Study On I/O Characteristics Of CT And CC Used In Tanδ Measurement

Off-line testing and on-line monitoring tanδ for electrical equipmentinsulation has important practical significance for insulation condition diagnosisand condition based maintenance. Accurate measurement of current throughinsulation is the premise of accurate measurement of insulation tanδ. Highaccuracy is requested for Current Transformer(CT) and Current Comparator(CC),especially when the CT and CC is used in the on site application, due to manyobjective factors caused the change of I/O characteristics of CT and CC. Findingout the changing rule of the I/O characteristics of CT and CC may provide thenecessary theoretical basis for the development of equipment of the off-line andonline monitoring tanδ.A kind of off-line automatic detection system and a hot-line monitoringtechnology of tanδ for EHV XLPE cable based on the balance technology areintroduced in this dissertation. In these systems introduced, the CC is the coredevice to measurement of the current of insulation. When the measuring systemis in unbalance status, the detection windings of CC is used to measure theunbalance current, and the CC works in CT status. The measurement accuracy ofunbalanced current directly affects test speed. The experiments are design to textconversion factor K and phase error of detection coil of the CC under thetemperature between-30℃and55℃, at the frequency from30Hz to1000Hz andcurrent amplitude between0.01mA and100mA. The experimental data on theeffects of temperature, frequency and current amplitude on I/O characteristics areprocessed by the variance analysis.The results of variance analysis show that the impact of the three factors onI/O characteristics of CC detection coil significantly from large to small isfrequency, temperature, and current amplitude. The two interaction effect ofconversion factor K which is temperature with frequency and current amplitude with temperature is significantly. The interaction effects of temperature withfrequency and current amplitude with frequency on the phase error aresignificantly.The dissertation summarized the impact of three factors to I/Ocharacteristics of CT and CC. The results provide the basis for nonlinearregression analysis of the data and error correction, and provide reference fordesigns and development of CT and CC.