33kv on-Load Tap Changing Transformers

33kv SZ11 Type On-load Tap Changing Transformers
1. Low loss, therefore significantly energy-saving. The average no-load loss is 35% lower, and the load loss 10~20% lower, than prescribed by the present National standard GB/T 6451.
2. The core laminations are made up from imported high-quality cold-rolled grain-oriented silicon steel sheets with miter joints and without punched holes, and are stacked without the upper yoke sheets in place. After stacking, the core is pressed integrally and finally glued together by epoxy resin on the cut edges, so that the three limbs and the upper and lower yokes are bonded together into a rigid, vertically straightened entity, together with the plate-type upper and lower frame.
3. Zigzag directed flow of oil are provided within the windings, so that all parts of the windings can be cooled more evenly, thus reducing the temperature rise of the windings as a whole as well as the hot-spot temperature rise, prolonging the service life of transformers.
4. The regulating winding is a separate winding, apart from the high voltage main winding. In this way, total ampere-turn balance between windings can be obtained irrespective of the tapping position; and the axial electrodynamic force during short circuit can be much reduced, thus upgrading the short circuit withstand capability of the transformer as a whole. All the windings are perfectly dried before assembly. The radial clearances between windings and between low voltage winding and core are filled with pre-dried vertical spacers and insulating cylinders in such a way that the windings are tightly together radially with practically ‘zero’ allowance between them.
5. The windings of one phase are assembled into an integral phase block before placing onto the core. The low voltage winding is wound directly on strong thick paper cylinder. Vertical spacer strips are provided in spaces between windings and outside the outermost winding. The radial dimensions of all windings are kept within strict tolerance, so that a rigid winding phase block are obtained, capable of withstanding all the radial short-circuit forces encountered in service, and the possibility of buckling of the inner winding is obviated. Axially, the height of all windings is kept within close tolerance. Horizontal spacers between discs of a winding are pre-densified. The assembled winding phase black are pressed up and down by single support and pressure plates after careful adjustment of the heights of individual windings. Axial pressures are co-ordinated with the calculated short circuit force, so that the capability of the transformer to withstand axial short-circuit force is much increased.
6. The winding manufacture, winding assembly, and core and winding assembly work are all proceeded in totally closed clean rooms inside workshops. The cleanliness and temperature stability requirement of the area are the same as that required for the manufacture of 500kV class transformers. The final vapor phase drying of the core and coil assembly is practically a further cleaning process.
7. Core frames in the form of a flat plate are used for clamping the core, and are joined together by side beams. The core and coil assembly is fixed in the tank, being positioned against the tank at six sides rigidly, such that there can be no displacement of the assembly due to impacts during transport. Three-dimensional impact recorders are installed on transformers during transport to detect whether or not unacceptable impact force has been experienced and displacement of the core and coil assembly occurred during transportation. If not, lifting of the core and coil assembly out of the tank is not necessary. Flat cover permits the bushings to be mounted in a vertical position, thus eliminating oil l