Virtual grounding identification technology in neutral point non-effectively grouned system
Gang Lü · Power System Protection and Control · 2010
Zero-sequence voltage will rise when single-phase-to-earth occurs in neutral point non-grounded system.So it is with the resonance in the above said system.Traditional line selection equipment will start only when zero-sequence voltage and current exceed set value.As they could not tell the difference between single-phase-to-earth and resonance,malfunction may be caused.After study of theory,characteristics of PT ferroresonance and line broken resonance of arc-suppression coil are emphatically analyzed,three-phase voltage and zero-sequence voltage in case of single-phase grounding and resonance are compared with each other in detail.On this basis,the technology is put forward based on comprehensive comparison of zero-sequence voltage and three-phase voltage.The technology is verified by field data,which reveals that the technology could effectively increase the reliability of line selection equipment and therefore could satisfy the practical requirements.