Integrated methods to detect earth fault in DC systems
- JI Tao,SUN Tong-jing,XU Bing-yin,SUN Bo
JOURNAL OF SHANDONG UNIVERSITY (ENGINEERING SCIENCE). 2006, 36(1):
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To solve the difficult problem of fault detection in DC systems, a new method combining leakage current and waveform analysis methods is proposed to identify the branch with earth fault. The leakage current method is used to find fault in single wire. It detects imbalance DC current between positive and negative wires. The waveform analysis method is used to detect fault with insulation reduction in both wires. It injects a low frequency square wave signal to DC system. The insulation reduction of branch is detected by analyzing the relationships of phase and amplitude between fundamental and third harmonic components. The waveform analysis method can also be used in portable fault location instruments. These two methods were integrated to detect the fault perfectly. A distributed insulation monitoring system for substation DC source using LonWorks Fieldbus technology is introduced. Some key techniques, such as selection of the sensor, frequency and amplitude of square signal, reducing injected signal's influence to DC systems and locating fault point exactly are discussed. Experimental tests verify the correctness and feasibility of the proposed method.