Cycle time reduction using intermittent DC internal heating in vapour phase drying of cellulose-based insulation used in transformers

Abstract

ABSTRACT For the commissioning of a new transformer, a delay in delivery caused owing to the long-drying process at the manufacturer is not acceptable in order to avoid erratic power supplies and extensive down times. To increase productivity, ensure on-time delivery, avoid unplanned power outages, reduce the cost, increase the efficiency of energy utilisation and maintain the quality parameters of the transformer insulation thereby increasing its service life, cycle time of insulation drying at the manufacturer needs to be reduced. As of today, the latest technology for insulation drying of transformers at the manufacturer’s factory is the vapour phase drying (VPD) method. The cycle time in VPD may span for 4–5 days for a power transformer. This establishes the need to reduce the cycle time in VPD of transformer insulation. In this work, experimentation was carried out on 11 kV transformers for developing a system to reduce the cycle time in VPD.