CN111541219B - Composite frequency superposition protection method for direct current grounding electrode circuit - Google Patents

Composite frequency superposition protection method for direct current grounding electrode circuit Download PDF

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CN111541219B
CN111541219B CN202010286000.8A CN202010286000A CN111541219B CN 111541219 B CN111541219 B CN 111541219B CN 202010286000 A CN202010286000 A CN 202010286000A CN 111541219 B CN111541219 B CN 111541219B
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grounding electrode
frequency
signal
electrode line
formula
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CN111541219A (en
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李斌
孙强
何佳伟
李晔
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Tianjin University
Hefei University of Technology
State Grid Anhui Electric Power Co Ltd
State Grid Electric Power Research Institute
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Tianjin University
Hefei University of Technology
State Grid Anhui Electric Power Co Ltd
State Grid Electric Power Research Institute
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/40—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to ratio of voltage and current
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems

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Abstract

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 source1、f2The high-frequency signal of (2); step 2, obtaining the frequencies f respectively when the grounding electrode circuit normally operates1、f2Corresponding to the high-frequency signal of (2)n1、Zn2(ii) a Step 3, calculating the frequency f by using FFT (fast Fourier transform) every time a preset judgment period T passes1Signal grounding electrode line head end current phasor
Figure DDA0002448531590000011
And voltage phasor
Figure DDA0002448531590000012
And calculating the measured impedance
Figure DDA0002448531590000013
Step 4, judging the frequency f1Signal corresponding measured impedance Zf1If the formula (3) is satisfied, selecting an alarm; step 6, judging the frequency f2Signal corresponding measured impedance Zf2And 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.

Description

Composite frequency superposition protection method for direct current grounding electrode circuit
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 of
Figure BDA0002448531570000021
Wherein 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、Zn2；Zn1、Zn2Calculated using the formula:
Figure BDA0002448531570000022
Figure BDA0002448531570000023
in the formula (I), the compound is shown in the specification,
Figure BDA0002448531570000024
frequency f representing normal operation of earth electrode line1The current and voltage phasors at the head end of the signal,
Figure BDA0002448531570000025
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 phasor
Figure BDA0002448531570000026
And voltage phasor
Figure BDA0002448531570000027
And calculating the measured impedance
Figure BDA0002448531570000028
Step 4, judging the frequency f1Signal corresponding measured impedance Zf1Whether formula (3) is satisfied:
|Zf1-Zn1|＞kZn1 (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 phasor
Figure BDA0002448531570000031
And voltage phasor
Figure BDA0002448531570000032
And calculating the measured impedance
Figure BDA0002448531570000033
Step 5;
step 6, judging the frequency f2Signal corresponding measured impedance Zf2Whether formula (4) is satisfied:
|Zf2-Zn2|＞kZn2 (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 of
Figure BDA0002448531570000041
Where l represents the ground electrode line length, v represents the ground mode wave velocity of the injected signal, and v remains constant at 2.6 × 10 for the frequency range of the signal taken5km/s；
Step 2,When the grounding electrode circuit normally operates, the obtained frequencies are respectively f1、f2Corresponding to the high-frequency signal of (2)n1、Zn2；
Zn1、Zn2Calculated using the formula:
Figure BDA0002448531570000042
Figure BDA0002448531570000043
in the formula (I), the compound is shown in the specification,
Figure BDA0002448531570000044
frequency f representing normal operation of earth electrode line1The current and voltage phasors at the head end of the signal,
Figure BDA0002448531570000045
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 phasor
Figure BDA0002448531570000046
And voltage phasor
Figure BDA0002448531570000047
And calculating the measured impedance
Figure BDA0002448531570000048
Step 4, judging the frequency f1Signal corresponding measured impedance Zf1Whether formula (3) is satisfied:
|Zf1-Zn1|＞kZn1 (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 phasor
Figure BDA0002448531570000051
And voltage phasor
Figure BDA0002448531570000052
And calculating the measured impedance
Figure BDA0002448531570000053
Step 5;
step 6, judging the frequency f2Signal corresponding measured impedance Zf2Whether formula (4) is satisfied:
|Zf2-Zn2|＞kZn2 (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.

Claims (2)

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 of
Figure FDA0003353669550000011
Wherein 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、Zn2；Zn1、Zn2Calculated using the formula:
Figure FDA0003353669550000012
Figure FDA0003353669550000013
in the formula (I), the compound is shown in the specification,
Figure FDA0003353669550000014
frequency f representing normal operation of earth electrode line1The current and voltage phasors at the head end of the signal,
Figure FDA0003353669550000015
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 phasor
Figure FDA0003353669550000016
And voltage phasor
Figure FDA0003353669550000017
And calculating the measured impedance
Figure FDA0003353669550000018
Step 4, judging the frequency f1Signal corresponding measured impedance Zf1Whether formula (3) is satisfied:
|Zf1-Zn1|＞kZn1 (3)
considering the measurement error factor of the mutual inductor, the value of k is 0.1;
if the formula (3) is met, determining that a fault occurs on the grounding electrode line, and sending a warning signal that a line I in the double-circuit type grounding electrode line has a fault;
and 5, if the formula (3) is not satisfied, continuing to calculate the frequency f by using the FFT2Signal grounding electrode line head end current phasor
Figure FDA0003353669550000021
And voltage phasor
Figure FDA0003353669550000022
And calculating the measured impedance
Figure FDA0003353669550000023
Step 6, judging the frequency f2Signal corresponding measured impedance Zf2Whether formula (4) is satisfied:
|Zf2-Zn2|＞kZn2 (4)
taking the measurement error factor of the mutual inductor into consideration, taking k as 0.1;
if the formula (4) is satisfied, determining that a fault occurs on the grounding electrode line, and sending out a warning signal that a fault occurs on a line two in the double-circuit grounding electrode line;
and 7, if the formula (4) is not satisfied, determining that the grounding electrode circuit is in normal operation and has no fault in the judgment period T.
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.
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