An experimental assessment of the intermittent heating and cooling operation effect on power transformer insulation

In the future grid with a high share of renewables, grid flexibility is becoming an important issue to solve. Dynamic Transformer Rating (DTR) is a technology that allows to unlock additional grid capacity and provide extra flexibility to power system operation. However, since DTR is a fairly novel operation method, the effect of this type of operation on the rate of insulation ageing has not been studied in detail yet. Dynamic change of load and insulation temperature can introduce new extreme to the operation and lower the insulation lifetime. Therefore, this work studies the impact of dynamic rating on transformer insulation when exposed to different heating cycles. This work proposes an experimental evaluation of the impact that different heating cycles can have on insulation degradation. The setup consists of the control loop, heating element and paper-oil samples. The main focus is on the moisture exchange between insulating paper and oil when the samples are exposed to different temperature cycles. Moisture has been measured for both oil and paper and compared to a control group. This report presents published data from the first performed lab test. The experiment has to be repeated several times to increase the validity of the results. Consequently, the experiment has been documented carefully in order to ensure its replicability. It is shown that the limited interaction of the inner paper layers with the oil has forced the moisture to stay there. Moreover, part of the samples exposed to the highest temperatures is observed to be damaged. QC 20210710