Manufacturing - Process
CORE

The magnetic core of the transformers is built up of cold rolled grain oriented silicon steel laminations. Coils in varous grades of M3, M4, M5 and HiB (ZDKH, ZH, MOH etc) with thickness ranging from 0.23mm to 0.35mm. Hi-B grade and laser scri bed lamination is used to reduce the no load losses and noise level. Laminations are cut at an angle of 45. Core leg and yoke laminations are interleaved in mitred joints in order to facilitate the passage of the magnetic flux and to avoid hot spots and reduce no load losses, no load current and low noise level.

WINDING

The windings are designed to optimize Dynamic, Thermal, Mechanical & Electrical stresses depending upon the current & voltage requirements. Spiral, cross over, Helical, continuous disc, partly interleaved or fully interleaved winding are used depending on the specific design criteria. SteeV Wood winding mandrels are used to ensure tight tolerances. The winding machines are equipped with hydraulic braking devices which ensure that the proper tension is maintained on the winding. Dovetailed key spaces are employed to give the winding extra strength. Axial and radial cooling ducts in and between sections of the windings allow the free flow of oil around the conductor. Individual coils are dried and hydraulically pressed to size in accordance with the calculated short circuit forces to obtain the design height and to guarantee full short circuit resistance.

CORE-COIL ASSEMBLY, CONNECTION - OIL COOLED TRANSFORMERS
  • Coil winding Winding is done using electrolytic high conductivity paper covered copper or aluminium conductors for LV & HV separately. These coils are designed to meet dynamic & thermal stress also to meet short circuit forces.
  • Coils are interlayered with high electrolytic insulating paper and press board / pre compressed board ducts are provided between the winding layers for better cooling.
  • All the core bolts and tie rods are provided with SRBP Tube.
  • All connections are electrically brazed with Silver Phosphate material.
  • Tappings are provided in the form of links, to the tap switch which in turn can be operated from outside transformer body in Open circuit only.
  • The H.T. & L.T. Terminals are provided with suitable Porcelain Insulators.
  • Suitable Bus Bars are provided at L.T.
CORE-COIL ASSEMBLY, CONNECTION - AIR COOLED TRANSFORMERS
  • Fibre Glass Cylinders, Spacers and Ducts are provided between Core and L.V. Coils and also between L.V. Coils and H.V. Coils for adequate cooling
  • A Common Ring for each Phase provides uniform strength & helps compress all coils.
  • The Clamping Frame structure is insulated from Core with Fibre Glass sheet and rigidly clamped on both the axis to provide mechanical strength.
  • Clamping Frame structure is painted with Heat Resistant Paint.
  • All the core bolts and tie rods are provided with Fibre Glass Tube.
  • All connections are electrically brazed with Silver Phosphate material.
  • Tappings are provided in the form of links, which can be changed in Open circuit only.
  • The H.T. & L.T. Terminals are provided with suitable Epoxy or Porcelain Insulators as required.
  • Suitable Bus Bars are provided at L.T.
DRYING
A transformer may contain no trace of humidity, otherwise there will be a danger of flash over within the windings. The active part of the transformer is completely dried before the transformer is filled with oil. The rising oil drives out any remaining air and the active part is completely immersed.
TANK AND BOX UP
The tank is of rectangular / octoganal shape and provided with corrugated wall pannels or fin type radiators on sides for natural cooling. The tank base, sides and frames are of welded construction, and all weldings are inspected, for oil leakage. Further, when the tank is completed, it is subjected to leak test before painting operations called air pressure test. Tank cover which includes thermometer pockets, bushings, tap changer drive and lifting lugs mounted on the tank cover sufficient for lifting of the complete transformer the lifting of core and windings assembly is put in transformer tank and are then fastened by nut bolts. The connection items (bolts, nuts, bushing holders, studs, etc.) on the cover, and arching horns on HV bushing which are subject to rust, are made of specially surface treated steel material. Cover gasket is made of high quality cork-rubber. The rollers of uni-directional/bidirectional are provided as per customers request. To attain satisfactory protection against corrosion, and rusting, all surfaces of steel parts are prepared. Thereafter tanks and steel parts are painted with one primer and one final coat painting of required colour.