Research Of Testing Methods Of Capacitive Current For Medium Voltage Grid

Small current neutral grounding systems, namely, isolated neutral system, resonantearthed system as well neutral grounding system via resistance, are widely used to improvethe operational reliability of the medium voltage power network. When single-phase earthfault occurs, it’s prone to produce capacitive current on ground point and arc light on weaksection of insulation line. The intermittent arc light can develop into overvoltage which resultsin insulation breakdown and causes phase fault even three phase short circuit, so the size ofcapacitive current needs to be measured precisely and the capacitance of extinction coil oughtto be allocated rationally to cut down damages of capacitive current.In this paper, firstly, a simulation model of power supply system with6kV is built bySIMULINK, parameter values of each module, including three-phase supply, distributedcircuit, potential transformer and so on are offered to operate engineering estimating of thecapacitive current for the whole power system, on the basis of which error analyses forcommon used measuring methods, such as single phase metal grounding method, additionalcapacitance method, as well signal injection method, are conducted adding to the comparisonand contrast of those methods from the aspects of measuring principle, limitation, safety, etc.The innovation of this paper lines in the increase of measurement accuracy for variablefrequency signal injection method which is tested and verified by simulation experiment.Secondly, connections and measurement steps of capacitive current on spot test are statedwith accuracy and clearness. Thirdly, the influence of problems caused by nonlinear loads,like system asymmetry, waveform distortion, signal transmission attenuation, etc, on constantfrequency signal injection method are analyzed and studied in the paper.Studies reveal that the rational selection for the injection of signal intensity andfrequency range can reduce measuring errors. Findings of this paper have a promising reference value for spot tests as well development for the measuring and test instruments.