阅读说明：本技术 一种针对于直流接地极线路的复合频率叠加保护方法 (Composite frequency superposition protection method for direct current grounding electrode circuit ) 是由 李斌 孙强 何佳伟 李晔 于 2020-04-13 设计创作，主要内容包括：本发明公开了一种针对于直流接地极线路的复合频率叠加保护方法,步骤1、持续地通过高频电流源向接地极线路中注入频率分别为f<Sub>1</Sub>、f<Sub>2</Sub>的高频信号；步骤2、于接地极线路正常运行时,获得频率分别为f<Sub>1</Sub>、f<Sub>2</Sub>的高频信号对应的的测量阻抗Z<Sub>n1</Sub>、Z<Sub>n2</Sub>；步骤3、每经过一个预先设定的判断周期T,利用FFT计算频率f<Sub>1</Sub>信号接地极线路首端电流相量<Image he="69" wi="63" file="DDA0002448531590000011.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>和电压相量<Image he="59" wi="105" file="DDA0002448531590000012.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>并计算测量阻抗<Image he="150" wi="242" file="DDA0002448531590000013.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>步骤4、判断频率f<Sub>1</Sub>信号对应的测量阻抗Z<Sub>f1</Sub>是否满足式(3),选择告警；步骤6、判断频率f<Sub>2</Sub>信号对应的测量阻抗Z<Sub>f2</Sub>是否满足式(4),选择告警或正常运行。本发明能够较为准确判断接地极线路的故障发生,提高保护的准确性、灵敏性,能够大幅改善其保护性能的方法；大幅消除了单一频率信号注入时的死区问题。(The invention discloses a composite frequency superposition protection method for a direct current grounding electrode circuit, which comprises the following steps of 1, continuously injecting frequencies f into the grounding electrode circuit through a high-frequency current source 1 、f 2 The high-frequency signal of (2); step 2, obtaining the frequencies f respectively when the grounding electrode circuit normally operates 1 、f 2 Corresponding to the high-frequency signal of (2) n1 、Z n2 (ii) a Step 3, calculating the frequency f by using FFT (fast Fourier transform) every time a preset judgment period T passes 1 Signal grounding electrode line head end current phasor And voltage phasor And calculating the measured impedance Step 4, judging the frequency f 1 Signal corresponding measured impedance Z f1 If the formula (3) is satisfied, selecting an alarm; step 6, judging the frequency f 2 Signal corresponding measured impedance Z f2 And if the formula (4) is satisfied, selecting alarm or normal operation. The method can accurately judge the fault of the grounding electrode circuit, improve the accuracy and the sensitivity of protection and greatly improve the protection performance; the problem of dead zones when single-frequency signals are injected is greatly eliminated.)

1. A composite frequency superposition protection method for a direct current grounding electrode circuit realizes a fault alarm strategy of the direct current grounding electrode circuit by utilizing the relation between the injection method dead zone position and the injection frequency, and is characterized by comprising the following steps:

step 1, continuously injecting frequencies f into a grounding electrode circuit through a high-frequency current source₁、f₂Of the high-frequency signal ofWherein l represents the length of the grounding electrode line, and v represents the wave speed of the ground mode wave of the injection signal;

step 2, obtaining the frequencies f respectively when the grounding electrode circuit normally operates₁、f₂Corresponding to the high-frequency signal of (2)_n1、Z_n2；Z_n1、Z_n2Calculated using the formula:

in the formula (I), the compound is shown in the specification,frequency f representing normal operation of earth electrode line₁The current and voltage phasors at the head end of the signal,frequency f representing normal operation of earth electrode line₂Signal head end current and voltage phasors;

step 3, acquiring voltage and current signals at the head end of the line every time a preset judgment period T passes, and calculating the frequency f by using FFT (fast Fourier transform)₁Signal grounding electrode line head end current phasorAnd voltage phasorAnd calculating the measured impedance

