Modelling and performance evaluation of a three-phase capacitive voltage sensor topology

[摘要] This research project investigates the design, modelling and application of an open-air capacitivevoltage sensor assembly for the measurement of wideband High Voltage signals on three-phasetransmission lines. The advantages and disadvantages of conventional methods used to measurethese voltages are reviewed and the advantages of the open-air capacitive sensor are established.The main research objective of this project involves extending the application of previouslydeveloped single-phase capacitive sensor topologies to three-phase applications. A three-phaseset of mobile, compact and relatively inexpensive capacitive voltage sensors for open-airapplication under overhead transmission lines are designed and constructed, including a dataacquisition triggering system for the measurement of transient waveforms. Equivalent circuitmodels, using a Thévenin equivalent approach, are developed for the three-phase sensor topologyand the associated three-phase transmission line configuration. A number of different methodsfor simplifying the associated Thévenin equivalent impedance and voltage equations areevaluated.The decoupling of the voltage waveforms measured by the individual sensors for a three-phasetransmission line configuration is subsequently examined with the view to derive mathematicalrelationships for determining the phase conductor voltages from the measured sensor voltages.The performance of the sensor assembly is experimentally evaluated under laboratory conditionsas well as field conditions. An outdoor HV test facility, representing a scaled three-phase flattransmission line structure, is developed for evaluation of the three-phase sensor topology in acontrolled environment. The methodology for decoupling the phase voltages and reconstructingthe phase conductor voltages from the voltages induced on the sensors is evaluated usingmeasured data obtained with this HV test facility. It is shown that the three-phase capacitivevoltage sensor topology as applied in the test facility delivers good results for the measurement ofthree-phase transient voltage waveforms.

[发布机构] Stellenbosch University