Cast Resin Transformer

Cast Resin Transformer Technical Specification



This specification is prepared for the three phase, dry type (cat sresin) encapsulated, dry type transformer with natural air cooling (AN) suitable for drip-proof Indoor service.


Electrical equipments covered by this specification will be designed, manufactured and tested in accordance with IEC 60076-11 and purchaser’s requirements and manufacturer’s standard unless otherwise specified in this specification.


The transformer will be suitable for operation at it’s rating under the following service condition

  • Installation site : INDOOR
  • Ambient temperature : Max. 40℃
  • Relative humidity : Max. 100%
  • Altitude of installation : Not exceeding 1,000meters above sea level


The guaranteed values of finished articles will conform to the tolerance Specified in IEC 60076-11




The core is made exclusively of cold-rolled grain-oriented sheet coated with magnesium-silicate phosphate insulation on both sides.

To fully utilize the grain or orientation of the lamination, the ends of the limbs and yokes are mitered and stacked together by overlapping the laminations in pairs, which will reduce the no-load losses and thus the power required for magnetizing the core.

The core will be rigidly clamped with positive locking devices to ensure adequate mechanical strength to support the winding and also to prevent shifting of laminations during transport and further to minimize vibration during operation


Windings are insulated with an epoxy resin/quartz powder mixture that makes the windings Maintenance-free, moisture resistant, tropicalize, flame retardant and self-extinguishing.

The coils of the high-voltage windings are of aluminum foil, because foil windings combine a simple winding technique with a high degree of electrical safety. The insulation is subjected to less electrical stress than in other types of windings.

It never exceeds the plain voltage per turn because each layer consists of only one winding turn.

The thermal expansion coefficients of aluminum and cast resin are so similar that thermal stress due to load changes are kept to a minimum. The high-voltage windings are potted with epoxy resin under vacuum at a high temperature. This procedure prevents undesirable gas inclusions. The quality of the potting combined with the electrical advantages of the foil winding plays a decisive role in providing freedom from partial discharges.

The low-voltage strip winding is also aluminum. The width of the aluminum strip is equal to the length of the coil. This considerably reduces axial short circuit forces in the transformer. The conductor strip and the insulation material are bonded together by heating, and thus form a compact unit with sufficient strength to withstand radial forces reliably.


Transformer is provided with a re-connectable link tap changing device on the primary voltage side of the transformer after confirming of de-energizing. Change the ratio of the transformation. The device is sturdy in construction, and links are clearly identifiable as to the tap selected.


The following tests measurements will be carried out in accordance with the IEC 60076-11 standard unless otherwise specified in this specification.