8. Tests with Combined and Composite Voltages

In power systems, the over-voltage stresses of insulations are often combinations of the operational voltage with over voltages. This can be neglected as long as the over-voltage value includes the contribution of the operational voltage. It cannot be neglected when the insulation between phases or of switching devices is considered. In that case, the resulting voltage is the combination of two voltage stresses on three-terminal test objects. In other cases, the stressing voltage is composed of two different voltage components, e.g. in certain HVDC insulations, as a composite voltage of AC and DC components. This chapter is related to the definition, generation and measurement of combined and composite test voltages on the basis of IEC 60060-1:2010 and IEEE Std. 4. Also some examples for tests with combined and composite voltages are given. It should be mentioned that these voltages are sometimes called “hybrid” or “superimposed” voltages, also the summarizing term “mixed” voltages is in use. This book follows the terminology of the Standard IEC 60060-1 (2010).