A Novel Double-terminal Resonant Measurement Method of Insulation-to-ground Parameters for Resonant Grounding Distribution Network

In order to solve the measurement error problems of insulation-to-ground parameters for resonant grounding distribution network caused by the leakage impedance of voltage transformer and damping resistance of neutral grounding branch, a novel dual-terminal resonant measurement method of insulation-to-ground parameters for resonant grounding distribution network is proposed. This method utilizes dual voltage transformer. A characteristic constant current signal with variable frequency is injected into distribution network through either the internal voltage transformer of the arc-suppression coil or zero-sequence voltage transformer while the returned characteristic-frequency voltage signal is measured by another one. After the equivalent transformation of zero-sequence resonant circuit with damping resistance, the system capacitance to ground and leakage conductance can be accurately calculated by searching the precise resonant frequency of the system. Both the current injection and the voltage measuring unit of the proposed method directly act on the branch of insulation-to-ground parameters, which eliminates the effect of the leakage impedance of voltage transformer and damping resistance and greatly improves the measurement accuracy of insulation-to-ground parameters. The proposed real-time measurement technology of insulation-to-ground parameters is simulated, analyzed and verified in PSCAD/EMTDC simulation environment by field test in a 10 kV substation. The analysis results show that the proposed method has high measurement accuracy. The parameters measuring process has no impact on the normal power supply of distribution network, and is safe, fast and easy to operate. © 2020 Automation of Electric Power Systems Press.