Download EECE 581

EECE 581
HW #5
1. Given the transformer test results below, draw the simplified transformer circuit with
all impedance values given on the primary side. Assume the transformer is rated
16,200/480 V, and 10 kVA.
OC Test (done on secondary side): Voc = 480 V, Ioc = 0.5 A, Poc = 200 W
SC Test (done on primary side): Vsc = 1000 V, Isc = 15 A, Psc = 2000 W
2. Assume a system consisting of a voltage source, connected to a j5 Ohm transmission
line to a transformer which has a 20 kW (pf = 0.8 lag) load connected to it’s
secondary. Assume a 25 kVA, 4800/120 V transformer with Req = 3 Ohms, Xeq =
5 Ohms, Rc = 500 Ohms, and Xm = 700 Ohms. Assume the load is at the rated
voltage.
a. Draw the complete circuit in pu using Sbase = 25 kVA and the transformer ratings
for the base voltages.
b. Find the source current in pu and in Amps.
3. A 3-phase 345 kV/16.2 kV transformer bank is to be connected in a Delta-Y
connection.
a. What must the voltage ratings of the three individual transformers be?
b. Draw the transformers and their connections to the lines.
4. 3 single-phase, 16.2 kV/208 V transformers are to be connected Y-Delta with a load
on the low voltage side. The load takes 20 Amps at a power factor of 0.7 lag when it
is at the rated voltage. Each transformer has Req = 2 Ohms, Xeq = 3 Ohms and Rc
& Xm infinite.
a. What is the line voltage on the high voltage side of the transformer?
b. What is the phase angle difference between the line voltages on either side of the
transformer? What causes this?