Question
Asked 15th Jan, 2015
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Is anyone aware of a thermo-hydrualic, electrodynamic simulation of transformer insulation degradation impacts on the frequency response trace?

Most of the literature reflect a position of "mechanical faults impacting on the SFR trace", and these are largely built up on the premise that insulation and other winding parameters will be perceptibly altered so as to appreciably show up on the SFR trace. But lets assume that throughout its service life, the unit never experiences a drastic shock event (thereby minimizing any potential mechanical effects on the windings) and that the only mechanism at work is  natural ageing under the influence of thermal cycling. Allowing for the conceivable loss of clamping pressure under this circumstance and whatever displacements (I don't imagine them to be very significant) occur due to energization inrush and normal load cycling, how appreciable is the effect of insulation change on the SFR? Lets assume that we may neglect any moisture ingress and any other internal woes (inter-turn faults, grounded core etc)

All Answers (2)

16th Jan, 2015
Francesco Palone
Terna
The expeced effect is almost nil, as transformer insulation degradation does not change the inductance and capacitance of windings. SFRA can only assess the mechanical integrity of windings, tap changers, connections  and clamping structures of power transformers, as also stated in IEC 60076-18 and in CIGRE TB 342. From the theoretical point of view maybe the amplitude of some peaks at higher frequencies in the SFR could change due to the increase of loss factor (tanδ) caused by insulation degradation, but this effect would be minimal. However in this case tanδ itself (as well as furan concentration in oil) would be a much better index of insulation degradation!
Hello Francesco. Many thanks for your reply indeed! I shall take these points into consideration.
Kind Regards.

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