is 50 Ω in the inter-electrode short-circuit fault simulation of example 1. The ranging results of the unipolar ground fault and the inter-electrode short-circuit fault are shown in tables 1 and 2.

TABLE 1 monopole ground fault ranging results

TABLE 2 interpolar short-circuit fault ranging results

In order to verify the ranging effectiveness of the invention under different system parameters, the inter-pole fault of the direct current line of the direct current distribution network built in the embodiment under the 5 Ω transition resistance is taken as a research object. Considering three common parameter differentiation influence factors, the following three two-side system asymmetric parameter situations are set to simulate the actual operation condition:

case 1) DAB Outlet capacitances on both sides are different

The total calculated capacitance of the 1-terminal DAB module outlet is set to 2000 muF, the total calculated capacitance of the 2-terminal DAB module outlet is set to 1000 muF, and other parameter settings are kept unchanged, and the ranging results are shown as case 1 in Table 4.

Case 2) DAB Outlet inductances are different on both sides

Setting the single-pole inductance at the outlet of the 1-end DAB module to be 2mH, setting the single-pole inductance at the outlet of the 2-end DAB module to be 1mH, keeping other parameter settings unchanged, and setting the distance measurement result to be 2 in a table 4.

Case 3) both sides DAB outlet capacitance and inductance are different

Setting the total calculated capacitance of the outlet of the 1-end DAB module to be 1000 muF and the outlet single-pole inductance to be 2 mH; the 2-terminal DAB module outlet total calculated capacitance was 2000 muf, the outlet monopole inductance was 1mH, and the ranging results are case 3 in table 4.

And respectively setting the fault distances to be 0.5Km, 3Km, 5Km, 7Km and 9.5Km under the same transition resistance to carry out fault distance measurement simulation verification. The ranging results for the three system asymmetry parameters are shown in table 3.

TABLE 3 ranging results under different system parameters

The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

1. A fault location method for double ends of a direct current distribution line based on current harmonic quantity is characterized in that fault location is carried out on the basis of fault characteristic analysis of a direct current distribution network containing a power electronic transformer, a fault stage is divided firstly, and fault transient current recorded from a wave recording device is eliminated and fault high-frequency components are extracted in the first stage of a fault, namely an RLC resonance stage; and then, by utilizing the characteristic that the voltages on the transition resistors from the two ends of the outlet of the converter to the line fault point are the same, the functional relation among the fault distance, the system parameters and the harmonic current is deduced, so that the fault distance measurement is realized.

2. The method of claim 1, wherein the failure phase is: when a fault of the direct-current power distribution network occurs, the power electronic transformer automatically locks an RLC resonance stage; recording transient current data of fault electrode current by a wave recording device, recording the positive fault current as Ip, recording the negative fault current as In, and selecting the length of a data window as 4 ms; comparing and judging the measured two-pole current through calculation to obtain a fault type;

3. The method of claim 1, wherein the RLC resonance phase is a transient discharge phase of the RLC resonance phase when both a single-pole ground fault and an inter-pole short fault occur in the dc line, and wherein the transient current of the RLC resonance phase contains a plurality of harmonics.

4. The method of claim 1, wherein the fault transient current is selected from the group consisting of: the current of the fault electrode is taken as the current of the anode when the current of the fault electrode is in the short circuit between the electrodes during the single-pole grounding fault: 1 terminal fault pole current is marked as I₁And the 2-terminal fault pole current is marked as I₂。

5. The method according to claim 1, wherein the fault high frequency component is decomposed into a 250Hz component and its frequency multiplication component by full-cycle fourier algorithm, and the maximum is decomposed into 3 frequency multiplication.

6. The method of claim 1, wherein the functional relationship between fault distance and system parameters and harmonic currents is: applying 1 st-3 th harmonic waves in the fault high-frequency component to an RL line model during a single-pole earth fault or an interelectrode fault, calculating a ranging result under the harmonic waves, and finally calculating the average value of the ranging results under all the harmonic waves to obtain a final ranging result, wherein:

the RL line model includes:

ranging formula in case of single-pole ground fault:

distance measurement formula when interelectrode trouble:

There is some subharmonic component with frequency f and angular frequency ω.

7. The method of claim 1, wherein the final ranging result is: and sequentially calculating the ranging result under three current harmonic quantities of 250Hz, 500Hz and 750Hz respectively, and obtaining the final ranging result after arithmetic averaging.