Question

The core of a three-phase, 50Hz, 11 000/550 V mesh/star, 300 kVA transformer has a gross cross sectional are of 13000mm2. If the core density should not exceed 1,3 testa and the stacking factor is 0,9 .

calculate the emf per turn.

Show all work, use drawing to show

Answer 1

Given that,

Primary induced EMF, E1= 11000 V

Secondary induced EMF, E2= 550 V

Core density B_max = 1.5 T

Supply frequency f= 50 Hz

Cross sectional area =a= 13000mm² = 0.013 m²

Now,

Cross sectional area =a= flux/ flux density = ɸ/ B_max

Flux ɸ = area * flux density = 0.013*1.5 = 0.0195 Wb

We know E1= 4.44fN₁ɸ

N₁ = E1/ 4.44f ɸ = 11000/4.44*50*0.0195 = 2541 turns                    =No. of primary turns

N1 = E1/ EMF per turn

EMF per turn = E1/N1 = 11000/2541 = 4 V

Can be verified by calculating on secondary side,

Similarly

N₂ = E2/ 4.44f ɸ = 550/4.44*50*0.0195 = 127 turns                           =No. of secondary turns

EMF per turn = 550/ 127 = 4 V

Hence emf per turn is 4V