A Composite Frequency Superposition Protection Method for DC Grounding Electrode Lines

Abstract

The invention discloses a composite frequency superposition protection method for direct current grounding pole lines. Step 1, continuously injecting frequencies into the grounding pole lines through a high-frequency current source are respectively f 1 , f 2 high-frequency signal; step 2, when the grounding electrode line is in normal operation, the obtained frequencies are f 1 , f 2 The measured impedance Z corresponding to the high-frequency signal n1 ,Z n2 ; Step 3, use FFT to calculate the frequency f every time a preset judgment cycle T is passed 1 The current phasor and voltage phasor at the head end of the signal ground electrode line and calculate the measured impedance Step 4. Judgment frequency f 1 The measured impedance Z corresponding to the signal f1 Whether it satisfies the formula (3), select the alarm; step 6, judge the frequency f 2 The measured impedance Z corresponding to the signal f2 Whether it satisfies formula (4), choose alarm or normal operation. The invention can more accurately judge the occurrence of faults in the ground electrode line, improve the accuracy and sensitivity of the protection, and can greatly improve the protection performance; the problem of the dead zone when a single frequency signal is injected is largely eliminated.

Description

technical field [0001] The invention relates to the field of power system protection and control, in particular to a method for protecting a DC grounding electrode line. Background technique [0002] like figure 1 As shown in , it is a schematic diagram of the HVDC system model including the grounding electrode line. For the true bipolar DC system, the grounding electrode is an important part of it. If the grounding electrode line fails, the converter station will be blocked. Since the DC arc does not have a natural zero-crossing point, it is not easy to extinguish, and the DC system needs to be shut down to extinguish the arc. Therefore, timely identification of faults and rapid troubleshooting can effectively improve system stability. Accurate identification of ground electrode line faults is a problem that must be considered in the construction of HVDC projects. At present, the protection methods for ground electrode line faults are mainly based on the injection method...

AI Technical Summary

Problems solved by technology

[0004] Aiming at the problem of poor protection performance of the existing injection method for the grounding electrode line of the high-voltage DC system, the present invention proposes a composite frequency superposition protection method for the DC grounding electrode line, and proposes an improved injection method, using the composite frequency superposition technology , by injecting two high-frequency signals of different frequencies into the ground electrode line at the same time, measuring their impedance at the head end and judging whether the impedance is abnormal, and taking the result of "or" logic relationship to eliminate the dead zone between the two frequency signals

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