Aged transformers can require the removal of moisture from cellulose to reduce the risk of dielectric failure and to extend transformer cellulose life. Moisture levels in cellulose can increase over time due to ingress from the atmosphere and as a by-product of cellulose aging.
Conventional field processes of vacuum and hot oil circulation are efficient for removal of surface moisture such as during transformer installation or routine maintenance, however they have limited effectiveness for major moisture removal in cellulose. The Low Frequency Heating (LFH) technology can achieve large moisture reductions in cellulose for transformers.
The LFH principle is that electronic power conversion provides low frequency power to the high voltage windings of a transformer while the secondary windings are shorted. In this manner, high current can be applied to all windings in a controlled manner with near negligible leakage flux due to the low applied frequency (low mHz values). High uniform temperatures in the winding can be achieved.