HIGH PERMEABILITY STEEL USED IN TRANSFORMER CORE BASIC INFORMATION

Use of cold-rolled grain-oriented steel as described above continued with only steady refinement and improvement in the production process until the late 1960s.

However, in 1965 the Japanese Nippon Steel Corporation announced a step-change in the quality of their electrical steel: high-permeability grainoriented silicon steel.

Production is simplified by the elimination of one of the coldrolling stages because of the introduction of around 0.025% of aluminium to the melt and the resulting use of aluminium nitride as a growth inhibitor.

The final product has a better orientation than cold-rolled grain-oriented steel (in this context, generally termed ‘conventional’ steel), with most grains aligned within 3° of the ideal, but the grain size, average 1 cm diameter, was very large compared to the 0.3 mm average diameter of conventional material.

At flux densities of 1.7 T and higher, its permeability was three times higher than that of the best conventional steel, and the stress sensitivity of loss and magnetostriction were lower because of the improved orientation and the presence of a high tensile stress introduced by the so-called stress coating.

The stress coating imparts a tensile stress to the material which helps to reduce eddy-current loss which would otherwise be high in a large-grain material.

The total loss is further offset by some reduction in hysteresis loss due to the improved coating. However, the low losses of high-permeability steels are mainly due to a reduction of 30 40% in hysteresis brought about by the improved grain orientation.

The Nippon Steel Corporation product became commercially available in 1968, and it was later followed by\ high-permeability materials based MnSe plus Sb (Kawasaki Steel, 1973) and Boron (Allegheny Ludlum Steel Corporation, 1975).

OPEN DELTA CONNECTION FOR LIGHT AND POWER BASIC AND TUTORIALS

Standard Connection
When the secondary circuits are to supply both light and power, the open-delta bank takes this form. In addition to the applications listed above for the open-delta bank for power, this type of bank is used where there is a large single-phase load and only a small three-phase load.

In this case, the two transformers would be of of different kva sizes, the one across which the lighting load is connected being the larger. This is also the connection that should be used when protected transformers are employed in a three-phase bank supplying both light and power.


Simplified Connection
This is similar to the connection above but gives a nonstandard 180° angular displacement. Otherwise the information given above is applicable to this connection.