made of cold-rolled grain-oriented silicon steel sheets with high magnetic conductivity, with inclined joint laminated structure. Section of the core limbs is of multi-class ladder round, with uniform section with that of yoke. 

Winding 
The winding adopts corrugated oil duct with non-dipping process, bound by shrinkable tape; all windings are of concentric coils; taps of HV winding with corresponding tapping voltage shall be led to the tap switch, and the switch shall be installed on the box cover. Power supply must be cut off first when changing the tapping voltage.

Installation of protection device 
●Transformers of all capacity specifications have been equipped with pressure relief valve; 
●Gas relay with alarm and tripping terminals is available on request. 

Oil-temperature measurement device 
●All the transformers are equipped with tube holder for glass-stem thermometer that is set on the top of oil tank, and immersed in oil for about 120±10mm;
●1000~2000kVA transformer is equipped with outdoor signal thermometer;

Transformer oil tank 
●Transformer oil tank is composed of corrugated walls with powder painted surface and reinforced with film. Corrugated cooling fin not only has cooling function, but also has “breathing” function, the elasticity of corrugated cooling fin make it adapt to the change of oil volume due to change of temperature. So this hermetically sealed transformer does not have oil conservator, which decreases the height of transformer. 
●The transformer adopts vacuum oil-injection technology during encapsulation that thoroughly removes the moisture from transformer, and keeps the transformer oil from contacting the air. This technology also avoid insulation performance reduction or oil aging due to entering of oxygen or moisture, it improves operation reliability of transformer.