The choice of operating flux density of a core has a very significant impact on the overall size, material cost and performance of a transformer. For the currently available various grades of CRGO(Cold-Rolled Grain Oriented silicon steel) material, although losses and magnetizing voltamperes are lower for better grades, viz. Hi-B material (M0H, M1H, M2H), laser scribed, mechanical scribed, etc., as compared to CGO material (M2, M3, M4,M5, M6, etc.), the saturation flux density has remained same (about 2.0 T). The peak operating flux density (Bmp) gets limited by the over-excitation conditions specified by users. The slope of B-H curve of CRGO material significantly worsens after about 1.9 T (for a small increase in flux density, relatively much higher magnetizing current is drawn). Hence, the point corresponding to 1.9 T can be termed as knee-point of the B-H curve. It has been seen in example 1.1 that the simultaneous over-voltage and under-frequency conditions increase the flux density in the core. Hence, for an over-excitation condition (over-voltage and under-frequency) of a%, general guideline can be to use operating peak flux density of [1.9/(1+α/100)>. For the 10% continuous over-excitation specification, Bmp of 1.73 T [=1.9/(1+0.1)> can be the upper limit. For a power system, in which a voltage profile is well maintained, a continuous over-excitation condition of 5% is specified. In this case, Bmp of 1.8 T may be used as long as the core temperature and noise levels are within permissible limits; these limits are generally achievable with the step-lap core construction.