Download ECE320-HW4

HOME WORK # 4 – ECE 320
1.
Figures (a) and (b) show two possible connections for a 20 kVA, 2300/230V transformer to be
used as an autotransformer. With a source voltage of 2300 V, calculate the kVA rating and the
power output at full load of unity power factor (p.f=1) of the autotransformer for both the
connections.
2. A 6.6 kVA 10kV/230 V, 60Hz, single-phase transformer has following parameters referred to the
high voltage side: Req = 20 , Leq = 9 H, RC = 250 k, Lm = 10 kH.
a) What are the open circuit (rated voltage on the low voltage side) and short circuit (rated
current on the high voltage side) voltage, current and power test results.
b) If the secondary voltage is 230 V, and the power is 5 kW at .866 lagging, calculate the
efficiency in p.u. values.
3. A three-phase transformer is made from three single-phase ones, each single-phase transformer
is rated 10 kVA, 20 kV/200V; rated winding losses 100 W, core losses 50 W. The three-phase
transformer is connected in delta on the high voltage side and in star on the low voltage side.
What are the voltage ratings, current ratings, core loss (at the rated voltage), winding loss (at the
rated current) for the 3-phase transformer?