Impulse Volt-Time Characteristics of Oil and OIP Insulation
Estimation of insulation strength of transformer oil and Oil Impregnated Paper
(OIP) insulation, which constitutes major portion of insulation in power transformer,
is an important task. Also, it is often necessary to evaluate the breakdown strength
of oil and OIP under non-standard impulse voltages, since the oil and OIP insulation
is subjected to non-standard waveshapes between inter-disc and inter-turn insulation.
This necessitates for a generalized model to estimate the insulation strength
of it. In this study impulse strength of transformer oil and OIP insulation have
been extensively analysed for very small electrode gap distances ranging from
0.1 to 2.5 mm, which represents the inter-turn and inter-disc thickness of the
insulation. The statistical mean volt-time characteristics for uniform and highly
non-uniform electrode configurations are obtained experimentally for few gap distances.
A Hyperbolic model is developed based on the Disruptive Effect (DE) model parameters,
namely onset voltage (Uo) and Critical Disruptive Effect Area (DE * ) to predict
the volt-time characteristics. The DE parameters are also utilised to predict
the impulse breakdown characteristics of oil and OIP under non-standard impulse
voltages of standard and unidirectional oscillatory impulse waveshapes for all
the gap distances and the errors are found to be less than 10%.