Step 4, judging the frequency f₁Signal corresponding measured impedance Z_f1Whether formula (3) is satisfied:

|Z_f1-Z_n1|＞kZ_n1(3)

taking factors such as measurement errors of the mutual inductor into consideration, the k value is 0.1;

if the formula (3) is satisfied, it is determined that a fault occurs on the ground electrode line, and an alarm signal indicating that a fault occurs on a first line in the double-circuit type ground electrode line is sent out, step 41; if the formula (3) is not satisfied, the FFT is continuously used to calculate the frequency f₂Signal grounding electrode line head end current phasorAnd voltage phasorAnd calculating the measured impedanceStep 5;

step 6, judging the frequency f₂Signal corresponding measured impedance Z_f2Whether formula (4) is satisfied:

|Z_f2-Z_n2|＞kZ_n2(4)

taking factors such as measurement errors of the mutual inductor into consideration, and taking k as 0.1;

if the formula (4) is satisfied, it is determined that a fault occurs on the grounding electrode line, and an alarm signal indicating that a fault occurs on a line two in the double-circuit grounding electrode line is sent out, step 61; if the formula (4) is not satisfied, it is determined that the grounding electrode line is in normal operation and has no fault in the determination period T, and step 7.

2. The composite frequency superposition protection method for the direct current grounding electrode line is characterized in that the method is suitable for the grounding electrode line with single-loop or double-loop ground faults and under different fault distances and transition resistances.

Technical Field

The invention relates to the field of protection and control of power systems, in particular to a protection method of a direct current grounding electrode circuit.

Background

Fig. 1 is a schematic diagram of a model of a hvdc system including a ground electrode line. For a true bipolar dc system, the earth is an important component, and if the earth line fails, the converter station will be locked. Because the direct current arc does not have a natural zero crossing point and is not easy to extinguish, the direct current system needs to be stopped to extinguish the arc, so that the fault is identified in time and eliminated quickly, and the stability of the system can be effectively improved. The accurate identification of the earth electrode line fault is a problem which must be considered in the high-voltage direct-current engineering construction. At present, a protection method for a ground electrode line fault is mainly based on an injection method, and whether the fault occurs is judged by measuring impedance through a head end. However, in the existing method, because the injection frequency is high, a plurality of protection dead zones exist, the protection performance is poor, and the fault can be refused when a certain position along the line is in fault. In view of the current situation, there is a need to provide an improved method for accurate and effective ground electrode line injection protection.

At present, fewer protection methods are provided for earth electrode line faults, the existing methods have more dead zones and are easy to refuse to operate, good effects are difficult to obtain in practical application, and if the faults are not accurately judged, personal safety is easily damaged, and economic losses are caused.

Disclosure of Invention

The invention provides a composite frequency superposition protection method for a direct current grounding electrode circuit, and provides an improved injection method, aiming at the problem of poor protection performance of the existing injection method for the grounding electrode circuit of a high-voltage direct current system.

The invention relates to a composite frequency superposition protection method for a direct current grounding electrode circuit, which realizes a fault alarm strategy of the direct current grounding electrode circuit by utilizing the relation between the dead zone position of an injection method and injection frequency, and comprises the following steps:

step 1, continuously injecting frequencies f into a grounding electrode circuit through a high-frequency current source₁、f₂Of the high-frequency signal ofWherein l represents the length of the grounding electrode line, and v represents the wave speed of the ground mode wave of the injection signal;

step 2, obtaining the frequencies f respectively when the grounding electrode circuit normally operates₁、f₂Corresponding to the high-frequency signal of (2)_n1、Z_n2；Z_n1、Z_n2Calculated using the formula:

in the formula (I), the compound is shown in the specification,frequency f representing normal operation of earth electrode line₁The current and voltage phasors at the head end of the signal,frequency f representing normal operation of earth electrode line₂Signal head end current and voltage phasors;

step 3, acquiring voltage and current signals at the head end of the line every time a preset judgment period T passes, and calculating the frequency f by using FFT (fast Fourier transform)₁Signal grounding electrode line head end current phaseMeasurement ofAnd voltage phasorAnd calculating the measured impedance

Step 4, judging the frequency f₁Signal corresponding measured impedance Z_f1Whether formula (3) is satisfied:

|Z_f1-Z_n1|＞kZ_n1(3)

taking factors such as measurement errors of the mutual inductor into consideration, the k value is 0.1;

if the formula (3) is satisfied, it is determined that a fault occurs on the ground electrode line, and an alarm signal indicating that a fault occurs on a first line in the double-circuit type ground electrode line is sent out, step 41; if the formula (3) is not satisfied, the FFT is continuously used to calculate the frequency f₂Signal grounding electrode line head end current phasorAnd voltage phasorAnd calculating the measured impedanceStep 5;

step 6, judging the frequency f₂Signal corresponding measured impedance Z_f2Whether formula (4) is satisfied:

|Z_f2-Z_n2|＞kZ_n2(4)

taking factors such as measurement errors of the mutual inductor into consideration, and taking k as 0.1;

if the formula (4) is satisfied, it is determined that a fault occurs on the grounding electrode line, and an alarm signal indicating that a fault occurs on a line two in the double-circuit grounding electrode line is sent out, step 61; if the formula (4) is not satisfied, it is determined that the grounding electrode line is in normal operation and has no fault in the determination period T, and step 7.

