Date
Duration
Eastern Mediterranean University
Department of Electrical and Electronic Engineering
EE 457 POWER SYSTEM ANALYSIS I
MIDTERM EXAM I
: 24 Nov. 1998
SOLVE ALL 3 QUESTIONS
: 90 min.
ALL QUESTIONS CARRY EQUAL MARKS ( 35 pts.)
1-) In the circuit shown below , E1 = 100  V and E2 = 1000 V .
(a) With  = 60 find the real and reactive powers generated or absorbed by E2 .
(b) Find  so that the real power generated by E1 is maximum.
j10
+
+
E2
E1
2-) A 50-Hz three-phase lossless transmission line is 500 km. long. The parameters of the
line are
z = j 0.4  / km
,
y = j 210-6 S / km
The sending end voltage is Vs = 100 kV line-to-neutral . There is a short circuit at the
receiving end .
(a) Find the short circuit current at the receiving end.
(b) Find the total three-phase reactive power supplied to the line.
3-) Consider the single-phase transformer circuit shown below. Transformer ratings and
reactances are :
Transformer A
: 40 kVA , 200 / 800 V ,
X = 0.10 pu
Transformer B
: 50 kVA , 600 / 300 V ,
X = 0.15 pu
The transmission line can be represented as a series impedance Z = 2.0 + j 4.0  . Choose a
base of 50 kVA , 120 V in the voltage source ( Vs ) circuit.
(a) Draw the impedance diagram for this circuit, with all impedances in per unit.
(b) With Vs = 120  0 V , find the voltage across the load in per unit and in volts.
1 : 4
+
Vs
_
A
2
transmission line
: 1
B
ZL
= 5+j2 
Useful Information :
1.) Lossless transmission line equations
V(x) = VR cos x + j Zc IR sin x
j=zy
I(x) = IR cos x + j ( VR / Zc ) sin x
2-) Change of per unit basis
Sb
Z pu  Z pu
S 
b
2
Vb
2
Vb
Zc =  z / y