Abstract
To solve the problem of the location of the fault point of single-pole-to-ground faults in the transmission lines of MMC-HVDC systems, this paper designs a fault location system based on support vector machine (SVM). The waveform of the traveling wave after the fault occurs is collected as a feature, and the regression mechanism of the SVM is utilized to achieve fault location. Because it is very difficult to locate high-resistance ground faults, this paper first analyzes the waveform characteristics of high-resistance ground faults. Next, three steps are proposed to reduce the influence of grounding resistance on fault location. These steps include using the active pulse waveform as a new feature, classifying the samples according to ground resistance values before training regression models, and a method for adaptively extracting fault distance features is proposed. Finally, a complete location system design is proposed, and its workflow is illustrated. After the simulation test, the proposed location system only needs to obtain a single-ended fault voltage waveform at a fault recording frequency of 20 kHz to achieve an accurate location of single-pole-to-ground faults for different values of grounding resistance.
Highlights
Modular multilevel converter (MMC) technology has gradually replaced two-level or three-level voltage source converters (VSCs) as a new direction for the development of flexible DC transmission technology
When a single-pole ground fault occurs in the MMC-HVDC system, if the fault point can be quickly and accurately found, the fault can be eliminated in time, the line can be repaired, and normal operation of the system can be resumed in a short time
According to the fault characteristics of the waveform, this paper proposes a method for extracting distance features using phase-mode transformation and complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) decomposition
Summary
Modular multilevel converter (MMC) technology has gradually replaced two-level or three-level voltage source converters (VSCs) as a new direction for the development of flexible DC transmission technology. The MMC-HVDC system has many advantages, such as a low switching frequency, low operating loss, high efficiency, and high reliability It has broad application prospects in the fields of new energy generation through grid connections, urban distribution network capacity expansion, and long-distance load power supply [1],[2]. The transmission lines of MMC-HVDC are generally long and pass through various complicated terrains along the way, which tends to result in various line faults. It is usually built in the wilderness and exposed to unpredictable environment, so its failure rate will be higher than other power systems[3]. When a single-pole ground fault occurs in the MMC-HVDC system, if the fault point can be quickly and accurately found, the fault can be eliminated in time, the line can be repaired, and normal operation of the system can be resumed in a short time
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