Power Transformers

CRGO Silicon Steel Transformers

Availability of latest manufacturing process helps BRG to ensure quality of the transformer. Liquid filled Transformers in order to be built comprises of the following stages

The magnetic circuit is of the three-column type with mitred joints and with step lap design. It is manufactured with grain oriented magnetic, cold-rolled silicon steel laminations. Silicon Steel Lamination is cut on high precision cutting machines, as per the designs. It is ensured that CRGO laminations are produced with minimum burr and subsequent annealing (if required) provides minimum magnetic flux distortion.

Cut Laminations of stipulated designs are then assembled carefully on a customized platform to build the Limbs and yokes following which the built core is clamped down in order to reduce vibrations and minimize noise levels. These customized platforms yield in lower building factors which also minimize the human handling. The construction of this core is generally a "Step lap process" which reduces the No load losses and the sound level in a Transformer.

Windings comprises of Conduction and Insulation material which is generally kraft paper or enamel. The conductors used are a high grade electrolytic copper or aluminum. LV windings are made layer by layer on the winding machines using covered conductors. These winding machines have been indigenously built by BRG’s Research and Development Wing. Highly skilled workers then wind these wires over a specific mandrel which has prefixed diameters as per the specification from the engineering department.

The HV windings are wound either with round, double enamel insulated, or rectangular, paper insulated wire over the LV windings for Distribution Transformers. This process of HV winding over LV winding provides better short-circuit withstand ability and generally has been found to be very productive. For the power transformers, both LV and HV Windings are usually 'continuously DISC wound' using rectangular paper covered conductors.

The built core assembly with the top yoke removed is placed on a work station with the limbs of the core tightly wrapped with cotton tape and then varnished. Press board Cylinders made out of insulating press board is wrapped on all the three limbs and then Low Voltage Coil is placed on the insulated core limbs. Insulating block of specified thickness and number are placed both at the top and bottom of the LV Coils Cylinder made out of corrugated paper or plain cylinder with oil ducts are provided over LV Coils.

HV Coils are placed over the cylinder and the Gaps between each section of H.V. Coils including top & bottom clearances is maintained with the help of oil ducts, as per the design/drawings. The Top Yoke is refilled and bolts and tie rods then fixed in position. Primary and secondary windings are connected as per the requirements.

The winding leads are then carefully brought out on the top or side as per the wiring diagram. The tap changers and necessary accessories such as lugs are then attached to the winding leads. On the LV side copper bars are then brazed to the winding leads. The CCA is then ratio tested to check the uniformity of the number of turns in the winding.

These core coil assemblies are then sent to the tanking department for further process.

Tanks are brought out from sub vendors who are carefully evaluated after a strict quality check in the fabrication units for any leaks or dimensional deviations. BRG is very soon going to kick-start a semi automatic fabrication plant to manufacture the tanks using latest state of the art technologies such as Plasma cutting, Robotic Welding and Unmanned Shot Blasting.

The core coil assembly from the CCA stage is then brought on for tanking. Before the tanking takes place, the CCA’s are sent in an oven for removal of any moisture content from the windings. They are then compressed using hydraulic jacks to arrive at the designed dimensions such as the axial height.

The CCA is then housed inside the MS tank and oil is filled under vacuum by an oil pump. The sub assembled transformer is then fitted with all the relevant accessories and fittings as per the customer’s requirement and then sent for final testing. After final testing and clearance from the quality department, the transformers are lined up for dispatches from where they are shipped to different project sites based on the requirements in trucks.

Online testing is done continuously as to avoid maximum backlogs during any production stage which reduces the costing of the product.

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