Quality Standards Followed

Burr Level	Max 0.022 mm.
Width Cutting Tolerance	+/-0.3 mm
Length Cutting Tolerance	+/-0.3 mm
Losses	As certified by the mill Guarantee
Stacking factor (%)	95 Min.
Flatness	Wave height to length Ratio:- 1.5 Max.
Ductility	Minimum Number of bends :- > = 3

Special Features :

• Ranging from 25 KVA to 10000 KVA
• Available with 'V' Notching
• Available with Holing Facilities

Distribution and power transformer laminations in upto 75 MVA.

Step Lap laminations with Tip Cutting(both horizontal & vertical step lap)to give reduced losses.

Stress relief annealed laminations to give lower losses and lower current values.

It was not so long ago that mitred "stacked core" designs superseded cores which used rectangular joints.The development of mitred corner joints and in particular yokes with "V" notches to locate the centre leg allowed less core steel to be used, thus reducing the cost of transformer.Typically with overlap designs sheets are laid in pairs( 2 by 2 or 3 by 3). The choice is a balance between faster core building and the overall efficiency of the core.

There has been a constant drive to reduce material and manufacturing costs in the design of distribution transformers. When considering the various material in a transformer of paramount importance is the overall cost of the core steel used.This cost is influence by a number of factors, namely the loss factor of the silicon steel, the weight required (affected by the loss factor of the silicon steel) and the design of the core.There are many permutations which can be played between the raw cost of silicon steel, its loss factor, the amount required in a core and hence the material cost of the core.

About 30 years ago Westinghouse, in its research to reduce costs, invented a novel system of cross step-lap. In this design the overlap at the joints is much less than traditional overlap (3 - 5 mm compared to 10 -15 mm} but the shift progresses for 5 to 7 sheets before starting again. A key part of the Westinghouse design is the centre-leg where the notch in the yoke is progressively moved across the yoke according to the number of steps (the centre-leg length remains the same). There are three principle benefits of Westinghouse step-lap, firstly educed material costs, as less core steel is required for the same losses, secondly faster assembly of the core and thirdly lower noise.

The building factor used with cores manufactured like this will be between 1.10 and 1.14. whereas hand cut cores will typically use building factors of between 1.25 and 1.30.

This means there is the potential to make a material saving of up to 20%

Winding on-the-leg allows even more material savings as the windings are that much closer to the core less copper (or aluminium) can be used.

NOISE REDUCTION
An important benefit of step-lap cores is-they exhibit lower noise compared to overlap cores. This can be particularly important as there is increasing requirement to reduces the noise of transformers.