1) A transformer:100kvA, 50Hz, 600v/230v has been tested as follow:

at no load: V1=6000v, V20=240v, Iο=0.5A, Pο=400w at short circuit :

V1sc=200v, I1sc=16A, P1sc=1500w

a. determine the secondary voltage for the normal secondary current and with

1. cosØ=1

2. cosØ=0.7 leading and lagging.

b. the same machine, determine the efficiency for animal current and power factor

0.7 lagging.

c. determine the value of r and x for this calculate the value of relative

voltage drop for a current equal to the half of the nominal current and

a power factor of 0.6 lagging.

2) A 20kvA 8000/480v distribution transformer has the following resistances and

Reactances: Rp=32Ω Rs=0.5Ω

Xp=45Ω Xs=0.6Ω

Rc=250kΩ Xm=30kΩ

The excitation branch impedances are given referred to the high-voltage

Side of the transformer

a. find the equivalent circuit of this transformer referred to the voltage side

b. find the per-unit equivalent circuit of transformer

c. assume that this transformer is supplying rated load at 80v and 0.8pf lagging what is this transformers input voltage

d. what is the transformers efficiency under the condition of part(c)