Modelling and performance evaluation of an HV impulse test arrangement with HVDC bias

[摘要] ENGLISH ABSTRACT: From a systems operation and design perspective, it is important to understand the behaviourof HVDC system insulation when presented with high voltage transients, such as induced bylightning and switching operations. Therefore, this thesis investigates the design, operationand performance of a circuit arrangement that can be used in high voltage laboratories togenerate impulse voltage waveforms superimposed on a dc bias voltage. The circuitarrangement consists of an impulse generator and a dc source that supplies continuous dcvoltage to stress the test object, which can be any type of insulator, i.e. composite, porcelain,glass, gap arrangements, etc. The composite waveform obtained from the test arrangement isused experimentally to investigate the impulse flashover of insulators.For modelling and analysis purposes, the test circuit was transformed to a Laplace equivalentin order to derive the applicable nodal voltage equations. After substitution of circuitparameter values, the voltage equations are then transformed to time domain equations thatpredict the time-domain behaviour of the circuit. To validate this mathematical approach, thevoltage waveforms obtained with this mathematical model is compared with the waveformsmeasured under laboratory conditions and also with waveforms simulated with HSPICEsoftware. These comparisons are performed using graphical representations. Good correlationwas obtained and the results are presented in this thesis.The final stage of this thesis discusses the application of the designed test arrangement forflashover and withstands tests on a silicon rubber insulator. The determination of the flashovervalues is done by using the existing statistical methods. The insulator was tested under dryconditions and also under polluted wet conditions for both positive and negative impulsescompared to the DC bias voltage polarity. The results show that the dc bias voltage does notaffect the total voltage flashover of the insulator significantly. It was also observed thatwetting affects the flashover for negative impulse more severely, while the influence ofwetting is minimal with positive impulse voltages

[发布机构] Stellenbosch University