The Simulation Research in Active Grounding Protection of the Small Current Grounding System Based on Active Protection

摘要

The small current grounding system has many problems: low ability of extinguishing arc grounding and personal sense of electric system, none security and protection ability to indirect grounding over voltage, equipment internal fault grounding. Especially with the rapid development of urban distribution network construction, the cable line users increasing, causing the system of single-phase grounding capacitive current keeps increasing, which caused a single-phase earth fault in power grid and rapid expansion of the accident. Firstly, the small current grounding system is briefly introduced in this paper. Then according to the research on the change of steady state and transient state, line selection methods are designed for different electric parameters. Active protection method for single-phase grounding fault happens in small current grounding system is put forward. This method selects the fault line according to the difference of high frequency component amplitude of zero sequence current before and after the fault and polarity of zero sequence current after the bus initiatively grounds. Finally in order to prove the validity and effectiveness of the proposed method, simulation model is built in PSCAD/EMTDC with the overhead line using the Bergeron model. The output current of different lines is then decomposed by the wavelet transform.