2.
4
Determine, using the values given in TABLE A, the cu
ent / in the
circuit of FIGURE 2by:
(a) mesh analysis
(b) nodal analysis.
FIG.2 TABLE A
V.
J<-
ZI
I
vt tzoln2v
v2 t2obto v
V.
J 2o4f. v
z1 2Q
z2 -js a
Z"
J 1Q
z1 -js a
Z.
J j1a
aJ
You are encouraged to use the spreadsheet accompanying the assignment
on Bluckbourd to solve complex simultaneous equations,
1. FIGURE I shows a 50 Q load being fed from two voltage sources via
their associated reactances. Determine the cu
ent i flowing in the load by:
(a) applying Th6venin's theorem
(b) applying the superposition theorem
(c) by transforming the two voltage sources and their associated
eactances into cu
ent sources (and thus form a pair of Norlon
generators).
.il4
,,
I
I
t"
v1 =
12=
Ji x4tstor(toonr)
6 r+tsrin (roonr )
FIG. 1
volts
volts
s0Q
@ 0.7 p,f. lag
{llngirc
iflE)
y
5
3. For the balanced three-phase loads shown in FIGURE 3,
Zy : (15 + jl5) O and Zo: (45 + j45) O. Determine:
(a) the equivalent single A-connected load,
(b)the equivalent single Y-connected load obtained from the
A-Y transformation of (a) above,
(c) the equivalent single Y-connected load obtained by transforming
the A sub-load of FIGURE 3 to a Y and with the star-points of
the fwo Y-sub-circuits connected together,
(d)the total power consumed in case (a) above if the line voltage of
the three-phase supply is 415 V at 50}I2.
115 V
FIG. 3
:
=-afl|rfi--ltr-E?T I
6
4. FIGURE a@) shows two inductances connected in parallel across an
a.c. supply.
(a) Apply Kirchhoff's voltage law to loop abef and to loop abcdef of
the circuit.
(b)Hence or otherwise obtain the cu
ent ratio ! ,n terms of the
I2
circuit inductances.
(c) See if you can show that L, and L2 can be replaced by the
equivalent inductor, Z"o, of FIGURE 4(b) where
Lcq
* r-14 tl1
Lt * L", 2l,l
(d) A 1 nF capacitor is placed across the two inductors
(FIGIIRE a (c)). lf L1 : Lz: L and k: 0.5, determine the required
value of Z if the minimum cu
ent 1flows from the supply when it is
at a frequency of I MHz.
lliil{ne ,'nnE)
:-_
I1
-------
M L,,
e
(a) (b)
It
-="-
M
(c)
FIG. 4
7
c
5. A 415V to 11 kV transformer has a rating of 200 kVA. The
winding resistance and leakage reactance when refe
ed to the primary
are 0.014 O and 0.057 O respectively.
(a) Determine the o/oregulation ofthe transformer at 0.8 power facto
lagging.
(b) In designing a particular 415V to 11 kV 200 kVA transformer,
the primary winding resistance is to be 10 mQ. Find the maximum
winding resistance of the secondary winding if the transformer is
to have 2o/o regulation at unity power factor.
( t asinc.,nng)
c