Evaluation of composite voltage test parameters in the case of the combination power frequency and switching impulse

The integration of renewable energy sources into the power grid and the extension of power transfer capabilities is one important step towards a reduction in CO2 emissions, a sustainable infrastructure and environment friendly power generation. In the electric grid this is causing a shift from the centralized generation of energy by big rotating AC generators towards more complicated, distributed, often semiconductor-based grid components using DC power in the process of power generation and often higher system voltages. The latter is underlined by the trend of ultra high voltage (UHV) power transmission. This leads to the need of more adequate, adapted test principles for the examination of the capabilities of grid components. In this context the work on the next revision of the standard IEC 60060 series considers the implementation of combined and composite voltages for impulse voltage tests. Until now there is no uniform procedure for the evaluation of the parameters of these novel test voltages. In particular for the case of more complex composite wave shapes. The Example this paper features is an impulse superimposed to a 50 Hz AC signal which record does cover only a small number of whole periods. In this paper we would like to investigate approaches in how to obtain concise and comparable results when working with combined and composite test voltages. These voltages consist out of lightning impulses (LI) or switching impulses (SI) superimposed to a conventional power supply voltage that is either an AC or a DC Voltage. Subject to this investigation is also the use of nonlinear regression in the process of the evaluation.