Rating of machines
Rating of a motor is the power output or the designated operating power limit based upon certain definite conditions assigned to it by the manufacturer.
The rating of machine refer to the whole of the numerical values of electrical and mechanical quantities with their duration and sequence assigned to the machines by the manufacturer and stated on the rating plate, the machine complying with the specified conditions.
Rating of a single phase & three phase transformer in KVA is given as
Q = 2.22 f Bm δ Kw Aw Ai * 10-3
Q = 3.33 f Bm δ Kw Aw Ai * 10-3
Where f = frequency, Hz
Bm = maximum flux density, Wb/m2
δ = current density, A/mm2
Kw = Window space factor Aw = Window area, m2
Ai = Net core area, m2