Compared with the prior art, the composite frequency superposition protection method for the direct current grounding electrode circuit can achieve the following positive technical effects:

1) when the grounding electrode circuit has a single-circuit or double-circuit grounding fault, and under different fault distances and transition resistances, the fault occurrence of the grounding electrode circuit can be accurately judged, the accuracy and the sensitivity of protection are improved, and the protection performance of the grounding electrode circuit can be greatly improved;

2) the influences of personal safety, economic loss and the like caused by protection refusal are avoided.

3) The problem of dead zone during single frequency signal injection is greatly eliminated.

Drawings

FIG. 1 is a schematic diagram of a model of a high voltage DC system with a ground line;

fig. 2 is a schematic overall flow chart of a composite frequency superposition protection method for a dc ground electrode line according to the present invention;

fig. 3 is a schematic diagram of a double-loop type ground electrode line fault network.

Detailed Description

The technical invention is clearly and completely described in the following with reference to the accompanying drawings and embodiments.

As shown in fig. 2, an overall flow diagram of a composite frequency superposition protection method for a dc ground electrode line according to the present invention is shown, where the flow utilizes a relation between an injection method dead zone position and an injection frequency to implement a fault alarm strategy for the dc ground electrode line, and specifically includes the following steps:

step 1, continuously injecting frequencies f into a grounding electrode circuit through a high-frequency current source₁、f₂Of the high-frequency signal ofWhere l represents the ground trace length and v represents the ground mode wave velocity of the injected signal, and v remains constant at 2.6 × 10 for the signal frequency range taken⁵km/s；

Step 2, obtaining the frequencies f respectively when the grounding electrode circuit normally operates₁、f₂Corresponding to the high-frequency signal of (2)_n1、Z_n2；

Z_n1、Z_n2Calculated using the formula:

in the formula (I), the compound is shown in the specification,frequency f representing normal operation of earth electrode line₁The current and voltage phasors at the head end of the signal,frequency f representing normal operation of earth electrode line₂Signal head end current and voltage phasors;

step 3, acquiring voltage and current signals at the head end of the line every time a preset judgment period T passes, and calculating the frequency f by using FFT (fast Fourier transform)₁Signal grounding electrode line head end current phasorAnd voltage phasorAnd calculating the measured impedance

Step 4, judging the frequency f₁Signal corresponding measured impedance Z_f1Whether formula (3) is satisfied:

|Z_f1-Z_n1|＞kZ_n1(3)

taking factors such as measurement errors of the mutual inductor into consideration, the k value is 0.1;

if the formula (3) is satisfied, it is determined that a fault occurs on the ground electrode line, and an alarm signal indicating that a fault occurs on the double-circuit type ground electrode line is sent out, step 41; if the formula (3) is not satisfied, the FFT is continuously used to calculate the frequency f₂Signal grounding electrode line head end current phasorAnd voltage phasorAnd calculating the measured impedanceStep 5;

step 6, judging the frequency f₂Signal corresponding measured impedance Z_f2Whether formula (4) is satisfied:

|Z_f2-Z_n2|＞kZ_n2(4)

taking factors such as measurement errors of the mutual inductor into consideration, and taking k as 0.1;

if the formula (4) is satisfied, a fault occurs on the grounding electrode line, and a warning signal of the fault occurs on the double-circuit grounding electrode line is sent out, step 61; if the formula (4) is not satisfied, it is determined that the grounding electrode line is in normal operation and has no fault in the determination period T, and step 7.

Fig. 3 is a schematic diagram of a double-loop ground fault network. During operation, the frequencies respectively measured at the head end of the grounding electrode line and injected into the grounding electrode line are respectively f₁、f₂If the measured impedance corresponding to the signal of one of the frequencies has a large change, the grounding electrode line is determined to have a fault.