| Transformers operating in power systems should have the ability to operate satisfactorily under steep front and oscillatory impulse voltages. In order to assess transformer performance, a knowledge of surface strength of the processed pressboard in mineral oil under steep front and oscillatory impulse voltages is therefore essential. In this study the surface strength volt-time characteristics of cylindrical processed pressboard have been investigated experimentally under lightning, steep front and high frequency oscillatory impulse voltages. Emphasis was placed on the surface strength volt-time characteristics of processed pressboard under steep front impulse voltages with gap lengths of 5 and 10 mm. The surface strength volt-time characteristics of the cylindrical processed pressboard in mineral oil was also conducted under high frequency oscillatory impulse voltages in the range of frequency from 0.2 MHz to 1.15 MHz and damping factor from 0.65 to 0.8. Finally, the surface breakdown characteristics of processed pressboard in aged oil was investigated under steep front and high frequency oscillatory impulses for the purpose of comparison with data obtained by using fresh unaged oil. (Abstract shortened by UMI.). |
