Single-pole grounding fault line selection method for multi-terminal small-current grounding flexible direct-current system

A single-pole grounding fault and low-current grounding technology, applied in fault location, fault detection by conductor type, short-circuit test, etc., can solve problems such as difficulty in line selection, and achieve the effect of reducing investment, avoiding communication delay, and quickly identifying

Pending Publication Date: 2021-01-29
TAIYUAN UNIV OF TECH
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Problems solved by technology

[0005] In order to solve the problem of difficult line selection for single-pole ground faults in DC distribution networks under the traditional low-curren

Method used

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  • Single-pole grounding fault line selection method for multi-terminal small-current grounding flexible direct-current system
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  • Single-pole grounding fault line selection method for multi-terminal small-current grounding flexible direct-current system

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Embodiment Construction

[0023]The present invention will be further described below in conjunction with specific embodiments.

[0024]This embodiment takes the four-terminal low-current grounded ring-shaped flexible DC distribution network as the research object, and its system structure is asfigure 1 As shown, the AC system is connected to the MMC converter through a connecting transformer. The medium voltage system uses pseudo-bipolar wiring to save costs. The positive and negative poles of the DC lines L1-L4 are equipped with protection devices P12-P41, F1-f3 are single-pole ground fault points respectively. The system adopts the common master-slave control strategy of medium voltage DC power distribution system, suppose MMC1 adopts constant DC voltage and constant AC voltage control, and the other three terminals adopt constant active power and constant AC voltage control.

[0025]figure 2 Middle: Larmk Is the equivalent inductance of the converter bridge arm, Carmk Is the equivalent capacitance of the conve...

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Abstract

The invention discloses a single-pole grounding fault line selection method for a multi-terminal small-current grounding flexible direct-current system, and relates to the field of relay protection ofmulti-terminal flexible direct-current systems. Aiming at the problem of difficulty in single-pole grounding fault line selection of a direct-current power distribution network in a low-current grounding mode, the single-pole grounding fault line selection method comprises the following specific steps of: firstly, reading voltage and current data, iteratively recording the current data of 256 sampling points, then determining a starting criterion and electrode selection judgment, judging whether a fault exists or not according to the starting criterion, if so, judging whether a positive electrode fault or a negative electrode fault exists according to the electrode selection judgment, after selecting the positive/negative electrode fault, carrying out noise reduction processing on currentwaveforms of the positive and negative electrode lines by utilizing wavelet transformation, representing the difference of fault currents of the positive and negative electrode lines by utilizing a ratio of residual absolute values after noise reduction, comparing the difference with a threshold value, determining a faulty line, and sending out a fault signal. According to the single-pole grounding fault line selection method, the problem of difficult threshold setting caused by noise interference and current amplitude change is avoided, and the reliability of a line selection scheme is improved.

Description

Technical field[0001]The invention relates to the field of relay protection of a multi-terminal flexible DC system, in particular to a single-pole grounding fault line selection method for a multi-terminal low-current grounded flexible DC system.Background technique[0002]In recent years, with the development of power electronic devices, DC distribution systems have developed rapidly due to the advantages of large power transmission capacity, easy access to distributed energy, low line loss, reliability and high power supply quality. At present, from the perspectives of power quality, economy, power supply reliability, etc., medium voltage DC power distribution systems widely use modular multilevel converters (modular multilevel converter, MMC), and most of the grounding methods use small current grounding methods. When a single-pole ground fault occurs on the line, the fault current is small and the fault line is difficult to detect and identify, but the non-fault pole transient ove...

Claims

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Application Information

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IPC IPC(8): G01R31/52G01R31/08
CPCG01R31/52G01R31/086Y04S10/52
Inventor 秦文萍夏福良牛原左鹏飞陈晓乾任春光李胜文刘翼肇王磊孟润泉
Owner TAIYUAN UNIV OF TECH
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