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EECE 581 HW #4
1.
Assume a 1 + j 5 Ohm transmission line connects a 240 V source to a 50 + j60 Ohm, 240 V
load. Assume the load is operating at it's rated voltage.
a. Assume no transformers are present in the circuit and find the real and reactive power
absorbed by the line.
b. Now place two 4000/240 V ideal transformers in the circuit to step up the voltage in the
line and step it back down at the load. Find the real and reactive power absorbed by
the line in this situation.
c. Find the percent difference between the losses in the two cases.
2.
A 25 kVA, 480/220 V transformer has R1 = 1 Ohm, R2 = 0.4 Ohms, X1 = 2 Ohms, X2 = 1
Ohm, Xm = 500 Ohms, and Rc = 700 Ohms. Assume a load is attached to the low voltage
side and has an impedance of 10 + j 20 Ohms. Assume that the source voltage on the high
voltage side is 475 V.
a. Draw the simplified transformer circuit including impedance values.
b. Find the load current.
c. Find the load voltage.
d. Find the efficiency of the transformer under this load condition.
e. Find the voltage regulation for this load condition.
3.
A 50 kVA, 550/120 V transformer has Req = 2 Ohms, Xeq = 7 Ohms, Xm = 700 Ohms, and
Rc = 400 Ohms. Assume a rated load with a power factor of 0.9 lag is attached to the
secondary, and the load is at it's rated voltage.
a. Find the load current.
b. Find the source current.
c. Find the efficiency of the transformer under this load condition.
d. Find the voltage regulation for this load condition.