Просмотр полной версии : Non-vacuum induction heating of power transformers

13.07.2012, 16:20
Induction heating method can be applied in transformers of 110 – 150 kV, with non vacuum tanks. The tanks of such transformers are purged with vacuums pumps adjusted to create residual pressure of at least 55 kPa. The drying process can be divided into the following consequent stages: temperature increase, insulation heating, drying with air flow, airless drying and saturation of insulation with oil.

Gradual temperature increase and insulation heating is done the same way as during vacuum drying. At 110 kV, the minimum times for insulation heating are as follows:

Above 80 MVA 60 hours
From 16 to 80 MVA 35 hours
From 6.3 to 16 MVA 30 hours
Below 6.3 MVA 25 hours

After the heating is complete, the vacuum pump is started; pressure in the tank is gradually reduced by 13.5 kPa every 15 minutes to 60 kPa. Then, hot air is pulled into the tank through a filter, 60 kPa is maintained, and drying continuous until insulation parameters stabilize. At that point, air suction is stopped, 55 kPa residual pressure is created in the tank and drying continuous until insulation parameters (R60, tgδ и ∆С/С) stabilize and moisture is no longer deposited in the cooling section for at least 48 hours. Drying without air inflow must take at least 10 days. Then the core cools down, the tank bottom is rinsed, the transformer is filled with dry oil and insulation is saturated.

Drying of transformers 35 kV and below does not require vacuum equipment. To purge the core during the drying process, transformer lid is removed, or a special manifold may be installed to created natural or forced circulation of dry air in the tank.