Ageing study of ZnO-based varistors in transformer oil

Abstract

In this paper the AC ageing of ZnO-based varistors in transformer oil is studied by an accelerated ageing during 6000 hours. Three kinds of varistors: 1-non-coated, 2-coated by resin and 3-coated by glass have been studied. As well the thermal behaviour of varistors has been studied in different temperatures and voltages. It is found that the coating and environmental conditions have a great influence on the thermal behaviour and the life-time of varistors. The oil improves their thermal behaviour. As well it improves the I(V) characteristics of the coated varistors while for the naked ones it causes a premature degradation. It is seen that glass could be, from the thermal point of view, a good material for coating the varistors.

Aging Study and Lifetime Estimation of Transformer Mineral Oil

“…Figure 7 shows that the oil resistivity decreases in the time and consequently its evolution can be considered too as a sign of the aging. But as we know from the literature, tan δ and resistivity also depend seriously on the oil humidity, suspended particles and dirt of oil and can change significantly by filtering and heating [7][8][9] . Of course by examination of the experimental results, we find that the variation of several characteristics such as the resistivity, dissipation factor, density, viscosity and flash point with the oil ageing has a logical meaning.…”

“…Where: t = The time T = The temperature A and B = The experimental constants which are based on the reacting materials, reaction conditions and the system of units [8][9] For example, accelerated aging tests have been accomplished on insulating study and pressboard by Montsinger during 70 weeks at the temperatures ranging from 7-110°C, by Dakin during 100 weeks at the temperatures of 100-135°C, by Shroff during 16 weeks at the temperatures of 110-140°C, by Moser during 57 weeks at the temperatures of 90-135°C and again by Moser during 3 weeks at the temperatures of 145-190°C and finally by Oomen during one week at the temperatures of 120-180°C. All these experiments have proved the validity of the Arrhenius law for the degradation phenomena of the insulating study and pressboard.…”