Core
High grade cold-roled grain- oriented silicon steel sheets are used as core plates. The core plates. The core plates are made without stamped holes, thereby reducing core loss and the risk of
core-bolt short. The sheets are cut by automatic cut-to-length line, insuring the burrs to be well below 0.02mm.
To reduce the increase of loss caused by handing the sheets, the core is stacked without the upper yoke. Winding block can be mounted on each core limb soon after the stacked core has been
erected, eliminating the conventional process of dismantling the upper yoke sheets after erection of the core.
Winding
The HV winding is generally a partially interleaved continuous winding. Inteleaving increases the series capacitance of the Winding, thus educing the voltage stress under lightning impulse. The
pressboard spacers are rounded at the edges so as to insure smooth contact between spacer and winding conductor.
Oil flowing within the winding is generally directed, thus lowering the winding oil gradient and the hot-spot temperature, ensuring a prolonged life for the winding.
Both the HV and MV the winding are generally provided with separate regulating windings, so that the ampere-turns of all the windings are completely balanced, effectively eliminating the axial
electrode dynamic force during external short circuit. The dynamic stability under external short circuit is thus much improved. Adopting standing rolling machine to rolling the windings. The
improvement makes the windings quality more higher.
Active part
Active part assemble advanced and reliable oriented device. Windings are drying under pressure. To obtain the high Quality, active part adopting treatment of vapour-phase drying filling the oil
in the vacuum state.
Tank
Bell-type tank is most commonly used. The tank wall is made of a corrugated shape by heavy press. Mechanical strength is much improved by the corrugation and welding work reduced, and the
outlook appearance is improved too. The tank cover is flat to facilitate maintenance people working there. Double oil resistant synthetic gasket is provided between the flanges of the upper and
the lower tank. Limiters are usually located on the flange of the lower tank.
Cooling and accessory equipments
Transformers are generally ONAF/ONAN cooling, with oil natural circulation and air natural or forced circulation. Transformers are designed to be operated at full load when fans are in
operation, and at 67% full load when fans are shut down. Plate fin type radiators are used for cooling with seam weld between the individual fin elements so as to ensure reliable quality. A
more compact size can be obtained for transformers equipped with such radiators. The fans generally blow horizontally with low speed an low noise. The operation of the fans is controlled by
both the oil temperature and the load. A control cabinet is installed on transformer tank. Conservators are provided with diaphragm bag. The bag is made of oil resistant air tight composite
material, separating the air inside the bag and the oil outside the conservator. For further reliability, the air chamber of diaphragm bag is breathed through silica dehydrating
breather.
