Volt-time characteristics of OIP under non-standard impulses

The insulation of the power system equipment is stressed by internal and external overvoltages. For a reliable design of power system the proper insulation coordination among the power system components must be achieved. Insulation coordination is generally done by considering the behavior of insulation under standard lightning and switching impulses. In practice the system components might be stressed with the overvoltages of non-standard impulses like VFTO and oscillatory impulses. This necessitates the study of non-standard impulses on insulating materials. Transformers are considered as the major equipment in power system, which requires the detailed analysis on v-t characteristics of its insulation. In this paper an attempt has been made to analyze the breakdown characteristics of Oil Impregnated Paper (OIP) for different impulse waveshapes with varying front times from tens of nanoseconds to few microseconds and CIGRE representative waveforms. The v-t characteristics are mathematically modelled using Hyperbolic model. Thus developed models are used for predicting the v-t characteristics for any type of overvoltages of the above mentioned categories and compared with the experimental results.