Overview of methods of insulation parameters determination in live unearthed electrical networks

In the publication there is presented an overview of existing methods of insulation-to-ground parameters determination in live electrical networks with isolated neutral point. These parameters are necessary for calculation of ground fault currents and overvoltages occurring in these systems. There are described few methods of determination of insulation admittance parameters (leakage conductance and capacitance) based on measurement of voltages and computational processing of obtained results. To execute the presented procedures it is necessary to measure network voltages (RMS values or phasors) in certain operational conditions, namely in healthy operation and/or during an intentional grounding of a selected phase through a special element. Chapter 1 of the paper deals with determination of insulation equivalent admittance parameters whereas chapter 2 explains how to get insulation admittance parameters for single phases. Majority of available methods were developed abroad but very few have been applied in practice. In the paper limitations and shortcomings of respective procedures are pointed out. A modified method for general case of these parameters asymmetry in 3-phase networks is proposed.